Seasonal and interannual variability of canopy transpiration of a hedgerow in southern England.

PubMed

Herbst, Mathias; Roberts, John M; Rosier, Paul T W; Gowing, David J

2007-03-01

Transpiration from a hawthorn (Crataegus monogyna L.) dominated hedgerow in southern England was measured continuously over two growing seasons by the sap flow technique. Accompanying measurements of structural parameters, microclimate and leaf stomatal and boundary layer conductances were used to establish the driving factors of hedgerow transpiration. Observed transpiration rates, reaching peak values of around 8 mm day(-1) and a seasonal mean of about 3.5 mm day(-1), were higher than those reported for most other temperate deciduous woodlands, except short-rotation coppice and wet woodlands. The high rates were caused by the structural and physiological characteristics of hawthorn leaves, which exhibited much higher stomatal and boundary-layer conductances than those of the second-most abundant woody species in the hedgerow, field maple (Acer campestre L.). Only in the hot summer of 2003 did stomatal conductance, and thus transpiration, decrease substantially. The hedgerow canopy was always closely coupled to the atmosphere. Hedgerow transpiration equaled potential evaporation (calculated by the Priestley-Taylor formula) in 2003 and exceeded it in 2004, which meant that a substantial fraction of the energy (21% in 2003 and more than 37% in 2004) came from advection. Hedgerow canopy conductance (g(c)), as inferred from the sap flow data by inverting the Penman-Monteith equation, responded to solar radiation (R(G)) and vapor pressure deficit (D). Although the response to R(G) showed no systematic temporal variation, the response to D, described as g(c)(D) = g(cref) - mln(D), changed seasonally. The reference g(c) depended on leaf area index and the ratio of -m/g(cref) on long-term mean daytime D. A model is proposed based on these observations that predicts canopy conductance for the hawthorn hedge from standard weather data.

Stomatal conductance, canopy temperature, and leaf area index estimation using remote sensing and OBIA techniques

Treesearch

S. Panda; D.M. Amatya; G. Hoogenboom

2014-01-01

Remotely sensed images including LANDSAT, SPOT, NAIP orthoimagery, and LiDAR and relevant processing tools can be used to predict plant stomatal conductance (gs), leaf area index (LAI), and canopy temperature, vegetation density, albedo, and soil moisture using vegetation indices like normalized difference vegetation index (NDVI) or soil adjusted...

Seasonal changes in Cyclobalanopsis glauca transpiration and canopy stomatal conductance and their dependence on subterranean water and climatic factors in rocky karst terrain

NASA Astrophysics Data System (ADS)

Huang, Yuqing; Li, Xiankun; Zhang, Zhongfeng; He, Chengxin; Zhao, Ping; You, Yeming; Mo, Ling

2011-05-01

SummaryThe presence of forest on south China karst is presumed to increase perennial epikarst spring flow, partly because there is adequate storage in bedrock fractures underlying the shallow soil in the forest. If true, transpiration of the ecosystem would not be strongly reduced by temperate drought if trees develop deep roots to reach the perched epikarst water. Therefore, in karst ecosystem the epikarst-soil-plant-atmosphere continuum (ESPAC) would be different from the SPAC in non-karst system. We measured transpiration and canopy conductance from a Cyclobalanopsis glauca (syn. Quercus glauca) stand on a rocky hill slope in South China during 2006-2007 by using the Granier's sap-flow method. Annual stand transpiration (836 mm y -1) accounted for 48.7% of the rainfall during the experimental year. Per month, daily stand transpiration ( E c) maximums varied between 2.1 mm d -1 in January (cool season) to 5.1 mm d -1 in July (hot season). In the driest months, September and October, E c of C. glauca was still high with maximum E c 3.82 mm d -1 and 2.96 mm d -1 respectively. Solar radiation ( PAR), vapor pressure deficiency ( VPD), and air temperature were simple influences on transpiration of C. glauca, which contributed to a quadratic power model, while soil water content ( SWC) moisture influence on transpiration was complicated, which SWC influenced E c greatly under higher VPD, but did not influence E c under low VPD. High stomatal openness occurred in C. glauca in the early morning and declined throughout the day. The relation coefficient between canopy stomatal conductance ( G c) and E c was high when VPD was more than 1.0 kPa, moderate when 0.5 kPa < VPD < 1.0 kPa, and low with VPD of less than 0.5 kPa. Under high VPD, stomatal control of transpiration is high. The pattern of seasonal change of transpiration and canopy stomatal conductance of the plant in karst regions is different from that in non-karst regions, with the stand transpiration and canopy stomatal conductance being high even during the dry season in the karst region because karst plants obtain water partially from the epikarst. With high stand transpiration and canopy stomatal conductance, karst vegetation is presumed to be the most important "pathway" for ESPAC.

The role of mesophyll conductance in the economics of nitrogen and water use in photosynthesis.

PubMed

Buckley, Thomas N; Warren, Charles R

2014-02-01

A recent resurgence of interest in formal optimisation theory has begun to improve our understanding of how variations in stomatal conductance and photosynthetic capacity control the response of whole plant photosynthesis and growth to the environment. However, mesophyll conductance exhibits similar variation and has similar impact on photosynthesis as stomatal conductance; yet, the role of mesophyll conductance in the economics of photosynthetic resource use has not been thoroughly explored. In this article, we first briefly summarise the knowledge of how mesophyll conductance varies in relation to environmental factors that also affect stomatal conductance and photosynthetic capacity, and then we use a simple analytical approach to begin to explore how these important controls on photosynthesis should mutually co-vary in a plant canopy in the optimum. Our analysis predicts that when either stomatal or mesophyll conductance is limited by fundamental biophysical constraints in some areas of a canopy, e.g. reduced stomatal conductance in upper canopy leaves due to reduced water potential, the other of the two conductances should increase in those leaves, while photosynthetic capacity should decrease. Our analysis also predicts that if mesophyll conductance depends on nitrogen investment in one or more proteins, then nitrogen investment should shift away from Rubisco and towards mesophyll conductance if hydraulic or other constraints cause chloroplastic CO2 concentration to decline. Thorough exploration of these issues awaits better knowledge of whether and how mesophyll conductance is itself limited by nitrogen investment, and about how these determinants of photosynthetic CO2 supply and demand co-vary among leaves in real plant canopies.

Comparison of infrared canopy temperature in a rubber plantation and tropical rain forest

NASA Astrophysics Data System (ADS)

Song, Qing-Hai; Deng, Yun; Zhang, Yi-Ping; Deng, Xiao-Bao; Lin, You-Xing; Zhou, Li-Guo; Fei, Xue-Hai; Sha, Li-Qing; Liu, Yun-Tong; Zhou, Wen-Jun; Gao, Jin-Bo

2017-10-01

Canopy temperature is a result of the canopy energy balance and is driven by climate conditions, plant architecture, and plant-controlled transpiration. Here, we evaluated canopy temperature in a rubber plantation (RP) and tropical rainforest (TR) in Xishuangbanna, southwestern China. An infrared temperature sensor was installed at each site to measure canopy temperature. In the dry season, the maximum differences (Tc - Ta) between canopy temperature (Tc) and air temperature (Ta) in the RP and TR were 2.6 and 0.1 K, respectively. In the rainy season, the maximum (Tc - Ta) values in the RP and TR were 1.0 and -1.1 K, respectively. There were consistent differences between the two forests, with the RP having higher (Tc - Ta) than the TR throughout the entire year. Infrared measurements of Tc can be used to calculate canopy stomatal conductance in both forests. The difference in (Tc - Ta) at three gc levels with increasing direct radiation in the RP was larger than in the TR, indicating that change in (Tc - Ta) in the RP was relatively sensitive to the degree of stomatal closure.

Forest response and recovery following disturbance in upland forests of the Atlantic Coastal Plain.

PubMed

Schäfer, Karina V R; Renninger, Heidi J; Carlo, Nicholas J; Vanderklein, Dirk W

2014-01-01

Carbon and water cycling of forests contribute significantly to the Earth's overall biogeochemical cycling and may be affected by disturbance and climate change. As a larger body of research becomes available about leaf-level, ecosystem and regional scale effects of disturbances on forest ecosystems, a more mechanistic understanding is developing which can improve modeling efforts. Here, we summarize some of the major effects of physical and biogenic disturbances, such as drought, prescribed fire, and insect defoliation, on leaf and ecosystem-scale physiological responses as well as impacts on carbon and water cycling in an Atlantic Coastal Plain upland oak/pine and upland pine forest. During drought, stomatal conductance and canopy stomatal conductance were reduced, however, defoliation increased conductance on both leaf-level and canopy scale. Furthermore, after prescribed fire, leaf-level stomatal conductance was unchanged for pines but decreased for oaks, while canopy stomatal conductance decreased temporarily, but then rebounded the following growing season, thus exhibiting transient responses. This study suggests that forest response to disturbance varies from the leaf to ecosystem level as well as species level and thus, these differential responses interplay to determine the fate of forest structure and functioning post disturbance.

Coupled hydraulic and photosynthetic feedbacks on forest transpiration throughout the growing season

NASA Astrophysics Data System (ADS)

Mackay, D. S.; Ewers, B. E.

2007-12-01

Ecosystem models account for vegetative controls on water fluxes using environmental drivers and hydraulic and/or biochemical limits on canopy stomatal conductance (Gs), variations in space and time of leaf area index (L), and species or biome specific parameters. However, some parameters, such as maximum stomatal conductance or its reference proxy at vapor pressure deficit of 1 kPa (Gsref), may not be strictly time-independent suggesting as yet undefined mechanisms in the models. We developed a model of coupled canopy water and carbon exchange, which allowed us to examine photosynthetic and hydraulic feedbacks on Gsref spanning the whole growing season for several dominant tree species in wetland and upland positions that collectively account for most a 1600 square km region centered on the WLEF AmeriFlux tower in Wisconsin, USA. The model assimilated half-hourly sap flux and micrometeorological data to quantify and explain temporal variations in Gsref for trembling aspen, sugar maple, and red pine in upland sites, and speckled alder and white cedar in wetland sites. Results show (1) phenological effects on photosynthetic activity with feedback on Gsref in all species, and (2) lags of up to two months between maximum per unit leaf area photosynthetic rates for conifer versus deciduous species. These results show that for given environmental conditions canopy transpiration depends on both L and timing of biochemical activation, both of which have implications for regional ecosystem water cycling.

Estimating maximum mean canopy stomatal conductance for use in models

Treesearch

Brent E. Ewers; Ram Oren; Kurt H. Johnsen; J.J Landsberg

2001-01-01

Fertilized (F) and irrigated and fertilized (IF) stands of Pinus taeda L. produced twice the leaf area index of irrigated (I) and control (C) stands. Based on sap flux-scaled mean stomatal conductance (GS), we found that stomatal conductance in F was half that in other treatments. During the growing season, GS was related to...

Photosynthesis and stomatal conductance related to reflectance on the canopy scale

NASA Technical Reports Server (NTRS)

Verma, S. B.; Sellers, P. J.; Walthall, C. L.; Hall, F. G.; Kim, J.; Goetz, S. J.

1993-01-01

Field measurements of carbon dioxide and water vapor fluxes were analyzed in conjunction with reflectances obtained from a helicopter-mounted Modular Multiband Radiometer at a grassland study site during the First International Satellite Land Surface Climatology Project Field Experiment. These measurements are representative of the canopy scale and were made over a range of meteorological and soil moisture conditions during different stages in the annual life cycle of the prairie vegetation, and thus provide a good basis for investigating hpotheses/relationships potentially useful in remote sensing applications. We tested the hypothesis (Sellers, 1987) that the simple ratio vegetation index should be near-linearly related to the derivatives of the unstressed canopy stomatal conductance and the unstressed canopy photosynthesis with respect to photosynthetically active radiation. Even though there is some scatter in our data, the results seem to support this hypothesis.

Analyses of Assumptions and Erros in the Calculation of Stomatal Conductance from Sap Flux Measurements

Treesearch

Brent E. Ewers; Ram Oren

2000-01-01

We analyzed assumptions and measurement errors in estimating canopy transpiration (EL) from sap flux (JS) measured with Granier-type sensors, and in calculating canopy stomata1 conductance (GS) from EL...

Simulating soybean canopy temperature as affected by weather variables and soil water potential

NASA Technical Reports Server (NTRS)

Choudhury, B. J.

1982-01-01

Hourly weather data for several clear sky days during summer at Phoenix and Baltimore which covered a wide range of variables were used with a plant atmosphere model to simulate soybean (Glycine max L.) leaf water potential, stomatal resistance and canopy temperature at various soil water potentials. The air and dew point temperatures were found to be the significant weather variables affecting the canopy temperatures. Under identical weather conditions, the model gives a lower canopy temperature for a soybean crop with a higher rooting density. A knowledge of crop rooting density, in addition to air and dew point temperatures is needed in interpreting infrared radiometric observations for soil water status. The observed dependence of stomatal resistance on the vapor pressure deficit and soil water potential is fairly well represented. Analysis of the simulated leaf water potentials indicates overestimation, possibly due to differences in the cultivars.

Genetic effects on transpiration, canopy conductance, stomatal sensitivity to vapour pressure deficit, and cavitation resistance in loblolly pine

Treesearch

Michael J Aspinwall; John S King; Jean-Christophe Domec; Steven E McKeand; Isik Fikret

2011-01-01

Physiological uniformity and genetic effects on canopy-level gas-exchange and hydraulic function could impact loblolly pine (Pinus taeda L.) plantation sustainability and ecosystem dynamics under projected changes in climate. Over a 1-year period, we examined genetic effects on mean and maximum mid-day canopy conductance (Gs, Gsmax...

Modeling stomatal conductance in the Earth system: linking leaf water-use efficiency and water transport along the soil-plant-atmosphere continuum

NASA Astrophysics Data System (ADS)

Bonan, G. B.; Williams, M.; Fisher, R. A.; Oleson, K. W.

2014-05-01

The empirical Ball-Berry stomatal conductance model is commonly used in Earth system models to simulate biotic regulation of evapotranspiration. However, the dependence of stomatal conductance (gs) on vapor pressure deficit (Ds) and soil moisture must both be empirically parameterized. We evaluated the Ball-Berry model used in the Community Land Model version 4.5 (CLM4.5) and an alternative stomatal conductance model that links leaf gas exchange, plant hydraulic constraints, and the soil-plant-atmosphere continuum (SPA) to numerically optimize photosynthetic carbon gain per unit water loss while preventing leaf water potential dropping below a critical minimum level. We evaluated two alternative optimization algorithms: intrinsic water-use efficiency (Δ An/Δ gs, the marginal carbon gain of stomatal opening) and water-use efficiency (Δ An/Δ El, the marginal carbon gain of water loss). We implemented the stomatal models in a multi-layer plant canopy model, to resolve profiles of gas exchange, leaf water potential, and plant hydraulics within the canopy, and evaluated the simulations using: (1) leaf analyses; (2) canopy net radiation, sensible heat flux, latent heat flux, and gross primary production at six AmeriFlux sites spanning 51 site-years; and (3) parameter sensitivity analyses. Without soil moisture stress, the performance of the SPA stomatal conductance model was generally comparable to or somewhat better than the Ball-Berry model in flux tower simulations, but was significantly better than the Ball-Berry model when there was soil moisture stress. Functional dependence of gs on soil moisture emerged from the physiological theory linking leaf water-use efficiency and water flow to and from the leaf along the soil-to-leaf pathway rather than being imposed a priori, as in the Ball-Berry model. Similar functional dependence of gs on Ds emerged from the water-use efficiency optimization. Sensitivity analyses showed that two parameters (stomatal efficiency and root hydraulic conductivity) minimized errors with the SPA stomatal conductance model. The critical stomatal efficiency for optimization (ι) was estimated from leaf trait datasets and is related to the slope parameter (g1) of the Ball-Berry model. The optimized parameter value was consistent with this estimate. Optimized root hydraulic conductivity was consistent with estimates from literature surveys. The two central concepts embodied in the stomatal model, that plants account for both water-use efficiency and for hydraulic safety in regulating stomatal conductance, imply a notion of optimal plant strategies and provide testable model hypotheses, rather than empirical descriptions of plant behavior.

Comparison of infrared canopy temperature in a rubber plantation and tropical rain forest.

PubMed

Song, Qing-Hai; Deng, Yun; Zhang, Yi -Ping; Deng, Xiao-Bao; Lin, You-Xing; Zhou, Li-Guo; Fei, Xue-Hai; Sha, Li-Qing; Liu, Yun-Tong; Zhou, Wen-Jun; Gao, Jin-Bo

2017-10-01

Canopy temperature is a result of the canopy energy balance and is driven by climate conditions, plant architecture, and plant-controlled transpiration. Here, we evaluated canopy temperature in a rubber plantation (RP) and tropical rainforest (TR) in Xishuangbanna, southwestern China. An infrared temperature sensor was installed at each site to measure canopy temperature. In the dry season, the maximum differences (T c  - T a ) between canopy temperature (T c ) and air temperature (T a ) in the RP and TR were 2.6 and 0.1 K, respectively. In the rainy season, the maximum (T c  - T a ) values in the RP and TR were 1.0 and -1.1 K, respectively. There were consistent differences between the two forests, with the RP having higher (T c  - T a ) than the TR throughout the entire year. Infrared measurements of T c can be used to calculate canopy stomatal conductance in both forests. The difference in (T c  - T a ) at three g c levels with increasing direct radiation in the RP was larger than in the TR, indicating that change in (T c  - T a ) in the RP was relatively sensitive to the degree of stomatal closure.

Circadian rhythms have significant effects on leaf-to-canopy scale gas exchange under field conditions.

PubMed

Resco de Dios, Víctor; Gessler, Arthur; Ferrio, Juan Pedro; Alday, Josu G; Bahn, Michael; Del Castillo, Jorge; Devidal, Sébastien; García-Muñoz, Sonia; Kayler, Zachary; Landais, Damien; Martín-Gómez, Paula; Milcu, Alexandru; Piel, Clément; Pirhofer-Walzl, Karin; Ravel, Olivier; Salekin, Serajis; Tissue, David T; Tjoelker, Mark G; Voltas, Jordi; Roy, Jacques

2016-10-20

Molecular clocks drive oscillations in leaf photosynthesis, stomatal conductance, and other cell and leaf-level processes over ~24 h under controlled laboratory conditions. The influence of such circadian regulation over whole-canopy fluxes remains uncertain; diurnal CO 2 and H 2 O vapor flux dynamics in the field are currently interpreted as resulting almost exclusively from direct physiological responses to variations in light, temperature and other environmental factors. We tested whether circadian regulation would affect plant and canopy gas exchange at the Montpellier European Ecotron. Canopy and leaf-level fluxes were constantly monitored under field-like environmental conditions, and under constant environmental conditions (no variation in temperature, radiation, or other environmental cues). We show direct experimental evidence at canopy scales of the circadian regulation of daytime gas exchange: 20-79 % of the daily variation range in CO 2 and H 2 O fluxes occurred under circadian entrainment in canopies of an annual herb (bean) and of a perennial shrub (cotton). We also observed that considering circadian regulation improved performance by 8-17 % in commonly used stomatal conductance models. Our results show that circadian controls affect diurnal CO 2 and H 2 O flux patterns in entire canopies in field-like conditions, and its consideration significantly improves model performance. Circadian controls act as a 'memory' of the past conditions experienced by the plant, which synchronizes metabolism across entire plant canopies.

Modelling bidirectional fluxes of methanol and acetaldehyde with the FORCAsT canopy exchange model

DOE PAGES

Ashworth, Kirsti; Chung, Serena H.; McKinney, Karena A.; ...

2016-12-15

Here, the FORCAsT canopy exchange model was used to investigate the underlying mechanisms governing foliage emissions of methanol and acetaldehyde, two short chain oxygenated volatile organic compounds ubiquitous in the troposphere and known to have strong biogenic sources, at a northern mid-latitude forest site. The explicit representation of the vegetation canopy within the model allowed us to test the hypothesis that stomatal conductance regulates emissions of these compounds to an extent that its influence is observable at the ecosystem scale, a process not currently considered in regional- or global-scale atmospheric chemistry models. Here, we found that FORCAsT could only reproducemore » the magnitude and diurnal profiles of methanol and acetaldehyde fluxes measured at the top of the forest canopy at Harvard Forest if light-dependent emissions were introduced to the model. With the inclusion of such emissions, FORCAsT was able to successfully simulate the observed bidirectional exchange of methanol and acetaldehyde. Although we found evidence that stomatal conductance influences methanol fluxes and concentrations at scales beyond the leaf level, particularly at dawn and dusk, we were able to adequately capture ecosystem exchange without the addition of stomatal control to the standard parameterisations of foliage emissions, suggesting that ecosystem fluxes can be well enough represented by the emissions models currently used.« less

Reference Canopy Stomatal Conductance Explains Spatiotemporal Patterns of Tree Transpiration

NASA Astrophysics Data System (ADS)

Loranty, M. M.; Mackay, D. S.; Ewers, B. E.; Kruger, E. L.; Traver, E.

2007-12-01

Increased heterogeneity in patterns of whole tree transpiration (EC) with increasing atmospheric vapor pressure deficit (D) suggests a dynamic response of sap flow velocity (JS) to environmental drivers. We hypothesized that differences in reference stomatal conductance (GSref), stomatal conductance at D = 1kPa, would explain the spatiotemporal dynamics of JS. Using a coupled model of plant hydraulic and biochemical processes we tested this hypothesis with sap flux data for 106 aspen ( Populus tremuloides) and 108 sugar maple ( Acer saccharum) trees collected from plots using in 2-D cyclic sampling scheme during the summer of 2005 in northern Wisconsin. Inverse modeling is used to estimate GSref for each tree. For each species, trees from across the ranges of JS and diameter distributions are compared. GSref explained temporal variability in spatial patterns of EC We explore several possible mechanistic explanations for differences in GSref among trees. Topoedaphic factors are considered to determine if location within a stand has an effect. We also consider competition with neighboring individuals as a possible explanation. Variations in GSref in aspen were explained in part by competition for light between neighboring individuals, while competition for light was not a significant factor for sugar maple. Based on simulation analysis we identify possible biochemical feedbacks as drivers of the variability in plant hydraulics. Other factors examined included micro-topography within both sites.

Circadian rhythms have significant effects on leaf-to-canopy scale gas exchange under field conditions

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

Resco de Dios, Víctor; Gessler, Arthur; Ferrio, Juan Pedro

Background Molecular clocks drive oscillations in leaf photosynthesis, stomatal conductance, and other cell and leaf-level processes over ~24 h under controlled laboratory conditions. The influence of such circadian regulation over whole-canopy fluxes remains uncertain; diurnal CO 2 and H 2O vapor flux dynamics in the field are currently interpreted as resulting almost exclusively from direct physiological responses to variations in light, temperature and other environmental factors. We tested whether circadian regulation would affect plant and canopy gas exchange at the Montpellier European Ecotron. Canopy and leaf-level fluxes were constantly monitored under field-like environmental conditions, and under constant environmental conditions (nomore » variation in temperature, radiation, or other environmental cues). Results We show direct experimental evidence at canopy scales of the circadian regulation of daytime gas exchange: 20–79 % of the daily variation range in CO 2 and H 2O fluxes occurred under circadian entrainment in canopies of an annual herb (bean) and of a perennial shrub (cotton). We also observed that considering circadian regulation improved performance by 8–17 % in commonly used stomatal conductance models. Conclusions Our results show that circadian controls affect diurnal CO 2 and H 2O flux patterns in entire canopies in field-like conditions, and its consideration significantly improves model performance. Lastly, circadian controls act as a ‘memory’ of the past conditions experienced by the plant, which synchronizes metabolism across entire plant canopies.« less

Circadian rhythms have significant effects on leaf-to-canopy scale gas exchange under field conditions

DOE PAGES

Resco de Dios, Víctor; Gessler, Arthur; Ferrio, Juan Pedro; ...

