Effects of Inundation, Nutrient Availability and Plant Species Diversity on Fine Root Mass and Morphology Across a Saltmarsh Flooding Gradient

PubMed Central

Redelstein, Regine; Dinter, Thomas; Hertel, Dietrich; Leuschner, Christoph

2018-01-01

Saltmarsh plants are exposed to multiple stresses including tidal inundation, salinity, wave action and sediment anoxia, which require specific root system adaptations to secure sufficient resource capture and firm anchorage in a temporary toxic environment. It is well known that many saltmarsh species develop large below-ground biomass (roots and rhizomes) but relations between fine roots, in particular, and the abiotic conditions in salt marshes are widely unknown. We studied fine root mass (<2 mm in diameter), fine root depth distribution and fine root morphology in three typical communities (Spartina anglica-dominated pioneer zone, Atriplex portulacoides-dominated lower marsh, Elytrigia atherica-dominated upper marsh) across elevational gradients in two tidal salt marshes of the German North Sea coast [a mostly sandy marsh on a barrier island (Spiekeroog), and a silty-clayey marsh on the mainland coast (Westerhever)]. Fine root mass in the 0–40 cm profile ranged between 750 and 2,500 g m−2 in all plots with maxima at both sites in the lower marsh with intermediate inundation frequency and highest plant species richness indicating an effect of biodiversity on fine root mass. Fine root mass and, even more, total fine root surface area (maximum 340 m2 m−2) were high compared to terrestrial grasslands, and were greater in the nutrient-poorer Spiekeroog marsh. Fine root density showed only a slight or no decrease toward 40 cm depth. We conclude that the standing fine root mass and morphology of these salt marshes is mainly under control of species identity and nutrient availability, but species richness is especially influential. The plants of the pioneer zone and lower marsh possess well adapted fine roots and large standing root masses despite the often water-saturated sediment. PMID:29467778

Variations in Soil Properties and Herbicide Sorption Coefficients with Depth in Relation to PRZM (Pesticide Root Zone Model) Calculations

USDA-ARS?s Scientific Manuscript database

There are few experimental data available on how herbicide sorption coefficients change across small increments within soil profiles. Soil profiles were obtained from three landform elements (eroded upper slope, deposition zone, and eroded waterway) in a strongly eroded agricultural field and segmen...

Global patterns of groundwater table depth.

PubMed

Fan, Y; Li, H; Miguez-Macho, G

2013-02-22

Shallow groundwater affects terrestrial ecosystems by sustaining river base-flow and root-zone soil water in the absence of rain, but little is known about the global patterns of water table depth and where it provides vital support for land ecosystems. We present global observations of water table depth compiled from government archives and literature, and fill in data gaps and infer patterns and processes using a groundwater model forced by modern climate, terrain, and sea level. Patterns in water table depth explain patterns in wetlands at the global scale and vegetation gradients at regional and local scales. Overall, shallow groundwater influences 22 to 32% of global land area, including ~15% as groundwater-fed surface water features and 7 to 17% with the water table or its capillary fringe within plant rooting depths.

Salinization of the soil solution decreases the further accumulation of salt in the root zone of the halophyte Atriplex nummularia Lindl. growing above shallow saline groundwater.

PubMed

Alharby, Hesham F; Colmer, Timothy D; Barrett-Lennard, Edward G

2018-01-01

Water use by plants in landscapes with shallow saline groundwater may lead to the accumulation of salt in the root zone. We examined the accumulation of Na + and Cl - around the roots of the halophyte Atriplex nummularia Lindl. and the impacts of this increasing salinity for stomatal conductance, water use and growth. Plants were grown in columns filled with a sand-clay mixture and connected at the bottom to reservoirs containing 20, 200 or 400 mM NaCl. At 21 d, Na + and Cl - concentrations in the soil solution were affected by the salinity of the groundwater, height above the water table and the root fresh mass density at various soil depths (P < 0.001). However, by day 35, the groundwater salinity and height above the water table remained significant factors, but the root fresh mass density was no longer significant. Regression of data from the 200 and 400 mM NaCl treatments showed that the rate of Na + accumulation in the soil increased until the Na + concentration reached ~250 mM within the root zone; subsequent decreases in accumulation were associated with decreases in stomatal conductance. Salinization of the soil solution therefore had a feedback effect on further salinization within the root zone. © 2017 John Wiley & Sons Ltd.

Root distributions of Eurotia lanata in association with two species of agropyron on disturbed soils

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bonham, C.D.; Mack, S.E.

1990-12-01

Root distributions of Eurotia lanata in association with Agropyron inerme and A. smithii on soils that were mechanically disturbed were studied. Root diagrams and measurements were made for plants in competitive pairs from soils representing two depths of soil disturbance (30 cm and 1 m) and control areas. Soil disturbance was observed to reduce significantly depth of root penetration and root concentration of E. lanata. Root depth, maximum lateral spread of roots, and zone of root concentration of E. lanata plants were greatest in pure stand pairs. Eurotia lanata associated with A. inerme had the smallest root concentration. The areamore » occupied by E. lanata roots was 59% greater in pure stands than when found adjacent to A. inerme. Agropyron inerme apparently used more available soil water in the top 20 cm of soil than did the shrub and resulted in reduced root growth for E. lanata. On the other hand, the asexual reproductive strategy of A. smithii, where roots and rhizomes were distributed both vertically and laterally, enables the grass species to minimize detrimental effects of its association with E. lanata. The results have important implications for selection of species combinations to reseed disturbed soils in semiarid or arid environments. In particular, attention should be given to use of species that have differing specializations as indicated by their growth and morphology.« less

Minimalistic models of the vertical distribution of roots under stochastic hydrological forcing

NASA Astrophysics Data System (ADS)

Laio, Francesco

2014-05-01

The assessment of the vertical root profile can be useful for multiple purposes: the partition of water fluxes between evaporation and transpiration, the evaluation of root soil reinforcement for bioengineering applications, the influence of roots on biogeochemical and microbial processes in the soil, etc. In water-controlled ecosystems the shape of the root profile is mainly determined by the soil moisture availability at different depths. The long term soil water balance in the root zone can be assessed by modeling the stochastic incoming and outgoing water fluxes, influenced by the stochastic rainfall pulses and/or by the water table fluctuations. Through an ecohydrological analysis one obtains that in water-controlled ecosystems the vertical root distribution is a decreasing function with depth, whose parameters depend on pedologic and climatic factors. The model can be extended to suitably account for the influence of the water table fluctuations, when the water table is shallow enough to exert an influence on root development, in which case the vertical root distribution tends to assume a non-monotonic form. In order to evaluate the validity of the ecohydrological estimation of the root profile we have tested it on a case study in the north of Tuscany (Italy). We have analyzed data from 17 landslide-prone sites: in each of these sites we have assessed the pedologic and climatic descriptors necessary to apply the model, and we have measured the mean rooting depth. The results show a quite good matching between observed and modeled mean root depths. The merit of this minimalistic approach to the modeling of the vertical root distribution relies on the fact that it allows a quantitative estimation of the main features of the vertical root distribution without resorting to time- and money-demanding measuring surveys.

Inter-Annual Variability of Soil Moisture Stress Function in the Wheat Field

NASA Astrophysics Data System (ADS)

Akuraju, V. R.; Ryu, D.; George, B.; Ryu, Y.; Dassanayake, K. B.

2014-12-01

Root-zone soil moisture content is a key variable that controls the exchange of water and energy fluxes between land and atmosphere. In the soil-vegetation-atmosphere transfer (SVAT) schemes, the influence of root-zone soil moisture on evapotranspiration (ET) is parameterized by the soil moisture stress function (SSF). Dependence of actual ET: potential ET (fPET) or evaporative fraction to the root-zone soil moisture via SSF can also be used inversely to estimate root-zone soil moisture when fPET is estimated by remotely sensed land surface states. In this work we present fPET versus available soil water (ASW) in the root zone observed in the experimental farm sites in Victoria, Australia in 2012-2013. In the wheat field site, fPET vs ASW exhibited distinct features for different soil depth, net radiation, and crop growth stages. Interestingly, SSF in the wheat field presented contrasting shapes for two cropping years of 2012 and 2013. We argue that different temporal patterns of rainfall (and resulting soil moisture) during the growing seasons in 2012 and 2013 are responsible for the distinctive SSFs. SSF of the wheat field was simulated by the Agricultural Production Systems sIMulator (APSIM). The APSIM was able to reproduce the observed fPET vs. ASW. We discuss implications of our findings for existing modeling and (inverse) remote sensing approaches relying on SSF and alternative growth-stage-dependent SSFs.

Estimation of the Potential for Atrazine Transport in a Silt Loam Soil

USGS Publications Warehouse

Eckhardt, D.A.V.; Wagenet, R.J.

1996-01-01

The transport potential of the herbicide atrazine (2-chloro-4-ethyl-6-isopropyl-s-triazine) through a 1-meter-thick root zone of corn (Zea mays L.) in a silty-loam soil in Kansas was estimated for a 22-year period (1972-93) using the one-dimensional water-flow and solute-transport model LEACHM. Results demonstrate that, for this soil, atrazine transport is directly related to the amount and timing of rain that follows spring applications of atrazine. Two other critical transport factors were important in wet years - [1] variability in atrazine application rate, and [2] atrazine degradation rates below the root zone. Results demonstrate that the coincidence of heavy rain soon after atrazine application can cause herbicide to move below the rooting zone into depths at which biodegradation rates are assumed to be low but are often unknown. Atrazine that reaches below the rooting zone and persists in the underlying soil can subsequently be transported into ground water as soil water drains, typically after the growing season. A frequency analysis of atrazine concentrations in subsurface drainage, combined with field data, demonstrates the relative importance of critical transport factors and confirms a need for definitive estimates of atrazine-degradation rates below the root zone. The analysis indicates that periodic leaching of atrazine can be expected for this soil when rainfall that exceeds 20 cm/mo coincides with atrazine presence in soil.

Cariotester, a new device for assessment of dentin lesion remineralization in vitro.

PubMed

Utaka, Sachiko; Nakashima, Syozi; Sadr, Alireza; Ikeda, Masaomi; Nikaido, Toru; Shimizu, Akihiko; Tagami, Junji

2013-01-01

This study aimed to evaluate the potential of a new device (Cariotester) for monitoring of incipient carious lesion remineralization in root dentin by topical fluoride in vitro. Demineralized bovine dentin specimens were treated by fluoride solutions (APF or neutral NaF) and remineralized for 4 weeks. Cariotester was used to measure penetration depth (CTR depth) of the indenter into the de- and remineralized specimen surface. The specimens were assessed by transverse microradiography (TMR) to determine lesion parameters (depth: LD, mineral loss: ΔZ). Pearson's correlation analysis showed an overall significant relationship between CTR depth and both TMR parameters. CTR depth appeared to distinguish the positive effect that topical fluoride application had on the remineralization of the outer zone of dentin lesions. Cariotester had the potential to serve as a quantitative tool for monitoring of incipient carious lesion remineralization in root dentin.

Water movement through a thick unsaturated zone underlying an intermittent stream in the western Mojave Desert, southern California, USA

USGS Publications Warehouse

Izbicki, J.A.; Radyk, J.; Michel, R.L.

2000-01-01

Previous studies indicated that small amounts of recharge occur as infiltration of intermittent streamflow in washes in the upper Mojave River basin, in the western Mojave Desert, near Victorville, California. These washes flow only a few days each year after large storms. To reach the water table, water must pass through an unsaturated zone that is more than 130 m thick. Results of this study, done in 1994-1998, showy that infiltration to depths below the root zone did not occur at control sites away from the wash. At these sites, volumetric water contents were as low as 0.01 and water potentials (measured as the combination of solute and matric potentials using a water activity meter) were as negative as -14,000 kPa. Water-vapor movement was controlled by highly negative solute potentials associated with the accumulation of soluble salts in the unsaturated zone. Highly negative matric potentials above and below the zone of maximum solute accumulation result from movement of water vapor toward the highly negative solute potentials at that depth. The ??18O and ??D (delta oxygen-18 and delta deuterium) isotopic composition of water in coarse-grained deposits plots along a Rayleigh distillation line consistent with removal of water in coarse-grained layers by vapor transport. Beneath Oro Grande Wash, water moved to depths below the root zone and, presumably, to the water table about 130 m below land surface. Underneath Oro Grande Wash, volumetric water contents were as high as 0.27 and water potentials (measured as matric potential using tensiometers) were between -1.8 and -50 kPa. On the basis of tritium data, water requires at least 180-260 years to infiltrate to the water table. Clay layers impede the downward movement of water. Seasonal changes in water vapor composition underneath the wash are consistent with the rapid infiltration of a small quantity of water to great depths and subsequent equilibration of vapor with water in the surrounding material. It may be possible to supplement natural recharge from the wash with imported water. Recharge to the wash may be advantageous because the unsaturated zone is not as dry as most areas in the desert and concentrations of soluble salts are generally lower underneath the wash.Previous studies indicated that small amounts of recharge occur as infiltration of intermittent streamflow in washes in the upper Mojave River basin, in the western Mojave Desert, near Victorville, California. These washes flow only a few days each year after large storms. To reach the water table, water must pass through an unsaturated zone that is more than 130 m thick. Results of this study, done in 1994-1998, show that infiltration to depths below the root zone did not occur at control sites away from the wash. At these sites, volumetric water contents were as low as 0.01 and water potentials (measured as the combination of solute and matric potentials using a water activity meter) were as negative as -14,000 kPa. Water-vapor movement was controlled by highly negative solute potentials associated with the accumulation of soluble salts in the unsaturated zone. Highly negative matric potentials above and below the zone of maximum solute accumulation result from movement of water vapor toward the highly negative solute potentials at that depth. The ??18O and ??D (delta oxygen-18 and delta deuterium) isotopic composition of water in coarse-grained deposits plots along a Rayleigh distillation line consistent with removal of water in coarse-grained layers by vapor transport. Beneath Oro Grande Wash, water moved to depths below the root zone and, presumably, to the water table about 130 m below land surface. Underneath Oro Grande Wash, volumetric water contents were as high as 0.27 and water potentials (measured as matric potential using tensiometers) were between -1.8 and -50 kPa. On the basis of tritium data, water requires at least 180-260 years to infiltrate to the water table. Clay layers impede the downwa

Controls on deep drainage beneath the root soil zone in snowmelt-dominated environments

NASA Astrophysics Data System (ADS)

Hammond, J. C.; Harpold, A. A.; Kampf, S. K.

2017-12-01

Snowmelt is the dominant source of streamflow generation and groundwater recharge in many high elevation and high latitude locations, yet we still lack a detailed understanding of how snowmelt is partitioned between the soil, deep drainage, and streamflow under a variety of soil, climate, and snow conditions. Here we use Hydrus 1-D simulations with historical inputs from five SNOTEL snow monitoring sites in each of three regions, Cascades, Sierra, and Southern Rockies, to investigate how inter-annual variability on water input rate and duration affects soil saturation and deep drainage. Each input scenario was run with three different soil profiles of varying hydraulic conductivity, soil texture, and bulk density. We also created artificial snowmelt scenarios to test how snowmelt intermittence affects deep drainage. Results indicate that precipitation is the strongest predictor (R2 = 0.83) of deep drainage below the root zone, with weaker relationships observed between deep drainage and snow persistence, peak snow water equivalent, and melt rate. The ratio of deep drainage to precipitation shows a stronger positive relationship to melt rate suggesting that a greater fraction of input becomes deep drainage at higher melt rates. For a given amount of precipitation, rapid, concentrated snowmelt may create greater deep drainage below the root zone than slower, intermittent melt. Deep drainage requires saturation below the root zone, so saturated hydraulic conductivity serves as a primary control on deep drainage magnitude. Deep drainage response to climate is mostly independent of soil texture because of its reliance on saturated conditions. Mean water year saturations of deep soil layers can predict deep drainage and may be a useful way to compare sites in soils with soil hydraulic porosities. The unit depth of surface runoff often is often greater than deep drainage at daily and annual timescales, as snowmelt exceeds infiltration capacity in near-surface soil layers. These results suggest that processes affecting the duration of saturation below the root zone could compromise deep recharge, including changes in snowmelt rate and duration as well as the depth and rate of ET losses from the soil profile.

Mantle transition zone structure beneath the Canadian Shield

NASA Astrophysics Data System (ADS)

Thompson, D. A.; Helffrich, G. R.; Bastow, I. D.; Kendall, J. M.; Wookey, J.; Eaton, D. W.; Snyder, D. B.

2010-12-01

The Canadian Shield is underlain by one of the deepest and most laterally extensive continental roots on the planet. Seismological constraints on the mantle structure beneath the region are presently lacking due to the paucity of stations in this remote area. Presented here is a receiver function study on transition zone structure using data from recently deployed seismic networks from the Hudson Bay region. High resolution images based on high signal-to-noise ratio data show clear arrivals from the 410 km and 660 km discontinuities, revealing remarkably little variation in transition zone structure. Transition zone thickness is close to the global average (averaging 245 km across the study area), and any deviations in Pds arrival time from reference Earth models can be readily explained by upper-mantle velocity structure. The 520 km discontinuity is not a ubiquitous feature, and is only weakly observed in localised areas. These results imply that the Laurentian root is likely confined to the upper-mantle and if any mantle downwelling exists, possibly explaining the existence of Hudson Bay, it is also confined to the upper 400 km. Any thermal perturbations at transition zone depths associated with the existence of the root, whether they be cold downwellings or elevated temperatures due to the insulating effect of the root, are thus either non-existent or below the resolution of the study.

Estimating soil water content from ground penetrating radar coarse root reflections

NASA Astrophysics Data System (ADS)

Liu, X.; Cui, X.; Chen, J.; Li, W.; Cao, X.

2016-12-01

Soil water content (SWC) is an indispensable variable for understanding the organization of natural ecosystems and biodiversity. Especially in semiarid and arid regions, soil moisture is the plants primary source of water and largely determine their strategies for growth and survival, such as root depth, distribution and competition between them. Ground penetrating radar (GPR), a kind of noninvasive geophysical technique, has been regarded as an accurate tool for measuring soil water content at intermediate scale in past decades. For soil water content estimation with surface GPR, fixed antenna offset reflection method has been considered to have potential to obtain average soil water content between land surface and reflectors, and provide high resolution and few measurement time. In this study, 900MHz surface GPR antenna was used to estimate SWC with fixed offset reflection method; plant coarse roots (with diameters greater than 5 mm) were regarded as reflectors; a kind of advanced GPR data interpretation method, HADA (hyperbola automatic detection algorithm), was introduced to automatically obtain average velocity by recognizing coarse root hyperbolic reflection signals on GPR radargrams during estimating SWC. In addition, a formula was deduced to determine interval average SWC between two roots at different depths as well. We examined the performance of proposed method on a dataset simulated under different scenarios. Results showed that HADA could provide a reasonable average velocity to estimate SWC without knowledge of root depth and interval average SWC also be determined. When the proposed method was applied to estimation of SWC on a real-field measurement dataset, a very small soil water content vertical variation gradient about 0.006 with depth was captured as well. Therefore, the proposed method could be used to estimate average soil water content from ground penetrating radar coarse root reflections and obtain interval average SWC between two roots at different depths. It is very promising for measuring root-zone-soil-moisture and mapping soil moisture distribution around a shrub or even in field plot scale.

Nitrogen fluxes through unsaturated zones in five agricultural settings across the USA

NASA Astrophysics Data System (ADS)

Green, C. T.; Fisher, L. H.; Bekins, B. A.

2006-12-01

The main controls on nitrogen (N) fluxes between the root zone and the water table were determined for agricultural sites in California, Washington, Nebraska, Indiana, and Maryland in 2004 and 2005. Sites included irrigated and non-irrigated fields; soil textures ranging from clay to sand; crops including corn, soybeans, almonds, and pasture; and unsaturated zone thicknesses ranging from 0.5 to 20 m. Chemical analyses of water from lysimeters, shallow wells, and sediment cores indicate that advective transport of nitrate is the dominant process affecting the rate of N transport below the root zone. Vertical profiles of (1) N species, (2) stable N and O isotopes, and (3) oxygen gas in unsaturated zone air and shallow ground water, and correlations between N and other agricultural chemicals indicate that reactions do not greatly affect N concentrations between the root zone and the capillary fringe. Relatively stable concentrations at depths greater than a few meters allow calculation of nitrogen fluxes to the saturated zone. These fluxes are equivalent to 14 - 64% of the N application rates. At the same locations, median vertical fluxes of N in ground water are generally lower, ranging from 4 - 37% of N application rates. The lower nitrate fluxes in ground water reflect processes including lateral flow to tile drains and denitrification in the capillary fringe, as well as historical changes in N inputs.

Plant-Sediment Interactions in Salt Marshes - An Optode Imaging Study of O2, pH, and CO 2 Gradients in the Rhizosphere.

PubMed

Koop-Jakobsen, Ketil; Mueller, Peter; Meier, Robert J; Liebsch, Gregor; Jensen, Kai

2018-01-01

In many wetland plants, belowground transport of O 2 via aerenchyma tissue and subsequent O 2 loss across root surfaces generates small oxic root zones at depth in the rhizosphere with important consequences for carbon and nutrient cycling. This study demonstrates how roots of the intertidal salt-marsh plant Spartina anglica affect not only O 2 , but also pH and CO 2 dynamics, resulting in distinct gradients of O 2 , pH, and CO 2 in the rhizosphere. A novel planar optode system (VisiSens TD ® , PreSens GmbH) was used for taking high-resolution 2D-images of the O 2 , pH, and CO 2 distribution around roots during alternating light-dark cycles. Belowground sediment oxygenation was detected in the immediate vicinity of the roots, resulting in oxic root zones with a 1.7 mm radius from the root surface. CO 2 accumulated around the roots, reaching a concentration up to threefold higher than the background concentration, and generally affected a larger area within a radius of 12.6 mm from the root surface. This contributed to a lowering of pH by 0.6 units around the roots. The O 2 , pH, and CO 2 distribution was recorded on the same individual roots over diurnal light cycles in order to investigate the interlinkage between sediment oxygenation and CO 2 and pH patterns. In the rhizosphere, oxic root zones showed higher oxygen concentrations during illumination of the aboveground biomass. In darkness, intraspecific differences were observed, where some plants maintained oxic root zones in darkness, while others did not. However, the temporal variation in sediment oxygenation was not reflected in the temporal variations of pH and CO 2 around the roots, which were unaffected by changing light conditions at all times. This demonstrates that plant-mediated sediment oxygenation fueling microbial decomposition and chemical oxidation has limited impact on the dynamics of pH and CO 2 in S. anglica rhizospheres, which may in turn be controlled by other processes such as root respiration and root exudation.

Micro 3D ERT tomography for data assimilation modelling of active root zone

NASA Astrophysics Data System (ADS)

Vanella, Daniela; Busato, Laura; Boaga, Jacopo; Cassiani, Giorgio; Binley, Andrew; Putti, Mario; Consoli, Simona

2016-04-01

Within the soil-plant-atmosphere system, root activity plays a fundamental role, as it connects different domains and allows a large part of the water and nutrient exchanges necessary for plant sustenance. The understanding of these processes is not only useful from an environmental point of view, making a fundamental contribution to the understanding of the critical zone dynamics, but also plays a pivotal role in precision agriculture, where the optimisation of water resources exploitation is mandatory and often carried out through deficit irrigation techniques. In this work, we present the results of non-invasive monitoring of the active root zone of two orange trees (Citrus sinensis, cv Tarocco Ippolito) located in an orange orchard in eastern Sicily (Italy) and drip irrigated with two different techniques: partial root drying and 100% crop evapotranspiration. The main goal of the monitoring activity is to assess possible differences between the developed root systems and the root water uptake between the two irrigation strategies. The monitoring is conducted using 3D micro-electrical resistivity tomography (ERT) based on an apparatus composed of a number of micro-boreholes (about 1.2 m deep) housing 12 electrodes each, plus a number of surface electrodes. Time-lapse measurements conducted both with long-term periodicity and short-term repetition before and after irrigation clearly highlight the presence and distribution of root water uptake zone both at shallow and larger depth, likely to correspond to zones utilized during the irrigation period (shallow) and during the time when the crop is not irrigated (deep). Subsidiary information is available in terms of precipitation, sap flow measurements and micrometeorological evapotranspiration estimates. This data ensemble lends itself to the assimilation into a variably saturated flow model, where both soil hydraulic parameters and root distribution shall be identified. Preliminary results in this directions show the potential of the method and its exciting outlook.

Altering recharge dynamics through woody vegetation removal: a study on the Carrizo-Wilcox aquifer of south Texas

NASA Astrophysics Data System (ADS)

Mattox, A. M.

2011-12-01

Grasslands in many semi-arid regions of the world have seen an expansion of woody vegetation over the past century and many now exist largely as woodlands or shrublands. This "woody encroachment" results in numerous changes to ecosystem function, including alteration of element and water cycles. As in many parts of the world, these shrublands in south Texas have been subjected to a variety of management practices intended to reduce woody vegetation and increase the dominance of herbaceous vegetation. In addition to the intended change in vegetation structure, this activity has the potential to affect hydrologic fluxes and potentially increase deep drainage through reduced transpiration and rooting depths. However, there is significant uncertainty about the hydrologic response of vegetation to woody vegetation removal. We report here the results of a large manipulative experiment designed to assess the effects of woody vegetation removal on soil moisture movement in the vadose zone in an area that serves as a recharge zone for an unconsolidated sediment aquifer (Carrizo-Wilcox). In this study woody vegetation has been removed using a mechanical method (roller chopping) as well as a mechanical and chemical method (chainsaw removal + stump herbicide). The treated plots are located on three different soil types that represent the range of soils typical in this area. A water balance approach is used to assess soil moisture fluxes and potential deep drainage. In this first year of the study we quantified ecological and edaphic components that have the greatest effect on deep drainage, namely rooting depth, soil texture and antecedent soil water conditions. Exceptionally dry conditions this year have provided a unique opportunity to understand plant soil water interactions in the critical zone given the strong soil moisture limitations observed in the surface soil horizons. Understanding these interactions across different plant communities and soil textures are the initial steps to determining if ground water recharge may be increased through brush management. Rooting depth and volumetric water content were determined in the Chacon clay loam, Webb sandy loam and Antosa-Bobillo loamy sands. Two soil cores were taken to depths of 2 m in each of the 1/4 acre plots in each of the treated and untreated plots for a total of 54 cores. Rooting depths were determined through a combination of hydro-pneumatic root elutriation, comparison of soil water profiles in treated and untreated plots, as well as stem and soil water isotope analysis. Initial data indicates hydraulic redistribution is occurring in the loamy sand as well as the clay loam soils. Neutron probe measurements suggest that vegetation may be facilitating the movement of water into deeper soil horizons in the clay loam soils. In addition to improving our understanding of the relationships between vegetation structure and vadose zone hydrology, our results will be useful for managing water resources under increasing demand, climate change, and varied priorities for entities tasked with managing water resources.

Documentation of Computer Program INFIL3.0 - A Distributed-Parameter Watershed Model to Estimate Net Infiltration Below the Root Zone

USGS Publications Warehouse

,

2008-01-01

This report documents the computer program INFIL3.0, which is a grid-based, distributed-parameter, deterministic water-balance watershed model that calculates the temporal and spatial distribution of daily net infiltration of water across the lower boundary of the root zone. The bottom of the root zone is the estimated maximum depth below ground surface affected by evapotranspiration. In many field applications, net infiltration below the bottom of the root zone can be assumed to equal net recharge to an underlying water-table aquifer. The daily water balance simulated by INFIL3.0 includes precipitation as either rain or snow; snowfall accumulation, sublimation, and snowmelt; infiltration into the root zone; evapotranspiration from the root zone; drainage and water-content redistribution within the root-zone profile; surface-water runoff from, and run-on to, adjacent grid cells; and net infiltration across the bottom of the root zone. The water-balance model uses daily climate records of precipitation and air temperature and a spatially distributed representation of drainage-basin characteristics defined by topography, geology, soils, and vegetation to simulate daily net infiltration at all locations, including stream channels with intermittent streamflow in response to runoff from rain and snowmelt. The model does not simulate streamflow originating as ground-water discharge. Drainage-basin characteristics are represented in the model by a set of spatially distributed input variables uniquely assigned to each grid cell of a model grid. The report provides a description of the conceptual model of net infiltration on which the INFIL3.0 computer code is based and a detailed discussion of the methods by which INFIL3.0 simulates the net-infiltration process. The report also includes instructions for preparing input files necessary for an INFIL3.0 simulation, a description of the output files that are created as part of an INFIL3.0 simulation, and a sample problem that illustrates application of the code to a field setting. Brief descriptions of the main program routine and of each of the modules and subroutines of the INFIL3.0 code, as well as definitions of the variables used in each subroutine, are provided in an appendix.

The pattern of deep structure and recent tectonics of the Greater Caucasus in the Ossetian sector from the complex geophysical data

NASA Astrophysics Data System (ADS)

Gorbatikov, A. V.; Rogozhin, E. A.; Stepanova, M. Yu.; Kharazova, Yu. V.; Andreeva, N. V.; Perederin, F. V.; Zaalishvili, V. B.; Mel'kov, D. A.; Dzeranov, B. V.; Dzeboev, B. A.; Gabaraev, A. F.

2015-01-01

Microseismic sounding along the profile in the Ossetian sector of the Greater Caucasus revealed two domains with characteristic properties and morphology deep beneath the mountain system. One subvertical domain is marked with low velocities and the other, also subvertical, has high velocities. The high-velocity zone is largely located beneath the northern limb and axial part of the Greater Caucasus mega-anticlinorium, whereas the low velocity zone projects on the southern limb. Almost throughout the entire structure of the block part of the northern limb of mega-anticlinorium, the top of the high-velocity zone beneath it is consistently horizontal at a depth of ˜10 km. This pattern is violated by the apparent steep rise of the top of the high-velocity zone to the surface in the southern direction, which starts approximately from the main thrust. Beneath the southern limb, the top boundary can also be guessed at a depth of ˜10 km, although less reliably. The roots of the low-velocity zone stretch to a depth of ˜50-60 km and narrow with the depth. The weak regional seismicity quite distinctly maps onto the high-velocity zone. In the depth interval of 10 to 25 km, weak seismicity abruptly drops northwards at the transition to the low-velocity zone. The independent magnetotelluric data show that electric resistivity of the low-velocity zone significantly exceeds the resistivity of the hosting rocks. The model of a medium filled with isolated fractures with mineralized fluid is suggested for the low-velocity zone. According to a series of features, the low-velocity zone tends to float up; in particular, there is a high lateral correlation between the most elevated part of the mountain relief, morphology, and age of the rocks, on one hand, and the position of the low-velocity zone, on the other hand.

Sensitivity of transpiration to subsurface properties: Exploration with a 1-D model

NASA Astrophysics Data System (ADS)

Vrettas, Michail D.; Fung, Inez Y.

2017-06-01

The amount of moisture transpired by vegetation is critically tied to the moisture supply accessible to the root zone. In a Mediterranean climate, integrated evapotranspiration (ET) is typically greater in the dry summer when there is an uninterrupted period of high insolation. We present a 1-D model to explore the subsurface factors that may sustain ET through the dry season. The model includes a stochastic parameterization of hydraulic conductivity, root water uptake efficiency, and hydraulic redistribution by plant roots. Model experiments vary the precipitation, the magnitude and seasonality of ET demand, as well as rooting profiles and rooting depths of the vegetation. The results show that the amount of subsurface moisture remaining at the end of the wet winter is determined by the competition among abundant precipitation input, fast infiltration, and winter ET demand. The weathered bedrock retains ˜30% of the winter rain and provides a substantial moisture reservoir that may sustain ET of deep-rooted (>8 m) trees through the dry season. A small negative feedback exists in the root zone, where the depletion of moisture by ET decreases hydraulic conductivity and enhances the retention of moisture. Hence, hydraulic redistribution by plant roots is impactful in a dry season, or with a less conductive subsurface. Suggestions for implementing the model in the CESM are discussed.

Reliance on shallow soil water in a mixed-hardwood forest in central Pennsylvania.

PubMed

Gaines, Katie P; Stanley, Jane W; Meinzer, Frederick C; McCulloh, Katherine A; Woodruff, David R; Chen, Weile; Adams, Thomas S; Lin, Henry; Eissenstat, David M

2016-04-01

We investigated depth of water uptake of trees on shale-derived soils in order to assess the importance of roots over a meter deep as a driver of water use in a central Pennsylvania catchment. This information is not only needed to improve basic understanding of water use in these forests but also to improve descriptions of root function at depth in hydrologic process models. The study took place at the Susquehanna Shale Hills Critical Zone Observatory in central Pennsylvania. We asked two main questions: (i) Do trees in a mixed-hardwood, humid temperate forest in a central Pennsylvania catchment rely on deep roots for water during dry portions of the growing season? (ii) What is the role of tree genus, size, soil depth and hillslope position on the depth of water extraction by trees? Based on multiple lines of evidence, including stable isotope natural abundance, sap flux and soil moisture depletion patterns with depth, the majority of water uptake during the dry part of the growing season occurred, on average, at less than ∼60 cm soil depth throughout the catchment. While there were some trends in depth of water uptake related to genus, tree size and soil depth, water uptake was more uniformly shallow than we expected. Our results suggest that these types of forests may rely considerably on water sources that are quite shallow, even in the drier parts of the growing season. © The Author 2015. Published by Oxford University Press.

Reliance on shallow soil water in a mixed-hardwood forest in central Pennsylvania

PubMed Central

Gaines, Katie P.; Stanley, Jane W.; Meinzer, Frederick C.; McCulloh, Katherine A.; Woodruff, David R.; Chen, Weile; Adams, Thomas S.; Lin, Henry; Eissenstat, David M.

2016-01-01

We investigated depth of water uptake of trees on shale-derived soils in order to assess the importance of roots over a meter deep as a driver of water use in a central Pennsylvania catchment. This information is not only needed to improve basic understanding of water use in these forests but also to improve descriptions of root function at depth in hydrologic process models. The study took place at the Susquehanna Shale Hills Critical Zone Observatory in central Pennsylvania. We asked two main questions: (i) Do trees in a mixed-hardwood, humid temperate forest in a central Pennsylvania catchment rely on deep roots for water during dry portions of the growing season? (ii) What is the role of tree genus, size, soil depth and hillslope position on the depth of water extraction by trees? Based on multiple lines of evidence, including stable isotope natural abundance, sap flux and soil moisture depletion patterns with depth, the majority of water uptake during the dry part of the growing season occurred, on average, at less than ∼60 cm soil depth throughout the catchment. While there were some trends in depth of water uptake related to genus, tree size and soil depth, water uptake was more uniformly shallow than we expected. Our results suggest that these types of forests may rely considerably on water sources that are quite shallow, even in the drier parts of the growing season. PMID:26546366

Desirable plant root traits for protecting unstable slopes against landslides

NASA Astrophysics Data System (ADS)

Stokes, A.; Atger, C.; Bengough, G.; Fourcaud, T.; Sidle, R. C.

2009-04-01

A trait is defined as a distinct, quantitative property of organisms, usually measured at the individual level and used comparatively across species. Plant quantitative traits are extremely important for understanding the local ecology of any site. Plant height, architecture, root depth, wood density, leaf size and leaf nitrogen concentration control ecosystem processes and define habitat for other taxa. An engineer conjecturing as to how plant traits may directly influence physical processes occurring on sloping land just needs to consider how e.g. canopy architecture and litter properties influence the partitioning of rainfall among interception loss, infiltration and runoff. Plant traits not only influence abiotic processes occurring at a site, but also the habitat for animals and invertebrates. Depending on the goal of the landslide engineer, the immediate and long-term effects of plant traits in an environment must be considered if a site is to remain viable and ecologically successful. When vegetation is considered in models of slope stability, usually the only root parameters taken into consideration are tensile strength and root area ratio. Root system spatial structure is not considered, although the length, orientation and diameter of roots are recognized as being of importance. Thick roots act like soil nails on slopes, reinforcing soil in the same way that concrete is reinforced with steel rods. The spatial position of these thick roots also has an indirect effect on soil fixation in that the location of thin and fine roots will depend on the arrangement of thick roots. Thin and fine roots act in tension during failure on slopes and if they cross the slip surface, are largely responsible for reinforcing soil on slopes. Therefore, the most important trait to consider initially is rooting depth. To stabilize a slope against a shallow landslide, roots must cross the shear surface. The number and thickness of roots in this zone will therefore largely determine slope stability. Rooting depth is species dependent when soil conditions are not limiting and the number of horizontal lateral roots borne on the vertical roots usually changes with depth. Therefore, the number and orientation of roots that the shear surface intersects will change significantly with rooting depth for the same plant, even for magnitudes of only several cm. Similarly, depending on the geometry of the root system, the angle at which a root crosses the shear surface can also have an influence on its resistance to pullout and breakage. The angle at which a root emerges from the parent root is dependent on root type, depth and species (when soil conditions are not limiting). Due to the physiology of roots, a root branch can be initiated at any point along a parent root, but not necessarily emerge fully from the parent root. These traits, along with others including size, relative growth rate, regeneration strategies, wood structure and strength will be discussed with regard to their influence on slope stability. How each of these traits is influenced by soil conditions and plantation techniques is also of extreme importance to the landslide engineer. The presence of obstacles in the soil, as well as compaction, affects root length and branching pattern. Roots of many species of woody plants on shallow soils also tend to grow along fractures deep into the underlying bedrock which allows roots to locate supplies of nutrient and water rich pockets. Rooting depths of herbaceous species in water-limited environments are highly correlated with infiltration depth, but waterlogged soils can asphyxiate tree roots, resulting in shallow root systems. The need to understand and integrate each of these traits for a species is not easy. Therefore, we suggest a hierarchy whereby traits are considered in order of importance, along with how external factors influence their expression over time.

Durum wheat seedlings in saline conditions: Salt spray versus root-zone salinity

NASA Astrophysics Data System (ADS)

Spanò, Carmelina; Bottega, Stefania

2016-02-01

Salinity is an increasingly serious problem with a strong negative impact on plant productivity. Though many studies have been made on salt stress induced by high NaCl concentrations in the root-zone, few data concern the response of plants to saline aerosol, one of the main constraints in coastal areas. In order to study more in depth wheat salinity tolerance and to evaluate damage and antioxidant response induced by various modes of salt application, seedlings of Triticum turgidum ssp. durum, cv. Cappelli were treated for 2 and 7 days with salt in the root-zone (0, 50 and 200 mM NaCl) or with salt spray (400 mM NaCl + 0 or 200 mM NaCl in the root-zone). Seedlings accumulated Na+ in their leaves and therefore part of their ability to tolerate high salinity seems to be due to Na+ leaf tissue tolerance. Durum wheat, confirmed as a partially tolerant plant, shows a higher damage under airborne salinity, when both an increase in TBA-reactive material (indicative of lipid peroxidation) and a decrease in root growth were recorded. A different antioxidant response was activated, depending on the type of salt supply. Salt treatment induced a depletion of the reducing power of both ascorbate and glutathione while the highest contents of proline were detected under salt spray conditions. In the short term catalase and ascorbate peroxidase co-operated with glutathione peroxidase in the scavenging of hydrogen peroxide, in particular in salt spray-treated plants. From our data, the durum wheat cultivar Cappelli seems to be sensitive to airborne salinity.

Soil Water and Shallow Groundwater Relations in an Agricultural Hillslope

NASA Astrophysics Data System (ADS)

Logsdon, S. D.; Schilling, K. E.

2007-12-01

Shallow water tables contribute to soil water variations under rolling topography, and soil properties contribute to shallow water table fluctutations. Preferential flow through large soil pores can cause a rise in the water table with little increase in soil water except near the soil surface. Lateral groundwater flow can cause a large rise in water table at toeslope and depressional landscape positions. As plants transpire, water can move up into the root zone from the water table and wet soil below the root zone. Roots can utilize water in the capillary fringe. The purpose of this study was to interface automated measurements of soil water content and water table depth for determining the importance of drainage and upward movement. In 2006 soil water and water table depth were monitored at three positions: shoulder, backslope, and toeslope. Neutron access tubes were manually monitored to 2.3 m depth, and automated soil moisture was measured using CS616 probes installed at 0.3, 0.5, 0.7, and 0.9 m depth. Water table depths were monitored manually and automated, but the automated measurements failed during the season at two sites. In 2007, similar measurements were made at one toeslope position, but the CS616 probes were installed at nine depths and better quality automated well depth equipment was used. The 2006 data revealed little landscape position effect on daytime soil water loss on a wetter date; however, on a dry day just before a rain, daytime water loss was greatest for the toeslope positon and least for the shoulder position. After a period of intense rain, a rapid and significant water table rise occurred at the toeslope position but little water table rise occurred at the other landscape positions. The rapid toeslope water table rise was likely caused by lateral groundwater flow whereas minor water table rise at the other positions was likely due to preferential flow since the soil had not wet up below 0.6 m. Use of automated equipment has improved our understanding of the relations of soil water to water table fluctuations in an agricultural field.

Validation of SMAP Root Zone Soil Moisture Estimates with Improved Cosmic-Ray Neutron Probe Observations

NASA Astrophysics Data System (ADS)

Babaeian, E.; Tuller, M.; Sadeghi, M.; Franz, T.; Jones, S. B.

2017-12-01

Soil Moisture Active Passive (SMAP) soil moisture products are commonly validated based on point-scale reference measurements, despite the exorbitant spatial scale disparity. The difference between the measurement depth of point-scale sensors and the penetration depth of SMAP further complicates evaluation efforts. Cosmic-ray neutron probes (CRNP) with an approximately 500-m radius footprint provide an appealing alternative for SMAP validation. This study is focused on the validation of SMAP level-4 root zone soil moisture products with 9-km spatial resolution based on CRNP observations at twenty U.S. reference sites with climatic conditions ranging from semiarid to humid. The CRNP measurements are often biased by additional hydrogen sources such as surface water, atmospheric vapor, or mineral lattice water, which sometimes yield unrealistic moisture values in excess of the soil water storage capacity. These effects were removed during CRNP data analysis. Comparison of SMAP data with corrected CRNP observations revealed a very high correlation for most of the investigated sites, which opens new avenues for validation of current and future satellite soil moisture products.

Expression of Lithospheric Shear Zones in Rock Elasticity Tensors and in Anisotropic Receiver Functions and Inferences on the Roots of Faults and Lower Crustal Deformation

NASA Astrophysics Data System (ADS)

Schulte-Pelkum, V.; Condit, C.; Brownlee, S. J.; Mahan, K. H.; Raju, A.

2016-12-01

We investigate shear zone-related deformation fabric from field samples, its dependence on conditions during fabric formation, and its detection in situ using seismic data. We present a compilation of published rock elasticity tensors measured in the lab or calculated from middle and deep crustal samples and compare the strength and symmetry of seismic anisotropy as a function of location within a shear zone, pressure-temperature conditions during formation, and composition. Common strengths of seismic anisotropy range from a few to 10 percent. Apart from the typically considered fabric in mica, amphibole and quartz also display fabrics that induce seismic anisotropy, although the interaction between different minerals can result in destructive interference in the total measured anisotropy. The availability of full elasticity tensors enables us to predict the seismic signal from rock fabric at depth. A method particularly sensitive to anisotropy of a few percent in localized zones of strain at depth is the analysis of azimuthally dependent amplitude and polarity variations in teleseismic receiver functions. We present seismic results from California and Colorado. In California, strikes of seismically detected fabric show a strong alignment with current strike-slip motion between the Pacific and North American plates, with high signal strength near faults and from depths below the brittle-ductile transition. These results suggest that the faults have roots in the ductile crust; determining the degree of localization, i.e., the width of the fault-associated shear zones, would require an analysis with denser station coverage, which now exists in some areas. In Colorado, strikes of seismically detected fabric show a broad NW-SE to NNW-SSE alignment that may be related to Proterozoic fabric developed at high temperatures, but locally may also show isotropic dipping contrasts associated with Laramide faulting. The broad trend is punctuated with NE-SW-trending strikes parallel to exhumed and highly localized structures such as the Idaho Springs-Ralston and Black Canyon shear zones. In either case, denser seismic studies should elucidate the width of the deep seismic expression of the shear zones.

Layered Plant-Growth Media for Optimizing Gaseous, Liquid and Nutrient Requirements: Modeling, Design and Monitoring

NASA Astrophysics Data System (ADS)

Heinse, R.; Jones, S. B.; Bingham, G.; Bugbee, B.

2006-12-01

Rigorous management of restricted root zones utilizing coarse-textured porous media greatly benefits from optimizing the gas-water balance within plant-growth media. Geophysical techniques can help to quantify root- zone parameters like water content, air-filled porosity, temperature and nutrient concentration to better address the root systems performance. The efficiency of plant growth amid high root densities and limited volumes is critically linked to maintaining a favorable water content/air-filled porosity balance while considering adequate fluxes to replenish water at decreasing hydraulic conductivities during uptake. Volumes adjacent to roots also need to be optimized to provide adequate nutrients throughout the plant's life cycle while avoiding excessive salt concentrations. Our objectives were to (1) design and model an optimized root zone system using optimized porous media layers, (2) verify our design by monitoring the water content distribution and tracking nutrient release and transport, and (3) mimic water and nutrient uptake using plants or wicks to draw water from the root system. We developed a unique root-zone system using layered Ottawa sands promoting vertically uniform water contents and air-filled porosities. Watering was achieved by maintaining a shallow saturated layer at the bottom of the column and allowing capillarity to draw water upward, where coarser particle sizes formed the bottom layers with finer particles sizes forming the layers above. The depth of each layer was designed to optimize water content based on measurements and modeling of the wetting water retention curves. Layer boundaries were chosen to retain saturation between 50 and 85 percent. The saturation distribution was verified by dual-probe heat-pulse water-content sensors. The nutrient experiment involved embedding slow release fertilizer in the porous media in order to detect variations in electrical resistivity versus time during the release, diffusion and uptake of nutrients. The experiment required a specific geometry for the acquisition of ERT data using the heat-pulse water-content sensor's steel needles as electrodes. ERT data were analyzed using the sensed water contents and deriving pore-water resistivities using Archie's law. This design should provide a more optimal root-zone environment by maintaining a more uniform water content and on-demand supply of water than designs with one particle size at all column heights. The monitoring capability offers an effective means to describe the relationship between root-system performance and plant growth.

A combined monitoring and modeling approach to quantify water and nitrate leaching using effective soil column hydraulic properties

NASA Astrophysics Data System (ADS)

Couvreur, V.; Kandelous, M. M.; Moradi, A. B.; Baram, S.; Mairesse, H.; Hopmans, J. W.

2014-12-01

There is a worldwide growing concern for agricultural lands input to groundwater pollution. Nitrate contamination of groundwater across the Central Valley of California has been related to its diverse and intensive agricultural practices. However, there has been no study comparing leaching of nitrate in each individual agricultural land within the complex and diversely managed studied area. A combined field monitoring and modeling approach was developed to quantify from simple measurements the leaching of water and nitrate below the root zone. The monitored state variables are soil water content at several depths within the root zone, soil matric potential at two depths below the root zone, and nitrate concentration in the soil solution. In the modeling part, unsaturated water flow and solute transport are simulated with the software HYDRUS in a soil profile fragmented in up to two soil hydraulic types, whose effective hydraulic properties are optimized with an inverse modeling method. The applicability of the method will first be demonstrated "in-silico", with synthetic soil water dynamics data generated with HYDRUS, and considering the soil column as the layering of several soil types characterized in-situ. The method will then be applied to actual soil water status data from various crops in California including tomato, citrus, almond, pistachio, and walnut. Eventually, improvements of irrigation and fertilization management practices (i.e. mainly questions of quantity and frequency of application minimizing leaching under constraint of water and nutrient availability) will be investigated using coupled modeling and optimization tools.

Effects of partial root-zone irrigation on hydraulic conductivity in the soil–root system of maize plants

PubMed Central

Hu, Tiantian; Kang, Shaozhong; Li, Fusheng; Zhang, Jianhua

2011-01-01

Effects of partial root-zone irrigation (PRI) on the hydraulic conductivity in the soil–root system (Lsr) in different root zones were investigated using a pot experiment. Maize plants were raised in split-root containers and irrigated on both halves of the container (conventional irrigation, CI), on one side only (fixed PRI, FPRI), or alternately on one of two sides (alternate PRI, APRI). Results show that crop water consumption was significantly correlated with Lsr in both the whole and irrigated root zones for all three irrigation methods but not with Lsr in the non-irrigated root zone of FPRI. The total Lsr in the irrigated root zone of two PRIs was increased by 49.0–92.0% compared with that in a half root zone of CI, suggesting that PRI has a significant compensatory effect of root water uptake. For CI, the contribution of Lsr in a half root zone to Lsr in the whole root zone was ∼50%. For FPRI, the Lsr in the irrigated root zone was close to that of the whole root zone. As for APRI, the Lsr in the irrigated root zone was greater than that of the non-irrigated root zone. In comparison, the Lsr in the non-irrigated root zone of APRI was much higher than that in the dried zone of FPRI. The Lsr in both the whole and irrigated root zones was linearly correlated with soil moisture in the irrigated root zone for all three irrigation methods. For the two PRI treatments, total water uptake by plants was largely determined by the soil water in the irrigated root zone. Nevertheless, the non-irrigated root zone under APRI also contributed to part of the total crop water uptake, but the continuously non-irrigated root zone under FPRI gradually ceased to contribute to crop water uptake, suggesting that it is the APRI that can make use of all the root system for water uptake, resulting in higher water use efficiency. PMID:21527627

High-performance etching of multilevel phase-type Fresnel zone plates with large apertures

NASA Astrophysics Data System (ADS)

Guo, Chengli; Zhang, Zhiyu; Xue, Donglin; Li, Longxiang; Wang, Ruoqiu; Zhou, Xiaoguang; Zhang, Feng; Zhang, Xuejun

2018-01-01

To ensure the etching depth uniformity of large-aperture Fresnel zone plates (FZPs) with controllable depths, a combination of a point source ion beam with a dwell-time algorithm has been proposed. According to the obtained distribution of the removal function, the latter can be used to optimize the etching time matrix by minimizing the root-mean-square error between the simulation results and the design value. Owing to the convolution operation in the utilized algorithm, the etching depth error is insensitive to the etching rate fluctuations of the ion beam, thereby reducing the requirement for the etching stability of the ion system. As a result, a 4-level FZP with a circular aperture of 300 mm was fabricated. The obtained results showed that the etching depth uniformity of the full aperture could be reduced to below 1%, which was sufficiently accurate for meeting the use requirements of FZPs. The proposed etching method may serve as an alternative way of etching high-precision diffractive optical elements with large apertures.

Sensitivity of transpiration to subsurface properties: Exploration with a 1-D model

DOE PAGES

Vrettas, Michail D.; Fung, Inez Y.

2017-05-04

The amount of moisture transpired by vegetation is critically tied to the moisture supply accessible to the root zone. In a Mediterranean climate, integrated evapotranspiration (ET) is typically greater in the dry summer when there is an uninterrupted period of high insolation. We present a 1-D model to explore the subsurface factors that may sustain ET through the dry season. The model includes a stochastic parameterization of hydraulic conductivity, root water uptake efficiency, and hydraulic redistribution by plant roots. Model experiments vary the precipitation, the magnitude and seasonality of ET demand, as well as rooting profiles and rooting depths ofmore » the vegetation. The results show that the amount of subsurface moisture remaining at the end of the wet winter is determined by the competition among abundant precipitation input, fast infiltration, and winter ET demand. The weathered bedrock retains math formula of the winter rain and provides a substantial moisture reservoir that may sustain ET of deep-rooted (>8 m) trees through the dry season. A small negative feedback exists in the root zone, where the depletion of moisture by ET decreases hydraulic conductivity and enhances the retention of moisture. Hence, hydraulic redistribution by plant roots is impactful in a dry season, or with a less conductive subsurface. Suggestions for implementing the model in the CESM are discussed.« less

Basaltic Diatreme To Root Zone Volcanic Processes In Tuzo Kimberlite Pipe (Gahcho Kué Kimberlite Field, NWT, Canada)

NASA Astrophysics Data System (ADS)

Seghedi, I.; Kurszlaukis, S.; Maicher, D.

2009-05-01

Tuzo pipe is infilled by a series of coherent and fragmental kimberlite facies types typical for a diatreme to root zone transition level. Coherent or transitional coherent kimberlite facies dominate at depth, but also occur at shallow levels, either as dikes or as individual or agglutinated coherent kimberlite clasts (CKC). Several fragmental kimberlite varieties fill the central and shallow portions of the pipe. The definition, geometry and extent of the geological units are complex and are controlled by vertical elements. Specific for Tuzo is: (1) high abundance of locally derived xenoliths (granitoids and minor diabase) between and within the kimberlite phases, varying in size from sub-millimeter to several tens of meters, frequent in a belt-like domain between 120-200 m depth in the pipe; (2) the general presence of CKC, represented by round-subround, irregular to amoeboid-shaped clasts with a macrocrystic or aphanitic texture, mainly derived from fragmentation of erupting magma and less commonly from previously solidified kimberlite, as well as recycled pyroclasts. In addition, some CKC are interpreted to be intersections of a complex dike network. This diversity attests formation by various volcanic processes, extending from intrusive to explosive; (3) the presence of bedded polymict wall- rock and kimberlite breccia occurring mostly in deep levels of the pipe below 345 m depth. The gradational contact relationships of these deposits with the surrounding kimberlite rocks and their location suggest that they formed in situ. The emplacement of Tuzo pipe involved repetitive volcanic explosions alternating with periods of relative quiescence causing at least partial consolidation of some facies. The volume deficit in the diatreme-root zone after each eruption was compensated by gravitational collapse of overlying diatreme tephra and pre-fragmented wall-rock xenoliths. Highly explosive phases were alternating with weak explosions or intrusive phases, suggesting an external factor to control the explosive behaviour of the magma. The overall constant volatile content of the kimberlite does not explain the observed extreme change in emplacement behaviour. The facies architecture of fragmental facies dominated by vertical elements is similar to that in non- kimberlitic diatremes and indicates deposition from debris jets marking separate and repeated explosive volcanic events. In basaltic pipes, such jets are generated by phreatomagmatic explosions in the explosion chamber(s) of the root zone, causing abundant country rock fragmentation and further efficient mixture of the various particles. Phases of high explosivity formed the finely fragmented kimberlites containing a high percentage of wall-rock xenoliths, while the fluidal-shaped and partly welded texturally variable and wall-rock- poor transitional coherent facies suggest phases of repetitive, hot, and low-energy fragmentation forming kimberlite spatter. Peperite hosted in kimberlite tephra is also typically found in basaltic root zones. Time gaps in between volcanic eruptive periods are indicated by cognate pyroclasts and reworked wall-rock deposits emplaced by sporadic sedimentation events in subterranean cavities under the widening roof of the pipe. The presence of temporary caves in the root zone is proposed also by the occurrence of spherical CKC in deep- seated fragmental kimberlite and by spatter found in transitional coherent rocks. Evidence for caves was mostly preserved at deeper pipe levels advocating continuously recurring processes during the life span of Tuzo.

Effects of soil water availability on water fluxes in winter wheat

NASA Astrophysics Data System (ADS)

Cai, G.; Vanderborght, J.; Langensiepen, M.; Vereecken, H.

2014-12-01

Quantifying soil water availability in water-limited ecosystems on plant water use continues to be a practical problem in agronomy. Transpiration which represents plant water demand is closely in relation to root water uptake in the root zone and sap flow in plant stems. However, few studies have been concentrated on influences of soil moisture on root water uptake and sap flow in crops. This study was undertaken to investigate (i) whether root water uptake and sap flow correlate with the transpiration estimated by the Penman-Monteith model for winter wheat(Triticum aestivum), and (ii) for which soil water potentials in the root zone, the root water uptake and sap flow rates in crop stems would be reduced. Therefore, we measured sap flow velocities by an improved heat-balance approach (Langensiepen et al., 2014), calculated crop transpiration by Penman-Monteith model, and simulated root water uptake by HYDRUS-1D on an hourly scale for different soil water status in winter wheat. In order to assess the effects of soil water potential on root water uptake and sap flow, an average soil water potential was calculated by weighting the soil water potential at a certain depth with the root length density. The temporal evolution of root length density was measured using horizontal rhizotubes that were installed at different depths.The results showed that root water uptake and sap flow matched well with the computed transpiration by Penman-Monteith model in winter wheat when the soil water potential was not limiting root water uptake. However, low soil water content restrained root water uptake, especially when soil water potential was lower than -90 kPa in the top soil. Sap flow in wheat was not affected by the observed soil water conditions, suggesting that stomatal conductance was not sensitive to soil water potentials. The effect of drought stress on root water uptake and sap flow in winter wheat was only investigated in a short time (after anthesis). Further research could focus on a long time (e.g. from vegetation to maturity) effect under different soil water conditions, such as irrigated, sheltered and normal status. Langensiepen, M., Kupisch, M., Graf, A., Schmidt, M. and Ewert, F., 2014. Improving the stem heat balance method for determining sap-flow in wheat. Agricultural and Forest Meteorology, 186: 34-42.

Predicting root zone soil moisture with soil properties and satellite near-surface moisture data across the conterminous United States

NASA Astrophysics Data System (ADS)

Baldwin, D.; Manfreda, S.; Keller, K.; Smithwick, E. A. H.

2017-03-01

Satellite-based near-surface (0-2 cm) soil moisture estimates have global coverage, but do not capture variations of soil moisture in the root zone (up to 100 cm depth) and may be biased with respect to ground-based soil moisture measurements. Here, we present an ensemble Kalman filter (EnKF) hydrologic data assimilation system that predicts bias in satellite soil moisture data to support the physically based Soil Moisture Analytical Relationship (SMAR) infiltration model, which estimates root zone soil moisture with satellite soil moisture data. The SMAR-EnKF model estimates a regional-scale bias parameter using available in situ data. The regional bias parameter is added to satellite soil moisture retrievals before their use in the SMAR model, and the bias parameter is updated continuously over time with the EnKF algorithm. In this study, the SMAR-EnKF assimilates in situ soil moisture at 43 Soil Climate Analysis Network (SCAN) monitoring locations across the conterminous U.S. Multivariate regression models are developed to estimate SMAR parameters using soil physical properties and the moderate resolution imaging spectroradiometer (MODIS) evapotranspiration data product as covariates. SMAR-EnKF root zone soil moisture predictions are in relatively close agreement with in situ observations when using optimal model parameters, with root mean square errors averaging 0.051 [cm3 cm-3] (standard error, s.e. = 0.005). The average root mean square error associated with a 20-fold cross-validation analysis with permuted SMAR parameter regression models increases moderately (0.082 [cm3 cm-3], s.e. = 0.004). The expected regional-scale satellite correction bias is negative in four out of six ecoregions studied (mean = -0.12 [-], s.e. = 0.002), excluding the Great Plains and Eastern Temperate Forests (0.053 [-], s.e. = 0.001). With its capability of estimating regional-scale satellite bias, the SMAR-EnKF system can predict root zone soil moisture over broad extents and has applications in drought predictions and other operational hydrologic modeling purposes.

Simulations and field observations of root water uptake in plots with different soil water availability.

NASA Astrophysics Data System (ADS)

Cai, Gaochao; Vanderborght, Jan; Couvreur, Valentin; Javaux, Mathieu; Vereecken, Harry

2015-04-01

Root water uptake is a main process in the hydrological cycle and vital for water management in agronomy. In most models of root water uptake, the spatial and temporal soil water status and plant root distributions are required for water flow simulations. However, dynamic root growth and root distributions are not easy and time consuming to measure by normal approaches. Furthermore, root water uptake cannot be measured directly in the field. Therefore, it is necessary to incorporate monitoring data of soil water content and potential and root distributions within a modeling framework to explore the interaction between soil water availability and root water uptake. But, most models are lacking a physically based concept to describe water uptake from soil profiles with vertical variations in soil water availability. In this contribution, we present an experimental setup in which root development, soil water content and soil water potential are monitored non-invasively in two field plots with different soil texture and for three treatments with different soil water availability: natural rain, sheltered and irrigated treatment. Root development is monitored using 7-m long horizontally installed minirhizotubes at six depths with three replicates per treatment. The monitoring data are interpreted using a model that is a one-dimensional upscaled version of root water uptake model that describes flow in the coupled soil-root architecture considering water potential gradients in the system and hydraulic conductances of the soil and root system (Couvreur et al., 2012). This model approach links the total root water uptake to an effective soil water potential in the root zone. The local root water uptake is a function of the difference between the local soil water potential and effective root zone water potential so that compensatory uptake in heterogeneous soil water potential profiles is simulated. The root system conductance is derived from inverse modelling using measurements of soil water potentials, water contents, and root distributions. The results showed that this modelling approach reproduced soil water dynamics well in the different plots and treatments. Root water uptake reduced when the effective soil water potential decreased to around -70 to -100 kPa in the root zone. Couvreur, V., Vanderborght, J., and Javaux, M.: A simple three dimensional macroscopic root water uptake model based on the hydraulic architecture approach, Hydrol. Earth Syst. Sci., 16, 2957-2971, doi:10.5194/hess-16-2957-2012, 2012.

Groundwater control of mangrove surface elevation: shrink and swell varies with soil depth

USGS Publications Warehouse

Whelan, K.R.T.; Smith, T. J.; Cahoon, D.R.; Lynch, J.C.; Anderson, G.H.

2005-01-01

We measured monthly soil surface elevation change and determined its relationship to groundwater changes at a mangrove forest site along Shark River, Everglades National Park, Florida. We combined the use of an original design, surface elevation table with new rod-surface elevation tables to separately track changes in the mid zone (0?4 m), the shallow root zone (0?0.35 m), and the full sediment profile (0?6 m) in response to site hydrology (daily river stage and groundwater piezometric pressure). We calculated expansion and contraction for each of the four constituent soil zones (surface [accretion and erosion; above 0 m], shallow zone [0?0.35 m], middle zone [0.35?4 m], and bottom zone [4?6 m]) that comprise the entire soil column. Changes in groundwater pressure correlated strongly with changes in soil elevation for the entire profile (Adjusted R2 5 0.90); this relationship was not proportional to the depth of the soil profile sampled. The change in thickness of the bottom soil zone accounted for the majority (R2 5 0.63) of the entire soil profile expansion and contraction. The influence of hydrology on specific soil zones and absolute elevation change must be considered when evaluating the effect of disturbances, sea level rise, and water management decisions on coastal wetland systems.

The Nutrient Pool of Five Important Bottomland Hardwood Soils

Treesearch

John K. Francis

1988-01-01

Heretofore, with the exception of N, the concentration of total nutrients and the amount of variation in nutrient concentrations among and within soil series and depths within the rooting zone of forested alluvial soils of the South was unknown. Information about total nutrient concentrations is important in studying the danger of nutrient depletion posed by total tree...

In situ sensors, weighing lysimeters and COSMOS under vegetated and bare conditions with subsurface drip irrigation

USDA-ARS?s Scientific Manuscript database

Long term weighing lysimeter records may have utility for assessment of climate changes occurring during the period of record. They typically enclose a depth of soil that exceeds the root zone of vegetation normally grown on them and have drainagy systems so that more or less natural hydrologic flux...

The influence of vegetation cover and soil physical properties on deflagration of shallow landslides - Nova Friburgo, RJ / Brazil

NASA Astrophysics Data System (ADS)

de Oliveira Marques, Maria Clara; Silva, Roberta; Fraga, Joana; Luiza Coelho Netto, Ana; Mululo Sato, Anderson

2017-04-01

In 2011, the mountainous region of the State of Rio de Janeiro (Brazil) suffered enormous social and economic losses due to thousands of landslides caused by an extreme rainfall event. The mapping of the scars of these landslides in an area of 421 km2 in the municipality of Nova Friburgo, RJ - Brazil resulted in a total of 3622, and 89% of these scars were located in areas covered by grasses and forests. Despite the unexpected result (64% of scars in forest areas), field evidence has shown that most of the forest fragments in the municipality are in the initial stages of succession and in different states of degradation, evidencing the need for a better understanding of the role of these forests in the detonation and propagation of landslides. Two slope forest areas with different ages (20 and 50 years) were evaluated in relation to the vegetative aspects that influence the stability of the slopes in each area. Hydrological monitoring, including precipitation, interception by manual and automatic method, soil moisture and subsurface flows were performed in two different areas: forest and grass. Soil moisture was monitored by granular matrix sensors and flows by collecting troughs in trenches at depths of 0 cm, 20 cm, 50 cm, 100 cm, 150 cm and 220 cm, which were also analyzed for biomass and length of thick roots (> 2 mm diameter) and thin roots (< 2 mm diameter) and for the soil physical properties (particle size, aggregate stability, porosity and hydraulic conductivity in situ). In the grass area, the lower soil structure in relation to the forest areas makes it difficult to transmit the water through the soil matrix. During the monitoring period, that area preserved the moisture in depths of 100 cm, 150 cm and 220 cm. The fasciculate root system of the grasses increased the infiltration of water at the top of the soil, favouring the formation of more superficial saturation zones in the heavy rains, due to the hydraulic discontinuities. In forest areas, infiltration by preferential paths allows the concentration of water in the depths in which they are terminal increasing the pore water pressure. Soil saturation in this area also occurred in heavy rains, but more deeply due to the rapid movement and redirection of water in depth by tree roots. This process was also responsible for the higher subsurface flows found in the forest, that is, the greater aggregation of the soil, the existence of interconnected macropores, ducts and roots facilitate the transmission of water in depth. Associated with the high rainfall and high relative humidity, these vegetation favoured the formation of saturation zones and increased pore pressures of the water, causing landslides on lands between 0.5 m and 2.0 m. The results of hydraulic conductivity show that the difference (lateritic = 10-4 cm/s; saprolitic = 10-5 cm/s) between the layers of the soil can generate zones of hydraulic discontinuity in extreme rainfall events, which would justify the predominance of shallow translational landslides at these same depths.

Simulated fate and transport of metolachlor in the unsaturated zone, Maryland, USA

USGS Publications Warehouse

Bayless, E.R.; Capel, P.D.; Barbash, J.E.; Webb, R.M.T.; Hancock, T.L.C.; Lampe, D.C.

2008-01-01

An unsaturated-zone transport model was used to examine the transport and fate of metolachlor applied to an agricultural site in Maryland, USA. The study site was instrumented to collect data on soil-water content, soil-water potential, ground water levels, major ions, pesticides, and nutrients from the unsaturated zone during 2002-2004. The data set was enhanced with site-specific information describing weather, soils, and agricultural practices. The Root Zone Water Quality Model was used to simulate physical, chemical, and biological processes occurring in the unsaturated zone. Model calibration to bromide tracer concentrations indicated flow occurred through the soil matix. Simulated recharge rates were within the measured range of values. The pesticide transport model was calibrated to the intensive data collection period (2002-2004), and the calibrated model was then used to simulate the period 1984 through 2004 to examine the impact of sustained agricultural management practices on the concentrations of metolachlor and its degradates at the study site. Simulation results indicated that metolachlor degrades rapidly in the root zone but that the degradates are transported to depth in measurable quantities. Simulations indicated that degradate transport is strongly related to the duration of sustained use of metolachlor and the extent of biodegradation. 

Computer based imaging and analysis of root gravitropism

NASA Technical Reports Server (NTRS)

Evans, M. L.; Ishikawa, H.

1997-01-01

Two key issues in studies of the nature of the gravitropic response in roots have been the determination of the precise pattern of differential elongation responsible for downward bending and the identification of the cells that show the initial motor response. The main approach for examining patterns of differential growth during root gravitropic curvature has been to apply markers to the root surface and photograph the root at regular intervals during gravitropic curvature. Although these studies have provided valuable information on the characteristics of the gravitropic motor response in roots, their labor intensive nature limits sample size and discourages both high frequency of sampling and depth of analysis of surface expansion data. In this brief review we describe the development of computer-based video analysis systems for automated measurement of root growth and shape change and discuss some key features of the root gravitropic response that have been revealed using this methodology. We summarize the capabilities of several new pieces of software designed to measure growth and shape changes in graviresponding roots and describe recent progress in developing analysis systems for studying the small, but experimentally popular, primary roots of Arabidopsis. A key finding revealed by such studies is that the initial gravitropic response of roots of maize and Arabidopsis occurs in the distal elongation zone (DEZ) near the root apical meristem, not in the main elongation zone. Another finding is that the initiation of rapid elongation in the DEZ following gravistimulation appears to be related to rapid membrane potential changes in this region of the root. These observations have provided the incentive for ongoing studies examining possible links between potential growth modifying factors (auxin, calcium, protons) and gravistimulated changes in membrane potential and growth patterns in the DEZ.

Root zone soil water dynamics and its effects on above ground biomass in cellulosic and grain based bioenergy crops of Midwest USA

NASA Astrophysics Data System (ADS)

Bhardwaj, A. K.; Hamilton, S. K.; van Dam, R. L.; Diker, K.; Basso, B.; Glbrc-Sustainability Thrust-4. 3 Biogeochemistry

2010-12-01

Root-zone soil moisture constitutes an important variable for hydrological and agronomic models. In agriculture, crop yields are directly related to soil moisture, levels that are most important in the root zone area of the soil. One of the most accurate in-situ methods that has established itself as a recognized standard around the world uses Time Domain Reflectometry (TDR) to determine volumetric water content of the soil. We used automated field-to-desk TDR based systems to monitor temporal (1-hr interval) soil moisture variability in 10 different bioenergy cropping systems at the Great Lakes Bioenergy Research Center’s (GLBRC) sustainability research site in south western Michigan, U.S.A. These crops range from high-diversity, low-input grass mixes to low-diversity, high-input crop monocultures. We equipped the 28 x 40 m vegetation plots with 30 cm long TDR probes at seven depths from 10 cm to 1.25 m below surface. The parent material at the site consists of coarse sandy glacial tills in which a soil with an approximately 50cm thick A-Bt horizon has developed. Additional equipment permanently installed for each system includes soil moisture access tubes, multi-depth temperature sensors, and multi-electrode resistivity arrays. The access tubes were monitored using a portable TDR system at bi-weekly intervals. 2D dipole-dipole electrical resistivity tomography (ERT) data are collected in 4-week intervals, while a subset of the electrodes is used for bi-hourly monitoring. The continuous scans (1 hr) provided us the real time changes in water content, replenishment and depletion, providing indications of water uptake by plant roots and potential seasonal water limitation of biomass accumulation. The results show significant seasonal variations between the crops and cropping systems. Significant relationships were observed between soil moisture stress, above-ground biomass and rooting characteristics. The overall goal of the study is to quantify the components of water balance, and identify water quality and water use implications of these cropping systems.Key Words

Effects of application methods of metam sodium and plastic covers on horizontal and vertical distributions of methyl isothiocyanate in bedded field plots.

PubMed

Ou, Li-Tse; Thomas, John E; Allen, L Hartwell; Vu, Joseph C; Dickson, Donald W

2006-08-01

This study was conducted to examine the effects of three application methods of metam sodium (broadcast, single irrigation drip tape delivery, and double irrigation drip tape delivery) and two plastic covers (polyethylene film and virtually impermeable film) on volatilization and on horizontal and vertical distributions of the biologically active product of metam sodium, methyl isothiocyanate (MITC), in field plots in a Florida sandy soil. Volatilization of MITC from field beds lasted for about 20 hours after completion of metam sodium application regardless of application methods. Virtually impermeable film (VIF) was a better barrier to reduce volatilization loss than polyethylene film (PE). Since water was not applied during broadcast application, MITC was mainly retained in the shallow soil layer (0- to 20-cm depth) and downward movement of MITC was limited to about 30 cm. Large values of standard deviation indicated that initial spatial distribution of MITC in the root zone (10- and 20-cm depths) of the two broadcast applied beds covered with PE or VIF was variable. Twice more water was delivered through the single drip tape than through individual tapes of double drip tape treatments during drip application of metam sodium. More water from the single drip tape likely facilitated downward movement of MITC to at least 60-cm depth, but MITC did not penetrate to this depth in the double drip tape beds. On the other hand, horizontal distribution of MITC in the root zone (10- and 20-cm depths) in the double drip tape beds was more uniform than in the single drip tape beds. More MITC was retained in the subsurface of the VIF-covered beds regardless of application methods than in the PE-covered beds.

Root-zone temperatures affect phenology of bud break, flower cluster development, shoot extension growth and gas exchange of 'Braeburn' (Malus domestica) apple trees.

PubMed

Greer, Dennis H; Wünsche, Jens N; Norling, Cara L; Wiggins, Harry N

2006-01-01

We investigated the effects of root-zone temperature on bud break, flowering, shoot growth and gas exchange of potted mature apple (Malus domestica (Borkh.)) trees with undisturbed roots. Soil respiration was also determined. Potted 'Braeburn' apple trees on M.9 rootstock were grown for 70 days in a constant day/night temperature regime (25/18 degrees C) and one of three constant root-zone temperatures (7, 15 and 25 degrees C). Both the proportion and timing of bud break were significantly enhanced as root-zone temperature increased. Rate of floral cluster opening was also markedly increased with increasing root-zone temperature. Shoot length increased but shoot girth growth declined as root-zone temperatures increased. Soil respiration and leaf photosynthesis generally increased as root-zone temperatures increased. Results indicate that apple trees growing in regions where root zone temperatures are < or = 15 degrees C have delayed bud break and up to 20% fewer clusters than apple trees exposed to root zone temperatures of > or = 15 degrees C. The effect of root-zone temperature on shoot performance may be mediated through the mobilization of root reserves, although the role of phytohormones cannot be discounted. Variation in leaf photosynthesis across the temperature treatments was inadequately explained by stomatal conductance. Given that root growth increases with increasing temperature, changes in sink activity induced by the root-zone temperature treatments provide a possible explanation for the non-stomatal effect on photosynthesis. Irrespective of underlying mechanisms, root-zone temperatures influence bud break and flowering in apple trees.

Waterlogging-induced changes in root architecture of germplasm accessions of the tropical forage grass Brachiaria humidicola.

PubMed

Cardoso, Juan Andrés; Jiménez, Juan de la Cruz; Rao, Idupulapati M

2014-04-08

Waterlogging is one of the major factors limiting the productivity of pastures in the humid tropics. Brachiaria humidicola is a forage grass commonly used in zones prone to temporary waterlogging. Brachiaria humidicola accessions adapt to waterlogging by increasing aerenchyma in nodal roots above constitutive levels to improve oxygenation of root tissues. In some accessions, waterlogging reduces the number of lateral roots developed from main root axes. Waterlogging-induced reduction of lateral roots could be of adaptive value as lateral roots consume oxygen supplied from above ground via their parent root. However, a reduction in lateral root development could also be detrimental by decreasing the surface area for nutrient and water absorption. To examine the impact of waterlogging on lateral root development, an outdoor study was conducted to test differences in vertical root distribution (in terms of dry mass and length) and the proportion of lateral roots to the total root system (sum of nodal and lateral roots) down the soil profile under drained or waterlogged soil conditions. Plant material consisted of 12 B. humidicola accessions from the gene bank of the International Center for Tropical Agriculture, Colombia. Rooting depth was restricted by 21 days of waterlogging and confined to the first 30 cm below the soil surface. Although waterlogging reduced the overall proportion of lateral roots, its proportion significantly increased in the top 10 cm of the soil. This suggests that soil flooding increases lateral root proliferation of B. humidicola in the upper soil layers. This may compensate for the reduction of root surface area brought about by the restriction of root growth at depths below 30 cm. Further work is needed to test the relative efficiency of nodal and lateral roots for nutrient and water uptake under waterlogged soil conditions. Published by Oxford University Press on behalf of the Annals of Botany Company.

Estimating Soil and Root Parameters of Biofuel Crops using a Hydrogeophysical Inversion

NASA Astrophysics Data System (ADS)

Kuhl, A.; Kendall, A. D.; Van Dam, R. L.; Hyndman, D. W.

2017-12-01

Transpiration is the dominant pathway for continental water exchange to the atmosphere, and therefore a crucial aspect of modeling water balances at many scales. The root water uptake dynamics that control transpiration are dependent on soil water availability, as well as the root distribution. However, the root distribution is determined by many factors beyond the plant species alone, including climate conditions and soil texture. Despite the significant contribution of transpiration to global water fluxes, modelling the complex critical zone processes that drive root water uptake remains a challenge. Geophysical tools such as electrical resistivity (ER), have been shown to be highly sensitive to water dynamics in the unsaturated zone. ER data can be temporally and spatially robust, covering large areas or long time periods non-invasively, which is an advantage over in-situ methods. Previous studies have shown the value of using hydrogeophysical inversions to estimate soil properties. Others have used hydrological inversions to estimate both soil properties and root distribution parameters. In this study, we combine these two approaches to create a coupled hydrogeophysical inversion that estimates root and retention curve parameters for a HYDRUS model. To test the feasibility of this new approach, we estimated daily water fluxes and root growth for several biofuel crops at a long-term ecological research site in Southwest Michigan, using monthly ER data from 2009 through 2011. Time domain reflectometry data at seven depths was used to validate modeled soil moisture estimates throughout the model period. This hydrogeophysical inversion method shows promise for improving root distribution and transpiration estimates across a wide variety of settings.

A Functional Trait Approach for Evaluation of Agroforestry Species Adaptation Potentiel to Changing Climate

NASA Astrophysics Data System (ADS)

Munson, A. D.; Marone, D.; Olivier, A.

2017-12-01

Traditional agroforestry systems have been used for generations in the Sahel region of Africa to assure local food security. However, an understanding of the functional ecology of these systems is lacking, which would contribute to assessing both the provision of current ecological services, and the potential for adaptation to global change. We have studied five native tree and shrub species across a transect of different soil types in the semi-arid zone of the Niayes region of Senegal, to document changes in above and belowground traits in response to soil and land use change. Root traits in particular influence access to limiting resources such as water and nutrients. We studied fine root depth distribution and specific root length (SRL) with soil depth of Acacia raddiana, Balanites aegyptiaca, Euphorbia balsamifera, Faidherbia albida, Neocarya macrophylla, on three different soil textures for three systems (fallow, parkland and rangeland), in order to understand potential exploitation of soil resources and potential contribution of roots to soil carbon stocks at different depths. The maximum root biomass of four of the species (Acacia raddiana, Balanites aegyptiaca, Euphorbia balsamifera, Neocarya macrophylla) occurred in the 40-60 cm layer, where the two evergreen species (A. raddiana, N. macrophylla) developed the most biomass. Root biomass decreased for all species except F. albida, after 60 cm depth. The Mimosaceae species (A. raddiana, F. albida) developed the most root biomass within the 100 cm sampling depth. The maximum fine root biomass was found in fallow lands and clay soils. For all species, the highest SRL was observed during the hot dry season, in sandy or sandy loam soil. The SRL was lowest in the rainy season on clay soil. Evergreens had higher SRL than deciduous species, regardless of soil texture and growing season conditions. Parkland and rangelands exhibited higher SRL than fallow land, most likely due to higher soil fertility. Differences between evergreen and deciduous SRL relied on adaptive strategies that seem to be conditioned by season, soil and land use. We also examined intraspecific variability of above and belowground traits to assess plasticity in response to environment. Evergreen species showed more variability in response to soil and to seasonal changes in temperature and moisture.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ben-Avraham, Z.; Nur, A.

The elevation above sea level of circum-Pacific volcanoes situated on continental crust varies greatly, not only between various chains but also within chains. Their edifice heights, however, are essentially constant with each chain. This pattern is reversed for oceanic volcanoes: The elevation circum-Pacific volcanoes situated on oceanic curst is constant within arcs, while edifice heights are greatly variable. In continents the depth to the root zones of volcanoes may be within the elastic part of the lithosphere, whereas in the oceans it may be well below the elastic part of the lithosphere. We suggest that melting, or the onset ofmore » the volcanic uprising, may be controlled in both cases primarily by pressure: in the continental lithosphere by the overburden pressure determined by depth below the local surface and in the oceanic lithosphere by the isostatically compensated pressure zone controlled by depth below sea level. The pattern seems to hold even in complex geological regions and may be used to identify the nature of the crust in such regions.« less

Root zone salinity and sodicity under seasonal rainfall due to feedback of decreasing hydraulic conductivity

NASA Astrophysics Data System (ADS)

van der Zee, S. E. A. T. M.; Shah, S. H. H.; Vervoort, R. W.

2014-12-01

Soil sodicity, where the soil cation exchange complex is occupied for a significant fraction by Na+, may lead to vulnerability to soil structure deterioration. With a root zone flow and salt transport model, we modeled the feedback effects of salt concentration (C) and exchangeable sodium percentage (ESP) on saturated hydraulic conductivity Ks(C, ESP) for different groundwater depths and climates, using the functional approach of McNeal (1968). We assume that a decrease of Ks is practically irreversible at a time scale of decades. Representing climate with a Poisson rainfall process, the feedback hardly affects salt and sodium accumulation compared with the case that feedback is ignored. However, if salinity decreases, the much more buffered ESP stays at elevated values, while Ks decreases. This situation may develop if rainfall has a seasonal pattern where drought periods with accumulation of salts in the root zone alternate with wet rainfall periods in which salts are leached. Feedback that affects both drainage/leaching and capillary upward flow from groundwater, or only drainage, leads to opposing effects. If both fluxes are affected by sodicity-induced degradation, this leads to reduced salinity (C) and sodicity (ESP), which suggests that the system dynamics and feedback oppose further degradation. Experiences in the field point in the same direction.

Ground Penetrating Radar For Estimating Root Biomass Through Empirical Analysis

NASA Astrophysics Data System (ADS)

Wolfe, M.; Dobreva, I. D.; Delgado, A.; Hays, D. B.; Bishop, M. P.; Huo, D.; Wang, X.; Teare, B. L.; Burris, S.

2017-12-01

Variability in soil carbon storage due to agricultural practices is an important component of the carbon cycle. Enhancing soil organic content is a means for restoring degraded soils and for improving soil quality, but also for carbon sequestration. In particular, accurate estimates of soil organic content are essential for quantifying carbon sequestration capabilities of agricultural systems. This project aims to advance the technological and analytical capabilities of Ground Penetrating Radar (GPR) for diagnoses of the soil carbon storage occurring due to the perennial grasses which are often utilized as biofuels. A new GPR processing workflow applied via a prototype software was tested on simulated GPR data of roots with different densities and depths to determine the sensitivity and capability of this technology to quantify these parameters. Field experiments were also conducted in long-term trials of different genotypes of perennial grasses over field sites in Texas to determine the application in authentic environments. GPR scans and soil samples were collected, and root dry biomass was obtained. Evaluation of pre-processing techniques was conducted to provide optimal resolution for assessment. The novel backscatter spatial structure workflow was implemented, and empirical relationships between root biomass and GPR derived observations were developed. Preliminary results suggest that the backscatter spatial structure changes in the presence of high density root biomass conditions, and these variations are indicative of root zone depth and density. Our results illustrate promising applications in root detection, and therefore, the soil organic content accumulation that is pertinent to a healthy soil system.

Rooting depths of plants relative to biological and environmental factors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Foxx, T S; Tierney, G D; Williams, J M

1984-11-01

In 1981 to 1982 an extensive bibliographic study was completed to document rooting depths of native plants in the United States. The data base presently contains 1034 citations with approximately 12,000 data elements. In this paper the data were analyzed for rooting depths as related to life form, soil type, geographical region, root type, family, root depth to shoot height ratios, and root depth to root lateral ratios. Average rooting depth and rooting frequencies were determined and related to present low-level waste site maintenance.

An Investigation into Palladium-Catalyzed Reduction of Perchlorate in Water

DTIC Science & Technology

2005-03-01

phytoremediation may help “naturally” reduce the spread of perchlorate in the environment. Rhizodegradation may be particularly effective for reducing...depth beyond the plant root zone, phytoremediation would be not affect the transport of perchlorate. Also, once perchlorate is dispersed in a large... Germany . At Spangdahlem, he led the Environmental Protection Element of the Bioenvironmental Engineering Flight and also led the 52nd Medical

Plant root and shoot dynamics during subsurface obstacle interaction

NASA Astrophysics Data System (ADS)

Conn, Nathaniel; Aguilar, Jeffrey; Benfey, Philip; Goldman, Daniel

As roots grow, they must navigate complex underground environments to anchor and retrieve water and nutrients. From gravity sensing at the root tip to pressure sensing along the tip and elongation zone, the complex mechanosensory feedback system of the root allows it to bend towards greater depths and avoid obstacles of high impedance by asymmetrically suppressing cell elongation. Here we investigate the mechanical and physiological responses of roots to rigid obstacles. We grow Maize, Zea mays, plants in quasi-2D glass containers (22cm x 17cm x 1.4cm) filled with photoelastic gel and observe that, regardless of obstacle interaction, smaller roots branch off the primary root when the upward growing shoot (which contains the first leaf) reaches an average length of 40 mm, coinciding with when the first leaf emerges. However, prior to branching, contacts with obstacles result in reduced root growth rates. The growth rate of the root relative to the shoot is sensitive to the angle of the obstacle surface, whereby the relative root growth is greatest for horizontally oriented surfaces. We posit that root growth is prioritized when horizontal obstacles are encountered to ensure anchoring and access to nutrients during later stages of development. NSF Physics of Living Systems.

Long-term tillage and crop rotation effects on residual nitrate in the crop root zone and nitrate accumulation in the intermediate vadose zone

USGS Publications Warehouse

Katupitiya, A.; Eisenhauer, D.E.; Ferguson, R.B.; Spalding, R.F.; Roeth, F.W.; Bobier, M.W.

1997-01-01

Tillage influences the physical and biological environment of soil. Rotation of crops with a legume affects the soil N status. A furrow irrigated site was investigated for long-term tillage and crop rotation effects on leaching of nitrate from the root zone and accumulation in the intermediate vadose zone (IVZ). The investigated tillage systems were disk-plant (DP), ridge-till (RT) and slot-plant (SP). These tillage treatments have been maintained on the Hastings silt loam (Udic Argiustoll) and Crete silt loam (Pachic Argiustoll) soils since 1976. Continuous corn (CC) and corn soybean (CS) rotations were the subtreatments. Since 1984, soybeans have been grown in CS plots in even calendar years. All tillage treatments received the same N rate. The N rate varied annually depending on the root zone residual N. Soybeans were not fertilized with N-fertilizer. Samples for residual nitrate in the root zone were taken in 8 of the 15 year study while the IVZ was only sampled at the end of the study. In seven of eight years, root zone residual soil nitrate-N levels were greater with DP than RT and SP. Residual nitrate-N amounts were similar in RT and SP in all years. Despite high residual nitrate-N with DP and the same N application rate, crop yields were higher in RT and SP except when DP had an extremely high root zone nitrate level. By applying the same N rates on all tillage treatments, DP may have been fertilized in excess of crop need. Higher residual nitrate-N in DP was most likely due to a combination of increased mineralization with tillage and lower yield compared to RT and SP. Because of higher nitrate availability with DP, the potential for nitrate leaching from the root zone was greater with DP as compared to the RT and SP tillage systems. Spring residual nitrate-N contents of DP were larger than RT and SP in both crop rotations. Ridge till and SP systems had greater nitrate-N with CS than CC rotations. Nitrate accumulation in IVZ at the upstream end of the field was twice as high with DP compared to RT and SP. At the downstream end, it was 2.4 and 1.6 times greater with DP than RT and SP, respectively. Nitrate concentration was greater in the IVZ of DP compared to RT and SP tillage systems. Nitrate accumulations in IVZ of RT and SP were not different. Continuous corn had slightly higher nitrate levels in IVZ than CS. The depth of nitrate penetration at the upstream end was greater than that of the downstream end. Estimated rates of nitrate movement ranged from 0.87 to 0.92 m yr-1 at the upstream end and 0.73 to 0.78 m yr-1 at the downstream end.

Analysis of the NASA AirMOSS Root Zone Soil Water and Soil Temperature from Three North American Ecosystems

NASA Astrophysics Data System (ADS)

Hagimoto, Y.; Cuenca, R. H.

2015-12-01

Root zone soil water and temperature are controlling factors for soil organic matter accumulation and decomposition which contribute significantly to the CO2 flux of different ecosystems. An in-situ soil observation protocol developed at Oregon State University has been deployed to observe soil water and temperature dynamics in seven ecological research sites in North America as part of the NASA AirMOSS project. Three instrumented profiles defining a transect of less than 200 m are installed at each site. All three profiles collect data for in-situ water and temperature dynamics employing seven soil water and temperature sensors installed at seven depth levels and one infrared surface temperature sensor monitoring the top of the profile. In addition, two soil heat flux plates and associated thermocouples are installed at one of three profiles at each site. At each profile, a small 80 cm deep access hole is typically made, and all below ground sensors are installed into undisturbed soil on the side of the hole. The hole is carefully refilled and compacted so that root zone soil water and temperature dynamics can be observed with minimum site disturbance. This study focuses on the data collected from three sites: a) Tonzi Ranch, CA; b) Metolius, OR and c) BERMS Old Jack Pine Site, Saskatchewan, Canada. The study describes the significantly different seasonal root zone water and temperature dynamics under the various physical and biological conditions at each site. In addition, this study compares the soil heat flux values estimated by the standard installation using the heat flux plates and thermocouples installed near the surface with those estimated by resolving the soil heat storage based on the soil water and temperature data collected over the total soil profile.

Identifying Developmental Zones in Maize Lateral Root Cell Length Profiles using Multiple Change-Point Models

PubMed Central

Moreno-Ortega, Beatriz; Fort, Guillaume; Muller, Bertrand; Guédon, Yann

2017-01-01

The identification of the limits between the cell division, elongation and mature zones in the root apex is still a matter of controversy when methods based on cellular features, molecular markers or kinematics are compared while methods based on cell length profiles have been comparatively underexplored. Segmentation models were developed to identify developmental zones within a root apex on the basis of epidermal cell length profiles. Heteroscedastic piecewise linear models were estimated for maize lateral roots of various lengths of both wild type and two mutants affected in auxin signaling (rtcs and rum-1). The outputs of these individual root analyses combined with morphological features (first root hair position and root diameter) were then globally analyzed using principal component analysis. Three zones corresponding to the division zone, the elongation zone and the mature zone were identified in most lateral roots while division zone and sometimes elongation zone were missing in arrested roots. Our results are consistent with an auxin-dependent coordination between cell flux, cell elongation and cell differentiation. The proposed segmentation models could extend our knowledge of developmental regulations in longitudinally organized plant organs such as roots, monocot leaves or internodes. PMID:29123533

Rooting for food security in Sub-Saharan Africa

NASA Astrophysics Data System (ADS)

Guilpart, Nicolas; Grassini, Patricio; van Wart, Justin; Yang, Haishun; van Ittersum, Martin K.; van Bussel, Lenny G. J.; Wolf, Joost; Claessens, Lieven; Leenaars, Johan G. B.; Cassman, Kenneth G.

2017-11-01

There is a persistent narrative about the potential of Sub-Saharan Africa (SSA) to be a ‘grain breadbasket’ because of large gaps between current low yields and yield potential with good management, and vast land resources with adequate rainfall. However, rigorous evaluation of the extent to which soils can support high, stable yields has been limited by lack of data on rootable soil depth of sufficient quality and spatial resolution. Here we use location-specific climate data, a robust spatial upscaling approach, and crop simulation to assess sensitivity of rainfed maize yields to root-zone water holding capacity. We find that SSA could produce a modest maize surplus but only if rootable soil depths are comparable to that of other major breadbaskets, such as the US Corn Belt and South American Pampas, which is unlikely based on currently available information. Otherwise, producing surplus grain for export will depend on expansion of crop area with the challenge of directing this expansion to regions where soil depth and rainfall are supportive of high and consistent yields, and where negative impacts on biodiversity are minimal.

Fine root dynamics along an elevational gradient in tropical Amazonian and Andean forests

NASA Astrophysics Data System (ADS)

Girardin, C. A. J.; Aragão, L. E. O. C.; Malhi, Y.; Huaraca Huasco, W.; Metcalfe, D. B.; Durand, L.; Mamani, M.; Silva-Espejo, J. E.; Whittaker, R. J.

2013-01-01

The key role of tropical forest belowground carbon stocks and fluxes is well recognised as one of the main components of the terrestrial ecosystem carbon cycle. This study presents the first detailed investigation of spatial and temporal patterns of fine root stocks and fluxes in tropical forests along an elevational gradient, ranging from the Peruvian Andes (3020 m) to lowland Amazonia (194 m), with mean annual temperatures of 11.8°C to 26.4 °C and annual rainfall values of 1900 to 1560 mm yr-1, respectively. Specifically, we analyse abiotic parameters controlling fine root dynamics, fine root growth characteristics, and seasonality of net primary productivity along the elevation gradient. Root and soil carbon stocks were measured by means of soil cores, and fine root productivity was recorded using rhizotron chambers and ingrowth cores. We find that mean annual fine root below ground net primary productivity in the montane forests (0-30 cm depth) ranged between 4.27±0.56 Mg C ha-1 yr-1 (1855 m) and 1.72±0.87 Mg C ha-1 yr-1 (3020 m). These values include a correction for finest roots (<0.6 mm diameter), which we suspect are under sampled, resulting in an underestimation of fine roots by up to 31% in current ingrowth core counting methods. We investigate the spatial and seasonal variation of fine root dynamics using soil depth profiles and an analysis of seasonal amplitude along the elevation gradient. We report a stronger seasonality of NPPFineRoot within the cloud immersion zone, most likely synchronised to seasonality of solar radiation. Finally, we provide the first insights into root growth characteristics along a tropical elevation transect: fine root area and fine root length increase significantly in the montane cloud forest. These insights into belowground carbon dynamics of tropical lowland and montane forests have significant implications for our understanding of the global tropical forest carbon cycle.

Water uptake of trees in a montane forest catchment and the geomorphological potential of root growth in Boulder Creek Critical Zone Observatory, Rocky Mountains, Colorado

NASA Astrophysics Data System (ADS)

Skeets, B.; Barnard, H. R.; Byers, A.

2011-12-01

The influence of vegetation on the hydrological cycle and the possible effect of roots in geomorphological processes are poorly understood. Gordon Gulch watershed in the Front Range of the Rocky Mountains, Colorado, is a montane climate ecosystem of the Boulder Creek Critical Zone Observatory whose study adds to the database of ecohydrological work in different climates. This work sought to identify the sources of water used by different tree species and to determine how trees growing in rock outcrops may contribute to the fracturing and weathering of rock. Stable isotopes (18O and 2H) were analyzed from water extracted from soil and xylem samples. Pinus ponderosa on the south-facing slope consumes water from deeper depths during dry periods and uses newly rain-saturated soils, after rainfall events. Pinus contorta on the north -facing slope shows a similar, expected response in water consumption, before and after rain. Two trees (Pinus ponderosa) growing within rock outcrops demonstrate water use from cracks replenished by new rains. An underexplored question in geomorphology is whether tree roots growing in rock outcrops contribute to long-term geomorphological processes by physically deteriorating the bedrock. The dominant roots of measured trees contributed approximately 30 - 80% of total water use, seen especially after rainfall events. Preliminary analysis of root growth rings indicates that root growth is capable of expanding rock outcrop fractures at an approximate rate of 0.6 - 1.0 mm per year. These results demonstrate the significant role roots play in tree physiological processes and in bedrock deterioration.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lin, J.S.; Miyamoto, Y.