2016-10-20

Background Molecular clocks drive oscillations in leaf photosynthesis, stomatal conductance, and other cell and leaf-level processes over ~24 h under controlled laboratory conditions. The influence of such circadian regulation over whole-canopy fluxes remains uncertain; diurnal CO 2 and H 2O vapor flux dynamics in the field are currently interpreted as resulting almost exclusively from direct physiological responses to variations in light, temperature and other environmental factors. We tested whether circadian regulation would affect plant and canopy gas exchange at the Montpellier European Ecotron. Canopy and leaf-level fluxes were constantly monitored under field-like environmental conditions, and under constant environmental conditions (nomore » variation in temperature, radiation, or other environmental cues). Results We show direct experimental evidence at canopy scales of the circadian regulation of daytime gas exchange: 20–79 % of the daily variation range in CO 2 and H 2O fluxes occurred under circadian entrainment in canopies of an annual herb (bean) and of a perennial shrub (cotton). We also observed that considering circadian regulation improved performance by 8–17 % in commonly used stomatal conductance models. Conclusions Our results show that circadian controls affect diurnal CO 2 and H 2O flux patterns in entire canopies in field-like conditions, and its consideration significantly improves model performance. Lastly, circadian controls act as a ‘memory’ of the past conditions experienced by the plant, which synchronizes metabolism across entire plant canopies.« less

Sap flux-upscaled canopy transpiration, stomatal conductance, and water use efficiency in an old growth forest in the Great Lakes region of the United States

NASA Astrophysics Data System (ADS)

Tang, Jianwu; Bolstad, Paul V.; Ewers, Brent E.; Desai, Ankur R.; Davis, Kenneth J.; Carey, Eileen V.

2006-06-01

Combining sap flux and eddy covariance measurements provides a means to study plant stomatal conductance and the relationship between transpiration and photosynthesis. We measured sap flux using Granier-type sensors in a northern hardwood-dominated old growth forest in Michigan, upscaled to canopy transpiration, and calculated canopy conductance. We also measured carbon and water fluxes with the eddy covariance method and derived daytime gross primary production (GPP). The diurnal patterns of sap flux and canopy transpiration were mainly controlled by vapor pressure deficit (D) and photosynthetically active radiation (PAR). Daily sums of sap flux and canopy transpiration had exponential relationships to D that saturated at higher D and had linear relationships to PAR. Sugar maple (Acer saccharum) and yellow birch (Betula alleghaniesis) had higher sap flux per unit of sapwood area than eastern hemlock (Tsuga canadensis), while sugar maple and hemlock had higher canopy transpiration per unit of leaf area than yellow birch. Sugar maple dominated canopy transpiration per ground area. Canopy transpiration averaged 1.57 mm d-1, accounting for 65% of total evapotranspiration in the growing season. Canopy conductance was controlled by both D and PAR, but the day-to-day variation in canopy conductance mainly followed a negatively logarithmic relationship with D. By removing the influences of PAR, half-hourly canopy conductance was also negatively logarithmically correlated with D. Water use efficiency (WUE) had a strong exponential relationship with D on a daily basis and approached a minimum of 4.4 mg g-1. WUE provides an alternative to estimate GPP from measurements of sap flux.

Increasing canopy photosynthesis in rice can be achieved without a large increase in water use-A model based on free-air CO2 enrichment.

PubMed

Ikawa, Hiroki; Chen, Charles P; Sikma, Martin; Yoshimoto, Mayumi; Sakai, Hidemitsu; Tokida, Takeshi; Usui, Yasuhiro; Nakamura, Hirofumi; Ono, Keisuke; Maruyama, Atsushi; Watanabe, Tsutomu; Kuwagata, Tsuneo; Hasegawa, Toshihiro

2018-03-01

Achieving higher canopy photosynthesis rates is one of the keys to increasing future crop production; however, this typically requires additional water inputs because of increased water loss through the stomata. Lowland rice canopies presently consume a large amount of water, and any further increase in water usage may significantly impact local water resources. This situation is further complicated by changing the environmental conditions such as rising atmospheric CO 2 concentration ([CO 2 ]). Here, we modeled and compared evapotranspiration of fully developed rice canopies of a high-yielding rice cultivar (Oryza sativa L. cv. Takanari) with a common cultivar (cv. Koshihikari) under ambient and elevated [CO 2 ] (A-CO 2 and E-CO 2 , respectively) via leaf ecophysiological parameters derived from a free-air CO 2 enrichment (FACE) experiment. Takanari had 4%-5% higher evapotranspiration than Koshihikari under both A-CO 2 and E-CO 2 , and E-CO 2 decreased evapotranspiration of both varieties by 4%-6%. Therefore, if Takanari was cultivated under future [CO 2 ] conditions, the cost for water could be maintained at the same level as for cultivating Koshihikari at current [CO 2 ] with an increase in canopy photosynthesis by 36%. Sensitivity analyses determined that stomatal conductance was a significant physiological factor responsible for the greater canopy photosynthesis in Takanari over Koshihikari. Takanari had 30%-40% higher stomatal conductance than Koshihikari; however, the presence of high aerodynamic resistance in the natural field and lower canopy temperature of Takanari than Koshihikari resulted in the small difference in evapotranspiration. Despite the small difference in evapotranspiration between varieties, the model simulations showed that Takanari clearly decreased canopy and air temperatures within the planetary boundary layer compared to Koshihikari. Our results indicate that lowland rice varieties characterized by high-stomatal conductance can play a key role in enhancing productivity and moderating heat-induced damage to grain quality in the coming decades, without significantly increasing crop water use. © 2017 John Wiley & Sons Ltd.

A high CO2 -driven decrease in plant transpiration leads to perturbations in the hydrological cycle and may link terrestrial and marine loss of biodiversity: deep-time evidence.

NASA Astrophysics Data System (ADS)

Steinthorsdottir, Margret; Woodward, F. Ian; Surlyk, Finn; McElwain, Jennifer C.

2013-04-01

CO2 is obtained and water vapor simultaneously transpired through plant stomata, driving the water uptake of roots. Stomata are key elements of the Earth's hydrological cycle, since a large part of the evapotranspiration from the surface to the atmosphere takes place via stomatal pores. Plants exercise stomatal control, by adjusting stomatal size and/or density in order to preserve water while maintaining carbon uptake for photosynthesis. A global decrease in stomatal density and/or size causes a decrease in transpiration and has the potential to increase global runoff. Here we show, from 91 fossil leaf cuticle specimens from the Triassic/Jurassic boundary transition (Tr-J) of East Greenland, that both stomatal size and density decreased dramatically during the Tr-J, coinciding with mass extinctions, major environmental upheaval and a negative C-isotope excursion. We estimate that these developmental and structural changes in stomata resulted in a 50-60% drop in stomatal and canopy transpiration as calibrated using a stomatal model, based on empirical measurements and adjusted for fossil plants. We additionally present new field evidence indicating a change to increased erosion and bad-land formation at the Tr-J. We hypothesize that plant physiological responses to high carbon dioxide concentrations at the Tr-J may have increased runoff at the local and perhaps even regional scale. Increased runoff may result in increased flux of nutrients from land to oceans, leading to eutrophication, anoxia and ultimately loss of marine biodiversity. High-CO2 driven changes in stomatal and canopy transpiration therefore provide a possible mechanistic link between terrestrial ecological crisis and marine mass extinction at the Tr-J.

Photosynthesis, transpiration and water use efficiencies of a plant canopy and plant leaves under restricted air current conditions

NASA Astrophysics Data System (ADS)

Kitaya, Yoshiaki; Shibuya, Toshio; Tsuruyama, Joshin

A fundamental study was conducted to obtain the knowledge for culturing plants and exchanging gases with plants under restricted air circulation conditions in space agriculture. The effects of air velocities less than 1.3 m s-1 on net photosynthetic rates (Pn), transpiration rates (Tr) and Pn/Tr, water use efficiencies (WUE), of a canopy of cucumber seedlings and of single leaves of cucumber, sweet potato and barley were assessed with assimilation chamber methods in ground based experiments. The cucumber seedling canopy, which had a LAI of 1.4 and height of 0.1 m, was set in a wind tunnel installed in a plant canopy assimilation chamber. Each of the attached single leaves was set in a leaf assimilation chamber. The Pn and Tr of the plant canopy increased to 1.2 and 2.8 times, respectively, and WUE decreased to 0.4 times with increasing the air velocity from 0.02 to 1.3 m s-1. The Pn and Tr of the single leaves of all the species increased by 1.3-1.7 and 1.9-2.2 times, respectively, and WUE decreased to 0.6-0.8 times as the air velocity increased from 0.05 to 0.8 m s-1. The effect of air velocity was more significant on Tr than on Pn and thus WUE decreased with increasing air velocity in both the plant canopy and the individual leaves. The leaf boundary layer resistance was approximately proportional to the minus 1/3 power of the air velocity. Stomatal resistance was almost constant during the experiment. The CO2 concentrations in the sub-stomatal cavity in leaves of cucumber, sweet potato and barley, respectively, were 43, 31 and 58 mmol mol-1 lower at the air velocity of 0.05 m s-1 than at the air velocity of 0.8 m s-1, while the water vapor pressure in the sub-stomatal cavity was constant. We concluded that the change in the CO2 concentration in the sub-stomatal cavity was a cause of the different effect of the air velocity on Pn and Tr, and thus on WUE. The phenomenon will be more remarkable under restricted air convection conditions at lower gravity in space.

Scaling up stomatal conductance from leaf to canopy using a dual-leaf model for estimating crop evapotranspiration.

PubMed

Ding, Risheng; Kang, Shaozhong; Du, Taisheng; Hao, Xinmei; Zhang, Yanqun

2014-01-01

The dual-source Shuttleworth-Wallace model has been widely used to estimate and partition crop evapotranspiration (λET). Canopy stomatal conductance (Gsc), an essential parameter of the model, is often calculated by scaling up leaf stomatal conductance, considering the canopy as one single leaf in a so-called "big-leaf" model. However, Gsc can be overestimated or underestimated depending on leaf area index level in the big-leaf model, due to a non-linear stomatal response to light. A dual-leaf model, scaling up Gsc from leaf to canopy, was developed in this study. The non-linear stomata-light relationship was incorporated by dividing the canopy into sunlit and shaded fractions and calculating each fraction separately according to absorbed irradiances. The model includes: (1) the absorbed irradiance, determined by separately integrating the sunlit and shaded leaves with consideration of both beam and diffuse radiation; (2) leaf area for the sunlit and shaded fractions; and (3) a leaf conductance model that accounts for the response of stomata to PAR, vapor pressure deficit and available soil water. In contrast to the significant errors of Gsc in the big-leaf model, the predicted Gsc using the dual-leaf model had a high degree of data-model agreement; the slope of the linear regression between daytime predictions and measurements was 1.01 (R2 = 0.98), with RMSE of 0.6120 mm s-1 for four clear-sky days in different growth stages. The estimates of half-hourly λET using the dual-source dual-leaf model (DSDL) agreed well with measurements and the error was within 5% during two growing seasons of maize with differing hydrometeorological and management strategies. Moreover, the estimates of soil evaporation using the DSDL model closely matched actual measurements. Our results indicate that the DSDL model can produce more accurate estimation of Gsc and λET, compared to the big-leaf model, and thus is an effective alternative approach for estimating and partitioning λET.

Scaling Up Stomatal Conductance from Leaf to Canopy Using a Dual-Leaf Model for Estimating Crop Evapotranspiration

PubMed Central

Ding, Risheng; Kang, Shaozhong; Du, Taisheng; Hao, Xinmei; Zhang, Yanqun

2014-01-01

The dual-source Shuttleworth-Wallace model has been widely used to estimate and partition crop evapotranspiration (λET). Canopy stomatal conductance (Gsc), an essential parameter of the model, is often calculated by scaling up leaf stomatal conductance, considering the canopy as one single leaf in a so-called “big-leaf” model. However, Gsc can be overestimated or underestimated depending on leaf area index level in the big-leaf model, due to a non-linear stomatal response to light. A dual-leaf model, scaling up Gsc from leaf to canopy, was developed in this study. The non-linear stomata-light relationship was incorporated by dividing the canopy into sunlit and shaded fractions and calculating each fraction separately according to absorbed irradiances. The model includes: (1) the absorbed irradiance, determined by separately integrating the sunlit and shaded leaves with consideration of both beam and diffuse radiation; (2) leaf area for the sunlit and shaded fractions; and (3) a leaf conductance model that accounts for the response of stomata to PAR, vapor pressure deficit and available soil water. In contrast to the significant errors of Gsc in the big-leaf model, the predicted Gsc using the dual-leaf model had a high degree of data-model agreement; the slope of the linear regression between daytime predictions and measurements was 1.01 (R2 = 0.98), with RMSE of 0.6120 mm s−1 for four clear-sky days in different growth stages. The estimates of half-hourly λET using the dual-source dual-leaf model (DSDL) agreed well with measurements and the error was within 5% during two growing seasons of maize with differing hydrometeorological and management strategies. Moreover, the estimates of soil evaporation using the DSDL model closely matched actual measurements. Our results indicate that the DSDL model can produce more accurate estimation of Gsc and λET, compared to the big-leaf model, and thus is an effective alternative approach for estimating and partitioning λET. PMID:24752329

Stomatal conductance at Duke FACE: Leveraging the lessons from 11 years of scaled sap flux measurements for region-wide analyses

NASA Astrophysics Data System (ADS)

Ward, E. J.; Bell, D.; Clark, J. S.; McCarthy, H. R.; Kim, H.; domec, J.; Noormets, A.; McNulty, D.; Sun, G.; Oren, R.

2013-12-01

A network of thermal dissipation probes (TDPs) monitoring sap flux density was used to estimate leaf-specific transpiration (EL) and canopy-averaged stomatal conductance (GS) in Pinus taeda (L.) exposed to +200 ppm atmospheric CO2 levels (eCO2) and nitrogen fertilization as part of the Duke FACE study. Data from scaling half-hourly measurements from hundreds of sensors over 11 years indicated that P. taeda in eCO2 intermittently (49% of monthly values) decreased stomatal conductance relative to the control, with a mean reduction of 13% in both total EL and mean daytime GS. This intermittent response was related to changes in a hydraulic allometry index (AH), defined as sapwood area per unit leaf area per unit canopy height, which was linearly related to GS at reference conditions (GSR) during the growing season across years (R2=0.67). Overall, AH decreased a mean of 15% with eCO2 over the course of the study, due mostly to a mean 19% increase in leaf area. Throughout the southeastern U.S., other P. taeda stands have been monitored with TDPs, such as the US-NC2 Ameriflux site and four fertilizer × throughfall displacement studies recently begun as part of the PINEMAP research network in VA, GA, FL and OK. We will also discuss the challenges and benefits of using a common modeling platform to combine FACE TDP data with that from a diversity of sites and treatments to draw inferences about EL and GS responses to environmental drivers and climate change, as well as their relation to AH, across the range of P. taeda.

Spatiotemporal variation of crown-scale stomatal conductance in an arid Vitis vinifera L. cv. Merlot vineyard: direct effects of hydraulic properties and indirect effects of canopy leaf area.

PubMed

Zhang, Yanqun; Oren, Ram; Kang, Shaozhong

2012-03-01

Vineyards were planted in the arid region of northwest China to meet the local economic strategy while reducing agricultural water use. Sap flow, environmental variables, a plant characteristic (sapwood-to-leaf area ratio, A(s)/A(l)) and a canopy characteristic (leaf area index, L) were measured in a vineyard in the region during the growing season of 2009, and hourly canopy stomatal conductance (G(si)) was estimated for individual vines to quantify the relationships between G(si) and these variables. After accounting for the effects of vapor pressure deficit (D) and solar radiation (R(s)) on G(si), much of the remaining variation of reference G(si) (G(siR)) was driven by that of leaf-specific hydraulic conductivity, which in turn was driven by that of A(s)/A(l). After accounting for that effect on G(siR), appreciable temporal variation remained in the decline rate of G(siR) with decreasing vineyard-averaged relative extractable soil water (θ(E)). This variation was related to the differential decline ofθ(E) near each monitored vine, decreasing faster between irrigation events near vines where L was greater, thus adding to the spatiotemporal variation of G(siR) observed in the vineyard. We also found that the vines showed isohydric-like behavior whenθ(E) was low, but switched to anisohydric-like behavior with increasingθ(E). Modeledθ(E) and associated G(s) of a canopy with even L (1.9 m(2) m(-2)) were greater than that of the same average L but split between the lowest and highest L observed along sections of rows in the vineyard (1.2 and 2.6 m(2) m(-2)) by 6 and 12%, respectively. Our results suggest that managing sectional L near the average, rather than allowing a wide variation, can reduce soil water depletion, maintaining G(s) higher, thus potentially enhancing yield.

Turbulent mixing and removal of ozone within an Amazon rainforest canopy

NASA Astrophysics Data System (ADS)

Freire, L. S.; Gerken, T.; Ruiz-Plancarte, J.; Wei, D.; Fuentes, J. D.; Katul, G. G.; Dias, N. L.; Acevedo, O. C.; Chamecki, M.

2017-03-01

Simultaneous profiles of turbulence statistics and mean ozone mixing ratio are used to establish a relation between eddy diffusivity and ozone mixing within the Amazon forest. A one-dimensional diffusion model is proposed and used to infer mixing time scales from the eddy diffusivity profiles. Data and model results indicate that during daytime conditions, the upper (lower) half of the canopy is well (partially) mixed most of the time and that most of the vertical extent of the forest can be mixed in less than an hour. During nighttime, most of the canopy is predominantly poorly mixed, except for periods with bursts of intermittent turbulence. Even though turbulence is faster than chemistry during daytime, both processes have comparable time scales in the lower canopy layers during nighttime conditions. Nonchemical loss time scales (associated with stomatal uptake and dry deposition) for the entire forest are comparable to turbulent mixing time scale in the lower canopy during the day and in the entire canopy during the night, indicating a tight coupling between turbulent transport and dry deposition and stomatal uptake processes. Because of the significant time of day and height variability of the turbulent mixing time scale inside the canopy, it is important to take it into account when studying chemical and biophysical processes happening in the forest environment. The method proposed here to estimate turbulent mixing time scales is a reliable alternative to currently used models, especially for situations in which the vertical distribution of the time scale is relevant.

Sensitivity of stand transpiration to wind velocity in a mixed broadleaved deciduous forest

Treesearch

Dohyoung Kim; Ram Oren; A. Christopher Oishi; Cheng-I Hsieh; Nathan Phillips; Kimberly A. Novick; Paul C. Stoy

2014-01-01

Wind velocity (U) within and above forest canopies can alter the coupling between the vapor-saturated sub-stomatal airspace and the drier atmosphere aloft, thereby influencing transpiration rates. In practice, however, the actual increase in transpiration with increasing U depends on the aerodynamic resistance (RA) to vapor transfer compared to canopy resistance to...

How light competition between plants affects their response to climate change.

PubMed

van Loon, Marloes P; Schieving, Feike; Rietkerk, Max; Dekker, Stefan C; Sterck, Frank; Anten, Niels P R

2014-09-01

How plants respond to climate change is of major concern, as plants will strongly impact future ecosystem functioning, food production and climate. Here, we investigated how vegetation structure and functioning may be influenced by predicted increases in annual temperatures and atmospheric CO2 concentration, and modeled the extent to which local plant-plant interactions may modify these effects. A canopy model was developed, which calculates photosynthesis as a function of light, nitrogen, temperature, CO2 and water availability, and considers different degrees of light competition between neighboring plants through canopy mixing; soybean (Glycine max) was used as a reference system. The model predicts increased net photosynthesis and reduced stomatal conductance and transpiration under atmospheric CO2 increase. When CO2 elevation is combined with warming, photosynthesis is increased more, but transpiration is reduced less. Intriguingly, when competition is considered, the optimal response shifts to producing larger leaf areas, but with lower stomatal conductance and associated vegetation transpiration than when competition is not considered. Furthermore, only when competition is considered are the predicted effects of elevated CO2 on leaf area index (LAI) well within the range of observed effects obtained by Free air CO2 enrichment (FACE) experiments. Together, our results illustrate how competition between plants may modify vegetation responses to climate change. © 2014 The Authors. New Phytologist © 2014 New Phytologist Trust.

An observational constraint on stomatal function in forests: evaluating coupled carbon and water vapor exchange with carbon isotopes in the Community Land Model (CLM4.5)

NASA Astrophysics Data System (ADS)

Raczka, Brett; Duarte, Henrique F.; Koven, Charles D.; Ricciuto, Daniel; Thornton, Peter E.; Lin, John C.; Bowling, David R.

2016-09-01

Land surface models are useful tools to quantify contemporary and future climate impact on terrestrial carbon cycle processes, provided they can be appropriately constrained and tested with observations. Stable carbon isotopes of CO2 offer the potential to improve model representation of the coupled carbon and water cycles because they are strongly influenced by stomatal function. Recently, a representation of stable carbon isotope discrimination was incorporated into the Community Land Model component of the Community Earth System Model. Here, we tested the model's capability to simulate whole-forest isotope discrimination in a subalpine conifer forest at Niwot Ridge, Colorado, USA. We distinguished between isotopic behavior in response to a decrease of δ13C within atmospheric CO2 (Suess effect) vs. photosynthetic discrimination (Δcanopy), by creating a site-customized atmospheric CO2 and δ13C of CO2 time series. We implemented a seasonally varying Vcmax model calibration that best matched site observations of net CO2 carbon exchange, latent heat exchange, and biomass. The model accurately simulated observed δ13C of needle and stem tissue, but underestimated the δ13C of bulk soil carbon by 1-2 ‰. The model overestimated the multiyear (2006-2012) average Δcanopy relative to prior data-based estimates by 2-4 ‰. The amplitude of the average seasonal cycle of Δcanopy (i.e., higher in spring/fall as compared to summer) was correctly modeled but only when using a revised, fully coupled An - gs (net assimilation rate, stomatal conductance) version of the model in contrast to the partially coupled An - gs version used in the default model. The model attributed most of the seasonal variation in discrimination to An, whereas interannual variation in simulated Δcanopy during the summer months was driven by stomatal response to vapor pressure deficit (VPD). The model simulated a 10 % increase in both photosynthetic discrimination and water-use efficiency (WUE) since 1850 which is counter to established relationships between discrimination and WUE. The isotope observations used here to constrain CLM suggest (1) the model overestimated stomatal conductance and (2) the default CLM approach to representing nitrogen limitation (partially coupled model) was not capable of reproducing observed trends in discrimination. These findings demonstrate that isotope observations can provide important information related to stomatal function driven by environmental stress from VPD and nitrogen limitation. Future versions of CLM that incorporate carbon isotope discrimination are likely to benefit from explicit inclusion of mesophyll conductance.

Midday depression of leaf CO2 exchange within the crown of Dipterocarpus sublamellatus in a lowland dipterocarp forest in Peninsular Malaysia.