The fracture behavior of graded Al{sub 2}O{sub 3}/TiC/Ni materials with a symmetric structure was investigated using single-edge notch-bend (SENB) specimens with surface compression. The fracture toughness of the graded materials was determined according to ASTM Standard E399. The results show that the effective fracture toughness increases with an increase in notch depth in the compressive stress zone, and reaches the maximum of 39.2 MPa m{sup 1/2} at the interface of compressive/tensile stress zones. Finite elements analysis reveals that the surface compression will be intensified at the notch root once the specimen is edge-notched because of the stress concentration, and themore » digress of the compressive stress intensification increases with an increase in notch depth. The dependence of the effective fracture toughness of the graded materials on the notch depth shows a behavior similar to the R-curve that is usually associated with microstructural toughening mechanisms. This toughening behavior is caused by the intensification of the compressive stress concentration with the increase of the notch depth. A theoretical analysis based on fracture mechanics verifies that the mechanical reliability of brittle ceramics can be improved effectively by tailoring and controlling the internal stresses.« less

Nocturnal and daytime stomatal conductance respond to root-zone temperature in ‘Shiraz’ grapevines

PubMed Central

Rogiers, Suzy Y.; Clarke, Simon J.

2013-01-01

Background and Aims Daytime root-zone temperature may be a significant factor regulating water flux through plants. Water flux can also occur during the night but nocturnal stomatal response to environmental drivers such as root-zone temperature remains largely unknown. Methods Here nocturnal and daytime leaf gas exchange was quantified in ‘Shiraz’ grapevines (Vitis vinifera) exposed to three root-zone temperatures from budburst to fruit-set, for a total of 8 weeks in spring. Key Results Despite lower stomatal density, night-time stomatal conductance and transpiration rates were greater for plants grown in warm root-zones. Elevated root-zone temperature resulted in higher daytime stomatal conductance, transpiration and net assimilation rates across a range of leaf-to-air vapour pressure deficits, air temperatures and light levels. Intrinsic water-use efficiency was, however, lowest in those plants with warm root-zones. CO2 response curves of foliar gas exchange indicated that the maximum rate of electron transport and the maximum rate of Rubisco activity did not differ between the root-zone treatments, and therefore it was likely that the lower photosynthesis in cool root-zones was predominantly the result of a stomatal limitation. One week after discontinuation of the temperature treatments, gas exchange was similar between the plants, indicating a reversible physiological response to soil temperature. Conclusions In this anisohydric grapevine variety both night-time and daytime stomatal conductance were responsive to root-zone temperature. Because nocturnal transpiration has implications for overall plant water status, predictive climate change models using stomatal conductance will need to factor in this root-zone variable. PMID:23293018

Nocturnal and daytime stomatal conductance respond to root-zone temperature in 'Shiraz' grapevines.

PubMed

Rogiers, Suzy Y; Clarke, Simon J

2013-03-01

Daytime root-zone temperature may be a significant factor regulating water flux through plants. Water flux can also occur during the night but nocturnal stomatal response to environmental drivers such as root-zone temperature remains largely unknown. Here nocturnal and daytime leaf gas exchange was quantified in 'Shiraz' grapevines (Vitis vinifera) exposed to three root-zone temperatures from budburst to fruit-set, for a total of 8 weeks in spring. Despite lower stomatal density, night-time stomatal conductance and transpiration rates were greater for plants grown in warm root-zones. Elevated root-zone temperature resulted in higher daytime stomatal conductance, transpiration and net assimilation rates across a range of leaf-to-air vapour pressure deficits, air temperatures and light levels. Intrinsic water-use efficiency was, however, lowest in those plants with warm root-zones. CO(2) response curves of foliar gas exchange indicated that the maximum rate of electron transport and the maximum rate of Rubisco activity did not differ between the root-zone treatments, and therefore it was likely that the lower photosynthesis in cool root-zones was predominantly the result of a stomatal limitation. One week after discontinuation of the temperature treatments, gas exchange was similar between the plants, indicating a reversible physiological response to soil temperature. In this anisohydric grapevine variety both night-time and daytime stomatal conductance were responsive to root-zone temperature. Because nocturnal transpiration has implications for overall plant water status, predictive climate change models using stomatal conductance will need to factor in this root-zone variable.

Vegetative growth and cluster development in Shiraz grapevines subjected to partial root-zone cooling

PubMed Central

Rogiers, Suzy Y.; Clarke, Simon J.

2013-01-01

Heterogeneity in root-zone temperature both vertically and horizontally may contribute to the uneven vegetative and reproductive growth often observed across vineyards. An experiment was designed to assess whether the warmed half of a grapevine root zone could compensate for the cooled half in terms of vegetative growth and reproductive development. We divided the root system of potted Shiraz grapevines bilaterally and applied either a cool or a warm treatment to each half from budburst to fruit set. Shoot growth and inflorescence development were monitored over the season. Simultaneous cooling and warming of parts of the root system decreased shoot elongation, leaf emergence and leaf expansion below that of plants with a fully warmed root zone, but not to the same extent as those with a fully cooled root zone. Inflorescence rachis length, flower number and berry number after fertilization were smaller only in those vines exposed to fully cooled root zones. After terminating the treatments, berry enlargement and the onset of veraison were slowed in those vines that had been exposed to complete or partial root-zone cooling. Grapevines exposed to partial root-zone cooling were thus delayed in vegetative and reproductive development, but the inhibition was greater in those plants whose entire root system had been cooled. PMID:24244839

Anchorage failure of young trees in sandy soils is prevented by a rigid central part of the root system with various designs

PubMed Central

Danquechin Dorval, Antoine; Meredieu, Céline; Danjon, Frédéric

2016-01-01

Background and Aims Storms can cause huge damage to European forests. Even pole-stage trees with 80-cm rooting depth can topple. Therefore, good anchorage is needed for trees to survive and grow up from an early age. We hypothesized that root architecture is a predominant factor determining anchorage failure caused by strong winds. Methods We sampled 48 seeded or planted Pinus pinaster trees of similar aerial size from four stands damaged by a major storm 3 years before. The trees were gathered into three classes: undamaged, leaning and heavily toppled. After uprooting and 3D digitizing of their full root architectures, we computed the mechanical characteristics of the main components of the root system from our morphological measurements. Key Results Variability in root architecture was quite large. A large main taproot, either short and thick or long and thin, and guyed by a large volume of deep roots, was the major component that prevented stem leaning. Greater shallow root flexural stiffness mainly at the end of the zone of rapid taper on the windward side also prevented leaning. Toppling in less than 90-cm-deep soil was avoided in trees with a stocky taproots or with a very big leeward shallow root. Toppled trees also had a lower relative root biomass – stump excluded – than straight trees. Conclusions It was mainly the flexural stiffness of the central part of the root system that secured anchorage, preventing a weak displacement of the stump. The distal part of the longest taproot and attached deep roots may be the only parts of the root system contributing to anchorage through their maximum tensile load. Several designs provided good anchorage, depending partly on available soil depth. Pole-stage trees are in-between the juvenile phase when they fail by toppling and the mature phase when they fail by uprooting. PMID:27456136

3D Electrical Resistivity Tomography and Mise-à-la-Masse Method as Tools for the Characterization of Vine Roots

NASA Astrophysics Data System (ADS)

Boaga, J.; Mary, B.; Peruzzo, L.; Schmutz, M.; Wu, Y.; Hubbard, S. S.; Cassiani, G.

2017-12-01

The interest on non-invasive geophysical monitoring of soil properties and root architecture is rapidly growing. Despite this, few case studies exist concerning vineyards, which are economically one of the leading sectors of agriculture. In this study, we integrate different geophysical methods in order to gain a better imaging of the vine root system, with the aim of quantifying root development, a key factor to understand roots-soil interaction and water balance. Our test site is a vineyard located in Bordeaux (France), where we adopted the Mise-a-la-Masse method (MALM) and micro-scale electrical resistivity tomography (ERT) on the same 3D electrode configuration. While ERT is a well-established technique to image changes in soil moisture content by root activity, MALM is a relatively new approach in this field of research. The idea is to inject current directly in the plant trunk and verify the resulting voltage distribution in the soil, as an effect of current distribution through the root system. In order to distinguish the root effect from other phenomena linked to the soil heterogeneities, we conducted and compared MALM measurements acquired through injecting current into the stem and into the soil near the stem. Moreover, the MALM data measured in the field were compared with numerical simulations to improve the confidence in the interpretation. Differences obtained between the stem and soil injection clearly validated the assumption that the whole root system is acting as a current pathway, thus highlighting the locations at depth where current is entering the soil from the fine roots. The simulation results indicated that the best fit is obtained through considering distributed sources with depth, reflecting a probable root zone area. The root location and volume estimated using this procedure are in agreement with vineyard experimental evidence. This work suggests the promising application of electrical methods to locate and monitor root systems. Further work is necessary to effectively integrate the geophysical and plant physiology information.

Assessment of the geothermal potential of fault zones in Germany by numerical modelling

NASA Astrophysics Data System (ADS)

Kuder, Jörg

2017-04-01

Fault zones with significantly better permeabilities than host rocks can act as natural migration paths for ascending fluids that are able to transport thermal energy from deep geological formations. Under these circumstances, fault zones are interesting for geothermal utilization especially those in at least 7 km depth (Jung et al. 2002, Paschen et al. 2003). One objective of the joint project "The role of deep rooting fault zones for geothermal energy utilization" supported by the Federal Ministry for Economic Affairs and Energy was the evaluation of the geothermal potential of fault zones in Germany by means of numerical modelling with COMSOL. To achieve this goal a method was developed to estimate the potential of regional generalized fault zones in a simple but yet sophisticated way. The main problem for the development of a numerical model is the lack of geological and hydrological data. To address this problem the geothermal potential of a cube with 1 km side length including a 20 meter broad, 1000 m high and 1000 m long fault zone was calculated as a unified model with changing parameter sets. The properties of the surrounding host rock and the fault zone are assumed homogenous. The numerical models were calculated with a broad variety of fluid flow, rock and fluid property parameters for the depths of 3000-4000 m, 4000-5000 m, 5000-6000 m and 6000-7000 m. The fluid parameters are depending on temperature, salt load and initial pressure. The porosity and permeability values are provided by the database of the geothermal information system (GeotIS). The results are summarized in a table of values of geothermal energy modelled with different parameter sets and depths. The geothermal potential of fault zones in Germany was then calculated on the basis of this table and information of the geothermal atlas of Germany (2016).

Examining nitrogen dynamics in heterogeneous soils: preliminary work

NASA Astrophysics Data System (ADS)

Jolicoeur, J. L.; Salvage, K. M.

2004-05-01

A study is being conducted in the Catatonk Creek watershed, in the headwaters of the Susquehanna River, in order to determine the vulnerability of the valley-fill aquifers to nitrate contamination. The overall objective of this study is to evaluate the nitrogen retention mechanisms for a combination of different soil types and different agricultural land uses and is scheduled to last approximately 2 years with ongoing fieldwork starting the summer of 2003 to the spring of 2005. This project will investigate the residence time and the quantity of the nitrate leached below the root zone and due to enter eventually the groundwater, and the existence of subsurface flow draining the nitrate from the root zone to the adjacent streams. Finally, a numerical and an analytical model will be developed that can be used as a tool for predicting the long-term effect of fertilizer application as a source of nitrate loading to the underlying aquifer or to surface water. In order to address the objectives of this research, a field investigation of three experimental sites will be carried out. Data will be collected on land uses, agricultural practices, climatic factors, soil properties, nitrogen dynamics in the soil, and the flow pattern in the unsaturated soil zone. At each site soil physical and chemical properties will be determined for each layer of the root zone to a depth of 90 cm. The soil physical properties include soil moisture, saturated and unsaturated hydraulic conductivity, bulk density, soil temperature, particle size distribution and its water retention curve. Soil water content and matric potential will be monitored using conventional and geophysical techniques including matric potential blocks, water content reflectometer sensors, Time Domain Reflectometry (TDR) and Ground Penetrating Radar (GPR). The soil chemical properties include soil total organic carbon and total nitrogen, nitrate (NO3) and ammonium (NH4) and will be determined at the beginning and at the end of the field season. The soil water will be collected monthly at three depths at each site throughout the growing season and will be analyzed for nitrate and ammonium.

Root system-based limits to agricultural productivity and efficiency: the farming systems context

PubMed Central

Thorup-Kristensen, Kristian; Kirkegaard, John

2016-01-01

Background There has been renewed global interest in both genetic and management strategies to improve root system function in order to improve agricultural productivity and minimize environmental damage. Improving root system capture of water and nutrients is an obvious strategy, yet few studies consider the important interactions between the genetic improvements proposed, and crop management at a system scale that will influence likely success. Scope To exemplify these interactions, the contrasting cereal-based farming systems of Denmark and Australia were used, where the improved uptake of water and nitrogen from deeper soil layers has been proposed to improve productivity and environmental outcomes in both systems. The analysis showed that water and nitrogen availability, especially in deeper layers (>1 m), was significantly affected by the preceding crops and management, and likely to interact strongly with deeper rooting as a specific trait of interest. Conclusions In the semi-arid Australian environment, grain yield impacts from storage and uptake of water from depth (>1 m) could be influenced to a stronger degree by preceding crop choice (0·42 t ha–1), pre-crop fallow management (0·65 t ha–1) and sowing date (0·63 t ha–1) than by current genetic differences in rooting depth (0·36 t ha–1). Matching of deep-rooted genotypes to management provided the greatest improvements related to deep water capture. In the wetter environment of Denmark, reduced leaching of N was the focus. Here the amount of N moving below the root zone was also influenced by previous crop choice or cover crop management (effects up to 85 kg N ha–1) and wheat crop sowing date (up to 45 kg ha–1), effects which over-ride the effects of differences in rooting depth among genotypes. These examples highlight the need to understand the farming system context and important G × E × M interactions in studies on proposed genetic improvements to root systems for improved productivity or environmental outcomes. PMID:27411680

The potential use of storm water and effluent from a constructed wetland for re-vegetating a degraded pyrite trail in Queen Elizabeth National Park, Uganda

NASA Astrophysics Data System (ADS)

Osaliya, R.; Kansiime, F.; Oryem-Origa, H.; Kateyo, E.

During the operation of the Kilembe Mines (copper mining) a cobaltiferous stockpile was constructed, which began to erode after the closure of the mines in the early 1970s. The erosion of the pyrite stockpile resulted in a large acid trail all the way to Lake George (a Ramsar site). The acid trail contaminated a large area of Queen Elizabeth National Park (QENP) resulting in the death of most of the shallow-rooted vegetation. Processes and conditions created by storm water and effluent from a constructed wetland were assessed for vegetation regeneration in the degraded QENP pyrite trail. Cynodon dactylon, Imperata cylindrica and Hyparrhenia filipendula dominated the regeneration zone (RZ) where storm water and effluent from a constructed wetland was flowing; and the adjacent unpolluted area (UP) with importance value indices of 186.4 and 83.3 respectively. Typha latifolia and C. dactylon formed two distinct vegetation sub-zones within the RZ with the former inhabiting areas with a higher water table. Soil pH was significantly higher in the RZ, followed by UP and bare pyrite trail (BPT) at both 0-15 cm and 16-30 cm depths. Soil electrical conductivity was not significantly different in the RZ and BPT but significantly higher than that in UP for both depths. For 0-15 cm depth, RZ had significantly higher concentrations of copper than BPT and UP which had similar concentrations. Still at this depth (0-15 cm), the unpolluted area had significantly higher concentrations of total phosphorus and total nitrogen than the regeneration zone and the bare pyrite trail which had similar concentrations. The RZ dominated by Typha had significantly higher concentrations of TP and TN compared to the RZ dominated by Cynodon. The concentrations of NH 4-N were significantly lower in Typha regeneration zone than in CRZ at 0-15 cm depth but similar at 16-30 cm depth. At 16-30 cm depth, concentrations of copper were significantly higher in the regeneration zone followed by the bare pyrite trail and the unpolluted zone. The concentration of lead in the regeneration zone and bare pyrite trail were similar but significantly higher in the unpolluted zone. Concentrations of TP and TN were significantly higher in unpolluted zone, followed by regeneration zone and bare pyrite trail. Storm water and effluent from a constructed wetland enhanced the revegetation process by modifying soil pH, making plant growth nutrients available and by providing a steady supply of moisture necessary for plant growth. T. latifolia and C. dactylon which seem to have tolerance of high concentrations of metals were the dominant species in the regeneration zone. If storm water and effluent supply continues, the aforementioned vegetation will colonize the pyrite trail and will eventually protect QENP and Lake George from metal contamination.

Joint Local/Teleseismic Tomographic Inversion in Taiwan Using TAIGER and Other Data

NASA Astrophysics Data System (ADS)

Lee, E.; Wu, F. T.; Huang, B.; Liang, W.; Wang, C.; Rawlinson, N.; Okaya, D. A.

2008-12-01

Taiwan, one of the most active orogenic belts, is at the intersection of two subduction zones. In southern Taiwan, the South China Sea Slab (SCSS), part of Eurasian Plate (EP), subducts beneath the Luzon arc along the Manila trench. In northern Taiwan, the Philippine Sea Plate (PSP) subducts beneath the Ryukyu arc along the Ryukyu trench. The thin skinned model and lithospheric deformation model have been proposed to explain the formation of orogeny. To distinguish between these two geodynamically possible processes, imaging of the deep structures below Taiwan is necessary. In this study, explosion data, local/regional earthquakes and teleseisms are used to invert the velocity structures of Taiwan from surface to about 150 km. Temporary passive broadband (on land and at the ocean bottom), active sources array datasets of the TAIGER (TAiwan Integrated GEodynamics Research) project and permanent array datasets of the BATS (Broadband Array in Taiwan for Seismology) and CWB (Central Weather Bureau) are used in this study. FMTOMO (fast marching tomography) of Rawlinson et al. (2006) is employed to invert the 3D P-wavespeed beneath Taiwan. The derived velocity perturbations dVp (dVp= Vfinal-Vinital) are clearly related to geology and tectonics. At shallow depth (< 10km), dVp >0 under the Central Range (Pre-Tertiary metamorphic rocks) and dVp < 0 under the Foothills (Pliocene sedimentary). Below a depth about 20 km, the placement of the high and low anomalies is reversed, i.e., dVp>0 under the Foothills and dVp<0 under the Central Range; the low velocity core of the Central Ranges extend down to about 50 km, forming the mountain root. A steeply dipping high velocity zone lies under the thickening 'mountain root' in central Taiwan. In southern Taiwan, the high velocity zone dips eastward coinciding with the Benioff Zone. The geometry of the high velocity zones in the upper mantle are key to understanding the Taiwan orogeny.

Groundwater controls on vegetation composition and patterning in mountain meadows

NASA Astrophysics Data System (ADS)

Lowry, Christopher S.; Loheide, Steven P., II; Moore, Courtney E.; Lundquist, Jessica D.

2011-10-01

Mountain meadows are groundwater-dependent ecosystems that are hot spots of biodiversity and productivity. In the Sierra Nevada mountains of California, these ecosystems rely on shallow groundwater to support their vegetation communities during the dry summer growing season in the region's Mediterranean montane climate. Vegetation composition in this environment is influenced by both (1) oxygen stress that occurs when portions of the root zone are saturated and anaerobic conditions limit root respiration and (2) water stress that occurs when the water table drops and the root zone becomes water limited. A spatially distributed watershed model that explicitly accounts for snowmelt processes was linked to a fine-resolution groundwater flow model of Tuolumne Meadows in Yosemite National Park, California, to simulate water table dynamics. This linked hydrologic model was calibrated to observations from a well observation network for 2006-2009. A vegetation survey was also conducted at the site in which the three dominant species were identified at more than 200 plots distributed across the meadow. Nonparametric multiplicative regression was performed to create and select the best models for predicting vegetation dominance on the basis of the simulated hydrologic regime. The hydrologic niches of three vegetation types representing wet, moist, and dry meadow vegetation communities were found to be best described using both (1) a sum exceedance value calculated as the integral of water table position above a depth threshold of oxygen stress and (2) a sum exceedance value calculated as the integral of water table position below a depth threshold of water stress. This linked hydrologic and vegetative modeling framework advances our ability to predict the propagation of human-induced climatic and land use or land cover changes through the hydrologic system to the ecosystem. The hydroecologic functioning of meadows provides an example of the extent to which cascading hydrologic processes at watershed, hillslope, and riparian zones and within channels are reflected in the composition and distribution of riparian vegetation.

A method for simulating transient ground-water recharge in deep water-table settings in central Florida by using a simple water-balance/transfer-function model

USGS Publications Warehouse

O'Reilly, Andrew M.

2004-01-01

A relatively simple method is needed that provides estimates of transient ground-water recharge in deep water-table settings that can be incorporated into other hydrologic models. Deep water-table settings are areas where the water table is below the reach of plant roots and virtually all water that is not lost to surface runoff, evaporation at land surface, or evapotranspiration in the root zone eventually becomes ground-water recharge. Areas in central Florida with a deep water table generally are high recharge areas; consequently, simulation of recharge in these areas is of particular interest to water-resource managers. Yet the complexities of meteorological variations and unsaturated flow processes make it difficult to estimate short-term recharge rates, thereby confounding calibration and predictive use of transient hydrologic models. A simple water-balance/transfer-function (WBTF) model was developed for simulating transient ground-water recharge in deep water-table settings. The WBTF model represents a one-dimensional column from the top of the vegetative canopy to the water table and consists of two components: (1) a water-balance module that simulates the water storage capacity of the vegetative canopy and root zone; and (2) a transfer-function module that simulates the traveltime of water as it percolates from the bottom of the root zone to the water table. Data requirements include two time series for the period of interest?precipitation (or precipitation minus surface runoff, if surface runoff is not negligible) and evapotranspiration?and values for five parameters that represent water storage capacity or soil-drainage characteristics. A limiting assumption of the WBTF model is that the percolation of water below the root zone is a linear process. That is, percolating water is assumed to have the same traveltime characteristics, experiencing the same delay and attenuation, as it moves through the unsaturated zone. This assumption is more accurate if the moisture content, and consequently the unsaturated hydraulic conductivity, below the root zone does not vary substantially with time. Results of the WBTF model were compared to those of the U.S. Geological Survey variably saturated flow model, VS2DT, and to field-based estimates of recharge to demonstrate the applicability of the WBTF model for a range of conditions relevant to deep water-table settings in central Florida. The WBTF model reproduced independently obtained estimates of recharge reasonably well for different soil types and water-table depths.

The evolution of root zone moisture storage capacities after deforestation: a step towards hydrological predictions under change?

NASA Astrophysics Data System (ADS)

Nijzink, Remko C.; Hutton, Christopher; Pechlivanidis, Ilias; Capell, René; Arheimer, Berit; Freer, Jim; Han, Dawei; Wagener, Thorsten; McGuire, Kevin; Savenije, Hubert; Hrachowitz, Markus

2017-04-01

The moisture storage available to vegetation is a key parameter in the hydrological functioning of ecosystems. This parameter, the root zone storage capacity, determines the partitioning between runoff and transpiration, but is impossible to observe at the catchment scale. In this research, data from the experimental forests of HJ Andrews (Oregon, USA) and Hubbard Brook (New Hampshire, USA) was used to test the hypotheses that: (1) the root zone storage capacity significantly changes after deforestation, (2) changes in the root zone storage capacity can to a large extent explain post-treatment changes to the hydrological regimes and that (3) a time-dynamic formulation of the root zone storage can improve the performance of a hydrological model. At first, root zone storage capacities were estimated based on a simple, water-balance based method. Briefly, the maximum difference between cumulative rainfall and estimated transpiration was determined, which could be considered a proxy for root zone storage capacity. These values were compared with root zone storage capacities obtained from four conceptual models (HYPE, HYMOD, FLEX, TUW), calibrated for consecutive 2-year windows. Both methods showed a sharp decline in root zone storage capacity after deforestation, which was followed by a gradual recovery signal. It was found in a trend analysis that these recovery periods took between 5 and 13 years for the different catchments. Eventually, one of the models was adjusted to allow for a time-dynamic formulation of root zone storage capacity. This adjusted model showed improvements in model performance as evaluated by 28 hydrological signatures, such as rising limb density or peak flows. Thus, this research clearly shows the time-dynamic character of a crucial parameter, which is often considered to remain constant in time. Root zone storage capacities are strongly affected by deforestation, leading to changes in hydrological regimes, and time-dynamic formulations of root zone storage are therefore necessary in systems under change.

Hydrologic regulation of plant rooting depth

PubMed Central

Miguez-Macho, Gonzalo; Jobbágy, Esteban G.; Jackson, Robert B.; Otero-Casal, Carlos

2017-01-01

Plant rooting depth affects ecosystem resilience to environmental stress such as drought. Deep roots connect deep soil/groundwater to the atmosphere, thus influencing the hydrologic cycle and climate. Deep roots enhance bedrock weathering, thus regulating the long-term carbon cycle. However, we know little about how deep roots go and why. Here, we present a global synthesis of 2,200 root observations of >1,000 species along biotic (life form, genus) and abiotic (precipitation, soil, drainage) gradients. Results reveal strong sensitivities of rooting depth to local soil water profiles determined by precipitation infiltration depth from the top (reflecting climate and soil), and groundwater table depth from below (reflecting topography-driven land drainage). In well-drained uplands, rooting depth follows infiltration depth; in waterlogged lowlands, roots stay shallow, avoiding oxygen stress below the water table; in between, high productivity and drought can send roots many meters down to the groundwater capillary fringe. This framework explains the contrasting rooting depths observed under the same climate for the same species but at distinct topographic positions. We assess the global significance of these hydrologic mechanisms by estimating root water-uptake depths using an inverse model, based on observed productivity and atmosphere, at 30″ (∼1-km) global grids to capture the topography critical to soil hydrology. The resulting patterns of plant rooting depth bear a strong topographic and hydrologic signature at landscape to global scales. They underscore a fundamental plant–water feedback pathway that may be critical to understanding plant-mediated global change. PMID:28923923

Hydrologic regulation of plant rooting depth.

PubMed

Fan, Ying; Miguez-Macho, Gonzalo; Jobbágy, Esteban G; Jackson, Robert B; Otero-Casal, Carlos

2017-10-03

Plant rooting depth affects ecosystem resilience to environmental stress such as drought. Deep roots connect deep soil/groundwater to the atmosphere, thus influencing the hydrologic cycle and climate. Deep roots enhance bedrock weathering, thus regulating the long-term carbon cycle. However, we know little about how deep roots go and why. Here, we present a global synthesis of 2,200 root observations of >1,000 species along biotic (life form, genus) and abiotic (precipitation, soil, drainage) gradients. Results reveal strong sensitivities of rooting depth to local soil water profiles determined by precipitation infiltration depth from the top (reflecting climate and soil), and groundwater table depth from below (reflecting topography-driven land drainage). In well-drained uplands, rooting depth follows infiltration depth; in waterlogged lowlands, roots stay shallow, avoiding oxygen stress below the water table; in between, high productivity and drought can send roots many meters down to the groundwater capillary fringe. This framework explains the contrasting rooting depths observed under the same climate for the same species but at distinct topographic positions. We assess the global significance of these hydrologic mechanisms by estimating root water-uptake depths using an inverse model, based on observed productivity and atmosphere, at 30″ (∼1-km) global grids to capture the topography critical to soil hydrology. The resulting patterns of plant rooting depth bear a strong topographic and hydrologic signature at landscape to global scales. They underscore a fundamental plant-water feedback pathway that may be critical to understanding plant-mediated global change.

Hydrologic regulation of plant rooting depth

NASA Astrophysics Data System (ADS)

Fan, Ying; Miguez-Macho, Gonzalo; Jobbágy, Esteban G.; Jackson, Robert B.; Otero-Casal, Carlos

2017-10-01

Plant rooting depth affects ecosystem resilience to environmental stress such as drought. Deep roots connect deep soil/groundwater to the atmosphere, thus influencing the hydrologic cycle and climate. Deep roots enhance bedrock weathering, thus regulating the long-term carbon cycle. However, we know little about how deep roots go and why. Here, we present a global synthesis of 2,200 root observations of >1,000 species along biotic (life form, genus) and abiotic (precipitation, soil, drainage) gradients. Results reveal strong sensitivities of rooting depth to local soil water profiles determined by precipitation infiltration depth from the top (reflecting climate and soil), and groundwater table depth from below (reflecting topography-driven land drainage). In well-drained uplands, rooting depth follows infiltration depth; in waterlogged lowlands, roots stay shallow, avoiding oxygen stress below the water table; in between, high productivity and drought can send roots many meters down to the groundwater capillary fringe. This framework explains the contrasting rooting depths observed under the same climate for the same species but at distinct topographic positions. We assess the global significance of these hydrologic mechanisms by estimating root water-uptake depths using an inverse model, based on observed productivity and atmosphere, at 30″ (˜1-km) global grids to capture the topography critical to soil hydrology. The resulting patterns of plant rooting depth bear a strong topographic and hydrologic signature at landscape to global scales. They underscore a fundamental plant-water feedback pathway that may be critical to understanding plant-mediated global change.

The Iceland Deep Drilling Project 4.5 km deep well, IDDP-2, in the seawater-recharged Reykjanes geothermal field in SW Iceland has successfully reached its supercritical target

NASA Astrophysics Data System (ADS)

Friðleifsson, Guðmundur Ó.; Elders, Wilfred A.; Zierenberg, Robert A.; Stefánsson, Ari; Fowler, Andrew P. G.; Weisenberger, Tobias B.; Harðarson, Björn S.; Mesfin, Kiflom G.

2017-11-01

The Iceland Deep Drilling Project research well RN-15/IDDP-2 at Reykjanes, Iceland, reached its target of supercritical conditions at a depth of 4.5 km in January 2017. After only 6 days of heating, the measured bottom hole temperature was 426 °C, and the fluid pressure was 34 MPa. The southern tip of the Reykjanes peninsula is the landward extension of the Mid-Atlantic Ridge in Iceland. Reykjanes is unique among Icelandic geothermal systems in that it is recharged by seawater, which has a critical point of 406 °C at 29.8 MPa. The geologic setting and fluid characteristics at Reykjanes provide a geochemical analog that allows us to investigate the roots of a mid-ocean ridge submarine black smoker hydrothermal system. Drilling began with deepening an existing 2.5 km deep vertical production well (RN-15) to 3 km depth, followed by inclined drilling directed towards the main upflow zone of the system, for a total slant depth of 4659 m ( ˜ 4.5 km vertical depth). Total circulation losses of drilling fluid were encountered below 2.5 km, which could not be cured using lost circulation blocking materials or multiple cement jobs. Accordingly, drilling continued to the total depth without return of drill cuttings. Thirteen spot coring attempts were made below 3 km depth. Rocks in the cores are basalts and dolerites with alteration ranging from upper greenschist facies to amphibolite facies, suggesting that formation temperatures at depth exceed 450 °C. High-permeability circulation-fluid loss zones (feed points or feed zones) were detected at multiple depth levels below 3 km depth to bottom. The largest circulation losses (most permeable zones) occurred between the bottom of the casing and 3.4 km depth. Permeable zones encountered below 3.4 km accepted less than 5 % of the injected water. Currently, the project is attempting soft stimulation to increase deep permeability. While it is too early to speculate on the energy potential of this well and its economics, the IDDP-2 is a milestone in the development of geothermal resources and the study of hydrothermal systems. It is the first well that successfully encountered supercritical hydrothermal conditions, with potential high-power output, and in which on-going hydrothermal metamorphism at amphibolite facies conditions can be observed. The next step will be to carry out flow testing and fluid sampling to determine the chemical and thermodynamic properties of the formation fluids.

A microwave systems approach to measuring root zone soil moisture

NASA Technical Reports Server (NTRS)

Newton, R. W.; Paris, J. F.; Clark, B. V.

1983-01-01

Computer microwave satellite simulation models were developed and the program was used to test the ability of a coarse resolution passive microwave sensor to measure soil moisture over large areas, and to evaluate the effect of heterogeneous ground covers with the resolution cell on the accuracy of the soil moisture estimate. The use of realistic scenes containing only 10% to 15% bare soil and significant vegetation made it possible to observe a 60% K decrease in brightness temperature from a 5% soil moisture to a 35% soil moisture at a 21 cm microwave wavelength, providing a 1.5 K to 2 K per percent soil moisture sensitivity to soil moisture. It was shown that resolution does not affect the basic ability to measure soil moisture with a microwave radiometer system. Experimental microwave and ground field data were acquired for developing and testing a root zone soil moisture prediction algorithm. The experimental measurements demonstrated that the depth of penetration at a 21 cm microwave wavelength is not greater than 5 cm.

Multisensor Capacitance Probes for Simultaneously Monitoring Rice Field Soil-Water- Crop-Ambient Conditions.

PubMed

Brinkhoff, James; Hornbuckle, John; Dowling, Thomas

2017-12-26

Multisensor capacitance probes (MCPs) have traditionally been used for soil moisture monitoring and irrigation scheduling. This paper presents a new application of these probes, namely the simultaneous monitoring of ponded water level, soil moisture, and temperature profile, conditions which are particularly important for rice crops in temperate growing regions and for rice grown with prolonged periods of drying. WiFi-based loggers are used to concurrently collect the data from the MCPs and ultrasonic distance sensors (giving an independent reading of water depth). Models are fit to MCP water depth vs volumetric water content (VWC) characteristics from laboratory measurements, variability from probe-to-probe is assessed, and the methodology is verified using measurements from a rice field throughout a growing season. The root-mean-squared error of the water depth calculated from MCP VWC over the rice growing season was 6.6 mm. MCPs are used to simultaneously monitor ponded water depth, soil moisture content when ponded water is drained, and temperatures in root, water, crop and ambient zones. The insulation effect of ponded water against cold-temperature effects is demonstrated with low and high water levels. The developed approach offers advantages in gaining the full soil-plant-atmosphere continuum in a single robust sensor.

Experimentally increased nutrient availability at the permafrost thaw front selectively enhances biomass production of deep-rooting subarctic peatland species.

PubMed

Keuper, Frida; Dorrepaal, Ellen; van Bodegom, Peter M; van Logtestijn, Richard; Venhuizen, Gemma; van Hal, Jurgen; Aerts, Rien

2017-10-01

Climate warming increases nitrogen (N) mineralization in superficial soil layers (the dominant rooting zone) of subarctic peatlands. Thawing and subsequent mineralization of permafrost increases plant-available N around the thaw-front. Because plant production in these peatlands is N-limited, such changes may substantially affect net primary production and species composition. We aimed to identify the potential impact of increased N-availability due to permafrost thawing on subarctic peatland plant production and species performance, relative to the impact of increased N-availability in superficial organic layers. Therefore, we investigated whether plant roots are present at the thaw-front (45 cm depth) and whether N-uptake ( 15 N-tracer) at the thaw-front occurs during maximum thaw-depth, coinciding with the end of the growing season. Moreover, we performed a unique 3-year belowground fertilization experiment with fully factorial combinations of deep- (thaw-front) and shallow-fertilization (10 cm depth) and controls. We found that certain species are present with roots at the thaw-front (Rubus chamaemorus) and have the capacity (R. chamaemorus, Eriophorum vaginatum) for N-uptake from the thaw-front between autumn and spring when aboveground tissue is largely senescent. In response to 3-year shallow-belowground fertilization (S) both shallow- (Empetrum hermaphroditum) and deep-rooting species increased aboveground biomass and N-content, but only deep-rooting species responded positively to enhanced nutrient supply at the thaw-front (D). Moreover, the effects of shallow-fertilization and thaw-front fertilization on aboveground biomass production of the deep-rooting species were similar in magnitude (S: 71%; D: 111% increase compared to control) and additive (S + D: 181% increase). Our results show that plant-available N released from thawing permafrost can form a thus far overlooked additional N-source for deep-rooting subarctic plant species and increase their biomass production beyond the already established impact of warming-driven enhanced shallow N-mineralization. This may result in shifts in plant community composition and may partially counteract the increased carbon losses from thawing permafrost. © 2017 John Wiley & Sons Ltd.

Effects of fluoridated milk on root dentin remineralization.

PubMed

Arnold, Wolfgang H; Heidt, Bastian A; Kuntz, Sebastian; Naumova, Ella A

2014-01-01

The prevalence of root caries is increasing with greater life expectancy and number of retained teeth. Therefore, new preventive strategies should be developed to reduce the prevalence of root caries. The aim of this study was to investigate the effects of fluoridated milk on the remineralization of root dentin and to compare these effects to those of sodium fluoride (NaF) application without milk. Thirty extracted human molars were divided into 6 groups, and the root cementum was removed from each tooth. The dentin surface was demineralized and then incubated with one of the following six solutions: Sodium chloride NaCl, artificial saliva, milk, milk+2.5 ppm fluoride, milk+10 ppm fluoride and artificial saliva+10 ppm fluoride. Serial sections were cut through the lesions and investigated with polarized light microscopy and quantitative morphometry, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The data were statistically evaluated using a one-way ANOVA for multiple comparisons. The depth of the lesion decreased with increasing fluoride concentration and was the smallest after incubation with artificial saliva+10 ppm fluoride. SEM analysis revealed a clearly demarcated superficial remineralized zone after incubation with milk+2.5 ppm fluoride, milk+10 ppm fluoride and artificial saliva+10 ppm fluoride. Ca content in this zone increased with increasing fluoride content and was highest after artificial saliva+10 ppm fluoride incubation. In the artificial saliva+10 ppm fluoride group, an additional crystalline layer was present on top of the lesion that contained elevated levels of F and Ca. Incubation of root dentin with fluoridated milk showed a clear effect on root dentin remineralization, and incubation with NaF dissolved in artificial saliva demonstrated a stronger effect.

Root carbon decomposition and microbial biomass response at different soil depths

NASA Astrophysics Data System (ADS)

Rumpel, C.

2012-12-01

The relationship between root litter addition and soil organic matter (SOM) formation in top- versus subsoils is unknown. The aim of this study was to investigate root litter decomposition and stabilisation in relation to microbial parameters in different soil depths. Our conceptual approach included incubation of 13C-labelled wheat roots at 30, 60 and 90 cm soil depth for 36 months under field conditions. Quantitative root carbon contribution to SOM was assessed, changes of bulk root chemistry studied by solid-state 13C NMR spectroscopy and lignin content and composition was assessed after CuO oxidation. Compound-specific isotope analysis allowed to assess the role of root lignin for soil C storage in the different soil depths. Microbial biomass and community structure was determined after DNA extraction. After three years of incubation, O-alkyl C most likely assigned to polysaccharides decreased in all soil depth compared to the initial root material. The degree of root litter decomposition assessed by the alkyl/O-alkyl ratio decreased with increasing soil depth, while aryl/O-alkyl ratio was highest at 60 cm depth. Root-derived lignin showed depth specific concentrations (30 < 90 < 60 cm). Its composition was soil depth independent suggesting that microbial communities in all three soil depths had similar degradation abilities. Microbial biomass C and fungi contribution increased after root litter addition. Their community structure changed after root litter addition and showed horizon specific dynamics. Our study shows that root litter addition can contribute to C storage in subsoils but did not influence C storage in topsoil. We conclude that specific conditions of single soil horizons have to be taken into account if root C dynamics are to be fully understood.

Hydrologic Regulation of Plant Rooting Depth and Vice Versa

NASA Astrophysics Data System (ADS)

Fan, Y.; Miguez-Macho, G.

2017-12-01

How deep plant roots go and why may hold the answer to several questions regarding the co-evolution of terrestrial life and its environment. In this talk we explore how plant rooting depth responds to the hydrologic plumbing system in the soil/regolith/bedrocks, and vice versa. Through analyzing 2200 root observations of >1000 species along biotic (life form, genus) and abiotic (precipitation, soil, drainage) gradients, we found strong sensitivities of rooting depth to local soil water profiles determined by precipitation infiltration depth from the top (reflecting climate and soil), and groundwater table depth from below (reflecting topography-driven land drainage). In well-drained uplands, rooting depth follows infiltration depth; in waterlogged lowlands, roots stay shallow avoiding oxygen stress below the water table; in between, high productivity and drought can send roots many meters down to groundwater capillary fringe. We explore the global significance of this framework using an inverse model, and the implications to the coevolution of deep roots and the CZ in the Early-Mid Devonian when plants colonized the upland environments.

Polar transport of 45Ca2+ across the elongation zone of gravistimulated roots

NASA Technical Reports Server (NTRS)

Lee, J. S.; Evans, M. L.

1985-01-01

The movement of calcium across the elongation zone of gravistimulated primary roots of maize (Zea mays L.) was measured using 45Ca2+. Radioactive calcium was applied to one side of the elongation zone about 4 mm back from the root tip and the distribution of radioactivity across the root in the region of application was determined using scintillation spectrometry. The movement of 45Ca2+ across the elongation zone was non-polar in vertically oriented roots. In gravistimulated roots the movement of label was polarized with about twice as much label moving from top to bottom as from bottom to top. A variety of treatments which interfere with gravitropism was found to eliminate the polar movement of 45Ca2+ across the elongation zone. In maize cultivars which require light for gravitropic competency, dark grown roots exhibited neither gravitropism nor polar movement of 45Ca2+ across the elongation zone. Upon illumination the roots developed but gravitropic competency and gravity-induced polar movement of 45Ca2+ across the elongation zone. Similarly, roots of light-grown seedlings lost both gravitropic competency and 45Ca2+ transport polarity upon transfer to the dark. The results indicate a close correlation between calcium movement and gravitropism in primary roots in maize.

Of Mantle Plumes, Their Existence, and Their Nature: Insights from Whole Mantle SEM-Based Seismic Waveform Tomography

NASA Astrophysics Data System (ADS)

Romanowicz, B. A.; French, S. W.

2014-12-01

Many questions remain on the detailed morphology of mantle convection patterns. While high resolution P wave studies show a variety of subducted slab behaviors, some stagnating in the transition zone, others penetrating into the lower mantle (e.g. Fukao & Obayashi, 2013), low velocity structures - the upwelling part of flow - are more difficult to resolve at the same scale. Indeed, depth extent and morphology of the low velocity roots of hotspot volcanoes is still debated, along with the existence of "mantle plumes". Using spectral element waveform tomography, we previously constructed a global, radially anisotropic, upper mantle Vs model (SEMum2, French et al., 2013) and have now extended it to the whole mantle by adding shorter period waveform data (SEMUCB-WM1, French & Romanowicz, GJI, in revision). This model shows long wavelength structure in good agreement with other recent global Vs models derived under stronger approximations (Ritsema et al. 2011; Kustowski, et al. 2008), but exhibits better focused, finer scale structure throughout the mantle. SEMUCB-WM1 confirms the presence in all major ocean basins of the quasi-periodic, upper mantle low velocity anomalies, previously seen in SEMum2. At the same time, lower mantle low velocity structure is dominated by a small number (~15 globally) of quasi-vertical anomalies forming discrete "column"" rooted at the base of the mantle. Most columns are positioned near major hotspots, as defined by buoyancy flux, and are wider (~800-1000 km diameter) than expected from the thermal plume model - suggestive of thermo-chemical plumes, which may be stable for long times compared to purely thermal ones. Some columns reach the upper mantle, while others deflect horizontally near 1000 km - the same depth where many slabs appear to stagnate. As they reach the transition zone, the wide columnar structure can be lost, as these "plumes" appear to meander through the upper mantle, perhaps entrained by more vigorous, lower viscosity, convection. Most "plumes" in the Pacific LLSVP region appear as isolated columns rising from the CMB, such as beneath Hawaii (rooted near a known ultra low velocity zone, Cottaar & Romanowicz, 2012). Conversely, the African LLSVP region appears more massive up to mid-mantle depths, with isolated "plumes" at its borders, including that beneath Iceland.

Predicting unsaturated zone nitrogen mass balances in agricultural settings of the United States

USGS Publications Warehouse

Nolan, Bernard T.; Puckett, Larry J.; Ma, Liwang; Green, Christopher T.; Bayless, E. Randall; Malone, Robert W.

2009-01-01

Unsaturated zone N fate and transport were evaluated at four sites to identify the predominant pathways of N cycling: an almond [Prunus dulcis (Mill.) D.A. Webb] orchard and cornfield (Zea mays L.) in the lower Merced River study basin, California; and corn–soybean [Glycine max (L.) Merr.] rotations in study basins at Maple Creek, Nebraska, and at Morgan Creek, Maryland. We used inverse modeling with a new version of the Root Zone Water Quality Model (RZWQM2) to estimate soil hydraulic and nitrogen transformation parameters throughout the unsaturated zone; previous versions were limited to 3-m depth and relied on manual calibration. The overall goal of the modeling was to derive unsaturated zone N mass balances for the four sites. RZWQM2 showed promise for deeper simulation profiles. Relative root mean square error (RRMSE) values for predicted and observed nitrate concentrations in lysimeters were 0.40 and 0.52 for California (6.5 m depth) and Nebraska (10 m), respectively, and index of agreement (d) values were 0.60 and 0.71 (d varies between 0 and 1, with higher values indicating better agreement). For the shallow simulation profile (1 m) in Maryland, RRMSE and d for nitrate were 0.22 and 0.86, respectively. Except for Nebraska, predictions of average nitrate concentration at the bottom of the simulation profile agreed reasonably well with measured concentrations in monitoring wells. The largest additions of N were predicted to come from inorganic fertilizer (153–195 kg N ha−1 yr−1 in California) and N fixation (99 and 131 kg N ha−1 yr−1 in Maryland and Nebraska, respectively). Predicted N losses occurred primarily through plant uptake (144–237 kg N ha−1 yr−1) and deep seepage out of the profile (56–102 kg N ha−1 yr−1). Large reservoirs of organic N (up to 17,500 kg N ha−1 m−1 at Nebraska) were predicted to reside in the unsaturated zone, which has implications for potential future transfer of nitrate to groundwater.

The biologically active zone in upland habitats at the Hanford Site, Washington, USA: Focus on plant rooting depth and biomobilization.

PubMed

Lovtang, Sara; Delistraty, Damon; Rochette, Elizabeth

2018-07-01

We challenge the suggestion by Sample et al. (2015) that a depth of 305 cm (10 ft) exceeds the depth of biological activity in soils at the Hanford Site, Washington, USA, or similar sites. Instead, we support the standard point of compliance, identified in the Model Toxics Control Act in the state of Washington, which specifies a depth of 457 cm (15 ft) for the protection of both human and ecological receptors at the Hanford Site. Our position is based on additional information considered in our expanded review of the literature, the influence of a changing environment over time, plant community dynamics at the Hanford Site, and inherent uncertainty in the Sample et al. (2015) analysis. Integr Environ Assess Manag 2018;14:442-446. © 2018 SETAC. © 2018 SETAC.

Root growth, water uptake, and sap flow of winter wheat in response to different soil water conditions

NASA Astrophysics Data System (ADS)

Cai, Gaochao; Vanderborght, Jan; Langensiepen, Matthias; Schnepf, Andrea; Hüging, Hubert; Vereecken, Harry

2018-04-01

How much water can be taken up by roots and how this depends on the root and water distributions in the root zone are important questions that need to be answered to describe water fluxes in the soil-plant-atmosphere system. Physically based root water uptake (RWU) models that relate RWU to transpiration, root density, and water potential distributions have been developed but used or tested far less. This study aims at evaluating the simulated RWU of winter wheat using the empirical Feddes-Jarvis (FJ) model and the physically based Couvreur (C) model for different soil water conditions and soil textures compared to sap flow measurements. Soil water content (SWC), water potential, and root development were monitored noninvasively at six soil depths in two rhizotron facilities that were constructed in two soil textures: stony vs. silty, with each of three water treatments: sheltered, rainfed, and irrigated. Soil and root parameters of the two models were derived from inverse modeling and simulated RWU was compared with sap flow measurements for validation. The different soil types and water treatments resulted in different crop biomass, root densities, and root distributions with depth. The two models simulated the lowest RWU in the sheltered plot of the stony soil where RWU was also lower than the potential RWU. In the silty soil, simulated RWU was equal to the potential uptake for all treatments. The variation of simulated RWU among the different plots agreed well with measured sap flow but the C model predicted the ratios of the transpiration fluxes in the two soil types slightly better than the FJ model. The root hydraulic parameters of the C model could be constrained by the field data but not the water stress parameters of the FJ model. This was attributed to differences in root densities between the different soils and treatments which are accounted for by the C model, whereas the FJ model only considers normalized root densities. The impact of differences in root density on RWU could be accounted for directly by the physically based RWU model but not by empirical models that use normalized root density functions.

The role of root distribution in eco-hydrological modeling in semi-arid regions

NASA Astrophysics Data System (ADS)

Sivandran, G.; Bras, R. L.

2010-12-01

In semi arid regions, the rooting strategies employed by vegetation can be critical to its survival. Arid regions are characterized by high variability in the arrival of rainfall, and species found in these areas have adapted mechanisms to ensure the capture of this scarce resource. Niche separation, through rooting strategies, is one manner in which different species coexist. At present, land surface models prescribe rooting profiles as a function of only the plant functional type of interest with no consideration for the soil texture or rainfall regime of the region being modeled. These models do not incorporate the ability of vegetation to dynamically alter their rooting strategies in response to transient changes in environmental forcings and therefore tend to underestimate the resilience of many of these ecosystems. A coupled, dynamic vegetation and hydrologic model, tRIBS+VEGGIE, was used to explore the role of vertical root distribution on hydrologic fluxes. Point scale simulations were carried out using two vertical root distribution schemes: (i) Static - a temporally invariant root distribution; and (ii) Dynamic - a temporally variable allocation of assimilated carbon at any depth within the root zone in order to minimize the soil moisture-induced stress on the vegetation. The simulations were forced with a stochastic climate generator calibrated to weather stations and rain gauges in the semi-arid Walnut Gulch Experimental Watershed in Arizona. For the static root distribution scheme, a series of simulations were carried out varying the shape of the rooting profile. The optimal distribution for the simulation was defined as the root distribution with the maximum mean transpiration over a 200 year period. This optimal distribution was determined for 5 soil textures and using 2 plant functional types, and the results varied from case to case. The dynamic rooting simulations allow vegetation the freedom to adjust the allocation of assimilated carbon to different rooting depths in response to changes in stress caused by the redistribution and uptake of soil moisture. The results obtained from these experiments elucidate the strong link between plant functional type, soil texture and climate and highlight the potential errors in the modeling of hydrologic fluxes from imposing a static root profile.

Underplating along the northern portion of the Zagros suture zone, Iran

NASA Astrophysics Data System (ADS)

Motaghi, K.; Shabanian, E.; Kalvandi, F.

2017-07-01

A 2-D absolute shear wave velocity model has been resolved beneath a seismic profile across the northeastern margin of the Arabian Plate-Central Iran by simultaneously inverting data from P receiver functions and fundamental mode Rayleigh wave phase velocity. The data were gathered by a linear seismic array crossing the Zagros fold and thrust belt, Urmia-Dokhtar magmatic arc and Central Iran block assemblage as three major structural components of the Arabia-Eurasia collision. Our model shows a low-velocity tongue protruding from upper to lower crust which, north of the Zagros suture, indicates the signature of an intracontinent low-strength shear zone between the underthrusting and overriding continents. The velocity model confirms the presence of a significant crustal root as well as a thick high-velocity lithosphere in footwall of the suture, continuing northwards beneath the overriding continent for at least 200 km. These features are interpreted as underthrusting of Arabia beneath Central Iran. Time to depth migration of P receiver functions reveals an intracrustal flat interface at ∼17 km depth south of the suture; we interpret it as a significant decoupling within the upper crust. All these crustal scale structural features coherently explain different styles and kinematics of deformation in northern Zagros (Lorestan zone) with respect to its southern part (Fars zone).

Is rhizosphere remediation sufficient for sustainable revegetation of mine tailings?

PubMed

Huang, Longbin; Baumgartl, Thomas; Mulligan, David

2012-07-01

Revegetation of mine tailings (fine-grained waste material) starts with the reconstruction of root zones, consisting of a rhizosphere horizon (mostly topsoil and/or amended tailings) and the support horizon beneath (i.e. equivalent to subsoil - mostly tailings), which must be physically and hydro-geochemically stable. This review aims to discuss key processes involved in the development of functional root zones within the context of direct revegetation of tailings and introduces a conceptual process of rehabilitating structure and function in the root zones based on a state transition model. Field studies on the revegetation of tailings (from processing base metal ore and bauxite residues) are reviewed. Particular focus is given to tailings' properties that limit remediation effectiveness. Aspects of root zone reconstruction and vegetation responses are also discussed. When reconstructing a root zone system, it is critical to restore physical structure and hydraulic functions across the whole root zone system. Only effective and holistically restored systems can control hydro-geochemical mobility of acutely and chronically toxic factors from the underlying horizon and maintain hydro-geochemical stability in the rhizosphere. Thereafter, soil biological capacity and ecological linkages (i.e. carbon and nutrient cycling) may be rehabilitated to integrate the root zones with revegetated plant communities into sustainable plant ecosystems. A conceptual framework of system transitions between the critical states of root zone development has been proposed. This will illustrate the rehabilitation process in root zone reconstruction and development for direct revegetation with sustainable plant communities. Sustainable phytostabilization of tailings requires the systematic consideration of hydro-geochemical interactions between the rhizosphere and the underlying supporting horizon. It further requires effective remediation strategies to develop hydro-geochemically stable and biologically functional root zones, which can facilitate the recovery of the microbial community and ecological linkages with revegetated plant communities.

Precipitation patterns and moisture fluxes in a sandy, tropical environment with a shallow water table

NASA Astrophysics Data System (ADS)

Minihane, M. R.; Freyberg, D. L.

2011-08-01

Identifying the dominant mechanisms controlling recharge in shallow sandy soils in tropical climates has received relatively little attention. Given the expansion of coastal fill using marine sands and the growth of coastal populations throughout the tropics, there is a need to better understand the nature of water balances in these settings. We use time series of field observations at a coastal landfill in Singapore coupled with numerical modeling using the Richards' equation to examine the impact of precipitation patterns on soil moisture dynamics, including percolation past the root zone and recharge, in such an environment. A threshold in total precipitation event depth, much more so than peak precipitation intensity, is the strongest event control on recharge. However, shallow antecedent moisture, and therefore the timing between events along with the seasonal depth to water table, also play significant roles in determining recharge amounts. For example, at our field site, precipitation events of less than 3 mm per event yield little to no direct recharge, but for larger events, moisture content changes below the root zone are linearly correlated to the product of the average antecedent moisture content and the total event precipitation. Therefore, water resources planners need to consider identifying threshold precipitation volumes, along with the multiple time scales that capture variability in event antecedent conditions and storm frequency in assessing the role of recharge in coastal water balances in tropical settings.

In-situ atrazine biodegradation dynamics in wheat (Triticum) crops under variable hydrologic regime.

PubMed

la Cecilia, Daniele; Maggi, Federico

2017-08-01

A comprehensive biodegradation reaction network of atrazine (ATZ) and its 18 byproducts was coupled to the nitrogen cycle and integrated in a computational solver to assess the in-situ biodegradation effectiveness and leaching along a 5m deep soil cultivated with wheat in West Wyalong, New South Wales, Australia. Biodegradation removed 97.7% of 2kg/ha ATZ yearly applications in the root zone, but removal substantially decreased at increasing depths; dechlorination removed 79% of ATZ in aerobic conditions and 18% in anaerobic conditions, whereas deethylation and oxidation removed only 0.11% and 0.15% of ATZ, respectively. The residual Cl mass fraction in ATZ and 4 byproducts was 2.4% of the applied mass. ATZ half-life ranged from 150 to 247days in the soil surface. ATZ reached 5m soil depth within 200years and its concentration increased from 1×10 -6 to 4×10 -6 mg/kg dry-soil over time. The correlation between ATZ specific biomass degradation affinity Φ 0 and half-life t 1/2 , although relatively uncertain for both hydrolyzing and oxidizing bacteria, suggested that microorganisms with high Φ 0 led to low ATZ t 1/2 . Greater ATZ applications were balanced by small nonlinear increments of ATZ biodegraded fraction within the root zone and therefore less ATZ leached into the shallow aquifer. Copyright © 2017 Elsevier B.V. All rights reserved.

In-situ atrazine biodegradation dynamics in wheat (Triticum) crops under variable hydrologic regime

NASA Astrophysics Data System (ADS)

la Cecilia, Daniele; Maggi, Federico

2017-08-01

A comprehensive biodegradation reaction network of atrazine (ATZ) and its 18 byproducts was coupled to the nitrogen cycle and integrated in a computational solver to assess the in-situ biodegradation effectiveness and leaching along a 5 m deep soil cultivated with wheat in West Wyalong, New South Wales, Australia. Biodegradation removed 97.7% of 2 kg/ha ATZ yearly applications in the root zone, but removal substantially decreased at increasing depths; dechlorination removed 79% of ATZ in aerobic conditions and 18% in anaerobic conditions, whereas deethylation and oxidation removed only 0.11% and 0.15% of ATZ, respectively. The residual Cl mass fraction in ATZ and 4 byproducts was 2.4% of the applied mass. ATZ half-life ranged from 150 to 247 days in the soil surface. ATZ reached 5 m soil depth within 200 years and its concentration increased from 1 ×10-6 to 4 ×10-6 mg/kgdry-soil over time. The correlation between ATZ specific biomass degradation affinity Φ0 and half-life t1/2, although relatively uncertain for both hydrolyzing and oxidizing bacteria, suggested that microorganisms with high Φ0 led to low ATZ t1/2. Greater ATZ applications were balanced by small nonlinear increments of ATZ biodegraded fraction within the root zone and therefore less ATZ leached into the shallow aquifer.

Vitality of Enterococcus faecalis inside dentinal tubules after five root canal disinfection methods

PubMed Central

Vatkar, Niranjan Ashok; Hegde, Vivek; Sathe, Sucheta

2016-01-01

Aim: To compare the vitality of Enterococcus faecalis within dentinal tubules after subjected to five root canal disinfection methods. Materials and Methods: Dentin blocks (n = 60) were colonized with E. faecalis. After 4 weeks of incubation, the dentin blocks were divided into one control and five test groups (n = 10 each). The root canals of test groups were subjected to one of the disinfection methods, namely, normal saline (NS), sodium hypochlorite (NaOCl), chlorhexidine digluconate (CHX), neodymium-doped yttrium aluminum garnet (Nd: YAG) laser, and diode laser. The effect of disinfection methods was assessed by LIVE/DEAD BacLight stain under the confocal laser scanning microscopy to determine the “zone of dead bacteria” (ZDB). Mean values were calculated for ZDB and the difference between groups was established. Results: Penetration of E. faecalis was seen to a depth of >1000 μm. Viable bacteria were detected with NS irrigation. NaOCl and CHX showed partial ZDB. When the root canals were disinfected with Nd: YAG and diode lasers, no viable bacteria were found. Conclusion: E. faecalis has the ability to colonize inside dentinal tubules to a depth of >1000 μm. In contrast to conventional irrigants, both Nd: YAG and diode lasers were effective in eliminating the vitality of E. faecalis. NS, NaOCl, and CHX showed viable bacteria remaining in dentinal tubules. PMID:27656064

Evaluation of soil manipulation to prepare engineered earthen waste covers for revegetation

DOE PAGES

Waugh, W. Joseph; Benson, Craig H.; Albright, William H.; ...

2015-10-21

Seven ripping treatments designed to improve soil physical conditions for revegetation were compared on a test pad simulating an earthen cover for a waste disposal cell. The field test was part of study of methods to convert compacted-soil waste covers into evapotranspiration covers. The test pad consisted of a compacted layer of fine-textured soil simulating a barrier protection layer overlain by a gravelly sand bedding layer and a cobble armor layer. Treatments included combinations of soil-ripping implements (conventional shank [CS], wing-tipped shank [WTS], and parabolic oscillating shank with wings [POS]), ripping depths, and number of passes. Dimensions, dry density, moisturemore » content, and particle size distribution of disturbance zones were determined in two trenches excavated across rip rows. The goal was to create a root-zone dry density between 1.2 and 1.6 Mg m-3 and a seedbed soil texture ranging from clay loam to sandy loam with low rock content. All treatments created V-shaped disturbance zones as measured on trench faces. Disturbance zone size was most influenced by ripping depth. Winged implements created larger disturbance zones. All treatments lifted fines into the bedding layer, moved gravel and cobble down into the fine-textured protection layer, and thereby disrupted the capillary barrier at the interface. Changes in dry density within disturbance zones were comparable for the CS and WTS treatments but were highly variable among POS treatments. Water content increased in the bedding layer and decreased in the protection layer after ripping. The POS at 1.2-m depth and two passes created the largest zone with a low dry density (1.24 Mg m-3) and the most favorable seedbed soil texture (gravely silt loam). Furthermore, ripping also created large soil aggregates and voids in the protection layer that may produce preferential flow paths and reduce water storage capacity.« less

Floodplain ecohydrology: Climatic, anthropogenic, and local physical controls on partitioning of water sources to riparian trees.

PubMed

Singer, Michael Bliss; Sargeant, Christopher I; Piégay, Hervé; Riquier, Jérémie; Wilson, Rob J S; Evans, Cristina M

2014-05-01

Seasonal and annual partitioning of water within river floodplains has important implications for ecohydrologic links between the water cycle and tree growth. Climatic and hydrologic shifts alter water distribution between floodplain storage reservoirs (e.g., vadose, phreatic), affecting water availability to tree roots. Water partitioning is also dependent on the physical conditions that control tree rooting depth (e.g., gravel layers that impede root growth), the sources of contributing water, the rate of water drainage, and water residence times within particular storage reservoirs. We employ instrumental climate records alongside oxygen isotopes within tree rings and regional source waters, as well as topographic data and soil depth measurements, to infer the water sources used over several decades by two co-occurring tree species within a riparian floodplain along the Rhône River in France. We find that water partitioning to riparian trees is influenced by annual (wet versus dry years) and seasonal (spring snowmelt versus spring rainfall) fluctuations in climate. This influence depends strongly on local (tree level) conditions including floodplain surface elevation and subsurface gravel layer elevation. The latter represents the upper limit of the phreatic zone and therefore controls access to shallow groundwater. The difference between them, the thickness of the vadose zone, controls total soil moisture retention capacity. These factors thus modulate the climatic influence on tree ring isotopes. Additionally, we identified growth signatures and tree ring isotope changes associated with recent restoration of minimum streamflows in the Rhône, which made new phreatic water sources available to some trees in otherwise dry years. Water shifts due to climatic fluctuations between floodplain storage reservoirsAnthropogenic changes to hydrology directly impact water available to treesEcohydrologic approaches to integration of hydrology afford new possibilities.

Floodplain ecohydrology: Climatic, anthropogenic, and local physical controls on partitioning of water sources to riparian trees

PubMed Central

Singer, Michael Bliss; Sargeant, Christopher I; Piégay, Hervé; Riquier, Jérémie; Wilson, Rob J S; Evans, Cristina M

2014-01-01

Seasonal and annual partitioning of water within river floodplains has important implications for ecohydrologic links between the water cycle and tree growth. Climatic and hydrologic shifts alter water distribution between floodplain storage reservoirs (e.g., vadose, phreatic), affecting water availability to tree roots. Water partitioning is also dependent on the physical conditions that control tree rooting depth (e.g., gravel layers that impede root growth), the sources of contributing water, the rate of water drainage, and water residence times within particular storage reservoirs. We employ instrumental climate records alongside oxygen isotopes within tree rings and regional source waters, as well as topographic data and soil depth measurements, to infer the water sources used over several decades by two co-occurring tree species within a riparian floodplain along the Rhône River in France. We find that water partitioning to riparian trees is influenced by annual (wet versus dry years) and seasonal (spring snowmelt versus spring rainfall) fluctuations in climate. This influence depends strongly on local (tree level) conditions including floodplain surface elevation and subsurface gravel layer elevation. The latter represents the upper limit of the phreatic zone and therefore controls access to shallow groundwater. The difference between them, the thickness of the vadose zone, controls total soil moisture retention capacity. These factors thus modulate the climatic influence on tree ring isotopes. Additionally, we identified growth signatures and tree ring isotope changes associated with recent restoration of minimum streamflows in the Rhône, which made new phreatic water sources available to some trees in otherwise dry years. Key Points Water shifts due to climatic fluctuations between floodplain storage reservoirs Anthropogenic changes to hydrology directly impact water available to trees Ecohydrologic approaches to integration of hydrology afford new possibilities PMID:25506099

Effects of Agaricus lilaceps fairy rings on soil aggregation and microbial community structure in relation to growth stimulation of western wheatgrass (Pascopyrum smithii) in Eastern Montana rangeland.

PubMed

Caesar-Tonthat, The Can; Espeland, Erin; Caesar, Anthony J; Sainju, Upendra M; Lartey, Robert T; Gaskin, John F

2013-07-01

Stimulation of plant productivity caused by Agaricus fairy rings has been reported, but little is known about the effects of these fungi on soil aggregation and the microbial community structure, particularly the communities that can bind soil particles. We studied three concentric zones of Agaricus lilaceps fairy rings in Eastern Montana that stimulate western wheatgrass (Pascopyrum smithii): outside the ring (OUT), inside the ring (IN), and stimulated zone adjacent to the fungal fruiting bodies (SZ) to determine (1) soil aggregate proportion and stability, (2) the microbial community composition and the N-acetyl-β-D-glucosaminidase activity associated with bulk soil at 0-15 cm depth, (3) the predominant culturable bacterial communities that can bind to soil adhering to wheatgrass roots, and (4) the stimulation of wheatgrass production. In bulk soil, macroaggregates (4.75-2.00 and 2.00-0.25 mm) and aggregate stability increased in SZ compared to IN and OUT. The high ratio of fungal to bacteria (fatty acid methyl ester) and N-acetyl-β-D-glucosaminidase activity in SZ compared to IN and OUT suggest high fungal biomass. A soil sedimentation assay performed on the predominant isolates from root-adhering soil indicated more soil-binding bacteria in SZ than IN and OUT; Pseudomonas fluorescens and Stenotrophomonas maltophilia isolates predominated in SZ, whereas Bacillus spp. isolates predominated in IN and OUT. This study suggests that growth stimulation of wheatgrass in A. lilaceps fairy rings may be attributed to the activity of the fungus by enhancing soil aggregation of bulk soil at 0-15 cm depth and influencing the amount and functionality of specific predominant microbial communities in the wheatgrass root-adhering soil.

A minimalist probabilistic description of root zone soil water

USGS Publications Warehouse

Milly, P.C.D.

2001-01-01

The probabilistic response of depth‐integrated soil water to given climatic forcing can be described readily using an existing supply‐demand‐storage model. An apparently complex interaction of numerous soil, climate, and plant controls can be reduced to a relatively simple expression for the equilibrium probability density function of soil water as a function of only two dimensionless parameters. These are the index of dryness (ratio of mean potential evaporation to mean precipitation) and a dimensionless storage capacity (active root zone soil water capacity divided by mean storm depth). The first parameter is mainly controlled by climate, with surface albedo playing a subsidiary role in determining net radiation. The second is a composite of soil (through moisture retention characteristics), vegetation (through rooting characteristics), and climate (mean storm depth). This minimalist analysis captures many essential features of a more general probabilistic analysis, but with a considerable reduction in complexity and consequent elucidation of the critical controls on soil water variability. In particular, it is shown that (1) the dependence of mean soil water on the index of dryness approaches a step function in the limit of large soil water capacity; (2) soil water variance is usually maximized when the index of dryness equals 1, and the width of the peak varies inversely with dimensionless storage capacity; (3) soil water has a uniform probability density function when the index of dryness is 1 and the dimensionless storage capacity is large; and (4) the soil water probability density function is bimodal if and only if the index of dryness is <1, but this bimodality is pronounced only for artificially small values of the dimensionless storage capacity.

The Evolution of Root Zone Storage Capacity after Land Use Change

NASA Astrophysics Data System (ADS)

Nijzink, Remko C.; Hutton, Christopher; Pechlivanidis, Ilias; Capell, René; Arheimer, Berit; Wagener, Thorsten; Savenije, Hubert H. G.; Hrachowitz, Markus

2016-04-01

Root zone storage capacity forms a crucial parameter in ecosystem functioning as it is the key parameter that determines the partitioning between runoff and transpiration. There is increasing evidence from several case studies for specific plants that vegetation adapts to the critical situation of droughts. For example, trees will, on the long term, try to improve their internal hydraulic conductivity after droughts, for example by allocating more biomass for roots. In spite of this understanding, the water storage capacity in the root zone is often treated as constant in hydrological models. In this study, it was hypothesized that root zone storage capacities are altered by deforestation and the regrowth of the ecosystem. Three deforested sub catchments as well as not affected, nearby control catchments of the experimental forests of HJ Andrews and Hubbard Brook were selected for this purpose. Root zone storage capacities were on the one hand estimated by a climate-based approach similar to Gao et al. (2014), making use of simple water balance considerations to determine the evaporative demand of the system. In this way, the maximum deficit between evaporative demand and precipitation allows a robust estimation of the root zone storage capacity. On the other hand, three conceptual hydrological models (FLEX, HYPE, HYMOD) were calibrated in a moving window approach for all catchments. The obtained model parameter values representing the root zone storage capacities of the individual catchments for each moving window period were then compared to the estimates derived from climate data for the same periods. Model- and climate-derived estimates of root zone storage capacities both showed a similar evolution. In the deforested catchments, considerable reductions of the root zone storage capacities, compared to the pre-treatment situation and control catchments, were observed. In addition, the years after forest clearing were characterized by a gradual recovery of the root zone storage capacities, converging to new equilibrium conditions and linked to forest regrowth. Further trend analysis suggested a relatively quick hydrological recovery between 5 and 15 years in the study catchments. The results lend evidence to the role of both, climate and vegetation dynamics for the development of root zone systems and their controlling influence on hydrological response dynamics.

Rooting depth and root depth distribution of Trifolium repens × T. uniflorum interspecific hybrids.

PubMed

Nichols, S N; Hofmann, R W; Williams, W M; van Koten, C

2016-05-20

Traits related to root depth distribution were examined in Trifolium repens × T. uniflorum backcross 1 (BC 1 ) hybrids to determine whether root characteristics of white clover could be improved by interspecific hybridization. Two white clover cultivars, two T. uniflorum accessions and two BC 1 populations were grown in 1 -m deep tubes of sand culture. Maximum rooting depth and root mass distribution were measured at four harvests over time, and root distribution data were fitted with a regression model to provide measures of root system shape. Morphological traits were measured at two depths at harvest 3. Root system shape of the hybrids was more similar to T. uniflorum than to white clover. The hybrids and T. uniflorum had a higher rate of decrease in root mass with depth than white clover, which would result in higher proportions of root mass in the upper profile. Percentage total root mass at 100-200 mm depth was higher for T. uniflorum than white clover, and for Crusader BC 1 than 'Crusader'. Roots of the hybrids and T. uniflorum also penetrated deeper than those of white clover. T. uniflorum had thicker roots at 50-100 mm deep than the other entries, and more of its fine root mass at 400-500 mm. The hybrids and white clover had more of their fine root mass higher in the profile. Consequently, T. uniflorum had a higher root length density at 400-500 mm than most entries, and a smaller decrease in root length density with depth. These results demonstrate that rooting characteristics of white clover can be altered by hybridization with T. uniflorum, potentially improving water and nutrient acquisition and drought resistance. Root traits of T. uniflorum are likely to be adaptations to soil moisture and fertility in its natural environment. © The Author 2016. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Rooting depth and root depth distribution of Trifolium repens × T. uniflorum interspecific hybrids

PubMed Central

Nichols, S. N.; Hofmann, R. W.; Williams, W. M.; van Koten, C.

2016-01-01

Background and aims Traits related to root depth distribution were examined in Trifolium repens × T. uniflorum backcross 1 (BC1) hybrids to determine whether root characteristics of white clover could be improved by interspecific hybridization. Methods Two white clover cultivars, two T. uniflorum accessions and two BC1 populations were grown in 1 -m deep tubes of sand culture. Maximum rooting depth and root mass distribution were measured at four harvests over time, and root distribution data were fitted with a regression model to provide measures of root system shape. Morphological traits were measured at two depths at harvest 3. Key Results Root system shape of the hybrids was more similar to T. uniflorum than to white clover. The hybrids and T. uniflorum had a higher rate of decrease in root mass with depth than white clover, which would result in higher proportions of root mass in the upper profile. Percentage total root mass at 100–200 mm depth was higher for T. uniflorum than white clover, and for Crusader BC1 than ‘Crusader’. Roots of the hybrids and T. uniflorum also penetrated deeper than those of white clover. T. uniflorum had thicker roots at 50–100 mm deep than the other entries, and more of its fine root mass at 400–500 mm. The hybrids and white clover had more of their fine root mass higher in the profile. Consequently, T. uniflorum had a higher root length density at 400–500 mm than most entries, and a smaller decrease in root length density with depth. Conclusions These results demonstrate that rooting characteristics of white clover can be altered by hybridization with T. uniflorum, potentially improving water and nutrient acquisition and drought resistance. Root traits of T. uniflorum are likely to be adaptations to soil moisture and fertility in its natural environment. PMID:27208735

Vadose Zone Nitrate Transport Dynamics Resulting from Agricultural Groundwater Banking

NASA Astrophysics Data System (ADS)

Murphy, N. P.; McLaughlin, S.; Dahlke, H. E.

2017-12-01

In recent years, California's increased reliance on groundwater resources to meet agricultural and municipal demands has resulted in significant overdraft and water quality issues. Agricultural groundwater banking (AGB) has emerged as a promising groundwater replenishment opportunity in California; AGB is a form of managed aquifer recharge where farmland is flooded during the winter using excess surface water in order to recharge the underlying groundwater. Suitable farmland that is connected to water delivery systems is available for AGB throughout the Central Valley. However, questions remain how AGB could be implemented on fertilized agricultural fields such that nitrate leaching from the root zone is minimized. Here, we present results from field and soil column studies that investigate the transport dynamics of nitrogen in the root and deeper vadose zone during flooding events. We are specifically interested in estimating how timing and duration of flooding events affect percolation rates, leaching and nitrification/denitrification processes in three soil types within the Central Valley. Laboratory and field measurements include nitrogen (NO3-, NH4+, NO2-, N2O), redox potentials, total organic carbon, dissolved oxygen, moisture content and EC. Soil cores are collected in the field before and after recharge events up to a depth of 4m, while other sensors monitor field conditions continuously. Preliminary results from the three field sites show that significant portions of the applied floodwater (12-62 cm) infiltrated below the root zone: 96.1% (Delhi), 88.6% (Modesto) and 76.8% (Orland). Analysis of the soil cores indicate that 70% of the residual nitrate was flushed from the sandy soil, while the fine sandy loam showed only a 5% loss and in some cores even an increase in soil nitrate (in the upper 20cm). Column experiments support these trends and indicate that increases in soil nitrate in the upper root zone might be due to organic nitrogen mineralization and nitrification, facilitated by the added water. The next step will be to use field and laboratory data for the parameterization of the HP1 (Coupled Hydrus-1D and PHREEQC) model to develop an understanding of nitrogen transport in differing soil textures, and develop best management practices for future AGB projects.

CO2 dynamics in the Amargosa Desert: Fluxes and isotopic speciation in a deep unsaturated zone

USGS Publications Warehouse

Walvoord, Michelle Ann; Striegl, Robert G.; Prudic, David E.; Stonestrom, David A.

2005-01-01

Natural unsaturated-zone gas profiles at the U.S. Geological Survey's Amargosa Desert Research Site, near Beatty, Nevada, reveal the presence of two physically and isotopically distinct CO2 sources, one shallow and one deep. The shallow source derives from seasonally variable autotrophic and heterotrophic respiration in the root zone. Scanning electron micrograph results indicate that at least part of the deep CO2 source is associated with calcite precipitation at the 110-m-deep water table. We use a geochemical gas-diffusion model to explore processes of CO2 production and behavior in the unsaturated zone. The individual isotopic species 12CO2, 13CO2, and 14CO2 are treated as separate chemical components that diffuse and react independently. Steady state model solutions, constrained by the measured δ13C (in CO2), and δ14C (in CO2) profiles, indicate that the shallow CO2 source from root and microbial respiration composes ∼97% of the annual average total CO2 production at this arid site. Despite the small contribution from deep CO2 production amounting to ∼0.1 mol m−2 yr−1, upward diffusion from depth strongly influences the distribution of CO2 and carbon isotopes in the deep unsaturated zone. In addition to diffusion from deep CO2 production, 14C exchange with a sorbed CO2 phase is indicated by the modeled δ14C profiles, confirming previous work. The new model of carbon-isotopic profiles provides a quantitative approach for evaluating fluxes of carbon under natural conditions in deep unsaturated zones.

Root Apex Transition Zone As Oscillatory Zone

PubMed Central

Baluška, František; Mancuso, Stefano

2013-01-01

Root apex of higher plants shows very high sensitivity to environmental stimuli. The root cap acts as the most prominent plant sensory organ; sensing diverse physical parameters such as gravity, light, humidity, oxygen, and critical inorganic nutrients. However, the motoric responses to these stimuli are accomplished in the elongation region. This spatial discrepancy was solved when we have discovered and characterized the transition zone which is interpolated between the apical meristem and the subapical elongation zone. Cells of this zone are very active in the cytoskeletal rearrangements, endocytosis and endocytic vesicle recycling, as well as in electric activities. Here we discuss the oscillatory nature of the transition zone which, together with several other features of this zone, suggest that it acts as some kind of command center. In accordance with the early proposal of Charles and Francis Darwin, cells of this root zone receive sensory information from the root cap and instruct the motoric responses of cells in the elongation zone. PMID:24106493

Rooting depths of plants on low-level waste disposal sites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Foxx, T.S.; Tierney, G.D.; Williams, J.M.

1984-11-01

In 1981-1982 an extensive bibliographic study was done to reference rooting depths of native plants in the United States. The data base presently contains 1034 different rooting citations with approximately 12,000 data elements. For this report, data were analyzed for rooting depths related to species found on low-level waste (LLW) sites at Los Alamos National Laboratory. Average rooting depth and rooting frequencies were determined and related to present LLW maintenance. The data base was searched for information on rooting depths of 53 species found on LLW sites at Los Alamos National Laboratory. The study indicates 12 out of 13 grassesmore » found on LLW sites root below 91 cm. June grass (Koeleria cristata (L.) Pers.) (76 cm) was the shallowest rooting grass and side-oats grama (Bouteloua curtipendula (Michx.) Torr.) was the deepest rooting grass (396 cm). Forbs were more variable in rooting depths. Indian paintbrush (Castelleja spp.) (30 cm) was the shallowest rooting forb and alfalfa (Medicago sativa L.) was the deepest (>3900 cm). Trees and shrubs commonly rooted below 457 cm. The shallowest rooting tree was elm (Ulmus pumila L.) (127 cm) and the deepest was one-seed juniper (Juniperus monosperma (Engelm) Sarg.) (>6000 cm). Apache plume (Fallugia paradoxa (D. Don) Endl.) rooted to 140 cm, whereas fourwing saltbush (Atriplex canecens (Pursh) Nutt.) rooted to 762 cm.« less

Anchorage failure of young trees in sandy soils is prevented by a rigid central part of the root system with various designs.

PubMed

Danquechin Dorval, Antoine; Meredieu, Céline; Danjon, Frédéric

2016-07-25

Storms can cause huge damage to European forests. Even pole-stage trees with 80-cm rooting depth can topple. Therefore, good anchorage is needed for trees to survive and grow up from an early age. We hypothesized that root architecture is a predominant factor determining anchorage failure caused by strong winds. We sampled 48 seeded or planted Pinus pinaster trees of similar aerial size from four stands damaged by a major storm 3 years before. The trees were gathered into three classes: undamaged, leaning and heavily toppled. After uprooting and 3D digitizing of their full root architectures, we computed the mechanical characteristics of the main components of the root system from our morphological measurements. Variability in root architecture was quite large. A large main taproot, either short and thick or long and thin, and guyed by a large volume of deep roots, was the major component that prevented stem leaning. Greater shallow root flexural stiffness mainly at the end of the zone of rapid taper on the windward side also prevented leaning. Toppling in less than 90-cm-deep soil was avoided in trees with a stocky taproots or with a very big leeward shallow root. Toppled trees also had a lower relative root biomass - stump excluded - than straight trees. It was mainly the flexural stiffness of the central part of the root system that secured anchorage, preventing a weak displacement of the stump. The distal part of the longest taproot and attached deep roots may be the only parts of the root system contributing to anchorage through their maximum tensile load. Several designs provided good anchorage, depending partly on available soil depth. Pole-stage trees are in-between the juvenile phase when they fail by toppling and the mature phase when they fail by uprooting. © The Author 2016. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Evolution of Root Zone Storage after Land Use Change

NASA Astrophysics Data System (ADS)

Nijzink, R.; Hutton, C.; Capell, R.; Pechlivanidis, I.; Hrachowitz, M.; Savenije, H.

2015-12-01

It has been acknowledged for some time that a coupling exists between vegetation, climate and hydrological processes (e.g. Eagleson, 1982a, Rodriguez-Iturbe,2001 ). Recently, Gao et al.(2014) demonstrated that one of the core parameters of hydrological functioning, the catchment-scale root zone water storage capacity, can be estimated based on climate data alone. It was shown that ecosystems develop root zone storage capacities that allow vegetation to bridge droughts with return periods of about 20 years. As a consequence, assuming that the evaporative demand determines the root zone storage capacity, land use changes, such as deforestation, should have an effect on the development of this capacity . In this study it was tested to which extent deforestation affects root zone storage capacities. To do so, four different hydrological models were calibrated in a moving window approach after deforestation occurred. In this way, model based estimates of the storage capacity in time were obtained. This was compared with short term estimates of root zone storage capacities based on a climate based method similar to Gao et al.(2014). In addition, the equilibrium root zone storage capacity was determined with the total time series of an unaffected control catchment. Preliminary results indicate that models tend to adjust their storage capacity to the values found by the climate based method. This is strong evidence that the root zone storage is determined by the evaporative demand of vegetation. Besides, root zones storage capacities develop towards an equilibrium value where the ecosystem is in balance, further highlighting the evolving, time dynamic character of hydrological systems.

Cell Wall Pectin and its Methyl-esterification in Transition Zone Determine Al Resistance in Cultivars of Pea (Pisum sativum)

PubMed Central

Li, Xuewen; Li, Yalin; Qu, Mei; Xiao, Hongdong; Feng, Yingming; Liu, Jiayou; Wu, Lishu; Yu, Min

2016-01-01

The initial response of plants to aluminum (Al) is the inhibition of root elongation, while the transition zone is the most Al sensitive zone in the root apex, which may sense the presence of Al and regulate the responses of root to Al toxicity. In the present study, the effect of Al treatment (30 μM, 24 h) on root growth, Al accumulation, and properties of cell wall of two pea (Pisum sativum L.) cultivars, cv Onward (Al-resistant) and cv Sima (Al-sensitive), were studied to disclose whether the response of root transition zone to Al toxicity determines Al resistance in pea cultivars. The lower relative root elongation (RRE) and higher Al content were founded in cv Sima compared with cv Onward, which were related to Al-induced the increase of pectin in root segments of both cultivars. The increase of pectin is more prominent in Al-sensitive cultivar than in Al-resistant cultivar. Aluminum toxicity also induced the increase of pectin methylesterases (PME), which is 2.2 times in root transition zone in Al-sensitive cv Sima to that of Al resistant cv Onward, thus led to higher demethylesterified pectin content in root transition zone of Al-sensitive cv Sima. The higher demethylesterified pectin content in root transition zone resulted in more Al accumulation in the cell wall and cytosol in Al-sensitive cv Sima. Our results provide evidence that the increase of pectin content and PME activity under Al toxicity cooperates to determine Al sensitivity in root transition zone that confers Al resistance in cultivars of pea (Pisum sativum). PMID:26870060

Hydrologic processes in deep vadose zones in interdrainage arid environments

USGS Publications Warehouse

Walvoord, Michelle Ann; Scanlon, Bridget R.; Hogan, James F.; Phillips, Fred M.; Scanlon, Bridget R.

2004-01-01

A unifying theory for the hydrology of desert vadose zones is particularly timely considering the rising population and water stresses in arid and semiarid regions. Conventional models cannot reconcile the apparent discrepancy between upward flow indicated by hydraulic gradient data and downward flow suggested by environmental tracer data in deep vadose zone profiles. A conceptual model described here explains both hydraulic and tracer data remarkably well by incorporating the hydrologic role of desert plants that encroached former juniper woodland 10 to 15 thousand years ago in the southwestern United States. Vapor transport also plays an important role in redistributing moisture through deep soils, particularly in coarse-grained sediments. Application of the conceptual model to several interdrainage arid settings reproduces measured matric potentials and chloride accumulation by simulating the transition from downward flow to upward flow just below the root zone initiated by climate and vegetation change. Model results indicate a slow hydraulic drying response in deep vadose zones that enables matric potential profiles to be used to distinguish whether precipitation episodically percolated below the root zone or was completely removed via evapotranspiration during the majority of the Holocene. Recharge declined dramatically during the Holocene in interdrainage basin floor settings of arid and semiarid basins. Current flux estimates across the water table in these environmental settings, are on the order of 0.01 to 0.1 mm yr-1 and may be recharge (downward) or discharge (upward) depending on vadose zone characteristics, such as soil texture, geothermal gradient, and water table depth. In summary, diffuse recharge through the basin floor probably contributes only minimally to the total recharge in arid and semiarid basins.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lucash, M.S.; Farnsworth, B.; Winner, W.E.

This study tests the potential for interactions between root-zone temperature and CO{sub 2} for plants which co-occur in a habitat where root-zone temperature fluctuate throughout the day. Controlled environment studies were conducted to expose desert plants to combinations of low or high root zone temperatures and low or high CO{sub 2}. Artemisia tridentata, Sitanion hystrix, and Stipa thurberiana were chosen for study to represent eastern Oregon plants that differ in their life history strategies. Seeds were planted in pots containing native soils and were grown in environmentally controlled growth chambers for three months. Growth treatments were either ambient (380 ppm)more » or high (580 ppm) CO{sub 2} concentration and high (18{degrees}C) or low (13{degrees} C) root-zone temperature. A. tridentata (a perennial shrub) was relatively unresponsive to treatments. Growth of S. hystrix and S. thurberiana (both C{sub 3} grasses) was stimulated by root-zone warming at both ambient and elevated CO{sub 2} levels. CO{sub 2} stimulated growth occurred for both grass species at low root-zone temperatures but only for S. thurberiana at high root-zone temperatures. Biomass increases from elevated CO{sub 2} were enhanced by root-zone warming indicating treatment interactions. Leaf-level photosynthesis measurements were consistent across species, but could not explain growth responses to treatments. These studies indicate that grasses may be more responsive to environmental change than co-occurring shrubs.« less

VHF SoOp (Signal of Opportunity) Technology Demonstration for Soil Moisture Measurement Using Microwave Hydraulic Boom Truck Platform

NASA Technical Reports Server (NTRS)

Joseph, A. T.; Deshpande, M.; O'Neill, P. E.; Miles, L.

2017-01-01

A goal of this research is to test deployable VHF antennas for 6U Cubesat platforms to enable validation of root zone soil moisture (RZSM) estimation algorithms for signal of opportunity (SoOp) remote sensing over the 240-270 MHz frequency band. The proposed work provides a strong foundation for establishing a technology development path for maturing a global direct surface soil moisture (SM) and RZSM measurement system over a variety of land covers. Knowledge of RZSM up to a depth of 1 meter and surface SM up to a depth of 0.05 meter on a global scale, at a spatial resolution of 1-10 km through moderate-to-heavy vegetation, is critical to understanding global water resources and the vertical moisture gradient in the Earths surface layer which controls moisture interactions between the soil, vegetation, and atmosphere. Current observations of surface SM from space by L-band radiometers (1.4 GHz) and radars (1.26 GHz) are limited to measurements of surface SM up to a depth of 0.05 meter through moderate amounts of vegetation. This limitation is mainly due to the inability of L-band signals to penetrate through dense vegetation and deep into the soil column. Satellite observations of the surface moisture conditions are coupled to sophisticated models which extrapolate the surface SM into the root zone, thus providing an indirect estimate rather than a direct measurement of RZSM. To overcome this limitation, low-frequency airborne radars operating at 435 MHz and 118 MHz have been investigated, since these lower frequencies should penetrate denser vegetation and respond to conditions deeper in the soil.

Mechanical obstacles to the movement of continent-bearing plates

NASA Technical Reports Server (NTRS)

Lowman, P. D., Jr.

1985-01-01

Selected geophysical problems associated with the concept of continental drift as an incidental corollary of plate movement are discussed. The problems include the absence of a suitable plate-driving mechanism for plates with continental leading edges, the absence of the low-velocity zone under shields, and continental roots of 400 to 700 km depths. It is shown that if continental drift occurs, it must use mechanisms not now understood, or that it may not occur at all, plate movement being confined to ocean basins.

Ecophysiology of wetland plant roots: A modelling comparison of aeration in relation to species distribution

USGS Publications Warehouse

Sorrell, B.K.; Mendelssohn, I.A.; McKee, K.L.; Woods, R.A.

2000-01-01

This study examined the potential for inter-specific differences in root aeration to determine wetland plant distribution in nature. We compared aeration in species that differ in the type of sediment and depth of water they colonize. Differences in root anatomy, structure and physiology were applied to aeration models that predicted the maximum possible aerobic lengths and development of anoxic zones in primary adventitious roots. Differences in anatomy and metabolism that provided higher axial fluxes of oxygen allowed deeper root growth in species that favour more reducing sediments and deeper water. Modelling identified factors that affected growth in anoxic soils through their effects on aeration. These included lateral root formation, which occurred at the expense of extension of the primary root because of the additional respiratory demand they imposed, reducing oxygen fluxes to the tip and stele, and the development of stelar anoxia. However, changes in sediment oxygen demand had little detectable effect on aeration in the primary roots due to their low wall permeability and high surface impedance, but appeared to reduce internal oxygen availability by accelerating loss from laterals. The development of pressurized convective gas flow in shoots and rhizomes was also found to be important in assisting root aeration, as it maintained higher basal oxygen concentrations at the rhizome-root junctions in species growing into deep water. (C) 2000 Annals of Botany Company.

Soil water availability and rooting depth as determinants of hydraulic architecture of Patagonian woody species

Treesearch

Sandra J. Bucci; Fabian G. Scholz; Guillermo Goldstein; Frederick C. Meinzer; Maria E. Arce

2009-01-01

We studied the water economy of nine woody species differing in rooting depth in a Patagonian shrub steppe from southern Argentina to understand how soil water availability and rooting depth determine their hydraulic architecture. Soil water content and potentials, leaf water potentials (Leaf) hydraulic conductivity, wood density (Pw), rooting depth, and specific leaf...

Is rhizosphere remediation sufficient for sustainable revegetation of mine tailings?

PubMed Central

Huang, Longbin; Baumgartl, Thomas; Mulligan, David

2012-01-01

Background Revegetation of mine tailings (fine-grained waste material) starts with the reconstruction of root zones, consisting of a rhizosphere horizon (mostly topsoil and/or amended tailings) and the support horizon beneath (i.e. equivalent to subsoil – mostly tailings), which must be physically and hydro-geochemically stable. This review aims to discuss key processes involved in the development of functional root zones within the context of direct revegetation of tailings and introduces a conceptual process of rehabilitating structure and function in the root zones based on a state transition model. Scope Field studies on the revegetation of tailings (from processing base metal ore and bauxite residues) are reviewed. Particular focus is given to tailings' properties that limit remediation effectiveness. Aspects of root zone reconstruction and vegetation responses are also discussed. Conclusions When reconstructing a root zone system, it is critical to restore physical structure and hydraulic functions across the whole root zone system. Only effective and holistically restored systems can control hydro-geochemical mobility of acutely and chronically toxic factors from the underlying horizon and maintain hydro-geochemical stability in the rhizosphere. Thereafter, soil biological capacity and ecological linkages (i.e. carbon and nutrient cycling) may be rehabilitated to integrate the root zones with revegetated plant communities into sustainable plant ecosystems. A conceptual framework of system transitions between the critical states of root zone development has been proposed. This will illustrate the rehabilitation process in root zone reconstruction and development for direct revegetation with sustainable plant communities. Sustainable phytostabilization of tailings requires the systematic consideration of hydro-geochemical interactions between the rhizosphere and the underlying supporting horizon. It further requires effective remediation strategies to develop hydro-geochemically stable and biologically functional root zones, which can facilitate the recovery of the microbial community and ecological linkages with revegetated plant communities. PMID:22648878

High-resolution isotope measurements resolve rapid ecohydrological dynamics at the soil-plant interface.

PubMed

Volkmann, Till H M; Haberer, Kristine; Gessler, Arthur; Weiler, Markus

2016-05-01

Plants rely primarily on rainfall infiltrating their root zones - a supply that is inherently variable, and fluctuations are predicted to increase on most of the Earth's surface. Yet, interrelationships between water availability and plant use on short timescales are difficult to quantify and remain poorly understood. To overcome previous methodological limitations, we coupled high-resolution in situ observations of stable isotopes in soil and transpiration water. We applied the approach along with Bayesian mixing modeling to track the fate of (2) H-labeled rain pulses following drought through soil and plants of deciduous tree ecosystems. We resolve how rainwater infiltrates the root zones in a nonequilibrium process and show that tree species differ in their ability to quickly acquire the newly available source. Sessile oak (Quercus petraea) adjusted root uptake to vertical water availability patterns under drought, but readjustment toward the rewetted topsoil was delayed. By contrast, European beech (Fagus sylvatica) readily utilized water from all soil depths independent of water depletion, enabling faster uptake of rainwater. Our results demonstrate that species-specific plasticity and responses to water supply fluctuations on short timescales can now be identified and must be considered to predict vegetation functional dynamics and water cycling under current and future climatic conditions. © 2016 The Authors. New Phytologist © 2016 New Phytologist Trust.

Untangling the effects of shallow groundwater and deficit irrigation on irrigation water productivity in arid region: New conceptual model.

PubMed

Xue, Jingyuan; Huo, Zailin; Wang, Fengxin; Kang, Shaozhong; Huang, Guanhua

2018-04-01

Water scarcity and salt stress are two main limitations for agricultural production. Groundwater evapotranspiration (ET g ) with upward salt movement plays an important role in crop water use and water productivity in arid regions, and it can compensate the impact of deficit irrigation on crop production. Thus, comprehensive impacts of shallow groundwater and deficit irrigation on crop water use results in an improvement of irrigation water productivity (IWP). However, it is difficult to quantify the effects of groundwater and deficit irrigation on IWP. In this study, we built an IWP evaluation model coupled with a water and salt balance model and a crop yield estimation model. As a valuable tool of IWP simulation, the calibrated model was used to investigate the coupling response of sunflower IWP to irrigation water depths (IWDs), groundwater table depth (GTDs) and groundwater salinities (GSs). A total of 210 scenarios were run in which five irrigation water depths (IWDs) and seven groundwater table depths (GTDs) and six groundwater salinities (GSs) were used. Results indicate that increasing GS clearly increases the negative effect on a crop's actual evapotranspiration (ET a ) as salt accumulation in root zone. When GS is low (0.5-1g/L), increasing GTD produces more positive effect than negative effect. In regard to relatively high GS (2-5g/L), the negative effect of shallow-saline groundwater reaches a maximum at 2m GTD. Additionally, the salt concentration in the root zone maximizes its value at 2.0m GTD. In most cases, increasing GTD and GS reduces the benefits of irrigation water and IWP. The IWP increases with decreasing irrigation water. Overall, in arid regions, capillary rise of shallow groundwater can compensate for the lack of irrigation water and improve IWP. By improving irrigation schedules and taking advantages of shallow saline groundwater, we can obtain higher IWP. Copyright © 2017 Elsevier B.V. All rights reserved.

Relative Water Uptake as a Criterion for the Design of Trickle Irrigation Systems

NASA Astrophysics Data System (ADS)

Communar, G.; Friedman, S. P.

2008-12-01

Previously derived analytical solutions to the 2- and 3-dimensional water flow problems describing trickle irrigation are not being widely used in practice because those formulations either ignore root water uptake or refer to it as a known input. In this lecture we are going to describe a new modeling approach and demonstrate its applicability for designing the geometry of trickle irrigation systems, namely the spacing between the emitters and drip lines. The major difference between our and previous modeling approaches is that we refer to the root water uptake as to the unknown solution of the problem and not as to a known input. We postulate that the solution to the steady-state water flow problem with a root sink that is acting under constant, maximum suction defines un upper bound to the relative water uptake (water use efficiency) in actual transient situations and propose to use it as a design criterion. Following previous derivations of analytical solutions we assume that the soil hydraulic conductivity increases exponentially with its matric head, which allows the linearization of the Richards equation, formulated in terms of the Kirchhoff matric flux potential. Since the transformed problem is linear, the relative water uptake for any given configuration of point or line sources and sinks can be calculated by superposition of the Green's functions of all relevant water sources and sinks. In addition to evaluating the relative water uptake, we also derived analytical expressions for the steam functions. The stream lines separating the water uptake zone from the percolating water provide insight to the dependence of the shape and extent of the actual rooting zone on the source- sink geometry and soil properties. A minimal number of just 3 system parameters: Gardner's (1958) alfa as a soil type quantifier and the depth and diameter of the pre-assumed active root zone are sufficient to characterize the interplay between capillary and gravitational effects on water flow and the competition between the processes of root water uptake and percolation. For accounting also for evaporation from the soil surface, when significant, another parameter is required, adopting the solution of Lomen and Warrick (1978).

Developmental morphology of cover crop species exhibit contrasting behaviour to changes in soil bulk density, revealed by X-ray computed tomography

PubMed Central

Burr-Hersey, Jasmine E.; Mooney, Sacha J.; Bengough, A. Glyn; Mairhofer, Stefan

2017-01-01

Plant roots growing through soil typically encounter considerable structural heterogeneity, and local variations in soil dry bulk density. The way the in situ architecture of root systems of different species respond to such heterogeneity is poorly understood due to challenges in visualising roots growing in soil. The objective of this study was to visualise and quantify the impact of abrupt changes in soil bulk density on the roots of three cover crop species with contrasting inherent root morphologies, viz. tillage radish (Raphanus sativus), vetch (Vicia sativa) and black oat (Avena strigosa). The species were grown in soil columns containing a two-layer compaction treatment featuring a 1.2 g cm-3 (uncompacted) zone overlaying a 1.4 g cm-3 (compacted) zone. Three-dimensional visualisations of the root architecture were generated via X-ray computed tomography, and an automated root-segmentation imaging algorithm. Three classes of behaviour were manifest as a result of roots encountering the compacted interface, directly related to the species. For radish, there was switch from a single tap-root to multiple perpendicular roots which penetrated the compacted zone, whilst for vetch primary roots were diverted more horizontally with limited lateral growth at less acute angles. Black oat roots penetrated the compacted zone with no apparent deviation. Smaller root volume, surface area and lateral growth were consistently observed in the compacted zone in comparison to the uncompacted zone across all species. The rapid transition in soil bulk density had a large effect on root morphology that differed greatly between species, with major implications for how these cover crops will modify and interact with soil structure. PMID:28753645

Developmental morphology of cover crop species exhibit contrasting behaviour to changes in soil bulk density, revealed by X-ray computed tomography.

PubMed

Burr-Hersey, Jasmine E; Mooney, Sacha J; Bengough, A Glyn; Mairhofer, Stefan; Ritz, Karl

2017-01-01

Plant roots growing through soil typically encounter considerable structural heterogeneity, and local variations in soil dry bulk density. The way the in situ architecture of root systems of different species respond to such heterogeneity is poorly understood due to challenges in visualising roots growing in soil. The objective of this study was to visualise and quantify the impact of abrupt changes in soil bulk density on the roots of three cover crop species with contrasting inherent root morphologies, viz. tillage radish (Raphanus sativus), vetch (Vicia sativa) and black oat (Avena strigosa). The species were grown in soil columns containing a two-layer compaction treatment featuring a 1.2 g cm-3 (uncompacted) zone overlaying a 1.4 g cm-3 (compacted) zone. Three-dimensional visualisations of the root architecture were generated via X-ray computed tomography, and an automated root-segmentation imaging algorithm. Three classes of behaviour were manifest as a result of roots encountering the compacted interface, directly related to the species. For radish, there was switch from a single tap-root to multiple perpendicular roots which penetrated the compacted zone, whilst for vetch primary roots were diverted more horizontally with limited lateral growth at less acute angles. Black oat roots penetrated the compacted zone with no apparent deviation. Smaller root volume, surface area and lateral growth were consistently observed in the compacted zone in comparison to the uncompacted zone across all species. The rapid transition in soil bulk density had a large effect on root morphology that differed greatly between species, with major implications for how these cover crops will modify and interact with soil structure.

Determination of threshold value of soil water content for field and vegetable plants with lysimeter measurements

NASA Astrophysics Data System (ADS)

Knoblauch, S.

2009-04-01

Both the potential water consumption of plants and their ability to withdraw soil water are necessary in order to estimate actual evapotranspiration and to predict irrigation timing and amount. In relating to root water uptake the threshold value at which plants reducing evapotranspiration is an important parameter. Since transpiration is linearly correlated to dry matter production, under the condition that the AET/PET-Quotient is smaller than 1.0 (de Wit 1958, Tanner & Sinclair 1983), the dry matter production begins to decline too. Plants respond to drought with biochemical, physiological and morphological modifications in order to avoid damages, for instance by increasing the root water uptake. The objective of the study is to determine threshold values of soil water content and pressure head respectively for different field and vegetable plants with lysimeter measurements and to derive so called reduction functions. Both parameter, potenzial water demand in several growth stages and threshold value of soil water content or pressure head can be determined with weighable field lysimeter. The threshold value is reached, when the evapotranspiration under natural rainfall condition (AET) drop clearly (0.8 PET) below the value under well watered condition (PET). Basis for the presented results is the lysimeter plant Buttelstedt of the Thuringian State Institute of Agriculture. It consist of two lysimeter cellars, each with two weighable monolithic lysimeters. The lysimeter are 2.5 m deep with a surface area of 2 m2 to allow a non-restrictive root growth and to arrange a representative number of plants. The weighing accuracy amounts to 0.05 mm. The percolating water is collected by ceramic suction cups with suction up to 0.3 MPa at a depth of 2.3 m. The soil water content is measured by using neutron probe. One of the two lysimeter cellars represents the will irrigated, the other one the non irrigated and/or reduced irrigated part of field. The soil is a Haplic Phaeozem with silt-loamy texture developed from loess (water content at wilting point amounts between 0.167 and 0.270 cm3/cm3 and at field capacity (0.03 MPa) between 0.286 and 0.342 cm3/cm3). The mean annual temperature is 8.2°C and the mean annual precipitation is 550 mm. Results are as follows: Winter wheat begins to reduce evapotranspiration when the water content in the root zone to a depth of 2.0 m is smaller than 25 % of the available water holding capacity (AWC). That is equal to an amount of soil water of 171 mm. The threshold value of potatoes is 40 % of the AWC to a rooting depth of 0.6 m (49 mm soil water amount). The corresponding value for cabbage is 40 % of the AWC relating to a rooting depth of 1.2 m, for cauli flower 60 % of the AWC relating to a depth of 1.0 m and for onion 80 % of the AWC to a rooting depth of 0.3 m (90, 50 and 5 mm soil water amount). Nevertheless onion attain a maximum rooting depth of 0.9 m. The maximum rooting depths of winter wheat, potatoes, cabbage and cawli flower are 2.0, 1.0, 1.5 und 1.5 m. The date on which the threshold is reached is different, for winter wheat and cabbage just before harvest and for onion in a few days after 8-leaf-stage. However, it is assumed that these values are also the influence of weather reflect, particulary with regard to the transpiration demand of the atmosphere and the amount of rain fall during earlier growth stages which can prefer the development of adaptation mechanism. Although there are great differences between the plant species concerning root water uptake to avoid a decline of biomass production due to drought.

Long-distance abscisic acid signalling under different vertical soil moisture gradients depends on bulk root water potential and average soil water content in the root zone.

PubMed

Puértolas, Jaime; Alcobendas, Rosalía; Alarcón, Juan J; Dodd, Ian C

2013-08-01

To determine how root-to-shoot abscisic acid (ABA) signalling is regulated by vertical soil moisture gradients, root ABA concentration ([ABA](root)), the fraction of root water uptake from, and root water potential of different parts of the root zone, along with bulk root water potential, were measured to test various predictive models of root xylem ABA concentration [RX-ABA](sap). Beans (Phaseolus vulgaris L. cv. Nassau) were grown in soil columns and received different irrigation treatments (top and basal watering, and withholding water for varying lengths of time) to induce different vertical soil moisture gradients. Root water uptake was measured at four positions within the column by continuously recording volumetric soil water content (θv). Average θv was inversely related to bulk root water potential (Ψ(root)). In turn, Ψ(root) was correlated with both average [ABA](root) and [RX-ABA](sap). Despite large gradients in θv, [ABA](root) and root water potential was homogenous within the root zone. Consequently, unlike some split-root studies, root water uptake fraction from layers with different soil moisture did not influence xylem sap (ABA). This suggests two different patterns of ABA signalling, depending on how soil moisture heterogeneity is distributed within the root zone, which might have implications for implementing water-saving irrigation techniques. © 2013 John Wiley & Sons Ltd.

Thresholds in Soil Mineral Weathering and Relation to Streamwater Chemistry in Glaciated Catchments of the Northeastern USA

NASA Astrophysics Data System (ADS)

Bailey, S. W.; Ross, D. S.

2015-12-01

Primary mineral dissolution (i.e. weathering) is a critical process in forested catchments as an important consumer of acidity and CO2, the principle source of nutrients such as Ca, K, and P, as well as the source of toxic cations such as Al. Two common limitations of weathering studies are inadequate determination of mineralogic composition and insufficient sampling depth to determine location and advancement of weathering reactions. We determined mineral stocks through EPMA mapping of Al, Ca, Fe, P, and Si content of soil samples and development of an image analysis routine that assigned mineral composition based on the content of these five elements. Portions of the classified maps were confirmed by optical petrography and full elemental analysis by SEM-EDS. Samples were analyzed for soil profiles >2m depth (~1.5m past the upper boundary of the "unweathered" C horizon). Study sites spanned a range of weatherability found in catchments in glaciated northeastern USA including Winnisook, NY (sandstone parent material, 100 ppm Ca), Hubbard Brook, NH (granite, 0.9% Ca), and Sleepers River, VT (calcareous granulite, 3.5% Ca). All profiles exhibited a weathering front, or threshold above which the most reactive minerals (calcite, apatite) have been depleted. However, in all cases this threshold was below the rooting zone, and in many profiles, it was well below the C horizon interface. Catchment scale Ca exports reflect this deeper weathering source while rooting zone exchangeable Ca was highly variable, probably reflecting spatial patterns of hydrologic flowpaths which bring deeper weathering products to the surface only in certain landscape positions. These results suggest that nutrient cycling and critical loads models, which assume that ecologically relevant weathering is confined to the rooting zone, need to be refined to account for deeper weathering and spatial patterns of lateral and upward hydrologic fluxes. Similarly, recovery from cultural acidification may be limited in portions of catchments where hydrologic connections do not provide a vehicle for weathering products to recharge the biologically active portion of the subsurface.

Estimation of available water capacity components of two-layered soils using crop model inversion: Effect of crop type and water regime

NASA Astrophysics Data System (ADS)

Sreelash, K.; Buis, Samuel; Sekhar, M.; Ruiz, Laurent; Kumar Tomer, Sat; Guérif, Martine

2017-03-01

Characterization of the soil water reservoir is critical for understanding the interactions between crops and their environment and the impacts of land use and environmental changes on the hydrology of agricultural catchments especially in tropical context. Recent studies have shown that inversion of crop models is a powerful tool for retrieving information on root zone properties. Increasing availability of remotely sensed soil and vegetation observations makes it well suited for large scale applications. The potential of this methodology has however never been properly evaluated on extensive experimental datasets and previous studies suggested that the quality of estimation of soil hydraulic properties may vary depending on agro-environmental situations. The objective of this study was to evaluate this approach on an extensive field experiment. The dataset covered four crops (sunflower, sorghum, turmeric, maize) grown on different soils and several years in South India. The components of AWC (available water capacity) namely soil water content at field capacity and wilting point, and soil depth of two-layered soils were estimated by inversion of the crop model STICS with the GLUE (generalized likelihood uncertainty estimation) approach using observations of surface soil moisture (SSM; typically from 0 to 10 cm deep) and leaf area index (LAI), which are attainable from radar remote sensing in tropical regions with frequent cloudy conditions. The results showed that the quality of parameter estimation largely depends on the hydric regime and its interaction with crop type. A mean relative absolute error of 5% for field capacity of surface layer, 10% for field capacity of root zone, 15% for wilting point of surface layer and root zone, and 20% for soil depth can be obtained in favorable conditions. A few observations of SSM (during wet and dry soil moisture periods) and LAI (within water stress periods) were sufficient to significantly improve the estimation of AWC components. These results show the potential of crop model inversion for estimating the AWC components of two-layered soils and may guide the sampling of representative years and fields to use this technique for mapping soil properties that are relevant for distributed hydrological modelling.

Performance evaluation of different horizontal subsurface flow wetland types by characterization of flow behavior, mass removal and depth-dependent contaminant load.

PubMed

Seeger, Eva M; Maier, Uli; Grathwohl, Peter; Kuschk, Peter; Kaestner, Matthias

2013-02-01

For several pilot-scale constructed wetlands (CWs: a planted and unplanted gravel filter) and a hydroponic plant root mat (operating at two water levels), used for treating groundwater contaminated with BTEX, the fuel additive MTBE and ammonium, the hydrodynamic behavior was evaluated by means of temporal moment analysis of outlet tracer breakthrough curves (BTCs): hydraulic indices were related to contaminant mass removal. Detailed investigation of flow within the model gravel CWs allowed estimation of local flow rates and contaminant loads within the CWs. Best hydraulics were observed for the planted gravel filter (number of continuously stirred tank reactors N = 11.3, dispersion number = 0.04, Péclet number = 23). The hydroponic plant root mat revealed lower N and pronounced dispersion tendencies, whereby an elevated water table considerably impaired flow characteristics and treatment efficiencies. Highest mass removals were achieved by the plant root mat at low level: 98% (544 mg m⁻² d⁻¹), 78% (54 mg m⁻² d⁻¹) and 74% (893 mg m⁻² d⁻¹) for benzene, MTBE and ammonium-nitrogen, respectively. Within the CWs the flow behavior was depth-dependent, with the planting and the position of the outlet tube being key factors resulting in elevated flow rate and contaminant flux immediately below the densely rooted porous media zone in the planted CW, and fast bottom flow in the unplanted reference. Copyright © 2012 Elsevier Ltd. All rights reserved.

Farm scale application of EMI and FDR sensors to measuring and mapping soil water content

NASA Astrophysics Data System (ADS)

Rallo, Giovanni; Provenzano, Giuseppe

2017-04-01

Soil water content (SWC) controls most water exchange processes within and between the soil-plants-atmosphere continuum and can therefore be considered as a practical variable for irrigation farmer choices. A better knowledge of spatial SWC patterns could improve farmer's awareness about critical crop water status conditions and enhance their capacity to characterize their behavior at the field or farm scale. However, accurate soil moisture measurement across spatial and temporal scales is still a challenging task and, specifically at intermediate spatial (0.1-100 ha) and temporal (minutes to days) scales, a data gap remains that limits our understanding over reliability of the SWC spatial measurements and its practical applicability in irrigation scheduling. In this work we compare the integrated EM38 (Geonics Ltd. Canada) response, collected at different sensor positions above ground to that obtained by integrating the depth profile of volumetric SWC measured with Diviner 2000 (Sentek) in conjunction with the depth response function of the EM38 when operated in both horizontal and vertical dipole configurations. On a 1.0-ha Olive grove site in Sicliy (Italy), 200 data points were collected before and after irrigation or precipitation events following a systematic sampling grid with focused measurements around the tree. Inside two different zone of the field, characterized from different soil physical properties, two Diviner 2000 access tube (1.2 m) were installed and used for the EM38 calibration. After calibration, the work aimed to propose the combined use of the FDR and EMI sensors to measuring and mapping root zone soil water content. We found strong correlations (R2 = 0.66) between Diviner 2000 SWC averaged to a depth of 1.2 m and ECa from an EM38 held in the vertical mode above the soil surface. The site-specific relationship between FDR-based SWC and ECa was linear for the purposes of estimating SWC over the explored range of ECa monitored at field levels. Volumetric SWC changes in the root zone were observed by differencing the maps, where differences in the observed ECa are primarily the result of changes in soil water status. As with the data showed in the research, more structured patterns occur after wetting event, indicating the presence of subsurface flow or root water uptake paths. A vision for the future at hydrological watershed scale is to combine EMI measurements with FDR-based sensor networks, the last with the scope to constrain calibration of the EMI measurements.

Analysis of changes in relative elemental growth rate patterns in the elongation zone of Arabidopsis roots upon gravistimulation

NASA Technical Reports Server (NTRS)

Mullen, J. L.; Ishikawa, H.; Evans, M. L.

1998-01-01

Although Arabidopsis is an important system for studying root physiology, the localized growth patterns of its roots have not been well defined, particularly during tropic responses. In order to characterize growth rate profiles along the apex of primary roots of Arabidopsis thaliana (L.) Heynh (ecotype Columbia) we applied small charcoal particles to the root surface and analyzed their displacement during growth using an automated video digitizer system with custom software for tracking the markers. When growing vertically, the maximum elongation rate occurred 481 +/- 50 microns back from the extreme tip of the root (tip of root cap), and the elongation zone extended back to 912 +/- 137 microns. The distal elongation zone (DEZ) has previously been described as the apical region of the elongation zone in which the relative elemental growth rate (REGR) is < or = 30% of the peak rate in the central elongation zone. By this definition, our data indicate that the basal limit of the DEZ was located 248 +/- 30 microns from the root tip. However, after gravistimulation, the growth patterns of the root changed. Within the first hour of graviresponse, the basal limit of the DEZ and the position of peak REGR shifted apically on the upper flank of the root. This was due to a combination of increased growth in the DEZ and growth inhibition in the central elongation zone. On the lower flank, the basal limit of the DEZ shifted basipetally as the REGR decreased. These factors set up the gradient of growth rate across the root, which drives curvature.

Root-zone temperature and water availability affect early root growth of planted longleaf pine

Treesearch

M.A. Sword

1995-01-01

Longleaf pine seedlings from three seed sources were exposed to three root-zone temperatures and three levels of water availability for 28 days. Root growth declined as temperature and water availability decreased. Root growth differed by seed source. Results suggest that subtle changes in the regeneration environment may influence early root growth of longleaf pine...

GLEAM v3: satellite-based land evaporation and root-zone soil moisture

NASA Astrophysics Data System (ADS)

Martens, Brecht; Miralles, Diego G.; Lievens, Hans; van der Schalie, Robin; de Jeu, Richard A. M.; Fernández-Prieto, Diego; Beck, Hylke E.; Dorigo, Wouter A.; Verhoest, Niko E. C.

2017-05-01

The Global Land Evaporation Amsterdam Model (GLEAM) is a set of algorithms dedicated to the estimation of terrestrial evaporation and root-zone soil moisture from satellite data. Ever since its development in 2011, the model has been regularly revised, aiming at the optimal incorporation of new satellite-observed geophysical variables, and improving the representation of physical processes. In this study, the next version of this model (v3) is presented. Key changes relative to the previous version include (1) a revised formulation of the evaporative stress, (2) an optimized drainage algorithm, and (3) a new soil moisture data assimilation system. GLEAM v3 is used to produce three new data sets of terrestrial evaporation and root-zone soil moisture, including a 36-year data set spanning 1980-2015, referred to as v3a (based on satellite-observed soil moisture, vegetation optical depth and snow-water equivalent, reanalysis air temperature and radiation, and a multi-source precipitation product), and two satellite-based data sets. The latter share most of their forcing, except for the vegetation optical depth and soil moisture, which are based on observations from different passive and active C- and L-band microwave sensors (European Space Agency Climate Change Initiative, ESA CCI) for the v3b data set (spanning 2003-2015) and observations from the Soil Moisture and Ocean Salinity (SMOS) satellite in the v3c data set (spanning 2011-2015). Here, these three data sets are described in detail, compared against analogous data sets generated using the previous version of GLEAM (v2), and validated against measurements from 91 eddy-covariance towers and 2325 soil moisture sensors across a broad range of ecosystems. Results indicate that the quality of the v3 soil moisture is consistently better than the one from v2: average correlations against in situ surface soil moisture measurements increase from 0.61 to 0.64 in the case of the v3a data set and the representation of soil moisture in the second layer improves as well, with correlations increasing from 0.47 to 0.53. Similar improvements are observed for the v3b and c data sets. Despite regional differences, the quality of the evaporation fluxes remains overall similar to the one obtained using the previous version of GLEAM, with average correlations against eddy-covariance measurements ranging between 0.78 and 0.81 for the different data sets. These global data sets of terrestrial evaporation and root-zone soil moisture are now openly available at www.GLEAM.eu and may be used for large-scale hydrological applications, climate studies, or research on land-atmosphere feedbacks.

Three-dimensional crust and mantle structure of Kilauea Volcano, Hawaii

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ellsworth, W.L.; Koyanagi, R.Y.

1977-11-10

Teleseismic P wave arrival times recorded by a dense network of seismograph stations located on Kilauea volcano, Hawaii, are inverted to determine lateral variation in crust and upper mantle structure to a depth of 70 km. The crustal structure is dominated by relatively high velocities within the central summit complex and along the two radial rift zones compared with the nonrift flank of the volcano. Both the mean crustal velocity contrast between summit and nonrift flank and the distribution of velocities agree well with results from crustal refraction studies. Comparison of the velocity structure with Bouguer gravity anomalies over themore » volcano through a simple physical model also gives excellent agreement. Mantle structure appears to be more homogeneous than crustal structure. The root mean square velocity variation for the mantle averages only 1.5%, whereas variation within the crust exceeds 4%. The summit of Kilauea is underlain by normal velocity (8.1 km/s) material within the uppermost mantle (12--25 km), suggesting that large magma storage reservoirs are not present at this level and that the passageways from deeper sources must be quite narrow. No evidence is found for substantial volumes of partially molten rock (5%) within the mantle to depths of at least 40 km. Below about 30 km, low-velocity zones (1--2%) underlie the summits of Kilauea and nearby Mauna Loa and extend south of Kilauea into a broad offshore zone. Correlation of volcanic tremor source locations and persistent zones of mantle earthquakes with low-velocity mantle between 27.5- and 42.5-km depth suggests that a laterally extensive conduit system feeds magma to the volcanic summits from sources either at comparable depth or deeper within the mantle. The center of contemporary magmatic production and/or upwelling from deeper in the mantle appears to extend well to the south of the active volcanic summits, suggesting that the Hawaiian Island chain is actively extending to the southeast.« less

An invasive wetland grass primes deep soil carbon pools.

PubMed

Bernal, Blanca; Megonigal, J Patrick; Mozdzer, Thomas J

2017-05-01

Understanding the processes that control deep soil carbon (C) dynamics and accumulation is of key importance, given the relevance of soil organic matter (SOM) as a vast C pool and climate change buffer. Methodological constraints of measuring SOM decomposition in the field prevent the addressing of real-time rhizosphere effects that regulate nutrient cycling and SOM decomposition. An invasive lineage of Phragmites australis roots deeper than native vegetation (Schoenoplectus americanus and Spartina patens) in coastal marshes of North America and has potential to dramatically alter C cycling and accumulation in these ecosystems. To evaluate the effect of deep rooting on SOM decomposition we designed a mesocosm experiment that differentiates between plant-derived, surface SOM-derived (0-40 cm, active root zone of native marsh vegetation), and deep SOM-derived mineralization (40-80 cm, below active root zone of native vegetation). We found invasive P. australis allocated the highest proportion of roots in deeper soils, differing significantly from the native vegetation in root : shoot ratio and belowground biomass allocation. About half of the CO 2 produced came from plant tissue mineralization in invasive and native communities; the rest of the CO 2 was produced from SOM mineralization (priming). Under P. australis, 35% of the CO 2 was produced from deep SOM priming and 9% from surface SOM. In the native community, 9% was produced from deep SOM priming and 44% from surface SOM. SOM priming in the native community was proportional to belowground biomass, while P. australis showed much higher priming with less belowground biomass. If P. australis deep rooting favors the decomposition of deep-buried SOM accumulated under native vegetation, P. australis invasion into a wetland could fundamentally change SOM dynamics and lead to the loss of the C pool that was previously sequestered at depth under the native vegetation, thereby altering the function of a wetland as a long-term C sink. © 2016 John Wiley & Sons Ltd.

Movement of endogenous calcium in the elongating zone of graviresponding roots of Zea mays

NASA Technical Reports Server (NTRS)

Moore, R.; Cameron, I. L.; Smith, N. K.

1989-01-01

Endogenous calcium (Ca) accumulates along the lower side of the elongating zone of horizontally oriented roots of Zea mays cv. Yellow Dent. This accumulation of Ca correlates positively with the onset of gravicurvature, and occurs in the cytoplasm, cell walls and mucilage of epidermal cells. Corresponding changes in endogenous Ca do not occur in cortical cells of the elongating zone of intact roots. These results indicate that the calcium asymmetries associated with root gravicurvature occur in the outermost layers of the root.

Monitoring the effects of manure policy in the Peat region, Netherlands

NASA Astrophysics Data System (ADS)

Hooijboer, Arno; Buis, Eke; Fraters, Dico; Boumans, Leo; Lukacs, Saskia; Vrijhoef, Astrid

2014-05-01

Total N concentrations in farm ditches in the Peat region of the Netherlands are on the average twice as high as the Good Ecological Potential value of the Water Framework Directive. Since ditches are connected to regional surface water, they may contribute to eutrophication. The minerals policy aims to improve the water quality. In the Netherlands, the effectiveness of the minerals policy on water quality is evaluated with data from the National Minerals Policy Monitoring Programme (LMM). This regards farm data on the quality of water leaching from the root zone and on farm practices. The soil balance nitrogen surpluses decreased between 1996 and 2003 on dairy farms in the Peat region. However, no effect on root zone leaching was found. This study aims to show how monitoring in the Peat region can be improved in order to link water quality to agricultural practice. Contrary to the other Dutch regions, nitrate concentrations in root zone leaching on farms in the Peat region are often very low (90% of the farms below 25 mg/l) due to the reduction of nitrate (denitrification). The main nitrogen (N) components in the peat region waters are ammonium and organic N. Total N is therefore a better measure for N concentrations in the Peat region. The ammonium concentration in groundwater in Dutch peat soils increases with depth. It is assumed that the deeper ammonia-rich water is older and relates to anaerobic peat decomposition instead of agricultural practice. Recent infiltrated low-ammonium water, lies like a thin freshwater lens on the older water. In the Peat region, root zone leaching is monitored by taking samples from the upper meter of groundwater. Unintended, often both lens water and older water are sampled and this distorts the relation between agricultural practice and water quality. In the Peat region, the N surplus is transported with the precipitation surplus to ditches. The relation between the N surplus and the total N in ditch water is therefore better than between N surplus and total N in root zone leaching. The precipitation surplus flows to ditches directly or via open field drains. However, the ditches may be fed partly with older water (seepage of groundwater). In the open field drain only recent water will occur. We expect that monitoring the water quality of the open field drains may even better reflect changes in agricultural practices. These data may also improve the understanding of contribution of agricultural nitrogen and natural nitrogen, necessary to develop measures to decrease the total-N concentration in ditch water.

Organization of cortical microtubules in graviresponding maize roots

NASA Technical Reports Server (NTRS)

Blancaflor, E. B.; Hasenstein, K. H.

1993-01-01

Immunofluorescence labeling of cortical microtubules (MTs) was used to investigate the relationship between MT arrangement and changes in growth rate of the upper and lower sides of horizontally placed roots of maize (Zea mays L. cv. Merit). Cap cells and cells of the elongation zone of roots grown vertically in light or darkness showed MT arrangements that were transverse (perpendicular) to the growth direction. Microtubules of cells basal to the elongation zone typically showed oblique orientation. Two hours after horizontal reorientation, cap cells of gravicompetent, light-grown and curving roots contained MTs parallel to the gravity vector. The MT arrangement on the upper side of the elongation zone remained transverse but the MTs of the outer four to five layers of cortical cells along the lower side of the elongation zone showed reorientation parallel to the axis of the root. The MTs of the lower epidermis retained their transverse orientation. Dark-grown roots did not curve and did not show reorientation of MTs in cells of the root cap or elongation zone. The data indicate that MT depolymerization and reorientation is correlated with reduction in growth rate, and that MT reorientation is one of the steps of growth control of graviresponding roots.

Apoplastic Alkalinization Is Instrumental for the Inhibition of Cell Elongation in the Arabidopsis Root by the Ethylene Precursor 1-Aminocyclopropane-1-Carboxylic Acid1[W][OA

PubMed Central

Staal, Marten; De Cnodder, Tinne; Simon, Damien; Vandenbussche, Filip; Van Der Straeten, Dominique; Verbelen, Jean-Pierre; Elzenga, Theo; Vissenberg, Kris

2011-01-01

In Arabidopsis (Arabidopsis thaliana; Columbia-0) roots, the so-called zone of cell elongation comprises two clearly different domains: the transition zone, a postmeristematic region (approximately 200–450 μm proximal of the root tip) with a low rate of elongation, and a fast elongation zone, the adjacent proximal region (450 μm away from the root tip up to the first root hair) with a high rate of elongation. In this study, the surface pH was measured in both zones using the microelectrode ion flux estimation technique. The surface pH is highest in the apical part of the transition zone and is lowest at the basal part of the fast elongation zone. Fast cell elongation is inhibited within minutes by the ethylene precursor 1-aminocyclopropane-1-carboxylic acid; concomitantly, apoplastic alkalinization occurs in the affected root zone. Fusicoccin, an activator of the plasma membrane H+-ATPase, can partially rescue this inhibition of cell elongation, whereas the inhibitor N,N′-dicyclohexylcarbodiimide does not further reduce the maximal cell length. Microelectrode ion flux estimation experiments with auxin mutants lead to the final conclusion that control of the activity state of plasma membrane H+-ATPases is one of the mechanisms by which ethylene, via auxin, affects the final cell length in the root. PMID:21282405

SMERGE: A multi-decadal root-zone soil moisture product for CONUS

NASA Astrophysics Data System (ADS)

Crow, W. T.; Dong, J.; Tobin, K. J.; Torres, R.

2017-12-01

Multi-decadal root-zone soil moisture products are of value for a range of water resource and climate applications. The NASA-funded root-zone soil moisture merging project (SMERGE) seeks to develop such products through the optimal merging of land surface model predictions with surface soil moisture retrievals acquired from multi-sensor remote sensing products. This presentation will describe the creation and validation of a daily, multi-decadal (1979-2015), vertically-integrated (both surface to 40 cm and surface to 100 cm), 0.125-degree root-zone product over the contiguous United States (CONUS). The modeling backbone of the system is based on hourly root-zone soil moisture simulations generated by the Noah model (v3.2) operating within the North American Land Data Assimilation System (NLDAS-2). Remotely-sensed surface soil moisture retrievals are taken from the multi-sensor European Space Agency Climate Change Initiative soil moisture data set (ESA CCI SM). In particular, the talk will detail: 1) the exponential smoothing approach used to convert surface ESA CCI SM retrievals into root-zone soil moisture estimates, 2) the averaging technique applied to merge (temporally-sporadic) remotely-sensed with (continuous) NLDAS-2 land surface model estimates of root-zone soil moisture into the unified SMERGE product, and 3) the validation of the SMERGE product using long-term, ground-based soil moisture datasets available within CONUS.

The role of the distal elongation zone in the response of maize roots to auxin and gravity

NASA Technical Reports Server (NTRS)

Ishikawa, H.; Evans, M. L.

1993-01-01

We used a video digitizer system to (a) measure changes in the pattern of longitudinal surface extension in primary roots of maize (Zea mays L.) upon application and withdrawal of auxin and (b) compare these patterns during gravitropism in control roots and roots pretreated with auxin. Special attention was paid to the distal elongation zone (DEZ), arbitrarily defined as the region between the meristem and the point within the elongation zone at which the rate of elongation reaches 0.3 of the peak rate. For roots in aqueous solution, the basal limit of the DEZ is about 2.5 mm behind the tip of the root cap. Auxin suppressed elongation throughout the elongation zone, but, after 1 to 3 h, elongation resumed, primarily as a result of induction of rapid elongation in the DEZ. Withdrawal of auxin during the period of strong inhibition resulted in exceptionally rapid elongation attributable to the initiation of rapid elongation in the DEZ plus recovery in the main elongation zone. Gravistimulation of auxin-inhibited roots induced rapid elongation in the DEZ along the top of the root. This resulted in rapid gravitropism even though the elongation rate of the root was zero before gravistimulation. The results indicate that cells of the DEZ differ from cells in the bulk of the elongation zone with respect to auxin sensitivity and that DEZ cells play an important role in gravitropism.

PRZM-2, A MODEL FOR PREDICTING PESTICIDE FATE IN THE CROP ROOT AND UNSATURATED SOIL ZONES: USERS MANUAL FOR RELEASE 2.0

EPA Science Inventory

PRZM-2 links two subordinate models--PRZM and VADOFT--in order to predict pesticide transport and transformation down through the crop root and unsaturated zones. RZM is a one-dimensional, finite difference model that accounts for pesticide fate in the crop root zone. his release...

Variability of Root Traits in Spring Wheat Germplasm

PubMed Central

Narayanan, Sruthi; Mohan, Amita; Gill, Kulvinder S.; Prasad, P. V. Vara

2014-01-01

Root traits influence the amount of water and nutrient absorption, and are important for maintaining crop yield under drought conditions. The objectives of this research were to characterize variability of root traits among spring wheat genotypes and determine whether root traits are related to shoot traits (plant height, tiller number per plant, shoot dry weight, and coleoptile length), regions of origin, and market classes. Plants were grown in 150-cm columns for 61 days in a greenhouse under optimal growth conditions. Rooting depth, root dry weight, root: shoot ratio, and shoot traits were determined for 297 genotypes of the germplasm, Cultivated Wheat Collection (CWC). The remaining root traits such as total root length and surface area were measured for a subset of 30 genotypes selected based on rooting depth. Significant genetic variability was observed for root traits among spring wheat genotypes in CWC germplasm or its subset. Genotypes Sonora and Currawa were ranked high, and genotype Vandal was ranked low for most root traits. A positive relationship (R2≥0.35) was found between root and shoot dry weights within the CWC germplasm and between total root surface area and tiller number; total root surface area and shoot dry weight; and total root length and coleoptile length within the subset. No correlations were found between plant height and most root traits within the CWC germplasm or its subset. Region of origin had significant impact on rooting depth in the CWC germplasm. Wheat genotypes collected from Australia, Mediterranean, and west Asia had greater rooting depth than those from south Asia, Latin America, Mexico, and Canada. Soft wheat had greater rooting depth than hard wheat in the CWC germplasm. The genetic variability identified in this research for root traits can be exploited to improve drought tolerance and/or resource capture in wheat. PMID:24945438

Glyphosate in Runoff Waters and in the Root-Zone: A Review

PubMed Central

Saunders, Lyndsay E.; Pezeshki, Reza

2015-01-01

Glyphosate is the most commonly-used herbicide in the world. The present review summarizes the discovery, prevalence, chemical and physical properties, mode of action and effects in plants, glyphosate resistance and the environmental fate of glyphosate. Numerous studies are reviewed that demonstrate that glyphosate may run off of fields where it is applied, while other studies provide evidence that plant roots can take up glyphosate. Non-target vegetation may be exposed to glyphosate in the root-zone, where it has the potential to remove aqueous glyphosate from the system. Further study on the effects of root-zone glyphosate on non-target vegetation is required to develop best management practices for land managers seeking to ameliorate the effects of root-zone glyphosate exposure. PMID:29051473

Controlled environment crop production - Hydroponic vs. lunar regolith

NASA Technical Reports Server (NTRS)

Bugbee, Bruce G.; Salisbury, Frank B.

1989-01-01

The potential of controlled environment crop production in a lunar colony is discussed. Findings on the effects of optimal root-zone and aerial environments derived as part of the NASA CELSS project at Utah State are presented. The concept of growing wheat in optimal environment is discussed. It is suggested that genetic engineering might produce the ideal wheat cultivar for CELSS (about 100 mm in height with fewer leaves). The Utah State University hydroponic system is outlined and diagrams of the system and plant container construction are provided. Ratio of plant mass to solution mass, minimum root-zone volume, maintenance, and pH control are discussed. A comparison of liquid hydrophonic systems and lunar regoliths as substrates for plant growth is provided. The physiological processes that are affected by the root-zone environment are discussed including carbon partitioning, nutrient availability, nutrient absorption zones, root-zone oxygen, plant water potential, root-produced hormones, and rhizosphere pH control.

Seismic imaging of a mid-lithospheric discontinuity beneath Ontong Java Plateau

NASA Astrophysics Data System (ADS)

Tharimena, Saikiran; Rychert, Catherine A.; Harmon, Nicholas

2016-09-01

Ontong Java Plateau (OJP) is a huge, completely submerged volcanic edifice that is hypothesized to have formed during large plume melting events ∼90 and 120 My ago. It is currently resisting subduction into the North Solomon trench. The size and buoyancy of the plateau along with its history of plume melting and current interaction with a subduction zone are all similar to the characteristics and hypothesized mechanisms of continent formation. However, the plateau is remote, and enigmatic, and its proto-continent potential is debated. We use SS precursors to image seismic discontinuity structure beneath Ontong Java Plateau. We image a velocity increase with depth at 28 ± 4 km consistent with the Moho. In addition, we image velocity decreases at 80 ± 5 km and 282 ± 7 km depth. Discontinuities at 60-100 km depth are frequently observed both beneath the oceans and the continents. However, the discontinuity at 282 km is anomalous in comparison to surrounding oceanic regions; in the context of previous results it may suggest a thick viscous root beneath OJP. If such a root exists, then the discontinuity at 80 km bears some similarity to the mid-lithospheric discontinuities (MLDs) observed beneath continents. One possibility is that plume melting events, similar to that which formed OJP, may cause discontinuities in the MLD depth range. Plume-plate interaction could be a mechanism for MLD formation in some continents in the Archean prior to the onset of subduction.

Neural Network-Based Retrieval of Surface and Root Zone Soil Moisture using Multi-Frequency Remotely-Sensed Observations

NASA Astrophysics Data System (ADS)

Hamed Alemohammad, Seyed; Kolassa, Jana; Prigent, Catherine; Aires, Filipe; Gentine, Pierre

2017-04-01

Knowledge of root zone soil moisture is essential in studying plant's response to different stress conditions since plant photosynthetic activity and transpiration rate are constrained by the water available through their roots. Current global root zone soil moisture estimates are based on either outputs from physical models constrained by observations, or assimilation of remotely-sensed microwave-based surface soil moisture estimates with physical model outputs. However, quality of these estimates are limited by the accuracy of the model representations of physical processes (such as radiative transfer, infiltration, percolation, and evapotranspiration) as well as errors in the estimates of the surface parameters. Additionally, statistical approaches provide an alternative efficient platform to develop root zone soil moisture retrieval algorithms from remotely-sensed observations. In this study, we present a new neural network based retrieval algorithm to estimate surface and root zone soil moisture from passive microwave observations of SMAP satellite (L-band) and AMSR2 instrument (X-band). SMAP early morning observations are ideal for surface soil moisture retrieval. AMSR2 mid-night observations are used here as an indicator of plant hydraulic properties that are related to root zone soil moisture. The combined observations from SMAP and AMSR2 together with other ancillary observations including the Solar-Induced Fluorescence (SIF) estimates from GOME-2 instrument provide necessary information to estimate surface and root zone soil moisture. The algorithm is applied to observations from the first 18 months of SMAP mission and retrievals are validated against in-situ observations and other global datasets.

Application of time-lapse ERT to Characterize Soil-Water-Disease Interactions of Citrus Orchard - Case Study

NASA Astrophysics Data System (ADS)

Peddinti, S. R.; Kbvn, D. P.; Ranjan, S.; Suradhaniwar, S.; J, P. A.; R M, G.

2015-12-01

Vidarbha region in Maharashtra, India (home for mandarin Orange) experience severe climatic uncertainties resulting in crop failure. Phytopthora are the soil-borne fungal species that accumulate in the presence of moisture, and attack the root / trunk system of Orange trees at any stage. A scientific understanding of soil-moisture-disease relations within the active root zone under different climatic, irrigation, and crop cycle conditions can help in practicing management activities for improved crop yield. In this study, we developed a protocol for performing 3-D time-lapse electrical resistivity tomography (ERT) at micro scale resolution to monitor the changes in resistivity distribution within the root zone of Orange trees. A total of 40 electrodes, forming a grid of 3.5 m x 2 m around each Orange tree were used in ERT survey with gradient and Wenner configurations. A laboratory test on un-disturbed soil samples of the region was performed to plot the variation of electrical conductivity with saturation. Curve fitting techniques were applied to get the modified Archie's model parameters. The calibrated model was further applied to generate the 3-D soil moisture profiles of the study area. The point estimates of soil moisture were validated using TDR probe measurements at 3 different depths (10, 20, and 40 cm) near to the root zone. In order to understand the effect of soil-water relations on plant-disease relations, we performed ERT analysis at two locations, one at healthy and other at Phytopthora affected Orange tree during the crop cycle, under dry and irrigated conditions. The degree to which an Orange tree is affected by Phytopthora under each condition is evaluated using 'grading scale' approach following visual inspection of the canopy features. Spatial-temporal distribution of moisture profiles is co-related with grading scales to comment on the effect of climatic and irrigation scenarios on the degree and intensity of crop disease caused by Phytopthora.

Changes in Root Decomposition Rates Across Soil Depths

NASA Astrophysics Data System (ADS)

Hicks Pries, C.; Porras, R. C.; Castanha, C.; Torn, M. S.

2016-12-01

Over half of global soil organic carbon (SOC) is stored in subsurface soils (>30 cm). Turnover times of soil organic carbon (SOC) increases with depth as evidenced by radiocarbon ages of 1,000 to more than 10,000 years in many deep soil horizons but the reasons for this increase are unclear. Many factors that potentially control SOC decomposition change with depth such as increased protection of SOC in aggregates or organo-mineral complexes and increased spatial heterogeneity of SOC "hotspots" like roots, which limit the accessibility of SOC to microbes. Lower concentrations of organic matter at depth may inhibit microbial activity due to energy limitation, and the microbial community itself changes with depth. To investigate how SOC decomposition differs with depth, we inserted a 13C-labeled fine root substrate into three depths (15, 50, and 90 cm) in a coniferous forest Alfisol and measured the root carbon remaining in particulate (>2 mm), bulk (< 2mm), free light, and mineral soil fractions over 2.5 years. We also characterized how the microbial community and SOC changed with depth. Initial rates of decomposition were unaffected by soil depth—50% of root carbon was lost from all depths within the first year. However, after 2.5 years, decomposition rates were affected by soil depth with only 15% of the root carbon remaining at 15 cm while 35% remained at 90 cm. Microbial communities, based on phospholipid fatty acid analysis, changed with depth—fungal biomarkers decreased whereas actinomycetes biomarkers increased. However, the preferences of different microbial groups for the 13C-labeled root carbon were consistent with depth. In contrast, the amount of mineral-associated SOC did not change with depth. Thus, decreased decomposition rates in this deep soil are not due to mineral associations limiting SOC availability, but may instead be due to changes in microbial communities, particularly in the microbes needed to carry out the later stages of root decomposition.

Degradation of mangrove tissues and implications for peat formation in Belizean island forests

USGS Publications Warehouse

Middleton, B.A.; McKee, K.L.

2001-01-01

1. Macrofaunal leaf consumption and degradation of leaves, woody twigs and roots were studied in mangrove island forests on a Belizean island. Factors influencing accumulation of organic matter deposited both above and below ground in this oligotrophic, autochothonous system were assessed. 2. Leaf degradation rates of Rhizophora mangle (red mangrove), Avicennia germinans (black mangrove) and Laguncularia racemosa (white mangrove) measured in mesh bags, were much faster in the lower than the upper intertidal zone. Mass loss was most rapid in A. germinans but zonal effects were much larger than species differences. 3. Exposure to invertebrates such as crabs and amphipods tripled overall rates of leaf litter breakdown. In the lower intertidal, crabs completely consumed some unbagged leaves within 23 days. Crabs also had an effect on some upper intertidal sites, where degradation of leaves placed in artificial burrows was 2.4 times faster than when placed on the soil surface. 4. In contrast to leaves (27??5% remaining after 230 days), roots and woody twigs were highly refractory (40??2% and 51??6% remaining after 584 and 540 days, respectively). Root degradation did not vary by soil depth, zone or species. Twigs of R. mangle and A. germinans degraded faster on the ground than in the canopy, whereas those of L. racemosa were highly resistant to decay regardless of position. 5. Peat formation at Twin Cays has occurred primarily through deposition and slow turnover of mangrove roots, rather than above-ground tissues that are either less abundant (woody twigs) or more readily removed (leaves).

Medial meniscus anatomy-from basic science to treatment.

PubMed

Śmigielski, Robert; Becker, Roland; Zdanowicz, Urszula; Ciszek, Bogdan

2015-01-01

This paper focuses on the anatomical attachment of the medial meniscus. Detailed anatomical dissections have been performed and illustrated. Five zones can be distinguished in regard to the meniscus attachments anatomy: zone 1 (of the anterior root), zone 2 (anteromedial zone), zone 3 (the medial zone), zone 4 (the posterior zone) and the zone 5 (of the posterior root). The understanding of the meniscal anatomy is especially crucial for meniscus repair but also for correct fixation of the anterior and posterior horn of the medial meniscus.

Interactions Between Hydroclimate and Soil Properties Control the Risk For Altered Hydrologic Partitioning From Changing Snowmelt

NASA Astrophysics Data System (ADS)

Harpold, A. A.; Longley, P.; Weiss, S. G.; Kampf, S. K.; Flint, A. L.

2016-12-01

Mountain snowmelt is a critical water source for downstream human populations and local ecosystem health. Here we explore the relatively unknown hydrologic consequences of two observed trends in Western U.S. snowpack dynamics: 1) shifts from snow to rain and 2) earlier and slower snowmelt. We apply two modeling approaches to tease apart the hydrologic effects of altered winter water inputs: 1) highly resolved one-dimensional HYDRUS modeling based on the Richard's equation at intensively measured sites and 2) the distributed Basin Characterization Model (BCM) over the Southwestern U.S. with relatively simple subsurface processes. The HYDRUS model was trained using observations from ten Snow Telemetry (SNOTEL) sites to investigate drainage below the root zone under scenarios of rain only and slower snowmelt. We found that shifts to rain-only regimes and earlier snowmelt both resulted in greater fluxes below the root zone using the measured soil depths. However, drainage fluxes and differences among scenarios diminished precipitously when rooting depths were increased to account for uncertainty. Next using the BCM, we compared water partitioning during historical runs from 1940-2014 to a scenario with all precipitation as rain but identical climate. We found that ET generally increased from eliminating snowpack sublimation. Recharge and runoff exhibited diverging responses to shifting precipitation regimes; runoff typically decreased and recharge increased, with the exception of areas in western and southern California and central Arizona. The observed changes in annual runoff and recharge were primarily caused by changes in input intensity and not changes in input timing. Runoff was most sensitive in areas with wet winters and low soil water storage. Both modeling approaches corroborated the potential for diverging changes in mountain water budgets from altered winter water inputs that will be mediated precipitation regime (i.e. precipitation intensity and timing) and soil water storage. Efforts to link these results to water resources will be discussed.

Constraining the crustal root geometry beneath Northern Morocco

NASA Astrophysics Data System (ADS)

Díaz, J.; Gil, A.; Carbonell, R.; Gallart, J.; Harnafi, M.

2016-10-01

Consistent constraints of an over-thickened crust beneath the Rif Cordillera (N. Morocco) are inferred from analyses of recently acquired seismic datasets including controlled source wide-angle reflections and receiver functions from teleseismic events. Offline arrivals of Moho-reflected phases recorded in RIFSIS project provide estimations of the crustal thicknesses in 3D. Additional constraints on the onshore-offshore transition are inferred from shots in a coeval experiment in the Alboran Sea recorded at land stations in northern Morocco. A regional crustal thickness map is computed from all these results. In parallel, we use natural seismicity data collected throughout TopoIberia and PICASSO experiments, and from a new RIFSIS deployment, to obtain receiver functions and explore the crustal thickness variations with a H-κ grid-search approach. This larger dataset provides better resolution constraints and reveals a number of abrupt crustal changes. A gridded surface is built up by interpolating the Moho depths inferred for each seismic station, then compared with the map from controlled source experiments. A remarkably consistent image is observed in both maps, derived from completely independent data and methods. Both approaches document a large crustal root, exceeding 50 km depth in the central part of the Rif, in contrast with the rather small topographic elevations. This large crustal thickness, consistent with the available Bouguer anomaly data, favors models proposing that the high velocity slab imaged by seismic tomography beneath the Alboran Sea is still attached to the lithosphere beneath the Rif, hence pulling down the lithosphere and thickening the crust. The thickened area corresponds to a quiet seismic zone located between the western Morocco arcuate seismic zone, the deep seismicity area beneath western Alboran Sea and the superficial seismicity in Alhoceima area. Therefore, the presence of a crustal root seems to play also a major role in the seismicity distribution in northern Morocco.

Constraining the crustal root geometry beneath the Rif Cordillera (North Morocco)

NASA Astrophysics Data System (ADS)

Diaz, Jordi; Gil, Alba; Carbonell, Ramon; Gallart, Josep; Harnafi, Mimoun

2016-04-01

The analyses of wide-angle reflections of controlled source experiments and receiver functions calculated from teleseismic events provide consistent constraints of an over-thickened crust beneath the Rif Cordillera (North Morocco). Regarding active source data, we investigate now offline arrivals of Moho-reflected phases recorded in RIFSIS project to get new estimations of 3D crustal thickness variations beneath North Morocco. Additional constrains on the onshore-offshore transition are derived from onland recording of marine airgun shots from the coeval Gassis-Topomed profiles. A regional crustal thickness map is computed from all these results. In parallel, we use natural seismicity data collected throughout TopoIberia and PICASSO experiments, and from a new RIFSIS deployment, to obtain teleseismic receiver functions and explore the crustal thickness variations with a H-κ grid-search approach. The use of a larger dataset including new stations covering the complex areas beneath the Rif Cordillera allow us to improve the resolution of previous contributions, revealing abrupt crustal changes beneath the region. A gridded surface is built up by interpolating the Moho depths inferred for each seismic station, then compared with the map from controlled source experiments. A remarkably consistent image is observed in both maps, derived from completely independent data and methods. Both approaches document a large modest root, exceeding 50 km depth in the central part of the Rif, in contrast with the rather small topographic elevations. This large crustal thickness, consistent with the available Bouguer anomaly data, favor models proposing that the high velocity slab imaged by seismic tomography beneath the Alboran Sea is still attached to the lithosphere beneath the Rif, hence pulling down the lithosphere and thickening the crust. The thickened area corresponds to a quiet seismic zone located between the western Morocco arcuate seismic zone, the deep seismicity area beneath western Alboran Sea and the superficial seismicity in Alhoceima area. Therefore, the presence of a crustal root seems to play also a major role in the seismicity distribution in northern Morocco.

Seismic images of the transition zone: is Hawaiian volcanism produced by a secondary plume from the top of the lower mantle?

NASA Astrophysics Data System (ADS)

Cao, Q.; van der Hilst, R. D.; Shim, S.; De Hoop, M. V.

2011-12-01

The Hawaiian hotspot is often attributed to hot material rising from depth in the mantle, but efforts to detect a thermal plume seismically have been inconclusive. Most tomographic models reveal anomalously low wavespeeds beneath Hawaii, but the depth extent of this structure is not well known. S or P data used in traveltime inversions are associated with steep rays to distant sources, which degrades depth resolution, and surface wave dispersion does not have sufficient sensitivity at the depths of interest. To investigate pertinent thermal anomalies we mapped depth variations of upper mantle discontinuities using precursors of the surface-reflected SS wave. Instead of stacking the data over geographical bins, which leads to averaging of topography and hence loss of spatial resolution, we used a generalized Radon transform (GRT) to detect and map localized elasticity contrasts in the transition zone (Cao et al., PEPI, 2010). We apply the GRT to produce 3D image volumes beneath a large area of the Pacific Ocean, including Hawaii and the Hawaii-Emperor seamount chain (Cao et al., Science, 2011). The 3D image volumes reveal laterally continuous interfaces near 410 and 660 km depths, that is, the traditional boundaries of the transition zone, but also suggest (perhaps intermittent) scatter horizons near 300-350, 520-550, and 800-1000 km depth. The upper mantle appears generally hot beneath Hawaii, but the most conspicuous topographic (and probably thermal) anomalies are found west of Hawaii. The GRT images reveal a 800 km wide uplift of the 660 discontinuity just west of Hawaii, but there is no evidence for a corresponding localized depression of the 410 discontinuity. This expression of the 410 and 660 km topographies is consistent with some existed geodynamical modeling results, in which a deep-rooted mantle plume impinging on the transition zone, creating a broad pond of hot material underneath endothermic phase change at 660 km depth, and with secondary plumes stemming from this hot pool of materials and rising in the upper mantle to create the present-day hotspot at Earth's surface. West of the upwarp that we interpret as the elevated post-spinel the main interface deepens to nearly 700 km depth. Given this position, it is unlikely that this deep structure is due to low temperatures. Instead, it would be consistent with slightly elevated temperatures (compared to transition temperature of post-spinel) and transitions in the garnet phase. This interpretation, if correct, implies that the area of ponded hot material is at least 2,000 km wide. The presence of an 800- to 2,000-kilometer-wide thermal anomaly deep in the transition zone west of Hawaii suggests that hot material does not rise from the lower mantle through a narrow vertical plume but accumulates near the base of the transition zone before being entrained in flow toward Hawaii and, perhaps, other islands. This implies that geochemical trends in Hawaiian lavas cannot constrain lower mantle domains directly. This type of flow may be a better explanation of bathymetric features in the Pacific (including other seamount chains) than the canonical deep mantle plumes.

Plant responses to heterogeneous salinity: growth of the halophyte Atriplex nummularia is determined by the root-weighted mean salinity of the root zone

PubMed Central

Bazihizina, Nadia

2012-01-01

Soil salinity is generally spatially heterogeneous, but our understanding of halophyte physiology under such conditions is limited. The growth and physiology of the dicotyledonous halophyte Atriplex nummularia was evaluated in split-root experiments to test whether growth is determined by: (i) the lowest; (ii) the highest; or (iii) the mean salinity of the root zone. In two experiments, plants were grown with uniform salinities or horizontally heterogeneous salinities (10–450mM NaCl in the low-salt side and 670mM in the high-salt side, or 10mM NaCl in the low-salt side and 500–1500mM in the high-salt side). The combined data showed that growth and gas exchange parameters responded most closely to the root-weighted mean salinity rather than to the lowest, mean, or highest salinity in the root zone. In contrast, midday shoot water potentials were determined by the lowest salinity in the root zone, consistent with most water being taken from the least negative water potential source. With uniform salinity, maximum shoot growth was at 120–230mM NaCl; ~90% of maximum growth occurred at 10mM and 450mM NaCl. Exposure of part of the roots to 1500mM NaCl resulted in an enhanced (+40%) root growth on the low-salt side, which lowered root-weighted mean salinity and enabled the maintenance of shoot growth. Atriplex nummularia grew even with extreme salinity in part of the roots, as long as the root-weighted mean salinity of the root zone was within the 10–450mM range. PMID:23125356

Plant responses to heterogeneous salinity: growth of the halophyte Atriplex nummularia is determined by the root-weighted mean salinity of the root zone.

PubMed

Bazihizina, Nadia; Barrett-Lennard, Edward G; Colmer, Timothy D

2012-11-01

Soil salinity is generally spatially heterogeneous, but our understanding of halophyte physiology under such conditions is limited. The growth and physiology of the dicotyledonous halophyte Atriplex nummularia was evaluated in split-root experiments to test whether growth is determined by: (i) the lowest; (ii) the highest; or (iii) the mean salinity of the root zone. In two experiments, plants were grown with uniform salinities or horizontally heterogeneous salinities (10-450 mM NaCl in the low-salt side and 670 mM in the high-salt side, or 10 mM NaCl in the low-salt side and 500-1500 mM in the high-salt side). The combined data showed that growth and gas exchange parameters responded most closely to the root-weighted mean salinity rather than to the lowest, mean, or highest salinity in the root zone. In contrast, midday shoot water potentials were determined by the lowest salinity in the root zone, consistent with most water being taken from the least negative water potential source. With uniform salinity, maximum shoot growth was at 120-230 mM NaCl; ~90% of maximum growth occurred at 10 mM and 450 mM NaCl. Exposure of part of the roots to 1500 mM NaCl resulted in an enhanced (+40%) root growth on the low-salt side, which lowered root-weighted mean salinity and enabled the maintenance of shoot growth. Atriplex nummularia grew even with extreme salinity in part of the roots, as long as the root-weighted mean salinity of the root zone was within the 10-450 mM range.

Comparative water relations of adjacent california shrub and grassland communities.

PubMed

Davis, S D; Mooney, H A

1985-07-01

Much of the coastal mountains and foothills of central and southern California are covered by a mosaic of grassland, coastal sage scrub, and evergreen sclerophyllous shrubs (chaparral). In many cases, the borders between adjacent plant communities are stable. The cause of this stability is unknown. The purpose of our study was to examine the water use patterns of representative grasses, herbs, and shrubs across a grassland/chaparrel ecotone and determine the extent to which patterns of water use contribute to ecotone stability. In addition, we examined the effects of seed dispersal and animal herbivory. We found during spring months, when water was not limited, grassland species had a much higher leaf conductance to water vapor diffusion than chaparral plants. As the summer drought progressed, grassland species depleted available soil moisture first, bare zone plants second, and chaparral third, with one chaparral species (Quercus durata) showing no evidence of water stress. Soil moisture depletion patterns with depth and time corresponded to plant water status and root depth. Rabbit herbivory was highest in the chaparral and bare zone as indicated by high densities of rabbit pellets. Dispersal of grassland seeds into the chaparral and bare zone was low. Our results support the hypothesis that grassland species deplete soil moisture in the upper soil horizon early in the drought, preventing the establishment of chaparral seedlings or bare zone herbs. Also, grassland plants are prevented from invading the chaparral because of low seed dispersability and high animal herbivory in these regions.

The Automated Root Exudate System (ARES): a method to apply solutes at regular intervals to soils in the field.

PubMed

Lopez-Sangil, Luis; George, Charles; Medina-Barcenas, Eduardo; Birkett, Ali J; Baxendale, Catherine; Bréchet, Laëtitia M; Estradera-Gumbau, Eduard; Sayer, Emma J

2017-09-01

Root exudation is a key component of nutrient and carbon dynamics in terrestrial ecosystems. Exudation rates vary widely by plant species and environmental conditions, but our understanding of how root exudates affect soil functioning is incomplete, in part because there are few viable methods to manipulate root exudates in situ . To address this, we devised the Automated Root Exudate System (ARES), which simulates increased root exudation by applying small amounts of labile solutes at regular intervals in the field.The ARES is a gravity-fed drip irrigation system comprising a reservoir bottle connected via a timer to a micro-hose irrigation grid covering c . 1 m 2 ; 24 drip-tips are inserted into the soil to 4-cm depth to apply solutions into the rooting zone. We installed two ARES subplots within existing litter removal and control plots in a temperate deciduous woodland. We applied either an artificial root exudate solution (RE) or a procedural control solution (CP) to each subplot for 1 min day -1 during two growing seasons. To investigate the influence of root exudation on soil carbon dynamics, we measured soil respiration monthly and soil microbial biomass at the end of each growing season.The ARES applied the solutions at a rate of c . 2 L m -2  week -1 without significantly increasing soil water content. The application of RE solution had a clear effect on soil carbon dynamics, but the response varied by litter treatment. Across two growing seasons, soil respiration was 25% higher in RE compared to CP subplots in the litter removal treatment, but not in the control plots. By contrast, we observed a significant increase in microbial biomass carbon (33%) and nitrogen (26%) in RE subplots in the control litter treatment.The ARES is an effective, low-cost method to apply experimental solutions directly into the rooting zone in the field. The installation of the systems entails minimal disturbance to the soil and little maintenance is required. Although we used ARES to apply root exudate solution, the method can be used to apply many other treatments involving solute inputs at regular intervals in a wide range of ecosystems.

The locations and amounts of endogenous ions and elements in the cap and elongating zone of horizontally oriented roots of Zea mays L.: an electron-probe EDS study

NASA Technical Reports Server (NTRS)

Moore, R.; Cameron, I. L.; Hunter, K. E.; Olmos, D.; Smith, N. K.

1987-01-01

We used quantitative electron-probe energy-dispersive x-ray microanalysis to localize endogenous Na, Cl, K, P, S, Mg and Ca in cryofixed and freeze-dried cryosections of the cap (i.e. the putative site of graviperception) and elongating zone (i.e. site of gravicurvature) of horizontally oriented roots of Zea mays. Ca, Na, Cl, K and Mg accumulate along the lower side of caps of horizontally oriented roots. The most dramatic asymmetries of these ions occur in the apoplast, especially the mucilage. We could not detect any significant differences in the concentrations of these ions in the central cytoplasm of columella cells along the upper and lower sides of caps of horizontally-oriented roots. However, the increased amounts of Na, Cl, K and Mg in the longitudinal walls of columella cells along the lower side of the cap suggest that these ions may move down through the columella tissue of horizontally-oriented roots. Ca also accumulates (largely in the mucilage) along the lower side of the elongating zone of horizontally-oriented roots, while Na, P, Cl and K tend to accumulate along the upper side of the elongating zone. Of these ions, only K increases in concentration in the cytoplasm and longitudinal walls of cortical cells in the upper vs lower sides of the elongating zone. These results indicate that (1) gravity-induced asymmetries of ions differ significantly in the cap and elongating zone of graviresponding roots, (2) Ca accumulates along the lower side of the cap and elongating zone of graviresponding roots, (3) increased growth of the upper side of the elongating zone of horizontally-oriented roots correlates positively with increased amounts of K in the cytoplasm and longitudinal walls of cortical cells, and (4) the apoplast (especially the mucilage) may be an important component of the pathway via which ions move in graviresponding rots of Zea mays. These results are discussed relative to mechanisms for graviperception and gravicurvature of roots.

Investigating the water balance of on-farm techniques for improved crop productivity in rainfed systems: A case study of Makanya catchment, Tanzania

NASA Astrophysics Data System (ADS)

Makurira, H.; Savenije, H. H. G.; Uhlenbrook, S.; Rockström, J.; Senzanje, A.

Water scarcity is a perennial problem in sub-Saharan agricultural systems where extreme rainfall events dominate agricultural seasons. Dry spell occurrences between and during seasons negatively impact on crop yields especially if such dry spells exceed 14 days. The impact of dry spells is felt more at smallholder farming scales where subsistence farming is the only source of livelihood for many households. This paper presents results from on-going research to improve rainfed water productivity in arid and semi-arid regions. The study site is the Makanya catchment in northern Tanzania where rainfall rarely exceeds 400 mm/season. Rainwater alone is not sufficient to support maize which is the preferred crop. The research introduced new soil and water conservation measures to promote water availability into the root zone. The introduced techniques include deep tillage, runoff diversion, fanya juus (infiltration trenches with bunds) and infiltration pits. The research aims at understanding the effectiveness of these interventions in increasing moisture availability within the root zone. Time domain reflectometry (TDR) was used to measure soil moisture twice weekly at 10 cm depth intervals up to depths of 2 m. Soil moisture fluctuated in the range 5-25% of volume with the beginning of the season recording the driest moisture levels and periods after good rainfall/runoff events recording the highest moisture levels. From the field observations made, a spreadsheet model was developed to simulate soil moisture variations during different maize growth stages. The results obtained show that the zones of greatest soil moisture concentrations are those around the trenches and bunds. Soil moisture is least at the centre of the plots. The study confirms the effectiveness of the introduced techniques to help concentrate the little available rainfall into green water flow paths. Indirect benefits from these improved techniques are the creation of fertile and moist zones around the bunds where supplementary food crops (e.g. bananas and cassava) can be grown even in dry seasons.

Root-zone temperature and nitrogen affect the yield and secondary metabolite concentration of fall- and spring-grown, high-density leaf lettuce.

PubMed

Bumgarner, Natalie R; Scheerens, Joseph C; Mullen, Robert W; Bennett, Mark A; Ling, Peter P; Kleinhenz, Matthew D

2012-01-15

Understanding the effects of temperature and nitrogen levels on key variables, particularly under field conditions during cool seasons of temperate climates, is important. Here, we document the impact of root-zone heating and nitrogen (N) fertility on the accumulation and composition of fall- and spring-grown lettuce biomass. A novel, scalable field system was employed. Direct-seeded plots containing a uniform, semi-solid, and nearly stable rooting medium were established outdoors in 2009 and 2010; each contained one of eight combinations of root-zone heating (-/+) and N fertility (0, 72, 144, and 576 mg day(-1)). Root-zone heating increased but withholding N decreased biomass accumulation in both years. Low N supplies were also associated with greater anthocyanin and total antioxidant power but lower N and phosphorus levels. Tissue chlorophyll a and vitamin C levels tracked root-zone temperature and N fertility more closely in 2009 and 2010, respectively. Experimentally imposed root-zone temperature and N levels influenced the amount and properties of fall- and spring-grown lettuce tissue. Ambient conditions, however, dictated which of these factors exerted the greatest effect on the variables measured. Collectively, the results point to the potential for gains in system sustainability and productivity, including with respect to supplying human nutritional units. Copyright © 2011 Society of Chemical Industry.

The effect of EDTA in attachment gain and root coverage.

PubMed

Kassab, Moawia M; Cohen, Robert E; Andreana, Sebastiano; Dentino, Andrew R

2006-06-01

Root surface biomodification using low pH agents such as citric acid and tetracycline has been proposed to enhance root coverage following connective tissue grafting. The authors hypothesized that root conditioning with neutral pH edetic acid would improve vertical recession depth, root surface coverage, pocket depth, and clinical attachment levels. Twenty teeth in 10 patients with Miller class I and II recession were treated with connective tissue grafting. The experimental sites received 24% edetic acid in sterile distilled water applied to the root surface for 2 minutes before grafting. Controls were pretreated with only sterile distilled water. Measurements were evaluated before surgery and 6 months after surgery. Analysis of variance was used to determine differences between experimental and control groups. We found significant postoperative improvements in vertical recession depth, root surface coverage, and clinical attachment levels in test and control groups, compared to postoperative data. Pocket depth differences were not significant (P<.01).

User guide for the farm process (FMP1) for the U.S. Geological Survey's modular three-dimensional finite-difference ground-water flow model, MODFLOW-2000

USGS Publications Warehouse

Schmid, Wolfgang; Hanson, R.T.; Maddock, Thomas; Leake, S.A.

2006-01-01

There is a need to estimate dynamically integrated supply-and-demand components of irrigated agriculture as part of the simulation of surface-water and ground-water flow. To meet this need, a computer program called the Farm Process (FMP1) was developed for the U.S. Geological Survey three-dimensional finite-difference modular ground-water flow model, MODFLOW- 2000 (MF2K). The FMP1 allows MF2K users to simulate conjunctive use of surface- and ground water for irrigated agriculture for historical and future simulations, water-rights issues and operational decisions, nondrought and drought scenarios. By dynamically integrating farm delivery requirement, surface- and ground-water delivery, as well as irrigation-return flow, the FMP1 allows for the estimation of supplemental well pumpage. While farm delivery requirement and irrigation return flow are simulated by the FMP1, the surface-water delivery to the farm can be simulated optionally by coupling the FMP1 with the Streamflow Routing Package (SFR1) and the farm well pumping can be simulated optionally by coupling the FMP1 to the Multi-Node Well (MNW) Package. In addition, semi-routed deliveries can be specified that are associated with points of diversion in the SFR1 stream network. Nonrouted surface-water deliveries can be specified independently of any stream network. The FMP1 maintains a dual mass balance of a farm budget and as part of the ground-water budget. Irrigation demand, supply, and return flow are in part subject to head-dependent sources and sinks such as evapotranspiration from ground water and leakage between the conveyance system and the aquifer. Farm well discharge and farm net recharge are source/sink terms in the FMP1, which depend on transpiration uptake from ground water and other head dependent consumptive use components. For heads rising above the bottom of the root zone, the actual transpiration is taken to vary proportionally with the depth of the active root zone, which can be restricted by anoxia or wilting. Depths corresponding to anoxia- or wilting-related pressure heads within the root zone are found using analytical solutions of a vertical pseudo steady-state pressure- head distribution over the depth of the total root zone (Consumptive Use Concept 1). Alternatively, a simpler, conceptual model is available, which defines how consumptive use (CU) components vary with changing head (CU Concept 2). Subtracting the ground water and precipitation transpiration components from the total transpiration yields a transpiratory irrigation requirement for each cell. The total farm delivery requirement (TFDR) then is determined as cumulative transpiratory and evaporative irrigation requirements of all farm cells and increased sufficiently to compensate for inefficient use from irrigation with respect to plant consumption. The TFDR subsequently is satisfied with surface- and ground-water delivery, respectively constrained by allotments, water rights, or maximum capacities. Five economic and noneconomic drought response policies can be applied optionally, if the potential supply of surface water and ground water is insufficient to meet the crop demand: acreage-optimization with or without a water conservation pool, deficit irrigation with or without water-stacking, and zero policy.

Statistical characteristics of seismo-ionospheric GPS TEC disturbances prior to global Mw ≥ 5.0 earthquakes (1998-2014)

NASA Astrophysics Data System (ADS)

Shah, Munawar; Jin, Shuanggen

2015-12-01

Pre-earthquake ionospheric anomalies are still challenging and unclear to obtain and understand, particularly for different earthquake magnitudes and focal depths as well as types of fault. In this paper, the seismo-ionospheric disturbances (SID) related to global earthquakes with 1492 Mw ≥ 5.0 from 1998 to 2014 are investigated using the total electron content (TEC) of GPS global ionosphere maps (GIM). Statistical analysis of 10-day TEC data before global Mw ≥ 5.0 earthquakes shows significant enhancement 5 days before an earthquake of Mw ≥ 6.0 at a 95% confidence level. Earthquakes with a focal depth of less than 60 km and Mw ≥ 6.0 are presumably the root of deviation in the ionospheric TEC because earthquake breeding zones have gigantic quantities of energy at shallower focal depths. Increased anomalous TEC is recorded in cumulative percentages beyond Mw = 5.5. Sharpness in cumulative percentages is evident in seismo-ionospheric disturbance prior to Mw ≥ 6.0 earthquakes. Seismo-ionospheric disturbances related to strike slip and thrust earthquakes are noticeable for magnitude Mw6.0-7.0 earthquakes. The relative values reveal high ratios (up to 2) and low ratios (up to -0.5) within 5 days prior to global earthquakes for positive and negative anomalies. The anomalous patterns in TEC related to earthquakes are possibly due to the coupling of high amounts of energy from earthquake breeding zones of higher magnitude and shallower focal depth.

Leaf water status and root system water flux of shortleaf pine (Pinus echinata Mill.) seedlings in relation to new root growth after transplanting

Treesearch

John C. Brissette; Jim L. Chambers

1992-01-01

Water relations and root growth of shortleaf pine (Pinus echinata Mill.) were studied four weeks after seedlings from a half-sib family had been transplanted to one of three regimes of soil water availability at a root zone temperature of either 15 or 20 °C. About one-third of the variation in new root growth was explained by the root zone...

Health of native riparian vegetation and its relation to hydrologic conditions along the Mojave River, southern California

USGS Publications Warehouse

Lines, Gregory C.

1999-01-01

The health of native riparian vegetation and its relation to hydrologic conditions were studied along the Mojave River mainly during the growing seasons of 1997 and 1998. The study concentrated on cottonwood?willow woodlands (predominantly Populus fremontii and Salix gooddingii) and mesquite bosques (predominantly Prosopis glandulosa). Tree-growth characteristics were measured at 16 cottonwood?willow woodland sites and at 3 mesquite bosque sites. Density of live and dead trees, tree diameter and height, canopy density, live-crown volume, leaf-water potential, leaf-area index, mortality, and reproduction were measured or noted at each site. The sites included healthy and reproducing woodlands and bosques, stressed woodlands and bosques with no reproduction, and woodlands and bosques with high mortality. Tree roots were studied at seven sites to determine the vertical distribution of the root system and their relation to the water table at healthy, stressed, and high-mortality cottonwood?willow woodlands. In the six trenches that were dug for this study in May 1997, no cottonwood roots were observed that reached the water table. The root systems of healthy trees typically ended 1 to 2 feet above the water table. At sites with high mortality, the main root mass was commonly 7 to 8 feet above the water table. Water-table depth was monitored at each of the study sites. In addition, volumetric soil moisture and soil-water potential were monitored at varying depths at three cottonwood?willow woodland study sites and at two mesquite bosque sites. Ground, soil, river, lake, and plant (xylem sap) water were analyzed for concentrations of stable hydrogen and oxygen isotopes to determine the source of water used by the trees. On the basis of the root-distribution, soil- and leaf-water potential, and isotope data, it was concluded that cottonwood, willow, and mesquite trees mainly rely on ground water for their perennial sustained supply of water. The trees mainly utilize ground water that has moved upward from the water table into the capillary fringe and into unsaturated soil nearer to land surface. Most precipitation (average is 4 to 6 inches per year) is lost by evaporation and by transpiration of shallow-rooted xeric plants, and very little reaches the root zone of trees along the Mojave River. Water-table depth had no strong correlation to many individual tree-growth characteristics, such as density, diameter, height, and live-crown volume. However, leaf-area index (corrected for stem area) of both healthy and stressed cottonwood?willow woodlands had a highly significant statistical relation to water-table depth, and a curvilinear regression model was defined. As in cottonwood?willow woodlands, leaf-area index of mesquite bosques also decreased with increased water-table depth. However, because of the small number of sites, no significant statistical relation could be defined for mesquite bosques. Because it can be accurately measured repeatedly at the same locations, leaf-area index (corrected for stem area) is recommended as the primary growth characteristic that should be monitored. Future vegetation changes along the Mojave River can be quantified using the sites established for this study. Mortality was as high as 39 percent in healthy cottonwood?willow woodlands, but mortality of 50 to 100 percent was common where water-table depth was greater than about 7 feet or in areas where permanent water-table declines greater than about 5 feet had occurred. At a healthy mesquite bosque where the water-table depth ranged from about 8 to 11 feet, mortality was about 20 percent. Where the water table had been lowered an additional 10 to 25 feet by pumping, mortality of the mesquite was extremely high (80 to 99 percent). On the basis of observations of plant reproduction, it was concluded that established cottonwood?willow woodlands probably will reproduce, mainly by root sprouting of mature trees, if the water-t

Effects of shallow water table, salinity and frequency of irrigation water on the date palm water use

NASA Astrophysics Data System (ADS)

Askri, Brahim; Ahmed, Abdelkader T.; Abichou, Tarek; Bouhlila, Rachida

2014-05-01

In southern Tunisia oases, waterlogging, salinity, and water shortage represent serious threats to the sustainability of irrigated agriculture. Understanding the interaction between these problems and their effects on root water uptake is fundamental for suggesting possible options of improving land and water productivity. In this study, HYDRUS-1D model was used in a plot of farmland located in the Fatnassa oasis to investigate the effects of waterlogging, salinity, and water shortage on the date palm water use. The model was calibrated and validated using experimental data of sap flow density of a date palm, soil hydraulic properties, water table depth, and amount of irrigation water. The comparison between predicted and observed data for date palm transpiration rates was acceptable indicating that the model could well estimate water consumption of this tree crop. Scenario simulations were performed with different water table depths, and salinities and frequencies of irrigation water. The results show that the impacts of water table depth and irrigation frequency vary according to the season. In summer, high irrigation frequency and shallow groundwater are needed to maintain high water content and low salinity of the root-zone and therefore to increase the date palm transpiration rates. However, these factors have no significant effect in winter. The results also reveal that irrigation water salinity has no significant effect under shallow saline groundwater.

Rooting depth varies differentially in trees and grasses as a function of mean annual rainfall in an African savanna.

PubMed

Holdo, Ricardo M; Nippert, Jesse B; Mack, Michelle C

2018-01-01

A significant fraction of the terrestrial biosphere comprises biomes containing tree-grass mixtures. Forecasting vegetation dynamics in these environments requires a thorough understanding of how trees and grasses use and compete for key belowground resources. There is disagreement about the extent to which tree-grass vertical root separation occurs in these ecosystems, how this overlap varies across large-scale environmental gradients, and what these rooting differences imply for water resource availability and tree-grass competition and coexistence. To assess the extent of tree-grass rooting overlap and how tree and grass rooting patterns vary across resource gradients, we examined landscape-level patterns of tree and grass functional rooting depth along a mean annual precipitation (MAP) gradient extending from ~ 450 to ~ 750 mm year -1 in Kruger National Park, South Africa. We used stable isotopes from soil and stem water to make inferences about relative differences in rooting depth between these two functional groups. We found clear differences in rooting depth between grasses and trees across the MAP gradient, with grasses generally exhibiting shallower rooting profiles than trees. We also found that trees tended to become more shallow-rooted as a function of MAP, to the point that trees and grasses largely overlapped in terms of rooting depth at the wettest sites. Our results reconcile previously conflicting evidence for rooting overlap in this system, and have important implications for understanding tree-grass dynamics under altered precipitation scenarios.

An isotopic view of water and nitrate transport through the vadose zone in Oregon's southern Willamette Valley's Groundwater Management Area

NASA Astrophysics Data System (ADS)

Brooks, J. R.; Pearlstein, S.; Hutchins, S.; Faulkner, B. R.; Rugh, W.; Willard, K.; Coulombe, R.; Compton, J.

2017-12-01

Groundwater nitrate contamination affects thousands of households in Oregon's southern Willamette Valley and many more across the USA. The southern Willamette Valley Groundwater Management Area (GWMA) was established in 2004 due to nitrate levels in the groundwater exceeding the human health standard of 10 mg nitrate-N L-1. Much of the nitrogen (N) inputs to the GWMA comes from agricultural fertilizers, and thus efforts to reduce N inputs to groundwater are focused upon improving N management. However, the effectiveness of these improvements on groundwater quality is unclear because of the complexity of nutrient transport through the vadose zone and long groundwater residence times. Our objective was to focus on vadose zone transport and understand the dynamics and timing of N and water movement below the rooting zone in relation to N management and water inputs. Stable isotopes are a powerful tool for tracking water movement, and understanding N transformations. In partnership with local farmers and state agencies, we established lysimeters and groundwater wells in multiple agricultural fields in the GWMA, and have monitored nitrate, nitrate isotopes, and water isotopes weekly for multiple years. Our results indicate that vadose zone transport is highly complex, and the residence time of water collected in lysimeters was much longer than expected. While input precipitation water isotopes were highly variable over time, lysimeter water isotopes were surprisingly consistent, more closely resembling long-term precipitation isotope means rather than recent precipitation isotopic signatures. However, some particularly large precipitation events with unique isotopic signatures revealed high spatial variability in transport, with some lysimeters showing greater proportions of recent precipitation inputs than others. In one installation where we have groundwater wells and lysimeters at multiple depths, nitrate/nitrite concentrations decreased with depth. N concentrations and δ15N values indicated leaching at 1 m and denitrification at 3 m depth. However, these relationships showed spatial and temporal complexity. We are exploring how these vadose zone complexities can be incorporated into practical understanding of the impacts of N management on groundwater inputs.

Field tracer investigation of unsaturated zone flow paths and mechanisms in agricultural soils of northwestern Mississippi, USA

USGS Publications Warehouse

Perkins, K.S.; Nimmo, J.R.; Rose, C.E.; Coupe, R.H.

2011-01-01

In many farmed areas, intensive application of agricultural chemicals and withdrawal of groundwater for irrigation have led to water quality and supply issues. Unsaturated-zone processes, including preferential flow, play a major role in these effects but are not well understood. In the Bogue Phalia basin, an intensely agricultural area in the Delta region of northwestern Mississippi, the fine-textured soils often exhibit surface ponding and runoff after irrigation and rainfall as well as extensive surface cracking during prolonged dry periods. Fields are typically land-formed to promote surface flow into drainage ditches and streams that feed into larger river ecosystems. Downward flow of water below the root zone is considered minimal; regional groundwater models predict only 5% or less of precipitation recharges the heavily used alluvial aquifer. In this study transport mechanisms within and below the root zone of a fallow soybean field were assessed by performing a 2-m ring infiltration test with tracers and subsurface monitoring instruments. Seven months after tracer application, 48 continuous cores were collected for tracer extraction to define the extent of water movement and quantify preferential flow using a mass-balance approach. Vertical water movement was rapid below the pond indicating the importance of vertical preferential flow paths in the shallow unsaturated zone, especially to depths where agricultural disturbance occurs. Lateral flow of water at shallow depths was extensive and spatially non-uniform, reaching up to 10. m from the pond within 2. months. Within 1. month, the wetting front reached a textural boundary at 4-5. m between the fine-textured soil and sandy alluvium, now a potential capillary barrier which, prior to extensive irrigation withdrawals, was below the water table. Within 10. weeks, tracer was detectable at the water table which is presently about 12. m below land surface. Results indicate that 43% of percolation may be through preferential flow paths and that any water breaking through the capillary barrier (as potential recharge) likely does so in fingers which are difficult to detect with coring methods. In other areas where water levels have declined and soils have similar properties, the potential for transport of agricultural chemicals to the aquifer may be greater than previously assumed. ?? 2010 .

Seismic wide-angle constraints on the crust of the southern Urals

NASA Astrophysics Data System (ADS)

Carbonell, R.; Gallart, J.; PéRez-Estaún, A.; Diaz, J.; Kashubin, S.; Mechie, J.; Wenzel, F.; Knapp, J.

2000-06-01

A wide-angle seismic reflection/refraction data set was acquired during spring 1995 across the southern Urals to characterize the lithosphere beneath this Paleozoic orogen. The wide-angle reflectivity features a strong frequency dependence. While the lower crustal reflectivity is in the range of 6-15 Hz, the PmP is characterized by frequencies below 6 Hz. After detailed frequency filtering, the seismic phases constrain a new average P wave velocity crustal model that consists of an upper layer of 5.0-6.0 km/s, which correlates with the surface geology; 5-7 km depths at which the velocities increase to 6.2-6.3 km/s; 10-30 km depths at which, on average, the crust is characterized by velocities of 6.6 km/s; and finally, the lower crust, from 30-35 km down to the Moho, which has velocities ranging from 6.8 to 7.4 km/s. Two different S wave velocity models, one for the N-S and one for the E-W, were derived from the analysis of the horizontal component recordings. Crustal sections of Poisson's ratio and anisotropy were calculated from the velocity models. The Poisson's ratio increases in the lower crust at both sides of the root zone. A localized 2-3% anisotropy zone is imaged within the lower crust beneath the terranes east of the root. This feature is supported by time differences in the SmS phase and by the particle motion diagrams, which reveal two polarized directions of motion. Velocities are higher in the central part of the orogen than for the Siberian and eastern plates. These seismic recordings support a 50-56 km crustal thickness beneath the central part of the orogen in contrast to Moho depths of ≈ 45 km documented at the edges of the transect. The lateral variation of the PmP phase in frequency content and in waveform can be taken as evidence of different genetic origins of the Moho in the southern Urals.

Will changes in root-zone temperature in boreal spring affect recovery of photosynthesis in Picea mariana and Populus tremuloides in a future climate?

PubMed

Fréchette, Emmanuelle; Ensminger, Ingo; Bergeron, Yves; Gessler, Arthur; Berninger, Frank

2011-11-01

Future climate will alter the soil cover of mosses and snow depths in the boreal forests of eastern Canada. In field manipulation experiments, we assessed the effects of varying moss and snow depths on the physiology of black spruce (Picea -mariana (Mill.) B.S.P.) and trembling aspen (Populus tremuloides Michx.) in the boreal black spruce forest of western Québec. For 1 year, naturally regenerated 10-year-old spruce and aspen were grown with one of the following treatments: additional N fertilization, addition of sphagnum moss cover, removal of mosses, delayed soil thawing through snow and hay addition, or accelerated soil thawing through springtime snow removal. Treatments that involved the addition of insulating moss or snow in the spring caused lower soil temperature, while removing moss and snow in the spring caused elevated soil temperature and thus had a warming effect. Soil warming treatments were associated with greater temperature variability. Additional soil cover, whether moss or snow, increased the rate of photosynthetic recovery in the spring. Moss and snow removal, on the other hand, had the opposite effect and lowered photosynthetic activity, especially in spruce. Maximal electron transport rate (ETR(max)) was, for spruce, 39.5% lower after moss removal than with moss addition, and 16.3% lower with accelerated thawing than with delayed thawing. Impaired photosynthetic recovery in the absence of insulating moss or snow covers was associated with lower foliar N concentrations. Both species were affected in that way, but trembling aspen generally reacted less strongly to all treatments. Our results indicate that a clear negative response of black spruce to changes in root-zone temperature should be anticipated in a future climate. Reduced moss cover and snow depth could adversely affect the photosynthetic capacities of black spruce, while having only minor effects on trembling aspen.

Prediction of Root Zone Soil Moisture using Remote Sensing Products and In-Situ Observation under Climate Change Scenario

NASA Astrophysics Data System (ADS)

Singh, G.; Panda, R. K.; Mohanty, B.

2015-12-01

Prediction of root zone soil moisture status at field level is vital for developing efficient agricultural water management schemes. In this study, root zone soil moisture was estimated across the Rana watershed in Eastern India, by assimilation of near-surface soil moisture estimate from SMOS satellite into a physically-based Soil-Water-Atmosphere-Plant (SWAP) model. An ensemble Kalman filter (EnKF) technique coupled with SWAP model was used for assimilating the satellite soil moisture observation at different spatial scales. The universal triangle concept and artificial intelligence techniques were applied to disaggregate the SMOS satellite monitored near-surface soil moisture at a 40 km resolution to finer scale (1 km resolution), using higher spatial resolution of MODIS derived vegetation indices (NDVI) and land surface temperature (Ts). The disaggregated surface soil moisture were compared to ground-based measurements in diverse landscape using portable impedance probe and gravimetric samples. Simulated root zone soil moisture were compared with continuous soil moisture profile measurements at three monitoring stations. In addition, the impact of projected climate change on root zone soil moisture were also evaluated. The climate change projections of rainfall were analyzed for the Rana watershed from statistically downscaled Global Circulation Models (GCMs). The long-term root zone soil moisture dynamics were estimated by including a rainfall generator of likely scenarios. The predicted long term root zone soil moisture status at finer scale can help in developing efficient agricultural water management schemes to increase crop production, which lead to enhance the water use efficiency.

Soil water nitrate concentrations in giant cane and forest riparian buffer zones

Treesearch

Jon E. Schoonover; Karl W. J. Williard; James J. Zaczek; Jean C. Mangun; Andrew D. Carver

2003-01-01

Soil water nitrate concentrations in giant cane and forest riparian buffer zones along Cypress Creek in southern Illinois were compared to determine if the riparian zones were sources or sinks for nitrogen in the rooting zone. Suction lysimeters were used to collect soil water samples from the lower rooting zone in each of the two vegetation types. The cane riparian...

Specific features of the recent accumulation of 137Cs in tree roots of forest ecosystems within the zone of radioactive contamination

NASA Astrophysics Data System (ADS)

Shcheglov, Alexey; Tsvetnova, Ol'ga; Klyashtorin, Alexey; Popova, Evgenia

2015-04-01

Despite numerous studies of the accumulation of technogenic radionuclides in the root systems, no clear regularities of this process have been established. The tendencies found in the works of Russian and foreign researchers are rather discrepant. Some authors argue that the accumulation of radionuclides in the roots is more pronounced than that in the aboveground parts of the plants (Skovorodnikova, 2005; Romantseva, 2012; Sennerby et al., 1994; Mamikhin, 2002; Fircks et al., 2002}. Other works attest to a higher accumulation of radionuclides in the aboveground pars (Juznic et al., 1990; Chibowski, 2000; Zhianski et al., 2005), which is also typical of the stable isotopes of these elements, including 133Cs (Dong Jin Kang, YongJin Seo, Tsukasa Saito et al,2012). It is also stated that the accumulation of radionuclides in the aboveground and underground parts of plants may differ in dependence on the soil-ecological conditions and other factors (Kozhakhanov et al., 2011; Grabovskyi et al., 2013). The aim of our study was to evaluate the accumulation of 137Cs in the root systems of arboreal plants in forest ecosystems within the near zone of the Chernobyl fallout on the plots with similar soil and phytocenotic features. Pine and birch stands were studied within the 30-km-wide exclusion zone of the Chernobyl Nuclear Power Station in Ukraine in 1992-1993, when the density of the radioactive contamination of the upper (0-20 cm) layer with 137Cs reached 2153.8 kBq/m2), and in Bryansk oblast of Russia in 2013-2014, when the density of contamination varied from 1458.4 kBq/m2 (pine stand) to 2578.3 kBq/m2 (birch stand). The tree layer in these ecosystems was dominated by Pinus sylvestris (L.) and Betula pendula (Roth.), respectively. Quercus robur (L.), Picea abies (L.), and Sorbus aucuparia (L.) were also present. The specific activity of 137Cs was measured in the samples from the aboveground parts of model trees and their roots differentiated by size (0-3, 3-10, 10-20, and > 20 mm), and 10-cm-deep soil horizons down to the depth of 70 cm. At the initial stage of our studies (in 1992-1993), we found that the mean weighted values of the specific activity of 137Cs in the roots was 1.5-2.0 times higher than that in the aboveground parts of the trees and also exceeded the specific activity in the adjacent soil mass. These differences increased with the depth: the activity of the roots was two times higher in the upper 10 cm and up to 100 times higher in the layer of 30-70 cm (Shcheglov, 1999; Rafferty, Kliashtorin, Kuchma, Ruehm, Shcheglov, 1996; Shcheglov, Tsvetnova, Kliashtorin, 2001). The studies performed in 2013-2014 the stage of active uptake by the roots is characterized by somewhat different regularities of the distribution of radionuclides, In conifers, including pine, the specific activity of fine roots (<3 mm) was close to the specific activity of small branches, and the specific activity of coarse roots (3-10 mm) was close to the activity of large branches. For broadleaved species, such as birch, the activity of fine roots exceeded the activity in all the aboveground organs, and the specific activity of coarse roots was close to that in small branches. More detailed studies were performed for oak and mountain ash trees. They showed that the specific activity of fine roots (<3 mm) is close to that of the small branches. The ratios of the specific activities of the coarse roots to the specific activities in different aboveground organs may differ in dependence on the species composition of tree stands. In oak and birch trees, the specific activity of coarse roots is close to the specific activity of small branches; in mountain ash, it is closer to the specific activity of small branches.

Rice putative methyltransferase gene OsTSD2 is required for root development involving pectin modification

PubMed Central

Qu, Lianghuan; Wu, Chunyan; Zhang, Fei; Wu, Yangyang; Fang, Chuanying; Jin, Cheng; Liu, Xianqing; Luo, Jie

2016-01-01

Pectin synthesis and modification are vital for plant development, although the underlying mechanisms are still not well understood. Here, we report the functional characterization of the OsTSD2 gene, which encodes a putative methyltransferase in rice. All three independent T-DNA insertion lines of OsTSD2 displayed dwarf phenotypes and serial alterations in different zones of the root. These alterations included abnormal cellular adhesion and schizogenous aerenchyma formation in the meristematic zone, inhibited root elongation in the elongation zone, and higher lateral root density in the mature zone. Immunofluorescence (with LM19) and Ruthenium Red staining of the roots showed that unesterified homogalacturonan (HG) was increased in Ostsd2 mutants. Biochemical analysis of cell wall pectin polysaccharides revealed that both the monosaccharide composition and the uronic acid content were decreased in Ostsd2 mutants. Increased endogenous ABA content and opposite roles performed by ABA and IAA in regulating cellular adhesion in the Ostsd2 mutants suggested that OsTSD2 is required for root development in rice through a pathway involving pectin synthesis/modification. A hypothesis to explain the relationship among OsTSD2, pectin methylesterification, and root development is proposed, based on pectin’s function in regional cell extension/division in a zone-dependent manner. PMID:27497286

Induction of curvature in maize roots by calcium or by thigmostimulation: role of the postmitotic isodiametric growth zone

NASA Technical Reports Server (NTRS)

Ishikawa, H.; Evans, M. L.

1992-01-01

We examined the response of primary roots of maize (Zea mays L. cv Merit) to unilateral application of calcium with particular attention to the site of application, the dependence on growth rate, and possible contributions of thigmotropic stimulation during application. Unilateral application of agar to the root cap induced negative curvature whether or not the agar contained calcium. This apparent thigmotropic response was enhanced by including calcium in the agar. Curvature away from objects applied unilaterally to the extreme root tip occurred both in intact and detipped roots. When agar containing calcium chloride was applied to one side of the postmitotic isodiametric growth zone ( a region between the apical meristem and the elongation zone), the root curved toward the side of application. This response could not be induced by plain agar. We conclude that curvature away from calcium applied to the root tip results from a thigmotropic response to stimulation during application. In contrast, curvature toward the calcium applied to the postmitotic isodiametric growth zone results from direct calcium-induced inhibition of growth.

Beno Gutenberg contribution to seismic hazard assessment and recent progress in the European-Mediterranean region

NASA Astrophysics Data System (ADS)

Panza, Giuliano F.; Romanelli, Fabio

2001-10-01

The fundamental work of Beno Gutenberg has inspired and guided an appreciable part of research in modern seismology, both from the experimental and the theoretical point of view. Among the several topics of seismology that have benefited from the fundamental contribution of Gutenberg, we consider particularly relevant the description of the asthenospheric low-velocity channel, the definition of the surface waves magnitude and the Gutenberg-Richter law, since they are pivotal tools for seismic hazard assessment. The quite revolutionary model for the lithosphere-asthenosphere system in the European area predicts the existence of almost aseismic lithospheric roots. These roots are located in correspondence of most of the orogenic belts and interrupt the asthenosphere low velocity channel that has been identified by Beno Gutenberg in 1948. The model of the European upper mantle, proposed for the first time in 1979 and subsequently refined, has stimulated a considerable amount of research, which has nicely confirmed the major innovative features of the early model. At present, the subduction of the lithosphere at continent-continent collisions, supported not only by seismological data, is a widely accepted concept within the community of Earth scientists, even if it contradicts one of the basic dogmas of the original formulation of plate tectonics. The proposed model for the Alpine-Apennines area supplies a new and unifying framework for the interpretation of the Quaternary magmatism, at present generally accepted by petrologists and geochemists. The theoretical basis for the Gutenberg's surface-wave magnitude calibration function has been supplied by the use of complete synthetic seismograms, and thus it has been possible to formulate the theoretical MS depth correction. The introduction of the depth correction for MS enables the computation of surface wave magnitude for all earthquakes, regardless of their focal depth. This is especially important for the quantification of subcrustal historical earthquakes, for which the seismic moment may be difficult to estimate from recordings of early mechanical seismographs. The new MS calibrating function yield both distance- and depth-independent magnitude estimates. The analysis of the global seismicity, using the seismotectonic regionalization in subduction zones, mid oceanic ridge zones, island arcs, shows that a single Gutenberg-Richter (GR) relation is not universally applicable and that a multiscale seismicity model can reconcile two apparently conflicting paradigms: the Self-Organized Criticality mechanism and the Characteristic Earthquake concept. The multiscale representation has been applied to Italy, where the zones at the space scale of 400-500 km quite well reproduce the shapes of the regions used to apply the, globally tested, CN intermediate term earthquake prediction algorithm.