PubMed

Kosugi, Yoshiko; Takanashi, Satoru; Matsuo, Naoko; Nik, Abdul Rahim

2009-04-01

We observed diurnal and seasonal patterns of leaf-scale gas exchange within the crown of a Dipterocarpus sublamellatus Foxw. tree growing in a lowland dipterocarp forest at Pasoh, Peninsular Malaysia. Observations were carried out nine times over 6 years, from September 2002 to December 2007. Observation periods included both wet and mild-dry periods, and natural and saturated photosynthetic photon flux density (PPFD) light conditions. In situ measurements of the diurnal change in net photosynthetic rate and in stomatal conductance were carried out on canopy leaves of a 40-m-tall D. sublamellatus tree, which was accessed from a canopy corridor. A diurnal change in electron transport rate was observed under saturated PPFD conditions. The maximum net assimilation rate was approximately 10 micromol m(-2) s(-1). There was a clear inhibition of the net assimilation rate coupled with stomatal closure after late morning and this inhibition occurred year-round. Although the electron transport rate decreased alongside this inhibition, it sometimes followed on. Numerical analysis showed that the main factor in the inhibition of the net assimilation rate was patchy bimodal stomatal closure, which occurred in both mild-dry and wet periods. The midday depression occurred year-round, though there are fluctuations in soil moisture during the mild-dry and wet periods. The magnitude of the inhibition was not related to soil water content but was related to vapor pressure deficit (VPD): that is, whether the days were sunny and hot or cloudy and cool. On cloudy, cool days in the wet period, the net photosynthesis was only moderately inhibited, but it still decreased in the afternoon and was coupled with patchy stomatal closure, even in quite moderate VPD, leaf temperature and PPFD conditions. Our results suggest that patchy stomatal closure signaled by the increase in VPD, in transpiration and by circadian rhythms, was the key factor in constraining midday leaf gas exchange of the D. sublamellatus canopy leaves.

Modeling stomatal conductance in the earth system: linking leaf water-use efficiency and water transport along the soil-plant-atmosphere continuum

NASA Astrophysics Data System (ADS)

Bonan, G. B.; Williams, M.; Fisher, R. A.; Oleson, K. W.

2014-09-01

The Ball-Berry stomatal conductance model is commonly used in earth system models to simulate biotic regulation of evapotranspiration. However, the dependence of stomatal conductance (gs) on vapor pressure deficit (Ds) and soil moisture must be empirically parameterized. We evaluated the Ball-Berry model used in the Community Land Model version 4.5 (CLM4.5) and an alternative stomatal conductance model that links leaf gas exchange, plant hydraulic constraints, and the soil-plant-atmosphere continuum (SPA). The SPA model simulates stomatal conductance numerically by (1) optimizing photosynthetic carbon gain per unit water loss while (2) constraining stomatal opening to prevent leaf water potential from dropping below a critical minimum. We evaluated two optimization algorithms: intrinsic water-use efficiency (ΔAn /Δgs, the marginal carbon gain of stomatal opening) and water-use efficiency (ΔAn /ΔEl, the marginal carbon gain of transpiration water loss). We implemented the stomatal models in a multi-layer plant canopy model to resolve profiles of gas exchange, leaf water potential, and plant hydraulics within the canopy, and evaluated the simulations using leaf analyses, eddy covariance fluxes at six forest sites, and parameter sensitivity analyses. The primary differences among stomatal models relate to soil moisture stress and vapor pressure deficit responses. Without soil moisture stress, the performance of the SPA stomatal model was comparable to or slightly better than the CLM Ball-Berry model in flux tower simulations, but was significantly better than the CLM Ball-Berry model when there was soil moisture stress. Functional dependence of gs on soil moisture emerged from water flow along the soil-to-leaf pathway rather than being imposed a priori, as in the CLM Ball-Berry model. Similar functional dependence of gs on Ds emerged from the ΔAn/ΔEl optimization, but not the ΔAn /gs optimization. Two parameters (stomatal efficiency and root hydraulic conductivity) minimized errors with the SPA stomatal model. The critical stomatal efficiency for optimization (ι) gave results consistent with relationships between maximum An and gs seen in leaf trait data sets and is related to the slope (g1) of the Ball-Berry model. Root hydraulic conductivity (Rr*) was consistent with estimates from literature surveys. The two central concepts embodied in the SPA stomatal model, that plants account for both water-use efficiency and for hydraulic safety in regulating stomatal conductance, imply a notion of optimal plant strategies and provide testable model hypotheses, rather than empirical descriptions of plant behavior.

Carbonyl sulfide (COS) as a tracer for canopy photosynthesis, transpiration and stomatal conductance: potential and limitations

PubMed Central

Wohlfahrt, Georg; Brilli, Federico; Hörtnagl, Lukas; Xu, Xiaobin; Bingemer, Heinz; Hansel, Armin; Loreto, Francesco

2012-01-01

The theoretical basis for the link between the leaf exchange of carbonyl sulfide (COS), carbon dioxide (CO2) and water vapour (H2O) and the assumptions that need to be made in order to use COS as a tracer for canopy net photosynthesis, transpiration and stomatal conductance, are reviewed. The ratios of COS to CO2 and H2O deposition velocities used to this end are shown to vary with the ratio of the internal to ambient CO2 and H2O mole fractions and the relative limitations by boundary layer, stomatal and internal conductance for COS. It is suggested that these deposition velocity ratios exhibit considerable variability, a finding that challenges current parameterizations, which treat these as vegetation-specific constants. COS is shown to represent a better tracer for CO2 than H2O. Using COS as a tracer for stomatal conductance is hampered by our present poor understanding of the leaf internal conductance to COS. Estimating canopy level CO2 and H2O fluxes requires disentangling leaf COS exchange from other ecosystem sources/sinks of COS. We conclude that future priorities for COS research should be to improve the quantitative understanding of the variability in the ratios of COS to CO2 and H2O deposition velocities and the controlling factors, and to develop operational methods for disentangling ecosystem COS exchange into contributions by leaves and other sources/sinks. To this end, integrated studies, which concurrently quantify the ecosystem-scale CO2, H2O and COS exchange and the corresponding component fluxes, are urgently needed. We investigate the potential of carbonyl sulfide (COS) for being used as a tracer for canopy net photosynthesis, transpiration and stomatal conductance by examining the theoretical basis of the link between leaf COS, carbon dioxide (CO2) and water vapour (H2O) exchange. Our analysis identifies several limitations that need to be overcome to this end, however at present we lack appropriate ecosystem-scale field measurements for assessing their practical significance. It however appears that COS represents a better tracer for CO2 than H2O. Concurrent measurements of ecosystem scale COS, CO2 and H2O exchange are advocated. PMID:22017586

Effects of Disturbance on Carbon Sequestration in the New Jersey Pine Barrens

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

Schafer, Karina; Bohrer, Gil

While carbon and water cycling of forests contribute significantly to the Earth's overall biogeochemical cycling, it may be affected by disturbance and climate change. In this research, we contributed to the body of research on leaf-level, ecosystem and regional scale effects of disturbances on forest ecosystems, in an effort to foster more mechanistic understanding, which in turn can improve modeling efforts. Here, we summarize some of the major findings in this research of physical and biogenic disturbances, such as drought, prescribed fire, and insect defoliation, on leaf and ecosystem-scale physiological responses as well as impacts on carbon and water cyclingmore » in an Atlantic Coastal Plain upland oak/pine and upland pine forest. Following we have incorporated some of our findings into a new version of the Finite-element Tree-Crown Hydrodynamics (model version 2) model, which improved timing and hysteresis of transpiration modeling for trees. Furthermore, incorporation of hydrodynamics into modeling transpiration improved latent heat flux estimates. In our study on the physiology of the trees, we showed that during drought, stomatal conductance and canopy stomatal conductance were reduced, however, defoliation increased conductance on both leaf-level and canopy scale. Furthermore, after prescribed fire, leaf-level stomatal conductance was unchanged for pines but decreased for oaks, while canopy stomatal conductance decreased temporarily, but then rebounded the following growing season, thus exhibiting transient responses. This study suggests that forest response to disturbance varies from the leaf to ecosystem level as well as species level and thus, these differential responses interplay to determine the fate of forest structure and functioning post disturbance. Incorporating this responses improves model outcome.« less

Short-term effects of light quality on leaf gas exchange and hydraulic properties of silver birch (Betula pendula).

PubMed

Niglas, Aigar; Papp, Kaisa; Sekiewicz, Maciej; Sellin, Arne

2017-09-01

Leaves have to acclimatize to heterogeneous radiation fields inside forest canopies in order to efficiently exploit diverse light conditions. Short-term effects of light quality on photosynthetic gas exchange, leaf water use and hydraulic traits were studied on Betula pendula Roth shoots cut from upper and lower thirds of the canopy of 39- to 35-year-old trees growing in natural forest stand, and illuminated with white, red or blue light in the laboratory. Photosynthetic machinery of the leaves developed in different spectral conditions acclimated differently with respect to incident light spectrum: the stimulating effect of complete visible spectrum (white light) on net photosynthesis is more pronounced in upper-canopy layers. Upper-canopy leaves exhibit less water saving behaviour, which may be beneficial for the fast-growing pioneer species on a daily basis. Lower-canopy leaves have lower stomatal conductance resulting in more efficient water use. Spectral gradients existing within natural forest stands represent signals for the fine-tuning of stomatal conductance and tree water relations to afford lavish water use in sun foliage and enhance leaf water-use efficiency in shade foliage sustaining greater hydraulic limitations. Higher sensitivity of hydraulic conductance of shade leaves to blue light probably contributes to the efficient use of short duration sunflecks by lower-canopy leaves. © The Author 2017. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Resource use and efficiency, and stomatal responses to environmental drivers of oak and pine species in an Atlantic Coastal Plain forest.

PubMed

Renninger, Heidi J; Carlo, Nicholas J; Clark, Kenneth L; Schäfer, Karina V R

2015-01-01

Pine-oak ecosystems are globally distributed even though differences in anatomy and leaf habit between many co-occurring oaks and pines suggest different strategies for resource use, efficiency and stomatal behavior. The New Jersey Pinelands contain sandy soils with low water- and nutrient-holding capacity providing an opportunity to examine trade-offs in resource uptake and efficiency. Therefore, we compared resource use in terms of transpiration rates and leaf nitrogen content and resource-use efficiency including water-use efficiency (WUE) via gas exchange and leaf carbon isotopes and photosynthetic nitrogen-use efficiency (PNUE) between oaks (Quercus alba, Q. prinus, Q. velutina) and pines (Pinus rigida, P. echinata). We also determined environmental drivers [vapor pressure deficit (VPD), soil moisture, solar radiation] of canopy stomatal conductance (GS) estimated via sap flow and stomatal sensitivity to light and soil moisture. Net assimilation rates were similar between genera, but oak leaves used about 10% more water and pine foliage contained about 20% more N per unit leaf area. Therefore, oaks exhibited greater PNUE while pines had higher WUE based on gas exchange, although WUE from carbon isotopes was not significantly different. For the environmental drivers of GS, oaks had about 10% lower stomatal sensitivity to VPD normalized by reference stomatal conductance compared with pines. Pines exhibited a significant positive relationship between shallow soil moisture and GS, but only GS in Q. velutina was positively related to soil moisture. In contrast, stomatal sensitivity to VPD was significantly related to solar radiation in all oak species but only pines at one site. Therefore, oaks rely more heavily on groundwater resources but have lower WUE, while pines have larger leaf areas and nitrogen acquisition but lower PNUE demonstrating a trade-off between using water and nitrogen efficiently in a resource-limited ecosystem.

Resource use and efficiency, and stomatal responses to environmental drivers of oak and pine species in an Atlantic Coastal Plain forest

PubMed Central

Renninger, Heidi J.; Carlo, Nicholas J.; Clark, Kenneth L.; Schäfer, Karina V. R.

2015-01-01

Pine-oak ecosystems are globally distributed even though differences in anatomy and leaf habit between many co-occurring oaks and pines suggest different strategies for resource use, efficiency and stomatal behavior. The New Jersey Pinelands contain sandy soils with low water- and nutrient-holding capacity providing an opportunity to examine trade-offs in resource uptake and efficiency. Therefore, we compared resource use in terms of transpiration rates and leaf nitrogen content and resource-use efficiency including water-use efficiency (WUE) via gas exchange and leaf carbon isotopes and photosynthetic nitrogen-use efficiency (PNUE) between oaks (Quercus alba, Q. prinus, Q. velutina) and pines (Pinus rigida, P. echinata). We also determined environmental drivers [vapor pressure deficit (VPD), soil moisture, solar radiation] of canopy stomatal conductance (GS) estimated via sap flow and stomatal sensitivity to light and soil moisture. Net assimilation rates were similar between genera, but oak leaves used about 10% more water and pine foliage contained about 20% more N per unit leaf area. Therefore, oaks exhibited greater PNUE while pines had higher WUE based on gas exchange, although WUE from carbon isotopes was not significantly different. For the environmental drivers of GS, oaks had about 10% lower stomatal sensitivity to VPD normalized by reference stomatal conductance compared with pines. Pines exhibited a significant positive relationship between shallow soil moisture and GS, but only GS in Q. velutina was positively related to soil moisture. In contrast, stomatal sensitivity to VPD was significantly related to solar radiation in all oak species but only pines at one site. Therefore, oaks rely more heavily on groundwater resources but have lower WUE, while pines have larger leaf areas and nitrogen acquisition but lower PNUE demonstrating a trade-off between using water and nitrogen efficiently in a resource-limited ecosystem. PMID:25999966

Diurnal Reflectance Changes in Vegetation Observed with AVIRIS

NASA Technical Reports Server (NTRS)

Vanderbilt, V. C.; Ambrosia, V. G.; Ustin, S. L.

1998-01-01

Among the most important short-term dynamic biological processes are diurnal changes in canopy water relations. Plant regulation of water transport through stomatal openings affects other gaseous transport processes, often dramatically decreasing photosynthetic fixation of carbon dioxide during periods of water stress. Water stress reduces stomatal conductance of water vapor through the leaf surface and alters the diurnal timing of stomatal opening. Under non-water stressed conditions, stomates typically open soon after dawn and transpire water vapor throughout the daylight period. During stress periods, stomates may close for part of the day, generally near mid-day. Under prolonged stress conditions, stomatal closure shifts to earlier times during the day; stomates may close by mid-morning and remain closed until the following morning - or remain closed entirely. Under these conditions the relationship between canopy greenness (e.g., measured with a vegetation index or by spectral mixture analysis) and photosynthetic fixation of carbon is lost and the remotely sensed vegetation metric is a poor predictor of gas exchange. Prediction of stomatal regulation and exchange of water and trace gases is critical for ecosystem and climate models to correctly estimate budgets of these gases and understand or predict other processes like gross and net ecosystem primary production. Plant gas exchange has been extensively studied by physiologists at the leaf and whole plant level and by biometeorologists at somewhat larger scales. While these energy driven processes follow a predictable if somewhat asymmetric diurnal cycle dependent on soil water availability and the constraints imposed by the solar energy budget, they are nonetheless difficult to measure at the tree and stand levels using conventional methods. Ecologists have long been interested in the potential of remote sensing for monitoring physiological changes using multi-temporal images. Much of this research has focused on day-to-day changes in water use, especially for agricultural applications. Ustin et al. showed seasonal changes in canopy water content in chaparral shrub could be estimated using optical methods. Vanderbilt et al. followed asymmetric diurnal changes in the reflectance of a walnut orchard, but could not attribute specific reflectance changes to specific changes in canopy architecture or physiology. Forests and shrub lands in California experience prolonged periods of drought, sometimes extending six months without precipitation. The conifer and evergreen chaparral communities common to the foothill region around the central valley of California retain their foliage throughout the summer and have low transpiration rates despite high net radiation and temperature conditions. In contrast, grasslands and drought resistant deciduous species in the same habitat are seasonally dormant in summer. Because of differences in the mechanisms of drought tolerance, rooting depth and physiology between different plant communities in the region, it is likely that they display differences in diurnal water relations. The presence of diverse plant communities provides an opportunity to investigate possible diurnal landscape patterns in water relations that could be observed by an airborne hyperspectral scanner. This investigation of AVIRIS data collected over forest and shrub land represents the continuation of a prior investigation involving spectral mixture analysis of diurnal effects in the same AVIRIS data set.

Dynamics of transpiration, sap flow and use of stored water in tropical forest canopy trees.

Treesearch

Frederick C. Meinzer; Shelley A. James; Guillermo Goldstein

2004-01-01

In large trees the daily onset of transpiration causes water to be withdrawn from internal storage compartments resulting in lags between changes in transpiration and sap flow at the base of the tree. We measured time courses of sap flow, hydraulic resistance, plant water potential and stomatal resistance in co-occuring tropical forest canopy trees with trunk diameters...

Crop modeling: Studying the effect of water stress on the driving forces governing plant water potential

NASA Astrophysics Data System (ADS)

van Emmerik, T. H. M.; Mirfenderesgi, G.; Bohrer, G.; Steele-Dunne, S. C.; Van De Giesen, N.

2015-12-01

Water stress is one of the most important environmental factors that influence plant water dynamics. To prevent excessive water loss and physiological damage, plants can regulate transpiration by adjusting the stomatal aperture. This enhances survival, but also reduced photosynthesis and productivity. During periods of low water availability, stomatal regulation is a trade-off between optimization of either survival or production. Water stress defence mechanisms lead to significant changes in plant dynamics, e.g. leaf and stem water content. Recent research has shown that water content in a corn canopy can change up to 30% diurnally as a result of water stress, which has a considerable influence on radar backscatter from a corn canopy [1]. This highlighted the potential of water stress detection using radar. To fully explore the potential of water stress monitoring using radar, we need to understand the driving forces governing plant water potential. For this study, the recently developed the Finite-Element Tree-Crown Hydrodynamic model version 2 (FETCH2) model is applied to a corn canopy. FETCH2 is developed to resolve the hydrodynamic processes within a plant using the porous media analogy, allowing investigation of the influence of environmental stress factors on plant dynamics such as transpiration, photosynthesis, stomatal conductance, and leaf and stem water content. The model is parameterized and evaluated using a detailed dataset obtained during a three-month field experiment in Flevoland, the Netherlands, on a corn canopy. [1] van Emmerik, T., S. Steele-Dunne, J. Judge and N. van de Giesen: "Impact of Diurnal Variation in Vegetation Water Content on Radar Backscatter of Maize During Water Stress", Geosciences and Remote Sensing, IEEE Transactions on, vol. 52, issue 7, doi: 10.1109/TGRS.2014.2386142, 2015.

Evapotranspiration partitioning, stomatal conductance, and components of the water balance: A special case of a desert ecosystem in China

NASA Astrophysics Data System (ADS)

Zhao, Wenzhi; Liu, Bing; Chang, Xuexiang; Yang, Qiyue; Yang, Yuting; Liu, Zhiling; Cleverly, James; Eamus, Derek

2016-07-01

Partitioning evapotranspiration (ET) into its components reveals details of the processes that underlie ecosystem hydrologic budgets and their feedback to the water cycle. We measured rates of actual evapotranspiration (ETa), canopy transpiration (Tc), soil evaporation (Eg), canopy-intercepted precipitation (EI), and patterns of stomatal conductance of the desert shrub Calligonum mongolicum in northern China to determine the water balance of this ecosystem. The ETa was 251 ± 8 mm during the growing period, while EI, Tc, and Eg accounted for 3.2%, 63.9%, and 31.3%, respectively, of total water use (256 ± 4 mm) during the growing period. In this unique ecosystem, groundwater was the main water source for plant transpiration and soil evaporation, Tc and exceeded 60% of the total annual water used by desert plants. ET was not sensitive to air temperature in this unique desert ecosystem. Partitioning ET into its components improves our understanding of the mechanisms that underlie adaptation of desert shrubs, especially the role of stomatal regulation of Tc as a determinant of ecosystem water balance.

Divergence of actual and reference evapotranspiration observations for irrigated sugarcane with windy tropical conditions

NASA Astrophysics Data System (ADS)

Anderson, R. G.; Wang, D.; Tirado-Corbalá, R.; Zhang, H.; Ayars, J. E.

2015-01-01

Standardized reference evapotranspiration (ET) and ecosystem-specific vegetation coefficients are frequently used to estimate actual ET. However, equations for calculating reference ET have not been well validated in tropical environments. We measured ET (ETEC) using eddy covariance (EC) towers at two irrigated sugarcane fields on the leeward (dry) side of Maui, Hawaii, USA in contrasting climates. We calculated reference ET at the fields using the short (ET0) and tall (ETr) vegetation versions of the American Society for Civil Engineers (ASCE) equation. The ASCE equations were compared to the Priestley-Taylor ET (ETPT) and ETEC. Reference ET from the ASCE approaches exceeded ETEC during the mid-period (when vegetation coefficients suggest ETEC should exceed reference ET). At the windier tower site, cumulative ETr exceeded ETEC by 854 mm over the course of the mid-period (267 days). At the less windy site, mid-period ETr still exceeded ETEC, but the difference was smaller (443 mm). At both sites, ETPT approximated mid-period ETEC more closely than the ASCE equations ((ETPT-ETEC) < 170 mm). Analysis of applied water and precipitation, soil moisture, leaf stomatal resistance, and canopy cover suggest that the lower observed ETEC was not the result of water stress or reduced vegetation cover. Use of a custom-calibrated bulk canopy resistance improved the reference ET estimate and reduced seasonal ET discrepancy relative to ETPT and ETEC in the less windy field and had mixed performance in the windier field. These divergences suggest that modifications to reference ET equations may be warranted in some tropical regions.

Divergence of reference evapotranspiration observations with windy tropical conditions

NASA Astrophysics Data System (ADS)

Anderson, R. G.; Wang, D.; Tirado-Corbalá, R.; Zhang, H.; Ayars, J. E.

2014-06-01

Standardized reference evapotranspiration (ET) and ecosystem-specific vegetation coefficients are frequently used to estimate actual ET. However, equations for calculating reference ET have not been well validated in tropical environments. We measured ET (ETEC) using Eddy Covariance (EC) towers at two irrigated sugarcane fields on the leeward (dry) side of Maui, Hawaii, USA in contrasting climates. We calculated reference ET at the fields using the short (ET0) and tall (ETr) vegetation versions of the American Society for Civil Engineers (ASCE) equation. The ASCE equations were compared to the Priestley-Taylor ET (ETPT) and ETEC. Reference ET from the ASCE approaches exceeded ETEC during the mid-period (when vegetation coefficients suggest ETEC should exceed reference ET). At the windier tower site, cumulative ETr exceeded ETEC by 854 mm over the course of the mid-period (267 days). At the less windy site, mid-period ETr still exceeded ETEC, but the difference was smaller (443 mm). At both sites, ETPT approximated mid-period ETEC more closely than the ASCE equations ((ETPT-ETEC) < 170 mm). Analysis of applied water and precipitation, soil moisture, leaf stomatal resistance, and canopy cover suggest that the lower observed ETEC was not the result of water stress or reduced vegetation cover. Use of a custom calibrated bulk canopy resistance improved the reference ET estimate and reduced seasonal ET discrepancy relative to ETPT and ETEC for the less windy field and had mixed performance at the windier field. These divergences suggest that modifications to reference ET equations may be warranted in some tropical regions.

An observational constraint on stomatal function in forests: evaluating coupled carbon and water vapor exchange with carbon isotopes in the Community Land Model (CLM4.5)

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

Raczka, Brett; Duarte, Henrique F.; Koven, Charles D.