Amino acid production exceeds plant nitrogen demand in Siberian tundra

NASA Astrophysics Data System (ADS)

Wild, Birgit; Eloy Alves, Ricardo J.; Bárta, Jiři; Čapek, Petr; Gentsch, Norman; Guggenberger, Georg; Hugelius, Gustaf; Knoltsch, Anna; Kuhry, Peter; Lashchinskiy, Nikolay; Mikutta, Robert; Palmtag, Juri; Prommer, Judith; Schnecker, Jörg; Shibistova, Olga; Takriti, Mounir; Urich, Tim; Richter, Andreas

2018-03-01

Arctic plant productivity is often limited by low soil N availability. This has been attributed to slow breakdown of N-containing polymers in litter and soil organic matter (SOM) into smaller, available units, and to shallow plant rooting constrained by permafrost and high soil moisture. Using 15N pool dilution assays, we here quantified gross amino acid and ammonium production rates in 97 active layer samples from four sites across the Siberian Arctic. We found that amino acid production in organic layers alone exceeded literature-based estimates of maximum plant N uptake 17-fold and therefore reject the hypothesis that arctic plant N limitation results from slow SOM breakdown. High microbial N use efficiency in organic layers rather suggests strong competition of microorganisms and plants in the dominant rooting zone. Deeper horizons showed lower amino acid production rates per volume, but also lower microbial N use efficiency. Permafrost thaw together with soil drainage might facilitate deeper plant rooting and uptake of previously inaccessible subsoil N, and thereby promote plant productivity in arctic ecosystems. We conclude that changes in microbial decomposer activity, microbial N utilization and plant root density with soil depth interactively control N availability for plants in the Arctic.

Volcanology of Tuzo pipe (Gahcho Kué cluster) — Root-diatreme processes re-interpreted

NASA Astrophysics Data System (ADS)

Seghedi, I.; Maicher, D.; Kurszlaukis, S.

2009-11-01

The Middle Cambrian (~ 540 Ma) Gahcho Kué Kimberlite Field is situated about 275 km ENE of Yellowknife, NWT, Canada. The kimberlites were emplaced into 2.6 Ga Archean granitic rocks of the Yellowknife Supergroup. Four larger kimberlite bodies (5034, Tesla, Tuzo, and Hearne) as well as a number of smaller pipes and associated sheets occur in the field. In plan view, the Tuzo pipe has a circular outline at the surface, and it widens towards deeper levels. The pipe infill consists of several types of coherent and fragmental kimberlite facies. Coherent or apparent coherent (possibly welded) kimberlite facies dominate at depth, but also occur at shallow levels, as dikes intruded late in the eruptive sequence or individual coherent kimberlite clasts. The central and shallower portions of the pipe consist of several fragmental kimberlite varieties that are texturally classified as Tuffisitic Kimberlites. The definition, geometry and extent of the geological units are complex and zones controlled by vertical elements are most significant. The fluidal outlines of some of the coherent kimberlite clasts suggest that at least some are the product of disruption of magma that was in a semi-plastic state or even of welded material. Ragged clasts at low levels are inferred to form part of a complex peperite-like system that intrudes the base of the root zone. A variable, often high abundance of local wall-rock xenoliths between and within the kimberlite phases is observed, varying in size from sub-millimeter to several tens of meters. Wall-rock fragments are common at all locations within the pipe but are especially frequent in a domain with a belt-like geometry between 120 and 200 m depth in the pipe. Steeply outward-dipping bedded deposits made up of wall-rock fragments occur in deep levels of the pipe and are especially common under the downward-widening roof segments. The gradational contact relationships of these deposits with the surrounding kimberlite-bearing rocks as well as their location suggest that they formed more-or-less in situ. Different breccia facies inside the pipe suggest an origin by slumping, grain flows, rock fall or pyroclastic deposition. The shape and facies architecture of the Tuzo pipe suggests that the studied section of the pipe lies at a root zone-diatreme transitional structural level. Composite coherent kimberlite clasts imply that recycling processes were active over time, while reworked wall-rock rich deposits and ductily-deformed clasts of welded kimberlite point to the presence of temporary cavities in the root zone. The emplacement of the Tuzo pipe did not occur in a single, violent explosion, but involved repetitive volcanic explosions alternating with periods of relative quiescence. The observed features are typical of phreatomagmatic processes, which may include phases of less-explosive magmatic activity.

Common and distinguishing features of the bacterial and fungal communities in biological soil crusts and shrub root zone soils

USGS Publications Warehouse

Steven, Blaire; Gallegos-Graves, La Verne; Yeager, Chris; Belnap, Jayne; Kuske, Cheryl R.

2013-01-01

Soil microbial communities in dryland ecosystems play important roles as root associates of the widely spaced plants and as the dominant members of biological soil crusts (biocrusts) colonizing the plant interspaces. We employed rRNA gene sequencing (bacterial 16S/fungal large subunit) and shotgun metagenomic sequencing to compare the microbial communities inhabiting the root zones of the dominant shrub, Larrea tridentata (creosote bush), and the interspace biocrusts in a Mojave desert shrubland within the Nevada Free Air CO2 Enrichment (FACE) experiment. Most of the numerically abundant bacteria and fungi were present in both the biocrusts and root zones, although the proportional abundance of those members differed significantly between habitats. Biocrust bacteria were predominantly Cyanobacteria while root zones harbored significantly more Actinobacteria and Proteobacteria. Pezizomycetes fungi dominated the biocrusts while Dothideomycetes were highest in root zones. Functional gene abundances in metagenome sequence datasets reflected the taxonomic differences noted in the 16S rRNA datasets. For example, functional categories related to photosynthesis, circadian clock proteins, and heterocyst-associated genes were enriched in the biocrusts, where populations of Cyanobacteria were larger. Genes related to potassium metabolism were also more abundant in the biocrusts, suggesting differences in nutrient cycling between biocrusts and root zones. Finally, ten years of elevated atmospheric CO2 did not result in large shifts in taxonomic composition of the bacterial or fungal communities or the functional gene inventories in the shotgun metagenomes.

Maximum rooting depth of vegetation types at the global scale.

PubMed

Canadell, J; Jackson, R B; Ehleringer, J B; Mooney, H A; Sala, O E; Schulze, E-D

1996-12-01

The depth at which plants are able to grow roots has important implications for the whole ecosystem hydrological balance, as well as for carbon and nutrient cycling. Here we summarize what we know about the maximum rooting depth of species belonging to the major terrestrial biomes. We found 290 observations of maximum rooting depth in the literature which covered 253 woody and herbaceous species. Maximum rooting depth ranged from 0.3 m for some tundra species to 68 m for Boscia albitrunca in the central Kalahari; 194 species had roots at least 2 m deep, 50 species had roots at a depth of 5 m or more, and 22 species had roots as deep as 10 m or more. The average for the globe was 4.6±0.5 m. Maximum rooting depth by biome was 2.0±0.3 m for boreal forest. 2.1±0.2 m for cropland, 9.5±2.4 m for desert, 5.2±0.8 m for sclerophyllous shrubland and forest, 3.9±0.4 m for temperate coniferous forest, 2.9±0.2 m for temperate deciduous forest, 2.6±0.2 m for temperate grassland, 3.7±0.5 m for tropical deciduous forest, 7.3±2.8 m for tropical evergreen forest, 15.0±5.4 m for tropical grassland/savanna, and 0.5±0.1 m for tundra. Grouping all the species across biomes (except croplands) by three basic functional groups: trees, shrubs, and herbaceous plants, the maximum rooting depth was 7.0±1.2 m for trees, 5.1±0.8 m for shrubs, and 2.6±0.1 m for herbaceous plants. These data show that deep root habits are quite common in woody and herbaceous species across most of the terrestrial biomes, far deeper than the traditional view has held up to now. This finding has important implications for a better understanding of ecosystem function and its application in developing ecosystem models.

Graviresponsiveness of surgically altered primary roots of Zea mays

NASA Technical Reports Server (NTRS)

Maimon, E.; Moore, R.

1991-01-01

We examined the gravitropic responses of surgically altered primary roots of Zea mays to determine the route by which gravitropic inhibitors move from the root tip to the elongating zone. Horizontally oriented roots, from which a 1-mm-wide girdle of epidermis plus 2-10 layers of cortex were removed from the apex of the elongating zone, curve downward. However, curvature occurred only apical to the girdle. Filling the girdle with mucilage-like material transmits curvature beyond the girdle. Vertically oriented roots with a half-girdle' (i.e. the epidermis and 2-10 layers of the cortex removed from half of the circumference of the apex of the elongating zone) curve away from the girdle. Inserting the half-girdle at the base of the elongating zone induces curvature towards the girdle. Filling the half-circumference girdles with mucilage-like material reduced curvature significantly. Stripping the epidermis and outer 2-5 layers of cortex from the terminal 1.5 cm of one side of a primary root induces curvature towards the cut, irrespective of the root's orientation to gravity. This effect is not due to desiccation since treated roots submerged in water also curved towards their cut surface. Coating a root's cut surface with a mucilage-like substance minimizes curvature. These results suggest that the outer cell-layers of the root, especially the epidermis, play an important role in root gravicurvature, and the gravitropic signals emanating from the root tip can move apoplastically through mucilage.

Fine root biomass, necromass and chemistry during seven years of elevated aluminium concentrations in the soil solution of a middle-aged Picea abies stand.

PubMed

Eldhuset, Toril D; Lange, Holger; de Wit, Helene A

2006-10-01

Toxic effects of aluminium (Al) on Picea abies (L.) Karst. (Norway spruce) trees are well documented in laboratory-scale experiments, but field-based evidence is scarce. This paper presents results on fine root growth and chemistry from a field manipulation experiment in a P. abies stand that was 45 years old when the experiment started in 1996. Different amounts of dissolved aluminium were added as AlCl3 by means of periodic irrigation during the growing season in the period 1997-2002. Potentially toxic concentrations of Al in the soil solution were obtained. Fine roots were studied from direct cores (1996) and sequential root ingrowth cores (1999, 2001, 2002) in the mineral soil (0-40 cm). We tested two hypotheses: (1) elevated concentration of Al in the root zone leads to significant changes in root biomass, partitioning into fine, coarse, living or dead fractions, and distribution with depth; (2) elevated Al concentration leads to a noticeable uptake of Al and reduced uptake of Ca and Mg; this results in Ca and Mg depletion in roots. Hypothesis 1 was only marginally supported, as just a few significant treatment effects on biomass were found. Hypothesis 2 was supported in part; Al addition led to increased root concentrations of Al in 1999 and 2002 and reduced Mg/Al in 1999. Comparison of roots from subsequent root samplings showed a decrease in Al and S over time. The results illustrated that 7 years of elevated Al(tot) concentrations in the soil solution up to 200 microM are not likely to affect root growth. We also discuss possible improvements of the experimental approach.

Turnover of Grassland Roots in Mountain Ecosystems Revealed by Their Radiocarbon Signature: Role of Temperature and Management

PubMed Central

Leifeld, Jens; Meyer, Stefanie; Budge, Karen; Sebastia, Maria Teresa; Zimmermann, Michael; Fuhrer, Juerg

2015-01-01

Root turnover is an important carbon flux component in grassland ecosystems because it replenishes substantial parts of carbon lost from soil via heterotrophic respiration and leaching. Among the various methods to estimate root turnover, the root’s radiocarbon signature has rarely been applied to grassland soils previously, although the value of this approach is known from studies in forest soils. In this paper, we utilize the root’s radiocarbon signatures, at 25 plots, in mountain grasslands of the montane to alpine zone of Europe. We place the results in context of a global data base on root turnover and discuss driving factors. Root turnover rates were similar to those of a subsample of the global data, comprising a similar temperature range, but measured with different approaches, indicating that the radiocarbon method gives reliable, plausible and comparable results. Root turnover rates (0.06–1.0 y-1) scaled significantly and exponentially with mean annual temperatures. Root turnover rates indicated no trend with soil depth. The temperature sensitivity was significantly higher in mountain grassland, compared to the global data set, suggesting additional factors influencing root turnover. Information on management intensity from the 25 plots reveals that root turnover may be accelerated under intensive and moderate management compared to low intensity or semi-natural conditions. Because management intensity, in the studied ecosystems, co-varied with temperature, estimates on root turnover, based on mean annual temperature alone, may be biased. A greater recognition of management as a driver for root dynamics is warranted when effects of climatic change on belowground carbon dynamics are studied in mountain grasslands. PMID:25734640

The Colima volcano magmatic system

NASA Astrophysics Data System (ADS)

Spica, Z.; Perton, M.; Legrand, D.

2016-12-01

We show how and where magmas are produced and stored at Colima volcano, Mexico, by performing an ambient noise tomography inverting jointly the Rayleigh and Love wave dispersion curves for both phase and group velocities. We obtain shear wave velocity and radial anisotropy models. The shear wave velocity model shows a deep, large and well-delineated elliptic-shape magmatic reservoir below the Colima volcano complex at a depth of about 15 km. The radial anisotropy model shows an important negative feature rooting up to ≥35 km depth until the roof of the magma reservoir, suggesting the presence of vertical fractures where fluids migrate upward and accumulate in the magma reservoir. The convergence of both a low velocity zone and a negative anisotropy suggests that the magma is mainly stored in conduits or inter-fingered dykes as opposed to horizontally stratified magma reservoir.

Transition zone cells reach G2 phase before initiating elongation in maize root apex

PubMed Central

Alarcón, M. Victoria

2017-01-01

ABSTRACT Root elongation requires cell divisions in the meristematic zone and cell elongation in the elongation zone. The boundary between dividing and elongating cells is called the transition zone. In the meristem zone, initial cells are continuously dividing, but on the basal side of the meristem cells exit the meristem through the transition zone and enter in the elongation zone, where they stop division and rapidly elongate. Throughout this journey cells are accompanied by changes in cell cycle progression. Flow cytometry analysis showed that meristematic cells are in cycle, but exit when they enter the elongation zone. In addition, the percentage of cells in G2 phase (4C) strongly increased from the meristem to the elongation zone. However, we did not observe remarkable changes in the percentage of cells in cell cycle phases along the entire elongation zone. These results suggest that meristematic cells in maize root apex stop the cell cycle in G2 phase after leaving the meristem. PMID:28495964

Broad plumes rooted at the base of the Earth's mantle beneath major hotspots.

PubMed

French, Scott W; Romanowicz, Barbara

2015-09-03

Plumes of hot upwelling rock rooted in the deep mantle have been proposed as a possible origin of hotspot volcanoes, but this idea is the subject of vigorous debate. On the basis of geodynamic computations, plumes of purely thermal origin should comprise thin tails, only several hundred kilometres wide, and be difficult to detect using standard seismic tomography techniques. Here we describe the use of a whole-mantle seismic imaging technique--combining accurate wavefield computations with information contained in whole seismic waveforms--that reveals the presence of broad (not thin), quasi-vertical conduits beneath many prominent hotspots. These conduits extend from the core-mantle boundary to about 1,000 kilometres below Earth's surface, where some are deflected horizontally, as though entrained into more vigorous upper-mantle circulation. At the base of the mantle, these conduits are rooted in patches of greatly reduced shear velocity that, in the case of Hawaii, Iceland and Samoa, correspond to the locations of known large ultralow-velocity zones. This correspondence clearly establishes a continuous connection between such zones and mantle plumes. We also show that the imaged conduits are robustly broader than classical thermal plume tails, suggesting that they are long-lived, and may have a thermochemical origin. Their vertical orientation suggests very sluggish background circulation below depths of 1,000 kilometres. Our results should provide constraints on studies of viscosity layering of Earth's mantle and guide further research into thermochemical convection.

Maize and soybean root front velocity and maximum depth in the Iowa, USA

USDA-ARS?s Scientific Manuscript database

Quantitative measurements of root traits can improve our understanding of how crops respond to soil-weather conditions. However, such data are rare. Our objective was to quantify maximum root depth and root front velocity (RFV) for corn and soybean crops across a range of growing conditions in the M...

Role of Subsurface Physics in the Assimilation of Surface Soil Moisture Observations

NASA Technical Reports Server (NTRS)

Reichle, R. H.

2010-01-01

Root zone soil moisture controls the land-atmosphere exchange of water and energy and exhibits memory that may be useful for climate prediction at monthly scales. Assimilation of satellite-based surface soil moisture observations into a land surface model is an effective way to estimate large-scale root zone soil moisture. The propagation of surface information into deeper soil layers depends on the model-specific representation of subsurface physics that is used in the assimilation system. In a suite of experiments we assimilate synthetic surface soil moisture observations into four different models (Catchment, Mosaic, Noah and CLM) using the Ensemble Kalman Filter. We demonstrate that identical twin experiments significantly overestimate the information that can be obtained from the assimilation of surface soil moisture observations. The second key result indicates that the potential of surface soil moisture assimilation to improve root zone information is higher when the surface to root zone coupling is stronger. Our experiments also suggest that (faced with unknown true subsurface physics) overestimating surface to root zone coupling in the assimilation system provides more robust skill improvements in the root zone compared with underestimating the coupling. When CLM is excluded from the analysis, the skill improvements from using models with different vertical coupling strengths are comparable for different subsurface truths. Finally, the skill improvements through assimilation were found to be sensitive to the regional climate and soil types.

The Root Transition Zone: A Hot Spot for Signal Crosstalk.

PubMed

Kong, Xiangpei; Liu, Guangchao; Liu, Jiajia; Ding, Zhaojun

2018-05-01

The root transition zone (TZ), located between the apical meristem and basal elongation region, has a unique role in root growth and development. The root TZ is not only the active site for hormone crosstalk, but also the perception site for various environmental cues, such as aluminum (Al) stress and low phosphate (Pi) stress. We propose that the root TZ is a hot spot for the integration of diverse inputs from endogenous (hormonal) and exogenous (sensorial) stimuli to control root growth. Copyright © 2018 Elsevier Ltd. All rights reserved.

[Simulation of cropland soil moisture based on an ensemble Kalman filter].

PubMed

Liu, Zhao; Zhou, Yan-Lian; Ju, Wei-Min; Gao, Ping

2011-11-01

By using an ensemble Kalman filter (EnKF) to assimilate the observed soil moisture data, the modified boreal ecosystem productivity simulator (BEPS) model was adopted to simulate the dynamics of soil moisture in winter wheat root zones at Xuzhou Agro-meteorological Station, Jiangsu Province of China during the growth seasons in 2000-2004. After the assimilation of observed data, the determination coefficient, root mean square error, and average absolute error of simulated soil moisture were in the ranges of 0.626-0.943, 0.018-0.042, and 0.021-0.041, respectively, with the simulation precision improved significantly, as compared with that before assimilation, indicating the applicability of data assimilation in improving the simulation of soil moisture. The experimental results at single point showed that the errors in the forcing data and observations and the frequency and soil depth of the assimilation of observed data all had obvious effects on the simulated soil moisture.

Dynamics of oxygen and carbon dioxide in rhizospheres of Lobelia dortmanna - a planar optode study of belowground gas exchange between plants and sediment.

PubMed

Lenzewski, Nikola; Mueller, Peter; Meier, Robert Johannes; Liebsch, Gregor; Jensen, Kai; Koop-Jakobsen, Ketil

2018-04-01

Root-mediated CO 2 uptake, O 2 release and their effects on O 2 and CO 2 dynamics in the rhizosphere of Lobelia dortmanna were investigated. Novel planar optode technology, imaging CO 2 and O 2 distribution around single roots, provided insights into the spatiotemporal patterns of gas exchange between roots, sediment and microbial community. In light, O 2 release and CO 2 uptake were pronounced, resulting in a distinct oxygenated zone (radius: c. 3 mm) and a CO 2 -depleted zone (radius: c. 2 mm) around roots. Simultaneously, however, microbial CO 2 production was stimulated within a larger zone around the roots (radius: c. 10 mm). This gave rise to a distinct pattern with a CO 2 minimum at the root surface and a CO 2 maximum c. 2 mm away from the root. In darkness, CO 2 uptake ceased, and the CO 2 -depleted zone disappeared within 2 h. By contrast, the oxygenated root zone remained even after 8 h, but diminished markedly over time. A tight coupling between photosynthetic processes and the spatiotemporal dynamics of O 2 and CO 2 in the rhizosphere of Lobelia was demonstrated, and we suggest that O 2 -induced stimulation of the microbial community in the sediment increases the supply of inorganic carbon for photosynthesis by building up a CO 2 reservoir in the rhizosphere. © 2018 The Authors. New Phytologist © 2018 New Phytologist Trust.

Identifying the transition to the maturation zone in three ecotypes of Arabidopsis thaliana roots.

PubMed

Cajero Sánchez, Wendy; García-Ponce, Berenice; Sánchez, María de la Paz; Álvarez-Buylla, Elena R; Garay-Arroyo, Adriana

2018-01-01

The Arabidopsis thaliana (hereafter Arabidopsis) root has become a useful model for studying how organ morphogenesis emerge from the coordination and balance of cell proliferation and differentiation, as both processes may be observed and quantified in the root at different stages of development. Hence, being able to objectively identify and delimit the different stages of root development has been very important. Up to now, three different zones along the longitudinal axis of the primary root of Arabidopsis, have been identified: the root apical meristematic zone (RAM) with two domains [the proliferative (PD) and the transition domain (TD)], the elongation zone (EZ) and the maturation zone (MZ). We previously reported a method to quantify the length of the cells of the meristematic and the elongation zone, as well as the boundaries or transitions between the root domains along the growing part of the Arabidopsis root. In this study, we provide a more accurate criterion to identify the MZ. Traditionally, the transition between the EZ to the MZ has been established by the emergence of the first root-hair bulge in the epidermis, because this emergence coincides with cell maturation in this cell type. But we have found here that after the emergence of the first root-hair bulge some cells continue to elongate and we have confirmed this in three different Arabidopsis ecotypes. We established the limit between the EZ and the MZ by looking for the closest cortical cell with a longer length than the average cell length of 10 cells after the cortical cell closest to the epidermal cell with the first root-hair bulge in these three ecotypes. In Col-0 and Ws this cell is four cells above the one with the root hair bulge and, in the Ler ecotype, this cell is five cells above. To unambiguously identifying the site at which cells stop elongating and attain their final length and fate at the MZ, we propose to calculate the length of completely elongated cortical cells counting 10 cells starting from the sixth cell above the cortical cell closest to the epidermal cell with the first root-hair bulge. We validated this proposal in the three ecotypes analyzed and consider that this proposal may aid at having a more objective way to characterize root phenotypes and compare among them.

Identifying the transition to the maturation zone in three ecotypes of Arabidopsis thaliana roots

PubMed Central

Cajero Sánchez, Wendy; García-Ponce, Berenice; Sánchez, María de la Paz; Álvarez-Buylla, Elena R.; Garay-Arroyo, Adriana

2018-01-01

ABSTRACT The Arabidopsis thaliana (hereafter Arabidopsis) root has become a useful model for studying how organ morphogenesis emerge from the coordination and balance of cell proliferation and differentiation, as both processes may be observed and quantified in the root at different stages of development. Hence, being able to objectively identify and delimit the different stages of root development has been very important. Up to now, three different zones along the longitudinal axis of the primary root of Arabidopsis, have been identified: the root apical meristematic zone (RAM) with two domains [the proliferative (PD) and the transition domain (TD)], the elongation zone (EZ) and the maturation zone (MZ). We previously reported a method to quantify the length of the cells of the meristematic and the elongation zone, as well as the boundaries or transitions between the root domains along the growing part of the Arabidopsis root. In this study, we provide a more accurate criterion to identify the MZ. Traditionally, the transition between the EZ to the MZ has been established by the emergence of the first root-hair bulge in the epidermis, because this emergence coincides with cell maturation in this cell type. But we have found here that after the emergence of the first root-hair bulge some cells continue to elongate and we have confirmed this in three different Arabidopsis ecotypes. We established the limit between the EZ and the MZ by looking for the closest cortical cell with a longer length than the average cell length of 10 cells after the cortical cell closest to the epidermal cell with the first root-hair bulge in these three ecotypes. In Col-0 and Ws this cell is four cells above the one with the root hair bulge and, in the Ler ecotype, this cell is five cells above. To unambiguously identifying the site at which cells stop elongating and attain their final length and fate at the MZ, we propose to calculate the length of completely elongated cortical cells counting 10 cells starting from the sixth cell above the cortical cell closest to the epidermal cell with the first root-hair bulge. We validated this proposal in the three ecotypes analyzed and consider that this proposal may aid at having a more objective way to characterize root phenotypes and compare among them. PMID:29497470

Rice putative methyltransferase gene OsTSD2 is required for root development involving pectin modification.

PubMed

Qu, Lianghuan; Wu, Chunyan; Zhang, Fei; Wu, Yangyang; Fang, Chuanying; Jin, Cheng; Liu, Xianqing; Luo, Jie

2016-10-01

Pectin synthesis and modification are vital for plant development, although the underlying mechanisms are still not well understood. Here, we report the functional characterization of the OsTSD2 gene, which encodes a putative methyltransferase in rice. All three independent T-DNA insertion lines of OsTSD2 displayed dwarf phenotypes and serial alterations in different zones of the root. These alterations included abnormal cellular adhesion and schizogenous aerenchyma formation in the meristematic zone, inhibited root elongation in the elongation zone, and higher lateral root density in the mature zone. Immunofluorescence (with LM19) and Ruthenium Red staining of the roots showed that unesterified homogalacturonan (HG) was increased in Ostsd2 mutants. Biochemical analysis of cell wall pectin polysaccharides revealed that both the monosaccharide composition and the uronic acid content were decreased in Ostsd2 mutants. Increased endogenous ABA content and opposite roles performed by ABA and IAA in regulating cellular adhesion in the Ostsd2 mutants suggested that OsTSD2 is required for root development in rice through a pathway involving pectin synthesis/modification. A hypothesis to explain the relationship among OsTSD2, pectin methylesterification, and root development is proposed, based on pectin's function in regional cell extension/division in a zone-dependent manner. © The Author 2016. Published by Oxford University Press on behalf of the Society for Experimental Biology.

A Thick, Deformed Sedimentary Wedge in an Erosional Subduction Zone, Southern Costa Rica

NASA Astrophysics Data System (ADS)

Silver, E. A.; Kluesner, J. W.; Edwards, J. H.; Vannucchi, P.

2014-12-01

A paradigm of erosional subduction zones is that the lower part of the wedge is composed of strong, crystalline basement (Clift and Vannucchi, Rev. Geophys., 42, RG2001, 2004). The CRISP 3D seismic reflection study of the southern part of the Costa Rica subduction zone shows quite the opposite. Here the slope is underlain by a series of fault-cored anticlines, with faults dipping both landward and seaward that root into the plate boundary. Deformation intensity increases with depth, and young, near-surface deformation follows that of the deeper structures but with basin inversions indicating a dynamic evolution (Edwards et al., this meeting). Fold wavelength increases landward, consistent with the folding of a landward-thickening wedge. Offscraping in accretion is minimal because incoming sediments on the lower plate are very thin. Within the wedge, thrust faulting dominates at depth in the wedge, whereas normal faulting dominates close to the surface, possibly reflecting uplift of the deforming anticlines. Normal faults form a mesh of NNW and ENE-trending structures, whereas thrust faults are oriented approximately parallel to the dominant fold orientation, which in turn follows the direction of roughness on the subducting plate. Rapid subduction erosion just prior to 2 Ma is inferred from IODP Expedition 334 (Vannucchi et al., 2013, Geology, 49:995-998). Crystalline basement may have been largely removed from the slope region during this rapid erosional event, and the modern wedge may consist of rapidly redeposited material (Expedition 344 Scientists, 2013) that has been undergoing deformation since its inception, producing a structure quite different from that expected of an eroding subduction zone.

Distribution and Rate of Methane Oxidation in Sediments of the Florida Everglades †

PubMed Central

King, Gary M.; Roslev, Peter; Skovgaard, Henrik

1990-01-01

Rates of methane emission from intact cores were measured during anoxic dark and oxic light and dark incubations. Rates of methane oxidation were calculated on the basis of oxic incubations by using the anoxic emissions as an estimate of the maximum potential flux. This technique indicated that methane oxidation consumed up to 91% of the maximum potential flux in peat sediments but that oxidation was negligible in marl sediments. Oxygen microprofiles determined for intact cores were comparable to profiles measured in situ. Thus, the laboratory incubations appeared to provide a reasonable approximation of in situ activities. This was further supported by the agreement between measured methane fluxes and fluxes predicted on the basis of methane profiles determined by in situ sampling of pore water. Methane emissions from peat sediments, oxygen concentrations and penetration depths, and methane concentration profiles were all sensitive to light-dark shifts as determined by a combination of field and laboratory analyses. Methane emissions were lower and oxygen concentrations and penetration depths were higher under illuminated than under dark conditions; the profiles of methane concentration changed in correspondence to the changes in oxygen profiles, but the estimated flux of methane into the oxic zone changed negligibly. Sediment-free, root-associated methane oxidation showed a pattern similar to that for methane oxidation in the core analyses: no oxidation was detected for roots growing in marl sediment, even for roots of Cladium jamaicense, which had the highest activity for samples from peat sediments. The magnitude of the root-associated oxidation rates indicated that belowground plant surfaces may not markedly increase the total capacity for methane consumption. However, the data collectively support the notion that the distribution and activity of methane oxidation have a major impact on the magnitude of atmospheric fluxes from the Everglades. PMID:16348299

Belowground Plant Dynamics Across an Arctic Landscape

NASA Astrophysics Data System (ADS)

Salmon, V. G.; Iversen, C. M.; Breen, A. L.; Thornton, P. E.; Wullschleger, S.

2017-12-01

High-latitude ecosystems are made up of a mosaic of different plant communities, all of which are exposed to warming at a rate double that observed in ecosystems at lower latitudes. Arctic regions are an important component of global Earth system models due to the large amounts of soil carbon (C) currently stored in permafrost as well their potential for increased plant C sequestration under warmer conditions. Losses of C from thawing and decomposing permafrost may be offset by increased plant productivity, but plant allocation to belowground structures and acquisition of limiting nutrients remain key sources of uncertainty in these ecosystems. The relationship between belowground plant traits and environmental conditions is not well understood, nor are tradeoffs between above- and belowground plant traits. To address these knowledge gaps, we sampled above- and belowground plant tissues along the Kougarok Hillslope on the Seward Peninsula, Alaska. The vegetation communities sampled included Alder shrubland, willow birch tundra, tussock tundra, dwarf shrub lichen tundra, and non-acidic mountain complex. Within each plant community, aboveground biomass was quantified and specific leaf area, leaf chemistry (%C, %N, %P and δ15N), and wood density were measured. Belowground fine-root biomass and rooting depth distribution were also determined at the community level. Fine roots from shrubs and graminoids were separated so that specific root area, diameter, and chemistry (%C, %N, %P and δ15N) could be assessed for these contrasting plant functional types. Initial findings indicate fine root biomass pools across the widely varying plant communities are constrained by soil depth, regardless of whether the rooting zone is restricted by permafrost or rock. The presence of Alnus viridis subspp. fruticosa, a deciduous shrub that facilitates nitrogen (N) fixation within its root nodules by Frankia bacteria, in Alder shrubland and willow birch tundra communities was associated with increased soil N availability and altered chemistry in neighboring plants. This research aims to identify sources of variation in belowground plant traits and provide insight into how incorporating belowground plant dynamics into Earth system models may improve our ability to predict the fate of these rapidly warming ecosystems.

Effect of water table fluctuations on phreatophytic root distribution.

PubMed

Tron, Stefania; Laio, Francesco; Ridolfi, Luca

2014-11-07

The vertical root distribution of riparian vegetation plays a relevant role in soil water balance, in the partition of water fluxes into evaporation and transpiration, in the biogeochemistry of hyporheic corridors, in river morphodynamics evolution, and in bioengineering applications. The aim of this work is to assess the effect of the stochastic variability of the river level on the root distribution of phreatophytic plants. A function describing the vertical root profile has been analytically obtained by coupling a white shot noise representation of the river level variability to a description of the dynamics of root growth and decay. The root profile depends on easily determined parameters, linked to stream dynamics, vegetation and soil characteristics. The riparian vegetation of a river characterized by a high variability turns out to have a rooting system spread over larger depths, but with shallower mean root depths. In contrast, a lower river variability determines root profiles with higher mean root depths. Copyright © 2014 Elsevier Ltd. All rights reserved.

Using Isotopic Age of Water as a Constraint on Model Identification at a Critical Zone Observatory

NASA Astrophysics Data System (ADS)

Duffy, C.; Thomas, E.; Bhatt, G.; George, H.; Boyer, E. W.; Sullivan, P. L.

2016-12-01

This paper presents an ecohydrologic model constrained by comprehensive space and time observations of water and stable isotopes of oxygen and hydrogen for an upland catchment, the Susquehanna/Shale Hills Critical Zone Observatory (SSH_CZO). The paper first develops the theoretical basis for simulation of flow, isotope ratios and "age" as water moves through the canopy, to the unsaturated and saturated zones and finally to an intermittent stream. The model formulation demonstrates that the residence time and age of environmental tracers can be directly simulated without knowledge of the form of the underlying residence time distribution function and without the addition of any new physical parameters. The model is used to explore the observed rapid attenuation of event and seasonal isotopic ratios in precipitation over the depth of the soil zone and the impact of decreasing hydraulic conductivity with depth on the dynamics of streamflow and stream isotope ratios. The results suggest the importance of mobile macropore flow on recharge to groundwater during the non-growing cold-wet season. The soil matrix is also recharged during this season with a cold-season isotope signature. During the growing-dry season, root uptake and evaporation from the soil matrix along with a declining water table provides the main source of water for plants and determines the growing season signature. Flow path changes during storm events and transient overland flow is inferred by comparing the frequency distribution of groundwater and stream isotope histories with model results. Model uncertainty is evaluated for conditions of matrix-macropore partitioning and heterogeneous variations in conductivity with depth. The paper concludes by comparing the fully dynamical model with the simplified mixing model form in dynamic equilibrium. The comparison illustrates the importance of system memory on the time scales for flow and mixing processes and the limitations of the dynamic equilibrium assumption on estimated age and residence time.

Tests for Transmission of Prunus Necrotic Ringspot and Two Nepoviruses by Criconemella xenoplax

PubMed Central

Yuan, W-Q.; Barnett, O. W.; Westcott, S. W.; Scott, S. W.

1990-01-01

In two of three trials, detectable color reactions in ELISA for Prunus necrotic ringspot virus (PNRSV) were observed for Criconemella xenoplax handpicked from the root zone of infected peach trees. Criconemella xenoplax (500/pot) handpicked from root zones of peach trees infected with PNRSV failed to transmit the virus to cucumber or peach seedlings. The nematode also failed to transmit tomato ringspot (TomRSV) or tobacco ringspot viruses between cucumbers, although Xiphinema americanum transmitted TomRSV under the same conditions. Plants of peach, cucumber, Chenopodium quinoa, and Catharanthus roseus were not infected by PNRSV when grown in soil containing C. xenoplax collected from root zones of PNRSV-infected trees. Shirofugen cherry scions budded on Mazzard cherry seedling rootstocks remained symptomless when transplanted into root zones of PNRSV-infected trees. Virus transmission was not detected by ELISA when C. xenoplax individuals were observed to feed on cucumber root explants that were infected with PNRSV and subsequently fed on roots of Prunus besseyi in agar cultures. Even if virus transmission by C. xenoplax occurs via contamination rather than by a specific mechanism, it must be rare. PMID:19287748

Tests for Transmission of Prunus Necrotic Ringspot and Two Nepoviruses by Criconemella xenoplax.

PubMed

Yuan, W Q; Barnett, O W; Westcott, S W; Scott, S W

1990-10-01

In two of three trials, detectable color reactions in ELISA for Prunus necrotic ringspot virus (PNRSV) were observed for Criconemella xenoplax handpicked from the root zone of infected peach trees. Criconemella xenoplax (500/pot) handpicked from root zones of peach trees infected with PNRSV failed to transmit the virus to cucumber or peach seedlings. The nematode also failed to transmit tomato ringspot (TomRSV) or tobacco ringspot viruses between cucumbers, although Xiphinema americanum transmitted TomRSV under the same conditions. Plants of peach, cucumber, Chenopodium quinoa, and Catharanthus roseus were not infected by PNRSV when grown in soil containing C. xenoplax collected from root zones of PNRSV-infected trees. Shirofugen cherry scions budded on Mazzard cherry seedling rootstocks remained symptomless when transplanted into root zones of PNRSV-infected trees. Virus transmission was not detected by ELISA when C. xenoplax individuals were observed to feed on cucumber root explants that were infected with PNRSV and subsequently fed on roots of Prunus besseyi in agar cultures. Even if virus transmission by C. xenoplax occurs via contamination rather than by a specific mechanism, it must be rare.

Evidence of root zone hypoxia in Brassica rapa L. grown in microgravity.

PubMed

Stout, S C; Porterfield, D M; Briarty, L G; Kuang, A; Musgrave, M E

2001-03-01

A series of experiments was conducted aboard the U.S. space shuttle and the Mir space station to evaluate microgravity-induced root zone hypoxia in rapid-cycling Brassica (Brassica rapa L.), using both root and foliar indicators of low-oxygen stress to the root zone. Root systems from two groups of plants 15 and 30 d after planting, grown in a phenolic foam nutrient delivery system on the shuttle (STS-87), were harvested and fixed for microscopy or frozen for enzyme assays immediately postflight or following a ground-based control. Activities of fermentative enzymes were measured as indicators of root zone hypoxia and metabolism. Following 16 d of microgravity, ADH (alcohol dehydrogenase) activity was increased in the spaceflight roots 47% and 475% in the 15-d-old and 30-d-old plants, respectively, relative to the ground control. Cytochemical localization showed ADH activity in only the root tips of the space-grown plants. Shoots from plants that were grown from seed in flight in a particulate medium on the Mir station were harvested at 13 d after planting and quick-frozen and stored in flight in a gaseous nitrogen freezer or chemically fixed in flight for subsequent microscopy. When compared to material from a high-fidelity ground control, concentrations of shoot sucrose and total soluble carbohydrate were significantly greater in the spaceflight treatment according to enzymatic carbohydrate analysis. Stereological analysis of micrographs of sections from leaf and cotyledon tissue fixed in flight and compared with ground controls indicated no changes in the volume of protoplast, cell wall, and intercellular space in parenchyma cells. Within the protoplasm, the volume occupied by starch was threefold higher in the spaceflight than in the ground control, with a concomitant decrease in vacuolar volume in the spaceflight treatment. Both induction of fermentative enzyme activity in roots and accumulation of carbohydrates in foliage have been repeatedly shown to occur in response to root zone oxygen deprivation. These results indicate that root zone hypoxia is a persistent challenge in spaceflight plant growth experiments and may be caused by microgravity-induced changes in fluid and gas distribution.

Evidence of root zone hypoxia in Brassica rapa L. grown in microgravity

NASA Technical Reports Server (NTRS)

Stout, S. C.; Porterfield, D. M.; Briarty, L. G.; Kuang, A.; Musgrave, M. E.

2001-01-01

A series of experiments was conducted aboard the U.S. space shuttle and the Mir space station to evaluate microgravity-induced root zone hypoxia in rapid-cycling Brassica (Brassica rapa L.), using both root and foliar indicators of low-oxygen stress to the root zone. Root systems from two groups of plants 15 and 30 d after planting, grown in a phenolic foam nutrient delivery system on the shuttle (STS-87), were harvested and fixed for microscopy or frozen for enzyme assays immediately postflight or following a ground-based control. Activities of fermentative enzymes were measured as indicators of root zone hypoxia and metabolism. Following 16 d of microgravity, ADH (alcohol dehydrogenase) activity was increased in the spaceflight roots 47% and 475% in the 15-d-old and 30-d-old plants, respectively, relative to the ground control. Cytochemical localization showed ADH activity in only the root tips of the space-grown plants. Shoots from plants that were grown from seed in flight in a particulate medium on the Mir station were harvested at 13 d after planting and quick-frozen and stored in flight in a gaseous nitrogen freezer or chemically fixed in flight for subsequent microscopy. When compared to material from a high-fidelity ground control, concentrations of shoot sucrose and total soluble carbohydrate were significantly greater in the spaceflight treatment according to enzymatic carbohydrate analysis. Stereological analysis of micrographs of sections from leaf and cotyledon tissue fixed in flight and compared with ground controls indicated no changes in the volume of protoplast, cell wall, and intercellular space in parenchyma cells. Within the protoplasm, the volume occupied by starch was threefold higher in the spaceflight than in the ground control, with a concomitant decrease in vacuolar volume in the spaceflight treatment. Both induction of fermentative enzyme activity in roots and accumulation of carbohydrates in foliage have been repeatedly shown to occur in response to root zone oxygen deprivation. These results indicate that root zone hypoxia is a persistent challenge in spaceflight plant growth experiments and may be caused by microgravity-induced changes in fluid and gas distribution.

Leaching of glyphosate and amino-methylphosphonic acid from Danish agricultural field sites.

PubMed

Kjaer, Jeanne; Olsen, Preben; Ullum, Marlene; Grant, Ruth

2005-01-01

Pesticide leaching is an important process with respect to contamination risk to the aquatic environment. The risk of leaching was thus evaluated for glyphosate (N-phosphonomethyl-glycine) and its degradation product AMPA (amino-methylphosphonic acid) under field conditions at one sandy and two loamy sites. Over a 2-yr period, tile-drainage water, ground water, and soil water were sampled and analyzed for pesticides. At a sandy site, the strong soil sorption capacity and lack of macropores seemed to prevent leaching of both glyphosate and AMPA. At one loamy site, which received low precipitation with little intensity, the residence time within the root zone seemed sufficient to prevent leaching of glyphosate, probably due to degradation and sorption. Minor leaching of AMPA was observed at this site, although the concentration was generally low, being on the order of 0.05 microg L(-1) or less. At another loamy site, however, glyphosate and AMPA leached from the root zone into the tile drains (1 m below ground surface [BGS]) in average concentrations exceeding 0.1 microg L(-1), which is the EU threshold value for drinking water. The leaching of glyphosate was mainly governed by pronounced macropore flow occurring within the first months after application. AMPA was frequently detected more than 1.5 yr after application, thus indicating a minor release and limited degradation capacity within the soil. Leaching has so far been confined to the depth of the tile drains, and the pesticides have rarely been detected in monitoring screens located at lower depths. This study suggests that as both glyphosate and AMPA can leach through structured soils, they thereby pose a potential risk to the aquatic environment.

Structure of the Castillo granite, Southwest Spain: Variscan deformation of a late Cadomian pluton

NASA Astrophysics Data System (ADS)

EguíLuz, L.; Apraiz, A.; ÁBalos, B.

1999-12-01

A geometrical reconstruction of the 500 Ma old Castillo granite pluton (SW Iberia) is completed on the basis of structural and geophysical (rock magnetism) techniques. The pluton is intrusive into latest Proterozoic-earliest Cambrian metasediments and conforms a tabular intrusion 6 km in diameter and 1.7 km thick that was emplaced at a depth of 10 km. Its magnetic fabric reveals that the strike of moderately to steeply dipping magmatic flow planes forms a high angle to the regional tectonic trends. Magnetic foliations and associated moderately to gently plunging magnetic lineations represent magmatic flow planes and directions. The internal anisotropy of the granite together with the structure shown by the country rocks attest the lateral propagation of the pluton and its latter inflation. The pluton's root zone would correspond to a likely thin, subvertical feeder structure initiated near the orientation of regional σ1 at the time of emplacement. During the Variscan orogeny the pluton was tilted and underwent localized brittle-ductile strain in relation to shear zone deformation in the footwall of a major ductile thrust. Tilting permits the observation and study of a vertical profile of the intrusion. Localized deformation caused superposition of tectonic zonations on the magmatic ones, a reactivation of the basal contact of the pluton, and dismemberment from its root. This and other granitoid plutons of similar age emplaced at a similar depth constrained the creation of crustal mechanical heterogeneity and anisotropy. This controlled the site of pluton emplacement, the nucleation of a major ductile thrust, and localization of deformation and tectonic displacements along the pluton margins during later orogenic reactivation.

Ecohydrological control of deep drainage in arid and semiarid regions

USGS Publications Warehouse

Seyfried, M.S.; Schwinning, S.; Walvoord, Michelle Ann; Pockman, W. T.; Newman, B.D.; Jackson, R.B.; Phillips, F.M.

2005-01-01

The amount and spatial distribution of deep drainage (downward movement of water across the bottom of the root zone) and groundwater recharge affect the quantity and quality of increasingly limited groundwater in arid and semiarid regions. We synthesize research from the fields of ecology and hydrology to address the issue of deep drainage in arid and semiarid regions. We start with a recently developed hydrological model that accurately simulates soil water potential and geochemical profiles measured in thick (>50 m), unconsolidated vadose zones. Model results indicate that, since the climate change that marked the onset of the Holocene period 10 000–15 000 years ago, there has been no deep drainage in vegetated interdrainage areas and that continuous, relatively low (<−1 MPa) soil water potentials have been maintained at depths of 2–3 m. A conceptual model consistent with these results proposes that the native, xeric‐shrub‐dominated, plant communities that gained dominance during the Holocene generated and maintained these conditions. We present three lines of ecological evidence that support the conceptual model. First, xeric shrubs have sufficiently deep rooting systems with low extraction limits to generate the modeled conditions. Second, the characteristic deep‐rooted soil–plant systems store sufficient water to effectively buffer deep soil from climatic fluctuations in these dry environments, allowing stable conditions to persist for long periods of time. And third, adaptations resulting in deep, low‐extraction‐limit rooting systems confer significant advantages to xeric shrubs in arid and semiarid environments. We then consider conditions in arid and semiarid regions in which the conceptual model may not apply, leading to the expectation that portions of many arid and semiarid watersheds supply some deep drainage. Further ecohydrologic research is required to elucidate critical climatic and edaphic thresholds, evaluate the role of important physiological processes (such as hydraulic redistribution), and evaluate the role of deep roots in terms of carbon costs, nutrient uptake, and whole‐plant development.

Breakdown of middle lamella pectin by (●) OH during rapid abscission in Azolla.

PubMed

Yamada, Yoshiya; Koibuchi, Mizuki; Miyamoto, Kensuke; Ueda, Junichi; Uheda, Eiji

2015-08-01

Azolla, a small water fern, abscises its roots and branches within 30 min upon treatment with various stresses. This study was conducted to test whether, in the rapid abscission that occurs in Azolla, breakdown of wall components of abscission zone cells by (●) OH is involved. Experimentally generated (●) OH caused the rapid separation of abscission zone cells from detached roots and the rapid shedding of roots from whole plants. Electron microscopic observations revealed that (●) OH rapidly and selectively dissolved a well-developed middle lamella between abscission zone cells and resultantly caused rapid cell separation and shedding. Treatment of abscission zones of Impatiens leaf petiole with (●) OH also accelerated the separation of abscission zone cells. However, compared with that of Azolla roots, accelerative effects in Impatiens were weak. A large amount of (●) OH was cytochemically detected in abscission zone cells both of Azolla roots and of Impatiens leaf petioles. These results suggest that (●) OH is involved in the cell separation process not only in the rapid abscission in Azolla but also in the abscission of Impatiens. However, for rapid abscission to occur, a well-developed middle lamella, a unique structure, which is sensitive to the attack of (●) OH, might be needed. © 2015 John Wiley & Sons Ltd.

Quantifying the role of vegetation in controlling the time-variant age of evapotranspiration, soil water and stream flow

NASA Astrophysics Data System (ADS)

Smith, A.; Tetzlaff, D.; Soulsby, C.

2017-12-01

Identifying the sources of water which sustain plant water uptake is an essential prerequisite to understanding the interactions of vegetation and water within the critical zone. Estimating the sources of root-water uptake is complicated by ecohydrological separation, or the notion of "two-water worlds" which distinguishes more mobile and immobile water sources which respectively sustain streamflow and evapotranspiration. Water mobility within the soil determines both the transit time/residence time of water through/in soils and the subsequent age of root-uptake and xylem water. We used time-variant StorAge Selection (SAS) functions to conceptualise the transit/residence times in the critical zone using a dual-storage soil column differentiating gravity (mobile) and tension dependent (immobile) water, calibrated to measured stable isotope signatures of soil water. Storage-discharge relationships [Brutsaert and Nieber, 1977] were used to identify gravity and tension dependent storages. A temporally variable distribution for root water uptake was identified using simulated stable isotopes in xylem and soil water. Composition of δ2H and δ18O was measured in soil water at 4 depths (5, 10, 15, and 20 cm) on 10 occasions, and 5 times for xylem water within the dominant heather (Calluna sp. and Erica sp.) vegetation in a Scottish Highland catchment over a two-year period. Within a 50 cm soil column, we found that more than 53% of the total stored water was water that was present before the start of the simulation. Mean residence times of the mobile water in the upper 20 cm of the soil were 16, 25, 36, and 44 days, respectively. Mean evaporation transit time varied between 9 and 40 days, driven by seasonal changes and precipitation events. Lastly, mean transit times of xylem water ranged between 95-205 days, driven by changes in soil moisture. During low soil moisture (i.e. lower than mean soil moisture), root-uptake was from lower depths, while higher than mean soil moisture showed preferential uptake of near surface water. In our humid, low energy environment, we found that xylem water is comprised of both mobile and immobile water. The division of soil storage into two storages, gravity and tension dependent, has shown potential to identify the sources of plant water and vegetation and soil water interactions.

Selection of root-zone media for higher plant cultivation in space.

PubMed

Guo, Shuang-sheng; Ai, Wei-dang; Zhao, Cheng-jian; Han, Li-jun; Wang, Jian-xiao

2004-04-01

To investigate the cultivating effects of several mineral matters used as root-zone media for higher plant growth in space. Four kinds of artificial and natural mineral matters were used as plant root-zone media based on lots of investigation and analysis. Nutrient liquid was delivered into the media by a long capillary material, and roots of plants obtained nutrition and water from the media. The related parameters such as plant height and photosynthetic efficiency were measured and analyzed. The growing effect in a mixture of coarse and fine ceramic particles with equal quantity proportion was the best, that in fine ceramic particles was the second best, that in clinoptilolite particles was the third and that in diorite particles was the last. The mixture of coarse and fine ceramic particles with equal quantity possesses not only fine capillary action, but also good aerating ability, and therefore is capable of being utilized as an effective root-zone media for higher plants intended to be grown in space.

Vadose zone microbiology

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kieft, Thomas L.; Brockman, Fred J.

2001-01-17

The vadose zone is defined as the portion of the terrestrial subsurface that extends from the land surface downward to the water table. As such, it comprises the surface soil (the rooting zone), the underlying subsoil, and the capillary fringe that directly overlies the water table. The unsaturated zone between the rooting zone and the capillary fringe is termed the "intermediate zone" (Chapelle, 1993). The vadose zone has also been defined as the unsaturated zone, since the sediment pores and/or rock fractures are generally not completely water filled, but instead contain both water and air. The latter characteristic results inmore » the term "zone of aeration" to describe the vadose zone. The terms "vadose zone," "unsaturated zone", and "zone of aeration" are nearly synonymous, except that the vadose zone may contain regions of perched water that are actually saturated. The term "subsoil" has also been used for studies of shallow areas of the subsurface immediately below the rooting zone. This review focuses almost exclusively on the unsaturated region beneath the soil layer since there is already an extensive body of literature on surface soil microbial communities and process, e.g., Paul and Clark (1989), Metting (1993), Richter and Markowitz, (1995), and Sylvia et al. (1998); whereas the deeper strata of the unsaturated zone have only recently come under scrutiny for their microbiological properties.« less

Dynamics of soil exploration by fine roots down to a depth of 10 m throughout the entire rotation in Eucalyptus grandis plantations

PubMed Central

Laclau, Jean-Paul; da Silva, Eder A.; Rodrigues Lambais, George; Bernoux, Martial; le Maire, Guerric; Stape, José L.; Bouillet, Jean-Pierre; Gonçalves, José L. de Moraes; Jourdan, Christophe; Nouvellon, Yann

2013-01-01

Although highly weathered soils cover considerable areas in tropical regions, little is known about exploration by roots in deep soil layers. Intensively managed Eucalyptus plantations are simple forest ecosystems that can provide an insight into the belowground growth strategy of fast-growing tropical trees. Fast exploration of deep soil layers by eucalypt fine roots may contribute to achieving a gross primary production that is among the highest in the world for forests. Soil exploration by fine roots down to a depth of 10 m was studied throughout the complete cycle in Eucalyptus grandis plantations managed in short rotation. Intersects of fine roots, less than 1 mm in diameter, and medium-sized roots, 1–3 mm in diameter, were counted on trench walls in a chronosequence of 1-, 2-, 3.5-, and 6-year-old plantations on a sandy soil, as well as in an adjacent 6-year-old stand growing in a clayey soil. Two soil profiles were studied down to a depth of 10 m in each stand (down to 6 m at ages 1 and 2 years) and 4 soil profiles down to 1.5–3.0 m deep. The root intersects were counted on 224 m2 of trench walls in 15 pits. Monitoring the soil water content showed that, after clear-cutting, almost all the available water stored down to a depth of 7 m was taken up by tree roots within 1.1 year of planting. The soil space was explored intensively by fine roots down to a depth of 3 m from 1 year after planting, with an increase in anisotropy in the upper layers throughout the rotation. About 60% of fine root intersects were found at a depth of more than 1 m, irrespective of stand age. The root distribution was isotropic in deep soil layers and kriged maps showed fine root clumping. A considerable volume of soil was explored by fine roots in eucalypt plantations on deep tropical soils, which might prevent water and nutrient losses by deep drainage after canopy closure and contribute to maximizing resource uses. PMID:23847645

In what root-zone N concentration does nitrate start to leach significantly? A reasonable answer from modeling Mediterranean field data and closed root-zone experiments

NASA Astrophysics Data System (ADS)

Kurtzman, D.; Kanner, B.; Levy, Y.; Shapira, R. H.; Bar-Tal, A.

2017-12-01

Closed-root-zone experiments (e.g. pots, lyzimeters) reveal in many cases a mineral-nitrogen (N) concentration from which the root-N-uptake efficiency reduces significantly and nitrate leaching below the root-zone increases dramatically. A les-direct way to reveal this threshold concentration in agricultural fields is to calibrate N-transport models of the unsaturated zone to nitrate data of the deep samples (under the root-zone) by fitting the threshold concentration of the nitrate-uptake function. Independent research efforts of these two types in light soils where nitrate problems in underlying aquifers are common reviled: 1) that the threshold exists for most crops (filed, vegetables and orchards); 2) nice agreement on the threshold value between the two very different research methodologies; and 3) the threshold lies within 20-50 mg-N/L. Focusing on being below the threshold is a relatively simple aim in the way to maintain intensive agriculture with limited effects on the nitrate concentration in the underlying water resource. Our experience show that in some crops this threshold coincides with the end-of-rise of the N-yield curve (e.g. corn); in this case, it is relatively easy to convince farmers to fertilize below threshold. In other crops, although significant N is lost to leaching the crop can still use higher N concentration to increase yield (e.g. potato).

Measuring and modeling three-dimensional water uptake of a growing faba bean (Vicia faba) within a soil column

NASA Astrophysics Data System (ADS)

Huber, Katrin; Koebernick, Nicolai; Kerkhofs, Elien; Vanderborght, Jan; Javaux, Mathieu; Vetterlein, Doris; Vereecken, Harry

2014-05-01

A faba bean was grown in a column filled with a sandy soil, which was initially close to saturation and then subjected to a single drying cycle of 30 days. The column was divided in four hydraulically separated compartments using horizontal paraffin layers. Paraffin is impermeable to water but penetrable by roots. Thus by growing deeper, the roots can reach compartments that still contain water. The root architecture was measured every second day by X-ray CT. Transpiration rate, soil matric potential in four different depths, and leaf area were measured continously during the experiment. To investigate the influence of the partitioning of available soil water in the soil column on water uptake, we used R-SWMS, a fully coupled root and soil water model [1]. We compared a scenario with and without the split layers and investigated the influence on root xylem pressure. The detailed three-dimensional root architecture was obtained by reconstructing binarized root images manually with a virtual reality system, located at the Juelich Supercomputing Centre [2]. To verify the properties of the root system, we compared total root lengths, root length density distributions and root surface with estimations derived from Minkowski functionals [3]. In a next step, knowing the change of root architecture in time, we could allocate an age to each root segment and use this information to define age dependent root hydraulic properties that are required to simulate water uptake for the growing root system. The scenario with the split layers showed locally much lower pressures than the scenario without splits. Redistribution of water within the unrestricted soil column led to a more uniform distribution of water uptake and lowers the water stress in the plant. However, comparison of simulated and measured pressure heads with tensiometers suggested that the paraffin layers were not perfectly hydraulically isolating the different soil layers. We could show compensation efficiency of water uptake by the roots in the lower and wetter compartments. By comparing transpiration rates of experiments with and without additional paraffin layers, we were able to quantify restrictions of plant growth to available soil water. [1] Javaux, M., T. Schröder, J. Vanderborght, and H. Vereecken (2008), Use of a Three-Dimensional Detailed Modeling Approach for Predicting Root Water Uptake, Vadose Zone Journal, 7(3), 1079-1079. [2] Stingaciu, L., H. Schulz, A. Pohlmeier, S. Behnke, H. Zilken, M. Javaux, H. Vereecken (2013), In Situ Root System Architecture Extraction from Magnetic Resonance Imaging for Water Uptake Modeling, Vadose Zone Journal, 12(1). [3] Koebernick, N., U. Weller, K. Huber, S. Schlüter, H.-J. Vogel, R. Jahn; H. Vereecken, D. Vetterlein, In situ visualisation and quantification of root-system architecture and growth with X-ray CT, Manuscript submitted for publication.

Root reinforcement and its contribution to slope stability in the Western Ghats of Kerala, India

NASA Astrophysics Data System (ADS)

Lukose Kuriakose, Sekhar; van Beek, L. P. H.

2010-05-01

The Western Ghats of Kerala, India is prone to shallow landslides and consequent debris flows. An earlier study (Kuriakose et al., DOI:10.1002/esp.1794) with limited data had already demonstrated the possible effects of vegetation on slope hydrology and stability. Spatially distributed root cohesion is one of the most important data necessary to assess the effects of anthropogenic disturbances on the probability of shallow landslide initiation, results of which are reported in sessions GM6.1 and HS13.13/NH3.16. Thus it is necessary to the know the upper limits of reinforcement that the roots are able to provide and its spatial and vertical distribution in such an anthropogenically intervened terrain. Root tensile strength and root pull out tests were conducted on nine species of plants that are commonly found in the region. They are 1) Rubber (Hevea Brasiliensis), 2) Coconut Palm (Cocos nucifera), 3) Jackfruit trees (Artocarpus heterophyllus), 4) Teak (Tectona grandis), 5) Mango trees (Mangifera indica), 6) Lemon grass (Cymbopogon citratus), 7) Gambooge (Garcinia gummi-gutta), 8) Coffee (Coffea Arabica) and 9) Tea (Camellia sinensis). About 1500 samples were collected of which only 380 could be tested (in the laboratory) due to breakage of roots during the tests. In the successful tests roots failed in tension. Roots having diameters between 2 mm and 12 mm were tested. Each sample tested had a length of 15 cm. Root pull out tests were conducted in the field. Root tensile strength vs root diameter, root pull out strength vs diameter, root diameter vs root depth and root count vs root depth relationships were derived. Root cohesion was computed for nine most dominant plants in the region using the perpendicular root model of Wu et al. (1979) modified by Schimidt et al. (2001). A soil depth map was derived using regression kriging as suggested by Kuriakose et al., (doi:10.1016/j.catena.2009.05.005) and used along with the land use map of 2008 to distribute the computed root tensile strength both vertically and spatially. Root cohesion varies significantly with the type of land use and the depth of soil. The computation showed that a maximum root reinforcement of 40 kPa was available in the first 30 cm of soil while exponentially decreased with depth to just about 3 kPa at 3 m depth. Mixed crops land use unit had the maximum root cohesion while fallow land, degraded forest and young rubber plantation had the lowest root reinforcement. These are the upper limits of root reinforcement that the vegetation can provide. When the soil is saturated, the bond between soil and roots reduces and thus the applicable root reinforcement is limited by the root pullout strength. Root reinforcement estimated from pullout strength vs diameter relationships was significantly lower than those estimated from tensile strength vs diameter relationships.

Analysis of water application efficiency and emission uniformity of drip irrigation systems based on space-time analysis of soil moisture patterns in soils

NASA Astrophysics Data System (ADS)

Shabeeb, Ahmeed; Taha, Uday; dragonetti, giovanna; Lamaddalena, Nicola; Coppola, Antonio

2016-04-01

In order to evaluate how efficiently and uniformly drip irrigation systems can deliver water to emitters distributed around a field, we need some methods for measuring/calculating water application efficiency (WAE) and emission uniformity (EU). In general, the calculation of the WAE and of other efficiency indices requires the measurement of the water stored in the root zone. Measuring water storage in soils allows directly saying how much water a given location of the field retains having received a given amount of irrigation water. And yet, due to the difficulties of measuring water content variability under an irrigation system at field scale, it is quite common using EU as a proxy indicator of the irrigation performance. This implicitly means assuming that the uniformity of water application is immediately reflected in an uniformity of water stored in the root zone. In other words, that if a site receive more water it will store more water. Nevertheless, due to the heterogeneity of soil hydrological properties the same EU may correspond to very different distributions of water stored in the soil root zone. 1) In the case of isolated drippers, the storages measured in the soil root zone layer shortly after an irrigation event may be or not different from the water height applied at the surface depending on the vertical/horizontal development of the wetted bulbs. Specifically, in the case of dominant horizontal spreading the water storage is expected to reflect the distribution of water applied at the surface. To the contrary, in the case of relatively significant vertical spreading, deep percolation fluxes (fluxes leaving the root zone) may well induce water storages in the root zone significantly different from the water applied at the surface. 2) The drippers and laterals are close enough that the wetted bulbs below adjacent drippers may interact. In this case, lateral fluxes in the soil may well induce water storages in the root zone which may be significantly uncorrelated with the uniformity of the water applied at the surface. In both the cases, the size of lateral fluxes compared to the vertical ones throughout the rooting zone depends, besides the soil hydraulic properties, on the amount of water delivered to the soil. Larger water applications produce greater spreading, but in both the horizontal and vertical directions. Increased vertical spreading may be undesirable because water moving below the active root zone can result in wasted water, loss of nutrients, and groundwater pollution.

Phenotyping for the dynamics of field wheat root system architecture

NASA Astrophysics Data System (ADS)

Chen, Xinxin; Ding, Qishuo; Błaszkiewicz, Zbigniew; Sun, Jiuai; Sun, Qian; He, Ruiyin; Li, Yinian

2017-01-01

We investigated a method to quantify field-state wheat RSA in a phenotyping way, depicting the 3D topology of wheat RSA in 14d periods. The phenotyping procedure, proposed for understanding the spatio-temporal variations of root-soil interaction and the RSA dynamics in the field, is realized with a set of indices of mm scale precision, illustrating the gradients of both wheat root angle and elongation rate along soil depth, as well as the foraging potential along the side directions. The 70d was identified as the shifting point distinguishing the linear root length elongation from power-law development. Root vertical angle in the 40 mm surface soil layer was the largest, but steadily decreased along the soil depth. After 98d, larger root vertical angle appeared in the deep soil layers. PAC revealed a stable root foraging potential in the 0-70d period, which increased rapidly afterwards (70-112d). Root foraging potential, explained by MaxW/MaxD ratio, revealed an enhanced gravitropism in 14d period. No-till post-paddy wheat RLD decreased exponentially in both depth and circular directions, with 90% roots concentrated within the top 20 cm soil layer. RER along soil depth was either positive or negative, depending on specific soil layers and the sampling time.

Phenotyping for the dynamics of field wheat root system architecture

PubMed Central

Chen, Xinxin; Ding, Qishuo; Błaszkiewicz, Zbigniew; Sun, Jiuai; Sun, Qian; He, Ruiyin; Li, Yinian

2017-01-01

We investigated a method to quantify field-state wheat RSA in a phenotyping way, depicting the 3D topology of wheat RSA in 14d periods. The phenotyping procedure, proposed for understanding the spatio-temporal variations of root-soil interaction and the RSA dynamics in the field, is realized with a set of indices of mm scale precision, illustrating the gradients of both wheat root angle and elongation rate along soil depth, as well as the foraging potential along the side directions. The 70d was identified as the shifting point distinguishing the linear root length elongation from power-law development. Root vertical angle in the 40 mm surface soil layer was the largest, but steadily decreased along the soil depth. After 98d, larger root vertical angle appeared in the deep soil layers. PAC revealed a stable root foraging potential in the 0–70d period, which increased rapidly afterwards (70–112d). Root foraging potential, explained by MaxW/MaxD ratio, revealed an enhanced gravitropism in 14d period. No-till post-paddy wheat RLD decreased exponentially in both depth and circular directions, with 90% roots concentrated within the top 20 cm soil layer. RER along soil depth was either positive or negative, depending on specific soil layers and the sampling time. PMID:28079107

Imaging the magmatic system of Mono Basin, California with magnetotellurics in three--dimensions

USGS Publications Warehouse

Peacock, Jared R.; Mangan, Margaret T.; McPhee, Darcy K.; Ponce, David A.

2015-01-01

A three–dimensional (3D) electrical resistivity model of Mono Basin in eastern California unveils a complex subsurface filled with zones of partial melt, fluid–filled fracture networks, cold plutons, and regional faults. In 2013, 62 broadband magnetotelluric (MT) stations were collected in an array around southeastern Mono Basin from which a 3D electrical resistivity model was created with a resolvable depth of 35 km. Multiple robust electrical resistivity features were found that correlate with existing geophysical observations. The most robust features are two 300 ± 50 km3 near-vertical conductive bodies (3–10 Ω·m) that underlie the southeast and north-eastern margin of Mono Craters below 10 km depth. These features are interpreted as magmatic crystal–melt mush zones of 15 ± 5% interstitial melt surrounded by hydrothermal fluids and are likely sources for Holocene eruptions. Two conductive east–dipping structures appear to connect each magma source region to the surface. A conductive arc–like structure (< 0.9 Ω·m) links the northernmost mush column at 10 km depth to just below vents near Panum Crater, where the high conductivity suggests the presence of hydrothermal fluids. The connection from the southernmost mush column at 10 km depth to below South Coulée is less obvious with higher resistivity (200 Ω·m) suggestive of a cooled connection. A third, less constrained conductive feature (4–10 Ω·m) 15 km deep extending to 35 km is located west of Mono Craters near the eastern front of the Sierra Nevada escarpment, and is coincident with a zone of sporadic, long–period earthquakes that are characteristic of a fluid-filled (magmatic or metamorphic) fracture network. A resistive feature (103–105 Ω·m) located under Aeolian Buttes contains a deep root down to 25 km. The eastern edge of this resistor appears to structurally control the arcuate shape of Mono Craters. These observations have been combined to form a new conceptual model of the magmatic system beneath Mono Craters to a depth of 30 km.

Oceanic crust in the mid-mantle beneath Central-West Pacific subduction zones: Evidence from S-to-P converted waveforms

NASA Astrophysics Data System (ADS)

He, X.

2015-12-01

The fate of subducted slabs is enigmatic, yet intriguing. We analyze seismic arrivals at ~20-50 s after the direct P wave in an array in northeast China (NECESSArray) recordings of four deep earthquakes occurring beneath the west-central Pacific subduction zones (from the eastern Indonesia to Tonga region). We employ the array analyzing techniques of 4th root vespagram and beam-form analysis to constrain the slowness and back azimuth of later arrivals. Our analyses reveal that these arrivals have a slightly lower slowness value than the direct P wave and the back azimuth deviates slightly from the great-circle direction. Along with calculation of one-dimensional synthetic seismograms, we conclude that the later arrival is corresponding to an energy of S-to-P converted at a scatterer below the sources. Total five scatterers are detected at depths varying from ~700 to 1110 km in the study region. The past subducted oceanic crust most likely accounts for the seismic scatterers trapped in the mid-mantle beneath the west-central subduction zones. Our observation in turn reflects that oceanic crust at least partly separated from subducted oceanic lithosphere and may be trapped substantially in the mid-mantle surrounding subduction zones, in particular in the western Pacific subduction zones.

Monitoring soil moisture patterns in alpine meadows using ground sensor networks and remote sensing techniques

NASA Astrophysics Data System (ADS)

Bertoldi, Giacomo; Brenner, Johannes; Notarnicola, Claudia; Greifeneder, Felix; Nicolini, Irene; Della Chiesa, Stefano; Niedrist, Georg; Tappeiner, Ulrike

2015-04-01

Soil moisture content (SMC) is a key factor for numerous processes, including runoff generation, groundwater recharge, evapotranspiration, soil respiration, and biological productivity. Understanding the controls on the spatial and temporal variability of SMC in mountain catchments is an essential step towards improving quantitative predictions of catchment hydrological processes and related ecosystem services. The interacting influences of precipitation, soil properties, vegetation, and topography on SMC and the influence of SMC patterns on runoff generation processes have been extensively investigated (Vereecken et al., 2014). However, in mountain areas, obtaining reliable SMC estimations is still challenging, because of the high variability in topography, soil and vegetation properties. In the last few years, there has been an increasing interest in the estimation of surface SMC at local scales. On the one hand, low cost wireless sensor networks provide high-resolution SMC time series. On the other hand, active remote sensing microwave techniques, such as Synthetic Aperture Radars (SARs), show promising results (Bertoldi et al. 2014). As these data provide continuous coverage of large spatial extents with high spatial resolution (10-20 m), they are particularly in demand for mountain areas. However, there are still limitations related to the fact that the SAR signal can penetrate only a few centimeters in the soil. Moreover, the signal is strongly influenced by vegetation, surface roughness and topography. In this contribution, we analyse the spatial and temporal dynamics of surface and root-zone SMC (2.5 - 5 - 25 cm depth) of alpine meadows and pastures in the Long Term Ecological Research (LTER) Area Mazia Valley (South Tyrol - Italy) with different techniques: (I) a network of 18 stations; (II) field campaigns with mobile ground sensors; (III) 20-m resolution RADARSAT2 SAR images; (IV) numerical simulations using the GEOtop hydrological model (Rigon et al., 2006; Endrizzi et al., 2014). The objective of this work is to understand the physical controls of the observed SCM patterns. In particular, we want to investigate: • How the SMC signal propagates with depth, to understand the capability of SAR surface SMC observations to predict root-zone SMC. • The role of land management and vegetation properties with respect to soil and bedrock properties in determining SMC spatial variability and temporal patterns. In this context, we use the GEOtop model to understand if a relationship exists between the observed SMC patterns and the underlying runoff generation processes. Results show that meadows and pastures have different behaviours. Meadows are in general wetter because of irrigation and the presence of soils with higher organic content and higher water holding capacity. Moreover, surface and root depth SCM dynamics are correlated. In contrast, pastures are drier, with lower vegetation density and more compact soils due animal trampling. Because of shallow soils and impermeable bedrock, root zone SMC shows a different behaviour with respect to the surface, with occurrence of sub-surface saturation excess, as verified from numerical experiments performed with the hydrological model. Results suggest how SAR retrieved surface SMC can be used to extrapolate root zone SMC, when soil properties are homogenous and differences in vegetation density are properly accounted with a robust retrieval processes (Pasolli et al., in press 2015). However, in situations characterized by shallow subsurface saturation excess flow, a more sophisticated modelling approach is required to estimate root zone SMC using remote sensing observations. Bertoldi, G., Della, S., Notarnicola, C., Pasolli, L., Niedrist, G., & Tappeiner, U. (2014). Estimation of soil moisture patterns in mountain grasslands by means of SAR RADARSAT2 images and hydrological modeling, 516, 245-257. doi:10.1016/j.jhydrol.2014.02.018 Endrizzi, S., Gruber, S., Dall'Amico, M., & Rigon, R. (2014). GEOtop 2.0: simulating the combined energy and water balance at and below the land surface accounting for soil freezing, snow cover and terrain effects. Geoscientific Model Development, 7(6), 2831-2857. doi:10.5194/gmd-7-2831-2014 Pasolli, L., Notarnicola, C., Bertoldi, G., Bruzzone, L., Remegaldo, R., Niedrist, G, Della Chiesa S., Tappeiner, U., Zebisch, M. (2014): Multi-scale assessment of soil moisture variability in mountain areas by using active radar images. IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, in press 2015. Rigon, R., Bertoldi, G., & Over, T. M. (2006). GEOtop: A Distributed Hydrological Model with Coupled Water and Energy Budgets. Journal of Hydrometeorology, 7, 371-388. Vereecken, H., Huisman, J. A., Pachepsky, Y., Montzka, C., van der Kruk, J., Bogena, H., … Vanderborght, J. (2014). On the spatio-temporal dynamics of soil moisture at the field scale. Journal of Hydrology. doi:http://dx.doi.org/10.1016/j.jhydrol.2013.11.061

Trait-based characterisation of soil exploitation strategies of banana, weeds and cover plant species

PubMed Central

Tardy, Florence; Damour, Gaëlle; Dorel, Marc; Moreau, Delphine

2017-01-01

Cover plants can be introduced in cropping systems to provide agroecosystem services, including weed control via competition for resources. There is currently no consensus on how to identify the best cover plant species, while trait-based approaches are promising for screening plant species due to their agroecosystem service provision potential. This study was carried out to characterize soil exploitation strategies of cover plant species in banana agroecosystems using a trait-based approach, and in turn identify cover plant species with a high weed control potential via competition for soil resources in banana cropping systems. A field experiment was conducted on 17 cover plant species, two weed species and two banana cultivars grown individually. Four functional traits were measured. Two of them (i.e., the size of the zone explored by roots and the root impact density) were used to characterize root system soil exploration patterns. Two other traits (i.e., specific root length and root diameter) were used to characterize resource acquisition within the soil zone explored by the roots. All studied traits exhibited marked variations among species. The findings suggested a trade-off between the abilities of species to develop a limited number of large diameter roots exploring a large soil zone versus many thin roots exploring a smaller soil zone. Three soil-resource exploitation strategies were identified among species: (i) with large diameter roots that explore a large soil zone; (ii) with small diameter roots and a high specific length that explore a smaller soil zone; and (iii) with a high total root-impact density and an intermediate specific root length that explore the uppermost soil layers. Interestingly, in our panel of species, no correlations with regard to belowground and aboveground strategies were noted: species with an acquisitive belowground strategy could display an acquisitive or a conservative aboveground strategy. The findings of this study illustrated that a trait-based approach could be used to identify plant species with potential for competing with weeds, while minimising competition with banana. Six of the 17 studied cover crop species were identified as having this potential. The next step will be to assess them for their weed control performances in banana cropping systems with low reliance on herbicides. PMID:28257454

Trait-based characterisation of soil exploitation strategies of banana, weeds and cover plant species.

PubMed

Tardy, Florence; Damour, Gaëlle; Dorel, Marc; Moreau, Delphine

2017-01-01

Cover plants can be introduced in cropping systems to provide agroecosystem services, including weed control via competition for resources. There is currently no consensus on how to identify the best cover plant species, while trait-based approaches are promising for screening plant species due to their agroecosystem service provision potential. This study was carried out to characterize soil exploitation strategies of cover plant species in banana agroecosystems using a trait-based approach, and in turn identify cover plant species with a high weed control potential via competition for soil resources in banana cropping systems. A field experiment was conducted on 17 cover plant species, two weed species and two banana cultivars grown individually. Four functional traits were measured. Two of them (i.e., the size of the zone explored by roots and the root impact density) were used to characterize root system soil exploration patterns. Two other traits (i.e., specific root length and root diameter) were used to characterize resource acquisition within the soil zone explored by the roots. All studied traits exhibited marked variations among species. The findings suggested a trade-off between the abilities of species to develop a limited number of large diameter roots exploring a large soil zone versus many thin roots exploring a smaller soil zone. Three soil-resource exploitation strategies were identified among species: (i) with large diameter roots that explore a large soil zone; (ii) with small diameter roots and a high specific length that explore a smaller soil zone; and (iii) with a high total root-impact density and an intermediate specific root length that explore the uppermost soil layers. Interestingly, in our panel of species, no correlations with regard to belowground and aboveground strategies were noted: species with an acquisitive belowground strategy could display an acquisitive or a conservative aboveground strategy. The findings of this study illustrated that a trait-based approach could be used to identify plant species with potential for competing with weeds, while minimising competition with banana. Six of the 17 studied cover crop species were identified as having this potential. The next step will be to assess them for their weed control performances in banana cropping systems with low reliance on herbicides.

Crustal deformation of the Andean foreland at 31° 30‧S (Argentina) constrained by magnetotelluric survey

NASA Astrophysics Data System (ADS)

Orozco, Luz Amparo; Favetto, Alicia; Pomposiello, Cristina; Rossello, Eduardo; Booker, John

2013-01-01

Twenty-five new long-period magnetotelluric sites near 31.5°S were collected in a west-east profile. This profile and the previous one, aligned with and adjacent to the eastern end, have been merged to form a single profile of more than 700 km long, extending from the Precordillera to the Chaco-Pampean Plain. The geotectonic scenario is characterized by a modern flat subduction zone of the Nazca plate located at a depth of around 120 km and clearly defined by the distribution of earthquake hypocenters recorded by local and regional networks. A "bulge" shape at 68.5°W, with an anomalous dip to the west, is observed within this segment. The smooth slab deformation might result from the restriction on eastward motion due to the presence of an electrically resistive zone. The magnetotelluric model shows that this thick zone of increased resistivity is found from shallow crustal levels to upper mantle depths. The bulge geometry allows hot fluids and volatiles to rise from the deeper asthenospheric wedge, and reach the lower crust reducing its viscosity and letting it flow. The zones of low resistivity in the lower crust show spatial correlation with the areas of foreland deformation from Precordillera to the Sierras Pampeanas and may also suggest a ductile regime. Shear zones reactivated by Cenozoic faulting must necessarily have their roots in the levels of the ductile lower crust associated to conductive channels. The zone where the lower crust is closer to the surface coincides with the areas of greatest structural relief and erosion. The interface between the folded ductile lower crust and the brittle upper crust might act as the main level of décollement of the bordering structures between the Precordillera, Sierra de Pie de Palo and the Sierras Pampeanas. In addition, the geometry of the interface might be conditioning the vergence of those structures.

Characterization and modeling of illite crystal particles and growth mechanisms in a zoned hydrothermal deposit, Lake City, Colorado

USGS Publications Warehouse

Bove, D.J.; Eberl, D.D.; McCarty, D.K.; Meeker, G.P.

2002-01-01

Mean thickness measurements and crystal-thickness distributions (CTDs) of illite particles vary systematically with changes in hydrothermal alteration type, fracture density, and attendant mineralization in a large acid-sulfate/Mo-porphyry hydrothermal system at Red Mountain, near Lake City, Colorado. The hydrothermal illites characterize an extensive zone of quartz-sericite-pyrite alteration beneath two deeply rooted bodies of magmatic-related, quartz-alunite altered rock. Nineteen illites from a 3000 ft vertical drill hole were analyzed by XRD using the PVP-10 intercalation method and the computer program MudMaster (Bertaut-Warren-Averbach technique). Mean crystallite thicknesses, as determined from 001 reflections, range from 5-7 nanometers (nm) at depths from 0-1700 ft, then sharply increase to 10-16 nm at depths between 1800-2100 ft, and decrease again to 4-5 nm below this level. The interval of largest particle thickness correlates strongly with the zone of most intense quartz-sericite-pyrite alteration (QSP) and attendant high-density stockwork fracturing, and with the highest concentrations of Mo within the drill core. CTD shapes for the illite particles fall into two main categories: asymptotic and lognormal. The shapes of the CTDs are dependent on conditions of illite formation. The asymptotic CTDs correspond to a nucleation and growth mechanism, whereas surface-controlled growth was the dominant mechanism for the lognormal CTDs. Lognormal CTDs coincide with major through-going fractures or stockwork zones, whereas asymptotic CTDs are present in wallrock distal to these intense fracture zones. The increase in illite particle size and the associated zone of intense QSP alteration and stockwork veining was related by proximity to the dacitic magma(s), which supplied both reactants and heat to the hydrothermal system. However, no changes in illite polytype, which in other studies reflect temperature transitions, were observed within this interval.

Gravity-induced changes in intracellular potentials in elongating cortical cells of mung bean roots

NASA Technical Reports Server (NTRS)

Ishikawa, H.; Evans, M. L.

1990-01-01

Gravity-induced changes in intracellular potentials in primary roots of 2-day-old mung bean (Vigna mungo L. cv. black matpe) seedlings were investigated using glass microelectrodes held by 3-dimensional hydraulic micro-drives. The electrodes were inserted into outer cortical cells within the elongation zone. Intracellular potentials, angle of root orientation with respect to gravity, and position within the root of the impaled cortical cell were measured simultaneously. Gravistimulation caused intracellular potential changes in cortical cells of the elongation zone. When the roots were oriented vertically, the intracellular potentials of the outer cortical cells (2 mm behind the root apex) were approximately - 115 mV. When the roots were placed horizontally cortical cells on the upper side hyperpolarized to - 154 mV within 30 s while cortical cells on the lower side depolarized to about - 62 mV. This electrical asymmetry did not occur in cells of the maturation zone. Because attempts to insert the electrode into cells of the root cap were unsuccessful, these cells were not measured. The hyperpolarization of cortical cells on the upper side was greatly reduced upon application of N,N'-dicyclohexylcarbodiimide (DCCD), an inhibitor of respiratory energy coupling. When stimulated roots were returned to the vertical, the degree of hyperpolarization of cortical cells on the previous upper side decreased within 30 s and approached that of cortical cells in non-stimulated roots. This cycle of hyperpolarization/loss of hyperpolarization was repeatable at least ten times by alternately turning the root from the vertical to the horizontal and back again. The very short (<30 s) lag period of these electrical changes indicates that they may result from stimulus-perception and transduction within the elongation zone rather than from transmission of a signal from the root cap.

Remote sensing and landslide hazard assessment

NASA Technical Reports Server (NTRS)

Mckean, J.; Buechel, S.; Gaydos, L.

1991-01-01

Remotely acquired multispectral data are used to improve landslide hazard assessments at all scales of investigation. A vegetation map produced from automated interpretation of TM data is used in a GIS context to explore the effect of vegetation type on debris flow occurrence in preparation for inclusion in debris flow hazard modeling. Spectral vegetation indices map spatial patterns of grass senescence which are found to be correlated with soil thickness variations on hillslopes. Grassland senescence is delayed over deeper, wetter soils that are likely debris flow source areas. Prediction of actual soil depths using vegetation indices may be possible up to some limiting depth greater than the grass rooting zone. On forested earthflows, the slow slide movement disrupts the overhead timber canopy, exposes understory vegetation and soils, and alters site spectral characteristics. Both spectral and textural measures from broad band multispectral data are successful at detecting an earthflow within an undisturbed old-growth forest.

Digging a Little Deeper: Microbial Communities, Molecular Composition and Soil Organic Matter Turnover along Tropical Forest Soil Depth Profiles

NASA Astrophysics Data System (ADS)

Pett-Ridge, J.; McFarlane, K. J.; Heckman, K. A.; Reed, S.; Green, E. A.; Nico, P. S.; Tfaily, M. M.; Wood, T. E.; Plante, A. F.

2016-12-01

Tropical forest soils store more carbon (C) than any other terrestrial ecosystem and exchange vast amounts of CO2, water, and energy with the atmosphere. Much of this C is leached and stored in deep soil layers where we know little about its fate or the microbial communities that drive deep soil biogeochemistry. Organic matter (OM) in tropical soils appears to be associated with mineral particles, suggesting deep soils may provide greater C stabilization. However, few studies have evaluated sub-surface soils in tropical ecosystems, including estimates of the turnover times of deep soil C, the sensitivity of this C to global environmental change, and the microorganisms involved. We quantified bulk C pools, microbial communities, molecular composition of soil organic matter, and soil radiocarbon turnover times from surface soils to 1.5m depths in multiple soil pits across the Luquillo Experimental Forest, Puerto Rico. Soil C, nitrogen, and root and microbial biomass all declined exponentially with depth; total C concentrations dropped from 5.5% at the surface to <0.5% at 140cm depth. High-throughput sequencing highlighted distinct microbial communities in surface soils (Acidobacteria and Proteobacteria) versus those below the active rooting zone (Verrucomicrobia and Thaumarchaea). High resolution mass spectrometry (FTICR-MS) analyses suggest a shift in the composition of OM with depth (especially in the water soluble fraction), an increase in oxidation, and decreasing H/C with depth (indicating higher aromaticity). Additionally, surface samples were rich in lignin-like compounds of plant origin that were absent with depth. Soil OM 14C and mean turnover times were variable across replicate horizons, ranging from 3-1500 years at the surface, to 5000-40,000 years at depth. In comparison to temperate deciduous forests, these 14C values reflect far older soil C. Particulate organic matter (free light fraction), with a relatively modern 14C was found in low but measureable concentration in even the deepest soil horizons. Our results indicate these tropical subsoils contain small but metabolically active microbial communities that are highly OM limited and may persist via degradation of recent inputs.

The initiation of lateral roots in the primary roots of maize (Zea mays L.) implies a reactivation of cell proliferation in a group of founder pericycle cells.

PubMed

Alarcón, M Victoria; Lloret, Pedro G; Martín-Partido, Gervasio; Salguero, Julio

2016-03-15

The initiation of lateral roots (LRs) has generally been viewed as a reactivation of proliferative activity in pericycle cells that are committed to initiate primordia. However, it is also possible that pericycle founder cells that initiate LRs never cease proliferative activity but rather are displaced to the most distal root zones while undertaking successive stages of LR initiation. In this study, we tested these two alternative hypotheses by examining the incorporation of 5-bromo-2'-deoxyuridine (BrdU) into the DNA of meristematic root cells of Zea mays. According to the values for the length of the cell cycle and values for cell displacement along the maize root, our results strongly suggest that pericycle cells that initiate LR primordia ceased proliferative activity upon exiting the meristematic zone. This finding is supported by the existence of a root zone between 4 and 20mm from the root cap junction, in which neither mitotic cells nor labelled nuclei were observed in phloem pericycle cells. Copyright © 2016 Elsevier GmbH. All rights reserved.

Vertical Distribution of Pasteuria penetrans Parasitizing Meloidogyne incognita on Pittosporum tobira in Florida.

PubMed

Baidoo, Richard; Mengistu, Tesfamariam Mekete; Brito, Janete A; McSorley, Robert; Stamps, Robert H; Crow, William T

2017-09-01

Pasteuria penetrans is considered as the primary agent responsible for soil suppressiveness to root-knot nematodes widely distributed in many agricultural fields. A preliminary survey on a Pittosporum tobira field where the grower had experienced a continuous decline in productivity caused by Meloidogyne incognita showed that the nematode was infected with Pasteuria penetrans . For effective control of the nematode, the bacterium and the host must coexist in the same root zone. The vertical distribution of Pasteuria penetrans and its relationship with the nematode host in the soil was investigated to identify (i) the vertical distribution of P. penetrans endospores in an irrigated P. tobira field and (ii) the relationship among P. penetrans endospore density, M. incognita J2 population density, and host plant root distribution over time. Soil bioassays revealed that endospore density was greater in the upper 18 cm of the top soil compared with the underlying depths. A correlation analysis showed that the endospore density was positively related to the J2 population density and host plant root distribution. Thus, the vertical distribution of P. penetrans was largely dependent on its nematode host which in turn was determined by the distribution of the host plant roots. The Pasteuria was predominant mostly in the upper layers of the soil where their nematode host and the plant host roots are abundant, a factor which may be a critical consideration when using P. penetrans as a nematode biological control agent.

Vertical Distribution of Pasteuria penetrans Parasitizing Meloidogyne incognita on Pittosporum tobira in Florida

PubMed Central

Baidoo, Richard; Mengistu, Tesfamariam Mekete; Brito, Janete A.; McSorley, Robert; Stamps, Robert H.; Crow, William T.

2017-01-01

Pasteuria penetrans is considered as the primary agent responsible for soil suppressiveness to root-knot nematodes widely distributed in many agricultural fields. A preliminary survey on a Pittosporum tobira field where the grower had experienced a continuous decline in productivity caused by Meloidogyne incognita showed that the nematode was infected with Pasteuria penetrans. For effective control of the nematode, the bacterium and the host must coexist in the same root zone. The vertical distribution of Pasteuria penetrans and its relationship with the nematode host in the soil was investigated to identify (i) the vertical distribution of P. penetrans endospores in an irrigated P. tobira field and (ii) the relationship among P. penetrans endospore density, M. incognita J2 population density, and host plant root distribution over time. Soil bioassays revealed that endospore density was greater in the upper 18 cm of the top soil compared with the underlying depths. A correlation analysis showed that the endospore density was positively related to the J2 population density and host plant root distribution. Thus, the vertical distribution of P. penetrans was largely dependent on its nematode host which in turn was determined by the distribution of the host plant roots. The Pasteuria was predominant mostly in the upper layers of the soil where their nematode host and the plant host roots are abundant, a factor which may be a critical consideration when using P. penetrans as a nematode biological control agent. PMID:29062154

Improved Absolute Radiometric Calibration of a UHF Airborne Radar

NASA Technical Reports Server (NTRS)

Chapin, Elaine; Hawkins, Brian P.; Harcke, Leif; Hensley, Scott; Lou, Yunling; Michel, Thierry R.; Moreira, Laila; Muellerschoen, Ronald J.; Shimada, Joanne G.; Tham, Kean W.;

Finite Frequency Traveltime Tomography of Lithospheric and Upper Mantle Structures beneath the Cordillera-Craton Transition in Southwestern Canada

NASA Astrophysics Data System (ADS)

Chen, Y.; Gu, Y. J.; Hung, S. H.

2014-12-01

Based on finite-frequency theory and cross-correlation teleseismic relative traveltime data from the USArray, Canadian National Seismograph Network (CNSN) and Canadian Rockies and Alberta Network (CRANE), we present a new tomographic model of P-wave velocity perturbations for the lithosphere and upper mantle beneath the Cordillera-cration transition region in southwestern Canada. The inversion procedure properly accounts for the finite-volume sensitivities of measured travel time residuals, and the resulting model shows a greater resolution of upper mantle velocity heterogeneity beneath the study area than earlier approaches based on the classical ray-theoretical approach. Our model reveals a lateral change of P velocities from -0.5% to 0.5% down to ~200-km depth in a 50-km wide zone between the Alberta Basin and the foothills of the Rocky Mountains, which suggests a sharp structural gradient along the Cordillera deformation front. The stable cratonic lithosphere, delineated by positive P-velocity perturbations of 0.5% and greater, extends down to a maximum depth of ~180 km beneath the Archean Loverna Block (LB). In comparison, the mantle beneath the controversial Medicine Hat Block (MHB) exhibits significantly higher velocities in the uppermost mantle and a shallower (130-150 km depth) root, generally consistent with the average depth of the lithosphere-asthenosphere boundary beneath Southwest Western Canada Sedimentary Basin (WCSB). The complex shape of the lithospheric velocities under the MHB may be evidence of extensive erosion or a partial detachment of the Precambrian lithospheric root. Furthermore, distinct high velocity anomalies in LB and MHB, which are separated by 'normal' mantle block beneath the Vulcan structure (VS), suggest different Archean assembly and collision histories between these two tectonic blocks.

76 FR 67379 - Importation of Dracaena Plants From Costa Rica

Federal Register 2010, 2011, 2012, 2013, 2014

2011-11-01

... rooting zone for plants produced by air layering) to the farthest terminal growing point. Paragraph (y)(2... the soil line (or top of the rooting zone for plants produced by air layering) to the farthest...

Microsurgical removal of epidermal and cortical cells: evidence that the gravitropic signal moves through the outer cell layers in primary roots of maize

NASA Technical Reports Server (NTRS)

Yang, R. L.; Evans, M. L.; Moore, R.

1990-01-01

There is general agreement that during root gravitropism some sort of growth-modifying signal moves from the cap to the elongation zone and that this signal ultimately induces the curvature that leads to reorientation of the root. However, there is disagreement regarding both the nature of the signal and the pathway of its movement from the root cap to the elongation zone. We examined the pathway of movement by testing gravitropism in primary roots of maize (Zea mays L.) from which narrow (0.5 mm) rings of epidermal and cortical tissue were surgically removed from various positions within the elongation zone. When roots were girdled in the apical part of the elongation zone gravitropic curvature occurred apical to the girdle but not basal to the girdle. Filling the girdle with agar allowed curvature basal to the girdle to occur. Shallow girdles, in which only two or three cell layers (epidermis plus one or two cortical cell layers) were removed, prevented or greatly delayed gravitropic curvature basal to the girdle. The results indicate that the gravitropic signal moves basipetally through the outermost cell layers, perhaps through the epidermis itself.

Comparison of different assimilation methodologies of groundwater levels to improve predictions of root zone soil moisture with an integrated terrestrial system model

NASA Astrophysics Data System (ADS)

Zhang, Hongjuan; Kurtz, Wolfgang; Kollet, Stefan; Vereecken, Harry; Franssen, Harrie-Jan Hendricks

2018-01-01

The linkage between root zone soil moisture and groundwater is either neglected or simplified in most land surface models. The fully-coupled subsurface-land surface model TerrSysMP including variably saturated groundwater dynamics is used in this work. We test and compare five data assimilation methodologies for assimilating groundwater level data via the ensemble Kalman filter (EnKF) to improve root zone soil moisture estimation with TerrSysMP. Groundwater level data are assimilated in the form of pressure head or soil moisture (set equal to porosity in the saturated zone) to update state vectors. In the five assimilation methodologies, the state vector contains either (i) pressure head, or (ii) log-transformed pressure head, or (iii) soil moisture, or (iv) pressure head for the saturated zone only, or (v) a combination of pressure head and soil moisture, pressure head for the saturated zone and soil moisture for the unsaturated zone. These methodologies are evaluated in synthetic experiments which are performed for different climate conditions, soil types and plant functional types to simulate various root zone soil moisture distributions and groundwater levels. The results demonstrate that EnKF cannot properly handle strongly skewed pressure distributions which are caused by extreme negative pressure heads in the unsaturated zone during dry periods. This problem can only be alleviated by methodology (iii), (iv) and (v). The last approach gives the best results and avoids unphysical updates related to strongly skewed pressure heads in the unsaturated zone. If groundwater level data are assimilated by methodology (iii), EnKF fails to update the state vector containing the soil moisture values if for (almost) all the realizations the observation does not bring significant new information. Synthetic experiments for the joint assimilation of groundwater levels and surface soil moisture support methodology (v) and show great potential for improving the representation of root zone soil moisture.

Botanical ethnoveterinary therapies used by agro-pastoralists of Fafan zone, Eastern Ethiopia.

PubMed

Feyera, Teka; Mekonnen, Endalkachew; Wakayo, Befekadu Urga; Assefa, Solomon

2017-08-09

In Ethiopia, plant based remedies are still the most important and sometimes the only source of therapeutics in the management of livestock diseases. However, documentation of this indigenous knowledge of therapeutic system still remains at a minimum level. The aim of this study was, thus, to document the traditional knowledge of botanical ethnoveterinary therapies in the agro-pastoral communities of Fafan Zone, Eastern Ethiopia. The study employed a cross-sectional participatory survey. Purposive sampling technique was applied to select key respondents with desired knowledge in traditional animal health care system. Data were gathered from a total of 24 (22 males and 2 females) ethnoveterinary practitioners and herbalists using an in-depth-interview complemented with group discussion and field observation. The current ethnobotanical survey indicated that botanical ethnoveterinary therapies are the mainstay of livestock health care system in the studied communities. A total of 49 medicinal plants belonging to 21 families, which are used by traditional healers and livestock raisers for the treatment of 29 types of livestock ailments/health problems, were identified in the study area. The major plant parts used were leaves (43%) followed by roots (35%). In most cases, traditional plant remedies were prepared by pounding the remedial plant part and mixing it with water at room temperature. The various types of identified medicinal plants and their application in ethnoveternary practice of Fafan zone agro pastoralists indicate the depth of indigenous knowledge in ethnobotanical therapy. The identified medicinal plants could be potentially useful for future phytochemical and pharmacological studies.

Progressive Inhibition by Water Deficit of Cell Wall Extensibility and Growth along the Elongation Zone of Maize Roots Is Related to Increased Lignin Metabolism and Progressive Stelar Accumulation of Wall Phenolics1

PubMed Central

Fan, Ling; Linker, Raphael; Gepstein, Shimon; Tanimoto, Eiichi; Yamamoto, Ryoichi; Neumann, Peter M.

2006-01-01

Water deficit caused by addition of polyethylene glycol 6000 at −0.5 MPa water potential to well-aerated nutrient solution for 48 h inhibited the elongation of maize (Zea mays) seedling primary roots. Segmental growth rates in the root elongation zone were maintained 0 to 3 mm behind the tip, but in comparison with well-watered control roots, progressive growth inhibition was initiated by water deficit as expanding cells crossed the region 3 to 9 mm behind the tip. The mechanical extensibility of the cell walls was also progressively inhibited. We investigated the possible involvement in root growth inhibition by water deficit of alterations in metabolism and accumulation of wall-linked phenolic substances. Water deficit increased expression in the root elongation zone of transcripts of two genes involved in lignin biosynthesis, cinnamoyl-CoA reductase 1 and 2, after only 1 h, i.e. before decreases in wall extensibility. Further increases in transcript expression and increased lignin staining were detected after 48 h. Progressive stress-induced increases in wall-linked phenolics at 3 to 6 and 6 to 9 mm behind the root tip were detected by comparing Fourier transform infrared spectra and UV-fluorescence images of isolated cell walls from water deficit and control roots. Increased UV fluorescence and lignin staining colocated to vascular tissues in the stele. Longitudinal bisection of the elongation zone resulted in inward curvature, suggesting that inner, stelar tissues were also rate limiting for root growth. We suggest that spatially localized changes in wall-phenolic metabolism are involved in the progressive inhibition of wall extensibility and root growth and may facilitate root acclimation to drying environments. PMID:16384904

Field experiment with liquid manure and enhanced biochar

NASA Astrophysics Data System (ADS)

Dunst, Gerald

2017-04-01

Field experiments with low amounts of various liquid manure enhanced biochars. In 2016 a new machine was developed to inject liquid biochar based fertilizer directly into the crop root zone. A large-scale field experiment with corn and oil seed pumpkin was set-up on 42 hectares on 15 different fields in the south East of Austria. Three treatments were compared: (1) surface spreading of liquid manure as control (common practice), (2) 20 cm deep root zone injection with same amount of liquid manure, and (3) 20 cm deep root zone injection with same amount of liquid manure mixed with 1 to 2 tons of various nutrient enhanced biochars. The biochar were quenched with the liquid phase from a separated digestate from a biogas plant (feedstock: cow manure). From May to October nitrate and ammonium content was analyzed monthly from 0-30cm and 30-60cm soil horizons. At the end of the growing season the yield was determined. The root zone injection of the liquid manure reduced the nitrate content during the first two months at 13-16% compared to the control. When the liquid manure was blended with biochar, Nitrate soil content was lowest (reduction 40-47%). On average the root zone injection of manure-biochar increased the yield by 7% compared to the surface applied control and 3% compared to the root zone injected manure without biochar. The results shows, that biochar is able to reduce the Nitrate load in soils and increase the yield of corn at the same time. The nutrient efficiency of organic liquid fertilizers can be increased.

The Plumbing System Feeding the Lusi Eruption Revealed by Ambient Noise Tomography

NASA Astrophysics Data System (ADS)

Fallahi, Mohammad Javad; Obermann, Anne; Lupi, Matteo; Karyono, Karyono; Mazzini, Adriano

2017-10-01

Lusi is a sediment-hosted hydrothermal system featuring clastic-dominated geyser-like eruption behavior in East Java, Indonesia. We use 10 months of ambient seismic noise cross correlations from 30 temporary seismic stations to obtain a 3-D model of shear wave velocity anomalies beneath Lusi, the neighboring Arjuno-Welirang volcanic complex, and the Watukosek fault system connecting the two. Our work reveals a hydrothermal plume, rooted at a minimum 6 km depth that reaches the surface at the Lusi site. Furthermore, the inversion shows that this vertical anomaly is connected to the adjacent volcanic complex through a narrow ( 3 km wide) low velocity corridor slicing the survey area at a depth of 4-6 km. The NE-SW direction of this elongated zone matches the strike of the Watukosek fault system. Distinct magmatic chambers are also inferred below the active volcanoes. The large-scale tomography features an exceptional example of a subsurface connection between a volcanic complex and a solitary erupting hydrothermal system hosted in a hydrocarbon-rich back-arc sedimentary basin. These results are consistent with a scenario where deep-seated fluids (e.g., magmas and released hydrothermal fluids) flow along a region of enhanced transmissivity (i.e., the Watukosek fault system damage zone) from the volcanic arc toward the back arc basin where Lusi resides. The triggered metamorphic reactions occurring at depth in the organic-rich sediments generated significant overpressure and fluid upwelling that is today released at the spectacular Lusi eruption site.

Revisiting the two-layer hypothesis: coexistence of alternative functional rooting strategies in savannas.

PubMed

Holdo, Ricardo M

2013-01-01

The two-layer hypothesis of tree-grass coexistence posits that trees and grasses differ in rooting depth, with grasses exploiting soil moisture in shallow layers while trees have exclusive access to deep water. The lack of clear differences in maximum rooting depth between these two functional groups, however, has caused this model to fall out of favor. The alternative model, the demographic bottleneck hypothesis, suggests that trees and grasses occupy overlapping rooting niches, and that stochastic events such as fires and droughts result in episodic tree mortality at various life stages, thus preventing trees from otherwise displacing grasses, at least in mesic savannas. Two potential problems with this view are: 1) we lack data on functional rooting profiles in trees and grasses, and these profiles are not necessarily reflected by differences in maximum or physical rooting depth, and 2) subtle, difficult-to-detect differences in rooting profiles between the two functional groups may be sufficient to result in coexistence in many situations. To tackle this question, I coupled a plant uptake model with a soil moisture dynamics model to explore the environmental conditions under which functional rooting profiles with equal rooting depth but different depth distributions (i.e., shapes) can coexist when competing for water. I show that, as long as rainfall inputs are stochastic, coexistence based on rooting differences is viable under a wide range of conditions, even when these differences are subtle. The results also indicate that coexistence mechanisms based on rooting niche differentiation are more viable under some climatic and edaphic conditions than others. This suggests that the two-layer model is both viable and stochastic in nature, and that a full understanding of tree-grass coexistence and dynamics may require incorporating fine-scale rooting differences between these functional groups and realistic stochastic climate drivers into future models.

Revisiting the Two-Layer Hypothesis: Coexistence of Alternative Functional Rooting Strategies in Savannas

PubMed Central

Holdo, Ricardo M.

2013-01-01

The two-layer hypothesis of tree-grass coexistence posits that trees and grasses differ in rooting depth, with grasses exploiting soil moisture in shallow layers while trees have exclusive access to deep water. The lack of clear differences in maximum rooting depth between these two functional groups, however, has caused this model to fall out of favor. The alternative model, the demographic bottleneck hypothesis, suggests that trees and grasses occupy overlapping rooting niches, and that stochastic events such as fires and droughts result in episodic tree mortality at various life stages, thus preventing trees from otherwise displacing grasses, at least in mesic savannas. Two potential problems with this view are: 1) we lack data on functional rooting profiles in trees and grasses, and these profiles are not necessarily reflected by differences in maximum or physical rooting depth, and 2) subtle, difficult-to-detect differences in rooting profiles between the two functional groups may be sufficient to result in coexistence in many situations. To tackle this question, I coupled a plant uptake model with a soil moisture dynamics model to explore the environmental conditions under which functional rooting profiles with equal rooting depth but different depth distributions (i.e., shapes) can coexist when competing for water. I show that, as long as rainfall inputs are stochastic, coexistence based on rooting differences is viable under a wide range of conditions, even when these differences are subtle. The results also indicate that coexistence mechanisms based on rooting niche differentiation are more viable under some climatic and edaphic conditions than others. This suggests that the two-layer model is both viable and stochastic in nature, and that a full understanding of tree-grass coexistence and dynamics may require incorporating fine-scale rooting differences between these functional groups and realistic stochastic climate drivers into future models. PMID:23950900

The effect of partially exposed connective tissue graft on root-coverage outcomes: a systematic review and meta-analysis.

PubMed

Dodge, Austin; Garcia, Jeffrey; Luepke, Paul; Lai, Yu-Lin; Kassab, Moawia; Lin, Guo-Hao

2018-04-01

The aim of this systematic review was to compare the root-coverage outcomes of using a partially exposed connective tissue graft (CTG) technique with a fully covered CTG technique for root coverage. An electronic search up to February 28 th , 2017, was performed to identify human clinical studies with data comparing outcomes of root coverage using CTG, with and without a partially exposed graft. Five clinical studies were selected for inclusion in this review. For each study, the gain of keratinized gingiva, reduction of recession depth, number of surgical sites achieving complete root coverage, percentage of root coverage, gain of tissue thickness, and changes of probing depth and clinical attachment level were recorded. Meta-analysis for the comparison of complete root coverage between the two techniques presented no statistically significant differences. A statistically significant gain of keratinized tissue in favor of the sites with an exposed CTG and a tendency of greater reduction in recession depth were seen at the sites with a fully covered CTG. Based on the results, the use of a partially exposed CTG in root-coverage procedures could achieve greater gain in keratinized gingiva, while a fully covered CTG might be indicated for procedures aiming to reduce recession depth. © 2018 Eur J Oral Sci.

Major Crustal Fault Zone Trends and Their Relation to Mineral Belts in the North-Central Great Basin, Nevada

USGS Publications Warehouse

Rodriguez, Brian D.; Sampson, Jay A.; Williams, Jackie M.

2007-01-01

The Great Basin physiographic province covers a large part of the western United States and contains one of the world's leading gold-producing areas, the Carlin Trend. In the Great Basin, many sedimentary-rock-hosted disseminated gold deposits occur along such linear mineral-occurrence trends. The distribution and genesis of these deposits is not fully understood, but most models indicate that regional tectonic structures play an important role in their spatial distribution. Over 100 magnetotelluric (MT) soundings were acquired between 1994 and 2001 by the U.S. Geological Survey to investigate crustal structures that may underlie the linear trends in north-central Nevada. MT sounding data were used to map changes in electrical resistivity as a function of depth that are related to subsurface lithologic and structural variations. Two-dimensional (2-D) resistivity modeling of the MT data reveals primarily northerly and northeasterly trending narrow 2-D conductors (1 to 30 ohm-m) extending to mid-crustal depths (5-20 km) that are interpreted to be major crustal fault zones. There are also a few westerly and northwesterly trending 2-D conductors. However, the great majority of the inferred crustal fault zones mapped using MT are perpendicular or oblique to the generally accepted trends. The correlation of strike of three crustal fault zones with the strike of the Carlin and Getchell trends and the Alligator Ridge district suggests they may have been the root fluid flow pathways that fed faults and fracture networks at shallower levels where gold precipitated in favorable host rocks. The abundant northeasterly crustal structures that do not correlate with the major trends may be structures that are open to fluid flow at the present time.

In situ silicone tube microextraction: a new method for undisturbed sampling of root-exuded thiophenes from marigold (Tagetes erecta L.) in soil.

PubMed

Mohney, Brian K; Matz, Tricia; Lamoreaux, Jessica; Wilcox, David S; Gimsing, Anne Louise; Mayer, Philipp; Weidenhamer, Jeffrey D

2009-11-01

The difficulties of monitoring allelochemical concentrations in soil and their dynamics over time have been a major barrier to testing hypotheses of allelopathic effects. Here, we evaluate three diffusive sampling strategies that employ polydimethylsiloxane (PDMS) sorbents to map the spatial distribution and temporal dynamics of root-exuded thiophenes from the African marigold, Tagetes erecta. Solid phase root zone extraction (SPRE) probes constructed by inserting stainless steel wire into PDMS tubing were used to monitor thiophene concentrations at various depths beneath marigolds growing in PVC pipes. PDMS sheets were used to map the distribution of thiophenes beneath marigolds grown in thin glass boxes. Concentrations of the two major marigold thiophenes measured by these two methods were extremely variable in both space and time. Dissection and analysis of roots indicated that distribution of thiophenes in marigold roots also was quite variable. A third approach used 1 m lengths of PDMS microtubing placed in marigold soil for repeated sampling of soil without disturbance of the roots. The two ends of the tubing remained out of the soil so that solvent could be washed through the tubing to collect samples for HPLC analysis. Unlike the other two methods, initial experiments with this approach show more uniformity of response, and suggest that soil concentrations of marigold thiophenes are affected greatly even by minimal disturbance of the soil. Silicone tube microextraction gave a linear response for alpha-terthienyl when maintained in soils spiked with 0-10 ppm of this thiophene. This method, which is experimentally simple and uses inexpensive materials, should be broadly applicable to the measurement of non-polar root exudates, and thus provides a means to test hypotheses about the role of root exudates in plant-plant and other interactions.

The distribution and origins of extremely acidic saline groundwaters in the south of Western Australia - Groundwater and digital mapping datasets provide new insights

NASA Astrophysics Data System (ADS)

Lillicrap, Adam M.; Biermann, Vera; George, Richard J.; Gray, David J.; Oldham, Carolyn E.

2018-01-01

Some of the largest extents of naturally occurring acidic waters are found across southern Australia. The origins of these systems remain poorly understood with many hypotheses for their genesis. Australian government agency groundwater datasets and mapping data (vegetation, geology, regolith and soils) for south-western Australia, unavailable to previous researchers, were statistically analysed to better understand the origins of acidic groundwater and guide additional fieldwork to study the origins of acidic saline groundwater. The groundwater data showed a distinct bimodal distribution in pH; the 'acid' population had a median pH of 3.5 and the larger 'non-acid' population had a median pH of 6.6. Acidic groundwater became progressively more common further from the coast towards the drier internally drained regions. Acidic groundwater was mostly confined to the lower slopes and valley floors with localised controls on distribution. Paradoxically, subsoil alkalinity within the internally drained inland regions had the strongest correlation with acidic groundwater (r2 = 0.85). Vegetation was also a strong predictor of acidic groundwater. Acidic groundwater had the highest occurrence under Eucalyptus woodlands and shrublands that grew on alkaline calcareous soils. Pre-clearing soil data in areas with acidic saline groundwater showed that the upper 1 m of the unsaturated zone had a pH around 8 while the pH at depths greater than 5 m decreased to <4. Based on the observations it is proposed that biogenic formation of calcareous soils occurs in the upper 1 m of the profile, calcium is sourced from the deeper profile where the root biota exchanges calcium for hydrogen ions to maintain charge balance. Iron is mobilised from the upper soil profile and concentrates lower in the profile at depths >1.5 m. There, the iron is reduced around roots and the alkalinity generated by microbial iron reduction is removed by biogenic calcification processes. The iron moves in solution further down the profile following roots where it comes in contact with the oxygenated unsaturated zone matrix and is oxidised generating acid. The resulting acidic recharging solution acidifies the unsaturated zone matrix. Saline groundwater moving through the matrix becomes acidified due to ion exchange or direct recharge. The main chemical processes were modelled in PHREEQC to test the plausibility of the hypothesis and acidic solutions with a pH of 3.8 or lower were obtained.

Dependence of residual displacements on the width and depth of compliant fault zones: a 3D study

NASA Astrophysics Data System (ADS)

Kang, J.; Duan, B.

2011-12-01

Compliant fault zones have been detected along active faults by seismic investigations (trapped waves and travel time analysis) and InSAR observations. However, the width and depth extent of compliant fault zones are still under debate in the community. Numerical models of dynamic rupture build a bridge between theories and the geological and geophysical observations. Theoretical 2D plane-strain studies of elastic and inelastic response of compliant fault zones to nearby earthquake have been conducted by Duan [2010] and Duan et al [2010]. In this study, we further extend the experiments to 3D with a focus on elastic response. We are specifically interested in how residual displacements depend on the structure and properties of complaint fault zones, in particular on the width and depth extent. We conduct numerical experiments on various types of fault-zone models, including fault zones with a constant width along depth, with decreasing widths along depth, and with Hanning taper profiles of velocity reduction. . Our preliminary results suggest 1) the width of anomalous horizontal residual displacement is only indicative of the width of a fault zone near the surface, and 2) the vertical residual displacement contains information of the depth extent of compliant fault zones.

Increased symplasmic permeability in barley root epidermal cells correlates with defects in root hair development

PubMed Central

Marzec, M; Muszynska, A; Melzer, M; Sas-Nowosielska, H; Kurczynska, E U; Wick, S

2014-01-01

It is well known that the process of plant cell differentiation depends on the symplasmic isolation of cells. Before starting the differentiation programme, the individual cell or group of cells should restrict symplasmic communication with neighbouring cells. We tested the symplasmic communication between epidermal cells in the different root zones of parental barley plants Hordeum vulgare L., cv. ‘Karat’ with normal root hair development, and two root hairless mutants (rhl1.a and rhl1.b). The results clearly show that symplasmic communication was limited during root hair differentiation in the parental variety, whereas in both root hairless mutants epidermal cells were still symplasmically connected in the corresponding root zone. This paper is the first report on the role of symplasmic isolation in barley root cell differentiation, and additionally shows that a disturbance in the restriction of symplasmic communication is present in root hairless mutants. PMID:23927737

The composite water and solute transport of barley (Hordeum vulgare) roots: effect of suberized barriers

PubMed Central

Ranathunge, Kosala; Kim, Yangmin X.; Wassmann, Friedrich; Kreszies, Tino; Zeisler, Viktoria

2017-01-01

Abstract Background and Aims Roots have complex anatomical structures, and certain localized cell layers develop suberized apoplastic barriers. The size and tightness of these barriers depend on the growth conditions and on the age of the root. Such complex anatomical structures result in a composite water and solute transport in roots. Methods Development of apoplastic barriers along barley seminal roots was detected using various staining methods, and the suberin amounts in the apical and basal zones were analysed using gas chromatography–mass spectometry (GC-MS). The hydraulic conductivity of roots (Lpr) and of cortical cells (Lpc) was measured using root and cell pressure probes. Key Results When grown in hydroponics, barley roots did not form an exodermis, even at their basal zones. However, they developed an endodermis. Endodermal Casparian bands first appeared as ‘dots’ as early as at 20 mm from the apex, whereas a patchy suberin lamellae appeared at 60 mm. The endodermal suberin accounted for the total suberin of the roots. The absolute amount in the basal zone was significantly higher than in the apical zone, which was inversely proportional to the Lpr. Comparison of Lpr and Lpc suggested that cell to cell pathways dominate for water transport in roots. However, the calculation of Lpr from Lpc showed that at least 26 % of water transport occurs through the apoplast. Roots had different solute permeabilities (Psr) and reflection coefficients (σsr) for the solutes used. The σsr was below unity for the solutes, which have virtually zero permeability for semi-permeable membranes. Conclusions Suberized endodermis significantly reduces Lpr of seminal roots. The water and solute transport across barley roots is composite in nature and they do not behave like ideal osmometers. The composite transport model should be extended by adding components arranged in series (cortex, endodermis) in addition to the currently included components arranged in parallel (apoplastic, cell to cell pathways). PMID:28065927

Modeling the Hydraulics of Root Growth in Three Dimensions with Phloem Water Sources1[C][OA

PubMed Central

Wiegers, Brandy S.; Cheer, Angela Y.; Silk, Wendy K.

2009-01-01

Primary growth is characterized by cell expansion facilitated by water uptake generating hydrostatic (turgor) pressure to inflate the cell, stretching the rigid cell walls. The multiple source theory of root growth hypothesizes that root growth involves transport of water both from the soil surrounding the growth zone and from the mature tissue higher in the root via phloem and protophloem. Here, protophloem water sources are used as boundary conditions in a classical, three-dimensional model of growth-sustaining water potentials in primary roots. The model predicts small radial gradients in water potential, with a significant longitudinal gradient. The results improve the agreement of theory with empirical studies for water potential in the primary growth zone of roots of maize (Zea mays). A sensitivity analysis quantifies the functional importance of apical phloem differentiation in permitting growth and reveals that the presence of phloem water sources makes the growth-sustaining water relations of the root relatively insensitive to changes in root radius and hydraulic conductivity. Adaptation to drought and other environmental stresses is predicted to involve more apical differentiation of phloem and/or higher phloem delivery rates to the growth zone. PMID:19542299

Modeling the hydraulics of root growth in three dimensions with phloem water sources.

PubMed

Wiegers, Brandy S; Cheer, Angela Y; Silk, Wendy K

2009-08-01

Primary growth is characterized by cell expansion facilitated by water uptake generating hydrostatic (turgor) pressure to inflate the cell, stretching the rigid cell walls. The multiple source theory of root growth hypothesizes that root growth involves transport of water both from the soil surrounding the growth zone and from the mature tissue higher in the root via phloem and protophloem. Here, protophloem water sources are used as boundary conditions in a classical, three-dimensional model of growth-sustaining water potentials in primary roots. The model predicts small radial gradients in water potential, with a significant longitudinal gradient. The results improve the agreement of theory with empirical studies for water potential in the primary growth zone of roots of maize (Zea mays). A sensitivity analysis quantifies the functional importance of apical phloem differentiation in permitting growth and reveals that the presence of phloem water sources makes the growth-sustaining water relations of the root relatively insensitive to changes in root radius and hydraulic conductivity. Adaptation to drought and other environmental stresses is predicted to involve more apical differentiation of phloem and/or higher phloem delivery rates to the growth zone.

Contrasting physiological effects of partial root zone drying in field-grown grapevine (Vitis vinifera L. cv. Monastrell) according to total soil water availability

PubMed Central

Romero, Pascual; Dodd, Ian C.; Martinez-Cutillas, Adrian

2012-01-01

Different spatial distributions of soil moisture were imposed on field-grown grapevines by applying the same irrigation volumes to the entire (DI; deficit irrigation) or part of the (PRD; partial root zone drying) root zone. Five treatments were applied: controls irrigated at 60% ETc (crop evapotranspiration) for the whole season (308 mm year−1); DI-1 and PRD-1 that received the same irrigation as controls before fruit set, 30% ETc from fruit set to harvest and 45% ETc post-harvest (192 mm year−1); and DI-2 and PRD-2 that were the same, except that 15% ETc was applied from fruit set to harvest (142 mm year−1). Compared with DI-1, PRD-1 maintained higher leaf area post-veraison and increased root water uptake, whole-plant hydraulic conductance, leaf transpiration, stomatal conductance, and photosynthesis, but decreased intrinsic gas exchange efficiency without causing differences in leaf xylem abscisic acid (ABA) concentration. Compared with DI-2, PRD-2 increased leaf xylem ABA concentration and decreased root water uptake, whole-plant hydraulic conductance, leaf transpiration, stomatal conductance, and photosynthesis, mainly at the beginning of PRD cycles. Distinctive PRD effects (e.g. greater stomatal closure) depended on the volumetric soil water content of the wet root zone, as predicted from a model of root-to-shoot ABA signalling. PMID:22451721

Vertical Stability of Ephemeral Step-Pool Streams Largely Controlled By Tree Roots, Central Kentucky, USA

NASA Astrophysics Data System (ADS)

Macmannis, K. R.; Hawley, R. J.

2013-12-01

The mechanisms controlling stability on small streams in steep settings are not well documented but have many implications related to stream integrity and water quality. For example, channel instability on first and second order streams is a potential source of sediment in regulated areas with Total Maximum Daily Loads (TMDLs) on water bodies that are impaired for sedimentation, such as the Chesapeake Bay. Management strategies that preserve stream integrity and protect channel stability are critical to communities that may otherwise require large capital investments to meet TMDLs and other water quality criteria. To contribute to an improved understanding of ephemeral step-pool systems, we collected detailed hydrogeomorphic data on 4 steep (0.06 - 0.12 meter/meter) headwater streams draining to lower relief alluvial valleys in Spencer County, Kentucky, USA. The step-pool streams (mean step height of 0.47 meter, mean step spacing of 4 meters) drained small undeveloped catchments dominated by early successional forest. Data collection for each of the 4 streams included 2 to 3 cross section surveys, bed material particle counts at cross section locations, and profile surveys ranging from approximately 125 to 225 meters in length. All survey data was systematically processed to understand geometric parameters such as cross sectional area, depth, and top width; bed material gradations; and detailed profile measurements such as slope, pool and riffle lengths, pool spacing, pool depth, step height, and step length. We documented the location, frequency, and type of step-forming materials (i.e., large woody debris (LWD), rock, and tree roots), compiling a database of approximately 130 total steps. Lastly, we recorded a detailed tree assessment of all trees located within 2 meters of the top of bank, detailing the species of tree, trunk diameter, and approximate distance from the top of bank. Analysis of geometric parameters illustrated correlations between channel characteristics (e.g., step height was positively correlated to slope while pool spacing was inversely correlated to slope). Most importantly, we assessed the step-forming materials with respect to channel stability. LWD has been widely documented as an important component of geomorphic stability and habitat diversity across many settings; however, our research highlights the importance of roots in providing bed stability in steep, first and second-order ephemeral streams, as 40 percent of the steps in these step-pool systems were controlled by tree roots. Similar to the key member in naturally-occurring log jams, lateral tree roots frequently served as the anchor for channel steps that were often supplemented by rocks or LWD. Assessment of the trees throughout the riparian zone suggested average tree densities of 0.30 trees/square meter or 0.40 trees/meter could provide adequate riparian zone coverage to promote channel stability. These results have implications to land use planning and stormwater management. For example, on developments draining to step-pool systems, maintaining the integrity of the riparian zone would seem to be as important as ensuring hydrologic mimicry if channel integrity is to be preserved.

Changes in the soil C cycle at the arid-hyperarid transition in the Atacama Desert

USGS Publications Warehouse

Ewing, S.A.; Macalady, J.L.; Warren-Rhodes, K.; McKay, C.P.; Amundson, Ronald

2008-01-01

We examined soil organic C (OC) turnover and transport across the rainfall transition from a biotic, arid site to a largely abiotic, hyperarid site. With this transition, OC concentrations decrease, and C cycling slows precipitously, both in surface horizons and below ground. The concentration and isotopic character of soil OC across this transition reflect decreasing rates of inputs, decomposition, and downward transport. OC concentrations in the arid soil increase slightly with depth in the upper meter, but are generally low and variable (???0.05%; total inventory of 1.82 kg m-2); OC-??14C values decrease from modern (+7???) to very 14C-depleted (-966???) with depth; and OC-??13C values are variable (-23.7??? to -14.1???). Using a transport model, we show that these trends reflect relatively rapid cycling in the upper few centimeters, and spatially variable preservation of belowground OC from root inputs, possibly during a previous, wetter climate supporting higher soil OC concentrations. In the driest soil, the OC inventory is the lowest among the sites (0.19 kg m-2), and radiocarbon values are 14C-depleted (-365??? to -696???) but show no trend with depth, indicating belowground OC inputs and long OC residence times throughout the upper meter (104 y). A distinct depth trend in ??13C values and OC/ON values within the upper 40 cm at the driest site may reflect photochemical alteration of organic matter at the soil surface, combined with limited subsurface decomposition and downward transport. We argue that while root inputs are preserved at the wetter sites, C cycling in the most hyperarid soil occurs through infrequent, rapid dissolved transport of highly photodegraded organic matter during rare rain events, each followed by a pulse of decomposition and subsequent prolonged drought. These belowground inputs are likely a primary control on the character, activity, and depth distribution of small microbial populations. While the lack of water is the dominant control on C cycling, very low C/N ratios of organic matter suggest that when rainfall occurs, hyperarid soils are effectively C limited. The preservation of fossil root fragments in the sediment beneath the driest soil indicates that wetter climate conditions preceded formation of this soil, and that vadose zone microbial activity has been extremely limited for the past 2 My. Copyright 2008 by the American Geophysical Union.

The Abundance of Pink-Pigmented Facultative Methylotrophs in the Root Zone of Plant Species in Invaded Coastal Sage Scrub Habitat

PubMed Central

Irvine, Irina C.; Brigham, Christy A.; Suding, Katharine N.; Martiny, Jennifer B. H.

2012-01-01

Pink-pigmented facultative methylotrophic bacteria (PPFMs) are associated with the roots, leaves and seeds of most terrestrial plants and utilize volatile C1 compounds such as methanol generated by growing plants during cell division. PPFMs have been well studied in agricultural systems due to their importance in crop seed germination, yield, pathogen resistance and drought stress tolerance. In contrast, little is known about the PPFM abundance and diversity in natural ecosystems, let alone their interactions with non-crop species. Here we surveyed PPFM abundance in the root zone soil of 5 native and 5 invasive plant species along ten invasion gradients in Southern California coastal sage scrub habitat. PPFMs were present in every soil sample and ranged in abundance from 102 to 105 CFU/g dry soil. This abundance varied significantly among plant species. PPFM abundance was 50% higher in the root zones of annual or biennial species (many invasives) than perennial species (all natives). Further, PPFM abundance appears to be influenced by the plant community beyond the root zone; pure stands of either native or invasive species had 50% more PPFMs than mixed species stands. In sum, PPFM abundance in the root zone of coastal sage scrub plants is influenced by both the immediate and surrounding plant communities. The results also suggest that PPFMs are a good target for future work on plant-microorganism feedbacks in natural ecosystems. PMID:22383990

The abundance of pink-pigmented facultative methylotrophs in the root zone of plant species in invaded coastal sage scrub habitat.

PubMed

Irvine, Irina C; Brigham, Christy A; Suding, Katharine N; Martiny, Jennifer B H

2012-01-01

Pink-pigmented facultative methylotrophic bacteria (PPFMs) are associated with the roots, leaves and seeds of most terrestrial plants and utilize volatile C(1) compounds such as methanol generated by growing plants during cell division. PPFMs have been well studied in agricultural systems due to their importance in crop seed germination, yield, pathogen resistance and drought stress tolerance. In contrast, little is known about the PPFM abundance and diversity in natural ecosystems, let alone their interactions with non-crop species. Here we surveyed PPFM abundance in the root zone soil of 5 native and 5 invasive plant species along ten invasion gradients in Southern California coastal sage scrub habitat. PPFMs were present in every soil sample and ranged in abundance from 10(2) to 10(5) CFU/g dry soil. This abundance varied significantly among plant species. PPFM abundance was 50% higher in the root zones of annual or biennial species (many invasives) than perennial species (all natives). Further, PPFM abundance appears to be influenced by the plant community beyond the root zone; pure stands of either native or invasive species had 50% more PPFMs than mixed species stands. In sum, PPFM abundance in the root zone of coastal sage scrub plants is influenced by both the immediate and surrounding plant communities. The results also suggest that PPFMs are a good target for future work on plant-microorganism feedbacks in natural ecosystems.

Using Hydrus 2-D to assess the emitters optimal position for Eggplants under surface and subsurface drip irrigation

NASA Astrophysics Data System (ADS)

Ghazouani, Hiba; Autovino, Dario; Douh, Boutheina; Boujelben, Abdel Hamid; Provenznao, Giuseppe; Rallo, Giovanni

2014-05-01

The main objective of the work is to assess the emitters optimal position for Eggplant crop (Solanum melongena L.) in a sandy loam soil irrigated with surface or subsurface drip irrigation systems, by means of field measurements and simulations carried out with Hydrus-2D model. Initially, the performance of the model is evaluated on the basis of the comparison between simulated soil water contents (SWC) and the corresponding measured in two plots, in which laterals with coextruded emitters are laid on the soil surface (T0) and at 20 cm depth (T20), respectively. In order to choose the best position of the lateral, the results of different simulation runs, carried out by changing the installation depth of the lateral (5 cm, 15 cm and 45 cm) were compared in terms of ratio between actual transpiration and total amount of water provided during the entire growing season (WUE). Experiments were carried out, from April to June 2007, at Institut Supérieur Agronomique de Chott Mériem (Sousse, Tunisia). In the two plots, plants were spaced 0.40 m along the row and 1.2 m between the rows. Each plot was irrigated by means of laterals with coextruded emitters spaced 0.40 m and discharging a flow rate equal to 4.0 l h-1 at a nominal pressure of 100 kPa. In each plot, spatial and temporal variability of SWCs were acquired with a Time Domain Reflectometry probe (Trime-FM3), on a total of four 70 cm long access tubes, installed along the direction perpendicular to the plant row, at distances of 0, 20, 40 and 60 cm from the emitter. Irrigation water was supplied, accounting for the rainfall, every 7-10 days at the beginning of the crop cycle (March-April) and approximately once a week during the following stages till the harvesting (May-June), for a total of 15 one-hour watering. To run the model, soil evaporation, Ep, and crop transpiration, Tp were determined according to the modified FAO Penman-Monteith equation and the dual crop coefficient approach, whereas soil hydraulics and rooting system parameters were experimentally determined. Simulated SWCs resulted fairly close to the corresponding measured at different distances from the emitter and therefore the model was able to predict SWCs in the root zone with values of the Root Mean Square Error generally lower than 4%. This result is consequent to the appropriate schematization of the root distribution, as well as of the root water uptake. Simulations also evidenced the contribute of soil evaporation losses when laterals are installed from the soil surface to a 20 cm depth, whereas significant water losses by deep percolation occured at the highest installation depth. The values of WUE associated to the different examined installation depths tend to a very slight increase when the position of the lateral rises from 0 to 15 cm and start to decrease for the higher depths.

A deep crustal fluid channel into the San Andreas Fault system near Parkfield, California

USGS Publications Warehouse

Becken, M.; Ritter, O.; Park, S.K.; Bedrosian, P.A.; Weckmann, U.; Weber, M.

2008-01-01

Magnetotelluric (MT) data from 66 sites along a 45-km-long profile across the San Andreas Fault (SAF) were inverted to obtain the 2-D electrical resistivity structure of the crust near the San Andreas Fault Observatory at Depth (SAFOD). The most intriguing feature of the resistivity model is a steeply dipping upper crustal high-conductivity zone flanking the seismically defined SAF to the NE, that widens into the lower crust and appears to be connected to a broad conductivity anomaly in the upper mantle. Hypothesis tests of the inversion model suggest that upper and lower crustal and upper-mantle anomalies may be interconnected. We speculate that the high conductivities are caused by fluids and may represent a deep-rooted channel for crustal and/or mantle fluid ascent. Based on the chemical analysis of well waters, it was previously suggested that fluids can enter the brittle regime of the SAF system from the lower crust and mantle. At high pressures, these fluids can contribute to fault-weakening at seismogenic depths. These geochemical studies predicted the existence of a deep fluid source and a permeable pathway through the crust. Our resistivity model images a conductive pathway, which penetrates the entire crust, in agreement with the geochemical interpretation. However, the resistivity model also shows that the upper crustal branch of the high-conductivity zone is located NE of the seismically defined SAF, suggesting that the SAF does not itself act as a major fluid pathway. This interpretation is supported by both, the location of the upper crustal high-conductivity zone and recent studies within the SAFOD main hole, which indicate that pore pressures within the core of the SAF zone are not anomalously high, that mantle-derived fluids are minor constituents to the fault-zone fluid composition and that both the volume of mantle fluids and the fluid pressure increase to the NE of the SAF. We further infer from the MT model that the resistive Salinian block basement to the SW of the SAFOD represents an isolated body, being 5-8km wide and reaching to depths >7km, in agreement with aeromagnetic data. This body is separated from a massive block of Salinian crust farther to the SW. The NE terminus of resistive Salinian crust has a spatial relationship with a near-vertical zone of increased seismic reflectivity ???15km SW of the SAF and likely represents a deep-reaching fault zone. ?? 2008 The Authors Journal compilation ?? 2008 RAS.

Separation of abscission zone cells in detached Azolla roots depends on apoplastic pH.

PubMed

Fukuda, Kazuma; Yamada, Yoshiya; Miyamoto, Kensuke; Ueda, Junichi; Uheda, Eiji

2013-01-01

In studies on the mechanism of cell separation during abscission, little attention has been paid to the apoplastic environment. We found that the apoplastic pH surrounding abscission zone cells in detached roots of the water fern Azolla plays a major role in cell separation. Abscission zone cells of detached Azolla roots were separated rapidly in a buffer at neutral pH and slowly in a buffer at pH below 4.0. However, cell separation rarely occurred at pH 5.0-5.5. Light and electron microscopy revealed that cell separation was caused by a degradation of the middle lamella between abscission zone cells at both pH values, neutral and below 4.0. Low temperature and papain treatment inhibited cell separation. Enzyme(s) in the cell wall of the abscission zone cells might be involved in the degradation of the pectin of the middle lamella and the resultant, pH-dependent cell separation. By contrast, in Phaseolus leaf petioles, unlike Azolla roots, cell separation was slow and increased only at acidic pH. The rapid cell separation, as observed in Azolla roots at neutral pH, did not occur. Indirect immunofluorescence microscopy, using anti-pectin monoclonal antibodies, revealed that the cell wall pectins of the abscission zone cells of Azolla roots and Phaseolus leaf petioles looked similar and changed similarly during cell separation. Thus, the pH-related differences in cell separation mechanisms of Azolla and Phaseolus might not be due to differences in cell wall pectin, but to differences in cell wall-located enzymatic activities responsible for the degradation of pectic substances. A possible enzyme system is discussed. Copyright © 2012 Elsevier GmbH. All rights reserved.

Fluorescence Resonance Energy Transfer-Sensitized Emission of Yellow Cameleon 3.60 Reveals Root Zone-Specific Calcium Signatures in Arabidopsis in Response to Aluminum and Other Trivalent Cations1[W][OA

PubMed Central

Rincón-Zachary, Magaly; Teaster, Neal D.; Sparks, J. Alan; Valster, Aline H.; Motes, Christy M.; Blancaflor, Elison B.

2010-01-01

Fluorescence resonance energy transfer-sensitized emission of the yellow cameleon 3.60 was used to study the dynamics of cytoplasmic calcium ([Ca2+]cyt) in different zones of living Arabidopsis (Arabidopsis thaliana) roots. Transient elevations of [Ca2+]cyt were observed in response to glutamic acid (Glu), ATP, and aluminum (Al3+). Each chemical induced a [Ca2+]cyt signature that differed among the three treatments in regard to the onset, duration, and shape of the response. Glu and ATP triggered patterns of [Ca2+]cyt increases that were similar among the different root zones, whereas Al3+ evoked [Ca2+]cyt transients that had monophasic and biphasic shapes, most notably in the root transition zone. The Al3+-induced [Ca2+]cyt increases generally started in the maturation zone and propagated toward the cap, while the earliest [Ca2+]cyt response after Glu or ATP treatment occurred in an area that encompassed the meristem and elongation zone. The biphasic [Ca2+]cyt signature resulting from Al3+ treatment originated mostly from cortical cells located at 300 to 500 μ m from the root tip, which could be triggered in part through ligand-gated Glu receptors. Lanthanum and gadolinium, cations commonly used as Ca2+ channel blockers, elicited [Ca2+]cyt responses similar to those induced by Al3+. The trivalent ion-induced [Ca2+]cyt signatures in roots of an Al3+-resistant and an Al3+-sensitive mutant were similar to those of wild-type plants, indicating that the early [Ca2+]cyt changes we report here may not be tightly linked to Al3+ toxicity but rather to a general response to trivalent cations. PMID:20053711

Fluorescence resonance energy transfer-sensitized emission of yellow cameleon 3.60 reveals root zone-specific calcium signatures in Arabidopsis in response to aluminum and other trivalent cations.

PubMed

Rincón-Zachary, Magaly; Teaster, Neal D; Sparks, J Alan; Valster, Aline H; Motes, Christy M; Blancaflor, Elison B

2010-03-01

Fluorescence resonance energy transfer-sensitized emission of the yellow cameleon 3.60 was used to study the dynamics of cytoplasmic calcium ([Ca(2+)](cyt)) in different zones of living Arabidopsis (Arabidopsis thaliana) roots. Transient elevations of [Ca(2+)](cyt) were observed in response to glutamic acid (Glu), ATP, and aluminum (Al(3+)). Each chemical induced a [Ca(2+)](cyt) signature that differed among the three treatments in regard to the onset, duration, and shape of the response. Glu and ATP triggered patterns of [Ca(2+)](cyt) increases that were similar among the different root zones, whereas Al(3+) evoked [Ca(2+)](cyt) transients that had monophasic and biphasic shapes, most notably in the root transition zone. The Al(3+)-induced [Ca(2+)](cyt) increases generally started in the maturation zone and propagated toward the cap, while the earliest [Ca(2+)](cyt) response after Glu or ATP treatment occurred in an area that encompassed the meristem and elongation zone. The biphasic [Ca(2+)](cyt) signature resulting from Al(3+) treatment originated mostly from cortical cells located at 300 to 500 mu m from the root tip, which could be triggered in part through ligand-gated Glu receptors. Lanthanum and gadolinium, cations commonly used as Ca(2+) channel blockers, elicited [Ca(2+)](cyt) responses similar to those induced by Al(3+). The trivalent ion-induced [Ca(2+)](cyt) signatures in roots of an Al(3+)-resistant and an Al(3+)-sensitive mutant were similar to those of wild-type plants, indicating that the early [Ca(2+)](cyt) changes we report here may not be tightly linked to Al(3+) toxicity but rather to a general response to trivalent cations.

Dynamics and hydrodynamic mixing of reactive solutes at stable fresh-salt interfaces

NASA Astrophysics Data System (ADS)

van der Zee, Sjoerd E. A. T. M.; Eeman, Sara; Cirkel, Gijsbert; Leijnse, Toon

2014-05-01

In coastal zones with saline groundwater, but also in semi-arid regions, fresh groundwater lenses may form due to infiltration of rain water. The thickness of both the lens and the mixing zone, determines fresh water availability for plant growth. Due to recharge variation, the thickness of the lens and the mixing zone are not constant, which may adversely affect agricultural and natural vegetation if saline water reaches the root zone during the growing season. A similar situation is found in situations where groundwater is not saline, but has a different chemical signature than rainwater-affected groundwater. Then also, vegetation patches and botanic biodiversity may depend sensitively on the depth of the interface between different types of groundwater. In this presentation, we study the response of thin lenses and their mixing zone to variation of recharge. The recharge is varied using sinusoids with a range of amplitudes and frequencies. We vary lens properties by varying the Rayleigh number and Mass flux ratio of saline and fresh water, as these dominate on the thickness of thin lenses and their mixing zone. Numerical results show a linear relation between the normalised lens volume and the main lens and recharge characteristics, enabling an empirical approximation of the variation of lens thickness. Increase of the recharge amplitude causes increase and the increase of recharge frequency causes a decrease in the variation of lens thickness. The average lens thickness is not significantly influenced by these variations in recharge, contrary to the mixing zone thickness. The mixing zone thickness is compared to that of a Fickian mixing regime. A simple relation between the travelled distance of the centre of the mixing zone position due to variations in recharge and the mixing zone thickness is shown to be valid for both a sinusoidal recharge variation and actual records of irregularly varying daily recharge data. Starting from a step response function, convolution can be used to determine the effect of variable recharge in time. For a sinusoidal curve, we can determine delay of lens movement compared to the recharge curve as well as the lens amplitude, derived from the convolution integral. Together the proposed equations provide us with a first order approximation of lens characteristics using basic lens and recharge parameters without the use of numerical models. This enables the assessment of the vulnerability of any thin fresh water lens on saline, upward seeping groundwater to salinity stress in the root zone.

SMAP Level 4 Surface and Root Zone Soil Moisture

NASA Technical Reports Server (NTRS)

Reichle, R.; De Lannoy, G.; Liu, Q.; Ardizzone, J.; Kimball, J.; Koster, R.

2017-01-01

The SMAP Level 4 soil moisture (L4_SM) product provides global estimates of surface and root zone soil moisture, along with other land surface variables and their error estimates. These estimates are obtained through assimilation of SMAP brightness temperature observations into the Goddard Earth Observing System (GEOS-5) land surface model. The L4_SM product is provided at 9 km spatial and 3-hourly temporal resolution and with about 2.5 day latency. The soil moisture and temperature estimates in the L4_SM product are validated against in situ observations. The L4_SM product meets the required target uncertainty of 0.04 m(exp. 3)m(exp. -3), measured in terms of unbiased root-mean-square-error, for both surface and root zone soil moisture.

In Vitro Morphogenesis of Arabidopsis to Search for Novel Endophytic Fungi Modulating Plant Growth.

PubMed

Dovana, Francesco; Mucciarelli, Marco; Mascarello, Maurizio; Fusconi, Anna

2015-01-01

Fungal endophytes have shown to affect plant growth and to confer stress tolerance to the host; however, effects of endophytes isolated from water plants have been poorly investigated. In this study, fungi isolated from stems (stem-E) and roots (root-E) of Mentha aquatica L. (water mint) were identified, and their morphogenetic properties analysed on in vitro cultured Arabidopsis (L.) Heynh., 14 and 21 days after inoculation (DAI). Nineteen fungi were analysed and, based on ITS analysis, 17 isolates showed to be genetically distinct. The overall effect of water mint endophytes on Arabidopsis fresh (FW) and dry weight (DW) was neutral and positive, respectively, and the increased DW, mainly occurring 14 DAI, was possibly related to plant defence mechanism. Only three fungi increased both FW and DW of Arabidopsis at 14 and 21 DAI, thus behaving as plant growth promoting (PGP) fungi. E-treatment caused a reduction of root depth and primary root length in most cases and inhibition-to-promotion of root area and lateral root length, from 14 DAI. Only Phoma macrostoma, among the water mint PGP fungi, increased both root area and depth, 21 DAI. Root depth and area 14 DAI were shown to influence DWs, indicating that the extension of the root system, and thus nutrient uptake, was an important determinant of plant dry biomass. Reduction of Arabidopsis root depth occurred to a great extent when plants where treated with stem-E while root area decreased or increased under the effects of stem-E and root-E, respectively, pointing to an influence of the endophyte origin on root extension. M. aquatica and many other perennial hydrophytes have growing worldwide application in water pollution remediation. The present study provided a model for directed screening of endophytes able to modulate plant growth in the perspective of future field applications of these fungi.

User’s guide to the collection and analysis of tree cores to assess the distribution of subsurface volatile organic compounds

USGS Publications Warehouse

Vroblesky, Don A.

2008-01-01

Analysis of the volatile organic compound content of tree cores is an inexpensive, rapid, simple approach to examining the distribution of subsurface volatile organic compound contaminants. The method has been shown to detect several volatile petroleum hydrocarbons and chlorinated aliphatic compounds associated with vapor intrusion and ground-water contamination. Tree cores, which are approximately 3 inches long, are obtained by using an increment borer. The cores are placed in vials and sealed. After a period of equilibration, the cores can be analyzed by headspace analysis gas chromatography. Because the roots are exposed to volatile organic compound contamination in the unsaturated zone or shallow ground water, the volatile organic compound concentrations in the tree cores are an indication of the presence of subsurface volatile organic compound contamination. Thus, tree coring can be used to detect and map subsurface volatile organic compound contamination. For comparison of tree-core data at a particular site, it is important to maintain consistent methods for all aspects of tree-core collection, handling, and analysis. Factors affecting the volatile organic compound concentrations in tree cores include the type of volatile organic compound, the tree species, the rooting depth, ground-water chemistry, the depth to the contaminated horizon, concentration differences around the trunk related to variations in the distribution of subsurface volatile organic compounds, concentration differences with depth of coring related to volatilization loss through the bark and possibly other unknown factors, dilution by rain, seasonal influences, sorption, vapor-exchange rates, and within-tree volatile organic compound degradation.

Tracing the Trans-European Suture Zone into the Mantle Transition Zone

NASA Astrophysics Data System (ADS)

Knapmeyer-Endrun, B.; Krueger, F.

2012-12-01

The depth to which lithospheric roots of cratons influence the surrounding mantle has important consequences for our understanding of the thermal structure of the mantle and its geodynamics. For example, it has been proposed that the cratonic keel of the Kaapvaal craton extends even into the mantle transition zone (MTZ). Here, we use more than 19,000 P-receiver functions from 479 stations in central and eastern Europe to map the MTZ discontinuities beneath the western boundary of the East European Craton (EEC) and adjacent Phanerozoic Europe, across the Trans-European Suture Zone (TESZ), the most fundamental lithospheric boundary in Europe. The main data source in our study is the PASSEQ experiment, which achieved the densest coverage across the TESZ yet with about 200 temporary stations installed from 2006 to 2008 in Germany, the Czech Republic, Poland and Lithuania. These recordings are supplemented by national and regional networks and broad-band data from older temporary deployments. Receiver functions use P-to-S converted teleseismic waves, which yield relative travel times to the 410 km and 660 km discontinuities. They are especially useful in mapping variations in MTZ thickness. We observe significantly shorter travel times, by as much as 2 s compared to standard Earth models, for conversions from both MTZ discontinuities within the craton. This is an effect of the cratonic root and can be explained by about 5% higher velocities in the upper mantle, compared to IASP91, beneath the craton. By contrast, the differential travel time across the MTZ is normal to slightly raised. This implies that any insulating effect of the continental root does not reach the MTZ, comparable to recent observations for the North American Craton. In contrast to earlier observations in Siberia, we do not find any trace of a discontinuity at 520 km depth. If this discontinuity is caused by the transition of wadsleyite to ringwoodite, this means that the MTZ is rather dry beneath the EEC. Within most of covered Phanerozoic Europe, the MTZ differential travel time is remarkably uniform and in agreement with IASP91. No widespread thermal effects of the various episodes of Caledonian and Variscan subduction that took place during the amalgamation of the continent remain. Only more recent tectonic events can be traced. For example, we find evidence of cold material, i.e. the subducted lithosphere of the Alpine Tethys, pooled on top of the 660 km discontinuity, at the contact between Alpine and Carpathian arcs, the subvertical high-velocity anomaly of the Eastern Alpine slab, and heating by 100 K to 250 K at 410 km depth beneath the broader Eifel area. The most interesting result is a previously unobserved increase in MTZ differential travel time by 1.5 s in a linear region of about 350 km width along the TESZ. Taking into account results of recent S-tomographies, raised water content in the MTZ cannot be the main cause for the observed travel time increase. Accordingly, we explain the increase, equivalent to a 15 km thicker MTZ, by a temperature decrease of about 80 K. It could either be due to a remnant of (mainly Variscan) subduction along the present TESZ which got stuck in the MTZ, or an indication of downwelling due to small-scale, edge-driven convection caused by the contrast in lithospheric thickness across the TESZ.

Geophysical and geochemical constraints on the geodynamic origin of the Vrancea Seismogenic Zone Romania

NASA Astrophysics Data System (ADS)

Fillerup, Melvin A.

The Vrancea Seismogenic Zone (VSZ) of Romania is a steeply NW-dipping volume (30 x 70 x 200 km) of intermediate-depth seismicity in the upper mantle beneath the bend zone of the Eastern Carpathians. The majority of tectonic models lean heavily on subduction processes to explain the Vrancea mantle seismicity and the presence of a Miocene age calc-alkaline volcanic arc in the East Carpathian hinterland. However, recent deep seismic reflection data collected over the Eastern Carpathian bend zone image an orogen lacking (1) a crustal root and (2) dipping crustal-scale fabrics routinely imaged in modern and ancient subduction zones. The DRACULA I and DACIA-PLAN deep seismic reflection profiles show that the East Carpathian orogen is supported by crust only 30-33 km thick while the Focsani basin (foreland) and Transylvanian basin (hinterland) crust is 42 km and 46 km thick respectively. Here the VSZ is interpreted as the former Eastern Carpathian orogenic root which was removed as a result of continental lithospheric delamination and is seismically foundering beneath the East Carpathian bend zone. Because large volumes of calc-alkaline volcanism are typically associated with subduction settings existing geochemical analyses from the Calimani, Gurghiu, and Harghita Mountains (CGH) have been reinterpreted in light of the seismic data which does not advocate the subduction of oceanic lithosphere. CGH rocks exhibit a compositional range from basalt to rhyolite, many with high-Mg# (Mg/Mg+Fe > 0.60), high-Sr (>1000 ppm), and elevated delta-O18 values (6-8.7 /) typical of arc lavas, and are consistent with mixing of mantle-derived melts with a crustal component. The 143Nd/144Nd (0.5123-0.5129) and 87Sr/86Sr (0.7040-0.7103) ratios similarly suggest mixing of mantle and crustal end members to obtain the observed isotopic compositions. A new geochemical model is presented whereby delamination initiates a geodynamic process like subduction but with the distinct absence of subducted oceanic lithosphere to produce the CGH lavas. The origin of the VSZ presented here suggests that the delamination of continental lithosphere is a process capable of producing mantle earthquakes and calc-alkaline volcanism without subduction tectonics.

The 2011 Tohoku-oki Earthquake related to a large velocity gradient within the Pacific plate

NASA Astrophysics Data System (ADS)

Matsubara, Makoto; Obara, Kazushige

2015-04-01

We conduct seismic tomography using arrival time data picked by the high sensitivity seismograph network (Hi-net) operated by National Research Institute for Earth Science and Disaster Prevention (NIED). We used earthquakes off the coast outside the seismic network around the source region of the 2011 Tohoku-oki Earthquake with the centroid depth estimated from moment tensor inversion by NIED F-net (broadband seismograph network) as well as earthquakes within the seismic network determined by Hi-net. The target region, 20-48N and 120-148E, covers the Japanese Islands from Hokkaido to Okinawa. A total of manually picked 4,622,346 P-wave and 3,062,846 S-wave arrival times for 100,733 earthquakes recorded at 1,212 stations from October 2000 to August 2009 is available for use in the tomographic method. In the final iteration, we estimate the P-wave slowness at 458,234 nodes and the S-wave slowness at 347,037 nodes. The inversion reduces the root mean square of the P-wave traveltime residual from 0.455 s to 0.187 s and that of the S-wave data from 0.692 s to 0.228 s after eight iterations (Matsubara and Obara, 2011). Centroid depths are determined using a Green's function approach (Okada et al., 2004) such as in NIED F-net. For the events distant from the seismic network, the centroid depth is more reliable than that determined by NIED Hi-net, since there are no stations above the hypocenter. We determine the upper boundary of the Pacific plate based on the velocity structure and earthquake hypocentral distribution. The upper boundary of the low-velocity (low-V) oceanic crust corresponds to the plate boundary where thrust earthquakes are expected to occur. Where we do not observe low-V oceanic crust, we determine the upper boundary of the upper layer of the double seismic zone within high-V Pacific plate. We assume the depth at the Japan Trench as 7 km. We can investigate the velocity structure within the Pacific plate such as 10 km beneath the plate boundary since the rays from the hypocenter around the coseismic region of the Tohoku-oki earthquake take off downward and pass through the Pacific plate. The landward low-V zone with a large anomaly corresponds to the western edge of the coseismic slip zone of the 2011 Tohoku-oki earthquake. The initial break point (hypocenter) is associated with the edge of a slightly low-V and low-Vp/Vs zone corresponding to the boundary of the low- and high-V zone. The trenchward low-V and low-Vp/Vs zone extending southwestward from the hypocenter may indicate the existence of a subducted seamount. The high-V zone and low-Vp/Vs zone might have accumulated the strain and resulted in the huge coseismic slip zone of the 2011 Tohoku earthquake. The low-V and low-Vp/Vs zone is a slight fluctuation within the high-V zone and might have acted as the initial break point of the 2011 Tohoku earthquake. Reference Matsubara, M. and K. Obara (2011) The 2011 Off the Pacific Coast of Tohoku earthquake related to a strong velocity gradient with the Pacific plate, Earth Planets Space, 63, 663-667. Okada, Y., K. Kasahara, S. Hori, K. Obara, S. Sekiguchi, H. Fujiwara, and A. Yamamoto (2004) Recent progress of seismic observation networks in Japan-Hi-net, F-net, K-NET and KiK-net, Research News Earth Planets Space, 56, xv-xxviii.

Elevated CO2 and O3 effects on fine-root survivorship in ponderosa pine mesocosms.

PubMed

Phillips, Donald L; Johnson, Mark G; Tingey, David T; Storm, Marjorie J

2009-07-01

Atmospheric carbon dioxide (CO(2)) and ozone (O(3)) concentrations are rising, which may have opposing effects on tree C balance and allocation to fine roots. More information is needed on interactive CO(2) and O(3) effects on roots, particularly fine-root life span, a critical demographic parameter and determinant of soil C and N pools and cycling rates. We conducted a study in which ponderosa pine (Pinus ponderosa) seedlings were exposed to two levels of CO(2) and O(3) in sun-lit controlled-environment mesocosms for 3 years. Minirhizotrons were used to monitor individual fine roots in three soil horizons every 28 days. Proportional hazards regression was used to analyze effects of CO(2), O(3), diameter, depth, and season of root initiation on fine-root survivorship. More fine roots were produced in the elevated CO(2) treatment than in ambient CO(2). Elevated CO(2), increasing root diameter, and increasing root depth all significantly increased fine-root survivorship and median life span. Life span was slightly, but not significantly, lower in elevated O(3), and increased O(3) did not reduce the effect of elevated CO(2). Median life spans varied from 140 to 448 days depending on the season of root initiation. These results indicate the potential for elevated CO(2) to increase the number of fine roots and their residence time in the soil, which is also affected by root diameter, root depth, and phenology.

Nitrogen uptake in a Tibetan grasland and implications for a vulnerable ecosystem

NASA Astrophysics Data System (ADS)

Schleuß, Per; Heitkamp, Felix; Sun, Yue; Kuzyakov, Yakov

2016-04-01

Grasslands are very important regionally and globally because they store large amounts of carbon (C) and nitrogen (N) and provide food for grazing animals. Intensive degradation of alpine grasslands in recent decades has mainly impacted the upper root-mat/soil horizon, with severe consequences for nutrient uptake in these nutrient-limited ecosystems. We used 15N labelling to identify the role of individual soil layers for N-uptake by Kobresia pygmaea. We hypothesized a very efficient N-uptake corresponding mainly to the vertical distribution of living root biomass (topsoil > subsoil). We assume that K. pygmaea develops a very dense root mat, which has to be maintained by small aboveground biomass, to enable this efficient N-uptake. Consequently, we expect a higher N-investment into roots compared to shoots. The 15N recovery in the whole plants (~70%) indicated very efficient N-uptake from the upper injection depths. The highest 15N amounts were recovered in root biomass, whereby values strongly decreased with depth. In contrast, 15N recovery in shoots was generally low (~18%) and independent of the 15N injection depth. This clearly shows that the low N demand of Kobresia shoots can be easily covered by N-uptake from any depth. Less living root biomass in lower versus upper soil was compensated by a higher specific root activity for N-uptake. The 15N allocation into roots was on average 1.7 times higher than that into shoots, which agreed well with the very high R/S ratio. Increasing root biomass is an efficient strategy of K. pygmaea to compete for belowground resources at depths and periods when resources are available. This implies high C costs to maintain root biomass (~6.0 kg DM m-2), which must be covered by a very low amount of photosynthetically active shoots (0.3 kg DM m-2). It also suggests that Kobresia grasslands react extremely sensitively towards changes in climate and management that disrupt this above-/belowground trade-off mechanism.

Soil coring at multiple field environments can directly quantify variation in deep root traits to select wheat genotypes for breeding.

PubMed

Wasson, A P; Rebetzke, G J; Kirkegaard, J A; Christopher, J; Richards, R A; Watt, M

2014-11-01

We aim to incorporate deep root traits into future wheat varieties to increase access to stored soil water during grain development, which is twice as valuable for yield as water captured at younger stages. Most root phenotyping efforts have been indirect studies in the laboratory, at young plant stages, or using indirect shoot measures. Here, soil coring to 2 m depth was used across three field environments to directly phenotype deep root traits on grain development (depth, descent rate, density, length, and distribution). Shoot phenotypes at coring included canopy temperature depression, chlorophyll reflectance, and green leaf scoring, with developmental stage, biomass, and yield. Current varieties, and genotypes with breeding histories and plant architectures expected to promote deep roots, were used to maximize identification of variation due to genetics. Variation was observed for deep root traits (e.g. 111.4-178.5cm (60%) for depth; 0.09-0.22cm/°C day (144%) for descent rate) using soil coring in the field environments. There was significant variation for root traits between sites, and variation in the relative performance of genotypes between sites. However, genotypes were identified that performed consistently well or poorly at both sites. Furthermore, high-performing genotypes were statistically superior in root traits than low-performing genotypes or commercial varieties. There was a weak but significant negative correlation between green leaf score (-0.5), CTD (0.45), and rooting depth and a positive correlation for chlorophyll reflectance (0.32). Shoot phenotypes did not predict other root traits. This study suggests that field coring can directly identify variation in deep root traits to speed up selection of genotypes for breeding programmes. © The Author 2014. Published by Oxford University Press on behalf of the Society for Experimental Biology.

Assessing sea-level rise impact on saltwater intrusion into the root zone of a geo-typical area in coastal east-central Florida.

PubMed

Xiao, Han; Wang, Dingbao; Medeiros, Stephen C; Hagen, Scott C; Hall, Carlton R

2018-07-15

Saltwater intrusion (SWI) into root zone in low-lying coastal areas can affect the survival and spatial distribution of various vegetation species by altering plant communities and the wildlife habitats they support. In this study, a baseline model was developed based on FEMWATER to simulate the monthly variation of root zone salinity of a geo-typical area located at the Cape Canaveral Barrier Island Complex (CCBIC) of coastal east-central Florida (USA) in 2010. Based on the developed and calibrated baseline model, three diagnostic FEMWATER models were developed to predict the extent of SWI into root zone by modifying the boundary values representing the rising sea level based on various sea-level rise (SLR) scenarios projected for 2080. The simulation results indicated that the extent of SWI would be insignificant if SLR is either low (23.4cm) or intermediate (59.0cm), but would be significant if SLR is high (119.5cm) in that infiltration/diffusion of overtopping seawater in coastal low-lying areas can greatly increase root zone salinity level, since the sand dunes may fail to prevent the landward migration of seawater because the waves of the rising sea level can reach and pass over the crest under high (119.5cm) SLR scenario. Copyright © 2018 Elsevier B.V. All rights reserved.

Complex physiological and molecular processes underlying root gravitropism

NASA Technical Reports Server (NTRS)

Chen, Rujin; Guan, Changhui; Boonsirichai, Kanokporn; Masson, Patrick H.

2002-01-01

Gravitropism allows plant organs to guide their growth in relation to the gravity vector. For most roots, this response to gravity allows downward growth into soil where water and nutrients are available for plant growth and development. The primary site for gravity sensing in roots includes the root cap and appears to involve the sedimentation of amyloplasts within the columella cells. This process triggers a signal transduction pathway that promotes both an acidification of the wall around the columella cells, an alkalinization of the columella cytoplasm, and the development of a lateral polarity across the root cap that allows for the establishment of a lateral auxin gradient. This gradient is then transmitted to the elongation zones where it triggers a differential cellular elongation on opposite flanks of the central elongation zone, responsible for part of the gravitropic curvature. Recent findings also suggest the involvement of a secondary site/mechanism of gravity sensing for gravitropism in roots, and the possibility that the early phases of graviresponse, which involve differential elongation on opposite flanks of the distal elongation zone, might be independent of this auxin gradient. This review discusses our current understanding of the molecular and physiological mechanisms underlying these various phases of the gravitropic response in roots.

Deposition of ammonium and nitrate in the roots of maize seedlings supplied with different nitrogen salts.

PubMed

Bloom, Arnold J; Randall, Lesley; Taylor, Alison R; Silk, Wendy K

2012-03-01

This study measured total osmolarity and concentrations of NH(4)(+), NO(3)(-), K(+), soluble carbohydrates, and organic acids in maize seminal roots as a function of distance from the apex, and NH(4)(+) and NO(3)(-) in xylem sap for plants receiving NH(4)(+) or NO(3)(-) as a sole N-source, NH(4)(+) plus NO(3)(-), or no nitrogen at all. The disparity between net deposition rates and net exogenous influx of NH(4)(+) indicated that growing cells imported NH(4)(+) from more mature tissue, whereas more mature root tissues assimilated or translocated a portion of the NH(4)(+) absorbed. Net root NO(3)(-) influx under Ca(NO(3))(2) nutrition was adequate to account for pools found in the growth zone and provided twice as much as was deposited locally throughout the non-growing tissue. In contrast, net root NO(3)(-) influx under NH(4)NO(3) was less than the local deposition rate in the growth zone, indicating that additional NO(3)(-) was imported or metabolically produced. The profile of NO(3)(-) deposition rate in the growth zone, however, was similar for the plants receiving Ca(NO(3))(2) or NH(4)NO(3). These results suggest that NO(3)(-) may serve a major role as an osmoticant for supporting root elongation in the basal part of the growth zone and maintaining root function in the young mature tissues.

Deposition of ammonium and nitrate in the roots of maize seedlings supplied with different nitrogen salts

PubMed Central

Bloom, Arnold J.; Randall, Lesley; Taylor, Alison R.; Silk, Wendy K.

2012-01-01

This study measured total osmolarity and concentrations of NH4+, NO3–, K+, soluble carbohydrates, and organic acids in maize seminal roots as a function of distance from the apex, and NH4+ and NO3– in xylem sap for plants receiving NH4+ or NO3– as a sole N-source, NH4+ plus NO3–, or no nitrogen at all. The disparity between net deposition rates and net exogenous influx of NH4+ indicated that growing cells imported NH4+ from more mature tissue, whereas more mature root tissues assimilated or translocated a portion of the NH4+ absorbed. Net root NO3– influx under Ca(NO3)2 nutrition was adequate to account for pools found in the growth zone and provided twice as much as was deposited locally throughout the non-growing tissue. In contrast, net root NO3– influx under NH4NO3 was less than the local deposition rate in the growth zone, indicating that additional NO3– was imported or metabolically produced. The profile of NO3– deposition rate in the growth zone, however, was similar for the plants receiving Ca(NO3)2 or NH4NO3. These results suggest that NO3– may serve a major role as an osmoticant for supporting root elongation in the basal part of the growth zone and maintaining root function in the young mature tissues. PMID:22213811

The Influence of Tree Species on Subsurface Stormflow at the Hillslope Scale

NASA Astrophysics Data System (ADS)

Jost, G.; Weiler, M.

2006-12-01

This study investigates the effect of Norway spruce (Picea abies (L.) Karst) and European beech (Fagus sylvatica L.), two very common tree species in Central Europe, on soil water storage and runoff response to precipitation. We postulate that on the same type of soil, spruce with its shallow rooting system leads to different soil water storage and runoff responses than the deep rooting beech. To test this hypothesis, we chose a beech and a spruce stand with comparable soil type, a stagnic cambisol with a stagnic layer in about 50 cm soil depth. In each of the two stands we sprinkled a hillslope of 6 m by 10 m with intensities of 100 mm/h and 60 mm/h for one hour each. Surface and shallow interflow as well as interflow in different soil depths was collected by inserted sheet metals and gutters in 10 cm, 30 cm and 60 cm soil depth. Soil water storage responses were measured by 48 multiplexed TDR sensors at each hillslope. TDR wave-guides (20 cm long) were installed in a 45° angle in 10 cm, 30 cm, 50 cm and 70 cm soil depth. Volumetric water content was measured in 6 minute intervals. Sprinkling experiments show that even at intensities of 100 mm/h all the applied water infiltrates, independent of the vegetation cover. The deeper soil horizons respond immediately to the applied precipitation. This vertical water flux response is larger under beech. Under spruce most of the water transport happens in the topsoil layers (upper 40 cm), whereas under beech the entire soil profile down to 80 cm soil depth reacts to sprinkling. Under spruce at intensities of 100 mm/h the whole pore space is almost filled. The larger pores in the topsoil under beech stemming from higher biogenic activity and in the subsoil from more intense rooting are still far from reaching their maximum capacity. High antecedent soil water content (around field capacity) still doesn't cause infiltration excess overland flow but the time that it takes for the soil water storage to drain to its initial value is less than one hour. The hillslope at the spruce stand produces between 23% and 28% runoff. However, the beech hillslope produces roughly twice as much. These experiments show that the interactions between tree species and soil in the vadose zone lead to different pore systems and thus different responses to subsurface stormflow. Beech with its deeper rooting systems and its higher biogenic activity (lower C/N ratio) creates a very effective preferential flow path system that leads to greater amounts of subsurface stormflow. Under high antecedent soil water storage, saturation excess overland flow is more likely to occur in soils under spruce with its smaller preferential flow system.

Deep structure of Pyrenees range (SW Europe) imaged by joint inversion of gravity and teleseismic delay time

NASA Astrophysics Data System (ADS)

Dufréchou, G.; Tiberi, C.; Martin, R.; Bonvalot, S.; Chevrot, S.; Seoane, L.

2018-04-01

We present a new model of the lithosphere and asthenosphere structure down to 300 km depth beneath the Pyrenees from the joint inversion of recent gravity and teleseismic data. Unlike previous studies, crustal correction were not applied on teleseismic data in order (i) to preserve the consistency between gravity data, which are mainly sensitive to the density structure of the crust.lithosphere, and travel time data, and (ii) to avoid the introduction of biases resulting from crustal reductions. The density model down to 100 km depth is preferentially used here to discuss the lithospheric structure of the Pyrenees, whereas the asthenospheric structure from 100 km to 300 km depth is discussed from our velocity model. The absence of a high density anomaly in our model between 30-100 km depth (except the Labourd density anomaly) in the northern part of the Pyrenees seems to preclude eclogitization of the subducted Iberian crust at the scale of the entire Pyrenean range. Local eclogitization of the deep Pyrenean crust beneath the western part of the Axial Zone (West of Andorra) associated with the positive Central density anomaly is proposed. The Pyrenean lithosphere in density and velocity models appears segmented from East to West. No clear relation between the along-strike segmentation and mapped major faults is visible in our models. The Pyrenees' lithosphere segments are associated to different seismicity pattern in the Pyrenees suggesting a possible relation between the deep structure of the Pyrenees and its seismicity in the upper crust. The concentration of earthquakes localized just straight up the Central density anomaly can result of the subsidence and/or delamination of an eclogitized Pyrenean deep root. The velocity model in the asthenosphere is similar to previous studies. The absence of a high-velocity anomaly in the upper mantle and transition zone (i.e. 125 to 225 km depth) seems to preclude the presence of a detached oceanic lithosphere beneath the European lithosphere.

Localization of 15N uptake in a Tibetan alpine Kobresia pasture

NASA Astrophysics Data System (ADS)

Schleuß, Per-Marten; Kuzyakov, Yakov

2014-05-01

The Kobresia Pygmea ecotone covers approximately 450.000 km2 and is of large global and regional importance due several socio-ecological aspects. For instance Kobresia pastures store high amounts of carbon, nitrogen and other nutrients, represent large grazing areas for herbivores, provide a fast regrowth after grazing events and protect against mechanical degradation and soil erosion. However, Kobresia pastures are assumed to be a grazing induced and are accompanied with distinct root mats varying in thickness between 5-30 cm. Yet, less is known about the morphology and the functions of this root mats, especially in the background of a progressing degradation due to changes of climate and management. Thus we aimed to identify the importance of single soil layers for plant nutrition. Accordingly, nitrogen uptake from different soil depths and its remain in above-ground biomass (AGB), belowground biomass (BGB) and soil were determined by using a 15N pulse labeling approach during the vegetation period in summer 2012. 15N urea was injected into six different soil depths (0.5 cm, 2.5 cm, 7.5 cm, 12.5 cm, 17.5 cm, 22.5 cm / for each 4 replicates) and plots were sampled 45 days after the labeling. For soil and BGB samples were taken in strict sample intervals of 0-1 cm, 1-5 cm, 5-10 cm, 10-15 cm, 15-20 cm, 20-25 cm. Results indicate that total recovery (including AGB, BGB and soil) was highest, if tracer was injected into the top 5 cm and subsequently decreased with decreasing injection depth. This is especially the case for the 15N recovery of BGB, which is clearly attributed to the root density and strongly decreased with soil depth. In contrast, the root activity derived from the 15N content of roots increased with soil depth, which is primary associated to a proportionate increase of living roots related to dead roots. However, most 15N was captured in plant biomass (67.5-85.3 % of total recovery), indicating high 15N uptake efficiency possibly due to N limitation of Kobresia ecosystems. Considering only the nitrogen uptake of AGB hardly any differences appeared between the six injection depths. Nevertheless, it could be shown, that 50.4 % percent of total variance of AGB nitrogen uptake could be explained by combining root density and root activity. Concluding, from the upper root mat horizons highest amounts of nitrogen were taken up by plants, because root densities are correspondingly high. However, in deeper root mat layers the root activity increases and accordingly plays a key role for plant nitrogen supply in this depth. Underlying causes for increasing root activities may be better soil moisture conditions, lower variation of soil temperature and/or a higher access to plant available nitrogen in deeper soil layers.Please fill in your abstract text.

Mycorrhizal colonization across hydrologic gradients in restored and reference freshwater wetlands

USGS Publications Warehouse

Bauer, C.R.; Kellogg, C.H.; Bridgham, S.D.; Lamberti, G.A.

2003-01-01

Arbuscular mycorrhizae, which are plant root-fungal symbioses, are common associates of vascular plants. Such relationships, however, are thought to be rare in wetland plant roots, although several recent studies suggest that arbuscular mycorrhizae may be important in wetland ecosystems. Our objectives were to determine (1) the level of arbuscular mycorrhizal colonization of plant roots in three freshwater marshes and (2) the effect of restoration status, hydrologic zone, and plant species identity on mycorrhizal colonization. We quantified the percentage of plant roots colonized by mycorrhizal fungi in one reference and two restored freshwater marshes in northern Indiana, USA during summer 1999. Roots were collected from soil cores taken around dominant plant species present in each of three hydrologic zones and then stained for microscopic examination of mycorrhizal colonization. Mycorrhizae were present in each wetland, in all hydrologic zones and in all sampled plants, including Carex and Scirpus species previously thought to be non-mycorrhizal. Both restored and reference wetlands had moderate levels of mycorrhizal colonization, but no clear trends in colonization were seen with hydrologic zone, which has been hypothesized to regulate the formation of mycorrhizae in wetlands. Mycorrhizal colonization levels in the roots of individual species ranged from 3 to 90% and were particularly large in members of the Poaceae (grass) family. Our results suggest that arbuscular mycorrhizae may be widely distributed across plant species and hydrologic zones in both restored and reference freshwater marshes. Thus, future research should examine the functional role of mycorrhizal fungi in freshwater wetlands. ?? 2003, The Society of Wetland Scientists.

Comparative effects of auxin and abscisic acid on growth, hydrogen ion efflux and gravitropism in primary roots of maize

NASA Technical Reports Server (NTRS)

Evans, M. L.; Mulkey, T. J.

1984-01-01

In order to test the idea that auxin action on root growth may be mediated by H(+) movement, the correlation of auxin action on growth and H(+) movement in roots was examined along with changes in H(+) efflux patterns associated with the asymmetric growth which occurs during gravitropism. The effects of indoleacetic acid (IAA) and abscisic acid (AbA) on growth, H(+) secretion, and gravitropism in roots were compared. Results show a close correlation existent between H(+) efflux and growth in maize roots. In intact roots there is strong H(+) efflux from the elongation zone. Growth-promoting concentrations of IAA stimulate H(+) efflux. During gravitropism the H(+) efflux from the elongation zone becomes asymmetric; the evidence indicates that auxin redistribution contributes to the development of acid efflux asymmetry. That AbA stimulates root growth is reflected in its ability to stimulate H(+) efflux from apical root segments.

[Effects of tree species diversity on fine-root biomass and morphological characteristics in subtropical Castanopsis carlesii forests].

PubMed

Wang, Wei-Wei; Huang, Jin-Xue; Chen, Feng; Xiong, De-Cheng; Lu, Zheng-Li; Huang, Chao-Chao; Yang, Zhi-Jie; Chen, Guang-Shui

2014-02-01

Fine roots in the Castanopsis carlesii plantation forest (MZ), the secondary forest of C. carlesii through natural regeneration with anthropogenic promotion (AR), and the secondary forest of C. carlesii through natural regeneration (NR) in Sanming City, Fujian Province, were estimated by soil core method to determine the influence of tree species diversity on biomass, vertical distribution and morphological characteristics of fine roots. The results showed that fine root biomass for the 0-80 cm soil layer in the MZ, AR and NR were (182.46 +/- 10.81), (242.73 +/- 17.85) and (353.11 +/- 16.46) g x m(-2), respectively, showing an increased tendency with increasing tree species diversity. In the three forests, fine root biomass was significantly influenced by soil depth, and fine roots at the 0-10 cm soil layer accounted for more than 35% of the total fine root biomass. However, the interaction of stand type and soil depth on fine-root distribution was not significant, indicating no influence of tree species diversity on spatial niche segregation in fine roots. Root surface area density and root length density were the highest in NR and lowest in the MZ. Specific root length was in the order of AR > MZ > NR, while specific root surface area was in the order of NR > MZ > AR. There was no significant interaction of stand type and soil depth on specific root length and specific root surface area. Fine root morphological plasticity at the stand level had no significant response to tree species diversity.

Quantifying the Variation in Shear Zone Character with Depth: a Case Study from the Simplon Shear Zone, Central Alps

NASA Astrophysics Data System (ADS)

Cawood, T. K.; Platt, J. P.

2017-12-01

A widely-accepted model for the rheology of crustal-scale shear zones states that they comprise distributed strain at depth, in wide, high-temperature shear zones, which narrow to more localized, high-strain zones at lower temperature and shallower crustal levels. We test and quantify this model by investigating how the width, stress, temperature and deformation mechanisms change with depth in the Simplon Shear Zone (SSZ). The SSZ marks a major tectonic boundary in the central Alps, where normal-sense motion and rapid exhumation of the footwall have preserved evidence of older, deeper deformation in rocks progressively further into the currently-exposed footwall. As such, microstructures further from the brittle fault (which represents the most localized, most recently-active part of the SSZ) represent earlier, higher- temperature deformation from deeper crustal levels, while rocks closer to the fault have been overprinted by successively later, cooler deformation at shallower depths. This study uses field mapping and microstructural studies to identify zones representing deformation at various crustal levels, and characterize each in terms of zone width (representing width of the shear zone at that time and depth) and dominant deformation mechanism. In addition, quartz- (by Electron Backscatter Diffraction, EBSD) and feldspar grain size (measured optically) piezometry are used to calculate the flow stress for each zone, while the Ti-in-quartz thermometer (TitaniQ) is used to calculate the corresponding temperature of deformation. We document the presence of a broad zone in which quartz is recrystallized by the Grain Boundary Migration (GBM) mechanism and feldspar by Subgrain Rotation (SGR), which represents the broad, deep zone of deformation occurring at relatively high temperatures and low stresses. In map view, this transitions to successively narrower zones, respectively characterized by quartz SGR and feldspar Bulge Nucleation (BLG); quartz BLG and brittle deformation of feldspar; and finally, a zone of generally brittle deformation. These zones represent deformation in progressively narrower regions at shallower depths, under lower temperatures and higher stresses.

Corn stover harvest increases herbicide movement to subsurface drains – Root Zone Water Quality Model simulations

USDA-ARS?s Scientific Manuscript database

BACKGROUND: Removal of crop residues for bioenergy production can alter soil hydrologic properties, but there is little information on its impact on transport of herbicides and their degradation products to subsurface drains. The Root Zone Water Quality Model, previously calibrated using measured fl...

Benchmarking LSM root-zone soil mositure predictions using satellite-based vegetation indices

USDA-ARS?s Scientific Manuscript database

The application of modern land surface models (LSMs) to agricultural drought monitoring is based on the premise that anomalies in LSM root-zone soil moisture estimates can accurately anticipate the subsequent impact of drought on vegetation productivity and health. In addition, the water and energy ...

Transpiration Driven Hydrologic Transport in vegetated shallow water environments: Implications on Diel and Seasonal Soil Biogeochemical Processes and System Management

NASA Astrophysics Data System (ADS)

Bachand, P.; Bachand, S. M.; Fleck, J.; Anderson, F.

2011-12-01

Hydrology arguably plays the most important role in biogeochemical cycling of mercury in wetlands and other shallow aquatic systems. CFSTR, PFR and non-ideal reactor models are oftentimes currently used to hydrologically assess these systems and to account for the fate, transport and cycling of constituents of concern (COC) with systems assumed to be non-leaky and with diffusion dominating soil transport. Yet a number of results in the literature imply transpiration drives soil transport: transpiration into the root zone is in the range of 50 - 75% of ET seasonally; gaseous emissions from aquatic systems show a diel pattern that tracks diel ET patterns; in long detention time aquatic systems ET is the largest sink for applied surface waters; and non-reactive tracers when applied to surface waters can find themselves in the root zone and within plants. All these findings strongly suggest transpiration driven infiltration into the root zone, is a significant hydrologic pathway for constituents and is an important transport mechanism. This paper examines the annual water budget for four shallow aquatic land uses in the Yolo Bypass, California: rice, wild rice, fallowed fields and wetlands. Results indicate that differences in hydrology between the fields, particularly the temporal nature of transpiration, play a significant role in mercury transformations and transport. During the irrigation period, fallowed fields discharged 6 cm of surface water (15% applied water), rice fields 31 - 43 cm (27 - 31% applied water), and wild rice fields 16 - 39 cm (15 - 31% applied water). Evapotranspiration rates were in the range of 120 - 130 cm/y for all land uses (i.e. rice, wild rice, fallowed fields and seasonal wetlands) except for the permanent wetland which was about 1/3 higher at about 170 cm/y. During the summer, approximately 50% of the applied surface water was drawn into the root zone to meet transpiration demands. Based upon results from our water budget and utilizing modified Peclet No. calculations, we quantified the relative importance of upward diffusion from the sediments and downward advection from transpiration as hydrologic transport mechanisms in the root zone. Transpiration driven infiltration moves water past the diffusive zone within 1 - 2 days in this system during the summer months. With the waning seasons, evapotranspiration diminishes until by winter diffusion dominates throughout the entire root zone. This model has great implications on the analyses of soil biogeochemical process in the root zone of shallow aquatic systems. Downward advection is a major transport mechanism into the root zone of shallow flooded aquatic systems and provides an important physical mechanism that drives variability in the seasonal and diel storage; release and cycling of COCs; and the creation of both a physical and chemical barrierd to upward diffusion of soil-borne COCs into the water column. Models that do not account for root zone interactions may not be able to capture diel and seasonal differences. Moreover, these interactions may lead to unanticipated environmental consequences as a result of cultural practices.

Specialized zones of development in roots

NASA Technical Reports Server (NTRS)

Ishikawa, H.; Evans, M. L.

1995-01-01

The authors propose using the term "distal elongation zone" (DEZ) rather than "postmitotic isodiametric growth zone" to refer to the group of cells between the apical meristem and the elongation zone in plant roots. Reasons presented for the change are that the proposed DEZ includes many cells that are still dividing, most cells in the region are not isodiametric, and the pattern of cell expansion in this region varies with position in the region. Cells in the DEZ respond to gravistimulation, mechanical impedance, electrotropic stimulation, water stress, and auxin. Differences in gene expression patterns between DEZ cells and cells in the main elongation zone are noted.

Simulating the fate of water in field soil crop environment

NASA Astrophysics Data System (ADS)

Cameira, M. R.; Fernando, R. M.; Ahuja, L.; Pereira, L.

2005-12-01

This paper presents an evaluation of the Root Zone Water Quality Model(RZWQM) for assessing the fate of water in the soil-crop environment at the field scale under the particular conditions of a Mediterranean region. The RZWQM model is a one-dimensional dual porosity model that allows flow in macropores. It integrates the physical, biological and chemical processes occurring in the root zone, allowing the simulation of a wide spectrum of agricultural management practices. This study involved the evaluation of the soil, hydrologic and crop development sub-models within the RZWQM for two distinct agricultural systems, one consisting of a grain corn planted in a silty loam soil, irrigated by level basins and the other a forage corn planted in a sandy soil, irrigated by sprinklers. Evaluation was performed at two distinct levels. At the first level the model capability to fit the measured data was analyzed (calibration). At the second level the model's capability to extrapolate and predict the system behavior for conditions different than those used when fitting the model was assessed (validation). In a subsequent paper the same type of evaluation is presented for the nitrogen transformation and transport model. At the first level a change in the crop evapotranspiration (ETc) formulation was introduced, based upon the definition of the effective leaf area, resulting in a 51% decrease in the root mean square error of the ETc simulations. As a result the simulation of the root water uptake was greatly improved. A new bottom boundary condition was implemented to account for the presence of a shallow water table. This improved the simulation of the water table depths and consequently the soil water evolution within the root zone. The soil hydraulic parameters and the crop variety specific parameters were calibrated in order to minimize the simulation errors of soil water and crop development. At the second level crop yield was predicted with an error of 1.1 and 2.8% for grain and forage corn, respectively. Soil water was predicted with an efficiency ranging from 50 to 95% for the silty loam soil and between 56 and 72% for the sandy soil. The purposed calibration procedure allowed the model to predict crop development, yield and the water balance terms, with accuracy that is acceptable in practical applications for complex and spatially variable field conditions. An iterative method was required to account for the strong interaction between the different model components, based upon detailed experimental data on soils and crops.

Differential priming of soil carbon driven by soil depth and root impacts on carbon availability

DOE Office of Scientific and Technical Information (OSTI.GOV)

de Graaff, Marie-Anne; Jastrow, Julie D.; Gillette, Shay

2013-11-15

Enhanced root-exudate inputs can stimulate decomposition of soil carbon (C) by priming soil microbial activity, but the mechanisms controlling the magnitude and direction of the priming effect remain poorly understood. With this study we evaluated how differences in soil C availability affect the impact of simulated root exudate inputs on priming. We conducted a 60-day laboratory incubation with soils collected (60 cm depth) from under six switchgrass (Panicum virgatum) cultivars. Differences in specific root length (SRL) among cultivars were expected to result in small differences in soil C inputs and thereby create small differences in the availability of recent labilemore » soil C; whereas soil depth was expected to create large overall differences in soil C availability. Soil cores from under each cultivar (roots removed) were divided into depth increments of 0–10, 20–30, and 40–60 cm and incubated with addition of either: (1) water or (2) 13C-labeled synthetic root exudates (0.7 mg C/g soil). We measured CO2 respiration throughout the experiment. The natural difference in 13C signature between C3 soils and C4 plants was used to quantify cultivar-induced differences in soil C availability. Amendment with 13C-labeled synthetic root-exudate enabled evaluation of SOC priming. Our experiment produced three main results: (1) switchgrass cultivars differentially influenced soil C availability across the soil profile; (2) small differences in soil C availability derived from recent root C inputs did not affect the impact of exudate-C additions on priming; but (3) priming was greater in soils from shallow depths (relatively high total soil C and high ratio of labile-to-stable C) compared to soils from deep depths (relatively low total soil C and low ratio of labile-to-stable C). These findings suggest that the magnitude of the priming effect is affected, in part, by the ratio of root exudate C inputs to total soil C and that the impact of changes in exudate inputs on the priming of SOC is regulated differently in surface soil compared to subsoil.« less

Identifying multiple timescale rainfall controls on Mojave Desert ecohydrology using an integrated data and modeling approach for Larrea tridentata

USGS Publications Warehouse

Ng, Gene-Hua Crystal; Bedford, David R.; Miller, David M.

2015-01-01

The perennial shrub Larrea tridentata is widely successful in North American warm deserts but is also susceptible to climatic perturbations. Understanding its response to rainfall variability requires consideration of multiple timescales. We examine intra-annual to multi-year relationships using model simulations of soil moisture and vegetation growth over 50 years in the Mojave National Preserve in southeastern California (USA). Ecohydrological model parameters are conditioned on field and remote sensing data using an ensemble Kalman filter. Although no specific periodicities were detected in the rainfall record, simulated leaf-area-index exhibits multi-year dynamics that are driven by multi-year (∼3-years) rains, but with up to a 1-year delay in peak response. Within a multi-year period, Larrea tridentata is more sensitive to winter rains than summer. In the most active part of the root zone (above ∼80 cm), >1-year average soil moisture drives vegetation growth, but monthly average soil moisture is controlled by root uptake. Moisture inputs reach the lower part of the root zone (below ∼80 cm) infrequently, but once there they can persist over a year to help sustain plant growth. Parameter estimates highlight efficient plant physiological properties facilitating persistent growth and high soil hydraulic conductivity allowing deep soil moisture stores. We show that soil moisture as an ecological indicator is complicated by bidirectional interactions with vegetation that depend on timescale and depth. Under changing climate, Larrea tridentata will likely be relatively resilient to shorter-term moisture variability but will exhibit higher sensitivity to shifts in seasonal to multi-year moisture inputs.

The Regulation of Growth in the Distal Elongation Zone of Maize Roots

NASA Technical Reports Server (NTRS)

Evans, Michael L.

1998-01-01

The major goals of the proposed research were 1. To develop specialized software for automated whole surface root expansion analysis and to develop technology for controlled placement of surface electrodes for analysis of relationships between root growth and root pH and electrophysiological properties. 2. To measure surface pH patterns and determine the possible role of proton flux in gravitropic sensing or response, and 3. To determine the role of auxin transport in establishment of patterns of proton flux and electrical gradients during the gravitropic response of roots with special emphasis on the role of the distal elongation zone in the early phases of the gravitropic response.

Local recharge processes in glacial and alluvial deposits of a temperate catchment

NASA Astrophysics Data System (ADS)

Fragalà, Federico A.; Parkin, Geoff

2010-07-01

SummaryThis study demonstrates that the composition and structure of Quaternary deposits and topography significantly influence rates of recharge and distribution of diffuse agricultural pollution at the hillslope scale. Analyses were made of vertical profiles of naturally-occurring chloride and nitrate, and artificially introduced bromide, in unsaturated and saturated sections of borehole cores of glacial till and alluvium under different land uses in the Upper Eden valley (UK). Estimates of local potential recharge were made based on chloride mass balance and nitrate peak methods. Persistent chloride bulges below the root zone were observed, and are interpreted to result from filtration processes at lithological boundaries. Changes in the shape of chloride profiles downslope, corroborated by nitrate profiles, indicate the roles of surface or near-surface runoff and runon, and the existence of lateral subsurface flows at depth. These findings have implications for estimation of recharge rates through unsaturated zones in Quaternary deposits, and the interpretation of potential 'hot-spots' of diffuse agrochemicals, particularly nitrates, moving through Quaternary deposits into groundwater.

The composite water and solute transport of barley (Hordeum vulgare) roots: effect of suberized barriers.

PubMed

Ranathunge, Kosala; Kim, Yangmin X; Wassmann, Friedrich; Kreszies, Tino; Zeisler, Viktoria; Schreiber, Lukas

2017-03-01

Roots have complex anatomical structures, and certain localized cell layers develop suberized apoplastic barriers. The size and tightness of these barriers depend on the growth conditions and on the age of the root. Such complex anatomical structures result in a composite water and solute transport in roots. Development of apoplastic barriers along barley seminal roots was detected using various staining methods, and the suberin amounts in the apical and basal zones were analysed using gas chromatography-mass spectometry (GC-MS). The hydraulic conductivity of roots ( Lp r ) and of cortical cells ( Lp c ) was measured using root and cell pressure probes. When grown in hydroponics, barley roots did not form an exodermis, even at their basal zones. However, they developed an endodermis. Endodermal Casparian bands first appeared as 'dots' as early as at 20 mm from the apex, whereas a patchy suberin lamellae appeared at 60 mm. The endodermal suberin accounted for the total suberin of the roots. The absolute amount in the basal zone was significantly higher than in the apical zone, which was inversely proportional to the Lp r . Comparison of Lp r and Lp c suggested that cell to cell pathways dominate for water transport in roots. However, the calculation of Lp r from Lp c showed that at least 26 % of water transport occurs through the apoplast. Roots had different solute permeabilities ( P sr ) and reflection coefficients ( σ sr ) for the solutes used. The σ sr was below unity for the solutes, which have virtually zero permeability for semi-permeable membranes. Suberized endodermis significantly reduces Lp r of seminal roots. The water and solute transport across barley roots is composite in nature and they do not behave like ideal osmometers. The composite transport model should be extended by adding components arranged in series (cortex, endodermis) in addition to the currently included components arranged in parallel (apoplastic, cell to cell pathways). © The Author 2017. Published by Oxford University Press on behalf of the Annals of Botany Company.

Evaluation of diffuse and preferential flow pathways of infiltrated precipitation and irrigation using oxygen and hydrogen isotopes

NASA Astrophysics Data System (ADS)

Ma, Bin; Liang, Xing; Liu, Shaohua; Jin, Menggui; Nimmo, John R.; Li, Jing

2017-05-01

Subsurface-water flow pathways in three different land-use areas (non-irrigated grassland, poplar forest, and irrigated arable land) in the central North China Plain were investigated using oxygen (18O) and hydrogen (2H) isotopes in samples of precipitation, soils, and groundwater. Soil water in the top 10 cm was significantly affected by both evaporation and infiltration. Water at 10-40 cm depth in the grassland and arable land, and 10-60 cm in poplar forest, showed a relatively short residence time, as a substantial proportion of antecedent soil water was mixed with a 92-mm storm infiltration event, whereas below those depths (down to 150 cm), depleted δ18O spikes suggested that some storm water bypassed the shallow soil layers. Significant differences, in soil-water content and δ18O values, within a small area, suggested that the proportion of immobile soil water and water flowing in subsurface pathways varies depending on local vegetation cover, soil characteristics and irrigation applications. Soil-water δ18O values revealed that preferential flow and diffuse flow coexist. Preferential flow was active within the root zone, independent of antecedent soil-water content, in both poplar forest and arable land, whereas diffuse flow was observed in grassland. The depleted δ18O spikes at 20-50 cm depth in the arable land suggested the infiltration of irrigation water during the dry season. Temporal isotopic variations in precipitation were subdued in the shallow groundwater, suggesting more complete mixing of different input waters in the unsaturated zone before reaching the shallow groundwater.

The Integrated Role of Water Availability, Nutrient Dynamics, and Xylem Hydraulic Dysfunction on Plant Rooting Strategies in Managed and Natural Ecosystems

NASA Astrophysics Data System (ADS)

Mackay, D. S.; Savoy, P.; Pleban, J. R.; Tai, X.; Ewers, B. E.