Land surface models are useful tools to quantify contemporary and future climate impact on terrestrial carbon cycle processes, provided they can be appropriately constrained and tested with observations. Stable carbon isotopes of CO 2 offer the potential to improve model representation of the coupled carbon and water cycles because they are strongly influenced by stomatal function. Recently, a representation of stable carbon isotope discrimination was incorporated into the Community Land Model component of the Community Earth System Model. Here, we tested the model's capability to simulate whole-forest isotope discrimination in a subalpine conifer forest at Niwot Ridge, Colorado, USA. Wemore » distinguished between isotopic behavior in response to a decrease of δ 13C within atmospheric CO 2 (Suess effect) vs. photosynthetic discrimination (Δ canopy), by creating a site-customized atmospheric CO 2 and δ 13C of CO 2 time series. We implemented a seasonally varying V cmax model calibration that best matched site observations of net CO 2 carbon exchange, latent heat exchange, and biomass. The model accurately simulated observed δ 13C of needle and stem tissue, but underestimated the δ 13C of bulk soil carbon by 1–2 ‰. The model overestimated the multiyear (2006–2012) average Δ canopy relative to prior data-based estimates by 2–4 ‰. The amplitude of the average seasonal cycle of Δ canopy (i.e., higher in spring/fall as compared to summer) was correctly modeled but only when using a revised, fully coupled A n- g s (net assimilation rate, stomatal conductance) version of the model in contrast to the partially coupled A n- g s version used in the default model. The model attributed most of the seasonal variation in discrimination to A n, whereas interannual variation in simulated Δ canopy during the summer months was driven by stomatal response to vapor pressure deficit (VPD). The model simulated a 10 % increase in both photosynthetic discrimination and water-use efficiency (WUE) since 1850 which is counter to established relationships between discrimination and WUE. The isotope observations used here to constrain CLM suggest (1) the model overestimated stomatal conductance and (2) the default CLM approach to representing nitrogen limitation (partially coupled model) was not capable of reproducing observed trends in discrimination. These findings demonstrate that isotope observations can provide important information related to stomatal function driven by environmental stress from VPD and nitrogen limitation. Future versions of CLM that incorporate carbon isotope discrimination are likely to benefit from explicit inclusion of mesophyll conductance.« less

An observational constraint on stomatal function in forests: evaluating coupled carbon and water vapor exchange with carbon isotopes in the Community Land Model (CLM4.5)

DOE PAGES

Raczka, Brett; Duarte, Henrique F.; Koven, Charles D.; ...

2016-09-19

Land surface models are useful tools to quantify contemporary and future climate impact on terrestrial carbon cycle processes, provided they can be appropriately constrained and tested with observations. Stable carbon isotopes of CO 2 offer the potential to improve model representation of the coupled carbon and water cycles because they are strongly influenced by stomatal function. Recently, a representation of stable carbon isotope discrimination was incorporated into the Community Land Model component of the Community Earth System Model. Here, we tested the model's capability to simulate whole-forest isotope discrimination in a subalpine conifer forest at Niwot Ridge, Colorado, USA. Wemore » distinguished between isotopic behavior in response to a decrease of δ 13C within atmospheric CO 2 (Suess effect) vs. photosynthetic discrimination (Δ canopy), by creating a site-customized atmospheric CO 2 and δ 13C of CO 2 time series. We implemented a seasonally varying V cmax model calibration that best matched site observations of net CO 2 carbon exchange, latent heat exchange, and biomass. The model accurately simulated observed δ 13C of needle and stem tissue, but underestimated the δ 13C of bulk soil carbon by 1–2 ‰. The model overestimated the multiyear (2006–2012) average Δ canopy relative to prior data-based estimates by 2–4 ‰. The amplitude of the average seasonal cycle of Δ canopy (i.e., higher in spring/fall as compared to summer) was correctly modeled but only when using a revised, fully coupled A n- g s (net assimilation rate, stomatal conductance) version of the model in contrast to the partially coupled A n- g s version used in the default model. The model attributed most of the seasonal variation in discrimination to A n, whereas interannual variation in simulated Δ canopy during the summer months was driven by stomatal response to vapor pressure deficit (VPD). The model simulated a 10 % increase in both photosynthetic discrimination and water-use efficiency (WUE) since 1850 which is counter to established relationships between discrimination and WUE. The isotope observations used here to constrain CLM suggest (1) the model overestimated stomatal conductance and (2) the default CLM approach to representing nitrogen limitation (partially coupled model) was not capable of reproducing observed trends in discrimination. These findings demonstrate that isotope observations can provide important information related to stomatal function driven by environmental stress from VPD and nitrogen limitation. Future versions of CLM that incorporate carbon isotope discrimination are likely to benefit from explicit inclusion of mesophyll conductance.« less

Estimates of ion sources in deciduous and coniferous throughfall

USGS Publications Warehouse

Puckett, L.J.

1990-01-01

Estimates of external and internal sources of ions in net throughfall deposition were derived for a deciduous and coniferous canopy by use of multiple regression. The externel source component appears to be dominated by dry deposition of Ca2+, SO2 and NO3- during dormant and growing seasons for the two canopy types. Increases in the leaching rates of K+ and Mg2+ during the growing season reflect the presence of leaves in the deciduous canopy and increased physiological activity in both canopies. Internal leaching rates for SO42- doubled during the growing season presumably caused by increased physiological activity and uptake of SO2 through stomates. Net deposition of SO42- in throughfall during the growing season appears highly dependent on stomatal uptake of SO2. Estimates of SO2 deposition velocities were 0.06 cm s-1 and 0.13 cm s-1 for the deciduous and coniferous canopies, respectively, during the dormant season, and 0.30 cm s-1 and 0.43 cm s-1 for the deciduous and coniferous canopies, respectively, during the growing season. For the ions of major interest with respect to ecosystem effects, namely H+, NO3- and SO42-, precipitation inputs generally outweighed estimates of dry deposition input. However, net throughfall deposition of NO3- and SO42- accounted for 20-47 and 34-50 per cent, respectively, of total deposition of those ions. Error estimates of ion sources were at least 50-100 per cent and the method is subject to several assumptions and limitations.

Influence of leaf water potential on diurnal changes in CO2 and water vapour fluxes

NASA Astrophysics Data System (ADS)

Yu, Qiang; Xu, Shouhua; Wang, Jing; Lee, Xuhui

2007-08-01

Mass and energy fluxes between the atmosphere and vegetation are driven by meteorological variables, and controlled by plant water status, which may change more markedly diurnally than soil water. We tested the hypothesis that integration of dynamic changes in leaf water potential may improve the simulation of CO2 and water fluxes over a wheat canopy. Simulation of leaf water potential was integrated into a comprehensive model (the ChinaAgrosys) of heat, water and CO2 fluxes and crop growth. Photosynthesis from individual leaves was integrated to the canopy by taking into consideration the attenuation of radiation when penetrating the canopy. Transpiration was calculated with the Shuttleworth-Wallace model in which canopy resistance was taken as a link between energy balance and physiological regulation. A revised version of the Ball-Woodrow-Berry stomatal model was applied to produce a new canopy resistance model, which was validated against measured CO2 and water vapour fluxes over winter wheat fields in Yucheng (36°57' N, 116°36' E, 28 m above sea level) in the North China Plain during 1997, 2001 and 2004. Leaf water potential played an important role in causing stomatal conductance to fall at midday, which caused diurnal changes in photosynthesis and transpiration. Changes in soil water potential were less important. Inclusion of the dynamics of leaf water potential can improve the precision of the simulation of CO2 and water vapour fluxes, especially in the afternoon under water stress conditions.

The Role of Structural, Biochemical and Ecophysiological Plant Acclimation in the Eco-Hydrologic Response of Agro-Ecosystems to Global Change in the Central US

NASA Astrophysics Data System (ADS)

Drewry, D.; Kumar, P.; Long, S.; Sivapalan, M.; Bernacchi, C.; Liang, X.

2009-12-01

The acclimation of terrestrial vegetation to changes in ambient growth environment has significant implications for land-atmosphere exchange of carbon dioxide (CO2) and energy, as well as critical ecosystem services such as food production. Recent field campaigns at the SoyFACE Free Air Carbon Enrichment (FACE) facility in central Illinois have provided clear evidence of the modification of structural, biochemical and ecophysiological properties of key agricultural species at CO2 concentrations projected for the middle of this century. While these acclamatory responses have been linked to changes in leaf-level gas exchange and leaf states (ie. leaf temperature and stomatal conductance), determining the implications for these changes at the canopy-scale has remained a challenge. Here we present a simulation analysis that examines the role of observed plant acclimation in two key mid-west agricultural species, soy (C3 photosynthetic pathway) and corn (C4 photosynthetic pathway), in modifying future carbon uptake and surface energy partitioning, crop water use and resilience to water stress. The model canopies are divided into multiple layers, allowing for resolution of the shortwave and longwave radiation regimes that drive photosynthesis, stomatal conductance and leaf energy balance in each layer, along with the canopy microclimate. The canopy component of the model is coupled to a multi-layer soil-root model that computes soil moisture and root water uptake at each time period, accounting for the effects of moisture stress on canopy functioning. Model skill in capturing the sub-diurnal variability in canopy-atmosphere fluxes is demonstrated using multi-year records of eddy covariance CO2, water vapor and heat fluxes collected at the Bondville (Illinois) AmeriFlux site. An evaluation of the ability of the model to simulate observed changes in energy balance components, leaf-level photosynthetic assimilation, leaf temperature and stomatal conductance under elevated CO2 concentrations projected for 2050 (550 ppm) is conducted through observations collected at SoyFACE over several recent growing seasons. With this validated model we quantify the role of structural, biochemical and ecophysiological acclimation on canopy-atmosphere exchange of CO2, water vapor and heat, and examine the within-canopy variability of flux densities and states to elevated CO2 perturbations. The role of meteorological forcing conditions and soil moisture status on mediating the changes in canopy-atmosphere interactions is examined. The model is then used to investigate the magnitude and direction of changes in fluxes and water use efficiency as ambient CO2 is elevated across a range of concentrations expected through the coming century.

Successional change in photosynthetic capacities after wildfires across the North American boreal forests

NASA Astrophysics Data System (ADS)

Tahara, N.; Ueyama, M.; Iwata, H.; Ichii, K.; Harazono, Y.; Nagano, H.

2015-12-01

Wildfire is a major disturbance across the North American boreal forests. Canopy ecophysiology is important to understand recovery of carbon dioxide and water vapor fluxes after wildfires. We developed a big-leaf model coupled photosynthesis (Farquhar et al., 1980) and stomatal conductance (Ball et al., 1987) models. We inputted eddy covariance data from fire chronosequence across the North American boreal forests into the big-leaf model for optimizing parameters: maximum carboxylation rate at 25℃ (Vcmax25) and stomatal conductance parameters. The model was optimized with a global optimization technique: SCE-UA method (Duan et al., 1994). The estimated canopy-scale parameters were then downscaled into a leaf scale (vcmax25; values per sun leaf area) using a two-leaf radiation transfer model (de Pury and Farquhar, 1997) and leaf area index. We used 6 sites from two fire chronosequence in Alaska (1~, 3~, 5~, 15~ and 80~ years after fire; Liu et al., 2005; Iwata et al., 2011) and 6 sites from a Canadian chronosequence study (6~, 15~, 23~, 40~ and 74~ years after fire; Goulden et al., 2010). Preliminary results showed clear seasonal variations in canopy-scale Vcmax25 with the maximum during the summer. In Alaska, the downscaled vcmax25 for four years after fire exceeded those of mature forests, indicating that the photosynthetic capacity recovered quickly in the early successional stage. This quick recovery was not seen in gross primary productivity. We will show the variations of the ecophysiological parameters in terms of environment conditions and stand age. References Ball et al., 1987: In Progress in Photosynthesis Research, 221-224. de Pury and Farquhar, 1997: Plant, Cell and Environ., 20, 537-557. Duan et al., 1994: J. Hydrology, 158, 265-284. Farquhar et al., 1980: Planta, 149, 78-90. Goulden et al., 2010: Global Change Biol., 17, 855-871. Iwata et al., 2011: SOLA., 7, 105-108. Liu et al., 2005: J. Geophys. Res., 110, D13101.

Characterizing photosynthesis and transpiration of plant communities in controlled environments

NASA Technical Reports Server (NTRS)

Monje, O.; Bugbee, B.

1996-01-01

CO2 and water vapor fluxes of hydroponically grown wheat and soybean canopies were measured continuously in several environments with an open gas exchange system. Canopy CO2 fluxes reflect the photosynthetic efficiency of a plant community, and provide a record of plant growth and health. There were significant diurnal fluctuations in root and shoot CO2 fluxes, and in shoot water vapor fluxes. Canopy stomatal conductance (Gc) to water vapor was calculated from simultaneous measurements of canopy temperature (Tcan) and transpiration rates (Tr). Tr in the dark was substantial, and there were large diurnal fluctuations in both Gc and Tr. Canopy net Photosynthesis (Pnet), Tr, and Gc increased with increasing net radiation. Gc increased with Tr, suggesting that the stomata of plants in controlled environments (CEs) behave differently from field-grown plants. A transpiration model based on measurements of Gc was developed for CEs. The model accurately predicted Tr from a soybean canopy.

Carbon and water flux responses to physiology by environment interactions: a sensitivity analysis of variation in climate on photosynthetic and stomatal parameters

NASA Astrophysics Data System (ADS)

Bauerle, William L.; Daniels, Alex B.; Barnard, David M.

2014-05-01

Sensitivity of carbon uptake and water use estimates to changes in physiology was determined with a coupled photosynthesis and stomatal conductance ( g s) model, linked to canopy microclimate with a spatially explicit scheme (MAESTRA). The sensitivity analyses were conducted over the range of intraspecific physiology parameter variation observed for Acer rubrum L. and temperate hardwood C3 (C3) vegetation across the following climate conditions: carbon dioxide concentration 200-700 ppm, photosynthetically active radiation 50-2,000 μmol m-2 s-1, air temperature 5-40 °C, relative humidity 5-95 %, and wind speed at the top of the canopy 1-10 m s-1. Five key physiological inputs [quantum yield of electron transport ( α), minimum stomatal conductance ( g 0), stomatal sensitivity to the marginal water cost of carbon gain ( g 1), maximum rate of electron transport ( J max), and maximum carboxylation rate of Rubisco ( V cmax)] changed carbon and water flux estimates ≥15 % in response to climate gradients; variation in α, J max, and V cmax input resulted in up to ~50 and 82 % intraspecific and C3 photosynthesis estimate output differences respectively. Transpiration estimates were affected up to ~46 and 147 % by differences in intraspecific and C3 g 1 and g 0 values—two parameters previously overlooked in modeling land-atmosphere carbon and water exchange. We show that a variable environment, within a canopy or along a climate gradient, changes the spatial parameter effects of g 0, g 1, α, J max, and V cmax in photosynthesis- g s models. Since variation in physiology parameter input effects are dependent on climate, this approach can be used to assess the geographical importance of key physiology model inputs when estimating large scale carbon and water exchange.

Stomatal control and leaf thermal and hydraulic capacitances under rapid environmental fluctuations.

PubMed

Schymanski, Stanislaus J; Or, Dani; Zwieniecki, Maciej

2013-01-01

Leaves within a canopy may experience rapid and extreme fluctuations in ambient conditions. A shaded leaf, for example, may become exposed to an order of magnitude increase in solar radiation within a few seconds, due to sunflecks or canopy motions. Considering typical time scales for stomatal adjustments, (2 to 60 minutes), the gap between these two time scales raised the question whether leaves rely on their hydraulic and thermal capacitances for passive protection from hydraulic failure or over-heating until stomata have adjusted. We employed a physically based model to systematically study effects of short-term fluctuations in irradiance on leaf temperatures and transpiration rates. Considering typical amplitudes and time scales of such fluctuations, the importance of leaf heat and water capacities for avoiding damaging leaf temperatures and hydraulic failure were investigated. The results suggest that common leaf heat capacities are not sufficient to protect a non-transpiring leaf from over-heating during sunflecks of several minutes duration whereas transpirative cooling provides effective protection. A comparison of the simulated time scales for heat damage in the absence of evaporative cooling with observed stomatal response times suggested that stomata must be already open before arrival of a sunfleck to avoid over-heating to critical leaf temperatures. This is consistent with measured stomatal conductances in shaded leaves and has implications for water use efficiency of deep canopy leaves and vulnerability to heat damage during drought. Our results also suggest that typical leaf water contents could sustain several minutes of evaporative cooling during a sunfleck without increasing the xylem water supply and thus risking embolism. We thus submit that shaded leaves rely on hydraulic capacitance and evaporative cooling to avoid over-heating and hydraulic failure during exposure to typical sunflecks, whereas thermal capacitance provides limited protection for very short sunflecks (tens of seconds).

Transpiration in response to variation in microclimate and soil moisture in southeastern deciduous forests.

PubMed

Oren, Ram; Pataki, Diane E

2001-05-01

Responses of forests to changes in environmental conditions reflect the integrated behavior of their constituent species. We investigated sap flux-scaled transpiration responses of two species prevalent in upland eastern hardwood forests, Quercus alba in the upper canopy and Acer rubrum in the low to mid canopy, to changes in photosynthetically active radiation above the canopy (Q o ), vapor pressure deficit within the canopy (D), and soil moisture depletion during an entire growing season. Water loss before bud break (presumably through the bark) increased linearly with D, reaching 8% of daily stand transpiration (E C ) as measured when leaf area index was at maximum, and accounting for 5% of annual water loss. After leaves were completely expanded and when soil moisture was high, sap flux-scaled daily E C increased linearly with the daily sum of Q o . Species differences in this response were observed. Q. alba reached a maximum transpiration at low Q o , while A. rubrum showed increasing transpiration with Q o at all light levels. Daily E C increased in response to daily average D, with an asymptotic response due to the behavior of Q. alba. Transpiration of A. rubrum showed a greater response to soil moisture depletion than did that of Q. alba. When evaluated at a half-hourly scale under high Q o , mean canopy stomatal conductance (G S ) of individuals decreased with D. The sensitivity of G S to D was greater in species with higher intrinsic G S . Regardless of position in the canopy, diffuse-porous species in this and an additional, more mesic stand showed higher G S and greater stomatal sensitivity to environmental variation than do ring-porous species.

Sensitivity of stomatal conductance to soil moisture: implications for tropospheric ozone

NASA Astrophysics Data System (ADS)

Anav, Alessandro; Proietti, Chiara; Menut, Laurent; Carnicelli, Stefano; De Marco, Alessandra; Paoletti, Elena

2018-04-01

Soil moisture and water stress play a pivotal role in regulating stomatal behaviour of plants; however, in the last decade, the role of water availability has often been neglected in atmospheric chemistry modelling studies as well as in integrated risk assessments, despite the fact that plants remove a large amount of atmospheric compounds from the lower troposphere through stomata. The main aim of this study is to evaluate, within the chemistry transport model CHIMERE, the effect of soil water limitation on stomatal conductance and assess the resulting changes in atmospheric chemistry testing various hypotheses of water uptake by plants in the rooting zone. Results highlight how dry deposition significantly declines when soil moisture is used to regulate the stomatal opening, mainly in the semi-arid environments: in particular, over Europe the amount of ozone removed by dry deposition in one year without considering any soil water limitation to stomatal conductance is about 8.5 TgO3, while using a dynamic layer that ensures that plants maximize the water uptake from soil, we found a reduction of about 10 % in the amount of ozone removed by dry deposition ( ˜ 7.7 TgO3). Although dry deposition occurs from the top of canopy to ground level, it affects the concentration of gases remaining in the lower atmosphere, with a significant impact on ozone concentration (up to 4 ppb) extending from the surface to the upper troposphere (up to 650 hPa). Our results shed light on the importance of improving the parameterizations of processes occurring at plant level (i.e. from the soil to the canopy) as they have significant implications for concentration of gases in the lower troposphere and resulting risk assessments for vegetation or human health.

Canopy reflectance, photosynthesis, and transpiration. II - The role of biophysics in the linearity of their interdependence

NASA Technical Reports Server (NTRS)

Sellers, P. J.

1987-01-01

The ability of satellite sensor systems to estimate area-averaged canopy photosynthetic and transpirative properties is evaluated. The near linear relationship between the simple ratio (SR) and normalized difference (ND) and the surface biophysical properties of canopy photosynthetically active radiation (PAR) absorption, photosynthesis, and bulk stomatal resistance is studied. The models utilized to illustrate the processes of canopy reflectance, photosynthesis, and resistance are described. The dependence of SR, the absorbed fraction of PAR, and canopy photosynthesis and resistance on total leaf area index is analyzed. It is noted that the SR and ND vegetation indices and vegetation-dependent qualities are near-linearly related due to the proportion of leaf scattering coefficient in visible and near IR wavelength regions. The data reveal that satellite sensor systems are useful for the estimation of photosynthesis and transpirative properties.

Structural adjustments in resprouting trees drive differences in post-fire transpiration.

PubMed

Nolan, Rachael H; Mitchell, Patrick J; Bradstock, Ross A; Lane, Patrick N J

2014-02-01

Following disturbance many woody species are capable of resprouting new foliage, resulting in a reduced leaf-to-sapwood area ratio and altered canopy structure. We hypothesized that such changes would promote adjustments in leaf physiology, resulting in higher rates of transpiration per unit leaf area, consistent with the mechanistic framework proposed by Whitehead et al. (Whitehead D, Jarvis PG, Waring RH (1984) Stomatal conductance, transpiration and resistance to water uptake in a Pinus sylvestris spacing experiment. Can J For Res 14:692-700). We tested this in Eucalyptus obliqua L'Hér following a wildfire by comparing trees with unburnt canopies with trees that had been subject to 100% canopy scorch and were recovering their leaf area via resprouting. In resprouting trees, foliage was distributed along the trunk and on lateral branches, resulting in shorter hydraulic path lengths. We evaluated measurements of whole-tree transpiration and structural and physiological traits expected to drive any changes in transpiration. We used these structural and physiological measurements to parameterize the Whitehead et al. equation, and found that the expected ratio of transpiration per unit leaf area between resprouting and unburnt trees was 3.41. This is similar to the observed ratio of transpiration per unit leaf area, measured from sapflow observations, which was 2.89 (i.e., resprouting trees had 188% higher transpiration per unit leaf area). Foliage at low heights (<2 m) was found to be significantly different to foliage in the tree crown (14-18 m) in a number of traits, including higher specific leaf area, midday leaf water potential and higher rates of stomatal conductance and photosynthesis. We conclude that these post-fire adjustments in resprouting trees help to drive increased stomatal conductance and hydraulic efficiency, promoting the rapid return of tree-scale transpiration towards pre-disturbance levels. These transient patterns in canopy transpiration have important implications for modelling stand-level water fluxes in forests capable of resprouting, which is frequently done on the basis of the leaf area index.

Sensitivity Analysis of Biome-Bgc Model for Dry Tropical Forests of Vindhyan Highlands, India

NASA Astrophysics Data System (ADS)

Kumar, M.; Raghubanshi, A. S.

2011-08-01

A process-based model BIOME-BGC was run for sensitivity analysis to see the effect of ecophysiological parameters on net primary production (NPP) of dry tropical forest of India. The sensitivity test reveals that the forest NPP was highly sensitive to the following ecophysiological parameters: Canopy light extinction coefficient (k), Canopy average specific leaf area (SLA), New stem C : New leaf C (SC:LC), Maximum stomatal conductance (gs,max), C:N of fine roots (C:Nfr), All-sided to projected leaf area ratio and Canopy water interception coefficient (Wint). Therefore, these parameters need more precision and attention during estimation and observation in the field studies.

Satellite remote sensing of primary production

NASA Technical Reports Server (NTRS)

Tucker, C. J.; Sellers, P. J.

1986-01-01

Leaf structure and function are shown to result in distinctive variations in the absorption and reflection of solar radiation from plant canopies. The leaf properties that determine the radiation-interception characteristics of plant canopies are directly linked to photosynthesis, stomatal resistance and evapotranspiration and can be inferred from measurements of reflected solar energy. The effects of off-nadir viewing and atmospheric constituents, coupled with the need to measure changing surface conditions, emphasize the need for multitemporal measurements of reflected radiation if primary production is to be estimated.

Contribution of competition for light to within-species variability in stomatal conductance

NASA Astrophysics Data System (ADS)

Loranty, Michael M.; Mackay, D. Scott; Ewers, Brent E.; Traver, Elizabeth; Kruger, Eric L.