2015-12-01

Plants adapt or acclimate to changing environments in part by allocating biomass to roots and leaves to strike a balance between water and nutrient uptake requirements on the one hand and growth and hydraulic safety on the other hand. In a recent study examining experimental drought with the TREES model, which couples plant ecophysiology with rhizosphere-and-xylem hydraulics, we hypothesized that the asynchronous nature of soil water availability and xylem repair supported root-to-leaf area (RLA) proportionality that favored long-term survival over short-term carbon gain or water use. To investigate this as a possible general principal of plant adjustment to changing environmental conditions, TREES was modified to allocate carbon to fine and coarse roots organized in ten orders differing in biomass allocated per unit absorbing root area, root lifespan, and total absorbing root area in each of several soil-root zones with depth. The expanded model allowed for adjustment of absorbing root area and rhizosphere volume based on available carbohydrate production and nitrogen (N) availability, resulting in dynamic expansion and contraction of the supply-side of the rhizosphere-plant hydraulics and N uptake capacity in response to changing environmental conditions and plant-environment asynchrony. The study was conducted partly in a controlled experimental setting with six genotypes of a widely grown crop species, Brassica rapa. The implications for forests were investigated in controlled experiments and at Fluxnet sites representing temperate mixed forests, semi-arid evergreen needle-leaf, and Mediterranean biomes. The results showed that the effects of N deficiency on total plant growth was modulated by a relative increase in fine root biomass representing a larger absorbing root volume per unit biomass invested. We found that the total absorbing root area per unit leaf area was consistently lower than that needed to maximize short-term water uptake and carbohydrate gain. Moreover, the acclimated RLA fell within a small range for both crops and trees despite changing environmental conditions, demonstrating an adaptation that was consistent with empiricism on fine roots and thus pointing to a fundamental connection between ecological and hydrological processes.

Growth and development of the root apical meristem.

PubMed

Perilli, Serena; Di Mambro, Riccardo; Sabatini, Sabrina

2012-02-01

A key question in plant developmental biology is how cell division and cell differentiation are balanced to modulate organ growth and shape organ size. In recent years, several advances have been made in understanding how this balance is achieved during root development. In the Arabidopsis root meristem, stem cells in the apical region of the meristem self-renew and produce daughter cells that differentiate in the distal meristem transition zone. Several factors have been implicated in controlling the different functional zones of the root meristem to modulate root growth; among these, plant hormones have been shown to play a main role. In this review, we summarize recent findings regarding the role of hormone signaling and transcriptional networks in regulating root development. Copyright © 2011 Elsevier Ltd. All rights reserved.

The role of deep nitrogen and dynamic rooting profiles on vegetation dynamics and productivity in response to permafrost thaw and climate change in Arctic tundra

NASA Astrophysics Data System (ADS)

Hewitt, R. E.; Helene, G.; Taylor, D. L.; McGuire, A. D.; Mack, M. C.

2017-12-01

The release of permafrost-derived nitrogen (N) has the potential to fertilize tundra vegetation, modulating plant competition, stimulating productivity, and offsetting carbon losses from thawing permafrost. Dynamic rooting, mycorrhizal interactions, and coupling of N availability and root N uptake have been identified as gaps in ecosystem models. As a first step towards understanding whether Arctic plants can access deep permafrost-derived N, we characterized rooting profiles and quantified acquisition of 15N tracer applied at the permafrost boundary by moist acidic tundra plants subjected to almost three decades of warming at Toolik Lake, Alaska. In the ambient control plots the vegetation biomass is distributed between five plant functional types (PFTs): sedges, evergreen and deciduous shrubs, mosses and in lower abundance, forbs. The warming treatment has resulted in the increase of deciduous shrub biomass and the loss of sedges, evergreen shrubs, and mosses. We harvested roots by depth increment down to the top of the permafrost. Roots were classified by size class and PFT. The average thaw depth in the warmed plots was 58.3 cm ± 6.4 S.E., close to 18 cm deeper than the average thaw depth in the ambient plots (40.8 cm ± 1.8 S.E.). Across treatments the deepest rooting species was Rubus chamaemorus (ambient 40.8 cm ± 1.8 S.E., warmed 50.3 cm ± 9.8 S.E.), a non-mycorrhizal forb, followed by Eriophorum vaginatum, a non-mycorrhizal sedge. Ectomycorrhizal deciduous and ericoid mycorrhizal evergreen shrubs were rooted at more shallow depths. Deeply rooted non-mycorrhizal species had the greatest uptake of 15N tracer within 24 hours across treatments. Tracer uptake was greatest for roots of E. vaginatum in ambient plots and R. chamaemorus in warmed plots. Root profiles were integrated into a process-based ecosystem model coupled with a dynamic vegetation model. Functions modeling dynamic rooting profile relative to thaw depth were implemented for each PFT. The goal of the model simulations is to evaluate the relative effect of deep N acquisition and dynamic rooting profile on site level vegetation productivity. This modeling exercise will contribute to more accurate predictions of vegetation change in the Arctic modulated by belowground plant traits and changing soil resources with warming.

A rapid, controlled-environment seedling root screen for wheat correlates well with rooting depths at vegetative, but not reproductive, stages at two field sites

PubMed Central

Watt, M.; Moosavi, S.; Cunningham, S. C.; Kirkegaard, J. A.; Rebetzke, G. J.; Richards, R. A.

2013-01-01

Background and Aims Root length and depth determine capture of water and nutrients by plants, and are targets for crop improvement. Here we assess a controlled-environment wheat seedling screen to determine speed, repeatability and relatedness to performance of young and adult plants in the field. Methods Recombinant inbred lines (RILs) and diverse genotypes were grown in rolled, moist germination paper in growth cabinets, and primary root number and length were measured when leaf 1 or 2 were fully expanded. For comparison, plants were grown in the field and root systems were harvested at the two-leaf stage with either a shovel or a soil core. From about the four-leaf stage, roots were extracted with a steel coring tube only, placed directly over the plant and pushed to the required depth with a hydraulic ram attached to a tractor. Key Results In growth cabinets, repeatability was greatest (r = 0·8, P < 0·01) when the paper was maintained moist and seed weight, pathogens and germination times were controlled. Scanned total root length (slow) was strongly correlated (r = 0·7, P < 0·01) with length of the two longest seminal axile roots measured with a ruler (fast), such that 100–200 genotypes were measured per day. Correlation to field-grown roots at two sites at two leaves was positive and significant within the RILs and cultivars (r = 0·6, P = 0·01), and at one of the two sites at the five-leaf stage within the RILs (r = 0·8, P = 0·05). Measurements made in the field with a shovel or extracted soil cores were fast (5 min per core) and had significant positive correlations to scanner measurements after root washing and cleaning (>2 h per core). Field measurements at two- and five-leaf stages did not correlate with root depth at flowering. Conclusions The seedling screen was fast, repeatable and reliable for selecting lines with greater total root length in the young vegetative phase in the field. Lack of significant correlation with reproductive stage root system depth at the field sites used in this study reflected factors not captured in the screen such as time, soil properties, climate variation and plant phenology. PMID:23821620

High-precision measurements of wetland sediment elevation. II The rod surface elevation table

USGS Publications Warehouse

Cahoon, D.R.; Lynch, J.C.; Perez, B.C.; Segura, B.; Holland, R.D.; Stelly, C.; Stephenson, G.; Hensel, P.

2002-01-01

A new high-precision device for measuring sediment elevation in emergent and shallow water wetland systems is described. The rod surface-elevation table (RSET) is a balanced, lightweight mechanical leveling device that attaches to both shallow ( 1 m in order to be stable. The pipe is driven to refusal but typically to a depth shallower than the rod bench mark because of greater surface resistance of the pipe. Thus, the RSET makes it possible to partition change in sediment elevation over shallower (e.g., the root zone) and deeper depths of the sediment profile than is possible with the SET. The confidence intervals for the height of an individual pin measured by two different operators with the RSET under laboratory conditions were A? 1.0 and A? 1.5 mm. Under field conditions, confidence intervals for the measured height of an individual pin ranged from A? 1.3 mm in a mangrove forest up to A? 4.3 mm in a salt marsh.

[Antimicrobial effect of a new bio-ceramic material iRoot FM on Porphyromonas endodontalis].

PubMed

Bi, Jing; Liu, Yao; Chen, Xu

2017-10-01

To compare the antimicrobial effect of a new bio-ceramic material iRoot FM with traditional intracanal medicaments including calcium hydroxide [Ca(OH) 2 ] and triple antibiotic paste (TAP), on Porphyromonas endodontalis (P. endodontalis), and to evaluate the antimicrobial activity of iRoot FM, providing reference for clinical use of intracanal medicaments. P. endodontalis ATCC 35406 were used in this study. The study was divided into 3 experimental groups including iRoot FM, Ca(OH) 2 and TAP group. Sterile water was used as blank control. Frozen P. endodontalis were seeded and grown overnight in the liquid medium, then P. endodontalis were seeded on BHI-blood agar plates. After the plates were dried, the materials were filled on the plates which were made by a punching machine. Zones of inhibition (mm) were measured after 72 h of anaerobic incubation at 37degrees centigrade. The experimental data were analyzed statistically using SPSS 17.0 software package. The zones of inhibition in the 3 experimental groups: iRoot FM, Ca(OH) 2 and TAP group were (20.74±4.35)mm, (24.89±3.84)mm and (34.51±1.20)mm, respectively. The zones of inhibition of the iRoot FM group and Ca(OH) 2 group were significantly smaller compared with the TAP group (P<0.05), while there was no significant difference between the iRoot FM group and Ca(OH)2 groups (P>0.05). There were no zone of inhibition in the control group. As a new bio-ceramic material, iRoot FM shows a good antimicrobial activity against P. endodontalis and may be a promising intracanal material.

Deep subsurface drip irrigation using coal-bed sodic water: part I. water and solute movement

USGS Publications Warehouse

Bern, Carleton R.; Breit, George N.; Healy, Richard W.; Zupancic, John W.; Hammack, Richard

2013-01-01

Water co-produced with coal-bed methane (CBM) in the semi-arid Powder River Basin of Wyoming and Montana commonly has relatively low salinity and high sodium adsorption ratios that can degrade soil permeability where used for irrigation. Nevertheless, a desire to derive beneficial use from the water and a need to dispose of large volumes of it have motivated the design of a deep subsurface drip irrigation (SDI) system capable of utilizing that water. Drip tubing is buried 92 cm deep and irrigates at a relatively constant rate year-round, while evapotranspiration by the alfalfa and grass crops grown is seasonal. We use field data from two sites and computer simulations of unsaturated flow to understand water and solute movements in the SDI fields. Combined irrigation and precipitation exceed potential evapotranspiration by 300-480 mm annually. Initially, excess water contributes to increased storage in the unsaturated zone, and then drainage causes cyclical rises in the water table beneath the fields. Native chloride and nitrate below 200 cm depth are leached by the drainage. Some CBM water moves upward from the drip tubing, drawn by drier conditions above. Chloride from CBM water accumulates there as root uptake removes the water. Year over year accumulations indicated by computer simulations illustrate that infiltration of precipitation water from the surface only partially leaches such accumulations away. Field data show that 7% and 27% of added chloride has accumulated above the drip tubing in an alfalfa and grass field, respectively, following 6 years of irrigation. Maximum chloride concentrations in the alfalfa field are around 45 cm depth but reach the surface in parts of the grass field, illustrating differences driven by crop physiology. Deep SDI offers a means of utilizing marginal quality irrigation waters and managing the accumulation of their associated solutes in the crop rooting zone.

Phosphorus and other soil components in a dairy effluent sprayfield within the central Florida Ridge.

PubMed

Woodard, Kenneth R; Sollenberger, Lynn E; Sweat, Lewin A; Graetz, Donald A; Nair, Vimala D; Rymph, Stuart J; Walker, Leighton; Joo, Yongsung

2007-01-01

There is concern that P from dairy effluent sprayfields will leach into groundwater beneath Suwannee River basins in northern Florida. Our purpose was to describe the effects of dairy effluent irrigation on the movement of soil P and other nutrients within the upper soil profile of a sprayfield over three 12-mo cycles (April 1998-March 2001). Effluent P rates of 70, 110, and 165 kg ha(-1) cycle(-1) were applied to forages that were grown year-round. The soil is a deep, excessively drained sand (thermic, uncoated Typic Quartzipsamment). Mean P concentration in soil water below the rooting zone (152-cm depth) was < or = 0.1 mg L(-1) during 11 3-mo periods. Mehlich-1-extractable (M1) P, Al, and Ca in the topsoil increased over time but did not change in subsoil depths of 25 to 51, 51 to 71, 71 to 97, and 97 to 122 cm. Topsoil Ca increased as effluent rate increased. High Ca levels were found in dairy effluent (avg.: 305 mg L(-1)) and supplemental irrigation water (avg.: 145 mg L(-1)) which likely played a role in retaining P in the topsoil. An effect of effluent rate on P and Al concentrations in the topsoil was not detected, probably due to large and variable quantities present at project initiation. The P retention capacity (i.e., Al plus Fe) increased in the topsoil because Al increased. Dairy effluent contained Al (avg.: 31 mg L(-1)). Phosphorus saturation ratio (PSR) increased over time in the topsoil but not in subsoil layers. Regardless of effluent rate, the P retention capacity and PSR of subsoil, which contained 119 to 229 mg kg(-1) of Al, should be taken into account when assessing the risk of P moving below the rooting zone of most forage crops.

Nitrate fluxes to groundwater under citrus orchards in a Mediterranean climate: Observations, calibrated models, simulations and agro-hydrological conclusions

NASA Astrophysics Data System (ADS)

Kurtzman, Daniel; Shapira, Roi H.; Bar-Tal, Asher; Fine, Pinchas; Russo, David

2013-08-01

Nitrate contamination of groundwater under land used for intensive-agriculture is probably the most worrisome agro-hydrological sustainability problem worldwide. Vadose-zone samples from 0 to 9 m depth under citrus orchards overlying an unconfined aquifer were analyzed for variables controlling water flow and the fate and transport of nitrogen fertilizers. Steady-state estimates of water and NO3-N fluxes to groundwater were found to vary spatially in the ranges of 90-330 mm yr- 1 and 50-220 kg ha- 1 yr- 1, respectively. Calibration of transient models to two selected vadose-zone profiles required limiting the concentration of NO3-N in the solution that is taken up by the roots to 30 mg L- 1. Results of an independent lysimeter experiment showed a similar nitrogen-uptake regime. Simulations of past conditions revealed a significant correlation between NO3-N flux to groundwater and the previous year's precipitation. Simulations of different nitrogen-application rates showed that using half of the nitrogen fertilizer added to the irrigation water by farmers would reduce average NO3-N flux to groundwater by 70%, decrease root nitrogen uptake by 20% and reduce the average pore water NO3-N concentration in the deep vadose zone to below the Israeli drinking water standard; hence this rate of nitrogen application was found to be agro-hydrologically sustainable. Beyond the investigation of nitrate fluxes to groundwater under citrus orchards and the interesting case-study aspects, this work demonstrates a methodology that enables skillful decisions concerning joint sustainability of both the water resource and agricultural production in a common environmental setting.

Calibration of the Root Zone Water Quality Model and Application of Data Assimilation Techniques to Estimate Profile Soil Moisture

USDA-ARS?s Scientific Manuscript database

Estimation of soil moisture has received considerable attention in the areas of hydrology, agriculture, meteorology and environmental studies because of its role in the partitioning water and energy at the land surface. In this study, the USDA, Agricultural Research Service, Root Zone Water Quality ...

Root Zone Water Quality Model (RZWQM2): Model use, calibration, and validation

USDA-ARS?s Scientific Manuscript database

The Root Zone Water Quality Model (RZWQM2) has been used widely for simulating agricultural management effects on crop production and soil and water quality. Although it is a one-dimensional model it has many desirable features for the modeling community. This paper outlines the principles of calibr...

76 FR 10569 - Request for Comments on the Internet Assigned Numbers Authority (IANA) Functions

Federal Register 2010, 2011, 2012, 2013, 2014

2011-02-25

... responsibilities associated with Internet DNS root zone management; (3) the allocation of Internet numbering resources; and (4) other services related to the management of the .ARPA and .INT top- level domains. The... responsibilities associated with Internet DNS root zone management; (3) the allocation of Internet numbering...

Multi-decadal analysis of root-zone soil moisture applying the exponential filter across CONUS

USDA-ARS?s Scientific Manuscript database

his study applied the exponential filter to produce an estimate of root-zone soil moisture (RZSM). Four types of microwave-based, surface satellite soil moisture were used. The core remotely sensed data for this study came from NASA’s long lasting AMSR-E mission. Additionally three other products we...

Persistence and memory timescales in root-zone soil moisture dynamics

Treesearch

Khaled Ghannam; Taro Nakai; Athanasios Paschalis; Andrew C. Oishi; Ayumi Kotani; Yasunori Igarashi; Tomo' omi Kumagai; Gabriel G. Katul

2016-01-01

The memory timescale that characterizes root-zone soil moisture remains the dominant measure in seasonal forecasts of land-climate interactions. This memory is a quasi-deterministic timescale associated with the losses (e.g., evapotranspiration) from the soil column and is often interpreted as persistence in soil moisture states. Persistence, however,...

Root biomass, turnover and net primary productivity of a coffee agroforestry system in Costa Rica: effects of soil depth, shade trees, distance to row and coffee age

PubMed Central

Defrenet, Elsa; Roupsard, Olivier; Van den Meersche, Karel; Charbonnier, Fabien; Pastor Pérez-Molina, Junior; Khac, Emmanuelle; Prieto, Iván; Stokes, Alexia; Roumet, Catherine; Rapidel, Bruno; de Melo Virginio Filho, Elias; Vargas, Victor J.; Robelo, Diego; Barquero, Alejandra; Jourdan, Christophe

2016-01-01

Background and Aims In Costa Rica, coffee (Coffea arabica) plants are often grown in agroforests. However, it is not known if shade-inducing trees reduce coffee plant biomass through root competition, and hence alter overall net primary productivity (NPP). We estimated biomass and NPP at the stand level, taking into account deep roots and the position of plants with regard to trees. Methods Stem growth and root biomass, turnover and decomposition were measured in mixed coffee/tree (Erythrina poeppigiana) plantations. Growth ring width and number at the stem base were estimated along with stem basal area on a range of plant sizes. Root biomass and fine root density were measured in trenches to a depth of 4 m. To take into account the below-ground heterogeneity of the agroforestry system, fine root turnover was measured by sequential soil coring (to a depth of 30 cm) over 1 year and at different locations (in full sun or under trees and in rows/inter-rows). Allometric relationships were used to calculate NPP of perennial components, which was then scaled up to the stand level. Key Results Annual ring width at the stem base increased up to 2·5 mm yr−1 with plant age (over a 44-year period). Nearly all (92 %) coffee root biomass was located in the top 1·5 m, and only 8 % from 1·5 m to a depth of 4 m. Perennial woody root biomass was 16 t ha−1 and NPP of perennial roots was 1·3 t ha−1 yr−1. Fine root biomass (0–30 cm) was two-fold higher in the row compared with between rows. Fine root biomass was 2·29 t ha−1 (12 % of total root biomass) and NPP of fine roots was 2·96 t ha−1 yr−1 (69 % of total root NPP). Fine root turnover was 1·3 yr−1 and lifespan was 0·8 years. Conclusions Coffee root systems comprised 49 % of the total plant biomass; such a high ratio is possibly a consequence of shoot pruning. There was no significant effect of trees on coffee fine root biomass, suggesting that coffee root systems are very competitive in the topsoil. PMID:27551026

[Root system distribution and biomechanical characteristics of Bambusa oldhami].

PubMed

Zhou, Ben-Zhi; Xu, Sheng-Hua; An, Yan-Fei; Xu, Sheng-Hua

2014-05-01

To determine the mechanism of soil stabilizing through Bambusa oldhami root system, the vertical distribution of B. oldhami root system in soil was investigated, and the tensile strength of individual root and soil shear strength were measured in B. oldhami forest. The dry mass, length, surface area and volume of the B. oldhami root system decreased with the increasing soil depth, with more than 90% of the root system occurring in the 0-40 cm soil layer. The root class with D 1 mm occupied the highest percentage of the total in terms of root length, accounting for 79.6%, but the lowest percentage of the total in terms of root volume, accounting for 8.2%. The root class with D >2 mm was the opposite, and the root class with D= 1-2 mm stayed in between. The maximum tensile resistance of B. oldhami root, either with 12% moisture content or a saturated moisture content, increased with the increasing root diameter, while the tensile strength decreased with the increasing root diameter in accordance with power function. Tensile strength of the root, with either of the two moisture contents, was significantly different among the diameter classes, with the highest tensile strength occurring in the root with D < or = 1 mm and the lowest in the root with D > or = 2 mm. The tensile strength of root with 12% moisture content was significantly higher than that with the saturated moisture content, and less effect of moisture content on root tensile strength would occur in thicker roots. The shear strengths of B. oldhami forest soil and of bare soil both increased with the increasing soil depth. The shear strength of B. oldhami forest soil had a linear positive correlation with the root content in soil, and was significantly higher than that of bare soil. The shear strength increment in B. oldhami forest was positively correlated with the root content in soil according to an exponential function, but not related significantly with soil depth.

Time-lapse 3D electrical resistivity tomography to monitor soil-plant interactions

NASA Astrophysics Data System (ADS)

Boaga, Jacopo; Rossi, Matteo; Cassiani, Giorgio; Putti, Mario

2013-04-01

In this work we present the application of time-lapse non-invasive 3D micro- electrical tomography (ERT) to monitor soil-plant interactions in the root zone in the framework of the FP7 Project CLIMB (Climate Induced Changes on the Hydrology of Mediterranean Basins). The goal of the study is to gain a better understanding of the soil-vegetation interactions by the use of non-invasive techniques. We designed, built and installed a 3D electrical tomography apparatus for the monitoring of the root zone of a single apple tree in an orchard located in the Trentino region, Northern Italy. The micro-ERT apparatus consists of 48 buried electrodes on 4 instrumented micro boreholes plus 24 mini-electrodes on the surface spaced 0.1 m on a square grid. We collected repeated ERT and TDR soil moisture measurements for one year and performed two different controlled irrigation tests: one during a very dry Summer and one during a very wet and highly dynamic plant growing Spring period. We also ran laboratory analyses on soil specimens, in order to evaluate the electrical response at different saturation steps. The results demonstrate that 3D micro-ERT is capable of characterizing subsoil conditions and monitoring root zone activities, especially in terms of root zone suction regions. In particular, we note that in very dry conditions, 3D micro ERT can image water plumes in the shallow subsoil produced by a drip irrigation system. In the very dynamic growing season, under abundant irrigation, micro 3D ERT can detect the main suction zones caused by the tree root activity. Even though the quantitative use of this technique for moisture content balance suffers from well-known inversion difficulties, even the pure imaging of the active root zone is a valuable contribution. However the integration of the measurements in a fully coupled hydrogeophysical inversion is the way forward for a better understanding of subsoil interactions between biomass, hydrosphere and atmosphere.

Tracing the influence of the Trans-European Suture Zone into the mantle transition zone

NASA Astrophysics Data System (ADS)

Knapmeyer-Endrun, Brigitte; Krüger, Frank; Legendre, Cedric P.; Geissler, Wolfram H.

2013-04-01

Cratons with their thick lithospheric roots can influence the thermal structure, and thus the convective flow, in the surrounding mantle. As mantle temperatures are hard to measure directly, depth variations in the mantle transition zone (MTZ) discontinuities are often employed as a proxy. Here, we use a large new data set of P-receiver functions to map the 410 km and 660 km discontinuities beneath the western edge of the East European Craton and adjacent Phanerozoic Europe across the most fundamental lithospheric boundary in Europe, the Trans-European Suture Zone (TESZ). We observe significantly shorter travel times for conversions from both MTZ discontinuities within the craton, caused by the high velocities of the cratonic root. By contrast, the differential travel time across the MTZ is normal to only slightly raised. This implies that any insulating effect of the cratonic keel does not reach the MTZ. In contrast to earlier observations in Siberia, we do not find any trace of a discontinuity at 520 km depth, which indicates a rather dry MTZ beneath the western edge of the craton. Within most of covered Phanerozoic Europe, the MTZ differential travel time is remarkably uniform and in agreement with standard Earth models. No widespread thermal effects of the various episodes of Caledonian and Variscan subduction that took place during the amalgamation of the continent remain. Only more recent tectonic events, related to Alpine subduction and Quarternary volcanism in the Eifel area, can be traced. While the East European craton shows no distinct imprint into the MTZ, we discover the signature of the TESZ in the MTZ in the form of a linear region of about 350 km width with a 1.5 s increase in differential travel time, which could either be caused by high water content or decreased temperature. Taking into account results of recent S-wave tomographies, raised water content in the MTZ cannot be the main cause for this observation. Accordingly, we explain the increase, equivalent to a 15 km thicker MTZ, by a temperature decrease of about 80 K. We discuss two alternative models for this temperature reduction, either a remnant of subduction or an indication of downwelling due to small-scale, edge-driven convection caused by the contrast in lithospheric thickness across the TESZ. We consider an explanation by an ancient subducted slab in the MTZ more unlikely, though, as Eurasia has moved significantly northward since the Variscan orogeny, the last major episode of subduction in the area.

Tracing the influence of the Trans-European Suture Zone into the mantle transition zone

NASA Astrophysics Data System (ADS)

Knapmeyer-Endrun, B.; Krüger, F.; Legendre, C. P.; Geissler, W. H.; PASSEQ Working Group; Wilde-Piórko, M.; Geissler, W. H.; Plomerová, J.; Grad, M.; Babuška, V.; Brückl, E.; Cyziene, J.; Czuba, W.; England, R.; Gaczyński, E.; Gazdova, R.; Gregersen, S.; Guterch, A.; Hanka, W.; Hegedüs, E.; Heuer, B.; Jedlička, P.; Lazauskiene, J.; Keller, G. R.; Kind, R.; Klinge, K.; Kolinsky, P.; Komminaho, K.; Kozlovskaya, E.; Krüger, F.; Larsen, T.; Majdański, M.; Malek, J.; Motuza, G.; Novotný, O.; Pietrasiak, R.; Plenefisch, T.; Růžek, B.; Sliaupa, S.; Środa, P.; Świeczak, M.; Tiira, T.; Voss, P.; Wiejacz, P.

2013-02-01

Cratons with their thick lithospheric roots can influence the thermal structure, and thus the convective flow, in the surrounding mantle. As mantle temperatures are hard to measure directly, depth variations in the mantle transition zone (MTZ) discontinuities are often employed as a proxy. Here, we use a large new data set of P-receiver functions to map the 410 km and 660 km discontinuities beneath the western edge of the East European Craton and adjacent Phanerozoic Europe across the most fundamental lithospheric boundary in Europe, the Trans-European Suture Zone (TESZ). We observe significantly shorter travel times for conversions from both MTZ discontinuities within the craton, caused by the high velocities of the cratonic root. By contrast, the differential travel time across the MTZ is normal to only slightly raised. This implies that any insulating effect of the cratonic keel does not reach the MTZ. In contrast to earlier observations in Siberia, we do not find any trace of a discontinuity at 520 km depth, which indicates a rather dry MTZ beneath the western edge of the craton. Within most of covered Phanerozoic Europe, the MTZ differential travel time is remarkably uniform and in agreement with standard Earth models. No widespread thermal effects of the various episodes of Caledonian and Variscan subduction that took place during the amalgamation of the continent remain. Only more recent tectonic events, related to Alpine subduction and Quarternary volcanism in the Eifel area, can be traced. While the East European craton shows no distinct imprint into the MTZ, we discover the signature of the TESZ in the MTZ in the form of a linear region of about 350 km width with a 1.5 s increase in differential travel time, which could either be caused by high water content or decreased temperature. Taking into account results of recent S-wave tomographies, raised water content in the MTZ cannot be the main cause for this observation. Accordingly, we explain the increase, equivalent to a 15 km thicker MTZ, by a temperature decrease of about 80 K. We discuss two alternative models for this temperature reduction, either a remnant of subduction or an indication of downwelling due to small-scale, edge-driven convection caused by the contrast in lithospheric thickness across the TESZ. Any subducted lithosphere found in the MTZ at this location is unlikely to be related to Variscan subduction along the TESZ, though, as Eurasia has moved significantly northward since the Variscan orogeny.

Salt and N leaching and soil accumulation due to cover cropping practices

NASA Astrophysics Data System (ADS)

Gabriel, J. L.; Quemada, M.

2012-04-01

Nitrate leaching beyond the root zone can increase water contamination hazards and decrease crop available N. Cover crops used in spite of fallow are an alternative to reduce nitrate contamination in the vadose zone, because reducing drainage and soil mineral N accumulation. Cover crops can improve important characteristics in irrigated land as water retention capacity or soil aggregate stability. However, increasing evapotranspiration and consequent drainage below the root system reduction, could lead to soil salt accumulation. Salinity affects more than 80 million ha of arable land in many areas of the world, and one of the principal causes for yield reduction and even land degradation in the Mediterranean region. Few studies dealt with both problems at the same time. Therefore, it is necessary a long-term evaluation of the potential effect on soil salinity and nitrate leaching, in order to ensure that potential disadvantages that could originate from soil salt accumulation are compensated with all advantages of cover cropping. A study of the soil salinity and nitrate leaching was conducted during 4 years in a semiarid irrigated agricultural area of Central Spain. Three treatments were studied during the intercropping period of maize (Zea mays L.): barley (Hordeum vulgare L.), vetch (Vicia villosa L.) and fallow. Cover crops were killed in March allowing seeding of maize of the entire trial in April, and all treatments were irrigated and fertilised following the same procedure. Before sowing, and after harvesting maize and cover crops, soil salt and nitrate accumulation was determined along the soil profile. Soil analysis was conducted at six depths every 0.20 m in each plot in samples from four 0 to 1.2-m depth holes dug. The electrical conductivity of the saturated paste extract and soil mineral nitrogen was measured in each soil sample. A numerical model based on the Richards water balance equation was applied in order to calculate drainage at 1.2 m depth, using daily soil water content measurements, based on calibrated capacitance probes. Our results showed that drainage during the irrigated period was minimized, because irrigation water was adjusted to crop needs, leading to soil salt and nitrate accumulation on the upper layers after maize harvest. Then, during the intercrop period, most of salt and nitrate leaching occurred. Cover crops use led to shorter drainage period, lower drainage water amount and lower nitrate and salt leaching than treatment with fallow. These effects were related with a larger nitrate accumulation in the upper layers of the soil after cover crop treatments. But there was not soil salt accumulation increase in treatments with cover crops, and even decreased after years with a large cover crop biomass production. Then, adoption of cover crops in this kind of irrigated cropping system reduced water drainage beyond the root zone, salt and nitrate leaching diminished as a consequence but did not lead to salt accumulation in the upper soil layers. Acknowledgements: Financial support by CICYT, Spain (ref. AGL2005-00163 and AGL 2011-24732) and Comunidad de Madrid (project AGRISOST, S2009/AGR-1630).

Copper regulates primary root elongation through PIN1-mediated auxin redistribution.

PubMed

Yuan, Hong-Mei; Xu, Heng-Hao; Liu, Wen-Cheng; Lu, Ying-Tang

2013-05-01

The heavy metal copper (Cu) is an essential microelement required for normal plant growth and development, but it inhibits primary root growth when in excess. The mechanism underlying how excess Cu functions in this process remains to be further elucidated. Here, we report that a higher concentration of CuSO4 inhibited primary root elongation of Arabidopsis seedlings by affecting both the elongation and meristem zones. In the meristem zone, meristematic cell division potential was reduced by excess Cu. Further experiments showed that Cu can modulate auxin distribution, resulting in higher auxin activities in both the elongation and meristem zones of Cu-treated roots based on DR5::GUS expression patterns. This Cu-mediated auxin redistribution was shown to be responsible for Cu-mediated inhibition of primary root elongation. Additional genetic and physiological data demonstrated that it was PINFORMED1 (PIN1), but not PIN2 or AUXIN1 (AUX1), that regulated this process. However, Cu-induced hydrogen peroxide accumulation did not contribute to Cu-induced auxin redistribution for inhibition of root elongation. When the possible role of ethylene in this process was analyzed, Cu had a similar impact on the root elongation of both the wild type and the ein2-1 mutant, implying that Cu-mediated inhibition of primary root elongation was not due to the ethylene signaling pathway.

Shallow depth of seismogenic coupling in southern Mexico: implications for the maximum size of earthquakes in the subduction zone

NASA Astrophysics Data System (ADS)

Suárez, Gerardo; Sánchez, Osvaldo

1996-01-01

Studies of locally recorded microearthquakes and the centroidal depths of the largest earthquakes analyzed using teleseismic data show that the maximum depth of thrust faulting along the Mexican subduction zone is anomalously shallow. This observed maximum depth of about 25 ± 5 km is about half of that observed in most subduction zones of the world. A leveling line that crosses the rupture zone of the 19 September 1985 Michoacan event was revisited after the earthquake and it shows anomalously low deformation during the earthquake. The comparison between the observed coseismic uplift and dislocation models of the seismogenic interplate contact that extend to depths ranging from 20 to 40 km shows that the maximum depth at which seismic slip took place is about 20 km. This unusually shallow and narrow zone of seismogenic coupling apparently results in the occurrence of thrust events along the Mexican subduction zone that are smaller than would be expected for a trench where a relatively young slab subducts at a rapid rate of relative motion. A comparison with the Chilean subduction zone shows that the plate interface in Mexico is half that in Chile, not only in the down-dip extent of the seismogenic zone of plate contact, but also in the distance of the trench from the coast and in the thickness of the upper continental plate. It appears that the narrow plate contact produced by this particular plate geometry in Mexico is the controlling variable defining the size of the largest characteristic earthquakes in the Mexican subduction zone.

Biogeochemical Cycling of Iron and Phosphorous in Deep Saprolite

NASA Astrophysics Data System (ADS)

Buss, H. L.; Bruns, M. A.; Williams, J. Z.; White, A. F.; Brantley, S. L.

2006-12-01

Few microbiological studies have been conducted within the unsaturated zones between rooting depth and bedrock and thus the relationships between biological activity and mineral nutrient cycling in deep regolith are poorly understood. Here we investigate the weathering of primary minerals containing iron (hornblende and biotite) and phosphorous (apatite) and the role of resident microorganisms in the cycling of these elements in the deep saprolite of the Rio Icacos watershed in Puerto Rico's Luquillo Mountains. In the Rio Icacos watershed, which has one of the fastest documented chemical weathering rates of granitic rock in the world, the quartz diorite bedrock weathers spheroidally, producing a complex interface comprised of partially weathered rock layers called rindlets. This rindlet zone (0.2-2 m thick) is overlain by saprolite (2-8 m) topped by soil (0.5-1 m). With the objective of understanding interactions among mineral weathering, substrate availability and resident microorganisms, we made geochemical and microbiological measurements as a function of depth in 5 m of regolith (soil + saprolite) and examined mineral weathering reactions within a 0.5 m thick spheroidally weathering rindlet zone. We measured total cell densities, culturable aerobic chemoorganotrophs, and microbial DNA yields; and performed biochemical tests for iron-oxidizing bacteria in the regolith samples. Total cell densities, which ranged from 2.5 x 106 to 1.6 x 1010 g-1 regolith, were higher than 108 g-1 at three depths: in the upper 1 m, at 2.1 m, and between 3.7-4.9 m, just above the rindlet zone. Biochemical tests for aerobic iron-oxidizers were also positive at 0.15-0.6 m, at 2.1-2.4 m, and at 4.9 m depths. High proportions of inactive or unculturable cells were indicated throughout the profile by very low percentages of culturable chemoorganotrophs. The observed increases in total and culturable cells and DNA yields at lower depths were correlated with an increase in HCl-extractable Fe in the deep saprolite and coincided with decreases in mineral bound iron and phosphorous due to hornblende and apatite weathering, respectively. Within a 0.07 m zone spanning the rindlet-saprolite interface, we documented the fastest rate of hornblende dissolution in the field ever reported: 6.0 x 10^{-13 mol m-2 s-1. To interpret microbial populations within the context of weathering reactions, we developed a model for estimating growth rates of lithoautotrophs and chemoorganotrophs based on measured substrate fluxes. The calculations and observations are consistent with a model wherein electron donor flux driving bacterial growth at the saprolite-bedrock interface is dominated by the rapid release of Fe(II) during hornblende dissolution and where fixation of CO2 by autotrophic iron-oxidizing bacteria supports growth of chemoorganotrophic bacteria. Apatite weathering, which is the primary source of phosphorous to the deep saprolite ecosystem, occurs at a rate of 4.7 x 10^{-15} mol m-2 s-1 within the rindlet zone. Further measurements of phosphorous within the saprolite are underway and the influence of the phosphorous flux on the lithoautotrophic and chemoorganotrophic growth rates in the deep saprolite will be presented.

Root growth regulation and gravitropism in maize roots does not require the epidermis

NASA Technical Reports Server (NTRS)

Bjorkman, T.; Cleland, R. E.

1991-01-01

We have earlier published observations showing that endogenous alterations in growth rate during gravitropism in maize roots (Zea mays L.) are unaffected by the orientation of cuts which remove epidermal and cortical tissue in the growing zone (Bjorkman and Cleland, 1988, Planta 176, 513-518). We concluded that the epidermis and cortex are not essential for transporting a growth-regulating signal in gravitropism or straight growth, nor for regulating the rate of tissue expansion. This conclusion has been challenged by Yang et al. (1990, Planta 180, 530-536), who contend that a shallow girdle around the entire perimeter of the root blocks gravitropic curvature and that this inhibition is the result of a requirement for epidermal cells to transport the growth-regulating signal. In this paper we demonstrate that the entire epidermis can be removed without blocking gravitropic curvature and show that the position of narrow girdles does not affect the location of curvature. We therefore conclude that the epidermis is not required for transport of a growth-regulating substance from the root cap to the growing zone, nor does it regulate the growth rate of the elongating zone of roots.

Soil-water content characterisation in a modified Jarvis-Stewart model: A case study of a conifer forest on a shallow unconfined aquifer

NASA Astrophysics Data System (ADS)

Guyot, Adrien; Fan, Junliang; Oestergaard, Kasper T.; Whitley, Rhys; Gibbes, Badin; Arsac, Margaux; Lockington, David A.

2017-01-01

Groundwater-vegetation-atmosphere fluxes were monitored for a subtropical coastal conifer forest in South-East Queensland, Australia. Observations were used to quantify seasonal changes in transpiration rates with respect to temporal fluctuations of the local water table depth. The applicability of a Modified Jarvis-Stewart transpiration model (MJS), which requires soil-water content data, was assessed for this system. The influence of single depth values compared to use of vertically averaged soil-water content data on MJS-modelled transpiration was assessed over both a wet and a dry season, where the water table depth varied from the surface to a depth of 1.4 m below the surface. Data for tree transpiration rates relative to water table depth showed that trees transpire when the water table was above a threshold depth of 0.8 m below the ground surface (water availability is non-limiting). When the water table reached the ground surface (i.e., surface flooding) transpiration was found to be limited. When the water table is below this threshold depth, a linear relationship between water table depth and the transpiration rate was observed. MJS modelling results show that the influence of different choices for soil-water content on transpiration predictions was insignificant in the wet season. However, during the dry season, inclusion of deeper soil-water content data improved the model performance (except for days after isolated rainfall events, here a shallower soil-water representation was better). This study demonstrated that, to improve MJS simulation results, appropriate selection of soil water measurement depths based on the dynamic behaviour of soil water profiles through the root zone was required in a shallow unconfined aquifer system.

Mathematical model of mass transfer at electron beam treatment

NASA Astrophysics Data System (ADS)

Konovalov, Sergey V.; Sarychev, Vladimir D.; Nevskii, Sergey A.; Kobzareva, Tatyana Yu.; Gromov, Victor E.; Semin, Alexander P.

2017-01-01

The paper proposes a model of convective mass transfer at electron beam treatment with beams in titanium alloys subjected to electro-explosion alloying by titanium diboride powder. The proposed model is based on the concept that treatment with concentrated flows of energy results in the initiation of vortices in the melted layer. The formation mechanism of these vortices rooted in the idea that the availability of temperature drop leads to the initiation of the thermo-capillary convection. For the melted layer of metal the equations of the convective heat transfer and boundary conditions in terms of the evaporated material are written. The finite element solution of these equations showed that electron-beam treatment results in the formation of multi-vortex structure that in developing captures all new areas of material. It leads to the fact that the strengthening particles are observed at the depth increasing many times the depth of their penetration according to the diffusion mechanism. The distribution of micro-hardness at depth and the thickness of strengthening zone determined from these data supported the view that proposed model of the convective mass transfer describes adequately the processes going on in the treatment with low-energy high-current electron beam.

Subduction zone seismicity and the thermo-mechanical evolution of downgoing lithosphere

NASA Astrophysics Data System (ADS)

Wortel, M. J. R.; Vlaar, N. J.

1988-09-01

In this paper we discuss characteristic features of subduction zone seismicity at depths between about 100 km and 700 km, with emphasis on the role of temperature and rheology in controlling the deformation of, and the seismic energy release in downgoing lithosphere. This is done in two steps. After a brief review of earlier developments, we first show that the depth distribution of hypocentres at depths between 100 km and 700 km in subducted lithosphere can be explained by a model in which seismic activity is confined to those parts of the slab which have temperatures below a depth-dependent critical value T cr. Second, the variation of seismic energy release (frequency of events, magnitude) with depth is addressed by inferring a rheological evolution from the slab's thermal evolution and by combining this with models for the system of forces acting on the subducting lithosphere. It is found that considerable stress concentration occurs in a reheating slab in the depth range of 400 to 650 700 km: the slab weakens, but the stress level strongly increases. On the basis of this stress concentration a model is formulated for earthquake generation within subducting slabs. The model predicts a maximum depth of seismic activity in the depth range of 635 to 760 km and, for deep earthquake zones, a relative maximum in seismic energy release near the maximum depth of earthquakes. From our modelling it follows that, whereas such a maximum is indeed likely to develop in deep earthquake zones, zones with a maximum depth around 300 km (such as the Aleutians) are expected to exhibit a smooth decay in seismic energy release with depth. This is in excellent agreement with observational data. In conclusion, the incoroporation of both depth-dependent forces and depth-dependent rheology provides new insight into the generation of intermediate and deep earthquakes and into the variation of seismic activity with depth. Our results imply that no barrier to slab penetration at a depth of 650 700 km is required to explain the maximum depth of seismic activity and the pattern of seismic energy release in deep earthquake zones.

Integrated method of RS and GPR for monitoring the changes in the soil moisture and groundwater environment due to underground coal mining

NASA Astrophysics Data System (ADS)

Bian, Zhengfu; Lei, Shaogang; Inyang, Hilary I.; Chang, Luqun; Zhang, Richen; Zhou, Chengjun; He, Xiao

2009-03-01

Mining affects the environment in different ways depending on the physical context in which the mining occurs. In mining areas with an arid environment, mining affects plants’ growth by changing the amount of available water. This paper discusses the effects of mining on two important determinants of plant growth—soil moisture and groundwater table (GWT)—which were investigated using an integrated approach involving a field sampling investigation with remote sensing (RS) and ground-penetrating radar (GPR). To calculate and map the distribution of soil moisture for a target area, we initially analyzed four models for regression analysis between soil moisture and apparent thermal inertia and finally selected a linear model for modeling the soil moisture at a depth 10 cm; the relative error of the modeled soil moisture was about 6.3% and correlation coefficient 0.7794. A comparison of mined and unmined areas based on the results of limited field sampling tests or RS monitoring of Landsat 5-thermatic mapping (TM) data indicated that soil moisture did not undergo remarkable changes following mining. This result indicates that mining does not have an effect on soil moisture in the Shendong coal mining area. The coverage of vegetation in 2005 was compared with that in 1995 by means of the normalized difference vegetation index (NDVI) deduced from TM data, and the results showed that the coverage of vegetation in Shendong coal mining area has improved greatly since 1995 because of policy input RMB¥0.4 per ton coal production by Shendong Coal Mining Company. The factor most affected by coal mining was GWT, which dropped from a depth of 35.41 m before mining to a depth of 43.38 m after mining at the Bulianta Coal Mine based on water well measurements. Ground-penetrating radar at frequencies of 25 and 50 MHz revealed that the deepest GWT was at about 43.4 m. There was a weak water linkage between the unsaturated zone and groundwater, and the decline of water table primarily resulted from the well pumping for mining safety rather than the movement of cracking strata. This result is in agreement with the measurements of the water wells. The roots of nine typical plants in the study area were investigated. Populus was found to have the deepest root system with a depth of about 26 m. Based on an assessment of plant growth demands and the effect of mining on environmental factors, we concluded that mining will have less of an effect on plant growth at those sites where the primary GWT depth before mining was deep enough to be unavailable to plants. If the primary GWT was available for plant growth before mining, especially to those plants with deeper roots, mining will have a significant effect on the growth of plants and the mechanism of this effect will include the loss of water to roots and damage to the root system.

Rooting Depths of Red Maple (Acer Rubrum L.) on Various Sites in the Lake States

Treesearch

Carl L. Haag; James E. Johnson; Gayne G. Erdmann

1989-01-01

Rooting depth and habit of red maple were observed on 60 sites in northern Wisconsin and Michigan as part of a regional soil-site studay. Vertical woody root extension on dry, outwash sites averaged 174 cm, which was significantly greater than the extension on sites with fragipans (139 cm) and on wet sites (112 cm). Site index was higher on wet sites and non-woody...

Root Induced Heterogeneity In Agricultural Soils

NASA Astrophysics Data System (ADS)

Gomes, C.; Gabai, R.; Weisbrod, N.; Furman, A.

2012-12-01

In this study we investigate the role of plant induced heterogeneity on water dynamics in agricultural soils. We conducted three experiments in two sites (one still ongoing) in which a trench was excavated in the root zone of an orchard and the subsurface, to a depth of over 1 m, was instrumented in high resolution with water content, water potential and temperature sensors. High temporal resolution monitoring of soil state was carried for over a year, period that included natural (Mediterranean) climate boundary forcing. In addition, sprinkler, flood, and spray irrigation boundary conditions were forced for short time periods to explore the infiltration process under these conditions. One site was an Avocado orchard planted in red sandy soil while the other, still on-going, is in a grape vineyards irrigated by tap and treated wastewater, planted over alluvial clayey soil. In the vineyard, we are comparing soil irrigated with fresh water to soil irrigated with treated waste water for more than 10 years. Our preliminary results indicate several interesting phenomena. First, the role of plant roots is clearly seen as the major roots act as a conduit for water (and solute), providing a fast bypass of the upper soil. Further, we identified different regions of the subsurface that apparently were of the same texture, but in practice presented very different hydraulic properties. Second, the role of these roots depends on the boundary conditions. That is, the root bypass acts differently when soil is flooded than when flow is strictly unsaturated. As expected, simulation of the experimental results show good fit only if the domain heterogeneity of soil properties was incorporated. Results for the clayey soils were not available at time of abstract submission.

Landslide initiation in saprolite and colluvium in southern Brazil: Field and laboratory observations

NASA Astrophysics Data System (ADS)

Lacerda, Willy A.

2007-06-01

The weathering of granitic and gneissic rocks in tropical regions can reach depths of more than 100 m. In southeast Brazil there are situations where landslide initiation depends on the fluctuation of the groundwater level, on the impact of falling rocks and on intense rainfall, causing superficial slides. The fluctuation of groundwater induces cyclical variations of the pore water pressure, and consequently of the effective stresses. This variation causes cyclic expansion and contraction of the structure of the saprolitic soil, weakening the imbrication of grains and loss of the cementation that may exist. This could be called a "fatigue" phenomenon. The practical effect is the lowering of the Mohr shear strength envelope, and a sudden rupture of the soil at a lower groundwater level than that which would be compatible with the intact soil strength properties, initiating a landslide. Another situation arises during intense rains, when a rock slab or a rock block detaches from the uppermost parts of a slope. This occurs where steep rock outcrops exhibit relief joints or where residual blocks of granite roll down the slope, impacting the compressible, saturated colluvial soil overlying the saprolitic soil. The sudden increase of pore pressure can liquefy the soil. Finally, another mechanism is that of the advance of a saturation front in a steep slope of unsaturated saprolitic soil, reaching a depth below the root zone. The loss of the cohesion due to suction, without the beneficial contribution of the roots to the shearing strength, causes a sudden slide. During extreme rain episodes literally hundreds of such superficial slides, reaching 1 to 3 m in depth, occur in a given basin. The concentrated runoff that flows along the surface of the thalweg of the basin carries this soil in a muddy state, and a debris flow ensues.

Helioseismic Constraints on the Depth Dependence of Large-Scale Solar Convection

NASA Astrophysics Data System (ADS)

Woodard, Martin F.

2017-08-01

A recent helioseismic statistical waveform analysis of subsurface flow based on a 720-day time series of SOHO/MDI Medium-l spherical-harmonic coefficients has been extended to cover a greater range of subphotospheric depths. The latest analysis provides estimates of flow-dependent oscillation-mode coupling-strength coefficients b(s,t;n,l) over the range l = 30 to 150 of mode degree (angular wavenumber) for solar p-modes in the approximate frequency range 2 to 4 mHz. The range of penetration depths of this mode set covers most of the solar convection zone. The most recent analysis measures spherical harmonic (s,t) components of the flow velocity for odd s in the angular wavenumber range 1 to 19 for t not much smaller than s at a given s. The odd-s b(s,t;n,l) coefficients are interpreted as averages over depth of the depth-dependent amplitude of one spherical-harmonic (s,t) component of the toroidal part of the flow velocity field. The depth-dependent weighting function defining the average velocity is the fractional kinetic energy density in radius of modes of the (n,l) multiplet. The b coefficients have been converted to estimates of root velocity power as a function of l0 = nu0*l/nu(n,l), which is a measure of mode penetration depth. (nu(n,l) is mode frequency and nu0 is a reference frequency equal to 3 mHz.) A comparison of the observational results with simple convection models will be presented.

Pilot-scale in situ bioremediation of HMX and RDX in soil pore water in Hawaii.

PubMed

Payne, Zachary M; Lamichhane, Krishna M; Babcock, Roger W; Turnbull, Stephen J

2013-10-01

A nine-month in situ bioremediation study was conducted in Makua Military Reservation (MMR) in Oahu, Hawaii (USA) to evaluate the potential of molasses to enhance biodegradation of royal demolition explosive (RDX) and high-melting explosive (HMX) contaminated soil below the root zone. MMR has been in operation since the 1940's resulting in subsurface contamination that in some locations exceeds USEPA preliminary remediation goals for these chemicals. A molasses-water mixture (1 : 40 dilution) was applied to a treatment plot and clean water was applied to a control plot via seven flood irrigation events. Pore water samples were collected from 12 lysimeters installed at different depths in 3 boreholes in each test plot. The difference in mean concentrations of RDX in pore water samples from the two test plots was very highly significant (p < 0.001). The concentrations differences with depth were also very highly significant (p < 0.001) and degradation was greatly enhanced at depths from 5 to 13.5 ft. biodegradation was modeled as first order and the rate constant was 0.063 per day at 5 ft and decreased to 0.023 per day at 11 ft to 13.5 ft depth. Enhanced biodegradation of HMX was also observed in molasses treated plot samples but only at a depth of 5 ft. The difference in mean TOC concentration (surrogate for molasses) was highly significant with depth (p = 0.003) and very highly significant with treatment (p < 0.001). Mean total nitrogen concentrations also differed significantly with treatment (p < 0.001) and depth (p = 0.059). The molasses water mixture had a similar infiltration rate to that of plain water (average 4.12 ft per day) and reached the deepest sensor (31 ft) within 5 days of application. Most of the molasses was consumed by soil microorganisms by about 13.5 feet below ground surface and treatment of deeper depths may require greater molasses concentrations and/or more frequent flood irrigation. Use of the bioremediation method described herein could allow the sustainable use of live fire training ranges by enhancing biodegradation of explosives in situ and preventing them from migrating to through the vadose zone to underlying ground water and off-site.

Lithospheric structure of the Northern Ordos and adjacent regions from surface wave tomography: implications to the tectonics of the North China Craton

NASA Astrophysics Data System (ADS)

LI, S.; Guo, Z.; Chen, Y. J.

2017-12-01

We present a high-resolution upper mantle S velocity model of the northern Ordos block using ambient noise tomography and two-plane-wave tomography between 8 and 143 s. The Ordos block, regarded as the nuclei of the Archean craton of North China Craton, is underlain by high velocity down to 200 km, indicating the preservation of cratonic root at the interior. However, thick lithospheric keel (≥ 200 km) is not observed outside the Ordos, suggesting craton reworking around the Ordos. The most important findings is the prominent low velocity shown beneath the Datong volcano that migrates westward with depth. At 200 km depth, the low velocity locates almost 500 km west to the leading edge of the flat-lying Pacific slab in the mantle transition zone. This observation is in conflict with the previous interpretation that the Datong volcano is fed by the deep upwelling related to the subduction of the Pacific plate. The westward tilted low velocity beneath the Datong volcano, however, is in agreement with the predominant NW-SE trending alignment of fast direction revealed by SKS splitting in this area, suggesting the Datong volcano is likely due to the asthenospheric mantle flow from west. Two possible scenarios could be related to this mantle process. First, the low velocity beneath the Datong volcano may link to the large-scale, deep-rooted mantle upwelling beneath the Mongolia, northwest to the Datong volcano at deeper depth revealed by Zhang et al. (2016). We postulate that when the raising mantle materials reaches the shallow depth, it would be forced bent by the thick lithosphere beneath the Gobi in Mongolia and flow southeastward to Datong volcano. Second, it is also worth noting that the low velocity beneath the Datong volcano connects to the low velocity zone (LVZ) beneath the Ordos block below 200km, which further links the LVZ beneath the northeastern Tibet to the west. Therefore, the Datong volcano could be fed by the mantle flow from northeastern Tibet. The continuous slab-retreating of the western Pacific since the Cenozoic would have created void spaces in eastern Asia which could in turn suck new asthenospheric materials from the Mongolia and northeast Tibet through the northern TNCO. The upward mantle flow along the rapid thinning lithosphere to the northeast of Ordos had generated partial melting to supply the Datong volcano.

Insights into the structure and tectonic history of the southern South Island, New Zealand, from the 3-D distribution of P- and S-wave attenuation

NASA Astrophysics Data System (ADS)

Eberhart-Phillips, Donna; Reyners, Martin; Upton, Phaedra; Gubbins, David

2018-05-01

The Pacific-Australian plate boundary in the South Island of New Zealand is a transpressive boundary through continental lithosphere consisting of multiple terranes which were amalgamated during previous periods of subduction and plate reorganization. The style and locus of deformation within the present-day plate boundary is controlled by the mechanical behavior and distribution of these different lithospheric blocks. Geological studies are limited when it comes to illuminating lithospheric structure and rheology at depth. Imaging the 3-D seismic velocity and attenuation (1/Q), with distributed local earthquakes, helps unravel regional structure and variations in strength, fractures and fluids. We determine the 3-D distribution of Qp and Qs, which show much more variation than seismic velocity (Vp), underlining the utility of Q (1/attenuation). The Haast schist belt, previously shown as c. 25-km thick dry unit with moderate Vp and low Vp/Vs, is imaged with high Qs, and the highest Qs areas correlate with zones of higher grade schist. Below 25-km depth, the distribution of high Qp and Qs is markedly different from that of the overlying geological terranes. Both the strike and dip of the high Q regions indicate that they represent the subducted Hikurangi Plateau and its adjacent Cretaceous oceanic crust. The thickest part of the plateau, previously identified by Vp > 8.5 km/s from seismic tomography and P-wave precursors and associated with an eclogite layer at the base of the plateau, also has the highest Q. This confirms that the strong plateau extends southwestward as a narrow salient to the northern Fiordland subduction zone, where moderate-Q Eocene oceanic crust on the Australian plate is being subducted and bent to vertical. In the ductile crust, Q results suggest fluid saturation and elevated temperature conditions in the crustal root of the Southern Alps, and confirm that the shape of this crustal root is influenced by both the orientation and depth of the underlying plateau. Q also provides insight into the failed rifting that occurred in oceanic crust at the edges of the Hikurangi Plateau, with a region of relatively low Q at the on-land extension of the Bounty Trough and Canterbury Basin, at the narrowest part of the South Island. In the brittle crust above 10-km depth, low Q is related to regions of active recent seismicity which have high fracture density, with low Qs where fluids are present. In contrast, the locked Alpine fault does not exhibit low Q in the brittle crust.

Root density of cherry trees grafted on prunus mahaleb in a semi-arid region

NASA Astrophysics Data System (ADS)

Paltineanu, Cristian; Septar, Leinar; Gavat, Corina; Chitu, Emil; Oprita, Alexandru; Moale, Cristina; Lamureanu, Gheorghe; Vrinceanu, Andrei

2016-07-01

Root density was investigated using the trench method in a cherry (Prunus avium grafted on Prunus mahaleb) orchard with clean cultivation in inter-rows and in-row. Trenches of 1 m width and 1.2 m depth were dug up between neighbouring trees. The objectives of the paper were to clarify the spatial distribution of root density of cherry trees under the soil and climate conditions of the region to expand knowledge of optimum planting distance and orchard management for a broad area of chernozems. Some soil physical properties were significantly worsened in inter-rows versus in-row, mainly due to soil compaction, and there were higher root density values in in-row versus inter-rows. Root density decreased more intensely with soil depth than with distance from trees. The pattern of root density suggests that the cherry tree density and fruit yield could be increased. However, other factors concerning orchard management and fruit yield should also be considered. The results obtained have a potential impact to improve irrigation and fertilizer application by various methods, considering the soil depth and distance from trees to wet soil, in accordance with root development.

Quantifying rooting at depth in a wheat doubled haploid population with introgression from wild emmer.

PubMed

Clarke, Christina K; Gregory, Peter J; Lukac, Martin; Burridge, Amanda J; Allen, Alexandra M; Edwards, Keith J; Gooding, Mike J

2017-09-01

The genetic basis of increased rooting below the plough layer, post-anthesis in the field, of an elite wheat line (Triticum aestivum 'Shamrock') with recent introgression from wild emmer (T. dicoccoides), is investigated. Shamrock has a non-glaucous canopy phenotype mapped to the short arm of chromosome 2B (2BS), derived from the wild emmer. A secondary aim was to determine whether genetic effects found in the field could have been predicted by other assessment methods. Roots of doubled haploid (DH) lines from a winter wheat ('Shamrock' × 'Shango') population were assessed using a seedling screen in moist paper rolls, in rhizotrons to the end of tillering, and in the field post-anthesis. A linkage map was produced using single nucleotide polymorphism markers to identify quantitative trait loci (QTLs) for rooting traits. Shamrock had greater root length density (RLD) at depth than Shango, in the field and within the rhizotrons. The DH population exhibited diversity for rooting traits within the three environments studied. QTLs were identified on chromosomes 5D, 6B and 7B, explaining variation in RLD post-anthesis in the field. Effects associated with the non-glaucous trait on RLD interacted significantly with depth in the field, and some of this interaction mapped to 2BS. The effect of genotype was strongly influenced by the method of root assessment, e.g. glaucousness expressed in the field was negatively associated with root length in the rhizotrons, but positively associated with length in the seedling screen. To our knowledge, this is the first study to identify QTLs for rooting at depth in field-grown wheat at mature growth stages. Within the population studied here, our results are consistent with the hypothesis that some of the variation in rooting is associated with recent introgression from wild emmer. The expression of genetic effects differed between the methods of root assessment. © The Author 2017. Published by Oxford University Press on behalf of the Annals of Botany Company.

FREE-WATER DEPTH AS A MANAGEMENT TOOL FOR CONSTRUCTED WETLANDS

EPA Science Inventory

Marsh plants in constructed wetlands have shown the capacity to remove unwanted pollutants from storm water runoff. The plants can be established at the site from bare roots. However, plant growth from bare roots can be restricted by the elevated water depths. Using several wa...

Imaging the 2017 MW 8.2 Tehuantepec intermediate-depth earthquake using Teleseismic P Waves

NASA Astrophysics Data System (ADS)

Brudzinski, M.; Zhang, H.; Koper, K. D.; Pankow, K. L.

2017-12-01

The September 8, 2017 MW 8.1 Tehuantepec, Mexico earthquakes in the middle American subduction zone is one of the largest intermediate-depth earthquake ever recorded and could provide an unprecedented opportunity for understanding the mechanism of intermediate-depth earthquakes. While the hypocenter and centroid depths for this earthquake are shallower than typically considered for intermediate depth earthquakes, the normal faulting mechanism consistent with down-dip extension and location within the subducting plate align with properties of intermediate depth earthquakes. Back-projection of high-frequency teleseismic P-waves from two regional arrays for this earthquake shows unilateral rupture on a southeast-northwest striking fault that extends north of the Tehuantepec fracture zone (TFZ), with an average horizontal rupture speed of 3.0 km/s and total duration of 60 s. Guided by these back-projection results, 47 globally distributed low-frequency P-waves were inverted for a finite-fault model (FFM) of slip for both nodal planes. The FFM shows a slip deficit in proximity to the extension of the TFZ, as well as the minor rupture beyond the TFZ (confirmed by the synthetic tests), which indicates that the TFZ acted as a barrier for this earthquake. Analysis of waveform misfit leads to the preference of a subvertical plane as the causative fault. The FFM shows that the majority of the rupture is above the focal depth and consists of two large slip patches: the first one is near the hypocenter ( 55 km depth) and the second larger one near 30 km depth. The distribution of the two patches spatially agrees with seismicity that defines the upper and lower zones of a double Benioff zone (DBZ). It appears there was single fault rupture across the two depth zones of the DBZ. This is uncommon because a stark aseismic zone is typically observed between the upper and lower zones of the DBZ. This finding indicates that the mechanism for intraslab earthquakes must allow for rupture to propagate from one of the DBZ to the other despite seismic quiescence in between, suggesting the aseismic zone is conditionally stable: unable to nucleate earthquakes but able to host a large rupture going across.

Flavonols Mediate Root Phototropism and Growth through Regulation of Proliferation-to-Differentiation Transition.

PubMed

Silva-Navas, Javier; Moreno-Risueno, Miguel A; Manzano, Concepción; Téllez-Robledo, Bárbara; Navarro-Neila, Sara; Carrasco, Víctor; Pollmann, Stephan; Gallego, F Javier; Del Pozo, Juan C

2016-06-01

Roots normally grow in darkness, but they may be exposed to light. After perceiving light, roots bend to escape from light (root light avoidance) and reduce their growth. How root light avoidance responses are regulated is not well understood. Here, we show that illumination induces the accumulation of flavonols in Arabidopsis thaliana roots. During root illumination, flavonols rapidly accumulate at the side closer to light in the transition zone. This accumulation promotes asymmetrical cell elongation and causes differential growth between the two sides, leading to root bending. Furthermore, roots illuminated for a long period of time accumulate high levels of flavonols. This high flavonol content decreases both auxin signaling and PLETHORA gradient as well as superoxide radical content, resulting in reduction of cell proliferation. In addition, cytokinin and hydrogen peroxide, which promote root differentiation, induce flavonol accumulation in the root transition zone. As an outcome of prolonged light exposure and flavonol accumulation, root growth is reduced and a different root developmental zonation is established. Finally, we observed that these differentiation-related pathways are required for root light avoidance. We propose that flavonols function as positional signals, integrating hormonal and reactive oxygen species pathways to regulate root growth direction and rate in response to light. © 2016 American Society of Plant Biologists. All rights reserved.

Abscisic Acid Regulates Auxin Homeostasis in Rice Root Tips to Promote Root Hair Elongation

PubMed Central

Wang, Tao; Li, Chengxiang; Wu, Zhihua; Jia, Yancui; Wang, Hong; Sun, Shiyong; Mao, Chuanzao; Wang, Xuelu

2017-01-01

Abscisic acid (ABA) plays an essential role in root hair elongation in plants, but the regulatory mechanism remains to be elucidated. In this study, we found that exogenous ABA can promote rice root hair elongation. Transgenic rice overexpressing SAPK10 (Stress/ABA-activated protein kinase 10) had longer root hairs; rice plants overexpressing OsABIL2 (OsABI-Like 2) had attenuated ABA signaling and shorter root hairs, suggesting that the effect of ABA on root hair elongation depends on the conserved PYR/PP2C/SnRK2 ABA signaling module. Treatment of the DR5-GUS and OsPIN-GUS lines with ABA and an auxin efflux inhibitor showed that ABA-induced root hair elongation depends on polar auxin transport. To examine the transcriptional response to ABA, we divided rice root tips into three regions: short root hair, long root hair and root tip zones; and conducted RNA-seq analysis with or without ABA treatment. Examination of genes involved in auxin transport, biosynthesis and metabolism indicated that ABA promotes auxin biosynthesis and polar auxin transport in the root tip, which may lead to auxin accumulation in the long root hair zone. Our findings shed light on how ABA regulates root hair elongation through crosstalk with auxin biosynthesis and transport to orchestrate plant development. PMID:28702040

Flavonols Mediate Root Phototropism and Growth through Regulation of Proliferation-to-Differentiation Transition

PubMed Central

Silva-Navas, Javier; Moreno-Risueno, Miguel A.; Manzano, Concepción; Téllez-Robledo, Bárbara; Navarro-Neila, Sara; Carrasco, Víctor; Pollmann, Stephan

2016-01-01

Roots normally grow in darkness, but they may be exposed to light. After perceiving light, roots bend to escape from light (root light avoidance) and reduce their growth. How root light avoidance responses are regulated is not well understood. Here, we show that illumination induces the accumulation of flavonols in Arabidopsis thaliana roots. During root illumination, flavonols rapidly accumulate at the side closer to light in the transition zone. This accumulation promotes asymmetrical cell elongation and causes differential growth between the two sides, leading to root bending. Furthermore, roots illuminated for a long period of time accumulate high levels of flavonols. This high flavonol content decreases both auxin signaling and PLETHORA gradient as well as superoxide radical content, resulting in reduction of cell proliferation. In addition, cytokinin and hydrogen peroxide, which promote root differentiation, induce flavonol accumulation in the root transition zone. As an outcome of prolonged light exposure and flavonol accumulation, root growth is reduced and a different root developmental zonation is established. Finally, we observed that these differentiation-related pathways are required for root light avoidance. We propose that flavonols function as positional signals, integrating hormonal and reactive oxygen species pathways to regulate root growth direction and rate in response to light. PMID:26628743

Partial Root-Zone Drying of Olive (Olea europaea var. 'Chetoui') Induces Reduced Yield under Field Conditions.

PubMed

Dbara, Soumaya; Haworth, Matthew; Emiliani, Giovani; Ben Mimoun, Mehdi; Gómez-Cadenas, Aurelio; Centritto, Mauro

2016-01-01

The productivity of olive trees in arid and semi-arid environments is closely linked to irrigation. It is necessary to improve the efficiency of irrigation techniques to optimise the amount of olive fruit produced in relation to the volume of water used. Partial root-zone drying (PRD) is a water saving irrigation technique that theoretically allows the production of a root-to-shoot signal that modifies the physiology of the above-ground parts of the plant; specifically reducing stomatal conductance (gs) and improving water use efficiency (WUE). Partial root-zone drying has been successfully applied under field conditions to woody and non-woody crops; yet the few previous trials with olive trees have produced contrasting results. Thirty year-old olive trees (Olea europaea 'var. Chetoui') in a Tunisian grove were exposed to four treatments from May to October for three-years: 'control' plants received 100% of the potential evapotranspirative demand (ETc) applied to the whole root-zone; 'PRD100' were supplied with an identical volume of water to the control plants alternated between halves of the root-zone every ten-days; 'PRD50' were given 50% of ETc to half of the root-system, and; 'rain-fed' plants received no supplementary irrigation. Allowing part of the root-zone to dry resulted in reduced vegetative growth and lower yield: PRD100 decreased yield by ~47% during productive years. During the less productive years of the alternate bearing cycle, irrigation had no effect on yield; this suggests that withholding of water during 'off-years' may enhance the effectiveness of irrigation over a two-year cycle. The amount and quality of oil within the olive fruit was unaffected by the irrigation treatment. Photosynthesis declined in the PRD50 and rain-fed trees due to greater diffusive limitations and reduced biochemical uptake of CO2. Stomatal conductance and the foliar concentration of abscisic acid (ABA) were not altered by PRD100 irrigation, which may indicate the absence of a hormonal root-to-shoot signal. Rain-fed and PRD50 treatments induced increased stem water potential and increased foliar concentrations of ABA, proline and soluble sugars. The stomata of the olive trees were relatively insensitive to super-ambient increases in [CO2] and higher [ABA]. These characteristics of 'hydro-passive' stomatal behaviour indicate that the 'Chetoui' variety of olive tree used in this study lacks the physiological responses required for the successful exploitation of PRD techniques to increase yield and water productivity. Alternative irrigation techniques such as partial deficit irrigation may be more suitable for 'Chetoui' olive production.

Effects of spatiotemporal variation of soil salinity on fine root distribution in different plant configuration modes in new reclamation coastal saline field.

PubMed

Jiang, Hong; Du, Hongyu; Bai, Yingying; Hu, Yue; Rao, Yingfu; Chen, Chong; Cai, Yongli

2016-04-01

In order to study the effects of salinity on plant fine roots, we considered three different plant configuration modes (tree stand model (TSM), shrub stand model (SSM), and tree-shrub stand model (TSSM)). Soil samples were collected with the method of soil drilling. Significant differences of electrical conductivity (EC) in the soil depth of 0-60 cm were observed among the three modes (p < 0.05). In the above three modes, the variation of soil salinity among various soil layers and monthly variation of soil salinity were the highest in SSM and reached 2.30 and 2.23 mS/cm (EC1:5), respectively. Due to the effect of salinity, fine root biomass (FRB) showed significant differences in different soil depths (p < 0.05). More than 60% of FRB was concentrated in the soil depth above 30 cm. FRB showed exponential decline with soil depth (p < 0.05). FRB showed spatial heterogeneity in the 40-cm soil depth. In the above three modes, compared with FRB, specific root length (SRL) and fine root length density (FRLD) showed the similar changing trend. Fine roots showed significant seasonal differences among different modes (p < 0.05). FRB showed the bimodal variation and was the highest in July. However, we found that the high content of salts had obvious inhibitory effect on the distribution of FRB. Therefore, the salinity should be below 1.5 mS/cm, which was suitable for the growth of plant roots. Among the three modes, TSSM had the highest FRB, SRL, and FRLD and no obvious soil salt accumulation was observed. The results indicated that fine root biomass was affected by high salt and that TSSM had the strong effects of salt suppression and control. In our study, TSSM may be the optimal configuration mode for salt suppression and control in saline soil.

Airborne Detection of Cosmic-Ray Albedo Neutrons for Regional-Scale Surveys of Root-Zone Soil Water on Earth

NASA Astrophysics Data System (ADS)

Schrön, M.; Bannehr, L.; Köhli, M.; Zreda, M. G.; Weimar, J.; Zacharias, S.; Oswald, S. E.; Bumberger, J.; Samaniego, L. E.; Schmidt, U.; Zieger, P.; Dietrich, P.

2017-12-01

While the detection of albedo neutrons from cosmic rays became a standard method in planetary space science, airborne neutron sensing has never been conceived for hydrological research on Earth. We assessed the applicability of atmospheric neutrons to sense root-zone soil moisture averaged over tens of hectares using neutron detectors on an airborne vehicle. Large-scale quantification of near-surface water content is an urgent challenge in hydrology. Information about soil and plant water is crucial to accurately assess the risks for floods and droughts, to adjust regional weather forecasts, and to calibrate and validate the corresponding models. However, there is a lack of data at scales relevant for these applications. Most conventional ground-based geophysical instruments provide root-zone soil moisture only within a few tens of m2, while electromagnetic signals from conventional remote-sensing instruments can only penetrate the first few centimeters below surface, though at larger spatial areas.In the last couple of years, stationary and roving neutron detectors have been used to sense the albedo component of cosmic-ray neutrons, which represents the average water content within 10—15 hectares and 10—50 cm depth. However, the application of these instruments is limited by inaccessible terrain and interfering local effects from roads. To overcome these limitations, we have pioneered first simulations and experiments of such sensors in the field of airborne geophysics. Theoretical investigations have shown that the footprint increases substantially with height above ground, while local effects smooth out throughout the whole area. Campaigns with neutron detectors mounted on a lightweight gyrocopter have been conducted over areas of various landuse types including agricultural fields, urban areas, forests, flood plains, and lakes. The neutron signal showed influence of soil moisture patterns in heights of up to 180 m above ground. We found correlation with ground-truthing data, using mobile cosmic-ray neutron sensors, local soil samples, TDR, and buried wireless soil moisture monitoring networks. The work opens the path towards further systematic assessment of airborne neutron sensing, which could become a valuable addition - or even an alternative - to conventional remote-sensing methods.

In-depth morphological study of mesiobuccal root canal systems in maxillary first molars: review

PubMed Central

Chang, Seok-Woo; Lee, Jong-Ki; Lee, Yoon

2013-01-01

A common failure in endodontic treatment of the permanent maxillary first molars is likely to be caused by an inability to locate, clean, and obturate the second mesiobuccal (MB) canals. Because of the importance of knowledge on these additional canals, there have been numerous studies which investigated the maxillary first molar MB root canal morphology using in vivo and laboratory methods. In this article, the protocols, advantages and disadvantages of various methodologies for in-depth study of maxillary first molar MB root canal morphology were discussed. Furthermore, newly identified configuration types for the establishment of new classification system were suggested based on two image reformatting techniques of micro-computed tomography, which can be useful as a further 'Gold Standard' method for in-depth morphological study of complex root canal systems. PMID:23493453

Tree Age Effects on Fine Root Biomass and Morphology over Chronosequences of Fagus sylvatica, Quercus robur and Alnus glutinosa Stands

PubMed Central

Jagodzinski, Andrzej M.; Ziółkowski, Jędrzej; Warnkowska, Aleksandra; Prais, Hubert

2016-01-01

There are few data on fine root biomass and morphology change in relation to stand age. Based on chronosequences for beech (9–140 years old), oak (11–140 years) and alder (4–76 years old) we aimed to examine how stand age affects fine root biomass and morphology. Soil cores from depths of 0–15 cm and 16–30 cm were used for the study. In contrast to previously published studies that suggested that maximum fine root biomass is reached at the canopy closure stage of stand development, we found almost linear increases of fine root biomass over stand age within the chronosequences. We did not observe any fine root biomass peak in the canopy closure stage. However, we found statistically significant increases of mean fine root biomass for the average individual tree in each chronosequence. Mean fine root biomass (0–30 cm) differed significantly among tree species chronosequences studied and was 4.32 Mg ha-1, 3.71 Mg ha-1 and 1.53 Mg ha-1, for beech, oak and alder stands, respectively. The highest fine root length, surface area, volume and number of fine root tips (0–30 cm soil depth), expressed on a stand area basis, occurred in beech stands, with medium values for oak stands and the lowest for alder stands. In the alder chronosequence all these values increased with stand age, in the beech chronosequence they decreased and in the oak chronosequence they increased until ca. 50 year old stands and then reached steady-state. Our study has proved statistically significant negative relationships between stand age and specific root length (SRL) in 0–30 cm soil depth for beech and oak chronosequences. Mean SRLs for each chronosequence were not significantly different among species for either soil depth studied. The results of this study indicate high fine root plasticity. Although only limited datasets are currently available, these data have provided valuable insight into fine root biomass and morphology of beech, oak and alder stands. PMID:26859755

Ligament, nerve, and blood vessel anatomy of the lateral zone of the lumbar intervertebral foramina.

PubMed

Yuan, Shi-Guo; Wen, You-Liang; Zhang, Pei; Li, Yi-Kai

2015-11-01

To provide an anatomical basis for intrusive treatment using an approach through the lateral zones of the lumbar intervertebral foramina (LIF), especially for acupotomology lysis, percutaneous transforaminal endoscopy, and lumbar nerve root block. Blood vessels, ligaments, nerves, and adjacent structures of ten cadavers were exposed through the L1-2 to L5-S1 intervertebral foramina and examined. The lateral zones of the LIF were almost filled by ligaments, nerves, and blood vessels, which were separated into compartments by superior/inferior transforaminal ligaments and corporotransverse superior/inferior ligaments. Two zones relatively lacking in blood vessels and nerves (triangular working zones) were found beside the lamina of the vertebral arch and on the root of the transverse processus. Both the ascending lumbar vein and branches of the intervetebral vein were observed in 12 Kambin's triangles, and in only seven Kambin's triangles were without any veins. Nerves and blood vessels are fixed and protected by transforaminal ligaments and/or corporotransverse ligaments. It is necessary to distinguish the ligaments from nerves using transforaminal endoscopy so that the ligaments can be cut without damaging nerves. Care needs to be taken in intrusive operations because of the veins running through Kambin's triangle. We recommend injecting into the lamina of the vertebral arch and the midpoint between the adjacent roots of the transverse processus when administering nerve root block. Blind percutaneous incision and acupotomology lysis is dangerous in the lateral zones of the LIF, as they are filled with nerves and blood vessels.

Overestimation of Crop Root Biomass in Field Experiments Due to Extraneous Organic Matter.

PubMed

Hirte, Juliane; Leifeld, Jens; Abiven, Samuel; Oberholzer, Hans-Rudolf; Hammelehle, Andreas; Mayer, Jochen

2017-01-01

Root biomass is one of the most relevant root parameters for studies of plant response to environmental change, soil carbon modeling or estimations of soil carbon sequestration. A major source of error in root biomass quantification of agricultural crops in the field is the presence of extraneous organic matter in soil: dead roots from previous crops, weed roots, incorporated above ground plant residues and organic soil amendments, or remnants of soil fauna. Using the isotopic difference between recent maize root biomass and predominantly C3-derived extraneous organic matter, we determined the proportions of maize root biomass carbon of total carbon in root samples from the Swiss long-term field trial "DOK." We additionally evaluated the effects of agricultural management (bio-organic and conventional), sampling depth (0-0.25, 0.25-0.5, 0.5-0.75 m) and position (within and between maize rows), and root size class (coarse and fine roots) as defined by sieve mesh size (2 and 0.5 mm) on those proportions, and quantified the success rate of manual exclusion of extraneous organic matter from root samples. Only 60% of the root mass that we retrieved from field soil cores was actual maize root biomass from the current season. While the proportions of maize root biomass carbon were not affected by agricultural management, they increased consistently with soil depth, were higher within than between maize rows, and were higher in coarse (>2 mm) than in fine (≤2 and >0.5) root samples. The success rate of manual exclusion of extraneous organic matter from root samples was related to agricultural management and, at best, about 60%. We assume that the composition of extraneous organic matter is strongly influenced by agricultural management and soil depth and governs the effect size of the investigated factors. Extraneous organic matter may result in severe overestimation of recovered root biomass and has, therefore, large implications for soil carbon modeling and estimations of the climate change mitigation potential of soils.

Colonization and community structure of root-associated microorganisms of Sabina vulgaris with soil depth in a semiarid desert ecosystem with shallow groundwater.

PubMed

Taniguchi, Takeshi; Usuki, Hiroyuki; Kikuchi, Junichi; Hirobe, Muneto; Miki, Naoko; Fukuda, Kenji; Zhang, Guosheng; Wang, Linhe; Yoshikawa, Ken; Yamanaka, Norikazu

2012-08-01

Arbuscular mycorrhizal fungi (AMF) have been observed in deep soil layers in arid lands. However, change in AMF community structure with soil depth and vertical distributions of the other root-associated microorganisms are unclear. Here, we examined colonization by AMF and dark septate fungi (DSF), as well as the community structure of AMF and endophytic fungi (EF) and endophytic bacteria (EB) in association with soil depth in a semiarid desert with shallow groundwater. Roots of Sabina vulgaris and soils were collected from surface to groundwater level at 20-cm intervals. Soil chemistry (water content, total N, and available P) and colonization of AMF and DSF were measured. Community structures of AMF, EF, and EB were examined by terminal restriction fragment length polymorphism analysis. AMF colonization decreased with soil depth, although it was mostly higher than 50%. Number of AMF phylotypes decreased with soil depth, but more than five phylotypes were observed at depths up to 100 cm. Number of AMF phylotypes had a significant and positive relationship with soil moisture level within 0-15% of soil water content. DSF colonization was high but limited to soil surface. Number of phylotypes of EF and EB were diverse even in deep soil layers, and the community composition was associated with the colonization and community composition of AMF. This study indicates that AMF species richness in roots decreases but is maintained in deep soil layers in semiarid regions, and change in AMF colonization and community structure associates with community structure of the other root-associated microorganisms.

Geophysical constraints for terrane boundaries in southern Mongolia

NASA Astrophysics Data System (ADS)

Guy, Alexandra; Schulmann, Karel; Munschy, Marc; Miehe, Jean-Marc; Edel, Jean-Bernard; Lexa, Ondrej; Fairhead, Derek

2014-05-01

The Central Asian Orogenic Belt (CAOB) is a typical accretionary orogen divided into numerous lithostratigraphic terranes corresponding to magmatic arcs, back arcs, continental basement blocks, accretionary wedges and metamorphic blocks. These terranes should be in theory characterized by contrasting magnetic and gravity signatures thanks to their different petrophysical properties. To test this hypothesis, the stratigraphically defined terranes in southern Mongolia were compared with potential field data to constrain their boundaries and extent. The existence of terranes in southern Mongolia cannot be attested by the uniform geophysical fabrics due to the lack of systematic correspondence between the high/low amplitude and high/low frequency geophysical domains and major terranes. Processed magnetic and gravity grids show that both gravity and magnetic lineaments are E-W trending in the west and correlate with direction of some geological units. In the east, both magnetic and gravity lineaments are disrupted by NE-SW trending heterogeneities resulting in complete blurring of the geophysical pattern. Correlation of magnetic signal with geological map shows that the magnetic highs coincide with late Carboniferous-early Permian volcanic and plutonic belts. The matched-filtering shows good continuity of signal to the depth located along the boundaries of these high magnetic anomalies which may imply presence of deeply rooted tectono-magmatic zones. The axes of high density bodies in the western and central part of the studied CAOB are characterized by periodic alternations of NW-SE trending high frequency and high amplitude gravity anomalies corresponding to late Permian to Triassic cleavage fronts up to 20 km wide. The matched-filtering analysis shows that the largest deformation zones are deeply rooted down to 20 km depth. Such a gravity signal is explained by the verticalization of high density mantle and lower crustal rocks due to localized vertical shearing associated to upright folding. The magnetic signal is interpreted to result from a giant Permo-Triassic magmatic event associated lithosphere scale deformation whereas the gravity pattern is related to post-accretionary shortening of the CAOB in between North China and Siberia cratons. The blurring of the gravity signals to the west is attributed to activity of Triassic dextral shear zones parallel to the eastern Siberian boundary later on affected by Cretaceous extension and magmatism affecting the whole of eastern Asia.

A Physically-based Model for Predicting Soil Moisture Dynamics in Wetlands

NASA Astrophysics Data System (ADS)

Kalin, L.; Rezaeianzadeh, M.; Hantush, M. M.

2017-12-01

Wetlands are promoted as green infrastructures because of their characteristics in retaining and filtering water. In wetlands going through wetting/drying cycles, simulation of nutrient processes and biogeochemical reactions in both ponded and unsaturated wetland zones are needed for an improved understanding of wetland functioning for water quality improvement. The physically-based WetQual model can simulate the hydrology and nutrient and sediment cycles in natural and constructed wetlands. WetQual can be used in continuously flooded environments or in wetlands going through wetting/drying cycles. Currently, WetQual relies on 1-D Richards' Equation (RE) to simulate soil moisture dynamics in unponded parts of the wetlands. This is unnecessarily complex because as a lumped model, WetQual only requires average moisture contents. In this paper, we present a depth-averaged solution to the 1-D RE, called DARE, to simulate the average moisture content of the root zone and the layer below it in unsaturated parts of wetlands. DARE converts the PDE of the RE into ODEs; thus it is computationally more efficient. This method takes into account the plant uptake and groundwater table fluctuations, which are commonly overlooked in hydrologic models dealing with wetlands undergoing wetting and drying cycles. For verification purposes, DARE solutions were compared to Hydrus-1D model, which uses full RE, under gravity drainage only assumption and full-term equations. Model verifications were carried out under various top boundary conditions: no ponding at all, ponding at some point, and no rain. Through hypothetical scenarios and actual atmospheric data, the utility of DARE was demonstrated. Gravity drainage version of DARE worked well in comparison to Hydrus-1D, under all the assigned atmospheric boundary conditions of varying fluxes for all examined soil types (sandy loam, loam, sandy clay loam, and sand). The full-term version of DARE offers reasonable accuracy compared to the full RE solutions from Hydrus-1D, with a significant reduction in computational time. The full-term version of DARE estimated the moisture content with better accuracy for the root zone by considering zero pressure head at a fixed groundwater depth as the bottom boundary condition. The accuracy of this model is lower for the second layer.

Root gravitropism in maize and Arabidopsis

NASA Technical Reports Server (NTRS)

Evans, Michael L.

1993-01-01

Research during the period 1 March 1992 to 30 November 1993 focused on improvements in a video digitizer system designed to automate the recording of surface extension in plants responding to gravistimulation. The improvements included modification of software to allow detailed analysis of localized extension patterns in roots of Arabidopsis. We used the system to analyze the role of the postmitotic isodiametric growth zone (a region between the meristem and the elongation zone) in the response of maize roots to auxin, calcium, touch and gravity. We also used the system to analyze short-term auxin and gravitropic responses in mutants of Arabidopsis with reduced auxin sensitivity. In a related project, we studied the relationship between growth rate and surface electrical currents in roots by examining the effects of gravity and thigmostimulation on surface potentials in maize roots.

Overpressure and hydrocarbon accumulations in Tertiary strata, Gulf Coast of Louisiana

USGS Publications Warehouse

Nelson, Philip H.

2012-01-01

Many oil and gas reservoirs in Tertiary strata of southern Louisiana are located close to the interface between a sand-rich, normally pressured sequence and an underlying sand-poor, overpressured sequence. This association, recognized for many years by Gulf Coast explorationists, is revisited here because of its relevance to an assessment of undiscovered oil and gas potential in the Gulf Coast of Louisiana. The transition from normally pressured to highly overpressured sediments is documented by converting mud weights to pressure, plotting all pressure data from an individual field as a function of depth, and selecting a top and base of the pressure transition zone. Vertical extents of pressure transition zones in 34 fields across southern onshore Louisiana range from 300 to 9000 ft and are greatest in younger strata and in the larger fields. Display of pressure transition zones on geologic cross sections illustrates the relative independence of the depth of the pressure transition zone and geologic age. Comparison of the depth distribution of pressure transition zones with production intervals confirms previous findings that production intervals generally overlap the pressure transition zone in depth and that the median production depth lies above the base of the pressure transition zone in most fields. However, in 11 of 55 fields with deep drilling, substantial amounts of oil and gas have been produced from depths deeper than 2000 ft below the base of the pressure transition zone. Mud-weight data in 7 fields show that "local" pressure gradients range from 0.91 to 1.26 psi/ft below the base of the pressure transition zone. Pressure gradients are higher and computed effective stress gradients are negative in younger strata in coastal areas, indicating that a greater potential for fluid and sediment movement exists there than in older Tertiary strata.

An index for plant water deficit based on root-weighted soil water content

NASA Astrophysics Data System (ADS)

Shi, Jianchu; Li, Sen; Zuo, Qiang; Ben-Gal, Alon

2015-03-01

Governed by atmospheric demand, soil water conditions and plant characteristics, plant water status is dynamic, complex, and fundamental to efficient agricultural water management. To explore a centralized signal for the evaluation of plant water status based on soil water status, two greenhouse experiments investigating the effect of the relative distribution between soil water and roots on wheat and rice were conducted. Due to the significant offset between the distributions of soil water and roots, wheat receiving subsurface irrigation suffered more from drought than wheat under surface irrigation, even when the arithmetic averaged soil water content (SWC) in the root zone was higher. A significant relationship was found between the plant water deficit index (PWDI) and the root-weighted (rather than the arithmetic) average SWC over root zone. The traditional soil-based approach for the estimation of PWDI was improved by replacing the arithmetic averaged SWC with the root-weighted SWC to take the effect of the relative distribution between soil water and roots into consideration. These results should be beneficial for scheduling irrigation, as well as for evaluating plant water consumption and root density profile.

Root diversity in alpine plants: root length, tensile strength and plant age

NASA Astrophysics Data System (ADS)

Pohl, M.; Stroude, R.; Körner, C.; Buttler, A.; Rixen, C.

2009-04-01

A high diversity of plant species and functional groups is hypothesised to increase the diversity of root types and their subsequent effects for soil stability. However, even basic data on root characteristics of alpine plants are very scarce. Therefore, we determined important root characteristics of 13 plant species from different functional groups, i.e. grasses, herbs and shrubs. We excavated the whole root systems of 62 plants from a machine-graded ski slope at 2625 m a.s.l. and analysed the rooting depth, the horizontal root extension, root length and diameter. Single roots of plant species were tested for tensile strength. The age of herbs and shrubs was determined by growth-ring analysis. Root characteristics varied considerably between both plant species and functional groups. The rooting depth of different species ranged from 7.2 ± 0.97 cm to 20.5 ± 2.33 cm, but was significantly larger in the herb Geum reptans (70.8 ± 10.75 cm). The woody species Salix breviserrata reached the highest horizontal root extensions (96.8 ± 25.5 cm). Most plants had their longest roots in fine diameter classes (0.5

Root hydrotropism is controlled via a cortex-specific growth mechanism.

PubMed

Dietrich, Daniela; Pang, Lei; Kobayashi, Akie; Fozard, John A; Boudolf, Véronique; Bhosale, Rahul; Antoni, Regina; Nguyen, Tuan; Hiratsuka, Sotaro; Fujii, Nobuharu; Miyazawa, Yutaka; Bae, Tae-Woong; Wells, Darren M; Owen, Markus R; Band, Leah R; Dyson, Rosemary J; Jensen, Oliver E; King, John R; Tracy, Saoirse R; Sturrock, Craig J; Mooney, Sacha J; Roberts, Jeremy A; Bhalerao, Rishikesh P; Dinneny, José R; Rodriguez, Pedro L; Nagatani, Akira; Hosokawa, Yoichiroh; Baskin, Tobias I; Pridmore, Tony P; De Veylder, Lieven; Takahashi, Hideyuki; Bennett, Malcolm J

2017-05-08

Plants can acclimate by using tropisms to link the direction of growth to environmental conditions. Hydrotropism allows roots to forage for water, a process known to depend on abscisic acid (ABA) but whose molecular and cellular basis remains unclear. Here we show that hydrotropism still occurs in roots after laser ablation removed the meristem and root cap. Additionally, targeted expression studies reveal that hydrotropism depends on the ABA signalling kinase SnRK2.2 and the hydrotropism-specific MIZ1, both acting specifically in elongation zone cortical cells. Conversely, hydrotropism, but not gravitropism, is inhibited by preventing differential cell-length increases in the cortex, but not in other cell types. We conclude that root tropic responses to gravity and water are driven by distinct tissue-based mechanisms. In addition, unlike its role in root gravitropism, the elongation zone performs a dual function during a hydrotropic response, both sensing a water potential gradient and subsequently undergoing differential growth.

Root biomass, turnover and net primary productivity of a coffee agroforestry system in Costa Rica: effects of soil depth, shade trees, distance to row and coffee age.

PubMed

Defrenet, Elsa; Roupsard, Olivier; Van den Meersche, Karel; Charbonnier, Fabien; Pastor Pérez-Molina, Junior; Khac, Emmanuelle; Prieto, Iván; Stokes, Alexia; Roumet, Catherine; Rapidel, Bruno; de Melo Virginio Filho, Elias; Vargas, Victor J; Robelo, Diego; Barquero, Alejandra; Jourdan, Christophe

2016-08-21

In Costa Rica, coffee (Coffea arabica) plants are often grown in agroforests. However, it is not known if shade-inducing trees reduce coffee plant biomass through root competition, and hence alter overall net primary productivity (NPP). We estimated biomass and NPP at the stand level, taking into account deep roots and the position of plants with regard to trees. Stem growth and root biomass, turnover and decomposition were measured in mixed coffee/tree (Erythrina poeppigiana) plantations. Growth ring width and number at the stem base were estimated along with stem basal area on a range of plant sizes. Root biomass and fine root density were measured in trenches to a depth of 4 m. To take into account the below-ground heterogeneity of the agroforestry system, fine root turnover was measured by sequential soil coring (to a depth of 30 cm) over 1 year and at different locations (in full sun or under trees and in rows/inter-rows). Allometric relationships were used to calculate NPP of perennial components, which was then scaled up to the stand level. Annual ring width at the stem base increased up to 2·5 mm yr -1 with plant age (over a 44-year period). Nearly all (92 %) coffee root biomass was located in the top 1·5 m, and only 8 % from 1·5 m to a depth of 4 m. Perennial woody root biomass was 16 t ha -1 and NPP of perennial roots was 1·3 t ha -1 yr -1 Fine root biomass (0-30 cm) was two-fold higher in the row compared with between rows. Fine root biomass was 2·29 t ha -1 (12 % of total root biomass) and NPP of fine roots was 2·96 t ha -1 yr -1 (69 % of total root NPP). Fine root turnover was 1·3 yr -1 and lifespan was 0·8 years. Coffee root systems comprised 49 % of the total plant biomass; such a high ratio is possibly a consequence of shoot pruning. There was no significant effect of trees on coffee fine root biomass, suggesting that coffee root systems are very competitive in the topsoil. © The Author 2016. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

PRZM-3, A MODEL FOR PREDICTING PESTICIDE AND NITROGEN FATE IN THE CROP ROOT AND UNSATURATED SOIL ZONES: USER'S MANUAL FOR RELEASE 3.12.2

EPA Science Inventory

This publication contains documentation for the PRZM-3 model. PRZM-3 is the most recent version of a modeling system that links two subordinate models, PRZM and VADOFT, in order to predict pesticide transport and transformation down through the crop root and unsaturated soil zone...

Assessment of the SMAP Level-4 Surface and Root-Zone Soil Moisture Product Using In Situ Measurements

USDA-ARS?s Scientific Manuscript database

The Soil Moisture Active Passive (SMAP) mission Level-4 Surface and Root-Zone Soil Moisture (L4_SM) data product is generated by assimilating SMAP L-band brightness temperature observations into the NASA Catchment land surface model. The L4_SM product is available from 31 March 2015 to present (with...

Soil moisture inferences from thermal infrared measurements of vegetation temperatures

NASA Technical Reports Server (NTRS)

Jackson, R. D. (Principal Investigator)

1981-01-01

Thermal infrared measurements of wheat (Triticum durum) canopy temperatures were used in a crop water stress index to infer root zone soil moisture. Results indicated that one time plant temperature measurement cannot produce precise estimates of root zone soil moisture due to complicating plant factors. Plant temperature measurements do yield useful qualitative information concerning soil moisture and plant condition.

Oxidative Stress and NO Signalling in the Root Apex as an Early Response to Changes in Gravity Conditions

PubMed Central

Mugnai, Sergio; Monetti, Emanuela; Voigt, Boris; Volkmann, Dieter; Mancuso, Stefano

2014-01-01

Oxygen influx showed an asymmetry in the transition zone of the root apex when roots were placed horizontally on ground. The influx increased only in the upper side, while no changes were detected in the division and in the elongation zone. Nitric oxide (NO) was also monitored after gravistimulation, revealing a sudden burst only in the transition zone. In order to confirm these results in real microgravity conditions, experiments have been set up by using parabolic flights and drop tower. The production of reactive oxygen species (ROS) was also monitored. Oxygen, NO, and ROS were continuously monitored during normal and hyper- and microgravity conditions in roots of maize seedlings. A distinct signal in oxygen and NO fluxes was clearly detected only in the apex zone during microgravity, with no significant changes in normal and in hypergravity conditions. The same results were obtained by ROS measurement. The detrimental effect of D'orenone, disrupting the polarised auxin transport, on the onset of the oxygen peaks during the microgravity period was also evaluated. Results indicates an active role of NO and ROS as messengers during the gravitropic response, with probable implications in the auxin redistribution. PMID:25197662

Tomato growth as affected by root-zone temperature and the addition of gibberellic acid and kinetin to nutrient solutions

NASA Technical Reports Server (NTRS)

Bugbee, B.; White, J. W.; Salisbury, F. B. (Principal Investigator)

1984-01-01

The effect of root-zone temperature on young tomato plants (Lycopersicon esculentum Mill. cv. Heinz 1350) was evaluated in controlled environments using a recirculating solution culture system. Growth rates were measured at root-zone temperatures of 15 degrees, 20 degrees, 25 degrees, and 30 degrees C in a near optimum foliar environment. Optimum growth occurred at 25 degrees to 30 degrees during the first 4 weeks of growth and 20 degrees to 25 degrees during the 5th and 6th weeks. Growth was severely restricted at 15 degrees. Four concentrations of gibberellic acid (GA3) and kinetin were added to the nutrient solution in a separate trial; root-zone temperature was maintained at 15 degrees and 25 degrees. Addition of 15 micromoles GA3 to solutions increased specific leaf area, total leaf area, and dry weight production of plants in both temperature treatments. GA3-induced growth stimulation was greater at 15 degrees than at 25 degrees. GA3 may promote growth by increasing leaf area, enhancing photosynthesis per unit leaf area, or both. Kinetic was not useful in promoting growth at either temperature.