2010-05-01

Sap flux (JS) measurements were collected across two stands dominated by either trembling aspen or sugar maple in northern Wisconsin. Observed canopy transpiration (EC-obs) values derived from JS were used to parameterize the Terrestrial Regional Ecosystem Exchange Simulator ecosystem model. Modeled values of stomatal conductance (GS) were used to determine reference stomatal conductance (GSref), a proxy for GS that removes the effects of temporal responses to vapor pressure deficit (D) on spatial patterns of GS. Values of GSref were compared to observations of soil moisture, several physiological variables, and a competition index (CI) derived from a stand inventory, to determine the underlying cause of observed variability. Considerable variability in GSref between individual trees was found, with values ranging from 20 to 200 mmol m-2 s-1 and 20 to 100 mmol m-2 s-1 at the aspen and maple stands, respectively. Model-derived values of GSref and a sensitivity to D parameter (m) showed good agreement with a known empirical relationship for both stands. At both sites, GSref did not vary with topographic position, as indicated by surface soil moisture. No relationships were observed between GSref and tree height (HT), and a weak correlation with sapwood area (AS) was only significant for aspen. Significant nonlinear inverse relationships between GSref and CI were observed at both stands. Simulations with uniform reductions in incident photosynthetically active radiation (Q0) resulted in better agreement between observed and simulated EC. Our results suggest a link between photosynthesis and plant hydraulics whereby individual trees subject to photosynthetic limitation as a result of competitive shading exhibit a dynamic stomatal response resulting in a more conservative strategy for managing hydrologic resources.

Simulating sunflower canopy temperatures to infer root-zone soil water potential

NASA Technical Reports Server (NTRS)

Choudhury, B. J.; Idso, S. B.

1983-01-01

A soil-plant-atmosphere model for sunflower (Helianthus annuus L.), together with clear sky weather data for several days, is used to study the relationship between canopy temperature and root-zone soil water potential. Considering the empirical dependence of stomatal resistance on insolation, air temperature and leaf water potential, a continuity equation for water flux in the soil-plant-atmosphere system is solved for the leaf water potential. The transpirational flux is calculated using Monteith's combination equation, while the canopy temperature is calculated from the energy balance equation. The simulation shows that, at high soil water potentials, canopy temperature is determined primarily by air and dew point temperatures. These results agree with an empirically derived linear regression equation relating canopy-air temperature differential to air vapor pressure deficit. The model predictions of leaf water potential are also in agreement with observations, indicating that measurements of canopy temperature together with a knowledge of air and dew point temperatures can provide a reliable estimate of the root-zone soil water potential.

Vapor Pressure Deficit and Sap Velocity Dynamic Coupling in Canopy Dominant Trees in the Amazon basin

NASA Astrophysics Data System (ADS)

Chambers, J. Q.; Gimenez, B.; Jardine, K.; Negron Juarez, R. I.; Cobello, L. O.; Fontes, C.; Dawson, T. E.; Higuchi, N.

2017-12-01

In order to improve our ability to predict terrestrial water fluxes, an understanding of the interactions between plant physiology and environmental conditions is necessary, especially in tropical forests which recycle large fluxes of water to the atmosphere. This need has become more relevant due to observed records in global temperature. In this study we show a strong temporal correlation between sap velocity and leaf-to-air vapor pressure deficit (VPD) in canopy dominant trees in two primary rainforest sites in the Amazon basin (Santarém and Manaus, Brazil). As VPDs in the upper canopy (20-30 m) varied throughout the day and night, basal sap velocity (1.5 m) responded rapidly without an observable delay (< 15 min). Sap velocity showed a sigmoidal dependence on VPDs including an exponential increase, an inflection point, and a plateau, in all observed trees. Moreover, a clear diurnal hysteresis in sap velocity, stomatal conductance, and leaf water potential was evident with morning periods showing higher sensitivities to VPD than afternoon and night periods. Diurnal leaf gas exchange observations revealed a morning to midday peak in stomatal conductance, but midday to afternoon peak in transpiration and VPD. Thus, our study confirms that the temporal lag between the Gs peak and VPD peak are the major regulators of the hysteresis phenomenon as previously described by other studies. Moreover, out study provide direct evidence for the role of decreased stomatal conductance in the warm afternoon periods to reduce transpiration and allow for the partial recovery of leaf water potential to less negative values. Our results suggests the possibility of predicting evapotranspiration fluxes from ecosystem to regional scales using remote sensing of vegetation temperature from, for example, thermal images of satellites and drones.

Drought tolerance, xylem sap abscisic acid and stomatal conductance during soil drying: a comparison of canopy trees of three temperate deciduous angiosperms.

PubMed

Loewenstein, Nancy J.; Pallardy, Stephen G.

1998-07-01

Patterns of water relations, xylem sap abscisic acid concentration ([ABA]) and stomatal aperture were characterized and compared in drought-sensitive black walnut (Juglans nigra L.), less drought-sensitive sugar maple (Acer saccharum Marsh.) and drought-tolerant white oak (Quercus alba L.) trees co-occurring in a second-growth forest in Missouri, USA. There were strong correlations among reduction in predawn leaf water potential, increased xylem sap [ABA] and stomatal closure in all species. Stomatal conductance was more closely correlated with xylem sap ABA concentration than with ABA flux or xylem sap pH and cation concentrations. In isohydric black walnut, increased concentrations of ABA in the xylem sap appeared to be primarily of root origin, causing stomatal closure in response to soil drying. In anisohydric sugar maple and white oak, however, there were reductions in midday leaf water potential associated with stomatal closure, making it uncertain whether drought-induced xylem sap ABA was of leaf or root origin. The role of root-originated xylem sap ABA in these species as a signal to the shoot of the water status of the roots is, therefore, less certain.

What plant hydraulics can tell us about responses to climate-change droughts.

PubMed

Sperry, John S; Love, David M

2015-07-01

Climate change exposes vegetation to unusual drought, causing declines in productivity and increased mortality. Drought responses are hard to anticipate because canopy transpiration and diffusive conductance (G) respond to drying soil and vapor pressure deficit (D) in complex ways. A growing database of hydraulic traits, combined with a parsimonious theory of tree water transport and its regulation, may improve predictions of at-risk vegetation. The theory uses the physics of flow through soil and xylem to quantify how canopy water supply declines with drought and ceases by hydraulic failure. This transpiration 'supply function' is used to predict a water 'loss function' by assuming that stomatal regulation exploits transport capacity while avoiding failure. Supply-loss theory incorporates root distribution, hydraulic redistribution, cavitation vulnerability, and cavitation reversal. The theory efficiently defines stomatal responses to D, drying soil, and hydraulic vulnerability. Driving the theory with climate predicts drought-induced loss of plant hydraulic conductance (k), canopy G, carbon assimilation, and productivity. Data lead to the 'chronic stress hypothesis' wherein > 60% loss of k increases mortality by multiple mechanisms. Supply-loss theory predicts the climatic conditions that push vegetation over this risk threshold. The theory's simplicity and predictive power encourage testing and application in large-scale modeling. © 2015 The Authors. New Phytologist © 2015 New Phytologist Trust.

Modeling the Impact of Land Use Change on Regional Water Flux in Northern Wisconsin-Species Effects on Transpiration and Canopy Average Stomatal Conductance

NASA Astrophysics Data System (ADS)

Ewers, B. E.; Mackay, D. S.; Ahl, D. E.; Burrows, S. N.; Samanta, S. S.; Gower, S. T.

2001-05-01

Land use change has created a diversity of forest cover types in northern Wisconsin. Our objective was to determine if changes in forest cover would result in a significant change in regional water flux. To adequately sample these forest cover types we chose four cover types red pine, sugar maple/basswood, quaking aspen/balsam fir, and northern white-cedar/balsam fir/green alder that represent more than 80 percent of the ground area. The remainder of the ground area is mostly non-forested grassland, shrubland, and open water. Within each cover type we measured sap flux of 8 trees of each species. We scaled point measurements of sap flux to tree transpiration using sensors positioned radially into the conducting sapwood and on both the north and south sides of the tree. We found that aspen/balsam fir had the highest average daily transpiration rates. There was no difference in the northern white-cedar/balsam fir/green alder and red pine cover types. The sugar maple/basswood cover type had the lowest daily average transpiration rate. These changes in transpiration could not be explained by differences in leaf area index. Thus, we calculated canopy average stomatal conductance (GS) using an inversion of the Penman-Monteith equation and tree leaf area. We modified a regional hydrology model to include a simple tree hydraulic sub-model that assumes stomatal regulation of leaf water potential. We tested the behavior of the sub-model by evaluating GS response to vapor pressure deficit, radiation, temperature, and soil moisture for each species. We hypothesize that species with a high canopy average stomatal conductance at low vapor pressure deficit will have to have greater sensitivity to vapor pressure deficit in order to maintain minimal leaf water potential as suggested by the model. Our results indicate that changes to forest cover such as conversion from low transpiring sugar maple/basswood to high transpiring aspen/fir will result in predictable changes to the regional water balance of northern Wisconsin.

Evapotranspiration modelled from stands of three broad-leaved tropical trees in Costa Rica

NASA Astrophysics Data System (ADS)

Bigelow, Seth

2001-10-01

To examine the impact of tree species on the water cycle in a wet tropical region, annual evapotranspiration (ET) was estimated in Costa Rican plantations of three native, broad-leaved tree species that contrasted strongly in leaf size, leaf area and phenology. Evapotranspiration was estimated using the Penman-Monteith equation for transpiration from the dry canopy, the equilibrium equation for evaporation from the understory and a modified Rutter model of interception for evaporation of water from the canopy when wetted by rainfall. Canopy conductance was estimated from stomatal conductance, leaf area and leaf boundary-layer conductance; canopy storage capacity and filling rate were estimated from throughfall measurements. Micrometeorological instruments were mounted on a scaffolding tower.Mean stomatal conductance, which ranged from 0·1 to 0·7 mol m-2 s-1, was similar to boundary-layer conductance, 0·1 to 0·5 mol m-2 s-1, indicating decoupling of stomata from atmospheric conditions. Mean canopy conductance varied from 0·6 to 0·7 mol m-2 s-1 in the 1994 wet season then dropped to 0·3-0·4 mol m-2 s-1 in stands of the two deciduous species, Cordia and Cedrela, as a result of reduced leaf area during the dry season. Despite increased understory evaporation, dry-season ET from these stands was only 78-81% of ET in stands of the evergreen species, Hyeronima. Maximum canopy water depth varied from 0·2 to 2·2 mm, causing modelled interception to vary from 6% to 25% of annual ET. Higher dry-season transpiration rates along with high rates of evaporation of intercepted rainfall in all seasons led to 14% higher annual ET in Hyeronima stands (1509 mm) than in stands of the species with lowest ET,

Forest canopy hydraulics

Treesearch

David R. Woodruff; Frederick C. Meinzer; Katherine A. McCulloh

2016-01-01

Water and carbon cycles are strongly coordinated and water availability is a primary limiting factor in many terrestrial ecosystems. Photosynthesis requires sufficient water supply to leaves and constraints on delivery at any point in the hydraulic continuum can lead to stomatal closure and reduced photosynthesis. Thus, maximizing water transport enhances assimilation...

Seasonal patterns of cytokinins and microclimate and the mediation of gas exchange among canopy layers of mature Acer saccharum trees.

PubMed

Reeves, Ian; Emery, R J Neil

2007-11-01

Seasonal patterns of cytokinins (CKs) and microclimate were examined in the upper, middle and lower canopy layers of mature Acer saccharum Marsh. (sugar maple) trees to elucidate the potential role of CKs in the mediation of gas exchange. The upper canopy showed a distinctly dissimilar microclimate from the middle and lower canopy layers with higher photosynthetically active radiation and wind speed, but showed no corresponding differences in transpiration (E) or stomatal conductance (g(s)). Although E and g(s) tended to be higher in the upper canopy than in the middle and lower canopies, the differences were not significant, indicating regulation beyond the passive response to changes in microclimate. The upper canopy accumulated significantly higher concentrations of CKs, predominantly as ribosides, and all canopy layers showed distinct seasonal patterns in CK profiles. Multiple regression models showed significant relationships between both g(s) and E and foliar CK concentration, although these relationships varied among canopy layers. The relationships were strongest in the middle and lower canopy layers where there was less fluctuation in leaf water status and less variability in abiotic variables. The relationships between gas exchange parameters and leaf CK concentration began to decouple near the end of the growing season as foliar phytohormone concentrations changed with the approach of dormancy.

Making C4 crops more water efficient under current and future climate: Tradeoffs between carbon gain and water loss

NASA Astrophysics Data System (ADS)

Srinivasan, V.; Pignon, C.

2017-12-01

C4 plants have a carbon concentrating mechanism that has evolved under historically low CO2 concentrations of around 200 ppm. However, increases in global CO2 concentrations in recent times (current CO2 concentrations are at 400 ppm and it is projected to be 550 ppm by mid-century) have diminished the relative advantage of C4 plants over C3 plants, which lack the expensive carbon concentrating machinery. Here we show by employing model simulations that under pre-historic CO2 concentrations, C4 plants are near optimal in their stomatal behavior and nitrogen partitioning between carbon concentrating machinery and carboxylation machinery, and they are significantly supra-optimal under current and future elevated CO2 concentrations. Model simulations performed at current CO2 concentrations of 400 ppm show that, under high light conditions, decreasing stomatal conductance by 20% results in a 15% increase in water use efficiency with negligible loss in photosynthesis. Under future elevated CO2 concentrations of 550 ppm, a 40% decrease in stomatal conductance produces a 35% increase in water use efficiency. Furthermore, stomatal closure is shown to be more effective in decreasing whole canopy transpiration compared to canopy top leaf transpiration, since shaded leaves are more supra-optimal than sunlit leaves. Model simulations for optimizing nitrogen distribution in C4 leaves show that under high light conditions, C4 plants over invest in carbon concentrating machinery and under invest in carboxylation machinery. A 20% redistribution in leaf nitrogen results in a 10% increase in leaf carbon assimilation without significant increases in transpiration under current CO2 concentrations of 400 ppm. Similarly, a 40% redistribution in leaf nitrogen results in a 15% increase in leaf carbon assimilation without significant increases in transpiration under future elevated CO2 concentrations of 550 ppm. Our model optimality simulations show that C4 leaves a supra optimal in their stomatal behavior and leaf nitrogen distribution and by decreasing stomatal conductance and redistributing nitrogen away from carbon concentrating mechanism and towards carboxylation machinery, we can significantly decrease transpiration and increase carbon assimilation thereby increasing water use efficiency.

Stomatal sensitivity to vapour pressure deficit relates to climate of origin in Eucalyptus species.

PubMed

Bourne, Aimee E; Haigh, Anthony M; Ellsworth, David S

2015-03-01

Selecting plantation species to balance water use and production requires accurate models for predicting how species will tolerate and respond to environmental conditions. Although interspecific variation in water use occurs, species-specific parameters are rarely incorporated into physiologically based models because often the appropriate species parameters are lacking. To determine the physiological control over water use in Eucalyptus, five stands of Eucalyptus species growing in a common garden were measured for sap flux rates and their stomatal response to vapour pressure deficit (D) was assessed. Maximal canopy conductance and whole-canopy stomatal sensitivity to D and reduced water availability were lower in species originating from more arid climates of origin than those from humid climates. Species from humid climates showed a larger decline in maximal sap flux density (JSmax) with reduced water availability, and a lower D at which stomatal closure occurred than species from more arid climates, implying larger sensitivity to water availability and D in these species. We observed significant (P < 0.05) correlations of species climate of origin with mean vessel diameter (R(2) = 0.90), stomatal sensitivity to D (R(2) = 0.83) and the size of the decline in JSmax to restricted water availability (R(2) = 0.94). Thus aridity of climate of origin appears to have a selective role in constraining water-use response among the five Eucalyptus plantation species. These relationships emphasize that within this congeneric group of species, climate aridity constrains water use. These relationships have implications for species choices for tree plantation success against drought-induced losses and the ability to manage Eucalyptus plantations against projected changes in water availability and evaporation in the future. © The Author 2015. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Proposed Hydrodynamic Model Increases the Ability of Land-Surface Models to Capture Intra-Daily Dynamics of Transpiration and Canopy Structure Effects

NASA Astrophysics Data System (ADS)

Matheny, A. M.; Bohrer, G.; Mirfenderesgi, G.; Schafer, K. V.; Ivanov, V. Y.

2014-12-01

Hydraulic limitations are known to control transpiration in forest ecosystems when the soil is drying or when the vapor pressure deficit between the air and stomata is very large, but they can also impact stomatal apertures under conditions of adequate soil moisture and lower evaporative demand. We use the NACP dataset of latent heat flux measurements and model observations for multiple sites and models to demonstrate models' difficulties in capturing intra-daily hysteresis. We hypothesize that this is a result of un-resolved afternoon stomata closure due to hydrodynamic stresses. The current formulations for stomatal conductance and the empirical coupling between stomatal conductance and soil moisture used by these models does not resolve the hydrodynamic process of water movement from the soil to the leaves. This approach does not take advantage of advances in our understanding of water flow and storage in the trees, or of tree and canopy structure. A more thorough representation of the tree-hydrodynamic processes could potentially remedy this significant source of model error. In a forest plot at the University of Michigan Biological Station, we use measurements of sap flux and leaf water potential to demonstrate that trees of similar type - late successional deciduous trees - have very different hydrodynamic strategies that lead to differences in their temporal patterns of stomatal conductance and thus hysteretic cycles of transpiration. These differences will lead to large differences in conductance and water use based on the species composition of the forest. We also demonstrate that the size and shape of the tree branching system leads to differences in extent of hydrodynamic stress, which may change the forest respiration patterns as the forest grows and ages. We propose a framework to resolve tree hydrodynamics in global and regional models based on the Finite-Elements Tree-Crown Hydrodynamics model (FETCH) -a hydrodynamic model that can resolve the fast dynamics of stomatal conductance. FETCH simulates water flow through a tree as a system of porous media conduits and calculates the amount of hydraulic limitation to stomatal conductance, given the atmospheric and biological variables from the global model, and could replace the current empirical formulation for stomatal adjustment based on soil moisture.

Variation in morphological and biochemical O3 injury attributes of mature Jeffrey pine within canopies and between microsites.

PubMed

Grulke, N E; Johnson, R; Monschein, S; Nikolova, P; Tausz, M

2003-09-01

Crown morphology and leaf tissue chemical and biochemical attributes associated with ozone (O3) injury were assessed in the lower, mid- and upper canopy of Jeffrey pine (Pinus jeffreyi Grev. & Balf.) growing in mesic and xeric microsites in Sequoia National Park, California. Microsites were designated mesic or xeric based on topography and bole growth in response to years of above-average precipitation. In mesic microsites, canopy response to O3 was characterized by thinner branches, earlier needle fall, less chlorotic leaf mottling, and lower foliar antioxidant capacity, especially of the aqueous fraction. In xeric microsites, canopy response to O3 was characterized by higher chlorotic leaf mottling, shorter needles, lower needle chlorophyll concentration, and greater foliar antioxidant capacity. Increased leaf chlorotic mottle in xeric microsites was related to drought stress and increased concurrent internal production of highly reactive oxygen species, and not necessarily to stomatal O3 uptake. Within-canopy position also influenced the expression of O3 injury in Jeffrey pine.

Analysis of field measurements of carbon dioxide and water vapor fluxes

NASA Technical Reports Server (NTRS)

Verma, Shashi B.

1991-01-01

Analysis of the field measurements of carbon dioxide and water vapor fluxes is discussed. These data were examined in conjunction with reflectance obtained from helicopter mounted Modular Multiband Radiometer. These measurements are representative of the canopy scale (10 to 100 m)(exp 2) and provide a good basis for investigating the hypotheses/relationship potentially useful in remote sensing applications. All the micrometeorological data collected during FIFE-89 were processed and fluxes of CO2, water vapor, and sensible heat were calculated. Soil CO2 fluxes were also estimated. Employing these soil CO2 flux values, in conjunction with micrometeorological measurements, canopy photosynthesis is being estimated. A biochemical model of leaf photosynthesis was adapted to the prairie vegetation. The modeled leaf photosynthesis rates were scaled up to the canopy level. This model and a multiplicative stomatal conductance model are also used to calculate canopy conductance.

A multilayer model for inferring dry deposition using standard meteorological measurements

NASA Astrophysics Data System (ADS)

Meyers, Tilden P.; Finkelstein, Peter; Clarke, John; Ellestad, Thomas G.; Sims, Pamela F.

1998-09-01

In this paper, we describe the latest version of the dry deposition inferential model, which is used to estimate the deposition velocities (Vd) for SO2, O3, HNO3, and particles with diameters less than 2 μm. The dry deposition networks operated by the National Oceanic and Atmospheric Administration (NOAA) and the Environmental Protection Agency (EPA) use this model to estimate dry deposition on a weekly basis. This model uses a multilayer approach, discretizing the vegetated canopy into 20 layers. The use of canopy radiative transfer and simple wind profile models allows for estimates of stomatal (rs) and leaf boundary layer (rb) resistances to be determined at each layer in the plant canopy for both sunlit and shaded leaves. The effect of temperature, water stress, and vapor pressure deficits on the stomatal resistance (rs) have been included. Comparisons of modeled deposition velocities are made with extensive direct measurements performed at three different locations with different crops. The field experiment is discussed in some detail. Overall, modeled O3 deposition velocities are in good agreement with measured values with the average mean bias for all surfaces of the order of 0.01 cm/s or less. For SO2, mean biases range from -0.05 for corn to 0.15 cm/s for soybeans, while for HNO3, they range from 0.09 for corn to 0.47 cm/s for pasture.

Leaf water 18 O and 2 H enrichment along vertical canopy profiles in a broadleaved and a conifer forest tree.

PubMed

Bögelein, Rebekka; Thomas, Frank M; Kahmen, Ansgar

2017-07-01

Distinguishing meteorological and plant-mediated drivers of leaf water isotopic enrichment is prerequisite for ecological interpretations of stable hydrogen and oxygen isotopes in plant tissue. We measured input and leaf water δ 2 H and δ 18 O as well as micrometeorological and leaf morpho-physiological variables along a vertical gradient in a mature angiosperm (European beech) and gymnosperm (Douglas fir) tree. We used these variables and different enrichment models to quantify the influence of Péclet and non-steady state effects and of the biophysical drivers on leaf water enrichment. The two-pool model accurately described the diurnal variation of leaf water enrichment. The estimated unenriched water fraction was linked to leaf dry matter content across the canopy heights. Non-steady state effects and reduced stomatal conductance caused a higher enrichment of Douglas fir compared to beech leaf water. A dynamic effect analyses revealed that the light-induced vertical gradients of stomatal conductance and leaf temperature outbalanced each other in their effects on evaporative enrichment. We conclude that neither vertical canopy gradients nor the Péclet effect is important for estimates and interpretation of isotopic leaf water enrichment in hypostomatous trees. Contrarily, species-specific non-steady state effects and leaf temperatures as well as the water vapour isotope composition need careful consideration. © 2017 John Wiley & Sons Ltd.

Stomatal behavior of ozone-sensitive and -insensitive coneflowers ( Rudbeckia laciniata var. digitata ) in Great Smoky Mountains National Park

Treesearch

Nancy Grulke; H. S. Neufeld; A. W. Davison; M. Roberts; A. H. Chappelka

2006-01-01

• Morphological and physiological attributes were assessed to elucidate the underlying mechanisms of ozone (O3) sensitivity in a highly sensitive species, cutleaf coneflower (Rudbeckia laciniata var. digitata). • Foliage at the same height in the canopy on paired O3-...