[Relationships between soil moisture and needle-fall in Masson pine forests in acid rain region of Chongqing, Southwest China].

PubMed

Wang, Yi-Hao; Wang, Yan-Hui; Li, Zhen-Hua; Yu, Peng-Tao; Xiong, Wei; Hao, Jia; Duan, Jian

2012-10-01

From March 2009 to November 2011, an investigation was conducted on the spatiotemporal variation of soil moisture and its effects on the needle-fall in Masson pine (Pinus massoniana) forests in acid rain region of Chongqing, Southeast China, with the corresponding soil moisture thresholds determined. No matter the annual precipitation was abundant, normal or less than average, the seasonal variation of soil moisture in the forests could be obviously divided into four periods, i.e., sufficient (before May), descending (from June to July), drought (from August to September), and recovering (from October to November). With increasing soil depth, the soil moisture content increased after an initial decrease, but the difference of the soil moisture content among different soil layers decreased with decreasing annual precipitation. The amount of monthly needle-fall in the forests in growth season was significantly correlated with the water storage in root zone (0-60 cm soil layer), especially in the main root zone (20-50 cm soil layer). Soil field capacity (or capillary porosity) and 82% of field capacity (or 80% of capillary porosity) were the main soil moisture thresholds affecting the litter-fall. It was suggested that in acid rain region, Masson pine forest was easily to suffer from water deficit stress, especially in dry-summer period. The water deficit stress, together with already existed acid rain stress, would further threaten the health of the Masson forest.

Soil water content evaluation considering time-invariant spatial pattern and space-variant temporal change

NASA Astrophysics Data System (ADS)

Hu, W.; Si, B. C.

2013-10-01

Soil water content (SWC) varies in space and time. The objective of this study was to evaluate soil water content distribution using a statistical model. The model divides spatial SWC series into time-invariant spatial patterns, space-invariant temporal changes, and space- and time-dependent redistribution terms. The redistribution term is responsible for the temporal changes in spatial patterns of SWC. An empirical orthogonal function was used to separate the total variations of redistribution terms into the sum of the product of spatial structures (EOFs) and temporally-varying coefficients (ECs). Model performance was evaluated using SWC data of near-surface (0-0.2 m) and root-zone (0-1.0 m) from a Canadian Prairie landscape. Three significant EOFs were identified for redistribution term for both soil layers. EOF1 dominated the variations of redistribution terms and it resulted in more changes (recharge or discharge) in SWC at wetter locations. Depth to CaCO3 layer and organic carbon were the two most important controlling factors of EOF1, and together, they explained over 80% of the variations in EOF1. Weak correlation existed between either EOF2 or EOF3 and the observed factors. A reasonable prediction of SWC distribution was obtained with this model using cross validation. The model performed better in the root zone than in the near surface, and it outperformed conventional EOF method in case soil moisture deviated from the average conditions.

Applying electrical resistivity tomography and biological methods to assess the surface-groundwater interaction in two Mediterranean rivers (central Spain)

NASA Astrophysics Data System (ADS)

Iepure, Sanda; Gómez Ortiz, David; Lillo Ramos, Javier; Rasines Ladero, Ruben; Persoiu, Aurel

2014-05-01

Delineation of the extent of hyporheic zone (HZ) in river ecosystems is problematic due to the scarcity of spatial information about the structure of riverbed sediments and the magnitude and extent of stream interactions with the parafluvial and riparian zones. The several existing methods vary in both quality and quantity of information and imply the use of hydrogeological and biological methods. In the last decades, various non-invasive geophysical techniques were developed to characterise the streambed architecture and also to provide detailed spatial information on its vertical and horizontal continuity. All classes of techniques have their strengths and limitations; therefore, in order to assess their potential in delineating the lateral and vertical spatial extents of alluvial sediments, we have combined the near-surface images obtained by electrical resistivity tomography (ERT) with biological assessment of invertebrates in two Mediterranean lowland rivers from central Spain. We performed in situ imaging of the thickness and continuity of alluvial sediments under the riverbed and parafluvial zone during base-flow conditions (summer 2013 and winter 2014) at two different sites with distinct lithology along the Tajuña and Henares Rivers. ERT was performed by installing the electrodes (1 m spacing) on a 47 m long transect normal to the river channel using a Wener-Schlumberger array, across both the riparian zones and the river bed. Invertebrates were collected in the streambed from a depth of 20-40 cm, using the Bou-Rouch method, and from boreholes drilled to a depth of 1.5 m in the riparian zone. The ERT images obtained at site 1 (medium and coarse sand dominated lithology) shows resistivity values ranging from ~20 to 80 ohm•m for the in-stream sediments, indicating a permeable zone up to ~ 0.5 m thick and extending laterally for ca. 5 m from the channel. These sediments contribute to active surface/hyporheic water exchanges and to low water retention in stream sediments, as also indicated by the similar physico-chemical parameters in thw two zones, and the composition of hyporheic biota, dominated exclusively by surface-dwellers (e.g. Cladocera, Chironomidae, Cyclopoida (Microcyclops rubellus), Ostracoda (Pryonocypris zenkeri). A low resistivity (< 70 ohm•m) permeable zone located at 2.3 m depth bellow the streambed and unconnected with the river channel was also detected and associated with a shallow floodplain aquifer. In contrast, the resistivity image at site 2 (fine and very fine sand dominated lithology) shows a low permeability zone in the upper ~ 0.5 m of the profile, with resistivity values ranging from ~45 to 80 ohm•m, indicating a reduced HZ extension in both vertical and lateral dimensions. Here, both water retention and interaction between water and sediments are higher than at site 1 and consequently the water chemistry is distinct from that of the river channel (lower conductivity, temperature and dissolved oxygen in hyporheic waters). These features of the sedimentary layers create suitable habitats conditions in HZ for the development of a mixture of both epigean (e.g., Ostracoda (Darwinula stevensoni)) and hypogean stygobites dwellers (e.g., Cyclopoida (Acanthocyclops n. sp)). Furthermore, a low resistivity (< 30 ohm•m) high permeability zone was detected 2 m from the riverbed, at a depth of ca. 3 meters, being associated either to a suspended aquifer supplied with water from the terraces, or to water accumulation within tree roots, that might be temporary connected with the stream-hyporheic system. The two examples show that non-invasive ERT images and biological assessment provides complementary and valuable information about the characterisation of the sub-channel architecture and its potential connection with the parafluvial and riparian zones. Our results provide initial templates for high-resolution in situ studies with broad and integrated methods to identify the boundaries between hyporheic and parafluvial zones and the time-scale fluctuations in response to water exchanges with the surface stream.

Organelle sedimentation in gravitropic roots of Limnobium is restricted to the elongation zone

NASA Technical Reports Server (NTRS)

Sack, F. D.; Kim, D.; Stein, B.

1994-01-01

Roots of the aquatic angiosperm Limnobium spongia (Bosc) Steud. were evaluated by light and electron microscopy to determine the distribution of organelle sedimentation towards gravity. Roots of Limnobium are strongly gravitropic. The rootcap consists of only two layers of cells. Although small amyloplasts are present in the central cap cells, no sedimentation of any organelle, including amyloplasts, was found. In contrast, both amyloplasts and nuclei sediment consistently and completely in cells of the elongation zone. Sedimentation occurs in one cell layer of the cortex just outside the endodermis. Sedimentation of both amyloplasts and nuclei begins in cells that are in their initial stages of elongation and persists at least to the level of the root where root hairs emerge. This is the first modern report of the presence of sedimentation away from, but not in, the rootcap. It shows that sedimentation in the rootcap is not necessary for gravitropic sensing in at least one angiosperm. If amyloplast sedimentation is responsible for gravitropic sensing, then the site of sensing in Limnobium roots is the elongation zone and not the rootcap. These data do not necessarily conflict with the hypothesis that sensing occurs in the cap in other roots, since Limnobium roots are exceptional in rootcap origin and structure, as well as in the distribution of organelle sedimentation. Similarly, if nuclear sedimentation is involved in gravitropic sensing, then nuclear mass would function in addition to, not instead of, that of amyloplasts.

Depth and Diameter of the Parent Roots of Aspen Root Suckers

Treesearch

Robert E. Farmer

1962-01-01

Studies of the Populus tremuloides root system by Day (1944), Sandberg (1951) and Barnes (1959) have all shown lateral roots extending as much as 30 feet from tree base. These roots may branch extensively and sometimes exhibit an "undulating" growth habit. According to the above authors, suckers occur on the segments of these lateral roots...

Sub-Moho Reflectors, Mantle Faults and Lithospheric Rheology

NASA Astrophysics Data System (ADS)

Brown, L. D.

2013-12-01

One of the most unexpected and dramatic observations from the early years of deep reflection profiling of the continents using multichannel CMP techniques was the existing of prominent reflections from the upper mantle. The first of these, the Flannan thrust/fault/feature, was traced by marine profiling of the continental margin offshore Britain by the BIRPS program, which soon found them to be but one of several clear sub-crustal discontinuities in that area. Subsequently, similar mantle reflectors have been observed in many areas around the world, most commonly beneath Precambrian cratonic areas. Many, but not all, of these mantle reflections appear to arise from near the overlying Moho or within the lower crust before dipping well into the mantle. Others occur as subhorizontal events at various depths with the mantle, with one suite seeming to cluster at a depth of about 75 km. The dipping events have been variously interpreted as mantle roots of crustal normal faults or the deep extension of crustal thrust faults. The most common interpretation, however, is that these dipping events are the relicts of ancient subduction zones, the stumps of now detached Benioff zones long since reclaimed by the deeper mantle. In addition to the BIRPS reflectors, the best known examples include those beneath Fennoscandia in northern Europe, the Abitibi-Grenville of eastern Canada, and the Slave Province of northwestern Canada (e.g. on the SNORCLE profile). The most recently reported example is from beneath the Sichuan Basin of central China. The preservation of these coherent, and relatively delicate appearing, features beneath older continental crust and presumably within equally old (of not older) mantle lithosphere, has profound implications for the history and rheology of the lithosphere in these areas. If they represent, as widely believe, some form of faulting with the lithosphere, they provide corollary constraints on the nature of faulting in both the lower crust and upper mantle. The SNORCLE mantle reflectors, which can be traced deep within the early Precambrian (?) mantle by both surface (controlled source) reflection profiles and passive (receiver function) images most clearly illustrates the rheological implications of such feature. The SNORCLE events appear to root upwards into the lower crust and extend to depths approaching 200 km into the mantle. This would seem to require the preservation of undeformed mantle lithosphere for almost 2.5 billion years in this area. This preservation is clearly inconsistent with the interpretation of nearby shallower mantle interfaces as marking the modern lithosphere-asthenosphere boundary. In summary, dipping mantle reflections imply preservation of substantial thicknesses of mantle lithosphere for very long periods of time, and localization of mantle deformation during the formation of these structures along relatively narrow, discrete interfaces rather than across broad zones of diffuse deformation. .

The effect of modifying rooting depths and nitrification inhibitors on nutrient uptake from organic biogas residues in maize

NASA Astrophysics Data System (ADS)

Dietrich, Charlotte C.; Koller, Robert; Nagel, Kerstin A.; Schickling, Anke; Schrey, Silvia D.; Jablonowski, Nicolai D.

2017-04-01

Optimizing the application of and nutrient uptake from organic nutrient sources, such as the nutrient-rich residues ("digestates") from the biogas industry, is becoming a viable option in remediating fertility on previously unsuitable soils for agricultural utilization. Proposedly, concurrent changes in root system architecture and functioning could also serve as the basis of future phytomining approaches. Herein, we evaluate the effect of spatial nutrient availability and nitrification on maize root architecture and nutrient uptake. We test these effects by applying maize-based digestate at a rate of 170 kg/ha in layers of varying depths (10, 25 and 40 cm) and through either the presence or absence of nitrification inhibitors. In order to regularly monitor above- and below-ground plant biomass production, we used the noninvasive phenotyping platform, GROWSCREEN-Rhizo at the Forschungszentrum Jülich, using rhizotrons (Nagel et al., 2012). Measured parameters included projected plant height and leaf area, as well as root length and spatial distribution. Additionally, root diameters were quantified after the destructive harvest, 21 days after sowing (DAS). Spatial nutrient availability significantly affected root system architecture, as for example root system size -the area occupied by roots- increased alongside nutrient layer depths. Fertilization also positively affected root length density (RLD). Within fertilized layers, the presence of nitrification inhibitors increased RLD by up to 30% and was most pronounced in the fine root biomass fraction (0.1 to 0.5mm). Generally, nitrification inhibitors promoted early plant growth by up to 45% across treatments. However, their effect varied in dependence of layer depths, leading to a time-delayed response in deeper layers, accounting for plants having to grow significantly longer roots in order to reach fertilized substrate. Nitrification inhibitors also initiated the comparatively early on-set of growth differences in shallower layers, where their effect on plant growth was temporarily most pronounced. At final harvest (21 DAS) however, effects of nitrification inhibitors on plant height were visible only in deeper layers. Furthermore, the statistically significant interaction between the factors time x layer depths x nitrification inhibitors underlined the dynamic influence of nitrification inhibitors on plant growth over time and across rooting depths. This study offers insights into optimizing nutrient uptake and plant productivity by (re-) using residues from the biogas industry. It is among the first to monitor and try to explain the dynamics of nitrification inhibitors on root system architecture over time. A modified N-fertilization application scheme might also serve as a promising tool in optimizing phytoremediation and phytomining techniques through predictably altering root structure in fertilized layers. References: Nagel, K. A. ; Putz, A. ; Gilmer, F. ; Heinz, K. ; Fischbach, A. ; Pfeifer, J. ; Faget, M. ; Blossfeld, S. ; Ernst, M. ; Dimaki, C. ; Kastenholz, B. ; Kleinert, A.-K. ; Galinski, A. ; Scharr, H. ; Fiorani, F. ; Schurr, U. (2012): GROWSCREEN-Rhizo is a novel phenotyping robot enabling simultaneous measurements of root and shoot growth for plants grown in soil-filled rhizotrons.
Functional plant biology 39(11), 891-904.

Use of small scale electrical resistivity tomography to identify soil-root interactions during deficit irrigation

NASA Astrophysics Data System (ADS)

Vanella, D.; Cassiani, G.; Busato, L.; Boaga, J.; Barbagallo, S.; Binley, A.; Consoli, S.

2018-01-01

Plant roots activity affect the exchanges of mass and energy between the soil and atmosphere. However, it is challenging to monitor the activity of the root-zone because roots are not visible from the soil surface, and root systems undergo spatial and temporal variations in response to internal and external conditions. Therefore, measurements of the activity of root systems are interesting to ecohydrologists in general, and are especially important for specific applications, such as irrigation water management. This study demonstrates the use of small scale three-dimensional (3-D) electrical resistivity tomography (ERT) to monitor the root-zone of orange trees irrigated by two different regimes: (i) full rate, in which 100% of the crop evapotranspiration (ETc) is provided; and (ii) partial root-zone drying (PRD), in which 50% of ETc is supplied to alternate sides of the tree. We performed time-lapse 3-D ERT measurements on these trees from 5 June to 24 September 2015, and compared the long-term and short-term changes before, during, and after irrigation events. Given the small changes in soil temperature and pore water electrical conductivity, we interpreted changes of soil electrical resistivity from 3-D ERT data as proxies for changes in soil water content. The ERT results are consistent with measurements of transpiration flux and soil temperature. The changes in electrical resistivity obtained from ERT measurements in this case study indicate that root water uptake (RWU) processes occur at the 0.1 m scale, and highlight the impact of different irrigation schemes.

Evaluation of diffuse and preferential flow pathways of infiltratedprecipitation and irrigation using oxygen and hydrogen isotopes

USGS Publications Warehouse

Ma, Bin; Liang, Xing; Liu, Shaohua; Jin, Menggui; Nimmo, John R.; Li, Jingxin

2017-01-01

Subsurface-water flow pathways in three different land-use areas (non-irrigated grassland, poplar forest, and irrigated arable land) in the central North China Plain were investigated using oxygen (18O) and hydrogen (2H) isotopes in samples of precipitation, soils, and groundwater. Soil water in the top 10 cm was significantly affected by both evaporation and infiltration. Water at 10–40 cm depth in the grassland and arable land, and 10–60 cm in poplar forest, showed a relatively short residence time, as a substantial proportion of antecedent soil water was mixed with a 92-mm storm infiltration event, whereas below those depths (down to 150 cm), depleted δ18O spikes suggested that some storm water bypassed the shallow soil layers. Significant differences, in soil-water content and δ18O values, within a small area, suggested that the proportion of immobile soil water and water flowing in subsurface pathways varies depending on local vegetation cover, soil characteristics and irrigation applications. Soil-water δ18O values revealed that preferential flow and diffuse flow coexist. Preferential flow was active within the root zone, independent of antecedent soil-water content, in both poplar forest and arable land, whereas diffuse flow was observed in grassland. The depleted δ18O spikes at 20–50 cm depth in the arable land suggested the infiltration of irrigation water during the dry season. Temporal isotopic variations in precipitation were subdued in the shallow groundwater, suggesting more complete mixing of different input waters in the unsaturated zone before reaching the shallow groundwater.

The effect of Bahiagrass roots on soil erosion resistance of Aquults in subtropical China

NASA Astrophysics Data System (ADS)

Ye, Chao; Guo, Zhonglu; Li, Zhaoxia; Cai, Chongfa

2017-05-01

Herbaceous species, especially their roots, are believed to have an important role in enhancing soil strength and protecting soil against erosion. This study evaluated the effects of root distribution characteristics on soil shear resistance and soil detachment rates, correlations among root mechanical properties, root chemical composition and root parameters, and whether the Wu-Waldron model can accurately estimate soil reinforcement by roots. Bahiagrass (Paspalum notatum) was planted in planter boxes by overlapping four rectangle frames (0.4 × 0.1 × 0.1 m). A series of laboratory tests of direct shear strength and soil detachment were conducted on two soils that were derived from granite and shale with different soil depths and sowing densities. The results indicated that soil aggregate stability was positively correlated with root characteristics. Over 70% of the total measured root parameters were distributed in the upper 20 cm of the soil, and they decreased with increasing soil depth and decreasing sowing density. The tensile properties (root tensile strength and root tensile force) were significantly correlated with root diameter. The contents of root main chemical compositions were significantly correlated with root diameter while hemicellulose showed no obvious trend with root diameter (P = 0.12). Root tensile strength and root tensile force were also significantly correlated with the contents of these four compositions, except hemicellulose. The relative soil detachment demonstrated a significant negative correlation with root parameters with sowing densities from 5 to 30 g m- 2, and it remained at a relatively low value when the sowing density was > 20 g m- 2. The soil detachment rate, erodibility factor and critical flow shear stress were well correlated with the root area ratio, sowing density, and soil depth. The Wu-Waldron model was found to be inappropriate for these soils, as it overestimated additional soil shear strength due to roots by 152-366% in the upper 20 cm, and 11-48% in deeper soil layers. This study demonstrated that the root area ratio was a more suitable root characteristic parameter that contributes to soil reinforcement.

Cross-Shore Exchange on Natural Beaches

DTIC Science & Technology

2014-09-01

87   Figure 2.   Wave conditions measured by the ADCP in 13 m water depth of (a) root- mean-square wave height Hrms...horizontal velocity, Umean, measured in the reference level, ∑Tsig,pulse T3−hour ∑Tsig,pulse T3−hour xi (e) local water depth, h, and (f) local root...mean-square wave height normalized by the local water depth, Hrms/h, measured by ADCPin (blue) and ADCPout (red) during the 3HRLTs. Colored lines

Morphometric analysis of the working zone for endoscopic lumbar discectomy.

PubMed

Min, Jun-Hong; Kang, Shin-Hyuk; Lee, Jang-Bo; Cho, Tai-Hyoung; Suh, Jung-Keun; Rhyu, Im-Joo

2005-04-01

Our study's purpose was to analyze the working zone for the current practice of endoscopic discectomy at the lateral exit zone of the intervertebral foramen (IVF) and to define a safe point for clinical practice. One hundred eighty-six nerve roots of the lumbar IVFs of cadaveric spines were studied. Upon lateral inspection, we measured the distance from the nerve root to the most dorsolateral margin of the disc and to the lateral edge of the superior articular process of the vertebra below at the plane of the superior endplate of the vertebra below. The angle between the root and the plane of the disc was also measured. The results showed that the mean distance from the nerve root to the most dorsolateral margin of the disc was 3.4 +/- 2.7 mm (range 0.0-10.8 mm), the mean distance from the nerve root to the lateral edge of the superior articular process of the vertebra below was 11.6 +/- 4.6 mm (range 4.1-24.3 mm), and the mean angle between the nerve root and the plane of the disc was 79.1 degrees +/- 7.6 degrees (range 56.0-90.0 degrees ). The values of the base of the working zone have a wide distribution. Blind puncture of annulus by the working cannula or obturator may be dangerous. The safer procedure would be the direct viewing of the annulus by endoscopy before annulotomy; the working cannula should be inserted into the foramen as close as possible to the facet joint.

Root growth and spatial distribution characteristics for seedlings raised in substrate and transplanted cotton

PubMed Central

Han, Yingchun; Li, Yabing; Wang, Guoping; Feng, Lu; Yang, Beifang; Fan, Zhengyi; Lei, Yaping; Du, Wenli; Mao, Shuchun

2017-01-01

In this study, transplanting cotton seedlings grown in artificial substrate is considered due to recent increased interest in cotton planting labor saving approaches. The nursery methods used for growing cotton seedlings affect root growth. However, the underlying functional responses of root growth to variations in cotton seedling transplanting methods are poorly understood. We assessed the responses of cotton (Gossypium hirsutum L.) roots to different planting methods by conducting cotton field experiments in 2012 and 2013. A one-factor random block design was used with three replications and three different cotton planting patterns (substrate seedling transplanted cotton (SSTC), soil-cube seedling transplanted cotton (ScSTC) and directly sown cotton (DSC). The distributions and variances of the root area density (RAD) and root length density (RLD) at different cotton growing stages and several yield components were determined. Overall, the following results were observed: 1) The RAD and RLD were greatest near the plants (a horizontal distance of 0 cm) but were lower at W20 and W40 cm in the absence of film mulching than at E20 and E40 cm with film mulching. 2) The roots were confined to shallow depths (20–40 cm), and the root depths of SSTC and DSC were greater than the root depths of ScSTC. 3) Strong root growth was observed in the SSTC at the cotton flowering and boll setting stages. In addition, early onset root growth occurred in the ScSTC, and vigorous root growth occurred throughout all cotton growth stages in DSC. 4) The SSTC plants had more lateral roots with higher root biomass (RB) than the ScSTC, which resulted in higher cotton yields. However, the early onset root growth in the ScSTC resulted in greater pre-frost seed cotton (PFSC) yields. These results can be used to infer how cotton roots are distributed in soils and capture nutrients. PMID:29272298

Transport and fate of nitrate within soil units of glacial origin

NASA Astrophysics Data System (ADS)

Moore, Suzanna L.; Peterson, Eric W.

2007-08-01

Questions concerning the influence of soil type and crop cover on the fate and transport of nitrate (NO{3/-}) were examined. During a growing season, soils derived from glacial material underlying either corn or soybeans were sampled for levels of NO{3/-} within the pore water. Measured levels of NO{3/-} ranged from below detection limit to 14.9 g NO{3/-} per kilogram of soil (g/kg). In fields with the same crop cover, the silty-clayey soil exhibited a greater decrease in NO{3/-} levels with depth than the sandier soil. Crop uptake of NO{3/-} occurs within the root zone; however, the type of crop cover did not have a direct impact on the fate or transport during the growing season. The soils underlying soybeans had an increase in NO{3/-} levels following harvest, suggesting that the decomposition of the soybean roots contributed to the net gain of NO{3/-} in the shallow soil. For all of the soil types, conditions below 100 cm are conducive for microbial denitrification, with both a high water saturation level (>60%) and moderate organic carbon content (1-2%). At depths below 100 cm, temporal differences in NO{3/-} levels of over a magnitude, up to a 95% reduction, were recorded in the soil units as the growing season progressed. Physical properties that control the transport of NO{3/-} or denitrification have a larger influence on NO{3/-} levels than crop type.

Effect of green tea catechin, a local drug delivery system as an adjunct to scaling and root planing in chronic periodontitis patients: A clinicomicrobiological study

PubMed Central

Kudva, Praveen; Tabasum, Syeda Tawkhira; Shekhawat, Nirmal Kanwar

2011-01-01

Background: Evaluate the adjunctive use of locally delivered green tea catechin with scaling and root planing, as compared to scaling and root planing alone in the management of chronic periodontitis. Materials and Methods: Fourteen patients with two sites in the contralateral quadrants with probing pocket depth of 5–8mm were selected. Each of the sites was assessed for the plaque index, gingival index, and probing pocket depth at baseline and 21 days and for microbiological analysis at baseline, 1 week and 21 days. Test sites received scaling and root planing along with green tea catechin strips and control sites received scaling and root planning alone. Results: The result showed intercomparison of the plaque index and gingival index for test and control groups at 21 days was not significant with P>0.05, whereas the probing depth at 21 days was significant with P<0.001. Intercomparison between microbial results demonstrated a considerable reduction of occurrence of Aggregatibacter actinomycetemcomitans, Prevotella intermedia, Fusobacterium species and Capnocytophaga in test. Conclusion: Green tea catechin local delivery along with scaling and root planing is more effective than scaling and root planing alone. PMID:21772720

Acidic beverages increase the risk of in vitro tooth erosion.

PubMed

Ehlen, Leslie A; Marshall, Teresa A; Qian, Fang; Wefel, James S; Warren, John J

2008-05-01

Acidic beverages are thought to increase the potential for dental erosion. We report pH and titratable acidities (ie, quantity of base required to bring a solution to neutral pH) of beverages popular in the United States and lesion depths in enamel and root surfaces after beverage exposure, and we describe associations among pH, titratable acidity, and both enamel and root erosive lesion depths. The pH of 100% juices, regular sodas, diet sodas, and sports drinks upon opening and the titratable acidity both upon opening and after 60 minutes of stirring were measured. Enamel and root surfaces of healthy permanent molars and premolars were exposed to individual beverages (4 enamel and 4 root surfaces per beverage) for 25 hours, and erosion was measured. Statistical analyses included 2-sample t tests, analyses of variance with post hoc Tukey studentized range test; and Spearman rank correlation coefficients. All beverages were acidic; the titratable acidity of energy drinks was greater than that of regular and diet sodas that were greater than that of 100% juices and sports drinks (P < .05). Enamel lesion depths after beverage exposures were greatest for Gatorade, followed by those for Red Bull and Coke that were greater than those for Diet Coke and 100% apple juice (P < .05). Root lesion depths were greatest for Gatorade, followed by Red Bull, Coke, 100% apple juice, and Diet Coke (P < .05). Lesion depths were not associated with pH or titratable acidity. Beverages popular in the United States can produce dental erosion.

Root systems of chaparral shrubs.

PubMed

Kummerow, Jochen; Krause, David; Jow, William

1977-06-01

Root systems of chaparral shrubs were excavated from a 70 m 2 plot of a mixed chaparral stand located on a north-facing slope in San Diego County (32°54' N; 900 m above sea level). The main shrub species present were Adenostoma fasciculatum, Arctostaphylos pungens, Ceanothus greggii, Erigonum fasciculatum, and Haplopappus pinifolius. Shrubs were wired into their positions, and the soil was washed out beneath them down to a depth of approximately 60 cm, where impenetrable granite impeded further washing and root growth was severely restricted. Spacing and interweaving of root systems were recorded by an in-scale drawing. The roots were harvested in accordance to their depths, separated into diameter size classes for each species, and their dry weights measured. Roots of shrubs were largely confined to the upper soil levels. The roots of Eriogonum fasciculatum were concentrated in the upper soil layer. Roots of Adenostoma fasciculatum tended to be more superficial than those from Ceanothus greggii. It is hypothesized that the shallow soil at the excavation site impeded a clear depth zonation of the different root systems. The average dry weight root:shoot ratio was 0.6, ranging for the individual shrubs from 0.8 to 0.4. The root area always exceeded the shoot area, with the corresponding ratios ranging from 6 for Arctostaphylos pungens to 40 for Haplopappus pinifolius. The fine root density of 64 g dry weight per m 2 under the canopy was significantly higher than in the unshaded area. However, the corresponding value of 45 g dry weight per m 2 for the open ground is still high enough to make the establishment of other shrubs difficult.

Robustness of Global Radial Anisotropy Models of the Upper Mantle

NASA Astrophysics Data System (ADS)

Xing, Z.; Beghein, C.; Yuan, K.

2014-12-01

Radial anisotropy provides important constraints on mantle deformation. While its presence is well accepted in the uppermost mantle, large discrepancies remain among existing models, even at depths well sampled by seismic data, and its presence at greater depths is highly uncertain. Surface wave phase velocity dispersion measurements are routinely used to constrain lateral variations in mantle S-wave velocity (dlnVS) and radial anisotropy (ξ=VSH2/VSV2). Here, we employed the fundamental and higher mode surface wave phase velocity maps of Visser et al. (2008) that have unprecedented sensitivity to structure down to 800-1000km depth, and we adopted a probabilistic forward modeling approach, the Neighbourhood Algorithm, to quantify posterior model uncertainties and parameter trade-offs. We investigated the effect of prior crustal corrections on 3-D ξ and dlnVS models. To avoid mapping crustal structure onto mantle heterogeneities, it is indeed important to accurately account for 3-D crustal anomalies and variations in Moho depth. One approach is to solve the non-linear problem and simultaneously constrain Moho depth and mantle anomalies (Visser et al., 2008). Another approach, taken here, is to calculate non-linear crustal corrections with an a priori crustal model, which are then applied to the phase velocity maps before inverting the remaining signal for mantle structure. In this work, we also determined laterally varying sensitivity kernels to account for lateral changes in the crust. We compare models obtained using CRUST2.0 (Bassin et al., 2000) and the new CRUST1.0 (Laske et al., 2012) models, which mostly differ under continents. Our preliminary results show strong differences (ΔdlnVS>2%) between the two models in continental dlnVS for the upper 150-200km, and strong changes in x amplitudes in the top 200km (Δξ>2%). Some of the differences in ξ persist down to the transition zone, in particular beneath central Asia and South America. Despite these discrepancies, inferences on the depth of continental roots (~200-250km) based on either the extent of the dlnVS>0 anomalies or the depth at which ξ changes sign remain independent of the crustal model employed. We also note that VSV>VSH dominates the deep upper mantle except in central Pacific, which is characterized by VSH>VSV down to the transition zone.

Water flow and solute transport in floating fen root mats

NASA Astrophysics Data System (ADS)

Stofberg, Sija F.; EATM van der Zee, Sjoerd

2015-04-01

Floating fens are valuable wetlands, found in North-Western Europe, that are formed by floating root mats when old turf ponds are colonized by plants. These terrestrialization ecosystems are known for their biodiversity and the presence of rare plant species, and the root mats reveal different vegetation zones at a small scale. The vegetation zones are a result of strong gradients in abiotic conditions, including groundwater dynamics, nutrients and pH. To prevent irreversible drought effects such as land subsidence and mineralization of peat, water management involves import of water from elsewhere to maintain constant surface water levels. Imported water may have elevated levels of salinity during dry summers, and salt exposure may threaten the vegetation. To assess the risk of exposure of the rare plant species to salinity, the hydrology of such root mats must be understood. Physical properties of root mats have scarcely been investigated. We have measured soil characteristics, hydraulic conductivity, vertical root mat movement and groundwater dynamics in a floating root mat in the nature reserve Nieuwkoopse Plassen, in the Netherlands. The root mat mostly consists of roots and organic material, in which the soil has a high saturated water content, and strongly varies in its stage of decomposition. We have found a distinct negative correlation between degree of decomposition and hydraulic conductivity, similar to observations for bogs in the literature. Our results show that the relatively young, thin edge of the root mat that colonizes the surface water has a high hydraulic conductivity and floats in the surface water, resulting in very small groundwater fluctuations within the root mat. The older part of the root mat, that is connected to the deeper peat layers is hydrologically more isolated and the material has a lower conductivity. Here, the groundwater fluctuates strongly with atmospheric forcing. The zones of hydraulic properties and vegetation, appear to be very similar and likely functionally related. Our experimental field data were used for modelling water flow and solute transport in floating fens, using HYDRUS 2D. Fluctuations of surface water and root mat, as well as geometry and unsaturated zone parameters can have a major influence on groundwater fluctuations and the exchange between rain and surface water and the water in the root mats. In combination with the duration of salt pulses in surface water, and sensitivity of fen plants to salinity (Stofberg et al. 2014, submitted), risks for rare plants can be anticipated.

Measurement carbon dioxide concentration does not affect root respiration of nine tree species in the field

Treesearch

Andrew J. Burton; Kurt S. Pregitzer

2002-01-01

Inhibition of respiration has been reported as a short-term response of tree roots to elevated measurement CO2 concentration ([CO2]), calling into question the validity of root respiration rates determined at CO2 concentrations that differ from the soil [CO2] in the rooting zone...

WETLAND RESTORATION AND REMEDIATION IN SOUTHWEST LOUISIANA MARSHES: A STUDY OF SOIL ELEVATION, VERTICAL ACCRETION, SHALLOW SUBSIDENCE AND ROOT ZONE INFLUENCES IN MARSHES RESTORED USING A VARIETY OF TECHNIQUES

EPA Science Inventory

For Project 1, we will continue sampling of all restoration sites on a quarterly basis. We also will present findings at the 2003 Society of Wetland Scientists Meeting. We will prepare a final data set for a peer-reviewed journal publication. Below-ground root zone...

Methylmercury production in and export from agricultural wetlands in California, USA: the need to account for physical transport processes into and out of the root zone

USGS Publications Warehouse

Bachand, Philip A.M.; Bachand, Sandra M.; Fleck, Jacob A.; Alpers, Charles N.; Stephenson, Mark; Windham-Myers, Lisamarie

2014-01-01

Concentration and mass balance analyses were used to quantify methylmercury (MeHg) loads from conventional (white) rice, wild rice, and fallowed fields in northern California's Yolo Bypass. These analyses were standardized against chloride to distinguish transport pathways and net ecosystem production (NEP). During summer, chloride loads were both exported with surface water and moved into the root zone at a 2:1 ratio. MeHg and dissolved organic carbon (DOC) behaved similarly with surface water and root zone exports at ~ 3:1 ratio. These trends reversed in winter with DOC, MeHg, and chloride moving from the root zone to surface waters at rates opposite and exceeding summertime root zone fluxes. These trends suggest that summer transpiration advectively moves constituents from surface water into the root zone, and winter diffusion, driven by concentration gradients, subsequently releases those constituents into surface waters. The results challenge a number of paradigms regarding MeHg. Specifically, biogeochemical conditions favoring microbial MeHg production do not necessarily translate to synchronous surface water exports; MeHg may be preserved in the soils allowing for release at a later time; and plants play a role in both biogeochemistry and transport. Our calculations show that NEP of MeHg occurred during both summer irrigation and winter flooding. Wild rice wet harvesting and winter flooding of white rice fields were specific practices that increased MeHg export, both presumably related to increased labile organic carbon and disturbance. Outflow management during these times could reduce MeHg exports. Standardizing MeHg outflow:inflow concentration ratios against natural tracers (e.g. chloride, EC) provides a simple tool to identify NEP periods. Summer MeHg exports averaged 0.2 to 1 μg m− 2 for the different agricultural wetland fields, depending upon flood duration. Average winter MeHg exports were estimated at 0.3 μg m− 2. These exports are within the range reported for other shallow aquatic systems.

Methylmercury production in and export from agricultural wetlands in California, USA: the need to account for physical transport processes into and out of the root zone.

PubMed

Bachand, P A M; Bachand, S M; Fleck, J A; Alpers, C N; Stephenson, M; Windham-Myers, L

2014-02-15

Concentration and mass balance analyses were used to quantify methylmercury (MeHg) loads from conventional (white) rice, wild rice, and fallowed fields in northern California's Yolo Bypass. These analyses were standardized against chloride to distinguish transport pathways and net ecosystem production (NEP). During summer, chloride loads were both exported with surface water and moved into the root zone at a 2:1 ratio. MeHg and dissolved organic carbon (DOC) behaved similarly with surface water and root zone exports at ~3:1 ratio. These trends reversed in winter with DOC, MeHg, and chloride moving from the root zone to surface waters at rates opposite and exceeding summertime root zone fluxes. These trends suggest that summer transpiration advectively moves constituents from surface water into the root zone, and winter diffusion, driven by concentration gradients, subsequently releases those constituents into surface waters. The results challenge a number of paradigms regarding MeHg. Specifically, biogeochemical conditions favoring microbial MeHg production do not necessarily translate to synchronous surface water exports; MeHg may be preserved in the soils allowing for release at a later time; and plants play a role in both biogeochemistry and transport. Our calculations show that NEP of MeHg occurred during both summer irrigation and winter flooding. Wild rice wet harvesting and winter flooding of white rice fields were specific practices that increased MeHg export, both presumably related to increased labile organic carbon and disturbance. Outflow management during these times could reduce MeHg exports. Standardizing MeHg outflow:inflow concentration ratios against natural tracers (e.g. chloride, EC) provides a simple tool to identify NEP periods. Summer MeHg exports averaged 0.2 to 1 μg m(-2) for the different agricultural wetland fields, depending upon flood duration. Average winter MeHg exports were estimated at 0.3 μg m(-2). These exports are within the range reported for other shallow aquatic systems. Copyright © 2013 Elsevier B.V. All rights reserved.

Implementing Dynamic Root Optimization in Noah-MP for Simulating Phreatophytic Root Water Uptake

NASA Astrophysics Data System (ADS)

Wang, Ping; Niu, Guo-Yue; Fang, Yuan-Hao; Wu, Run-Jian; Yu, Jing-Jie; Yuan, Guo-Fu; Pozdniakov, Sergey P.; Scott, Russell L.

2018-03-01

Widely distributed in arid and semiarid regions, phreatophytic roots extend into the saturated zone and extract water directly from groundwater. In this paper, we implemented a vegetation optimality model of root dynamics (VOM-ROOT) in the Noah land surface model with multiparameterization options (Noah-MP LSM) to model the extraction of groundwater through phreatophytic roots at a riparian site with a hyperarid climate (with precipitation of 35 mm/yr) in northwestern China. VOM-ROOT numerically describes the natural optimization of the root profile in response to changes in subsurface water conditions. The coupled Noah-MP/VOM-ROOT model substantially improves the simulation of surface energy and water fluxes, particularly during the growing season, compared to the prescribed static root profile in the default Noah-MP. In the coupled model, more roots are required to grow into the saturated zone to meet transpiration demand when the groundwater level declines over the growing season. The modeling results indicate that at the study site, the modeled annual transpiration is 472 mm, accounting for 92.3% of the total evapotranspiration. Direct root water uptake from the capillary fringe and groundwater, which is supplied by lateral groundwater flow, accounts for approximately 84% of the total transpiration. This study demonstrates the importance of implementing a dynamic root scheme in a land surface model for adequately simulating phreatophytic root water uptake and the associated latent heat flux.

Changes in microbial structure and functional communities at different soil depths during 13C labelled root litter degradation

NASA Astrophysics Data System (ADS)

Sanaullah, Muhammad; Baumann, Karen; Chabbi, Abad; Dignac, Marie-France; Maron, Pierre-Alain; Kuzyakov, Yakov; Rumpel, Cornelia

2014-05-01

Soil organic matter turnover depends on substrate quality and microbial activity in soil but little is known about how addition of freshly added organic material modifies the diversity of soil microbial communities with in a soil profile. We took advantage of a decomposition experiment, which was carried out at different soil depths under field conditions and sampled litterbags with 13C-labelled wheat roots, incubated in subsoil horizons at 30, 60 and 90 cm depth for up to 36 months. The effect of root litter addition on microbial community structure, diversity and activity was studied by determining total microbial biomass, PLFA signatures, molecular tools (DNA genotyping and pyrosequencing of 16S and 18S rDNAs) and extracellular enzyme activities. Automated ribosomal intergenic spacer analysis (ARISA) was also carried out to determine the differences in microbial community structure. We found that with the addition of root litter, total microbial biomass as well as microbial community composition and structure changed at different soil depths and change was significantly higher at top 30cm soil layer. Moreover, in the topsoil, population of both gram-positive and gram-negative bacteria increased with root litter addition over time, while subsoil horizons were relatively dominated by fungal community. Extra-cellular enzyme activities confirmed relatively higher fungal community at subsoil horizons compared with surface soil layer with bacteria dominant microbial population. Bacterial-ARISA profiling illustrated that the addition of root litter enhanced the abundance of Actinobacteria and Proteobacteria, at all three soil depths. These bacteria correspond to copiotrophic attributes, which can preferentially consume of labile soil organic C pools. While disappearance of oligotrophic Acidobacteria confirmed the shifting of microbial communities due to the addition of readily available substrate. We concluded that root litter mixing altered microbial community development which was soil horizon specific and its effects on soil microbial activity may impact on nutrient cycling.

Spatial Regulation of Root Growth: Placing the Plant TOR Pathway in a Developmental Perspective

PubMed Central

Barrada, Adam; Montané, Marie-Hélène; Robaglia, Christophe; Menand, Benoît

2015-01-01

Plant cells contain specialized structures, such as a cell wall and a large vacuole, which play a major role in cell growth. Roots follow an organized pattern of development, making them the organs of choice for studying the spatio-temporal regulation of cell proliferation and growth in plants. During root growth, cells originate from the initials surrounding the quiescent center, proliferate in the division zone of the meristem, and then increase in length in the elongation zone, reaching their final size and differentiation stage in the mature zone. Phytohormones, especially auxins and cytokinins, control the dynamic balance between cell division and differentiation and therefore organ size. Plant growth is also regulated by metabolites and nutrients, such as the sugars produced by photosynthesis or nitrate assimilated from the soil. Recent literature has shown that the conserved eukaryotic TOR (target of rapamycin) kinase pathway plays an important role in orchestrating plant growth. We will summarize how the regulation of cell proliferation and cell expansion by phytohormones are at the heart of root growth and then discuss recent data indicating that the TOR pathway integrates hormonal and nutritive signals to orchestrate root growth. PMID:26295391

Root-zone acidity affects relative uptake of nitrate and ammonium from mixed nitrogen sources

NASA Technical Reports Server (NTRS)

Vessey, J. K.; Henry, L. T.; Chaillou, S.; Raper, C. D. Jr; Raper CD, J. r. (Principal Investigator)

1990-01-01

Soybean plants (Glycine max [L.] Merr. cv Ransom) were grown for 21 days on 4 sources of N (1.0 mM NO3-, 0.67 mM NO3- plus 0.33 mM NH4+, 0.33 mM NO3- plus 0.67 mM NH4+, and 1.0 mM NH4+) in hydroponic culture with the acidity of the nutrient solution controlled at pH 6.0, 5.5, 5.0, and 4.5. Dry matter and total N accumulation of the plants was not significantly affected by N-source at any of the pH levels except for decreases in these parameters in plants supplied solely with NH4+ at pH 4.5. Shoot-to-root ratios increased in plants which had an increased proportion [correction of proporiton] of NH4(+)-N in their nutrient solutions at all levels of root-zone pH. Uptake of NO3- and NH4+ was monitored daily by ion chromatography as depletion of these ions from the replenished hydroponic solutions. At all pH levels the proportion of either ion that was absorbed increased as the ratio of that ion increased in the nutrient solution. In plants which were supplied with sources of NO3- plus NH4+, NH4+ was absorbed at a ratio of 2:1 over NO3- at pH 6.0. As the pH of the root-zone declined, however, NH4+ uptake decreased and NO3- uptake increased. Thus, the NH4+ to NO3- uptake ratio declined with decreases in root-zone pH. The data indicate a negative effect of declining root-zone pH on NH4+ uptake and supports a hypothesis that the inhibition of growth of plants dependent on NH4(+)-N at low pH is due to a decline in NH4+ uptake and a consequential limitation of growth by N stress.

Auxin increases the hydrogen peroxide (H2O2) concentration in tomato (Solanum lycopersicum) root tips while inhibiting root growth

PubMed Central

Ivanchenko, Maria G.; den Os, Désirée; Monshausen, Gabriele B.; Dubrovsky, Joseph G.; Bednářová, Andrea; Krishnan, Natraj

2013-01-01

Background and Aims The hormone auxin and reactive oxygen species (ROS) regulate root elongation, but the interactions between the two pathways are not well understood. The aim of this study was to investigate how auxin interacts with ROS in regulating root elongation in tomato, Solanum lycopersicum. Methods Wild-type and auxin-resistant mutant, diageotropica (dgt), of tomato (S. lycopersicum ‘Ailsa Craig’) were characterized in terms of root apical meristem and elongation zone histology, expression of the cell-cycle marker gene Sl-CycB1;1, accumulation of ROS, response to auxin and hydrogen peroxide (H2O2), and expression of ROS-related mRNAs. Key Results The dgt mutant exhibited histological defects in the root apical meristem and elongation zone and displayed a constitutively increased level of hydrogen peroxide (H2O2) in the root tip, part of which was detected in the apoplast. Treatments of wild-type with auxin increased the H2O2 concentration in the root tip in a dose-dependent manner. Auxin and H2O2 elicited similar inhibition of cell elongation while bringing forth differential responses in terms of meristem length and number of cells in the elongation zone. Auxin treatments affected the expression of mRNAs of ROS-scavenging enzymes and less significantly mRNAs related to antioxidant level. The dgt mutation resulted in resistance to both auxin and H2O2 and affected profoundly the expression of mRNAs related to antioxidant level. Conclusions The results indicate that auxin regulates the level of H2O2 in the root tip, so increasing the auxin level triggers accumulation of H2O2 leading to inhibition of root cell elongation and root growth. The dgt mutation affects this pathway by reducing the auxin responsiveness of tissues and by disrupting the H2O2 homeostasis in the root tip. PMID:23965615

Disentangling the root- and detritus-based food chain in the micro-food web of an arable soil by plant removal

PubMed Central

Glavatska, Olena; Müller, Karolin; Butenschoen, Olaf; Schmalwasser, Andreas; Kandeler, Ellen; Scheu, Stefan; Totsche, Kai Uwe

2017-01-01

Soil food web structure and function is primarily determined by the major basal resources, which are living plant tissue, root exudates and dead organic matter. A field experiment was performed to disentangle the interlinkage of the root-and detritus-based soil food chains. An arable site was cropped either with maize, amended with maize shoot litter or remained bare soil, representing food webs depending on roots, aboveground litter and soil organic matter as predominant resource, respectively. The soil micro-food web, i.e. microorganisms and nematodes, was investigated in two successive years along a depth transect. The community composition of nematodes was used as model to determine the changes in the rhizosphere, detritusphere and bulk soil food web. In the first growing season the impact of treatments on the soil micro-food web was minor. In the second year plant-feeding nematodes increased under maize, whereas after harvest the Channel Index assigned promotion of the detritivore food chain, reflecting decomposition of root residues. The amendment with litter did not foster microorganisms, instead biomass of Gram-positive and Gram-negative bacteria as well as that of fungi declined in the rooted zone. Likely higher grazing pressure by nematodes reduced microbial standing crop as bacterial and fungal feeders increased. However, populations at higher trophic levels were not promoted, indicating limited flux of litter resources along the food chain. After two years of bare soil microbial biomass and nematode density remained stable, pointing to soil organic matter-based resources that allow bridging periods with deprivation. Nematode communities were dominated by opportunistic taxa that are competitive at moderate resource supply. In sum, removal of plants from the system had less severe effects than expected, suggesting considerable food web resilience to the disruption of both the root and detrital carbon channel, pointing to a legacy of organic matter resources in arable soils. PMID:28704438

Disentangling the root- and detritus-based food chain in the micro-food web of an arable soil by plant removal.

PubMed

Glavatska, Olena; Müller, Karolin; Butenschoen, Olaf; Schmalwasser, Andreas; Kandeler, Ellen; Scheu, Stefan; Totsche, Kai Uwe; Ruess, Liliane

2017-01-01

Soil food web structure and function is primarily determined by the major basal resources, which are living plant tissue, root exudates and dead organic matter. A field experiment was performed to disentangle the interlinkage of the root-and detritus-based soil food chains. An arable site was cropped either with maize, amended with maize shoot litter or remained bare soil, representing food webs depending on roots, aboveground litter and soil organic matter as predominant resource, respectively. The soil micro-food web, i.e. microorganisms and nematodes, was investigated in two successive years along a depth transect. The community composition of nematodes was used as model to determine the changes in the rhizosphere, detritusphere and bulk soil food web. In the first growing season the impact of treatments on the soil micro-food web was minor. In the second year plant-feeding nematodes increased under maize, whereas after harvest the Channel Index assigned promotion of the detritivore food chain, reflecting decomposition of root residues. The amendment with litter did not foster microorganisms, instead biomass of Gram-positive and Gram-negative bacteria as well as that of fungi declined in the rooted zone. Likely higher grazing pressure by nematodes reduced microbial standing crop as bacterial and fungal feeders increased. However, populations at higher trophic levels were not promoted, indicating limited flux of litter resources along the food chain. After two years of bare soil microbial biomass and nematode density remained stable, pointing to soil organic matter-based resources that allow bridging periods with deprivation. Nematode communities were dominated by opportunistic taxa that are competitive at moderate resource supply. In sum, removal of plants from the system had less severe effects than expected, suggesting considerable food web resilience to the disruption of both the root and detrital carbon channel, pointing to a legacy of organic matter resources in arable soils.

Partial Root-Zone Drying of Olive (Olea europaea var. 'Chetoui') Induces Reduced Yield under Field Conditions

PubMed Central

Dbara, Soumaya; Haworth, Matthew; Emiliani, Giovani; Ben Mimoun, Mehdi; Gómez-Cadenas, Aurelio; Centritto, Mauro

2016-01-01

The productivity of olive trees in arid and semi-arid environments is closely linked to irrigation. It is necessary to improve the efficiency of irrigation techniques to optimise the amount of olive fruit produced in relation to the volume of water used. Partial root-zone drying (PRD) is a water saving irrigation technique that theoretically allows the production of a root-to-shoot signal that modifies the physiology of the above-ground parts of the plant; specifically reducing stomatal conductance (gs) and improving water use efficiency (WUE). Partial root-zone drying has been successfully applied under field conditions to woody and non-woody crops; yet the few previous trials with olive trees have produced contrasting results. Thirty year-old olive trees (Olea europaea ‘var. Chetoui’) in a Tunisian grove were exposed to four treatments from May to October for three-years: ‘control’ plants received 100% of the potential evapotranspirative demand (ETc) applied to the whole root-zone; ‘PRD100’ were supplied with an identical volume of water to the control plants alternated between halves of the root-zone every ten-days; ‘PRD50’ were given 50% of ETc to half of the root-system, and; ‘rain-fed’ plants received no supplementary irrigation. Allowing part of the root-zone to dry resulted in reduced vegetative growth and lower yield: PRD100 decreased yield by ~47% during productive years. During the less productive years of the alternate bearing cycle, irrigation had no effect on yield; this suggests that withholding of water during ‘off-years’ may enhance the effectiveness of irrigation over a two-year cycle. The amount and quality of oil within the olive fruit was unaffected by the irrigation treatment. Photosynthesis declined in the PRD50 and rain-fed trees due to greater diffusive limitations and reduced biochemical uptake of CO2. Stomatal conductance and the foliar concentration of abscisic acid (ABA) were not altered by PRD100 irrigation, which may indicate the absence of a hormonal root-to-shoot signal. Rain-fed and PRD50 treatments induced increased stem water potential and increased foliar concentrations of ABA, proline and soluble sugars. The stomata of the olive trees were relatively insensitive to super-ambient increases in [CO2] and higher [ABA]. These characteristics of ‘hydro-passive’ stomatal behaviour indicate that the ‘Chetoui’ variety of olive tree used in this study lacks the physiological responses required for the successful exploitation of PRD techniques to increase yield and water productivity. Alternative irrigation techniques such as partial deficit irrigation may be more suitable for ‘Chetoui’ olive production. PMID:27315081

Life cycle stage and water depth affect flooding-induced adventitious root formation in the terrestrial species Solanum dulcamara

PubMed Central

Zhang, Qian; Visser, Eric J. W.; de Kroon, Hans; Huber, Heidrun

2015-01-01

Background and Aims Flooding can occur at any stage of the life cycle of a plant, but often adaptive responses of plants are only studied at a single developmental stage. It may be anticipated that juvenile plants may respond differently from mature plants, as the amount of stored resources may differ and morphological changes can be constrained. Moreover, different water depths may require different strategies to cope with the flooding stress, the expression of which may also depend on developmental stage. This study investigated whether flooding-induced adventitious root formation and plant growth were affected by flooding depth in Solanum dulcamara plants at different developmental stages. Methods Juvenile plants without pre-formed adventitious root primordia and mature plants with primordia were subjected to shallow flooding or deep flooding for 5 weeks. Plant growth and the timing of adventitious root formation were monitored during the flooding treatments. Key Results Adventitious root formation in response to shallow flooding was significantly constrained in juvenile S. dulcamara plants compared with mature plants, and was delayed by deep flooding compared with shallow flooding. Complete submergence suppressed adventitious root formation until up to 2 weeks after shoots restored contact with the atmosphere. Independent of developmental stage, a strong positive correlation was found between adventitious root formation and total biomass accumulation during shallow flooding. Conclusions The potential to deploy an escape strategy (i.e. adventitious root formation) may change throughout a plant’s life cycle, and is largely dependent on flooding depth. Adaptive responses at a given stage of the life cycle thus do not necessarily predict how the plant responds to flooding in another growth stage. As variation in adventitious root formation also correlates with finally attained biomass, this variation may form the basis for variation in resistance to shallow flooding among plants. PMID:26105188

Life cycle stage and water depth affect flooding-induced adventitious root formation in the terrestrial species Solanum dulcamara.

PubMed

Zhang, Qian; Visser, Eric J W; de Kroon, Hans; Huber, Heidrun

2015-08-01

Flooding can occur at any stage of the life cycle of a plant, but often adaptive responses of plants are only studied at a single developmental stage. It may be anticipated that juvenile plants may respond differently from mature plants, as the amount of stored resources may differ and morphological changes can be constrained. Moreover, different water depths may require different strategies to cope with the flooding stress, the expression of which may also depend on developmental stage. This study investigated whether flooding-induced adventitious root formation and plant growth were affected by flooding depth in Solanum dulcamara plants at different developmental stages. Juvenile plants without pre-formed adventitious root primordia and mature plants with primordia were subjected to shallow flooding or deep flooding for 5 weeks. Plant growth and the timing of adventitious root formation were monitored during the flooding treatments. Adventitious root formation in response to shallow flooding was significantly constrained in juvenile S. dulcamara plants compared with mature plants, and was delayed by deep flooding compared with shallow flooding. Complete submergence suppressed adventitious root formation until up to 2 weeks after shoots restored contact with the atmosphere. Independent of developmental stage, a strong positive correlation was found between adventitious root formation and total biomass accumulation during shallow flooding. The potential to deploy an escape strategy (i.e. adventitious root formation) may change throughout a plant's life cycle, and is largely dependent on flooding depth. Adaptive responses at a given stage of the life cycle thus do not necessarily predict how the plant responds to flooding in another growth stage. As variation in adventitious root formation also correlates with finally attained biomass, this variation may form the basis for variation in resistance to shallow flooding among plants. © The Author 2015. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Characterizing hydrology and the importance of ground-water discharge in natural and constructed wetlands

USGS Publications Warehouse

Hunt, Randall J.; Walker, John F.; Krabbenhoft, David P.

1999-01-01

Although considered the most important component for the establishment and persistence of wetlands, hydrology has been hard to characterize and linkages between hydrology and other environmental conditions are often poorly understood. In this work, methods for characterizing a wetland’s hydrology from hydrographs were developed, and the importance of ground water to the physical and geochemical conditions in the root zone was investigated. Detailed sampling of nearly continuous hydrographs showed that sites with greater ground-water discharge had higher water tables and more stable hydrographs. Subsampling of the continuous hydrograph failed to characterize the sites correctly, even though the wetland complex is located in a strong regional ground-water-discharge area. By comparing soil-moisture-potential measurements to the water-table hydrograph at one site, we noted that the amount of root-zone saturation was not necessarily driven by the water-table hydrograph but can be a result of other soil parameters (i.e., soil texture and associated capillary fringe). Ground-water discharge was not a significant determinant of maximum or average temperatures in the root zone. High ground-water discharge was associated with earliest date of thaw and shortest period of time that the root zone was frozen, however. Finally, the direction and magnitude of shallow ground-water flow was found to affect the migration and importance of a geochemical species. Areas of higher ground-water discharge had less downward penetration of CO2 generated in the root zone. In contrast, biotically derived CO2 was able to penetrate the deeper ground-water system in areas of ground-water recharge. Although ground-water flows are difficult to characterize, understanding these components is critical to the success of wetland restoration and creation efforts.

Hydrological modelling of the Mara River Basin, Kenya: Application of the Normalised Difference Infrared Index (NDII)

NASA Astrophysics Data System (ADS)

Hulsman, Petra; Savenije, Hubert; Bogaard, Thom

2017-04-01

In hydrology and water resources management, precipitation and discharge are the main time series for hydrological modelling. However, in African river catchments, the quantity and quality of the available precipitation stations and discharge measurements are unfortunately often inadequate for reliable hydrological modelling. To cope with these uncertainties, this study proposes to calibrate on water levels and to constrain the model using the Normalised Difference Infrared Index (NDII) as a proxy for root zone moisture stress. With the NDII, the leaf water content can be monitored. Previous studies related the NDII to the equivalent water thickness (EWT) of leaves, which is used to determine the vegetation water content (VWC). As the water content in the leaves is related to the water content in the root zone, the NDII can also be used as indicator of the soil moisture content in the root zone. In previous studies it was found that the root zone moisture content is exponentially correlated to the NDII during periods of moisture stress. In this study, the semi-distributed rainfall runoff model FLEX-Topo has been applied to the Mara River Basin. In this model seven sub-basins are distinguished and four hydrological response units with each a unique model structure based on the expected dominant flow processes. To calibrate the model, the water levels have been back-calculated from modelled discharges, using cross-section data and the Strickler formula calibrating parameter 'k•s1/2', and compared to measured water levels. In addition, the correlation between the NDII and root zone moisture content has been analysed for this river basin for each sub-catchment and hydrological response unit. Also, the application of the NDII as model constraint or for calibration has been analysed.

Do shallow soil, low water availability, or their combination increase the competition between grasses with different root systems in karst soil?

PubMed

Zhao, Yajie; Li, Zhou; Zhang, Jing; Song, Haiyan; Liang, Qianhui; Tao, Jianping; Cornelissen, Johannes H C; Liu, Jinchun

2017-04-01

Uneven soil depth and low water availability are the key limiting factors to vegetation restoration and reconstruction in limestone soils such as in vulnerable karst regions. Belowground competition will possibly increase under limited soil resources. Here, we investigate whether low resource availability (including shallow soil, low water availability, and shallow soil and low water availability combined) stimulates the competition between grasses with different root systems in karst soil, by assessing their growth response, biomass allocation, and morphological plasticity. In a full three-way factorial blocked design of soil depth by water availability by neighbor identity, we grew Festuca arundinacea (deep-rooted) and Lolium perenne (shallow-rooted) under normal versus shallow soil depth, high versus low water availability, and in monoculture (conspecific neighbor) versus mixture (neighbor of the other species). The key results were as follows: (1) total biomass and aboveground biomass in either of the species decreased with reduction of resources but were not affected by planting patterns (monoculture or mixture) even at low resource levels. (2) For F. arundinacea, root biomass, root mass fraction, total root length, and root volume were higher in mixture than in monoculture at high resource level (consistent with resource use complementarity), but lower in mixture than in monoculture at low resource levels (consistent with interspecific competition). In contrast for L. perenne, either at high or low resource level, these root traits had mostly similar values at both planting patterns. These results suggest that deep-rooted and shallow-rooted plant species can coexist in karst regions under current climatic regimes. Declining resources, due to shallow soil, a decrease in precipitation, or combined shallow soil and karst drought, increased the root competition between plants of deep-rooted and shallow-rooted species. The root systems of deep-rooted plants may be too small to get sufficient water and nutrients from dry, shallow soil, while shallow-rooted plants will maintain a dominant position with their already adaptive strategy in respect of root biomass allocation and root growth.

Thermal Aging of Oceanic Asthenosphere

NASA Astrophysics Data System (ADS)

Paulson, E.; Jordan, T. H.

2013-12-01

To investigate the depth extent of mantle thermal aging beneath ocean basins, we project 3D Voigt-averaged S-velocity variations from an ensemble of global tomographic models onto a 1x1 degree age-based regionalization and average over bins delineated by equal increments in the square-root of crustal age. From comparisons among the bin-averaged S-wave profiles, we estimate age-dependent convergence depths (minimum depths where the age variations become statistically insignificant) as well as S travel times from these depths to a shallow reference surface. Using recently published techniques (Jordan & Paulson, JGR, doi:10.1002/jgrb.50263, 2013), we account for the aleatory variability in the bin-averaged S-wave profiles using the angular correlation functions of the individual tomographic models, we correct the convergence depths for vertical-smearing bias using their radial correlation functions, and we account for epistemic uncertainties through Bayesian averaging over the tomographic model ensemble. From this probabilistic analysis, we can assert with 90% confidence that the age-correlated variations in Voigt-averaged S velocities persist to depths greater than 170 km; i.e., more than 100 km below the mean depth of the G discontinuity (~70 km). Moreover, the S travel time above the convergence depth decays almost linearly with the square-root of crustal age out to 200 Ma, consistent with a half-space cooling model. Given the strong evidence that the G discontinuity approximates the lithosphere-asthenosphere boundary (LAB) beneath ocean basins, we conclude that the upper (and probably weakest) part of the oceanic asthenosphere, like the oceanic lithosphere, participates in the cooling that forms the kinematic plates, or tectosphere. In other words, the thermal boundary layer of a mature oceanic plate appears to be more than twice the thickness of its mechanical boundary layer. We do not discount the possibility that small-scale convection creates heterogeneities in the oceanic upper mantle; however, the large-scale flow evidently advects these small-scale heterogeneities along with the plates, allowing the upper part of the asthenosphere to continue cooling with lithospheric age. The dominance of this large-scale horizontal flow may be related to the high stresses associated with its channelization in a thin (~100 km) asthenosphere, as well as the possible focusing of the subtectospheric strain in a low-viscosity channel immediately above the 410-km discontinuity. These speculations aside, the observed thermal aging of oceanic asthenosphere is inconsistent with a tenet of plate tectonics, the LAB hypothesis, which states that lithospheric plates are decoupled from deeper mantle flow by a shear zone in the upper part of the asthenosphere.

Yellow-Poplar Rooting Habits

Treesearch

John K. Francis

1979-01-01

Although the configuration of pole-sized yellow-poplar root systems in Tennessee is quite variable, a branched taproot with several widely spreading laterals is typical. Rooting depth is particularly limited by clayey texture, wetness, and firmness of subsoils.

Effect of tree roots on a shear zone: modeling reinforced shear stress.

Treesearch

Kazutoki Abe; Robert R. Ziemer

1991-01-01

Tree roots provide important soil reinforcement that impoves the stability of hillslopes. After trees are cut and roots begin to decay, the frequency of slope failures can increase. To more fully understand the mechanics of how tree roots reinforce soil, fine sandy soil containing pine roots was placed in a large shear box in horizontal layers and sheared across a...

Simplified method for the calculation of irregular waves in the coastal zone

NASA Astrophysics Data System (ADS)

Leont'ev, I. O.

2011-04-01

A method applicable for the estimation of the wave parameters along a set bottom profile is suggested. It takes into account the principal processes having an influence on the waves in the coastal zone: the transformation, refraction, bottom friction, and breaking. The ability to use a constant mean value of the friction coefficient under conditions of sandy shores is implied. The wave breaking is interpreted from the viewpoint of the concept of the limiting wave height at a given depth. The mean and root-mean-square wave heights are determined by the height distribution function, which transforms under the effect of the breaking. The verification of the method on the basis of the natural data shows that the calculation results reproduce the observed variations of the wave heights in a wide range of conditions, including profiles with underwater bars. The deviations from the calculated values mostly do not exceed 25%, and the mean square error is 11%. The method does not require a preliminary setting and can be implemented in the form of a relatively simple calculator accessible even for an inexperienced user.

Effects of Infection by Belonolaimus longicaudatus on Rooting Dynamics among St. Augustinegrass and Bermudagrass Genotypes.

PubMed

Aryal, Sudarshan K; Crow, William T; McSorley, Robert; Giblin-Davis, Robin M; Rowland, Diane L; Poudel, Bishow; Kenworthy, Kevin E

2015-12-01

Understanding rooting dynamics using the minirhizotron technique is useful for cultivar selection and to quantify nematode damage to roots. A 2-yr microplot study including five bermudagrass ('Tifway', Belonolaimus longicaudatus susceptible; two commercial cultivars [TifSport and Celebration] and two genotypes ['BA132' and 'PI 291590'], which have been reported to be tolerant to B. longicaudatus) and two St. Augustinegrass ('FX 313', susceptible, and 'Floratam' that was reported as tolerant to B. longicaudatus) genotypes in a 5 x 2 and 2 x 2 factorial design with four replications, respectively, was initiated in 2012. Two treatments included were uninoculated and B. longicaudatus inoculated. In situ root images were captured each month using a minirhizotron camera system from April to September of 2013 and 2014. Mixed models analysis and comparison of least squares means indicated significant differences in root parameters studied across the genotypes and soil depths of both grass species. 'Celebration', 'TifSport' and 'PI 291590' bermudagrass, and 'Floratam' St. Augustinegrass had significantly different root parameters compared to the corresponding susceptible genotypes (P ≤ 0.05). Only 'TifSport' had no significant root loss when infested with B. longicaudatus compared to non-infested. 'Celebration' and 'PI 291590' had significant root loss but retained significantly greater root densities than 'Tifway' in B. longicaudatus-infested conditions (P ≤ 0.05). Root lengths were greater at the 0 to 5 cm depth followed by 5 to 10 and 10 to 15 cm of vertical soil depth for both grass species (P ≤ 0.05). 'Celebration', 'TifSport', and 'PI 291590' had better root vigor against B. longicaudatus compared to Tifway.

Effects of Infection by Belonolaimus longicaudatus on Rooting Dynamics among St. Augustinegrass and Bermudagrass Genotypes

PubMed Central

Aryal, Sudarshan K.; Crow, William T.; McSorley, Robert; Giblin-Davis, Robin M.; Rowland, Diane L.; Poudel, Bishow; Kenworthy, Kevin E.

2015-01-01

Understanding rooting dynamics using the minirhizotron technique is useful for cultivar selection and to quantify nematode damage to roots. A 2-yr microplot study including five bermudagrass (‘Tifway’, Belonolaimus longicaudatus susceptible; two commercial cultivars [TifSport and Celebration] and two genotypes [‘BA132’ and ‘PI 291590’], which have been reported to be tolerant to B. longicaudatus) and two St. Augustinegrass (‘FX 313’, susceptible, and ‘Floratam’ that was reported as tolerant to B. longicaudatus) genotypes in a 5 x 2 and 2 x 2 factorial design with four replications, respectively, was initiated in 2012. Two treatments included were uninoculated and B. longicaudatus inoculated. In situ root images were captured each month using a minirhizotron camera system from April to September of 2013 and 2014. Mixed models analysis and comparison of least squares means indicated significant differences in root parameters studied across the genotypes and soil depths of both grass species. ‘Celebration’, ‘TifSport’ and ‘PI 291590’ bermudagrass, and ‘Floratam’ St. Augustinegrass had significantly different root parameters compared to the corresponding susceptible genotypes (P ≤ 0.05). Only ‘TifSport’ had no significant root loss when infested with B. longicaudatus compared to non-infested. ‘Celebration’ and ‘PI 291590’ had significant root loss but retained significantly greater root densities than ‘Tifway’ in B. longicaudatus-infested conditions (P ≤ 0.05). Root lengths were greater at the 0 to 5 cm depth followed by 5 to 10 and 10 to 15 cm of vertical soil depth for both grass species (P ≤ 0.05). ‘Celebration’, ‘TifSport’, and ‘PI 291590’ had better root vigor against B. longicaudatus compared to Tifway. PMID:26941461

Can increased nitrogen uptake at elevated CO2 be explained by an hypothesis of optimal root function?

NASA Astrophysics Data System (ADS)

McMurtrie, R. E.; Norby, R. J.; Näsholm, T.; Iversen, C.; Dewar, R. C.; Medlyn, B. E.

2011-12-01

Forest free-air CO2 enrichment (FACE) experiments have shown that annual nitrogen (N) uptake increases when trees are grown at elevated CO2 (eCO2) and that increased N uptake is critical for a sustained growth response to eCO2. Processes contributing to increased N uptake at eCO2 may include: accelerated decomposition of soil organic matter due to enhanced root carbon (C) exudation (so-called rhizosphere priming); increased C allocation to fine roots and increased root production at depth, both of which enhance N acquisition; differences in soil N availability with depth; changes in the abundance of N in chemical forms with differing mobility in soil; and reduced N concentrations, reduced maintenance respiration rates, and increased longevities of deeper roots. These processes have been synthesised in a model of annual N uptake in relation to the spatial distribution of roots. We hypothesise that fine roots are distributed spatially in order to maximise annual N uptake. The optimisation hypothesis leads to equations for the optimal vertical distribution of root biomass in relation to the distribution of available soil N and for maximum annual N uptake. We show how maximum N uptake and rooting depth are related to total root mass, and compare the optimal solution with an empirical function that has been fitted to root-distribution data from all terrestrial biomes. Finally, the model is used to explore the consequences of rhizosphere priming at eCO2 as observed at the Duke forest FACE experiment (Drake et al. 2011, Ecology Letters 14: 349-357) and of increasing N limitation over time as observed at the Oak Ridge FACE experiment (Norby et al. 2010, Proc. Nat. Acad. Sci. USA 107: 19368-19373).

Root depth and morphology in response to soil drought: comparing ecological groups along the secondary succession in a tropical dry forest.

PubMed

Paz, Horacio; Pineda-García, Fernando; Pinzón-Pérez, Luisa F

2015-10-01

Root growth and morphology may play a core role in species-niche partitioning in highly diverse communities, especially along gradients of drought risk, such as that created along the secondary succession of tropical dry forests. We experimentally tested whether root foraging capacity, especially at depth, decreases from early successional species to old-growth forest species. We also tested for a trade-off between two mechanisms for delaying desiccation, the capacity to forage deeper in the soil and the capacity to store water in tissues, and explored whether successional groups separate along such a trade-off. We examined the growth and morphology of roots in response to a controlled-vertical gradient of soil water, among seedlings of 23 woody species dominant along the secondary succession in a tropical dry forest of Mexico. As predicted, successional species developed deeper and longer root systems than old-growth forest species in response to soil drought. In addition, shallow root systems were associated with high plant water storage and high water content per unit of tissue in stems and roots, while deep roots exhibited the opposite traits, suggesting a trade-off between the capacities for vertical foraging and water storage. Our results suggest that an increased capacity of roots to forage deeper for water is a trait that enables successional species to establish under the warm-dry conditions of the secondary succession, while shallow roots, associated with a higher water storage capacity, are restricted to the old-growth forest. Overall, we found evidence that the root depth-water storage trade-off may constrain tree species distribution along secondary succession.

Constraints on the Velocity Structure and Accommodation of Shortening in the Atlas Mountains (Morocco) from Travel-Time Inversion of Refraction/Wide Angle Reflection Seismic Data

NASA Astrophysics Data System (ADS)

Ayarza, P.; Carbonell, R.; Palomeras, I.; Levander, A.; Teixell, A.; Zelt, C. A.; Kchikach, A.

2013-12-01

The Atlas Mountains are an intra-continental Cenozoic orogenic belt located at the southern edge of the diffuse plate boundary zone separating Africa and Europe. Its western part, the Moroccan Atlas, has long been under the scope of geoscientists investigating the origin of its high topography, locally exceeding 4000 m. Geological studies indicate that this mountain belt has experienced low to moderate shortening (<24% from balanced sections) and that topography and shortening do not keep a direct relationship. Forward modelling of the SIMA (Seismic Imaging of the Moroccan Atlas) refraction/wide angle reflection seismic data suggests that the total orogenic shortening, is resolved at depth with a Moho offset and a limited lower crust duplication that defines a 40 km-deep root in the northern part of the central High Atlas. However, the shortening accomodated by this feature (50 km) exceeds that estimated with surface data, and the position of the root appears to the north of the highest topography. In order to achieve a better definition of the crust/mantle boundary and to outline a tectonic model more coherent with surface data, we have used the RAYINVR code to carry out travel-time inversion of the SIMA data set. Inversion results depict a small shift to the south of the crustal root, formerly positioned in the northern part of the High Atlas, and define a thrusted mantle wedge. A limited crustal imbrication also appears in the Middle Atlas. The new velocity model implies complex ray trajectories but provides a better travel-time fit between the observed and the calculated data. Also, the amount of shortening implied by the this model is in agreement with that estimated from geological cross-sections. The final crustal thickness, as yet not exceeding 40 km in the root zone and less than 35 km elsewhere, still implies the need of a significant contribution from the mantle to support the topography of the Atlas mountains

Illuminating pathways of forest nutrient provision: relative release from soil mineral and organic pools

NASA Astrophysics Data System (ADS)

Hauser, E.; Billings, S. A.

2017-12-01

Depletion of geogenic nutrients during soil weathering can prompt vegetation to rely on other sources, such as organic matter (OM) decay, to meet growth requirements. Weathered soils also tend to permit deep rooting, a phenomenon sometimes attributed to vegetation foraging for geogenic nutrients. This study examines the extent to which OM recycling provides nutrients to vegetation growing in soils with diverse weathering states. We thus address the fundamental problem of how forest vegetation obtains sufficient nutrition to support productivity despite wide variation in soils' nutrient contents. We hypothesized that vegetation growing on highly weathered soils relies on nutrients released from OM decay to a greater extent than vegetation growing on less weathered, more nutrient-rich substrates. For four mineralogically diverse Critical Zone Observatories (CZO) and Critical Zone Exploratory Network sites, we calculated weathering indices and approximated vegetation nutrient demand and nutrient release from OM decay. We also measured nutrient release rates from OM decay at each site. We then assessed the relationship between degree of soil weathering and the estimated fraction of nutrient demand satisfied by OM derived nutrients. Results are consistent with our hypothesis. The chemical index of alteration (CIA), a weathering index that increases in value with mineral depletion, varies predictably from 90 at the highly weathered Calhoun CZO to 60 at the Catalina CZO, where soils are more recently developed. Estimates of rates of K release from OM decay increase with CIA values. The highest release rate is 2.4 gK m-2 y-1 at Calhoun, accounting for 30% of annual vegetation K uptake; at Catalina, less than 0.5 gm-2 y-1 K is released, meeting 14% of vegetation demand. CIA also co-varies with rooting depth across sites: the deepest roots at the Calhoun sites are growing in soils with the highest CIA values, while the deepest roots at Catalina sites are growing in soils with much lower CIA values. Thus, provision of plant-available nutrients from OM decay appears greater at more weathered sites, and dominant nutrient sources accessed by deep roots (OM- vs. rock-derived) may vary predictably with soil weathering stage. On-going incubations will permit us to assess these relationships for multiple geogenic nutrients.

How rice roots form their surrounding: Distinctive sub-zones of oxides, silicates and organic matter

NASA Astrophysics Data System (ADS)

Koelbl, Angelika; Mueller, Carsten; Hoeschen, Carmen; Lugmeier, Johann; Said-Pullicino, Daniel; Romani, Marco; Koegel-Knabner, Ingrid

2016-04-01

Most of the rice (Oryza sativa) worldwide is grown under flooded conditions in bunded fields (paddies). Inundation during long periods of the year leads to anoxic conditions in the soil. The rice plant is well adapted to these conditions by being able to transport oxygen via aerenchyma from the atmosphere to the roots. This plant mediated O2 transport also influences the adjacent soil. Driven by the O2 leakage into the rhizosphere, reddish ferric oxides and ferric hydroxides precipitate along the root channels. Thus, radial gradients of ferric Fe and with it co-precipitated organic substances form. Detailed investigations of element gradients on a submicron scale within the oxide coatings are still missing. Nano-scale secondary ion mass spectrometry (NanoSIMS) analyses can help to visualize and study the interplay of the various soil components at a submicron scale like, e.g., the attachment of organic material to minerals or the architecture of microstructures. The aim of the present study was to evaluate the composition and size of oxide coatings around rice roots concerning the distribution of organic matter and its spatial relation to oxides and silicates. Samples were taken from the plough pan of a paddy field close to the National Rice Research Centre, Castello d'Agogna (Pavia, Italy). Intact soil aggregates were air-dried, embedded in epoxy resin and then cut and polished in order to obtain a surface with low topography. Reflected-light microscopy was used (mm to μm scale) to visualize the aggregate architecture and to identify root channels in the embedded aggregate. In the next step, scanning electron microscopy (SEM) was applied to obtain images of high resolution and to define distinctive spots for subsequent NanoSIMS analyses. Using the Cameca NanoSIMS 50L at TU München, we simultaneously detected 12C-, 12C14N-, 28Si-, 32S-, 27Al16O- and 56Fe16O- at several areas around root channels in order to distinguish between organic material and different mineral particles (e.g. oxides, clay minerals). Beside single 40 x 40 μm sized spots, mosaics of 20 x 20 μm sized images were combined to investigate the region from the surface of the root channels into the soil matrix. The image data of all detected secondary ions was analysed using line scans and designation of regions of interest (ROI) to evaluate relative occurrences and spatial distributions. The results revealed that the oxic zone around rice roots can be subdivided in distinctive sub-zones. We identified a distinctive zone of approx. 20 μm around the root channels, where exclusively oxide-associated organic matter occurred. This zone can be clearly distinguished from a clay mineral-dominated zone. In addition, oxide-incrusted root cells revealed coexisting regions of Fe (hydr)oxides and Al-organic complexes.

Na+ extrusion from the cytosol and tissue-specific Na+ sequestration in roots confer differential salt stress tolerance between durum and bread wheat.

PubMed

Wu, Honghong; Shabala, Lana; Azzarello, Elisa; Huang, Yuqing; Pandolfi, Camilla; Su, Nana; Wu, Qi; Cai, Shengguan; Bazihizina, Nadia; Wang, Lu; Zhou, Meixue; Mancuso, Stefano; Chen, Zhonghua; Shabala, Sergey

2018-06-11

The progress in plant breeding for salinity stress tolerance is handicapped by the lack of understanding of the specificity of salt stress signalling and adaptation at the cellular and tissue levels. In this study, we used electrophysiological, fluorescence imaging, and real-time quantitative PCR tools to elucidate the essentiality of the cytosolic Na+ extrusion in functionally different root zones (elongation, meristem, and mature) in a large number of bread and durum wheat accessions. We show that the difference in the root's ability for vacuolar Na+ sequestration in the mature zone may explain differential salinity stress tolerance between salt-sensitive durum and salt-tolerant bread wheat species. Bread wheat genotypes also had on average 30% higher capacity for net Na+ efflux from the root elongation zone, providing the first direct evidence for the essentiality of the root salt exclusion trait at the cellular level. At the same time, cytosolic Na+ accumulation in the root meristem was significantly higher in bread wheat, leading to the suggestion that this tissue may harbour a putative salt sensor. This hypothesis was then tested by investigating patterns of Na+ distribution and the relative expression level of several key genes related to Na+ transport in leaves in plants with intact roots and in those in which the root meristems were removed. We show that tampering with this sensing mechanism has resulted in a salt-sensitive phenotype, largely due to compromising the plant's ability to sequester Na+ in mesophyll cell vacuoles. The implications of these findings for plant breeding for salinity stress tolerance are discussed.

Aluminum exclusion from root zone and maintenance of nutrient uptake are principal mechanisms of Al tolerance in Pisum sativum L.

PubMed

Kichigina, Natalia E; Puhalsky, Jan V; Shaposhnikov, Aleksander I; Azarova, Tatiana S; Makarova, Natalia M; Loskutov, Svyatoslav I; Safronova, Vera I; Tikhonovich, Igor A; Vishnyakova, Margarita A; Semenova, Elena V; Kosareva, Irina A; Belimov, Andrey A

2017-10-01

Our study aimed to evaluate intraspecific variability of pea ( Pisum sativum L.) in Al tolerance and to reveal mechanisms underlying genotypic differences in this trait. At the first stage, 106 pea genotypes were screened for Al tolerance using root re-elongation assay based on staining with eriochrome cyanine R. The root re-elongation zone varied from 0.5 mm to 14 mm and relationships between Al tolerance and provenance or phenotypic traits of genotypes were found. Tolerance index (TI), calculated as a biomass ratio of Al-treated and non-treated contrasting genotypes grown in hydroponics for 10 days, varied from 30% to 92% for roots and from 38% to 90% for shoots. TI did not correlate with root or shoot Al content, but correlated positively with increasing pH and negatively with residual Al concentration in nutrient solution in the end of experiments. Root exudation of organic acid anions (mostly acetate, citrate, lactate, pyroglutamate, pyruvate and succinate) significantly increased in several Al-treated genotypes, but did not correlate with TI. Al-treatment decreased Ca, Co, Cu, K, Mg, Mn, Mo, Ni, S and Zn contents in roots and/or shoots, whereas contents of several elements (P, B, Fe and Mo in roots and B and Fe in shoots) increased, suggesting that Al toxicity induced substantial disturbances in uptake and translocation of nutrients. Nutritional disturbances were more pronounced in Al sensitive genotypes. In conclusion, pea has a high intraspecific variability in Al tolerance and this trait is associated with provenance and phenotypic properties of plants. Transformation of Al to unavailable (insoluble) forms in the root zone and the ability to maintain nutrient uptake are considered to be important mechanisms of Al tolerance in this plant species.

Detecting overpressure using the Eaton and Equivalent Depth methods in Offshore Nova Scotia, Canada

NASA Astrophysics Data System (ADS)

Ernanda; Primasty, A. Q. T.; Akbar, K. A.

2018-03-01

Overpressure is an abnormal high subsurface pressure of any fluids which exceeds the hydrostatic pressure of column of water or formation brine. In Offshore Nova Scotia Canada, the values and depth of overpressure zone are determined using the eaton and equivalent depth method, based on well data and the normal compaction trend analysis. Since equivalent depth method is using effective vertical stress principle and Eaton method considers physical property ratio (velocity). In this research, pressure evaluation only applicable on Penobscot L-30 well. An abnormal pressure is detected at depth 11804 feet as possibly overpressure zone, based on pressure gradient curve and calculation between the Eaton method (7241.3 psi) and Equivalent Depth method (6619.4 psi). Shales within Abenaki formation especially Baccaro Member is estimated as possible overpressure zone due to hydrocarbon generation mechanism.

Overestimation of Crop Root Biomass in Field Experiments Due to Extraneous Organic Matter

PubMed Central

Hirte, Juliane; Leifeld, Jens; Abiven, Samuel; Oberholzer, Hans-Rudolf; Hammelehle, Andreas; Mayer, Jochen

2017-01-01

Root biomass is one of the most relevant root parameters for studies of plant response to environmental change, soil carbon modeling or estimations of soil carbon sequestration. A major source of error in root biomass quantification of agricultural crops in the field is the presence of extraneous organic matter in soil: dead roots from previous crops, weed roots, incorporated above ground plant residues and organic soil amendments, or remnants of soil fauna. Using the isotopic difference between recent maize root biomass and predominantly C3-derived extraneous organic matter, we determined the proportions of maize root biomass carbon of total carbon in root samples from the Swiss long-term field trial “DOK.” We additionally evaluated the effects of agricultural management (bio-organic and conventional), sampling depth (0–0.25, 0.25–0.5, 0.5–0.75 m) and position (within and between maize rows), and root size class (coarse and fine roots) as defined by sieve mesh size (2 and 0.5 mm) on those proportions, and quantified the success rate of manual exclusion of extraneous organic matter from root samples. Only 60% of the root mass that we retrieved from field soil cores was actual maize root biomass from the current season. While the proportions of maize root biomass carbon were not affected by agricultural management, they increased consistently with soil depth, were higher within than between maize rows, and were higher in coarse (>2 mm) than in fine (≤2 and >0.5) root samples. The success rate of manual exclusion of extraneous organic matter from root samples was related to agricultural management and, at best, about 60%. We assume that the composition of extraneous organic matter is strongly influenced by agricultural management and soil depth and governs the effect size of the investigated factors. Extraneous organic matter may result in severe overestimation of recovered root biomass and has, therefore, large implications for soil carbon modeling and estimations of the climate change mitigation potential of soils. PMID:28298919

Trunk and root sprouting on residual trees after thinning a Quercus chrysolepis stand

Treesearch

Timothy E. Paysen; Marcia G. Narog; Robert G. Tissell; Melody A. Lardner

1991-01-01

Canyon live oak (Quercus chrysolepis Liebm.) showed sprouting patterns on root and trunk zones foUowing forest thinning. Root sprouting was heaviest on north and east (downhill) sides of residual trees; bole sprouts were concentrated on the south and west (uphill). Root and bole sprouting appeared to be responding to different stimuli, or...

Effects of elevated root zone CO2 on xerophytic shrubs in re-vegetated sandy dunes at smaller spatial and temporal scales.

PubMed

Lei, Huang; Zhishan, Zhang

2015-01-01

The below-ground CO2 concentration in some crusted soils or flooded fields is usually ten or hundred times larger than the normal levels. Recently, a large number of studies have focused on elevated CO2 in the atmosphere; however, only few have examined the influence of elevated root zone CO2 on plant growth and vegetation succession. In the present study, a closed-air CO2 enrichment (CACE) system was designed to simulate elevated CO2 concentrations in the root zones. The physio-ecological characteristics of two typical xerophytic shrubs C. korshinskii and A. ordosica in re-vegetated desert areas were investigated at different soil CO2 concentrations from March 2011 to October 2013. Results showed that plant growth, phenophase, photosynthetic rate, stomatal conductance, transpiration rate, and water use efficiency for the two xerophytic shrubs were all increased at first and then decreased with increasing soil CO2 concentrations, and the optimal soil CO2 concentration thresholds for C. korshinskii and A. ordosica were 0.554 and 0.317%, respectively. And A. ordosica was more tolerate to root zone CO2 variation when compared with C. korshinskii, possible reasons and vegetation succession were also discussed.

Discrimination of plant root zone water status in greenhouse production based on phenotyping and machine learning techniques.

PubMed

Guo, Doudou; Juan, Jiaxiang; Chang, Liying; Zhang, Jingjin; Huang, Danfeng

2017-08-15

Plant-based sensing on water stress can provide sensitive and direct reference for precision irrigation system in greenhouse. However, plant information acquisition, interpretation, and systematical application remain insufficient. This study developed a discrimination method for plant root zone water status in greenhouse by integrating phenotyping and machine learning techniques. Pakchoi plants were used and treated by three root zone moisture levels, 40%, 60%, and 80% relative water content. Three classification models, Random Forest (RF), Neural Network (NN), and Support Vector Machine (SVM) were developed and validated in different scenarios with overall accuracy over 90% for all. SVM model had the highest value, but it required the longest training time. All models had accuracy over 85% in all scenarios, and more stable performance was observed in RF model. Simplified SVM model developed by the top five most contributing traits had the largest accuracy reduction as 29.5%, while simplified RF and NN model still maintained approximately 80%. For real case application, factors such as operation cost, precision requirement, and system reaction time should be synthetically considered in model selection. Our work shows it is promising to discriminate plant root zone water status by implementing phenotyping and machine learning techniques for precision irrigation management.

Application of Terrestrial Microwave Remote Sensing to Agricultural Drought Monitoring

NASA Astrophysics Data System (ADS)

Crow, W. T.; Bolten, J. D.

2014-12-01

Root-zone soil moisture information is a valuable diagnostic for detecting the onset and severity of agricultural drought. Current attempts to globally monitor root-zone soil moisture are generally based on the application of soil water balance models driven by observed meteorological variables. Such systems, however, are prone to random error associated with: incorrect process model physics, poor parameter choices and noisy meteorological inputs. The presentation will describe attempts to remediate these sources of error via the assimilation of remotely-sensed surface soil moisture retrievals from satellite-based passive microwave sensors into a global soil water balance model. Results demonstrate the ability of satellite-based soil moisture retrieval products to significantly improve the global characterization of root-zone soil moisture - particularly in data-poor regions lacking adequate ground-based rain gage instrumentation. This success has lead to an on-going effort to implement an operational land data assimilation system at the United States Department of Agriculture's Foreign Agricultural Service (USDA FAS) to globally monitor variations in root-zone soil moisture availability via the integration of satellite-based precipitation and soil moisture information. Prospects for improving the performance of the USDA FAS system via the simultaneous assimilation of both passive and active-based soil moisture retrievals derived from the upcoming NASA Soil Moisture Active/Passive mission will also be discussed.

Deformational mass transport and invasive processes in soil evolution

NASA Technical Reports Server (NTRS)

Brimhall, George H.; Chadwick, Oliver A.; Lewis, Chris J.; Compston, William; Williams, Ian S.; Danti, Kathy J.; Dietrich, William E.; Power, Mary E.; Hendricks, David; Bratt, James

1992-01-01

Channels left in soil by decayed roots and burrowing animals allow organic and inorganic precipitates and detritus to move through soil from above, to depths at which the minuteness of pores restricts further passage. Consecutive translocation-and-root-growth phases stir the soil, constituting an invasive, dilatational process which generates cumulative strains. Below the depths thus affected, mineral dissolution by descending organic acids leads to internal collapse; this softened/condensed precursor horizon is then transformed into soil via biological activity that mixes and expands the evolving residuum through root and micropore-network invasion.

Growth of the lower continental crust via the relamination of arc magma

NASA Astrophysics Data System (ADS)

He, Yumei; Zheng, Tianyu; Ai, Yinshuang; Hou, Guangbing; Chen, Qi-Fu

2018-01-01

How does continental crust transition from basaltic mantle-derived magmas into an andesitic composition? The relamination hypothesis has been presented as an alternative dynamical mechanism to classical delamination theory to explain new crust generation and has been supported by petrological and geochemical studies as well as by thermomechanical numerical modeling. However, direct evidence of this process from detailed seismic velocity structures is lacking. Here, we imaged the three-dimensional (3D) velocity structures of the crust and uppermost mantle beneath the geologically stable Ordos terrane of the North China Craton (NCC). We identify a region of continental crust that exhibits extreme growth using teleseismic data and an imaging technique that models the Common Conversion Point (CCP) stacking profiles. Our results show an approximately 400 × 400 km2 wide growth zone that underlies the primitive crust at depths of 30-50 km and exhibits a gradual increase of velocity with depth. The upper layer of the growth zone has a shear wave velocity of 3.6-3.9 km/s (Vp = 6.2-6.8 km/s), indicating felsic material, and the lower layer has a shear wave velocity of 4.1-4.3 km/s (Vp = 7.2-7.5 km/s), which corresponds to mafic material. We suggest that this vertical evolution of the layered structure could be created by relamination and that the keel structure formed by relamination may be the root of the supernormal stability of the ancient Ordos terrane.

Auxin distribution is differentially affected by nitrate in roots of two rice cultivars differing in responsiveness to nitrogen

PubMed Central

Song, Wenjing; Sun, Huwei; Li, Jiao; Gong, Xianpo; Huang, Shuangjie; Zhu, Xudong; Zhang, Yali; Xu, Guohua

2013-01-01

Background and Aims Although ammonium (NH4+) is the preferred form of nitrogen over nitrate (NO3−) for rice (Oryza sativa), lateral root (LR) growth in roots is enhanced by partial NO3− nutrition (PNN). The roles of auxin distribution and polar transport in LR formation in response to localized NO3− availability are not known. Methods Time-course studies in a split-root experimental system were used to investigate LR development patterns, auxin distribution, polar auxin transport and expression of auxin transporter genes in LR zones in response to localized PNN in ‘Nanguang’ and ‘Elio’ rice cultivars, which show high and low responsiveness to NO3−, respectively. Patterns of auxin distribution and the effects of polar auxin transport inhibitors were also examined in DR5::GUS transgenic plants. Key Results Initiation of LRs was enhanced by PNN after 7 d cultivation in ‘Nanguang’ but not in ‘Elio’. Auxin concentration in the roots of ‘Nanguang’ increased by approx. 24 % after 5 d cultivation with PNN compared with NH4+ as the sole nitrogen source, but no difference was observed in ‘Elio’. More auxin flux into the LR zone in ‘Nanguang’ roots was observed in response to NO3− compared with NH4+ treatment. A greater number of auxin influx and efflux transporter genes showed increased expression in the LR zone in response to PNN in ‘Nanguang’ than in ‘Elio’. Conclusions The results indicate that higher NO3− responsiveness is associated with greater auxin accumulation in the LR zone and is strongly related to a higher rate of LR initiation in the cultivar ‘Nanguang’. PMID:24095838

Vegetation induced diel signal and its meaning in recharge and discharge regions

NASA Astrophysics Data System (ADS)

Gribovszki, Zoltán; Tóth, Tibor; Csáfordi, Péter; Szabó, András; Móricz, Norbert; Kalicz, Péter

2017-04-01

Afforestation, promoted by the European Union is planned in Hungary in the next decades. One of the most important region for afforestation is the Hungarian Great Plain where the precipitation is far below potential ET so forests can not survive without significant water uptake from shallow groundwater. Diel fluctuations of hydrological variables (e.g., soil moisture, shallow groundwater level, streamflow rate) are rarely investigated in the hydrologic literature although these short-term fluctuations may incorporate useful information (like groundwater uptake) about hydro-ecological systems in shallow groundwater areas. Vegetation induced diel fluctuations are rarely compared under varying hydrologic conditions (such as recharge and discharge zones). In this study, the data of soil moisture and shallow groundwater monitoring under different surface covers (forest and neighboring agricultural plots) in discharge and recharge regions were analyzed to gain a better understanding of the vegetation hydrological impact or water uptake in changing climate. The pilot areas of the study are located in Hungarian Great Plain and in Western Hungary. The water table under the forest displayed a typical night-time recovery in the discharge region, indicating a significant groundwater supply. Certainly, the root system of the forest was able to tap the groundwater in depths measuring a few metres, while the shallower roots of the herbaceous vegetation generally did not reach the groundwater reservoir at these depths. In the recharge zone the water table under the forest showed step-like diel pattern that refer to a lack of additional groundwater supply from below. The low groundwater evapotranspiration of the forest in the recharge zone was due to the lack of the groundwater supply in the recharge area. Similar patterns can be detected in the soil moisture of recharge and discharge zones as well. Our results suggest that local estimations of groundwater evapotranspiration from water table or soil moisture measurements can only be achieved by understanding the different hydrological characteristics of recharge and discharge zones. In the context of climate change higher temperature and longer dry periods induced higher evapotranspiration constrain will probably reduce the groundwater level and so the spatial extent of shallow groundwater areas (reachable groundwater resources for vegetation). Therefore the better understanding of hydrological impact of different surface covers in shallow groundwater areas in changing climate is crucial, not only from water resources management point of view, but also from the viewpoint of agricultural and forest production or survival of forests with high water demand. This research has been mainly supported by the Agroclimate.2 VKSZ_12-1-2013-0034 project. The research of Zoltán Gribovszki was supported by the European Union and the State of Hungary, co-financed by the European Social Fund in the framework of TÁMOP 4.2.4. A/2-11-1-2012-0001 'National Excellence Program'.