Phototropins But Not Cryptochromes Mediate the Blue Light-Specific Promotion of Stomatal Conductance, While Both Enhance Photosynthesis and Transpiration under Full Sunlight12[C][W][OA

PubMed Central

Boccalandro, Hernán E.; Giordano, Carla V.; Ploschuk, Edmundo L.; Piccoli, Patricia N.; Bottini, Rubén; Casal, Jorge J.

2012-01-01

Leaf epidermal peels of Arabidopsis (Arabidopsis thaliana) mutants lacking either phototropins 1 and 2 (phot1 and phot2) or cryptochromes 1 and 2 (cry1 and cry2) exposed to a background of red light show severely impaired stomatal opening responses to blue light. Since phot and cry are UV-A/blue light photoreceptors, they may be involved in the perception of the blue light-specific signal that induces the aperture of the stomatal pores. In leaf epidermal peels, the blue light-specific effect saturates at low irradiances; therefore, it is considered to operate mainly under the low irradiance of dawn, dusk, or deep canopies. Conversely, we show that both phot1 phot2 and cry1 cry2 have reduced stomatal conductance, transpiration, and photosynthesis, particularly under the high irradiance of full sunlight at midday. These mutants show compromised responses of stomatal conductance to irradiance. However, the effects of phot and cry on photosynthesis were largely nonstomatic. While the stomatal conductance phenotype of phot1 phot2 was blue light specific, cry1 cry2 showed reduced stomatal conductance not only in response to blue light, but also in response to red light. The levels of abscisic acid were elevated in cry1 cry2. We conclude that considering their effects at high irradiances cry and phot are critical for the control of transpiration and photosynthesis rates in the field. The effects of cry on stomatal conductance are largely indirect and involve the control of abscisic acid levels. PMID:22147516

Phototropins but not cryptochromes mediate the blue light-specific promotion of stomatal conductance, while both enhance photosynthesis and transpiration under full sunlight.

PubMed

Boccalandro, Hernán E; Giordano, Carla V; Ploschuk, Edmundo L; Piccoli, Patricia N; Bottini, Rubén; Casal, Jorge J

2012-03-01

Leaf epidermal peels of Arabidopsis (Arabidopsis thaliana) mutants lacking either phototropins 1 and 2 (phot1 and phot2) or cryptochromes 1 and 2 (cry1 and cry2) exposed to a background of red light show severely impaired stomatal opening responses to blue light. Since phot and cry are UV-A/blue light photoreceptors, they may be involved in the perception of the blue light-specific signal that induces the aperture of the stomatal pores. In leaf epidermal peels, the blue light-specific effect saturates at low irradiances; therefore, it is considered to operate mainly under the low irradiance of dawn, dusk, or deep canopies. Conversely, we show that both phot1 phot2 and cry1 cry2 have reduced stomatal conductance, transpiration, and photosynthesis, particularly under the high irradiance of full sunlight at midday. These mutants show compromised responses of stomatal conductance to irradiance. However, the effects of phot and cry on photosynthesis were largely nonstomatic. While the stomatal conductance phenotype of phot1 phot2 was blue light specific, cry1 cry2 showed reduced stomatal conductance not only in response to blue light, but also in response to red light. The levels of abscisic acid were elevated in cry1 cry2. We conclude that considering their effects at high irradiances cry and phot are critical for the control of transpiration and photosynthesis rates in the field. The effects of cry on stomatal conductance are largely indirect and involve the control of abscisic acid levels.

Eddy Covariance Fluxes of the NO-O3-NO2 Triad above the Forest Canopy at the ATTO Site in the Amazon Basin

NASA Astrophysics Data System (ADS)

Tsokankunku, A.; Wolff, S.; Berger, M.; Zelger, M.; Dlugi, R. J. W.; Andreae, M. O.; Sörgel, M.

2017-12-01

Nitrogen monoxide (NO) and nitrogen dioxide (NO2) (denoted together as NOx) determine the abundance of the tropospheric oxidants OH, O3 and NO3 that regulate atmospheric self-cleaning. The three reactive trace gases NO, NO2 and O3 undergo a series of interconnected photochemical reactions and are therefore often referred to as the NO-O3-NO2 triad. Ozone deposition is mainly controlled by stomatal uptake, therefore resulting in oxidative stress for the plants. Similarly, nitrogen dioxide from above or below the canopy is deposited to leaves through stomatal uptake. NO emissions from soils contribute to above canopy O3 formation and accelerate OH recycling. Therefore, quantification of the biosphere-atmosphere exchange fluxes of these species is important for atmospheric chemistry and ecosystem research. The eddy covariance method is state of the art for direct measurements of ecosystem fluxes of trace gases. Eddy covariance measurements of NOx in pristine environments are rare because of lack of availability of instruments with the required precision to resolve concentrations characteristic of these environments with the required high time resolution. The Amazon Tall Tower Observatory (ATTO) is located in a pristine rainforest environment in the Amazon basin about 150 km northeast of the city of Manaus. It is the ideal site for studying the biosphere-atmosphere exchange of the NO-O3-NO2 triad, because of the absence of nearby anthropogenic sources. During an intensive measurement campaign in November 2015 at the ATTO site, measurements of NO, NO2 and O3 were carried out at 42 m above ground level on the 80 m walk-up tower with a fast (5 Hz) and sensitive (< 30 ppt) instrument (CLD790SR2, Eco Physics) for NO and NO2 and with 10 Hz for O3 (Enviscope GmbH). Additionally, a suite of micrometeorological instruments was installed, including a profile of 3-dimensional sonic anemometers and meteorological sensors. Vertical concentration profile measurements of NO, NO2 and O3 were available at 8 levels on the tower. From these measurements, we present eddy covariance fluxes of the NO-O3-NO2 triad. We relate the fluxes to the canopy-atmosphere exchange of the trace gases and other scalars using the profile data along the tower. Chemical and turbulent transport timescales of the triad constituents are presented and discussed.

Partitioning of water flux in a Sierra Nevada ponderosa pine plantation

USGS Publications Warehouse

Kurpius, M.R.; Panek, J.A.; Nikolov, N.T.; McKay, M.; Goldstein, Allen H.

2003-01-01

The weather patterns of the west side of the Sierra Nevada Mountains (cold, wet winters and hot, dry summers) strongly influence how water is partitioned between transpiration and evaporation and result in a specific strategy of water use by ponderosa pine trees (Pinus ponderosa) in this region. To investigate how year-round water fluxes were partitioned in a young ponderosa pine ecosystem in the Sierra Nevada Mountains, water fluxes were continually measured from June 2000 to May 2001 using a combination of sap flow and eddy covariance techniques (above- and below-canopy). Water fluxes were modeled at our study site using a biophysical model, FORFLUX. During summer and fall water fluxes were equally partitioned between transpiration and soil evaporation while transpiration dominated the water fluxes in winter and spring. The trees had high rates of canopy conductance and transpiration in the early morning and mid-late afternoon and a mid-day depression during the dry season. We used a diurnal centroid analysis to show that the timing of high canopy conductance and transpiration relative to high vapor pressure deficit (D) shifted with soil moisture: during periods of low soil moisture canopy conductance and transpiration peaked early in the day when D was low. Conversely, during periods of high soil moisture canopy conductance and transpiration peaked at the same time or later in the day than D. Our observations suggest a general strategy by the pine trees in which they maximize stomatal conductance, and therefore carbon fixation, throughout the day on warm sunny days with high soil moisture (i.e. warm periods in winter and late spring) and maximize stomatal conductance and carbon fixation in the morning through the dry periods. FORFLUX model estimates of evaporation and transpiration were close to measured/calculated values during the dry period, including the drought, but underestimated transpiration and overestimated evaporation during the wet period. ?? 2003 Elsevier Science B.V. All rights reserved.

Prolonged experimental drought reduces plant hydraulic conductance and transpiration and increases mortality in a piñon-juniper woodland.

PubMed

Pangle, Robert E; Limousin, Jean-Marc; Plaut, Jennifer A; Yepez, Enrico A; Hudson, Patrick J; Boutz, Amanda L; Gehres, Nathan; Pockman, William T; McDowell, Nate G

2015-04-01

Plant hydraulic conductance (k s) is a critical control on whole-plant water use and carbon uptake and, during drought, influences whether plants survive or die. To assess long-term physiological and hydraulic responses of mature trees to water availability, we manipulated ecosystem-scale water availability from 2007 to 2013 in a piñon pine (Pinus edulis) and juniper (Juniperus monosperma) woodland. We examined the relationship between k s and subsequent mortality using more than 5 years of physiological observations, and the subsequent impact of reduced hydraulic function and mortality on total woody canopy transpiration (E C) and conductance (G C). For both species, we observed significant reductions in plant transpiration (E) and k s under experimentally imposed drought. Conversely, supplemental water additions increased E and k s in both species. Interestingly, both species exhibited similar declines in k s under the imposed drought conditions, despite their differing stomatal responses and mortality patterns during drought. Reduced whole-plant k s also reduced carbon assimilation in both species, as leaf-level stomatal conductance (g s) and net photosynthesis (A n) declined strongly with decreasing k s. Finally, we observed that chronically low whole-plant k s was associated with greater canopy dieback and mortality for both piñon and juniper and that subsequent reductions in woody canopy biomass due to mortality had a significant impact on both daily and annual canopy E C and G C. Our data indicate that significant reductions in k s precede drought-related tree mortality events in this system, and the consequence is a significant reduction in canopy gas exchange and carbon fixation. Our results suggest that reductions in productivity and woody plant cover in piñon-juniper woodlands can be expected due to reduced plant hydraulic conductance and increased mortality of both piñon pine and juniper under anticipated future conditions of more frequent and persistent regional drought in the southwestern United States.

Prolonged experimental drought reduces plant hydraulic conductance and transpiration and increases mortality in a piñon–juniper woodland

PubMed Central

Pangle, Robert E; Limousin, Jean-Marc; Plaut, Jennifer A; Yepez, Enrico A; Hudson, Patrick J; Boutz, Amanda L; Gehres, Nathan; Pockman, William T; McDowell, Nate G

2015-01-01

Plant hydraulic conductance (ks) is a critical control on whole-plant water use and carbon uptake and, during drought, influences whether plants survive or die. To assess long-term physiological and hydraulic responses of mature trees to water availability, we manipulated ecosystem-scale water availability from 2007 to 2013 in a piñon pine (Pinus edulis) and juniper (Juniperus monosperma) woodland. We examined the relationship between ks and subsequent mortality using more than 5 years of physiological observations, and the subsequent impact of reduced hydraulic function and mortality on total woody canopy transpiration (EC) and conductance (GC). For both species, we observed significant reductions in plant transpiration (E) and ks under experimentally imposed drought. Conversely, supplemental water additions increased E and ks in both species. Interestingly, both species exhibited similar declines in ks under the imposed drought conditions, despite their differing stomatal responses and mortality patterns during drought. Reduced whole-plant ks also reduced carbon assimilation in both species, as leaf-level stomatal conductance (gs) and net photosynthesis (An) declined strongly with decreasing ks. Finally, we observed that chronically low whole-plant ks was associated with greater canopy dieback and mortality for both piñon and juniper and that subsequent reductions in woody canopy biomass due to mortality had a significant impact on both daily and annual canopy EC and GC. Our data indicate that significant reductions in ks precede drought-related tree mortality events in this system, and the consequence is a significant reduction in canopy gas exchange and carbon fixation. Our results suggest that reductions in productivity and woody plant cover in piñon–juniper woodlands can be expected due to reduced plant hydraulic conductance and increased mortality of both piñon pine and juniper under anticipated future conditions of more frequent and persistent regional drought in the southwestern United States. PMID:25937906

Climatic, biological, and land cover controls on the exchange of gas-phase semivolatile chemical pollutants between forest canopies and the atmosphere.

PubMed

Nizzetto, Luca; Perlinger, Judith A

2012-03-06

An ecophysiological model of a structured broadleaved forest canopy was coupled to a chemical fate model of the air-canopy exchange of gaseous semivolatile chemicals to dynamically assess the short-term (hours) and medium term (days to season) air-canopy exchange and the influence of biological, climatic, and land cover drivers on the dynamics of the air-canopy exchange and on the canopy storage for airborne semivolatile pollutants. The chemical fate model accounts for effects of short-term variations in air temperature, wind speed, stomatal opening, and leaf energy balance, all as a function of layer in the canopy. Simulations showed the potential occurrence of intense short/medium term re-emission of pollutants having log K(OA) up to 10.7 from the canopy as a result of environmental forcing. In addition, relatively small interannual variations in seasonally averaged air temperature, canopy biomass, and precipitation can produce relevant changes in the canopy storage capacity for the chemicals. It was estimated that possible climate change related variability in environmental parameters (e.g., an increase of 2 °C in seasonally averaged air temperature in combination with a 10% reduction in canopy biomass due to, e.g., disturbance or acclimatization) may cause a reduction in canopy storage capacity of up to 15-25%, favoring re-emission and potential for long-range atmospheric transport. On the other hand, an increase of 300% in yearly precipitation can increase canopy sequestration by 2-7% for the less hydrophobic compounds.

Continuous In-situ Measurements of Carbonyl Sulfide to Constrain Ecosystem Carbon and Water Exchange

NASA Astrophysics Data System (ADS)

Rastogi, B.; Kim, Y.; Berkelhammer, M. B.; Noone, D. C.; Lai, C. T.; Hollinger, D. Y.; Bible, K.; Leen, J. B.; Gupta, M.; Still, C. J.

2014-12-01

Understanding the processes that control the terrestrial exchange of carbon and water are critical for examining the role of forested ecosystems in changing climates. A small but increasing number of studies have identified Carbonyl Sulfide (OCS) as a potential tracer for photosynthesis. OCS is hydrolyzed by an irreversible reaction in leaf mesophyll cells that is catalyzed by the enzyme, carbonic anhydrase. Leaf-level field and greenhouse studies indicate that OCS uptake is controlled by stomatal activity and that the ratio of OCS and CO2 uptake is reasonably constant. Existing studies on ecosystem OCS exchange have been based on laboratory measurements or short field campaigns and therefore little information on OCS exchange in a natural ecosystem over longer timescales is available. The objective of this study is to further assess the stability of OCS as a tracer for canopy photosynthesis in an active forested ecosystem and also to assess its utility for constraining transpiration, since both fluxes are mediated by canopy stomatal conductance. An off-axis integrated cavity output spectroscopy analyzer (Los Gatos Research Inc.) was deployed at the Wind River Experimental Forest in Washington (45.8205°N, 121.9519°W). Canopy air was sampled from three heights to measure vertical gradients of OCS within the canopy, and OCS exchange between the forest and the atmosphere. Here we take advantage of simultaneous measurements of the stable isotopologues of H2O and CO2 at corresponding heights as well as NEE (Net Ecosystem Exchange) from eddy covariance measurements to compare GPP (Gross Primary Production) and transpiration estimates from a variety of independent techniques. Our findings seek to allow assessment of the environmental and ecophysicological controls on evapotranspiration rates, which are projected to change in coming decades, and are otherwise poorly constrained.

Evidence That Drought-Induced Stomatal Closure Is Not an Important Constraint on White Spruce Performance Near the Arctic Treeline in Alaska

NASA Astrophysics Data System (ADS)

Sullivan, P.; Brownlee, A.; Ellison, S.; Sveinbjornsson, B.

2014-12-01

Tree cores collected from trees growing at high latitudes have long been used to reconstruct past climates, because of close positive correlations between temperature and tree growth. However, in recent decades and at many sites, these relationships have deteriorated and have even become negative in some instances. The observation of declining tree growth in response to rising temperature has prompted many investigators to suggest that high latitude trees may be increasingly exhibiting drought-induced stomatal closure. In the Brooks Range of northern Alaska, the observation of low and declining growth of white spruce is more prevalent in the central and eastern parts of the range, where precipitation is lower, providing superficial support for the drought stress hypothesis. In this study, we investigated the occurrence of white spruce drought-induced stomatal closure in four watersheds along a west to east gradient near the Arctic treeline in the Brooks Range. We obtained a historical perspective on tree growth and water relations by collecting increment cores for analysis of ring widths and carbon isotopes in tree-ring alpha-cellulose. Meanwhile, we made detailed assessments of contemporary water relations at the scales of the whole canopy and the needle. All of our data indicate that drought-induced stomatal closure is probably not responsible for low and declining growth in the central and eastern Brooks Range. Carbon isotope discrimination has generally increased over the past century and our calculations indicate that needle inter-cellular CO2 concentration is much greater now than it was in the early 1900's. Measurements of needle gas exchange are consistent with the tree core record, in the sense that instances of low photosynthesis at our sites are not coincident with similarly low stomatal conductance and low inter-cellular CO2 concentration. Finally, hourly measurements of xylem sap flow indicate that trees at our study sites are able to maintain near peak canopy transpiration under the highest atmospheric vapor pressure deficits observed (>3.0 kPa). Thus, our tree-ring data provide further evidence of what has become known as the "divergence problem" in northern forests, but our physiological measurements suggest that drought-induced stomatal closure may not be the cause.

Components of ecosystem evaporation in a temperate coniferous rainforest, with canopy transpiration scaled using sapwood density.

PubMed

Barbour, M M; Hunt, J E; Walcroft, A S; Rogers, G N D; McSeveny, T M; Whitehead, D

2005-02-01

Here we develop and test a method to scale sap velocity measurements from individual trees to canopy transpiration (E(c)) in a low-productivity, old-growth rainforest dominated by the conifer Dacrydium cupressinum. Further, E(c) as a component of the ecosystem water balance is quantified in relation to forest floor evaporation rates and measurements of ecosystem evaporation using eddy covariance (E(eco)) in conditions when the canopy was dry and partly wet. Thermal dissipation probes were used to measure sap velocity of individual trees, and scaled to transpiration at the canopy level by dividing trees into classes based on sapwood density and canopy position (sheltered or exposed). When compared with ecosystem eddy covariance measurements, E(c) accounted for 51% of E(eco) on dry days, and 22% of E(eco) on wet days. Low transpiration rates, and significant contributions to E(eco) from wet canopy evaporation and understorey transpiration (35%) and forest floor evaporation (25%), were attributable to the unique characteristics of the forest: in particular, high rainfall, low leaf area index, low stomatal conductance and low productivity associated with severe nutrient limitation.

Effect of canopy structure and open-top chamber techniques on micrometeorological parameters and the gradients and transport of water vapor, carbon dioxide and ozone in the canopies of plum trees (`prunus salicina`) in the San Joaquin valley. Final report

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

Grantz, D.A.; Vaughn, D.L.; Metheny, P.A.

1995-03-15

Plum trees (Prunus salicina cv. Casselman) were exposed to ozone in open-top chambers (OTC) or chamberless plots, and trace gas concentrations and microenvironmental conditions were monitored within tree canopies inside the outside the OTC. Concentrations of ozone, carbon dioxide and water vapor, leaf and air temperature, light intensity, and wind speed were measured at nine positions in the tree canopies. The objectives were to: (1) map the distribution of microenvironmental parameters within the canopies inside and outside the OTC; (2) determine transport parameters for gas exchange, and (3) calculate ozone flux. Significant vertical and horizontal gradients were observed; gradients weremore » diminished and often inverted inside relative to outside the OTC due to air distribution at the bottom of the OCT. Ozone flux was readily modeled from measures of stomatal conductance, nonstomatal conductance and ozone concentration at the leaf surface.« less

Influence of irrigation and fertilization on transpiration and hydraulic properties of Populus deltoides

Treesearch

Lisa J. Samuelson; Thomas A. Stokes; Mark D. Coleman

2007-01-01

Long-term hydraulic acclimation to resource availability was explored in 3-year-old Populus deltoides Bartr. ex Marsh. clones by examining transpiration. leaf-specific hydraulic conductance (GL), canopy stomatal conductance (Gs) and leaf to sapwood area ratio (AL:Asi)n response to irrigation (13 and 551 mm in addition to ambient precipitation) and...

Effects of CO2 on stomatal conductance: do stomata open at very high CO2 concentrations?

NASA Technical Reports Server (NTRS)

Wheeler, R. M.; Mackowiak, C. L.; Yorio, N. C.; Sager, J. C.

1999-01-01

Potato and wheat plants were grown for 50 d at 400, 1000 and 10000 micromoles mol-1 carbon dioxide (CO2). and sweetpotato and soybean were grown at 1000 micromoles mol-1 CO2 in controlled environment chambers to study stomatal conductance and plant water use. Lighting was provided with fluorescent lamps as a 12 h photoperiod with 300 micromoles m-2 s-1 PAR. Mid-day stomatal conductances for potato were greatest at 400 and 10000 micromoles mol-1 and least at 1000 micromoles mol-1 CO2. Mid-day conductances for wheat were greatest at 400 micromoles mol-1 and least at 1000 and 10000 micromoles mol-1 CO2. Mid-dark period conductances for potato were significantly greater at 10000 micromoles mol-1 than at 400 or 1000 micromoles mol-1, whereas dark conductance for wheat was similar in all CO2 treatments. Temporarily changing the CO2 concentration from the native 1000 micromoles mol-1 to 400 micromoles mol-1 increased mid-day conductance for all species, while temporarily changing from 1000 to 10000 micromoles mol-1 also increased conductance for potato and sweetpotato. Temporarily changing the dark period CO2 from 1000 to 10000 micromoles mol-1 increased conductance for potato, soybean and sweetpotato. In all cases, the stomatal responses were reversible, i.e. conductances returned to original rates following temporary changes in CO2 concentration. Canopy water use for potato was greatest at 10000, intermediate at 400, and least at 1000 micromoles mol-1 CO2, whereas canopy water use for wheat was greatest at 400 and similar at 1000 and 10000 micromoles mol-1 CO2. Elevated CO2 treatments (i.e. 1000 and 10000 micromoles mol-1) resulted in increased plant biomass for both wheat and potato relative to 400 micromoles mol-1, and no injurious effects were apparent from the 10000 micromoles mol-1 treatment. Results indicate that super-elevated CO2 (i.e. 10000 micromoles mol-1) can increase stomatal conductance in some species, particularly during the dark period, resulting in increased water use and decreased water use efficiency.

Internal and external control of net photosynthesis and stomatal conductance of mature eastern white pine (Pinus strobus)

Treesearch

Chris A. Maier; R.O. Teskey

1992-01-01

Leaf gas exchange and water relations were monitored in the upper canopy of two 25 m tall eastern white pine (Pinus strobus L.) trees over two consecutive growing seasons (1986 and 1987). Examination of the seasonal and diurnal patterns of net photosynthesis and leaf conductance showed that both internal and external (environmental) factors were...

Capturing species-level drought responses in a temperate deciduous forest using ratios of photochemical reflectance indices between sunlit and shaded canopies

Treesearch

Taehee Hwang; Hamed Gholizadeh; Daniel A. Sims; Kimberly A. Novick; Edward R. Brzostek; Richard P. Phillips; Daniel T. Roman; Scott M. Robeson; Abdullah F. Rahman

2017-01-01

To classify trees along a spectrum of isohydric to anisohydric behavior is a promising new framework for identifying tree species' sensitivities to drought stress, directly related to the vulnerability of carbon uptake of terrestrial ecosystems with increased hydroclimate variability. Trees with isohydric strategies regulate stomatal conductance to maintain...

Foliar ozone injury on different-sized Prumus serotina Ehrh. trees

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

Fredericksen, T.S.; Skelly, J.M.; Steiner, K.C.

1995-06-01

Black cherry (Prunus serotina Ehrh.) is a common tree species in the eastern U.S. that is highly sensitive to ozone relative to other associated deciduous tree species. Because of difficulties in conducting exposure-response experiments on large trees, air pollution studies have often utilized seedlings and extrapolated the results to predict the potential response of larger forest trees. However, physiological differences between seedlings and mature forest trees may alter responses to air pollutants. A comparative study of seedling, sapling, and canopy black cherry trees was conducted to determine the response of different-sized trees to known ozone exposures and amounts of ozonemore » uptake. Apparent foliar sensitivity to ozone, observed as a dark adaxial leaf stipple, decreased with increasing tree size. An average of 46% of seedling leaf area was symptomatic by early September, compared to 15% - 20% for saplings and canopy trees. In addition to visible symptoms, seedlings also appeared to have greater rates of early leaf abscission than larger trees. Greater sensitivity (i.e., foliar symptoms) per unit exposure with decreasing tree size was closely correlated with rates of stomatal conductance. However, after accounting for differences in stomatal conductance, sensitivity appeared to increase with tree size.« less

How do rubber ( Hevea brasiliensis) plantations behave under seasonal water stress in northeastern Thailand and central Cambodia?

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

Kumagai, Tomo'omi; Mudd, Ryan G.; Giambelluca, Thomas W.

Plantation rubber ( Hevea brasiliensis Müll. Arg.) is a viable economic resource for Southeast Asian countries. Consequently, rubber plantations are rapidly expanding into both climatically optimal and sub-optimal environments throughout mainland Southeast Asia, potentially changing the partitioning of water, energy, and carbon at multiple scales, compared with the traditional land covers they are replacing. Delineating the characteristics of biosphere-atmosphere exchange in rubber plantations is therefore important to understanding the impacts of such land use change on environmental processes. We have conducted eddy flux measurements in two rubber plantation sites: (1) Som Sanuk (SS), located northern Thailand; and (2) Cambodian Rubbermore » Research Institute (CRRI), central Cambodia. Both sites have a distinct dry season. Measurements were made over a 3-year period. We used combination of actual evapotranspiration (E T) flux measurements and an inversed version of a simple 2-layer E T model for estimating the mean canopy stomatal conductances (g s), which is among the most effective measures for describing water and energy exchanges and tree water use characteristics. A main novelty in this analysis is that the rubber canopy conductance can be extracted from total surface conductance (including the canopy and the vegetation floor effects) and hence environmental and biological controls on rubber tree gs are explicitly compared at each site in different seasons and years. It is demonstrated how each studied rubber plantation copes with each strong seasonal drought via tree water use strategies. Potential tree water use deficit (precipitation (P) – potential evaporation (E T_POT)) for each season (i.e., December-February: DJF, March-May: MAM, June-August: JJA, and September-November: SON) revealed in which season and how the water use should be controlled. We found that in seasons when actual tree water use deficit (P – E T) was negative (i.e., DJF and MAM), the deficit was compensated by soil water from the previous season stored within the soil layer at depths of 0-2 m at the Thailand site, and at depths of 0-3 m at CRRI. Two ecophysiological parameters, the reference value of g s (g sref) and the sensitivity of g s to atmospheric demand (m), as well as their proportionality (m/g sref), were derived from the logarithmic response curve of g s to vapor pressure deficit (D) for each season and each site. At both sites, g sref and m appeared to be smaller in DJF and MAM than those in the other seasons (i.e., JJA and SON). On average in a whole year, m/g sref was less than 0.6 at SS and almost 0.6 at the CRRI site, suggesting that there was less sufficient stomatal regulation at SS, where the risk of water stress-induced hydraulic failure is low because of its high annual rainfall amount. In comparison, at CRRI where annual P – E T_POT was negative, there was stricter stomatal regulation that prevents excessive xylem cavitation. These tendencies imply that in the drier season, i.e., DJF and MAM, the rubber trees in SS and CRRI adopt the stomatal control strategy of changing g sref with reluctance and positive to change m, respectively.« less

Eddy covariance fluxes of the NO-O3-NO2 triad above the forest canopy at the ATTO Site in the Amazon Basin

NASA Astrophysics Data System (ADS)

Tsokankunku, Anywhere; Wolff, Stefan; Sörgel, Matthias; Berger, Martina; Zelger, Michael; Dlugi, Ralf

2017-04-01

Nitrogen monoxide (NO) and nitrogen dioxide (NO2) (denoted together as NOx) determine the abundance of the tropospheric oxidants OH, O3 and NO3 that regulate atmospheric self-cleaning. The three reactive trace gases NO, NO2 and O3 undergo a series of interconnected photochemical reactions and are often referred to as the NO-O3-NO2 triad. Ozone deposition is mainly controlled by stomatal uptake, thus contributes to oxidative stress for the plants. Similarly, nitrogen dioxide from above or below the canopy is deposited to leaves through stomatal uptake. NO emissions from soils contribute to above canopy O3 formation and accelerate OH recycling. Therefore, quantification of the exchange fluxes of these species between the atmosphere and the biosphere are important for atmospheric chemistry and ecosystem research as well. The eddy covariance method is state of the art for direct measurements of ecosystem fluxes of trace gases. Eddy covariance measurements of NOx in pristine environments are rare because of lack of availability of instruments with the required precision to resolve concentrations characteristic of these environments. The Amazon Tall Tower Observatory (ATTO) is located in a pristine rainforest environment in the Amazon basin about 150 km northeast of the city of Manaus. It is the ideal site for studying the biosphere-atmosphere exchange of the NO-O3-NO2 triad, being largely undisturbed by anthropogenic sources. During an intensive measurement campaign in November 2015 at the ATTO site, measurements of NO, NO2 and O3 were carried out at 42 m above ground level on the 80 m walk-up tower with a fast (5 Hz) and sensitive (< 30 ppt) instrument (CLD790SR2, Eco Physics) for NO and NO2 and with 10 Hz for O3 (Enviscope). Additionally, measurements of turbulent and micrometeorological parameters were conducted with a profile of 3-dimensional sonic anemometers and meteorological sensors for temperature, humidity and radiation. Vertical concentration profile measurements of NO, NO2 and O3 were available at 8 levels on the INSTANT tower from a reactive trace gas profile system which has been operational at the site since 2012. From these measurements, we present eddy covariance fluxes of the NO-O3-NO2 triad. We relate the fluxes to the canopy-atmosphere exchange of the trace gases and other scalars using the profile data along the tower. Chemical and turbulent transport timescales of the triad constituents are also presented. Coherent structures and canopy-atmosphere coupling is discussed, particularly in relation to the dynamics of O3 and its subsequent influence on the NOx fluxes. As far as we know, these are the first full simultaneous measurements of NO, NO2 and O3 fluxes using the eddy covariance method above an Amazonian rainforest.

Modeling canopy-induced turbulence in the Earth system: a unified parameterization of turbulent exchange within plant canopies and the roughness sublayer (CLM-ml v0)

NASA Astrophysics Data System (ADS)

Bonan, Gordon B.; Patton, Edward G.; Harman, Ian N.; Oleson, Keith W.; Finnigan, John J.; Lu, Yaqiong; Burakowski, Elizabeth A.

2018-04-01

Land surface models used in climate models neglect the roughness sublayer and parameterize within-canopy turbulence in an ad hoc manner. We implemented a roughness sublayer turbulence parameterization in a multilayer canopy model (CLM-ml v0) to test if this theory provides a tractable parameterization extending from the ground through the canopy and the roughness sublayer. We compared the canopy model with the Community Land Model (CLM4.5) at seven forest, two grassland, and three cropland AmeriFlux sites over a range of canopy heights, leaf area indexes, and climates. CLM4.5 has pronounced biases during summer months at forest sites in midday latent heat flux, sensible heat flux, gross primary production, nighttime friction velocity, and the radiative temperature diurnal range. The new canopy model reduces these biases by introducing new physics. Advances in modeling stomatal conductance and canopy physiology beyond what is in CLM4.5 substantially improve model performance at the forest sites. The signature of the roughness sublayer is most evident in nighttime friction velocity and the diurnal cycle of radiative temperature, but is also seen in sensible heat flux. Within-canopy temperature profiles are markedly different compared with profiles obtained using Monin-Obukhov similarity theory, and the roughness sublayer produces cooler daytime and warmer nighttime temperatures. The herbaceous sites also show model improvements, but the improvements are related less systematically to the roughness sublayer parameterization in these canopies. The multilayer canopy with the roughness sublayer turbulence improves simulations compared with CLM4.5 while also advancing the theoretical basis for surface flux parameterizations.

Use of sap flow measurements to validate stomatal functions for mature beech (Fagus sylvatica) in view of ozone uptake calculations.

PubMed

Braun, Sabine; Schindler, Christian; Leuzinger, Sebastian

2010-09-01

For a quantitative estimate of the ozone effect on vegetation reliable models for ozone uptake through the stomata are needed. Because of the analogy of ozone uptake and transpiration it is possible to utilize measurements of water loss such as sap flow for quantification of ozone uptake. This technique was applied in three beech (Fagus sylvatica) stands in Switzerland. A canopy conductance was calculated from sap flow velocity and normalized to values between 0 and 1. It represents mainly stomatal conductance as the boundary layer resistance in forests is usually small. Based on this relative conductance, stomatal functions to describe the dependence on light, temperature, vapour pressure deficit and soil moisture were derived using multivariate nonlinear regression. These functions were validated by comparison with conductance values directly estimated from sap flow. The results corroborate the current flux parameterization for beech used in the DO3SE model. Copyright (c) 2010 Elsevier Ltd. All rights reserved.

Physiological studies in young Eucalyptus stands in southern India and their use in estimating forest transpiration

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

Roberts, J.M.; Rosier, P.T.W.; Murthy, K.V.

1992-12-31

Stomatal conductance, leaf water potential and leaf area index were measured in adjacent plantations of Eucalyptus camaldulensis and Eucalyptus tereticornis at Puradal, near Shimoga, Karnataka, southern India. The data were collected in a range of climatic conditions during a two year period immediately following plantation establishment. Physiological differences between the two species were small and confined largely to leaf area index. Stomatal conductance was highest in the post-monsoon period and declined to minimum values immediately prior to the onset of the monsoon, with the lowest conductances observed after the plantations had been established for more than one year. Stomatal conductance,more » leaf area index and above-canopy meteorological data were combined in a multi-layer transpiration model and used to calculate hourly values of transpiration from the two species. Rates of transpiration up to 6 mm d{sup {minus}1} were estimated for the post-monsoon period but fell to below 1 mm d{sup {minus}1} prior to the monsoon.« less

Incorporating Plant Phenology Dynamics in a Biophysical Canopy Model

NASA Technical Reports Server (NTRS)

Barata, Raquel A.; Drewry, Darren

2012-01-01

The Multi-Layer Canopy Model (MLCan) is a vegetation model created to capture plant responses to environmental change. Themodel vertically resolves carbon uptake, water vapor and energy exchange at each canopy level by coupling photosynthesis, stomatal conductance and leaf energy balance. The model is forced by incoming shortwave and longwave radiation, as well as near-surface meteorological conditions. The original formulation of MLCan utilized canopy structural traits derived from observations. This project aims to incorporate a plant phenology scheme within MLCan allowing these structural traits to vary dynamically. In the plant phenology scheme implemented here, plant growth is dependent on environmental conditions such as air temperature and soil moisture. The scheme includes functionality that models plant germination, growth, and senescence. These growth stages dictate the variation in six different vegetative carbon pools: storage, leaves, stem, coarse roots, fine roots, and reproductive. The magnitudes of these carbon pools determine land surface parameters such as leaf area index, canopy height, rooting depth and root water uptake capacity. Coupling this phenology scheme with MLCan allows for a more flexible representation of the structure and function of vegetation as it responds to changing environmental conditions.

Field testing of thermal canopy models in a spruce-fir forest

NASA Technical Reports Server (NTRS)

1990-01-01

Recent advances in remote sensing technology allow the use of the thermal infrared region to gain information about vegetative surfaces. Extending existing models to account for thermal radiance transfers within rough forest canopies is of paramount importance. This is so since all processes of interest in the physical climate system and biogeochemical cycles are thermally mediated. Model validation experiments were conducted at a well established boreal forest; northern hardwood forest ecotone research site located in central Maine. Data was collected to allow spatial and temporal validation of thermal models. Emphasis was placed primarily upon enhancing submodels of stomatal behavior, and secondarily upon enhancing boundary layer resistance submodels and accounting for thermal storage in soil and vegetation.

Fertilization intensifies drought stress: water use and stomatal conductance of Pinus taeda in a midrotation fertilization and throughfall reduction experiment

Treesearch

Eric J. Ward; Jean-Christophe Domec; Marshall A. Laviner; Thomas R. Fox; Ge Sun; Steve McNulty; John King; Asko Noormets

2015-01-01

While mid-rotation fertilization increases productivity in many southern pine forests, it remains unclear what impact such management may have on stand water use. We examined the impact of nutrient and water availability on stem volume, leaf area, transpiration per unit ground area (EC) and canopy conductance per unit leaf area (GS...

Biochemical acclimation, stomatal limitation and precipitation patterns underlie decreases in photosynthetic stimulation of Soybean (Glycine max) at elevated [CO2] and temperatures under fully open air field conditions

USDA-ARS?s Scientific Manuscript database

The net effect of elevated [CO2] and temperature on photosynthetic acclimation and plant productivity is poorly resolved. We assessed the effects of canopy warming and fully open air [CO2] enrichment on 1) the acclimation of two biochemical parameters that frequently limit photosynthesis (A), the ma...

Prolonged experimental drought reduces plant hydraulic conductance and transpiration and increases mortality in a piñon–juniper woodland

DOE PAGES

Pangle, Robert E.; Limousin, Jean -Marc; Plaut, Jennifer A.; ...

2015-03-23

Plant hydraulic conductance (k s) is a critical control on whole-plant water use and carbon uptake and, during drought, influences whether plants survive or die. To assess long-term physiological and hydraulic responses of mature trees to water availability, we manipulated ecosystem-scale water availability from 2007 to 2013 in a piñon pine ( Pinus edulis) and juniper ( Juniperus monosperma) woodland. We examined the relationship between k s and subsequent mortality using more than 5 years of physiological observations, and the subsequent impact of reduced hydraulic function and mortality on total woody canopy transpiration (E C) and conductance (G C). Formore » both species, we observed significant reductions in plant transpiration (E) and k s under experimentally imposed drought. Conversely, supplemental water additions increased E and k s in both species. Interestingly, both species exhibited similar declines in k s under the imposed drought conditions, despite their differing stomatal responses and mortality patterns during drought. Reduced whole-plant k s also reduced carbon assimilation in both species, as leaf-level stomatal conductance (g s) and net photosynthesis (A n) declined strongly with decreasing k s. Finally, we observed that chronically low whole-plant k s was associated with greater canopy dieback and mortality for both piñon and juniper and that subsequent reductions in woody canopy biomass due to mortality had a significant impact on both daily and annual canopy E C and G C. Our data indicate that significant reductions in k s precede drought-related tree mortality events in this system, and the consequence is a significant reduction in canopy gas exchange and carbon fixation. Our results suggest that reductions in productivity and woody plant cover in piñon–juniper woodlands can be expected due to reduced plant hydraulic conductance and increased mortality of both piñon pine and juniper under anticipated future conditions of more frequent and persistent regional drought in the southwestern United States.« less

Prolonged experimental drought reduces plant hydraulic conductance and transpiration and increases mortality in a piñon–juniper woodland

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

Pangle, Robert E.; Limousin, Jean -Marc; Plaut, Jennifer A.

Plant hydraulic conductance (k s) is a critical control on whole-plant water use and carbon uptake and, during drought, influences whether plants survive or die. To assess long-term physiological and hydraulic responses of mature trees to water availability, we manipulated ecosystem-scale water availability from 2007 to 2013 in a piñon pine ( Pinus edulis) and juniper ( Juniperus monosperma) woodland. We examined the relationship between k s and subsequent mortality using more than 5 years of physiological observations, and the subsequent impact of reduced hydraulic function and mortality on total woody canopy transpiration (E C) and conductance (G C). Formore » both species, we observed significant reductions in plant transpiration (E) and k s under experimentally imposed drought. Conversely, supplemental water additions increased E and k s in both species. Interestingly, both species exhibited similar declines in k s under the imposed drought conditions, despite their differing stomatal responses and mortality patterns during drought. Reduced whole-plant k s also reduced carbon assimilation in both species, as leaf-level stomatal conductance (g s) and net photosynthesis (A n) declined strongly with decreasing k s. Finally, we observed that chronically low whole-plant k s was associated with greater canopy dieback and mortality for both piñon and juniper and that subsequent reductions in woody canopy biomass due to mortality had a significant impact on both daily and annual canopy E C and G C. Our data indicate that significant reductions in k s precede drought-related tree mortality events in this system, and the consequence is a significant reduction in canopy gas exchange and carbon fixation. Our results suggest that reductions in productivity and woody plant cover in piñon–juniper woodlands can be expected due to reduced plant hydraulic conductance and increased mortality of both piñon pine and juniper under anticipated future conditions of more frequent and persistent regional drought in the southwestern United States.« less

Modelling climate change responses in tropical forests: similar productivity estimates across five models, but different mechanisms and responses

NASA Astrophysics Data System (ADS)

Rowland, L.; Harper, A.; Christoffersen, B. O.; Galbraith, D. R.; Imbuzeiro, H. M. A.; Powell, T. L.; Doughty, C.; Levine, N. M.; Malhi, Y.; Saleska, S. R.; Moorcroft, P. R.; Meir, P.; Williams, M.

2014-11-01

Accurately predicting the response of Amazonia to climate change is important for predicting changes across the globe. However, changes in multiple climatic factors simultaneously may result in complex non-linear responses, which are difficult to predict using vegetation models. Using leaf and canopy scale observations, this study evaluated the capability of five vegetation models (CLM3.5, ED2, JULES, SiB3, and SPA) to simulate the responses of canopy and leaf scale productivity to changes in temperature and drought in an Amazonian forest. The models did not agree as to whether gross primary productivity (GPP) was more sensitive to changes in temperature or precipitation. There was greater model-data consistency in the response of net ecosystem exchange to changes in temperature, than in the response to temperature of leaf area index (LAI), net photosynthesis (An) and stomatal conductance (gs). Modelled canopy scale fluxes are calculated by scaling leaf scale fluxes to LAI, and therefore in this study similarities in modelled ecosystem scale responses to drought and temperature were the result of inconsistent leaf scale and LAI responses among models. Across the models, the response of An to temperature was more closely linked to stomatal behaviour than biochemical processes. Consequently all the models predicted that GPP would be higher if tropical forests were 5 °C colder, closer to the model optima for gs. There was however no model consistency in the response of the An-gs relationship when temperature changes and drought were introduced simultaneously. The inconsistencies in the An-gs relationships amongst models were caused by to non-linear model responses induced by simultaneous drought and temperature change. To improve the reliability of simulations of the response of Amazonian rainforest to climate change the mechanistic underpinnings of vegetation models need more complete validation to improve accuracy and consistency in the scaling of processes from leaf to canopy.

Continuous In-situ Measurements of Carbonyl Sulfide (OCS) and Carbon Dioxide Isotopes to Constrain Ecosystem Carbon and Water Exchanges

NASA Astrophysics Data System (ADS)

Rastogi, B.; Still, C. J.; Noone, D. C.; Berkelhammer, M. B.; Whelan, M.; Lai, C. T.; Hollinger, D. Y.; Gupta, M.; Leen, J. B.; Huang, Y. W.

2015-12-01

Understanding the processes that control the terrestrial exchange of carbon and water are critical for examining the role of forested ecosystems in changing climates. A small but increasing number of studies have identified Carbonyl Sulfide (OCS) as a potential tracer for photosynthesis. OCS is hydrolyzed by an irreversible reaction in leaf mesophyll cells that is catalyzed by the enzyme, carbonic anhydrase. Leaf- level field and greenhouse studies indicate that OCS uptake is controlled by stomatal activity and that the ratio of OCS and CO2 uptake is reasonably constant. Existing studies on ecosystem OCS exchange have been based on laboratory measurements or short field campaigns and therefore little information on OCS exchange in a natural ecosystem over longer timescales is available. The objective of this study is to further assess the stability of OCS as a tracer for canopy photosynthesis in an active forested ecosystem and also to assess its utility for constraining transpiration, since both fluxes are mediated by canopy stomatal conductance. An off-axis integrated cavity output spectroscopy analyzer (Los Gatos Research Inc.) was deployed at the Wind River Experimental Forest in Washington (45.8205°N, 121.9519°W). Canopy air was sampled from four heights as well as the soil to measure vertical gradients of OCS within the canopy, and OCS exchange between the forest and the atmosphere for the growing season. Here we take advantage of simultaneous measurements of the stable isotopologues of H2O and CO2 at corresponding heights as well as NEE (Net Ecosystem Exchange) from eddy covariance measurements to compare GPP (Gross Primary Production) and transpiration estimates from a variety of independent techniques. Our findings also seek to allow assessment of the environmental and ecophysicological controls on evapotranspiration rates, which are projected to change in coming decades, and are otherwise poorly constrained.

Gender-specific patterns of aboveground allocation, canopy conductance and water use in a dominant riparian tree species: Acer negundo.

PubMed

Hultine, K R; Bush, S E; West, A G; Burtch, K G; Pataki, D E; Ehleringer, J R

2008-09-01

Acer negundo Sarg. (box elder) is a dioecious tree species that dominates riparian systems at mid elevations throughout the southwest and Intermountain West of the United States. Previous studies have shown that female A. negundo trees occur at higher frequencies along stream margins, whereas males occur at higher frequencies in drier microsites. To better understand the adaptive significance of sex ratio biases and their impact on the ecohydrology of riparian ecosystems, we examined whole-plant water relations and hydraulic properties of mature male and female A. negundo trees occurring within 1 m of a perennial stream channel. We hypothesized that (1) females would have significantly greater canopy water fluxes than males (particularly during periods of seed production: May-June), and (2) xylem in females is more hydraulically efficient but more vulnerable to cavitation than xylem in males. Mean sap flux density (J(s)) during the early growing season (May and June) was 43% higher in female trees than in male trees (n = 6 and 7 trees respectively, P < 0.0001). Mean J(s) in July and August remained 17% higher in females than in males (P = 0.0009). Mean canopy stomatal conductance per unit leaf area (g(s,leaf)) in May and June was on average 140% higher in females than in males (P < 0.0001). Mean g(s,leaf) in July and August remained 69% higher in female trees than in male trees (P < 0.0001). Canopy stomatal conductance scaled to basal area was 90 and 31% higher in females relative to males during May-June and July-August, respectively (P < 0.0001 during both periods). Conversely, there were no apparent differences in either branch hydraulic conductance or branch xylem cavitation vulnerability between genders. These results improve our capacity to describe the adaptive forces that shape the spatial distribution of male and female trees in dioecious species, and their consequences for ecohydrological processes in riparian ecosystems.