The role of calcium and calmodulin in the response of roots to gravity

NASA Technical Reports Server (NTRS)

Evans, Michael L.

1992-01-01

There is general agreement that, in roots, the primary detection of the gravitropic signal occurs in the columella cells of the cap and that this results in the generation of a signal that moves into the elongation zone causing the asymmetric growth that leads to downward curvature. Recent work has generated considerable evidence that indicates that auxin is the ultimate mediator of differential growth during root (and shoot) gravitropism. Our studies of the time course of curvature, auxin redistribution and/or adaptation, and electrical potential changes in maize roots have led to the following generalizations: (1) downward curvature begins 18 to 32 min following gravistimulation; (2) asymmetric auxin redistribution across the root cap begins at about the same time as curvature or perhaps slight earlier; (3) there is a lag of approx. 15 min in the response of roots to applied auxin; and (4) gravi-induced changes in intracellular potentials of cortical cells within the elongation zone occur within 30 s following stimulation.

Gravity-regulated differential auxin transport from columella to lateral root cap cells

NASA Technical Reports Server (NTRS)

Ottenschlager, Iris; Wolff, Patricia; Wolverton, Chris; Bhalerao, Rishikesh P.; Sandberg, Goran; Ishikawa, Hideo; Evans, Mike; Palme, Klaus

2003-01-01

Gravity-induced root curvature has long been considered to be regulated by differential distribution of the plant hormone auxin. However, the cells establishing these gradients, and the transport mechanisms involved, remain to be identified. Here, we describe a GFP-based auxin biosensor to monitor auxin during Arabidopsis root gravitropism at cellular resolution. We identify elevated auxin levels at the root apex in columella cells, the site of gravity perception, and an asymmetric auxin flux from these cells to the lateral root cap (LRC) and toward the elongation zone after gravistimulation. We differentiate between an efflux-dependent lateral auxin transport from columella to LRC cells, and an efflux- and influx-dependent basipetal transport from the LRC to the elongation zone. We further demonstrate that endogenous gravitropic auxin gradients develop even in the presence of an exogenous source of auxin. Live-cell auxin imaging provides unprecedented insights into gravity-regulated auxin flux at cellular resolution, and strongly suggests that this flux is a prerequisite for root gravitropism.

Measuring and modeling of a three-dimensional tracer transport in a planted soil column

NASA Astrophysics Data System (ADS)

Schroeder, N.; Javaux, M.; Haber-Pohlmeier, S.; Pohlmeier, A. J.; Huber, K.; Vereecken, H.; Vanderborght, J.

2013-12-01

Water flow from soil to root is driven by the plant transpiration and an important component of the hydrological cycle. The model R-SWMS combines three-dimensional (3D) water flow and solute transport in soil with a detailed description of root structure in three dimensions [1,2]. This model offers the possibility to calculate root water and solute uptake and flow within the roots, which enables explicit studies with respect to the distribution of water and solutes around the roots as well as local processes at the root-soil interface. In this study, we compared measured data from a tracer experiment using Magnetic Resonance Imaging (MRI) with simulations in order to assess the distribution and magnitude of the water uptake of a young lupine plant. An aqueous solution of the Gadolinium-complex (Gd-DTPA2-) was chosen as a tracer, as it behaves conservatively and is ideally suited for MRI. Water flow in the soil towards the roots can thus be visualized by following the change in tracer concentrations over time. The data were obtained by MRI, providing high resolution 3D images of the tracer distribution and root architecture structures by using a spin echo pulse sequence, which is strongly T1- weighted to be tracer sensitive [3], and T2 -weighted for root imaging [4]. This experimental setup was simulated using the 3D high-resolution numerical model R-SWMS. The comparison between MRI data and the simulations showed extensive effects of root architecture parameters on solute spreading. Although the results of our study showed the strength of combining non-invasive measurements and 3D modeling of solute and water flow in soil-root systems, where the derivation of plant hydraulic parameters such as axial and radial root conductivities is possible, current limitations were found with respect to MRI measurements and process description. [1] Javaux, M., T. Schröder, J. Vanderborght, and H. Vereecken (2008), Use of a Three-Dimensional Detailed Modeling Approach for Predicting Root Water Uptake, Vadose Zone Journal, 7(3), 1079-1079. [2] Schröder, N., M. Javaux, J. Vanderborght, B. Steffen, and H. Vereecken (2012), Effect of Root Water and Solute Uptake on Apparent Soil Dispersivity: A Simulation Study, Vadose Zone Journal, 11(3). [3 ]Haber-Pohlmeier, S., Bechtold, M., Stapf, S., and Pohlmeier, A. (2010). Water Flow Monitored by Tracer Transport in Natural Porous Media Using Magnetic Resonance Imaging. Vadose Zone Journal (9),835-845. [4] Stingaciu, L. R., Schulz, H., Pohlmeier, A., Behnke, S., Zilken, H., Vereecken, H., and Javaux, M. (2013). In Situ Root System Architecture Extraction from Magnetic Resonance Imaging for Application to Water Uptake Modeling. Vadose Zone Journal.

Synchrotron X-ray microfluorescence measurement of metal distributions in Phragmites australis root system in the Yangtze River intertidal zone

DOE PAGES

Feng, Huan; Zhang, Weiguo; Qian, Yu; ...

2016-06-15

This paper investigates the distributions of Br, Ca, Cl, Cr, Cu, K, Fe, Mn, Pb, Ti, V and Zn in Phragmites australis root system and the function of Fe nanoparticles in scavenging metals in the root epidermis using synchrotron X-ray microfluorescence, synchrotron transmission X-ray microscope measurement and synchrotron X-ray absorption near-edge structure techniques. The purpose of this study is to understand the mobility of metals in wetland plant root systems after their uptake from rhizosphere soils. Phragmites australis samples were collected in the Yangtze River intertidal zone in July 2013. The results indicate that Fe nanoparticles are present in themore » root epidermis and that other metals correlate significantly with Fe, suggesting that Fe nanoparticles play an important role in metal scavenging in the epidermis.« less

Synchrotron X-ray microfluorescence measurement of metal distributions in Phragmites australis root system in the Yangtze River intertidal zone

DOE Office of Scientific and Technical Information (OSTI.GOV)

Feng, Huan; Zhang, Weiguo; Qian, Yu

This paper investigates the distributions of Br, Ca, Cl, Cr, Cu, K, Fe, Mn, Pb, Ti, V and Zn in Phragmites australis root system and the function of Fe nanoparticles in scavenging metals in the root epidermis using synchrotron X-ray microfluorescence, synchrotron transmission X-ray microscope measurement and synchrotron X-ray absorption near-edge structure techniques. The purpose of this study is to understand the mobility of metals in wetland plant root systems after their uptake from rhizosphere soils. Phragmites australis samples were collected in the Yangtze River intertidal zone in July 2013. The results indicate that Fe nanoparticles are present in themore » root epidermis and that other metals correlate significantly with Fe, suggesting that Fe nanoparticles play an important role in metal scavenging in the epidermis.« less

Monocular zones in stereoscopic scenes: A useful source of information for human binocular vision?

NASA Astrophysics Data System (ADS)

Harris, Julie M.

2010-02-01

When an object is closer to an observer than the background, the small differences between right and left eye views are interpreted by the human brain as depth. This basic ability of the human visual system, called stereopsis, lies at the core of all binocular three-dimensional (3-D) perception and related technological display development. To achieve stereopsis, it is traditionally assumed that corresponding locations in the right and left eye's views must first be matched, then the relative differences between right and left eye locations are used to calculate depth. But this is not the whole story. At every object-background boundary, there are regions of the background that only one eye can see because, in the other eye's view, the foreground object occludes that region of background. Such monocular zones do not have a corresponding match in the other eye's view and can thus cause problems for depth extraction algorithms. In this paper I will discuss evidence, from our knowledge of human visual perception, illustrating that monocular zones do not pose problems for our human visual systems, rather, our visual systems can extract depth from such zones. I review the relevant human perception literature in this area, and show some recent data aimed at quantifying the perception of depth from monocular zones. The paper finishes with a discussion of the potential importance of considering monocular zones, for stereo display technology and depth compression algorithms.

Acidic beverages increase the risk of in vitro tooth erosion

PubMed Central

Ehlen, Leslie A.; Marshall, Teresa A.; Qian, Fang; Wefel, James S.; Warren, John J.

2008-01-01

Acidic beverages are thought to increase the potential for dental erosion. We report pH and titratable acidities (i.e., quantity of base required to bring a solution to neutral pH) of beverages popular in the United States and lesion depths in enamel and root surfaces following beverage exposure, and we describe associations among pH, titratable acidity and both enamel and root erosive lesion depths. The pH of 100% juices, regular sodas, diet sodas and sports drinks upon opening, and the titratable acidity both upon opening and after 60 minutes of stirring were measured. Enamel and root surfaces of healthy permanent molars and premolars were exposed to individual beverages (4 enamel and 4 root surfaces per beverage) for 25 hours and erosion was measured. Statistical analyses included two-sample t-tests, analyses of variance with post hoc Tukey’s studentized range test; and Spearman rank correlation coefficients. All beverages were acidic; the titratable acidity of energy drinks was greater than regular sodas and diet sodas which were greater than 100% juices and sports drinks (P<0.05). Enamel lesion depths following beverage exposures were greatest for Gatorade® followed by Red Bull® and Coke® which were greater than Diet Coke® and 100% apple juice (P <0.05). Root lesion depths were greatest for Gatorade® followed by Red Bull®, Coke®, 100% apple juice and Diet Coke® (P<0.05). Lesion depths were not associated with pH or titratable acidity. Beverages popular in the United States can produce dental erosion. PMID:19083423

Stress Intensity Factor Plasticity Correction for Flaws in Stress Concentration Regions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Friedman, E.; Wilson, W.K.

2000-02-01

Plasticity corrections to elastically computed stress intensity factors are often included in brittle fracture evaluation procedures. These corrections are based on the existence of a plastic zone in the vicinity of the crack tip. Such a plastic zone correction is included in the flaw evaluation procedure of Appendix A to Section XI of the ASME Boiler and Pressure Vessel Code. Plasticity effects from the results of elastic and elastic-plastic explicit flaw finite element analyses are examined for various size cracks emanating from the root of a notch in a panel and for cracks located at fillet fadii. The results ofmore » these caluclations provide conditions under which the crack-tip plastic zone correction based on the Irwin plastic zone size overestimates the plasticity effect for crack-like flaws embedded in stress concentration regions in which the elastically computed stress exceeds the yield strength of the material. A failure assessment diagram (FAD) curve is employed to graphically c haracterize the effect of plasticity on the crack driving force. The Option 1 FAD curve of the Level 3 advanced fracture assessment procedure of British Standard PD 6493:1991, adjusted for stress concentration effects by a term that is a function of the applied load and the ratio of the local radius of curvature at the flaw location to the flaw depth, provides a satisfactory bound to all the FAD curves derived from the explicit flaw finite element calculations. The adjusted FAD curve is a less restrictive plasticity correction than the plastic zone correction of Section XI for flaws embedded in plastic zones at geometric stress concentrators. This enables unnecessary conservatism to be removed from flaw evaluation procedures that utilize plasticity corrections.« less

A new view into the Cascadia subduction zone and volcanic arc: Implications for earthquake hazards along the Washington margin

USGS Publications Warehouse

Parsons, T.; Trehu, A.M.; Luetgert, J.H.; Miller, K.; Kilbride, F.; Wells, R.E.; Fisher, M.A.; Flueh, E.; ten Brink, Uri S.; Christensen, N.I.

1998-01-01

In light of suggestions that the Cascadia subduction margin may pose a significant seismic hazard for the highly populated Pacific Northwest region of the United States, the U.S. Geological Survey (USGS), the Research Center for Marine Geosciences (GEOMAR), and university collaborators collected and interpreted a 530-km-long wide-angle onshore-offshore seismic transect across the subduction zone and volcanic arc to study the major structures that contribute to seismogenic deformation. We observed (1) an increase in the dip of the Juan de Fuca slab from 2°–7° to 12° where it encounters a 20-km-thick block of the Siletz terrane or other accreted oceanic crust, (2) a distinct transition from Siletz crust into Cascade arc crust that coincides with the Mount St. Helens seismic zone, supporting the idea that the mafic Siletz block focuses seismic deformation at its edges, and (3) a crustal root (35–45 km deep) beneath the Cascade Range, with thinner crust (30–35 km) east of the volcanic arc beneath the Columbia Plateau flood basalt province. From the measured crustal structure and subduction geometry, we identify two zones that may concentrate future seismic activity: (1) a broad (because of the shallow dip), possibly locked part of the interplate contact that extends from ∼25 km depth beneath the coastline to perhaps as far west as the deformation front ∼120 km offshore and (2) a crustal zone at the eastern boundary between the Siletz terrane and the Cascade Range.

A higher sink competitiveness of the rooting zone and invertases are involved in dark stimulation of adventitious root formation in Petunia hybrida cuttings.

PubMed

Klopotek, Yvonne; Franken, Philipp; Klaering, Hans-Peter; Fischer, Kerstin; Hause, Bettina; Hajirezaei, Mohammad-Reza; Druege, Uwe

2016-02-01

The contribution of carbon assimilation and allocation and of invertases to the stimulation of adventitious root formation in response to a dark pre-exposure of petunia cuttings was investigated, considering the rooting zone (stem base) and the shoot apex as competing sinks. Dark exposure had no effect on photosynthesis and dark respiration during the subsequent light period, but promoted dry matter partitioning to the roots. Under darkness, higher activities of cytosolic and vacuolar invertases were maintained in both tissues when compared to cuttings under light. This was partially associated with higher RNA levels of respective genes. However, activity of cell wall invertases and transcript levels of one cell wall invertase isogene increased specifically in the stem base during the first two days after cutting excision under both light and darkness. During five days after excision, RNA accumulation of four invertase genes indicated preferential expression in the stem base compared to the apex. Darkness shifted the balance of expression of one cytosolic and two vacuolar invertase genes towards the stem base. The results indicate that dark exposure before planting enhances the carbon sink competitiveness of the rooting zone and that expression and activity of invertases contribute to the shift in carbon allocation. Copyright © 2015 The Authors. Published by Elsevier Ireland Ltd.. All rights reserved.

Comparative evaluation of antimicrobial effect of herbal root canal irrigants (Morinda citrifolia, Azadirachta indica, Aloe vera) with sodium hypochlorite: An in vitro study.

PubMed

Babaji, Prashant; Jagtap, Kiran; Lau, Himani; Bansal, Nandita; Thajuraj, S; Sondhi, Priti

2016-01-01

Successful root canal treatment involves the complete elimination of microorganism from the root canal and the three-dimensional obturation of the canal space. Enterococcus faecalis is the most commonly found bacteria in failed root canal. Chemical irrigation of canals along with biomechanical preparation helps in the elimination of microorganisms. The present study was aimed to evaluate the antimicrobial effect of herbal root canal irrigants (Morinda citrifolia, Azadirachta indica extract, Aloe vera) with sodium hypochlorite (NaOCl). The bacterial E. faecalis (ATCC) culture was grown overnight in brain heart infusion (BHI) broth and inoculated in Mueller-Hinton agar plates. Antibacterial inhibition was assessed using agar well diffusion method. All five study irrigants were added to respective wells in agar plates and incubated at 37°C for 24 h. Bacterial inhibition zone around each well was recorded. Results were tabulated and statistically analyzed using Statistical Package for the Social Sciences software for Windows, version 19.0. (IBM Corp., Armonk, NY. Highest inhibitory zone against E. faecalis was seen in NaOCl fallowed by M. citrifolia and A. indica extract, and the least by A. vera extract. Tested herbal medicine (A. indica extract, M. citrifolia, A. vera) showed inhibitory zone against E. faecalis. Hence, these irrigants can be used as root canal irrigating solutions.

Root growth and hydraulic conductivity of southern pine seedlings in response to soil temperature and water availability after planting

Treesearch

Mary Anne Sword Sayer; John C. Brissette; James P. Barnett

2005-01-01

Comparison of the root system growth and water transport of southern pine species after planting in different root-zone environments is needed to guide decisions regarding when, and what species to plant. Evaluation of how seed source affects root system responses to soil conditions will allow seed sources to be matched to planting conditions. The root growth and...

The effect of locally delivered doxycycline as an adjunctive therapy to scaling and root planing in smokers

PubMed Central

Al Hulami, Hassan; Babay, Nadir; Awartani, Fatin; Anil, Sukumaran

2011-01-01

Background Locally delivered doxycycline is found to be effective in managing periodontitis as an adjunct to scaling and root planing. Aim To evaluate the effect of locally delivered doxycycline (10%) with scaling and root planing in the periodontal treatment of smokers and to compare it with scaling and root planing alone. Methods Twelve smokers with chronic periodontitis and a pocket depth (⩾5 mm) on posterior teeth that bleed on probing were selected. Patients were randomly assigned to scaling and root planing (SRP) or scaling and root planing followed by local application of doxycycline (SRP-D). Plaque, bleeding on probing, gingival recession, clinical attachment level (CAL), and probing depth (PD) were recorded at the baseline, 6 and 12 weeks. Results Both groups showed a significant reduction in Plaque, Bleeding on Probing and pocket depth at 6th and 12th week from the baseline. A statistically significant gain of attachment was observed in both groups after treatment. Even though the doxycycline group showed slightly higher attachment gain it was not statistically significant compared to the control group. Conclusion The observations of the study reveal that the additional benefit of topical application of doxycycline as an adjunct to scaling and root planing in smokers is not convincing. However, further clinical studies may be necessary to substantiate the present observations. PMID:23960508

TAA1-regulated local auxin biosynthesis in the root-apex transition zone mediates the aluminum-induced inhibition of root growth in Arabidopsis.

PubMed

Yang, Zhong-Bao; Geng, Xiaoyu; He, Chunmei; Zhang, Feng; Wang, Rong; Horst, Walter J; Ding, Zhaojun

2014-07-01

The transition zone (TZ) of the root apex is the perception site of Al toxicity. Here, we show that exposure of Arabidopsis thaliana roots to Al induces a localized enhancement of auxin signaling in the root-apex TZ that is dependent on TAA1, which encodes a Trp aminotransferase and regulates auxin biosynthesis. TAA1 is specifically upregulated in the root-apex TZ in response to Al treatment, thus mediating local auxin biosynthesis and inhibition of root growth. The TAA1-regulated local auxin biosynthesis in the root-apex TZ in response to Al stress is dependent on ethylene, as revealed by manipulating ethylene homeostasis via the precursor of ethylene biosynthesis 1-aminocyclopropane-1-carboxylic acid, the inhibitor of ethylene biosynthesis aminoethoxyvinylglycine, or mutant analysis. In response to Al stress, ethylene signaling locally upregulates TAA1 expression and thus auxin responses in the TZ and results in auxin-regulated root growth inhibition through a number of auxin response factors (ARFs). In particular, ARF10 and ARF16 are important in the regulation of cell wall modification-related genes. Our study suggests a mechanism underlying how environmental cues affect root growth plasticity through influencing local auxin biosynthesis and signaling. © 2014 American Society of Plant Biologists. All rights reserved.

Tree species diversity interacts with elevated CO2 to induce a greater root system response.

PubMed

Smith, Andrew R; Lukac, Martin; Bambrick, Michael; Miglietta, Franco; Godbold, Douglas L

2013-01-01

As a consequence of land-use change and the burning of fossil fuels, atmospheric concentrations of CO2 are increasing and altering the dynamics of the carbon cycle in forest ecosystems. In a number of studies using single tree species, fine root biomass has been shown to be strongly increased by elevated CO2 . However, natural forests are often intimate mixtures of a number of co-occurring species. To investigate the interaction between tree mixture and elevated CO2 , Alnus glutinosa, Betula pendula and Fagus sylvatica were planted in areas of single species and a three species polyculture in a free-air CO2 enrichment study (BangorFACE). The trees were exposed to ambient or elevated CO2 (580 μmol mol(-1) ) for 4 years. Fine and coarse root biomass, together with fine root turnover and fine root morphological characteristics were measured. Fine root biomass and morphology responded differentially to the elevated CO2 at different soil depths in the three species when grown in monocultures. In polyculture, a greater response to elevated CO2 was observed in coarse roots to a depth of 20 cm, and fine root area index to a depth of 30 cm. Total fine root biomass was positively affected by elevated CO2 at the end of the experiment, but not by species diversity. Our data suggest that existing biogeochemical cycling models parameterized with data from species grown in monoculture may be underestimating the belowground response to global change. © 2012 Blackwell Publishing Ltd.

Root length densities of UK wheat and oilseed rape crops with implications for water capture and yield

PubMed Central

White, Charlotte A.; Sylvester-Bradley, Roger; Berry, Peter M.

2015-01-01

Root length density (RLD) was measured to 1 m depth for 17 commercial crops of winter wheat (Triticum aestivum) and 40 crops of winter oilseed rape [Brassica napus; oilseed rape (OSR)] grown in the UK between 2004 and 2013. Taking the critical RLD (cRLD) for water capture as 1cm cm–3, RLDs appeared inadequate for full water capture on average below a depth of 0.32 m for winter wheat and below 0.45 m for OSR. These depths compare unfavourably (for wheat) with average depths of ‘full capture’ of 0.86 m and 0.48 m, respectively, determined for three wheat crops and one OSR crop studied in the 1970s and 1980s, and treated as references here. A simple model of water uptake and yield indicated that these shortfalls in wheat and OSR rooting compared with the reference data might be associated with shortfalls of up to 3.5 t ha–1 and 1.2 t ha–1, respectively, in grain yields under water-limited conditions, as increasingly occur through climate change. Coupled with decreased summer rainfall, poor rooting of modern arable crops could explain much of the yield stagnation that has been observed on UK farms since the 1990s. Methods of monitoring and improving rooting under commercial conditions are reviewed and discussed. PMID:25750427

Tamarack and black spruce adventitious root patterns are similar in their ability to estimate organic layer depths in northern temperate forests

Treesearch

Timothy J. Veverica; Evan S. Kane; Eric S. Kasischke

2012-01-01

Organic layer consumption during forest fires is hard to quantify. These data suggest that the adventitious root methods developed for reconstructing organic layer depths following wildfires in boreal black spruce forests can also be applied to mixed tamarack forests growing in temperate regions with glacially transported soils.

The model of root graviresponse with retarded arguments

NASA Astrophysics Data System (ADS)

Kondrachuk, Alexander

The graviperception mechanism (GPM) of the roots of higher plants localized in the cap region of a root and supposedly related to statoliths sedimentation produces the signals in response to the change of the root axis orientation relative to the gravity vector G. Meanwhile, the regions (Distal Elongation Zone -DEZ and Central Elongation Zone-CEZ), where the signals initiate the changes of the growth rates of the upper and lower flanks of the root, are located at the significant distances from the cap (thousands microns for some plants). It causes the time delays between the relocation of statoliths in statocytes and the change of the growth rates in elongation zones. It is suggested that the signal targeting the CEZ modulates the initially uniform lateral distribution of some specific substances (S) in the cap region. Then already nonhomogeneous lateral distribution of S is transferred to the CEZ to initiate the change of the growth rates of the opposite flanks. It results in the bending of the root in the line of G and thus in the change of the GPM signal in the cap region. In the present model the kinetics of a root apex bending (angle A) in response to the time (t)-dependent change of the G orientation is described by the integro-differential equation in A(t). The main peculiarity of this model is the presence of retarded (time-delayed) arguments t-TCEZ and t-TDEZ . In this case the solutions of this equation depend on the preceding kinetics of A(t) during the time delays TCEZ and TDEZ . It is suggested that the signals activating the CEZ and DEZ are of different nature. The work is focused on two problems concerning the modeling of the effects of time-delay(s) on the root bending. The first problem supposes the existence of one zone (CEZ) and one time-delay TCEZ . This equation was studied and solved using analytical and numerical methods. We analyzed the model as to whether it can be used to describe the kinetics of root graviresponse in the case of different orientations of the root apex relative to the G vector during the time interval equal to TCEZ (TCEZ > TDEZ ) that precedes the beginning of gravistimultion. Also we explored the conditions of the overshooting (the vertical) and non-overshooting regimes of gravistimulated root bending. Good correlation between the results of the modeling and known experimental data (Barlow et al, 1993, Stochkus, 1994, Mullen, 1998) was found. This allowed us to estimate and analyze the parameters of the model. The second problem supposed the existence of two zones of growth (CEZ and DEZ) and two corresponding time-delays. The effects of the second time-delay connected with the presence of the DEZ on the behavior of the model equation of the root graviresponse kinetics were analyzed and discussed.

Field-scale study of the influence of differing remediation strategies on trace metal geochemistry in metal mine tailings from the Irish Midlands.

PubMed

Perkins, William T; Bird, Graham; Jacobs, Suzanne R; Devoy, Cora

2016-03-01

Mine tailings represent a globally significant source of potentially harmful elements (PHEs) to the environment. The management of large volumes of mine tailings represents a major challenge to the mining industry and environmental managers. This field-scale study evaluates the impact of two highly contrasting remediation approaches to the management and stabilisation of mine tailings. The geochemistry of the tailings, overlying amendment layers and vegetation are examined in the light of the different management approaches. Pseudo-total As, Cd and Pb concentrations and solid-state partitioning (speciation), determined via sequential extraction, were established for two Tailings Management Facilities (TMFs) in Ireland subjected to the following: (1) a 'walk-away' approach (Silvermines) and (2) application of an amendment layer (Galmoy). PHE concentrations in roots and herbage of grasses growing on the TMFs were also determined. Results identify very different PHE concentration profiles with depth through the TMFs and the impact of remediation approach on concentrations and their potential bioavailability in the rooting zone of grass species. Data also highlight the importance of choice of grass species in remediation approaches and the benefits of relatively shallow-rooting Agrostis capillaris and Festuca rubra varieties. In addition, data from the Galmoy TMF indicate the importance of regional soil geochemistry for interpreting the influence of the PHE geochemistry of capping and amendment layers applied to mine tailings.

[Dynamics of diazotrophic bacteria number in the root zone of wheat Vrn lines isogenic by genes].

PubMed

Samoĭlov, A M; Zhmurko, V V

2012-01-01

The number of diazotrophic bacteria and nitrogenase activity in the root zone of isogenic monogene-dominant Vrn lines were measured in the field experiments throughout their vegetation from tillering to heading. The total number of diazotrophic bacteria and nitrogenase activity in the root zone of these lines during this period were increased irrespective of their genotypes. The above indices of the winter cultivar (Vrn loci bottom recessive) were lower than those of the spring lines--Vrn-A1, Vrn-B1 and Vrn-D1. Plants of Vrn-B1 line have the lowest indices among the spring lines with the exception of some indices. This line plants flowered later than those of Vrn-A1 and Vrn-D1 lines. We hypothesized the differences between plants of these lines as to nitrogen fixation activity and the number of diazotrophic bacteria are mediately determined by Vrn loci through their effects on metabolism intensity and assimilate reflux in the form of root exudates, therefore the total number of diazotrophic bacteria and nitrogenase activity increases.

``Rhizogenesis in vitro'' - as a model to study microgravity biological effects

NASA Astrophysics Data System (ADS)

Bulavin, Iliya

Functioning organisms is based on the physiological and biochemical processes in different tissues and cells. Numerous spaceflight biological experiments have shown the essential changes in cell behavior of multicellular and unicellular organisms in comparison with that on Earth. In our investigations, we used the model “Rhizogenesis in vitro” to study cell differentiation in the root cap and growth zones under clinorotation. Advantage of this model is the possibility to study the influence of clinorotation at the beginning of root initiation de novo and next morphogenetic processes unlike experiments in vivo with embryonal seedling roots formed in seeds. Arabidopsis thaliana plants of wild type and scr mutant (3999 by NASC database) were used. For rhizogenesis induction, rosette leaves with petioles were cut and transferred in Petri dishes on MS medium contained 1/10 of MS mineral salt, without vitamins and hormones. One half of Petri dishes were placed vertically (control), the other - on a slow horizontal clinostat (2 rpm). Anatomical investigation of A. thaliana wild type and scr mutant roots formed de novo showed that formation of root cap and growth zones (meristem, distal elongation zone (DEZ), central elongation zone (CEZ) and mature zone) under clinorotation was similar to that in control. A root cap consists of columella and peripheral cells. In the columella there are meristematic cells, statocytes (graviperceptive cells), and secretory cells. Epidermis, parenchyma, endodermis and central cylinder are distinguished in wild type roots. Unlike a wild type, a cortex of scr mutant was represented by one cell layer which had the parenchyma and endodermis characteristics. A root cap length and width were similar in control and under clinorotation. A cell number in the meristem and DEZ and a length of these growth zones did not differ in control and the experimental conditions. The ultrasructure of cap meristematic cells was typical for cells of this type. Statocytes preserved their polarity in control but it was disturbed under clinorotation due to amyloplast distribution in the cytoplasm whole volume and/or their localization in the cell center. Structural rearrangements occurred similarly in statocytes under their transformation in secretory cells in control and under clinorotation. A characteristic features of the root proper meristematic cells in the control and in the experiment are central nucleus location, the great diversity of a size and a shape of mitochondria and plastids, poorly ER development, the presence of some small ER-bodies. As cells passed in the DEZ, their size enlarged but a nucleus can preserve the central location. A quantity of ER-cistern, vacuoles, and ER-bodies increased also. Dictyosomes acquired polarity and produced many Golgi vesicles. In CEZ cells, a large vacuole occupied the cell center, and the cytoplasm with organelles was on the cell periphery. So, we can conclude that under clinorotation: 1) the structure of a cap and growth zones of A. thaliana wild type and scr mutant roots formed de novo in vitro as similar to that in control; 2) a gaviperceptive apparatus formed in both objects but did not function. The obtained data allow to propose the model “Rhizogenesis in vitro” for using in spaceflight experiments to study the influence of real microgravity on the cellular differentiation and basic processes.

Realization of arbitrarily long focus-depth optical vortices with spiral area-varying zone plates

NASA Astrophysics Data System (ADS)

Zheng, Chenglong; Zang, Huaping; Du, Yanli; Tian, Yongzhi; Ji, Ziwen; Zhang, Jing; Fan, Quanping; Wang, Chuanke; Cao, Leifeng; Liang, Erjun

2018-05-01

We provide a methodology to realize an optical vortex with arbitrarily long focus-depth. With a technique of varying each zone area of a phase spiral zone plate one can obtain optics capable of generating ultra-long focus-depth optical vortex from a plane wave. The focal property of such optics was analysed using the Fresnel diffraction theory, and an experimental demonstration was performed to verify its effectiveness. Such optics may bring new opportunity and benefits for optical vortex application such as optical manipulation and lithography.

Identification of a core set of rhizobial infection genes using data from single cell-types.

PubMed

Chen, Da-Song; Liu, Cheng-Wu; Roy, Sonali; Cousins, Donna; Stacey, Nicola; Murray, Jeremy D

2015-01-01

Genome-wide expression studies on nodulation have varied in their scale from entire root systems to dissected nodules or root sections containing nodule primordia (NP). More recently efforts have focused on developing methods for isolation of root hairs from infected plants and the application of laser-capture microdissection technology to nodules. Here we analyze two published data sets to identify a core set of infection genes that are expressed in the nodule and in root hairs during infection. Among the genes identified were those encoding phenylpropanoid biosynthesis enzymes including Chalcone-O-Methyltransferase which is required for the production of the potent Nod gene inducer 4',4-dihydroxy-2-methoxychalcone. A promoter-GUS analysis in transgenic hairy roots for two genes encoding Chalcone-O-Methyltransferase isoforms revealed their expression in rhizobially infected root hairs and the nodule infection zone but not in the nitrogen fixation zone. We also describe a group of Rhizobially Induced Peroxidases whose expression overlaps with the production of superoxide in rhizobially infected root hairs and in nodules and roots. Finally, we identify a cohort of co-regulated transcription factors as candidate regulators of these processes.

Silicon enhances suberization and lignification in roots of rice (Oryza sativa).

PubMed

Fleck, Alexander T; Nye, Thandar; Repenning, Cornelia; Stahl, Frank; Zahn, Marc; Schenk, Manfred K

2011-03-01

The beneficial element silicon (Si) may affect radial oxygen loss (ROL) of rice roots depending on suberization of the exodermis and lignification of sclerenchyma. Thus, the effect of Si nutrition on the oxidation power of rice roots, suberization and lignification was examined. In addition, Si-induced alterations of the transcript levels of 265 genes related to suberin and lignin synthesis were studied by custom-made microarray and quantitative Real Time-PCR. Without Si supply, the oxidation zone of 12 cm long adventitious roots extended along the entire root length but with Si supply the oxidation zone was restricted to 5 cm behind the root tip. This pattern coincided with enhanced suberization of the exodermis and lignification of sclerenchyma by Si supply. Suberization of the exodermis started, with and without Si supply, at 4-5 cm and 8-9 cm distance from the root tip (drt), respectively. Si significantly increased transcript abundance of 12 genes, while two genes had a reduced transcript level. A gene coding for a leucine-rich repeat protein exhibited a 25-fold higher transcript level with Si nutrition. Physiological, histochemical, and molecular-biological data showing that Si has an active impact on rice root anatomy and gene transcription is presented here.

Effect of flavonoids on remineralization of artificial root caries.

PubMed

Epasinghe, D J; Yiu, Cky; Burrow, M F

2016-06-01

This study compared the effects of three flavonoids, including proanthocyanidin, naringin and quercetin on remineralization of artificial root caries. Demineralized root fragments (n = 75) were randomly divided into five groups for treatment with the remineralizing agents for 10 minutes: (1) 6.5% proanthocyanidin; (2) 6.5% naringin; (3) 6.5% quercetin; (4) 1000 ppm fluoride; and (5) deionized water (control). The demineralized samples were pH-cycled through treatment solutions, acidic buffer and neutral buffer for eight days at six cycles per day. The remineralization effects were evaluated using Knoop microhardness, transverse microradiography (lesion depth and mineral loss) and confocal laser scanning microscopy. Microhardness at different lesion depths was analysed with two-way ANOVA and Tukey's test, while lesion depths and mineral loss were analysed with one-way ANOVA and Tukey's test. Artificial caries lesions treated with fluoride and flavonoids showed significantly greater hardness than the control group (p < 0.05). Both lesion depths and mineral loss of the flavonoid treated groups were significantly lower than the control group (p < 0.05), but significantly higher than the fluoride treated group. No significant difference in lesion depth and mineral loss was found among the three flavonoids (p > 0.05). All three flavonoids showed positive effects on artificial root caries remineralization, which are significantly lower than that of 1000 ppm fluoride. © 2016 Australian Dental Association.

Effect of weightlessness conditions on the somatic embryogenesis in the culture of carrot cells

NASA Technical Reports Server (NTRS)

Butenko, R. G.; Dmitriyeva, N. N.; Ongko, V.; Basyrova, L. V.

1977-01-01

A carrot cell culture seeded in Petri dishes in the United States and transported to the USSR was subjected to weightlessness for 20 days during the flight of Kosmos 782. The controls were cultures placed on a centrifuge (1 g) inside the satellite and cultures left on ground in the U.S.S.R. and the United States. A count of structures in the dishes after the flight showed that the number of developing embryonic structures and the extent of their differentiation in weightlessness did not reliably differ from the number and extent of differentiation in structures developed on the ground. Structures with long roots developed in weightlessness. Analysis of the root zones showed that these roots differed by the increased size of the zone of differentiated cells. The increased size of the zones of differentiated cells can indicate earlier development of embryonic structures.

Computer-based video digitizer analysis of surface extension in maize roots: kinetics of growth rate changes during gravitropism

NASA Technical Reports Server (NTRS)

Ishikawa, H.; Hasenstein, K. H.; Evans, M. L.

1991-01-01

We used a video digitizer system to measure surface extension and curvature in gravistimulated primary roots of maize (Zea mays L.). Downward curvature began about 25 +/- 7 min after gravistimulation and resulted from a combination of enhanced growth along the upper surface and reduced growth along the lower surface relative to growth in vertically oriented controls. The roots curved at a rate of 1.4 +/- 0.5 degrees min-1 but the pattern of curvature varied somewhat. In about 35% of the samples the roots curved steadily downward and the rate of curvature slowed as the root neared 90 degrees. A final angle of about 90 degrees was reached 110 +/- 35 min after the start of gravistimulation. In about 65% of the samples there was a period of backward curvature (partial reversal of curvature) during the response. In some cases (about 15% of those showing a period of reverse bending) this period of backward curvature occurred before the root reached 90 degrees. Following transient backward curvature, downward curvature resumed and the root approached a final angle of about 90 degrees. In about 65% of the roots showing a period of reverse curvature, the roots curved steadily past the vertical, reaching maximum curvature about 205 +/- 65 min after gravistimulation. The direction of curvature then reversed back toward the vertical. After one or two oscillations about the vertical the roots obtained a vertical orientation and the distribution of growth within the root tip became the same as that prior to gravistimulation. The period of transient backward curvature coincided with and was evidently caused by enhancement of growth along the concave and inhibition of growth along the convex side of the curve, a pattern opposite to that prevailing in the earlier stages of downward curvature. There were periods during the gravitropic response when the normally unimodal growth-rate distribution within the elongation zone became bimodal with two peaks of rapid elongation separated by a region of reduced elongation rate. This occurred at different times on the convex and concave sides of the graviresponding root. During the period of steady downward curvature the elongation zone along the convex side extended farther toward the tip than in the vertical control. During the period of reduced rate of curvature, the zone of elongation extended farther toward the tip along the concave side of the root. The data show that the gravitropic response pattern varies with time and involves changes in localized elongation rates as well as changes in the length and position of the elongation zone. Models of root gravitropic curvature based on simple unimodal inhibition of growth along the lower side cannot account for these complex growth patterns.

Root Hydraulics and Root Sap Flow in a Panamanian Low-Land Tropical Forest

NASA Astrophysics Data System (ADS)

Bretfeld, M.; Ewers, B. E.; Hall, J. S.; Ogden, F. L.; Beverly, D.; Speckman, H. N.

2017-12-01

In the tropics, trees are subjected to increasingly frequent and severe droughts driven by climate change. Given the hydrological benefits associated with tropical forests, such as reduced peak runoff during high precipitation events and increased base flow during drought periods ("sponge-effect"), the underlying plant-hydrological processes at the soil-plant interface have become the focus of recent research efforts. In Panama, the 2015/16 El Niño-Southern Oscillation (ENSO) event ranks amongst the driest and hottest periods on record, thus providing an excellent opportunity to study the effects of drought on tropical forests. Starting in 2015, we instrumented 76 trees with heat-ratio sap flow sensors in regrowing secondary forest (8-, 25-, and 80-year old stands) in the 15 km2 Agua Salud study area, located in central Panama. Of those trees, 16 individuals were instrumented with additional sap flow sensors on three roots each. Data were logged every 30 minutes and soil moisture was measured at 10, 30, 50, and 100 cm depth. Meteorological data were taken from a nearby met-station. Rooting depth and root density were assessed in eight 2×2×2 m soil pits. In April 2017, we measured hydraulic conductance and vulnerability to cavitation of eight species using the centrifuge technique. Trees in 8-year old forest limited transpiration during the drought whereas no such limitation was evident in trees of the 80-year old forest. Root sap flow data show seasonal shifts in water uptake between individual roots of a given tree, with sap flow decreasing in some roots while simultaneously increasing in other roots during the wet-dry season transition. Roots followed a typical log distribution along the profile, with overall root densities of 46, 43, and 52 roots m-2 in the 8-, 25-, and 80-yo stand, respectively. Roots were found up to 200 cm depth in all forests, with roots >5 cm occurring at lower depths (>125 cm) only in 25- and 80-year old forests. Maximum hydraulic conductances ranged from 2.3 to 48.4 cm3 m-2 s-1. Vulnerability to hydraulic failure was highly variable between species, ranging from hydraulic failure at 1 MPa to resilience up to 12 MPa. Our data suggest increasing resilience to drought with progressing forest age, likely due to access to deeper soil water and favorable hydrological soil properties in older forests.

DRO1 influences root system architecture in Arabidopsis and Prunus species

USDA-ARS?s Scientific Manuscript database

Roots provide essential uptake of water and nutrients from the soil, as well as anchorage and stability for the whole plant. Root orientation or angle is an important component of the overall architecture and depth of the root system; however, little is known about the genetic control of this trai...

Tritium plume dynamics in the shallow unsaturated zone in an arid environment

USGS Publications Warehouse

Maples, S.R.; Andraski, Brian J.; Stonestrom, David A.; Cooper, C.A.; Pohll, G.; Michel, R.L.

2014-01-01

The spatiotemporal variability of a tritium plume in the shallow unsaturated zone and the mechanisms controlling its transport were evaluated during a 10-yr study. Plume movement was minimal and its mass declined by 68%. Upward-directed diffusive-vapor tritium fluxes and radioactive decay accounted for most of the observed plume-mass declines.Effective isolation of tritium (3H) and other contaminants at waste-burial facilities requires improved understanding of transport processes and pathways. Previous studies documented an anomalously widespread (i.e., theoretically unexpected) distribution of 3H (>400 m from burial trenches) in a dry, sub-root-zone gravelly layer (1–2-m depth) adjacent to a low-level radioactive waste (LLRW) burial facility in the Amargosa Desert, Nevada, that closed in 1992. The objectives of this study were to: (i) characterize long-term, spatiotemporal variability of 3H plumes; and (ii) quantify the processes controlling 3H behavior in the sub-root-zone gravelly layer beneath native vegetation adjacent to the facility. Geostatistical methods, spatial moment analyses, and mass flux calculations were applied to a spatiotemporally comprehensive, 10-yr data set (2001–2011). Results showed minimal bulk-plume advancement during the study period and limited Fickian spreading of mass. Observed spreading rates were generally consistent with theoretical vapor-phase dispersion. The plume mass diminished more rapidly than would be expected from radioactive decay alone, indicating net efflux from the plume. Estimates of upward 3H efflux via diffusive-vapor movement were >10× greater than by dispersive-vapor or total-liquid movement. Total vertical fluxes were >20× greater than lateral diffusive-vapor fluxes, highlighting the importance of upward migration toward the land surface. Mass-balance calculations showed that radioactive decay and upward diffusive-vapor fluxes contributed the majority of plume loss. Results indicate that plume losses substantially exceeded any continuing 3H contribution to the plume from the LLRW facility during 2001 to 2011 and suggest that the widespread 3H distribution resulted from transport before 2001.

Spatial Distributions of Potassium, Solutes, and Their Deposition Rates in the Growth Zone of the Primary Corn Root 1

PubMed Central

Silk, Wendy Kuhn; Hsiao, Theodore C.; Diedenhofen, Ulrike; Matson, Christina

1986-01-01

Densities of osmoticum and potassium were measured as a function of distance from the tip of the primary root of Zea mays L. (cv WF9 × mo17). Millimeter segments were excised and analyzed for osmotic potential by a miniaturized freezing point depression technique, and for potassium by flame spectrophotometry. Local deposition rates were estimated from the continuity equation with values for density and growth velocity. Osmotic potential was uniform, −0.73 ± 0.05 megapascals, throughout the growth zone of well-watered roots. Osmoticum deposition rate was 260 μosmoles per gram fresh weight per hour. Potassium density fell from 117 micromoles per gram in the first mm region to 48 micromoles per gram at the base of the growth zone. Potassium deposition rates had a maximum of 29 micromoles per gram per hour at 3.5 millimeters from the tip and were positive (i.e. potassium was being added to the tissue) until 8 millimeters from the tip. The results are discussed in terms of ion relations of the growing zone and growth physics. PMID:16665121

Local root abscisic acid (ABA) accumulation depends on the spatial distribution of soil moisture in potato: implications for ABA signalling under heterogeneous soil drying

PubMed Central

Puértolas, Jaime; Conesa, María R.; Ballester, Carlos; Dodd, Ian C.

2015-01-01

Patterns of root abscisic acid (ABA) accumulation ([ABA]root), root water potential (Ψroot), and root water uptake (RWU), and their impact on xylem sap ABA concentration ([X-ABA]) were measured under vertical partial root-zone drying (VPRD, upper compartment dry, lower compartment wet) and horizontal partial root-zone drying (HPRD, two lateral compartments: one dry, the other wet) of potato (Solanum tuberosum L.). When water was withheld from the dry compartment for 0–10 d, RWU and Ψroot were similarly lower in the dry compartment when soil volumetric water content dropped below 0.22cm3 cm–3 for both spatial distributions of soil moisture. However, [ABA]root increased in response to decreasing Ψroot in the dry compartment only for HPRD, resulting in much higher ABA accumulation than in VPRD. The position of the sampled roots (~4cm closer to the surface in the dry compartment of VPRD than in HPRD) might account for this difference, since older (upper) roots may accumulate less ABA in response to decreased Ψroot than younger (deeper) roots. This would explain differences in root ABA accumulation patterns under vertical and horizontal soil moisture gradients reported in the literature. In our experiment, these differences in root ABA accumulation did not influence [X-ABA], since the RWU fraction (and thus ABA export to shoots) from the dry compartment dramatically decreased simultaneously with any increase in [ABA]root. Thus, HPRD might better trigger a long-distance ABA signal than VPRD under conditions allowing simultaneous high [ABA]root and relatively high RWU fraction. PMID:25547916

Local root abscisic acid (ABA) accumulation depends on the spatial distribution of soil moisture in potato: implications for ABA signalling under heterogeneous soil drying.

PubMed

Puértolas, Jaime; Conesa, María R; Ballester, Carlos; Dodd, Ian C

2015-04-01

Patterns of root abscisic acid (ABA) accumulation ([ABA]root), root water potential (Ψroot), and root water uptake (RWU), and their impact on xylem sap ABA concentration ([X-ABA]) were measured under vertical partial root-zone drying (VPRD, upper compartment dry, lower compartment wet) and horizontal partial root-zone drying (HPRD, two lateral compartments: one dry, the other wet) of potato (Solanum tuberosum L.). When water was withheld from the dry compartment for 0-10 d, RWU and Ψroot were similarly lower in the dry compartment when soil volumetric water content dropped below 0.22cm(3) cm(-3) for both spatial distributions of soil moisture. However, [ABA]root increased in response to decreasing Ψroot in the dry compartment only for HPRD, resulting in much higher ABA accumulation than in VPRD. The position of the sampled roots (~4cm closer to the surface in the dry compartment of VPRD than in HPRD) might account for this difference, since older (upper) roots may accumulate less ABA in response to decreased Ψroot than younger (deeper) roots. This would explain differences in root ABA accumulation patterns under vertical and horizontal soil moisture gradients reported in the literature. In our experiment, these differences in root ABA accumulation did not influence [X-ABA], since the RWU fraction (and thus ABA export to shoots) from the dry compartment dramatically decreased simultaneously with any increase in [ABA]root. Thus, HPRD might better trigger a long-distance ABA signal than VPRD under conditions allowing simultaneous high [ABA]root and relatively high RWU fraction. © The Author 2014. Published by Oxford University Press on behalf of the Society for Experimental Biology.

Reactive transport modelling to infer changes in soil hydraulic properties induced by non-conventional water irrigation

NASA Astrophysics Data System (ADS)

Valdes-Abellan, Javier; Jiménez-Martínez, Joaquín; Candela, Lucila; Jacques, Diederik; Kohfahl, Claus; Tamoh, Karim

2017-06-01

The use of non-conventional water (e.g., treated wastewater, desalinated water) for different purposes is increasing in many water scarce regions of the world. Its use for irrigation may have potential drawbacks, because of mineral dissolution/precipitation processes, such as changes in soil physical and hydraulic properties (e.g., porosity, permeability), modifying infiltration and aquifer recharge processes or blocking root growth. Prediction of soil and groundwater impacts is essential for achieving sustainable agricultural practices. A numerical model to solve unsaturated water flow and non-isothermal multicomponent reactive transport has been modified implementing the spatio-temporal evolution of soil physical and hydraulic properties. A long-term process simulation (30 years) of agricultural irrigation with desalinated water, based on a calibrated/validated 1D numerical model in a semi-arid region, is presented. Different scenarios conditioning reactive transport (i.e., rainwater irrigation, lack of gypsum in the soil profile, and lower partial pressure of CO2 (pCO2)) have also been considered. Results show that although boundary conditions and mineral soil composition highly influence the reactive processes, dissolution/precipitation of carbonate species is triggered mainly by pCO2, closely related to plant roots. Calcite dissolution occurs in the root zone, precipitation takes place under it and at the soil surface, which will lead a root growth blockage and a direct soil evaporation decrease, respectively. For the studied soil, a gypsum dissolution up to 40 cm depth is expected at long-term, with a general increase of porosity and hydraulic conductivity.

Aluminium-induced reduction of plant growth in alfalfa (Medicago sativa) is mediated by interrupting auxin transport and accumulation in roots.

PubMed

Wang, Shengyin; Ren, Xiaoyan; Huang, Bingru; Wang, Ge; Zhou, Peng; An, Yuan

2016-07-20

The objective of this study was to investigate Al(3+)-induced IAA transport, distribution, and the relation of these two processes to Al(3+)-inhibition of root growth in alfalfa. Alfalfa seedlings with or without apical buds were exposed to 0 or 100 μM AlCl3 and were foliar sprayed with water or 6 mg L(-1) IAA. Aluminium stress resulted in disordered arrangement of cells, deformed cell shapes, altered cell structure, and a shorter length of the meristematic zone in root tips. Aluminium stress significantly decreased the IAA concentration in apical buds and root tips. The distribution of IAA fluorescence signals in root tips was disturbed, and the IAA transportation from shoot base to root tip was inhibited. The highest intensity of fluorescence signals was detected in the apical meristematic zone. Exogenous application of IAA markedly alleviated the Al(3+)-induced inhibition of root growth by increasing IAA accumulation and recovering the damaged cell structure in root tips. In addition, Al(3+) stress up-regulated expression of AUX1 and PIN2 genes. These results indicate that Al(3+)-induced reduction of root growth could be associated with the inhibitions of IAA synthesis in apical buds and IAA transportation in roots, as well as the imbalance of IAA distribution in root tips.

Aluminium-induced reduction of plant growth in alfalfa (Medicago sativa) is mediated by interrupting auxin transport and accumulation in roots

PubMed Central

Wang, Shengyin; Ren, Xiaoyan; Huang, Bingru; Wang, Ge; Zhou, Peng; An, Yuan

2016-01-01

The objective of this study was to investigate Al3+-induced IAA transport, distribution, and the relation of these two processes to Al3+-inhibition of root growth in alfalfa. Alfalfa seedlings with or without apical buds were exposed to 0 or 100 μM AlCl3 and were foliar sprayed with water or 6 mg L−1 IAA. Aluminium stress resulted in disordered arrangement of cells, deformed cell shapes, altered cell structure, and a shorter length of the meristematic zone in root tips. Aluminium stress significantly decreased the IAA concentration in apical buds and root tips. The distribution of IAA fluorescence signals in root tips was disturbed, and the IAA transportation from shoot base to root tip was inhibited. The highest intensity of fluorescence signals was detected in the apical meristematic zone. Exogenous application of IAA markedly alleviated the Al3+-induced inhibition of root growth by increasing IAA accumulation and recovering the damaged cell structure in root tips. In addition, Al3+ stress up-regulated expression of AUX1 and PIN2 genes. These results indicate that Al3+-induced reduction of root growth could be associated with the inhibitions of IAA synthesis in apical buds and IAA transportation in roots, as well as the imbalance of IAA distribution in root tips. PMID:27435109

Root Zone Cooling and Exogenous Spermidine Root-Pretreatment Promoting Lactuca sativa L. Growth and Photosynthesis in the High-temperature Season

PubMed Central

Sun, Jin; Lu, Na; Xu, Hongjia; Maruo, Toru; Guo, Shirong

2016-01-01

Root zone high-temperature stress is a major factor limiting hydroponic plant growth during the high-temperature season. The effects of root zone cooling (RZC; at 25°C) and exogenous spermidine (Spd) root-pretreatment (SRP, 0.1 mM) on growth, leaf photosynthetic traits, and chlorophyll fluorescence characteristics of hydroponic Lactuca sativa L. grown in a high-temperature season (average temperature > 30°C) were examined. Both treatments significantly promoted plant growth and photosynthesis in the high-temperature season, but the mechanisms of photosynthesis improvement in the hydroponic grown lettuce plants were different between the RZC and SRP treatments. The former improved plant photosynthesis by increasing stoma conductance (Gs) to enhance CO2 supply, thus promoting photosynthetic electron transport activity and phosphorylation, which improved the level of the photochemical efficiency of photosystem II (PSII), rather than enhancing CO2 assimilation efficiency. The latter improved plant photosynthesis by enhancing CO2 assimilation efficiency, rather than stomatal regulation. Combination of RZC and SRP significantly improved PN of lettuce plants in a high-temperature season by both improvement of Gs to enhance CO2 supply and enhancement of CO2 assimilation. The enhancement of photosynthetic efficiency in both treatments was independent of altering light-harvesting or excessive energy dissipation. PMID:27047532

Root Zone Cooling and Exogenous Spermidine Root-Pretreatment Promoting Lactuca sativa L. Growth and Photosynthesis in the High-temperature Season.

PubMed

Sun, Jin; Lu, Na; Xu, Hongjia; Maruo, Toru; Guo, Shirong

2016-01-01

Root zone high-temperature stress is a major factor limiting hydroponic plant growth during the high-temperature season. The effects of root zone cooling (RZC; at 25°C) and exogenous spermidine (Spd) root-pretreatment (SRP, 0.1 mM) on growth, leaf photosynthetic traits, and chlorophyll fluorescence characteristics of hydroponic Lactuca sativa L. grown in a high-temperature season (average temperature > 30°C) were examined. Both treatments significantly promoted plant growth and photosynthesis in the high-temperature season, but the mechanisms of photosynthesis improvement in the hydroponic grown lettuce plants were different between the RZC and SRP treatments. The former improved plant photosynthesis by increasing stoma conductance (G s) to enhance CO2 supply, thus promoting photosynthetic electron transport activity and phosphorylation, which improved the level of the photochemical efficiency of photosystem II (PSII), rather than enhancing CO2 assimilation efficiency. The latter improved plant photosynthesis by enhancing CO2 assimilation efficiency, rather than stomatal regulation. Combination of RZC and SRP significantly improved P N of lettuce plants in a high-temperature season by both improvement of G s to enhance CO2 supply and enhancement of CO2 assimilation. The enhancement of photosynthetic efficiency in both treatments was independent of altering light-harvesting or excessive energy dissipation.

Comparison of the Antimicrobial Efficacy of Two Antibiotics Sparfloxacin and Augmentin as Experimental Root Canal Irrigating Solutions against Enterococcus faecalis - An Invitro Study

PubMed Central

Venigalla, Bhuvan Shome; Surakanti, Jayaprada Reddy; Thumu, Jayaprakash; Chennamaneni, Krishna Chaitanya; Kalluru, Rama S.

2016-01-01

Introduction One of the main goals of endodontic treatment is root canal disinfection and to prevent subsequent chances of reinfection. Adjuvant to instrumentation, root canal irrigants are required to eliminate the bacteria found on the root canal walls and lateral canals within the dentinal tubules. Aim To measure and compare the antibacterial efficacy of two antibiotics as experimental root canal irrigating solutions against Enterococcus faecalis (E. faecalis). Materials and Methods Fifteen Brain Heart Infusion agar plates were inoculated with Enterococcus faecalis-American Type Culture Collection (ATCC) 29212. 5 micrograms (mcg) Sparfloxacin discs, 30mcg Augmentin discs, and sterile paper test discs saturated with 2% Chlorhexidine (CHX), 3% Sodium Hypochlorite (NaOCl) and 5% NaOCl solutions were placed on agar plates. Sodium Chloride 0.9% (NaCl) paper discs were used as controls. Fifteen plates were incubated aerobically at 37°C. Results were expressed as per the terms of the diameter of the inhibition zone. Results Results suggested a statistically significant difference in the zones of inhibition between five irrigating solutions (p < 0.001). Conclusion Although, zones of inhibition were found in all the groups, 5mcg Sparfloxacin and 30mcg Augmentin showed maximum antimicrobial activity against E.faecalis. PMID:27135003

Global distribution of plant-extractable water capacity of soil

USGS Publications Warehouse

Dunne, K.A.; Willmott, C.J.

1996-01-01

Plant-extractable water capacity of soil is the amount of water that can be extracted from the soil to fulfill evapotranspiration demands. It is often assumed to be spatially invariant in large-scale computations of the soil-water balance. Empirical evidence, however, suggests that this assumption is incorrect. In this paper, we estimate the global distribution of the plant-extractable water capacity of soil. A representative soil profile, characterized by horizon (layer) particle size data and thickness, was created for each soil unit mapped by FAO (Food and Agriculture Organization of the United Nations)/Unesco. Soil organic matter was estimated empirically from climate data. Plant rooting depths and ground coverages were obtained from a vegetation characteristic data set. At each 0.5?? ?? 0.5?? grid cell where vegetation is present, unit available water capacity (cm water per cm soil) was estimated from the sand, clay, and organic content of each profile horizon, and integrated over horizon thickness. Summation of the integrated values over the lesser of profile depth and root depth produced an estimate of the plant-extractable water capacity of soil. The global average of the estimated plant-extractable water capacities of soil is 8??6 cm (Greenland, Antarctica and bare soil areas excluded). Estimates are less than 5, 10 and 15 cm - over approximately 30, 60, and 89 per cent of the area, respectively. Estimates reflect the combined effects of soil texture, soil organic content, and plant root depth or profile depth. The most influential and uncertain parameter is the depth over which the plant-extractable water capacity of soil is computed, which is usually limited by root depth. Soil texture exerts a lesser, but still substantial, influence. Organic content, except where concentrations are very high, has relatively little effect.

Simplified continuous simulation model for investigating effects of controlled drainage on long-term soil moisture dynamics with a shallow groundwater table.

PubMed

Sun, Huaiwei; Tong, Juxiu; Luo, Wenbing; Wang, Xiugui; Yang, Jinzhong

2016-08-01

Accurate modeling of soil water content is required for a reasonable prediction of crop yield and of agrochemical leaching in the field. However, complex mathematical models faced the difficult-to-calibrate parameters and the distinct knowledge between the developers and users. In this study, a deterministic model is presented and is used to investigate the effects of controlled drainage on soil moisture dynamics in a shallow groundwater area. This simplified one-dimensional model is formulated to simulate soil moisture in the field on a daily basis and takes into account only the vertical hydrological processes. A linear assumption is proposed and is used to calculate the capillary rise from the groundwater. The pipe drainage volume is calculated by using a steady-state approximation method and the leakage rate is calculated as a function of soil moisture. The model is successfully calibrated by using field experiment data from four different pipe drainage treatments with several field observations. The model was validated by comparing the simulations with observed soil water content during the experimental seasons. The comparison results demonstrated the robustness and effectiveness of the model in the prediction of average soil moisture values. The input data required to run the model are widely available and can be measured easily in the field. It is observed that controlled drainage results in lower groundwater contribution to the root zone and lower depth of percolation to the groundwater, thus helping in the maintenance of a low level of soil salinity in the root zone.

Recent developments and emergent challenges in Ecohydrology: Focus on the belowground frontier

NASA Astrophysics Data System (ADS)

Mackay, D. S.

2017-12-01

The broad spectrum of ecohydrology issues touch on many areas of research in hydrology. But what are the emerging themes and challenges that represent the core of ecohydrology as a maturing discipline? To answer this question the ecohydrology lens was applied to manuscripts published in Water Resources Research over period of 2015 through July 2017. The 235 manuscripts retrieved can be broadly grouped into catchment hydrology, riparian-hyporheic-stream processes, critical zone, land-atmosphere exchange, wetlands, and sustainability. Three dominant crosscutting themes (i.e., coevolution, interfaces, and energy exchange) account for more than half the papers retrieved. In the context of ecohydrology, coevolution refers to the development of physical systems in concert with biological systems and their interactions. In an ecohydrology context, interfaces refer to subsurface, and sometime surface connections that influence transport (e.g., solutes concentration-discharge) influenced by vegetative plumbing, ecophysiology, animal behavior, and microbial processes. Energy exchange in ecohydrology connects vegetative processes to movement of water to the atmosphere through evapotranspiration. Across these themes there is emerging theory and methodology that emphasizes the integrated roles of biology and hydrology in the subsurface. In particular, there is a notable surge of interest in the role of plant roots on subsurface processes. But these are hard to observe and remain challenging to model. By adopting principles of coevolution, in particular, significant advances will be made in modeling plant roots and their depths, corroborated with new geophysical and tracer tools, for improving understanding of critical zone development, subsurface flow processes, and land-atmosphere energy exchange.

Effects of Mulching on Soil Properties and Growth of Tea Olive (Osmanthus fragrans).

PubMed

Ni, Xue; Song, Weiting; Zhang, Huanchao; Yang, Xiulian; Wang, Lianggui

2016-01-01

Different mulches have variable effects on soil physical properties and plant growth. This study aimed to compare the effects of mulching with inorganic (round gravel, RG), organic (wood chips, WC), and living (manila turf grass, MG) materials on soil properties at 0-5-cm and 5-10-cm depths, as well as on the growth and physiological features of Osmanthus fragrans L. 'Rixianggui' plants. Soil samples were collected at three different time points from field plots of O. fragrans plants treated with the different mulching treatments. Moisture at both soil depths was significantly higher after mulching with RG and WC than that in the unmulched control (CK) treatment. Mulching did not affect soil bulk density, pH, or total nitrogen content, but consistently improved soil organic matter. The available nitrogen in the soil increased after RG and WC treatments, but decreased after MG treatment during the experimental period. Mulching improved plant growth by increasing root activity, soluble sugar, and chlorophyll a content, as well as by providing suitable moisture conditions and nutrients in the root zone. Plant height and trunk diameter were remarkably increased after mulching, especially with RG and WC. However, while MG improved plant growth at the beginning of the treatment, the 'Rixianggui' plants later showed no improvement in growth. This was probably because MG competed with the plants for water and available nitrogen in the soil. Thus, our findings suggest that RG and WC, but not MG, improved the soil environment and the growth of 'Rixianggui' plants. Considering the effect of mulching on soil properties and plant growth and physiology, round gravel and wood chips appear to be a better choice than manila turf grass in 'Rixianggui' nurseries. Further studies are required to determine the effects of mulch quality and mulch-layer thickness on shoot and root growths.

Morpho-anatomical and growth alterations induced by arsenic in Cajanus cajan (L.) DC (Fabaceae).

PubMed

Pita-Barbosa, Alice; Gonçalves, Elton Carvalho; Azevedo, Aristéa Alves

2015-08-01

Arsenic (As) is a toxic element to most organisms. Studies investigating anatomic alterations due to As exposure in plants are scarce but of utmost importance to the establishment of environmental biomonitoring techniques. So, this study aimed to investigate the effects of As on the development and initial root growth in Cajanus cajan (Fabaceae), characterize and quantify the possible damages, evaluate genotoxic effects, and identify structural markers to be used in environmental bioindication. Plants were exposed hydroponically to 0.5, 1.0, 1.5, and 2.0 mg As L(-1), as sodium arsenate. Growth parameters were measured, and in the end of the exposure, root samples were analyzed for qualitative and quantitative anatomical alterations. Arsenic genotoxicity was evaluated through analysis of the mitotic index in the root apex. Compared to the control, As-treated seedlings showed an altered architecture, with significantly decreased root length (due to the lower mitotic index in the apical meristem and reduced elongation of parenchyma cells) with darkened color, and abnormal development of the root cap. A significant increase in vascular cylinder/root diameter ratio was also detected, due to the reduction of the cellular spaces in the cortex. The secondary xylem vessel elements were reduced in diameter and had sinuous walls. The severest damage was visible in the ramification zone, where uncommon division planes of phellogen and cambium cells and disintegration of the parenchyma cells adjacent to lateral roots were observed. The high sensibility of C. cajan to As was confirmed, since it caused severe damages in root growth and anatomy. The main structural markers for As toxicity were the altered root architecture, with the reduction of the elongation zone and increase of ramification zone length, and the root primordia retained within the cortex. Our results show a new approach about As toxicity and indicate that C. cajan is a promising species to be used for bioindication of environmental contamination by As.

Anatomy of a local-scale drought: Application of assimilated remote sensing products, crop model, and statistical methods to an agricultural drought study

NASA Astrophysics Data System (ADS)

Mishra, Ashok K.; Ines, Amor V. M.; Das, Narendra N.; Prakash Khedun, C.; Singh, Vijay P.; Sivakumar, Bellie; Hansen, James W.

2015-07-01

Drought is of global concern for society but it originates as a local problem. It has a significant impact on water quantity and quality and influences food, water, and energy security. The consequences of drought vary in space and time, from the local scale (e.g. county level) to regional scale (e.g. state or country level) to global scale. Within the regional scale, there are multiple socio-economic impacts (i.e., agriculture, drinking water supply, and stream health) occurring individually or in combination at local scales, either in clusters or scattered. Even though the application of aggregated drought information at the regional level has been useful in drought management, the latter can be further improved by evaluating the structure and evolution of a drought at the local scale. This study addresses a local-scale agricultural drought anatomy in Story County in Iowa, USA. This complex problem was evaluated using assimilated AMSR-E soil moisture and MODIS-LAI data into a crop model to generate surface and sub-surface drought indices to explore the anatomy of an agricultural drought. Quantification of moisture supply in the root zone remains a gray area in research community, this challenge can be partly overcome by incorporating assimilation of soil moisture and leaf area index into crop modeling framework for agricultural drought quantification, as it performs better in simulating crop yield. It was noted that the persistence of subsurface droughts is in general higher than surface droughts, which can potentially improve forecast accuracy. It was found that both surface and subsurface droughts have an impact on crop yields, albeit with different magnitudes, however, the total water available in the soil profile seemed to have a greater impact on the yield. Further, agricultural drought should not be treated equal for all crops, and it should be calculated based on the root zone depth rather than a fixed soil layer depth. We envisaged that the results of this study will enhance our understanding of agricultural droughts in different parts of the world.

Electrical Imaging of Roots and Trunks

NASA Astrophysics Data System (ADS)

Al Hagrey, S.; Werban, U.; Meissner, R.; Ismaeil, A.; Rabbel, W.

2005-05-01

We applied geoelectric and GPR techniques to analyze problems of botanical structures and even processes, e.g., mapping root zones, internal structure of trunks, and water uptake by roots. The dielectric nature of root zones and trunks is generally a consequence of relatively high moisture content. The electric method, applied to root zones, can discriminate between old, thick, isolated roots (high resistivity) and the network of young, active, and hydraulically conductive zones (low resistivity). Both types of roots show low radar velocity and a strong attenuation caused by the dominant effect of moisture (high dielectric constant) on the electromagnetic wave propagation. Single root branches could be observed in radargrams by their reflection and diffraction parabolas. We have perfected the inversion method for perfect and imperfect cylindrical objects, such as trunks, and developed a new multielectrodes (needle or gel) ring array for fast applications on living trees and discs. Using synthetic models we tested the technique successfully and analyzed it as a function of total electrode number and configuration. Measurements at a trunk show a well established inverse relationship between the imaged resistivity and the moisture content determined from cores. The central resistivity maximum of healthy trees strongly decreases toward the rim. This agrees with the moisture decrease to the outside where active sap flow processes take place. Branching, growth anomalies (new or old shoots) and meteorological effects (sunshine and wind direction) lead to deviations of the concentric electric structure. The strongest anomalies are related to infections causing wet, rotting spots or cavities. The heartwood resistivity is highest in olive and oak trunks, intermediate in young fruit trees and lowest in cork oak trunks that are considered to be anomalously wet. Compared to acoustic tomography our electric technique shows a better resolution in imaging internal ring structures where moisture is the most dominating factor. We conclude that our imaging resistivity technique is applicable for investigating or controlling the botanical and physical conditions of endangered trees (health inspection) and capable to monitor dynamic processes of sap flow if adequate tracers are used.

Modelling the root system architecture of Poaceae. Can we simulate integrated traits from morphological parameters of growth and branching?

PubMed

Pagès, Loïc; Picon-Cochard, Catherine

2014-10-01

Our objective was to calibrate a model of the root system architecture on several Poaceae species and to assess its value to simulate several 'integrated' traits measured at the root system level: specific root length (SRL), maximum root depth and root mass. We used the model ArchiSimple, made up of sub-models that represent and combine the basic developmental processes, and an experiment on 13 perennial grassland Poaceae species grown in 1.5-m-deep containers and sampled at two different dates after planting (80 and 120 d). Model parameters were estimated almost independently using small samples of the root systems taken at both dates. The relationships obtained for calibration validated the sub-models, and showed species effects on the parameter values. The simulations of integrated traits were relatively correct for SRL and were good for root depth and root mass at the two dates. We obtained some systematic discrepancies that were related to the slight decline of root growth in the last period of the experiment. Because the model allowed correct predictions on a large set of Poaceae species without global fitting, we consider that it is a suitable tool for linking root traits at different organisation levels. © 2014 INRA. New Phytologist © 2014 New Phytologist Trust.

Vegetation Impact on Soil Strength: A State of the Knowledge Review

DTIC Science & Technology

2017-06-20

and 5 were amenity. Using soil columns containing four plants, with n indicating the number of replicate columns, they found a variety of root depths...fiber, TN, is given by (Gray and Barker 2004) = 2 � . (12) The shear-strength increase or reinforcement from n ...interface friction stress between root and soil; ER = root-fiber tensile modulus; D = root diameter; n = number of roots; L = root length; hr = the

Effect of channel size on sweet potato storage root enlargement in the Tuskegee University hydroponic nutrient film system

NASA Technical Reports Server (NTRS)

Morris, Carlton E.; Martinez, Edwin; Bonsi, C. K.; Mortley, Desmond G.; Hill, Walter A.; Ogbuehi, Cyriacus R.; Loretan, Phil A.

1989-01-01

The potential of the sweet potato as a food source for future long term manned space missions is being evaluated for NASA's Controlled Ecological Life Support Systems (CELSS) program. Sweet potatoes have been successfully grown in a specially designed Tuskegee University nutrient film technique (TU NFT) system. This hydroponic system yielded storage roots as high as 1790 g/plant fresh weight. In order to determine the effect of channel size on the yield of sweet potatoes, the width and depth of the growing channels were varied in two separate experiments. Widths were studied using the rectangular TU NFT channels with widths of 15 cm (6 in), 30 cm (12 in) and 45 cm (18 in). Channel depths of 5 cm (2 in), 10 cm (4 in), and 15 cm (6 in) were studied using a standard NASA fan shaped Biomass Production Chamber (BPC) channel. A comparison of preliminary results indicated that, except for storage root number, the growth and yield of sweet potatoes were not affected by channel width. Storage root yield was affected by channel depth although storage root number and foliage growth were not. Both experiments are being repeated.

Cellular specificity of the gravitropic motor response in roots

NASA Technical Reports Server (NTRS)

Evans, M. L.; Ishikawa, H.

1997-01-01

A number of features of the gravitropic response of roots are not readily accounted for by the classical Cholodny-Went theory. These include the observations that (i) in the later stages of the response the growth gradient is reversed with no evident reversal of the auxin gradient; (ii) a major component of the acceleration of growth along the upper side occurs in the distal elongation zone (DEZ), a group of cells located between the meristem and the main elongation, not within the central elongation zone; and (iii) the initiation of differential growth in the DEZ appears to be independent of the establishment of auxin asymmetry. Alternative candidates for mediation of differential growth in the DEZ include calcium ions and protons. Gravi-induced curvature is accompanied by polar movement of calcium toward the lower side of the maize root tip and the DEZ is shown to be particularly sensitive to growth inhibition by calcium. Also, gravistimulation of maize roots causes enhanced acid efflux from the upper side of the DEZ. Evidence for gravi-induced modification of ion movements in the root tip includes changes in intracellular potentials and current flow. It is clear that there is more than one motor region in the root with regard to gravitropic responses and there is evidence that the DEZ itself consists of more than one class of responding cells. In order to gain a more complete understanding of the mechanism of gravitropic curvature, the physiological properties of the sub-zones of the root apex need to be thoroughly characterized with regard to their sensitivity to hormones, calcium, acid pH and electrical perturbations.

Removal ratio of gaseous toluene and xylene transported from air to root zone via the stem by indoor plants.

PubMed

Kim, K J; Kim, H J; Khalekuzzaman, M; Yoo, E H; Jung, H H; Jang, H S

2016-04-01

This work was designed to investigate the removal efficiency as well as the ratios of toluene and xylene transported from air to root zone via the stem and by direct diffusion from the air into the medium. Indoor plants (Schefflera actinophylla and Ficus benghalensis) were placed in a sealed test chamber. Shoot or root zone were sealed with a Teflon bag, and gaseous toluene and xylene were exposed. Removal efficiency of toluene and total xylene (m, p, o) was 13.3 and 7.0 μg·m(-3)·m(-2) leaf area over a 24-h period in S. actinophylla, and was 13.0 and 7.3 μg·m(-3)·m(-2) leaf area in F. benghalensis. Gaseous toluene and xylene in a chamber were absorbed through leaf and transported via the stem, and finally reached to root zone, and also transported by direct diffusion from the air into the medium. Toluene and xylene transported via the stem was decreased with time after exposure. Xylene transported via the stem was higher than that by direct diffusion from the air into the medium over a 24-h period. The ratios of toluene transported via the stem versus direct diffusion from the air into the medium were 46.3 and 53.7% in S. actinophylla, and 46.9 and 53.1% in F. benghalensis, for an average of 47 and 53% for both species. The ratios of m,p-xylene transported over 3 to 9 h via the stem versus direct diffusion from the air into the medium was 58.5 and 41.5% in S. actinophylla, and 60.7 and 39.3% in F. benghalensis, for an average of 60 and 40% for both species, whereas the ratios of o-xylene transported via the stem versus direct diffusion from the air into the medium were 61 and 39%. Both S. actinophylla and F. benghalensis removed toluene and xylene from the air. The ratios of toluene and xylene transported from air to root zone via the stem were 47 and 60 %, respectively. This result suggests that root zone is a significant contributor to gaseous toluene and xylene removal, and transported via the stem plays an important role in this process.

Tritium Plume Dynamics in the Shallow Unsaturated Zone Adjacent to an Arid Waste Disposal Facility

NASA Astrophysics Data System (ADS)

Maples, S.; Andraski, B. J.; Stonestrom, D. A.; Cooper, C. A.; Michel, R. L.; Pohll, G. M.

2012-12-01

Previous studies at the U.S. Geological Survey's Amargosa Desert Research Site (ADRS) in southern Nevada have documented two plumes of tritiated water-vapor (3HHOg) adjacent to a closed, commercial low-level radioactive waste disposal facility. Wastes were disposed on-site from 1962-92. Tritium has moved long distances (> 400 m) through a shallow (1-2-m depth) dry gravelly layer—orders of magnitude further than anticipated by standard transport models. Geostatistical methods, spatial moment analyses and tritium flux calculations were applied to assess shallow plume dynamics. A grid-based plant-water sampling method was utilized to infer detailed, field-scale 3HHOg concentrations at 5-yr intervals during 2001-11. Results indicate that gravel-layer 3HHOg mass diminished faster than would be expected from radioactive decay (~70% in 10 yr). Both plumes exhibited center-of-mass stability, suggesting that bulk-plume movement is minimal during the period of study. Nonetheless, evidence of localized lateral advancement along some margins, combined with increases in the spatial covariance of concentration distribution, indicates intra-plume mass redistribution is ongoing. Previous studies have recognized that vertical movement of tritiated water from sub-root-zone gravel into the root-zone contributes to atmospheric release via evapotranspiration. Estimates of lateral and vertical tritium fluxes during the study period indicate (1) vertical tritiated water fluxes were dominated by diffusive-vapor fluxes (> 90%), and (2) vertical diffusive-vapor fluxes were roughly an order of magnitude greater than lateral diffusive-vapor fluxes. This behavior highlights the importance of the atmosphere as a tritium sink. Estimates of cumulative vertical diffusive-vapor flux and radioactive decay with time were comparable to observed declines in total shallow plume mass with time. This suggests observed changes in plume mass may (1) be attributed, in considerable part, to these removal mechanisms, and (2) appreciable input from the adjacent disposal facility is not occurring at this time.

Hydrogeomorphic and ecological control on carbonate dissolution in a patterned landscape in South Florida

NASA Astrophysics Data System (ADS)

Dong, X.; Heffernan, J. B.; Murray, A. B.; Cohen, M. J.; Martin, J. B.

2016-12-01

The evolution of the critical zone both shapes and reflects hydrologic, geochemical, and ecological processes. These interactions are poorly understood in karst landscapes with highly soluble bedrock. In this study, we used the regular-dispersed wetland basins of Big Cypress National Preserve in Florida as a focal case to model the hydrologic, geochemical, and biological mechanisms that affect soil development in karst landscapes. We addressed two questions: (1) What is the minimum timescale for wetland basin development, and (2) do changes in soil depth feed back on dissolution processes and if so by what mechanism? We developed an atmosphere-water-soil model with coupled water-solute transport, incorporating major ion equilibria and kinetic non-equilibrium chemistry, and biogenic acid production via roots distributed through the soil horizon. Under current Florida climate, weathering to a depth of 2 m (a typical depth of wetland basins) would take 4000 6000 yrs, suggesting that landscape pattern could have origins as recent as the most recent stabilization of sea level. Our model further illustrates that interactions between ecological and hydrologic processes influence the rate and depth-dependence of weathering. Absent inundation, dissolution rate decreased exponentially with distance from the bedrock to groundwater table. Inundation generally increased bedrock dissolution, but surface water chemistry and residence time produced complex and non-linear effects on dissolution rate. Biogenic acidity accelerated the dissolution rate by 50 and 1,000 times in inundated and exposed soils. Phase portrait analysis indicated that exponential decreases in bedrock dissolution rate with soil depth could produce stable basin depths. Negative feedback between hydro-period and total basin volume could stabilize the basin radius, but the lesser strength of this mechanism may explain the coalescence of wetland basins observed in some parts of the Big Cypress Landscape.

The Tubular Penetration Depth and Adaption of Four Sealers: A Scanning Electron Microscopic Study

PubMed Central

Chen, Huan; Zhao, Xinyuan; Qiu, Yu; Xu, Dengyou

2017-01-01

Background. The tubular penetration and adaptation of the sealer are important factors for successful root canal filling. The aim of this study was to evaluate the tubular penetration depth of four different sealers in the coronal, middle, and apical third of root canals as well as the adaptation of these sealers to root canal walls. Materials and Methods. 50 single-rooted teeth were prepared in this study. Forty-eight of them were filled with different sealers (Cortisomol, iRoot SP, AH-Plus, and RealSeal SE) and respective core filling materials. Then the specimens were sectioned and scanning electron microscopy was employed to assess the tubular penetration and adaptation of the sealers. Results. Our results demonstrated that the maximum penetration was exhibited by RealSeal SE, followed by AH-Plus, iRoot SP, and Cortisomol. As regards the adaptation property to root canal walls, AH-Plus has best adaptation capacity followed by iRoot SP, RealSeal SE, and Cortisomol. Conclusion. The tubular penetration and adaptation vary with the different sealers investigated. RealSeal SE showed the most optimal tubular penetration, whereas AH-Plus presented the best adaptation to the root canal walls. PMID:29479539

Regolith properties under trees and the biomechanical effects caused by tree root systems as recognized by electrical resistivity tomography (ERT)

NASA Astrophysics Data System (ADS)

Pawlik, Łukasz; Kasprzak, Marek

2018-01-01

Following previous findings regarding the influence of vascular plants (mainly trees) on weathering, soil production and hillslope stability, in this study, we attempted to test a hypothesis regarding significant impacts of tree root systems on soil and regolith properties. Different types of impacts from tree root system (direct and indirect) are commonly gathered under the key term of "biomechanical effects". To add to the discussion of the biomechanical effects of trees, we used a non-invasive geophysical method, electrical resistivity tomography (ERT), to investigate the profiles of four different configurations at three study sites within the Polish section of the Outer Western Carpathians. At each site, one long profile (up to 189 m) of a large section of a hillslope and three short profiles (up to 19.5 m), that is, microsites occupied by trees or their remnants, were made. Short profiles included the tree root zone of a healthy large tree, the tree stump of a decaying tree and the pit-and-mound topography formed after a tree uprooting. The resistivity of regolith and bedrock presented on the long profiles and in comparison with the short profiles through the microsites it can be seen how tree roots impact soil and regolith properties and add to the complexity of the whole soil/regolith profile. Trees change soil and regolith properties directly through root channels and moisture migration and indirectly through the uprooting of trees and the formation of pit-and-mound topography. Within tree stump microsites, the impact of tree root systems, evaluated by a resistivity model, was smaller compared to microsites with living trees or those with pit-and-mound topography but was still visible even several decades after the trees were windbroken or cut down. The ERT method is highly useful for quick evaluation of the impact of tree root systems on soils and regolith. This method, in contrast to traditional soil analyses, offers a continuous dataset for the entire microsite and at depths not normally reached by standard soil excavations. The non-invasive nature of ERT studies is especially important for protected areas as it was shown in the present study.

Stemflow-induced processes of soil water storage

NASA Astrophysics Data System (ADS)

Germer, Sonja

2013-04-01

Compared to stemflow production studies only few studies deal with the fate of stemflow at the near-stem soil. To investigate stemflow contribution to the root zone soil moisture by young and adult babassu palms (Attalea speciosa Mart.), I studied stemflow generation, subsequent soil water percolation and root distributions. Rainfall, stemflow and perched water tables were monitored on an event basis. Perched water tables were monitored next to adult palms at two depths and three stem distances. Dye tracer experiments monitored stemflow-induced preferential flow paths. Root distributions of fine and coarse roots were related to soil water redistribution. Average rainfall-collecting area per adult palm was 6.4 m², but variability between them was high. Funneling ratios ranged between 16-71 and 4-55 for adult and young palms, respectively. Nonetheless, even very small rainfall events of 1 mm can generate stemflow. On average, 9 liters of adult palm stemflow were intercepted and stemflow tended to decrease for-high intensity rainfall events. Young babassu palms funneled rainfall via their fronds, directly to their subterranean stems. The funneling of rainfall towards adult palm stems, in contrast, led to great stemflow fluxes down to the soil and induced initial horizontal water flows through the soil, leading to perched water tables next to palms, even after small rainfall events. The perched water tables extended, however, only a few decimeters from palm stems. After perched water tables became established, vertical percolation through the soil dominated. To my knowledge, this process has not been described before, and it can be seen as an addition to the two previously described stemflow-induced processes of Horton overland flow and fast, deep percolation along roots. This study has demonstrated that Babassu palms funnel water to their stems and subsequently store it in the soil next to their stems in areas where coarse root length density is very high. This might partly explain the competitive position of babassu palms on pastures or secondary forests.

Growth, gas exchange, and root respiration of Quercus rubra seedlings exposed to low root zone temperatures in solution culture

Treesearch

Kent G. Apostol; Douglass F. Jacobs; Barrett C. Wilson; K. Francis Salifu; R. Kasten Dumroese

2007-01-01

Spring planting is standard operational practice in the Central Hardwood Region, though little is known about potential impacts of low root temperature (RT) common during spring on establishment success of temperate deciduous forest tree species. The effects of low RTon growth, gas exchange, and root respiration following winter dormancy were studied in 1-year-old...

Root Water Uptake and Tracer Transport in a Lupin Root System: Integration of Magnetic Resonance Images and the Numerical Model RSWMS

NASA Astrophysics Data System (ADS)

Pohlmeier, Andreas; Vanderborght, Jan; Haber-Pohlmeier, Sabina; Wienke, Sandra; Vereecken, Harry; Javaux, Mathieu

2010-05-01

Combination of experimental studies with detailed deterministic models help understand root water uptake processes. Recently, Javaux et al. developed the RSWMS model by integration of Doussańs root model into the well established SWMS code[1], which simulates water and solute transport in unsaturated soil [2, 3]. In order to confront RSWMS modeling results to experimental data, we used Magnetic Resonance Imaging (MRI) technique to monitor root water uptake in situ. Non-invasive 3-D imaging of root system architecture, water content distributions and tracer transport by MR were performed and compared with numerical model calculations. Two MRI experiments were performed and modeled: i) water uptake during drought stress and ii) transport of a locally injected tracer (Gd-DTPA) to the soil-root system driven by root water uptake. Firstly, the high resolution MRI image (0.23x0.23x0.5mm) of the root system was transferred into a continuous root system skeleton by a combination of thresholding, region-growing filtering and final manual 3D redrawing of the root strands. Secondly, the two experimental scenarios were simulated by RSWMS with a resolution of about 3mm. For scenario i) the numerical simulations could reproduce the general trend that is the strong water depletion from the top layer of the soil. However, the creation of depletion zones in the vicinity of the roots could not be simulated, due to a poor initial evaluation of the soil hydraulic properties, which equilibrates instantaneously larger differences in water content. The determination of unsaturated conductivities at low water content was needed to improve the model calculations. For scenario ii) simulations confirmed the solute transport towards the roots by advection. 1. Simunek, J., T. Vogel, and M.T. van Genuchten, The SWMS_2D Code for Simulating Water Flow and Solute Transport in Two-Dimensional Variably Saturated Media. Version 1.21. 1994, U.S. Salinity Laboratory, USDA, ARS: Riverside, California. 2. Javaux, M., et al., Use of a Three-Dimensional Detailed Modeling Approach for Predicting Root Water Uptake. Vadose Zone J., 2008. 7(3): p. 1079-1088. 3. Schröder, T., et al., Effect of Local Soil Hydraulic Conductivity Drop Using a Three Dimensional Root Water Uptake Model. Vadose Zone J., 2008. 7(3): p. 1089-1098.

An endophytic Streptomyces sp. strain DHV3-2 from diseased root as a potential biocontrol agent against Verticillium dahliae and growth elicitor in tomato (Solanum lycopersicum).

PubMed

Cao, Peng; Liu, Chongxi; Sun, Pengyu; Fu, Xuepeng; Wang, Shaoxian; Wu, Fengzhi; Wang, Xiangjing

2016-12-01

Plant endophytes play important roles in biocontrol of plant diseases. Actinomycetes are used for biocontrol of fungal diseases caused by Verticillium dahliae. Many studies have focused on the endophytic actinomycetes isolated from the roots of healthy plants, but few on those from the roots of diseased plants. In the present research, actinomycetes were isolated from the roots of diseased and healthy tomato plants, respectively. The results showed that, in total, 86 endophytic actinomycetes were isolated for screening of their antimicrobial activities, 8 of which showed antagonism to V. dahliae in vitro. Among the 8 antagonistic strains, 5 (out of 36) were from the roots of diseased plants, with inhibition diameter zones ranging from 11.2 to 18.2 mm, whereas 3 (out of 50) were from the roots of healthy plants, with inhibition diameter zones ranging from 11.5 to 15.5 mm. Endophytic strain DHV3-2 was isolated from the root of a diseased plant and demonstrated a potent effect against V. dahliae and other pathogenic fungi by showing the largest inhibition diameter zones among all the eight antagonistic strains. Thus, strain DHV3-2 was chosen to investigate its biological control efficacies in vivo. Further study showed that the disease incidence and disease severity indices of tomato Verticillium wilt decreased significantly (P < 0.05). We also found that the plant shoot fresh weight and height increased greatly (P < 0.05) upon treatment with strain DHV3-2 compared to the plants uninoculated in greenhouse conditions. Root colonization showed that strain DHV3-2 had the higher root-colonizing capacity in the roots of infected plants compared with the roots of healthy plants. This isolate was identified as Streptomyces sp. based on morphological characteristics and 16S rRNA gene analysis. In conclusion, the roots of diseased tomato plants are a potential reservoir of biological control actinomycetes, and Streptomyces sp. strain DHV3-2 is a potential biocontrol agent against V. dahliae and growth elicitor in tomato.

Interacting vegetative and thermal contributions to water movement in desert soil

USGS Publications Warehouse

Garcia, C.A.; Andraski, Brian J.; Stonestrom, David A.; Cooper, C.A.; Šimůnek, J.; Wheatcraft, S.W.

2011-01-01

Thermally driven water-vapor flow can be an important component of total water movement in bare soil and in deep unsaturated zones, but this process is often neglected when considering the effects of soil–plant–atmosphere interactions on shallow water movement. The objectives of this study were to evaluate the coupled and separate effects of vegetative and thermal-gradient contributions to soil water movement in desert environments. The evaluation was done by comparing a series of simulations with and without vegetation and thermal forcing during a 4.7-yr period (May 2001–December 2005). For vegetated soil, evapotranspiration alone reduced root-zone (upper 1 m) moisture to a minimum value (25 mm) each year under both isothermal and nonisothermal conditions. Variations in the leaf area index altered the minimum storage values by up to 10 mm. For unvegetated isothermal and nonisothermal simulations, root-zone water storage nearly doubled during the simulation period and created a persistent driving force for downward liquid fluxes below the root zone (total net flux ~1 mm). Total soil water movement during the study period was dominated by thermally driven vapor fluxes. Thermally driven vapor flow and condensation supplemented moisture supplies to plant roots during the driest times of each year. The results show how nonisothermal flow is coupled with plant water uptake, potentially influencing ecohydrologic relations in desert environments.

Water flow and solute transport in the soil-plant-atmosphere continuum: Upscaling from rhizosphere to root zone

NASA Astrophysics Data System (ADS)

Lazarovitch, Naftali; Perelman, Adi; Guerra, Helena; Vanderborght, Jan; Pohlmeier, Andreas

2016-04-01

Root water and nutrient uptake are among the most important processes considered in numerical models simulating water content and fluxes in the subsurface, as they control plant growth and production as well as water flow and nutrient transport out of the root zone. Root water uptake may lead to salt accumulation at the root-soil interface, resulting in rhizophere salt concentrations much higher than in the bulk soil. This salt accumulation is caused by soluble salt transport towards the roots by mass flow through the soil, followed by preferential adsorption of specific nutrients by active uptake, thereby excluding most other salts at the root-soil interface or in the root apoplast. The salinity buildup can lead to large osmotic pressure gradients across the roots thereby effectively reducing root water uptake. The initial results from rhizoslides (capillary paper growth system) show that sodium concentration is decreasing with distance from the root, compared with the bulk that remained more stable. When transpiration rate was decreased under high salinity levels, sodium concentration was more homogenous compared with low salinity levels. Additionally, sodium and gadolinium distributions were measured nondestructively around tomato roots using magnetic resonance imaging (MRI). This technique could also observe the root structure and water content around single roots. Results from the MRI confirm the solutes concentration pattern around roots and its relation to their initial concentration. We conclude that local water potentials at the soil-root interface differ from bulk potentials. These relative differences increase with decreasing root density, decreasing initial salt concentration and increasing transpiration rate. Furthermore, since climate may significantly influence plant response to salinity a dynamic climate-coupled salinity reduction functions are critical in while using macroscopic numerical models.

Synchrotron X-ray microfluorescence measurement of metal distributions in Phragmites australis root system in the Yangtze River intertidal zone

DOE Office of Scientific and Technical Information (OSTI.GOV)

Feng, Huan; Zhang, Weiguo; Qian, Yu

2016-06-15

This study investigates the distributions of Br, Ca, Cl, Cr, Cu, K, Fe, Mn, Pb, Ti, V and Zn inPhragmites australisroot system and the function of Fe nanoparticles in scavenging metals in the root epidermis using synchrotron X-ray microfluorescence, synchrotron transmission X-ray microscope measurement and synchrotron X-ray absorption near-edge structure techniques. The purpose of this study is to understand the mobility of metals in wetland plant root systems after their uptake from rhizosphere soils.Phragmites australissamples were collected in the Yangtze River intertidal zone in July 2013. The results indicate that Fe nanoparticles are present in the root epidermis and thatmore » other metals correlate significantly with Fe, suggesting that Fe nanoparticles play an important role in metal scavenging in the epidermis.« less

High temperature effect on microflora of radish root-inhabited zone and nutrient solutions for radish growth

NASA Astrophysics Data System (ADS)

Borodina, E. V.; Tirranen, L. S.

The effect of high temperatures (35 and 45 °C) on microflora of the root zone of radish plants grown in phytotron was evaluated by the response of microorganisms from 9 indicator groups. Phytotron air temperature elevated to 35 °C for 20 hours caused no significant changes in qualitative and quantitative composition of the root microflora in experimental plants. By the end of the experiment, the species diversity of microflora had changed. The amount of phytopathogenic microorganisms decreased which can be interpreted as more stable co-existence of microflora with plants. The numbers of microbes from other indicator groups was in dynamic equilibrium. The plants' condition did not deteriorate either. Exposure to the temperature of 45 °C for 7 hours have been found to change the numbers and species diversity in the radish root zone microflora. The microorganisms were observed to increase their total numbers at the expense of certain indicator groups. Bacteria increased spore forms at the stage of spores. Colon bacillus bacteria of increased their numbers by the end of experiment by an order. By the end of experiment the roots of experiment plants had microscopic fungi from Mucor, Aspergillus, Trichoderma, Cladosporium genera. The observed changes in the microbial complex seem to be associated with the changes of root emissions and general deterioration of the plants' condition. It is suggested that the response of the microorganisms can be indicative of the condition of plants under investigation.

Ammonium Inhibits Primary Root Growth by Reducing the Length of Meristem and Elongation Zone and Decreasing Elemental Expansion Rate in the Root Apex in Arabidopsis thaliana

PubMed Central

Gao, Kun; Chen, Fanjun; Yuan, Lixing; Mi, Guohua

2013-01-01

The inhibitory effect of ammonium on primary root growth has been well documented; however the underlying physiological and molecular mechanisms are still controversial. To avoid ammonium toxicity to shoot growth, we used a vertical two-layer split plate system, in which the upper layer contained nitrate and the lower layer contained ammonium. In this way, nitrogen status was maintained and only the apical part of the root system was exposed to ammonium. Using a kinematic approach, we show here that 1 mM ammonium reduces primary root growth, decreasing both elemental expansion and cell production. Ammonium inhibits the length of elongation zone and the maximum elemental expansion rate. Ammonium also decreases the apparent length of the meristem as well as the number of dividing cells without affecting cell division rate. Moreover, ammonium reduces the number of root cap cells but appears to affect neither the status of root stem cell niche nor the distal auxin maximum at the quiescent center. Ammonium also inhibits root gravitropism and concomitantly down-regulates the expression of two pivotal auxin transporters, AUX1 and PIN2. Insofar as ammonium inhibits root growth rate in AUX1 and PIN2 loss-of-function mutants almost as strongly as in wild type, we conclude that ammonium inhibits root growth and gravitropism by largely distinct pathways. PMID:23577185