Development and evaluation of an ozone deposition scheme for coupling to a terrestrial biosphere model

NASA Astrophysics Data System (ADS)

Franz, Martina; Simpson, David; Arneth, Almut; Zaehle, Sönke

2017-01-01

Ozone (O3) is a toxic air pollutant that can damage plant leaves and substantially affect the plant's gross primary production (GPP) and health. Realistic estimates of the effects of tropospheric anthropogenic O3 on GPP are thus potentially important to assess the strength of the terrestrial biosphere as a carbon sink. To better understand the impact of ozone damage on the terrestrial carbon cycle, we developed a module to estimate O3 uptake and damage of plants for a state-of-the-art global terrestrial biosphere model called OCN. Our approach accounts for ozone damage by calculating (a) O3 transport from 45 m height to leaf level, (b) O3 flux into the leaf, and (c) ozone damage of photosynthesis as a function of the accumulated O3 uptake over the lifetime of a leaf. A comparison of modelled canopy conductance, GPP, and latent heat to FLUXNET data across European forest and grassland sites shows a general good performance of OCN including ozone damage. This comparison provides a good baseline on top of which ozone damage can be evaluated. In comparison to literature values, we demonstrate that the new model version produces realistic O3 surface resistances, O3 deposition velocities, and stomatal to total O3 flux ratios. A sensitivity study reveals that key metrics of the air-to-leaf O3 transport and O3 deposition, in particular the stomatal O3 uptake, are reasonably robust against uncertainty in the underlying parameterisation of the deposition scheme. Nevertheless, correctly estimating canopy conductance plays a pivotal role in the estimate of cumulative O3 uptake. We further find that accounting for stomatal and non-stomatal uptake processes substantially affects simulated plant O3 uptake and accumulation, because aerodynamic resistance and non-stomatal O3 destruction reduce the predicted leaf-level O3 concentrations. Ozone impacts on GPP and transpiration in a Europe-wide simulation indicate that tropospheric O3 impacts the regional carbon and water cycling less than expected from previous studies. This study presents a first step towards the integration of atmospheric chemistry and ecosystem dynamics modelling, which would allow for assessing the wider feedbacks between vegetation ozone uptake and tropospheric ozone burden.

Comparative measurements of transpiration and canopy conductance in two mixed deciduous woodlands differing in structure and species composition.

PubMed

Herbst, Mathias; Rosier, Paul T W; Morecroft, Michael D; Gowing, David J

2008-06-01

Transpiration of two heterogeneous broad-leaved woodlands in southern England was monitored by the sap flux technique throughout the 2006 growing season. Grimsbury Wood, which had a leaf area index (LAI) of 3.9, was dominated by oak (Quercus robur L.) and birch (Betula pubescens L.) and had a continuous hazel (Corylus avellana L.) understory. Wytham Woods, which had an LAI of 3.6, was dominated by ash (Fraxinus excelsior L.) and sycamore (Acer pseudoplatanus L.) and had only a sparse understory. Annual canopy transpiration was 367 mm for Grimsbury Wood and 397 mm for Wytham Woods. These values were similar to those for beech (Fagus sylvatica L.) plantations in the same region, and differ from one another by less than the typical margin of uncertainty of the sap flux technique. Canopy conductance (g(c)), calculated for both woodlands by inverting the Penman-Monteith equation, was related to incoming solar radiation (R(G)) and the vapor pressure deficit (D). The response of g(c) to R(G) was similar for both forests. Both reference conductance (g(cref)), defined as g(c) at D=1 kPa, and stomatal sensitivity (-m), defined as the slope of the logarithmic response curve of g(c) to D, increased during the growing season at Wytham Woods but not at Grimsbury Wood. The -m/g(cref) ratio was significantly lower at Wytham Woods than at Grimsbury Wood and was insufficient to keep the difference between leaf and soil water potentials constant, according to a simple hydraulic model. This meant that annual water consumption of the two woodlands was similar despite different regulatory mechanisms and associated short-term variations in canopy transpiration. The -m/g(cref) ratio depended on the range of D under which the measurements were made. This was shown to be particularly important for studies conducted under low and narrow ranges of D.

Water transport dynamics in trees and stands

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

Pallardy, S.G.; Cermak, J.; Ewers, F.W.

1995-07-01

Water transport dynamics in trees and stands of conifers have certain features that are characteristic of this group and are at least rare among angiosperms. Among these features is the xylem transport system that is dependent on tracheids for long-distance water transport. Tracheid-containing xylem is relatively inefficient, a property that can reduce submaximum allowable rates of gas exchange, but tracheids also offer substantial capacity for water storage and high resistance to freezing-induced dysfunction. Thus, they are quite compatible with the typical evergreen habit and long transpiration season of conifers. At the stand level, canopy transpiration in conifers is primarily controlledmore » by stomatal conductance. In contrast, in dense canopies of angio-sperms, particularly those of tropical forests with limited air mixing, stand transpiration is limited by radiation input rather than by stomatal control. Because of their evergreen habit a greater proportion of evapotranspiration in conifer forests is associated with evaporation of water intercepted by the tree crowns. Other features of transport dynamics are characteristic of most conifers, but are not unique to this group. Among these features are typically shallow root systems that often must supply water in winter to replace transpiration needs of evergreen species, common occurrence of mycorrhizae that enhance mineral and water uptake, and drought tolerance adaptations that include elements of both dehydration avoidance (e.g., stomatal closure under water stress, shifts in allocation of dry matter to below-ground sinks) and dehydration tolerance (e.g., capacity for acclimation of photosynthetic apparatus to drought, osmotic adjustment). Transpiration rates from conifer foliage often are lower than those of deciduous angiosperms, probably because of the lower maximum capacity of tracheid-bearing xylem to transport water.« less

Coupled carbon-water exchange of the Amazon rain forest, II. Comparison of predicted and observed seasonal exchange of energy, CO2, isoprene and ozone at a remote site in Rondônia

NASA Astrophysics Data System (ADS)

Simon, E.; Meixner, F. X.; Rummel, U.; Ganzeveld, L.; Ammann, C.; Kesselmeier, J.

2005-10-01

A one-dimensional multi-layer scheme describing the coupled exchange of energy and CO2, the emission of isoprene and the dry deposition of ozone is applied to a rain forest canopy in southwest Amazonia. The model was constrained using mean diel cycles of micrometeorological quantities observed during two periods in the wet and dry season 1999. Calculated net fluxes and concentration profiles for both seasonal periods are compared to observations made at two nearby towers.

The modeled day- and nighttime thermal stratification of the canopy layer is consistent with observations in dense canopies. The observed and modeled net fluxes above and H2O and CO2 concentration profiles within the canopy show a good agreement. The predicted net carbon sink decreases from 2.5 t C ha-1 yr-1 for wet season conditions to 1 t C ha-1 yr-1 for dry season conditions, whereas observed and modeled midday Bowen ratio increases from 0.5 to 0.8. The evaluation results confirmed a seasonal variability of leaf physiological parameters, as already suggested in a companion study. The calculated midday canopy net flux of isoprene increased from 7.1 mg C m-2 h-1 during the wet season to 11.4 mg C m-2 h-1 during the late dry season. Applying a constant emission capacity in all canopy layers, resulted in a disagreement between observed and simulated profiles of isoprene concentrations, suggesting a smaller emission capacity of shade adapted leaves and deposition to the soil or leaf surfaces. Assuming a strong light acclimation of emission capacity, equivalent to a 66% reduction of the standard emission factor for leaves in the lower canopy, resulted in a better agreement of observed and modeled concentration profiles and a 30% reduction of the canopy net flux compared to model calculations with a constant emission factor. The mean calculated ozone flux for dry season conditions at noontime was ≍12 n mol m-2 s-1, agreeing well with observed values. The corresponding deposition velocity increased from 0.8 cm s-1 to >1.6 cm s-1 in the wet season, which can not be explained by increased stomatal uptake. Considering reasonable physiological changes in stomatal regulation, the modeled value was not larger than 1.05 cm s-1. Instead, the observed fluxes could be explained with the model by decreasing the cuticular resistance to ozone deposition from 5000 to 1000 s m-1.

Advanced image processing approach for ET estimation with remote sensing data of varying spectral, spatial and temporal resolutions

Treesearch

Sudhanshu Panda; Devendra Amatya; Young Kim; Ge Sun

2016-01-01

Evapotranspiration (ET) is one of the most important hydrologic parameters for vegetation growth, carbon sequestration, and other associated biodiversity study and analysis. Plant stomatal conductance, leaf area index, canopy temperature, soil moisture, and wind speed values generally correlate well with ET. It is difficult to estimate these hydrologic parameters of...

What is the most prominent factor limiting photosynthesis in different layers of a greenhouse cucumber canopy?

PubMed Central

Chen, Tsu-Wei; Henke, Michael; de Visser, Pieter H. B.; Buck-Sorlin, Gerhard; Wiechers, Dirk; Kahlen, Katrin; Stützel, Hartmut

2014-01-01

Background and Aims Maximizing photosynthesis at the canopy level is important for enhancing crop yield, and this requires insights into the limiting factors of photosynthesis. Using greenhouse cucumber (Cucumis sativus) as an example, this study provides a novel approach to quantify different components of photosynthetic limitations at the leaf level and to upscale these limitations to different canopy layers and the whole plant. Methods A static virtual three-dimensional canopy structure was constructed using digitized plant data in GroIMP. Light interception of the leaves was simulated by a ray-tracer and used to compute leaf photosynthesis. Different components of photosynthetic limitations, namely stomatal (SL), mesophyll (ML), biochemical (BL) and light (LL) limitations, were calculated by a quantitative limitation analysis of photosynthesis under different light regimes. Key Results In the virtual cucumber canopy, BL and LL were the most prominent factors limiting whole-plant photosynthesis. Diffusional limitations (SL + ML) contributed <15 % to total limitation. Photosynthesis in the lower canopy was more limited by the biochemical capacity, and the upper canopy was more sensitive to light than other canopy parts. Although leaves in the upper canopy received more light, their photosynthesis was more light restricted than in the leaves of the lower canopy, especially when the light condition above the canopy was poor. An increase in whole-plant photosynthesis under diffuse light did not result from an improvement of light use efficiency but from an increase in light interception. Diffuse light increased the photosynthesis of leaves that were directly shaded by other leaves in the canopy by up to 55 %. Conclusions Based on the results, maintaining biochemical capacity of the middle–lower canopy and increasing the leaf area of the upper canopy would be promising strategies to improve canopy photosynthesis in a high-wire cucumber cropping system. Further analyses using the approach described in this study can be expected to provide insights into the influences of horticultural practices on canopy photosynthesis and the design of optimal crop canopies. PMID:24907313

What is the most prominent factor limiting photosynthesis in different layers of a greenhouse cucumber canopy?

PubMed

Chen, Tsu-Wei; Henke, Michael; de Visser, Pieter H B; Buck-Sorlin, Gerhard; Wiechers, Dirk; Kahlen, Katrin; Stützel, Hartmut

2014-09-01

Maximizing photosynthesis at the canopy level is important for enhancing crop yield, and this requires insights into the limiting factors of photosynthesis. Using greenhouse cucumber (Cucumis sativus) as an example, this study provides a novel approach to quantify different components of photosynthetic limitations at the leaf level and to upscale these limitations to different canopy layers and the whole plant. A static virtual three-dimensional canopy structure was constructed using digitized plant data in GroIMP. Light interception of the leaves was simulated by a ray-tracer and used to compute leaf photosynthesis. Different components of photosynthetic limitations, namely stomatal (S(L)), mesophyll (M(L)), biochemical (B(L)) and light (L(L)) limitations, were calculated by a quantitative limitation analysis of photosynthesis under different light regimes. In the virtual cucumber canopy, B(L) and L(L) were the most prominent factors limiting whole-plant photosynthesis. Diffusional limitations (S(L) + M(L)) contributed <15% to total limitation. Photosynthesis in the lower canopy was more limited by the biochemical capacity, and the upper canopy was more sensitive to light than other canopy parts. Although leaves in the upper canopy received more light, their photosynthesis was more light restricted than in the leaves of the lower canopy, especially when the light condition above the canopy was poor. An increase in whole-plant photosynthesis under diffuse light did not result from an improvement of light use efficiency but from an increase in light interception. Diffuse light increased the photosynthesis of leaves that were directly shaded by other leaves in the canopy by up to 55%. Based on the results, maintaining biochemical capacity of the middle-lower canopy and increasing the leaf area of the upper canopy would be promising strategies to improve canopy photosynthesis in a high-wire cucumber cropping system. Further analyses using the approach described in this study can be expected to provide insights into the influences of horticultural practices on canopy photosynthesis and the design of optimal crop canopies.

Quantifying energy and mass transfer in crop canopies: sensors for measurement of temperature and air velocity

NASA Technical Reports Server (NTRS)

Bugbee, B.; Monje, O.; Tanner, B.

1996-01-01

Here we report on the in situ performance of inexpensive, miniature sensors that have increased our ability to measure mass and energy fluxes from plant canopies in controlled environments: 1. Surface temperature. Canopy temperature measurements indicate changes in stomatal aperture and thus latent and sensible heat fluxes. Infrared transducers from two manufacturers (Exergen Corporation, Newton, MA; and Everest Interscience, Tucson, AZ, USA) have recently become available. Transducer accuracy matched that of a more expensive hand-held infrared thermometer. 2. Air velocity varies above and within plant canopies and is an important component in mass and energy transfer models. We tested commercially-available needle, heat-transfer anemometers (1 x 50 mm cylinder) that consist of a fine-wire thermocouple and a heater inside a hypodermic needle. The needle is heated and wind speed determined from the temperature rise above ambient. These sensors are particularly useful in measuring the low wind speeds found within plant canopies. 3. Accurate measurements of air temperature adjacent to plant leaves facilitates transport phenomena modeling. We quantified the effect of radiation and air velocity on temperature rise in thermocouples from 10 to 500 micrometers. At high radiation loads and low wind speeds, temperature errors were as large as 7 degrees C above air temperature.

The economics of leaf-gas exchange in a fluctuating environment and their upscaling to the canopy-level using turbulent transport theories

NASA Astrophysics Data System (ADS)

Katul, G. G.; Palmroth, S.; Manzoni, S.; Oren, R.

2012-12-01

Global climate models predict decreases in leaf stomatal conductance (gs) and transpiration due to increases in atmospheric CO2. The consequences of these reductions are increases in soil moisture availability and continental scale run-off at decadal time-scales. Thus, a theory explaining the differential sensitivity of stomata to changing atmospheric CO2 and other environmental conditions such as soil moisture at the ecosystem scale must be identified. Here, these responses are investigated using an optimality theory applied to stomatal conductance. An analytical model for gs is first proposed based on (a) Fickian mass transfer of CO2 and H2O through stomata; (b) a biochemical photosynthesis model that relates intercellular CO2 to net photosynthesis; and (c) a stomatal model based on optimization for maximizing carbon gains when water losses represent a cost. The optimization theory produced three gas exchange responses that are consistent with observations across a wide-range of species: (1) the sensitivity of gs to vapour pressure deficit (D) is similar to that obtained from a previous synthesis of more than 40 species, (2) the theory is consistent with the onset of an apparent 'feed-forward' mechanism in gs, and (3) the emergent non-linear relationship between the ratio of intercellular to atmospheric CO2 (ci/ca) and D agrees with the results available on this response. A simplified version of this leaf-scale approach recovers the linear relationship between stomatal conductance and leaf-photosynthesis employed in numerous climate models that currently use a variant on the 'Ball-Berry' or the 'Leuning' approaches provided the marginal water use efficiency increases linearly with atmospheric CO2. The model is then up-scaled to the canopy-level using novel theories about the structure of turbulence inside vegetation. This up-scaling proved to be effective in resolving the complex (and two-way) interactions between leaves and their immediate micro-climate. Extensions of this optimality approach to drought and salt-stressed cases are briefly presented.

Non-linear interactions between CO_2 radiative and physiological effects on Amazonian evapotranspiration in an Earth system model

NASA Astrophysics Data System (ADS)

Halladay, Kate; Good, Peter

2017-10-01

We present a detailed analysis of mechanisms underlying the evapotranspiration response to increased CO_2 in HadGEM2-ES, focussed on western Amazonia. We use three simulations from CMIP5 in which atmospheric CO_2 increases at 1% per year reaching approximately four times pre-industrial levels after 140 years. Using 3-hourly data, we found that evapotranspiration (ET) change was dominated by decreased stomatal conductance (g_s), and to a lesser extent by decreased canopy water and increased moisture gradient (specific humidity difference between surface and near-surface). There were large, non-linear decreases in ET in the simulation in which radiative and physiological forcings could interact. This non-linearity arises from non-linearity in the conductance term (includes aerodynamic and stomatal resistance and partitioning between the two, which is determined by canopy water availability), the moisture gradient, and negative correlation between these two terms. The conductance term is non-linear because GPP responds non-linearly to temperature and GPP is the dominant control on g_s in HadGEM2-ES. In addition, canopy water declines, mainly due to increases in potential evaporation, which further decrease the conductance term. The moisture gradient responds non-linearly owing to the non-linear response of temperature to CO_2 increases, which increases the Bowen ratio. Moisture gradient increases resulting from ET decline increase ET and thus constitute a negative feedback. This analysis highlights the importance of the g_s parametrisation in determining the ET response and the potential differences between offline and online simulations owing to feedbacks on ET via the atmosphere, some of which would not occur in an offline simulation.

Biological and environmental controls on tree transpiration in a suburban landscape

NASA Astrophysics Data System (ADS)

Peters, Emily B.; McFadden, Joseph P.; Montgomery, Rebecca A.

2010-12-01

Tree transpiration provides a variety of ecosystem services in urban areas, including amelioration of urban heat island effects and storm water management. Tree species vary in the magnitude and seasonality of transpiration owing to differences in physiology, response to climate, and biophysical characteristics, thereby complicating efforts to manage evapotranspiration at city scales. We report sap flux measurements during the 2007 and 2008 growing seasons for dominant tree species in a suburban neighborhood of Minneapolis-Saint Paul, Minnesota, USA. Evergreen needleleaf trees had significantly higher growing season means and annual transpiration per unit canopy area (1.90 kg H2O m-2 d-1 and 307 kg H2O m-2 yr-1, respectively) than deciduous broadleaf trees (1.11 kg H2O m-2 d-1 and 153 kg H2O m-2 yr-1, respectively) because of a smaller projected canopy area (31.1 and 73.6 m2, respectively), a higher leaf area index (8.8 and 5.5 m2 m-2, respectively), and a longer growth season (8 and 4 months, respectively). Measurements also showed patterns consistent with the species' differences in xylem anatomy (conifer, ring porous, and diffuse porous). As the growing season progressed, conifer and diffuse porous genera had increased stomatal regulation to high vapor pressure deficit, while ring porous genera maintained greater and more constant stomatal regulation. These results suggest that evaporative responses to climate change in urban ecosystems will depend in part on species composition. Overall, plant functional type differences in canopy structure and growing season length were most important in explaining species' differences in midsummer and annual transpiration, offering an approach to predicting the evapotranspiration component of urban water budgets.

Contrasting physiological responses to excess heat and irradiance in two tropical savanna sedges

PubMed Central

John-Bejai, C.; Farrell, A. D.; Cooper, F. M.; Oatham, M. P.

2013-01-01

Tropical hyperseasonal savannas provide a rare example of a tropical climax community dominated by graminoid species. Species living in such savannas are frequently exposed to excess heat and light, in addition to drought and waterlogging, and must possess traits to avoid or tolerate these stress factors. Here we examine the contrasting heat and light stress adaptations of two dominant savanna sedges: Lagenocarpus guianensis, which is restricted to the sheltered forest edge, and Lagenocarpus rigidus, which extends from the forest edge to the open savanna. An ecotone extending from the forest edge to the open savanna was used to assess differences in a range of physiological traits (efficiency of photosystem II, cell membrane thermostability, stomatal conductance, leaf surface reflectance and canopy temperature depression) and a range of leaf functional traits (length : width ratio, specific leaf area and degree of folding). Lagenocarpus guianensis showed significantly less canopy temperature depression than L. rigidus, which may explain why this species was restricted to the forest edge. The range of leaf temperatures measured was within the thermal tolerance of L. guianensis and allowed photosystem II to function normally, at least within the cool forest edge. The ability of L. rigidus to extend into the open savanna was associated with an ability to decouple leaf temperature from ambient temperature combined with enhanced cell membrane thermostability. The high degree of canopy temperature depression seen in L. rigidus was not explained by enhanced stomatal conductance or leaf reflectance, but was consistent with a capacity to increase specific leaf area and reduce leaf length: width ratio in the open savanna. Plasticity in leaf functional traits and in cell membrane thermostability are key factors in the ability of this savanna sedge to survive abiotic stress. PMID:24379971

Light acclimation optimizes leaf functional traits despite height-related constraints in a canopy shading experiment.

PubMed

Coble, Adam P; Cavaleri, Molly A

2015-04-01

Within-canopy gradients of leaf functional traits have been linked to both light availability and vertical gradients in leaf water potential. While observational studies can reveal patterns in leaf traits, within-canopy experimental manipulations can provide mechanistic insight to tease apart multiple interacting drivers. Our objectives were to disentangle effects of height and light environment on leaf functional traits by experimentally shading branches along vertical gradients within a sugar maple (Acer saccharum) forest. Shading reduced leaf mass per area (LMA), leaf density, area-based leaf nitrogen (N(area)), and carbon:nitrogen (C:N) ratio, and increased mass-based leaf nitrogen (N(mass)), highlighting the importance of light availability on leaf morphology and chemistry. Early in the growing season, midday leaf water potential (Ψ(mid)), LMA, and N(area) were driven primarily by height; later in the growing season, light became the most important driver for LMA and Narea. Carbon isotope composition (δ(13)C) displayed strong, linear correlations with height throughout the growing season, but did not change with shading, implying that height is more influential than light on water use efficiency and stomatal behavior. LMA, leaf density, N(mass), C:N ratio, and δ(13)C all changed seasonally, suggesting that leaf ageing effects on leaf functional traits are equally as important as microclimatic conditions. Overall, our results indicate that: (1) stomatal sensitivity to vapor pressure deficit or Ψ(mid) constrains the supply of CO2 to leaves at higher heights, independent of light environment, and (2) LMA and N(area) distributions become functionally optimized through morphological acclimation to light with increasing leaf age despite height-related constraints.

Short- and Long-Term Feedbacks on Vegetation Water Use: Unifying Evidence from Observations and Modeling

NASA Astrophysics Data System (ADS)

Mackay, D. S.

2001-05-01

Recent efforts to measure and model the interacting influences of climate, soil, and vegetation on soil water and nutrient dynamics have identified numerous important feedbacks that produce nonlinear responses. In particular, plant physiological factors that control rates of transpiration respond to soil water deficits and vapor pressure deficits (VPD) in the short-term, and to climate, nutrient cycling and disturbance in the long-term. The starting point of this presentation is the observation that in many systems, in particular forest ecosystems, conservative water use emerges as a result of short-term closure of stomata in response to high evaporative demand, and long-term vegetative canopy development under nutrient limiting conditions. Evidence for important short-term controls is presented from sap flux measurements of stand transpiration, remote sensing, and modeling of transpiration through a combination of physically-based modeling and Monte Carlo analysis. A common result is a strong association between stomatal conductance (gs) and the negative evaporative gain (∂ gs/∂ VPD) associated with the sensitivity of stomatal closure to rates of water loss. The importance of this association from the standpoint of modeling transpiration depends on the degree of canopy-atmosphere coupling. This suggests possible simplifications to future canopy component models for use in watershed and larger-scale hydrologic models for short-term processes. However, further results are presented from theoretical modeling, which suggest that feedbacks between hydrology and vegetation in current long-term (inter-annual to century) models may be too simple, as they do not capture the spatially variable nature of slow nutrient cycling in response to soil water dynamics and site history. Memory effects in the soil nutrient pools can leave lasting effects on more rapid processes associated with soil, vegetation, atmosphere coupling.

Water use efficiency and functional traits of a semiarid shrubland

NASA Astrophysics Data System (ADS)

Perez-Priego, Oscar; Lopez-Ballesteros, Ana; Sánchez-Cañete, Enrique P.; Serrano-Ortiz, Penélope; Carrara, Arnaud; Palomares-Palacio, Agustí; Oyonarte, Cecilio; Domingo, Francisco; Kowalski, Andrew S.

2013-04-01

In semiarid climates, water is the fundamental factor determining ecosystem productivity and thereby the capacity for carbon sequestration. Increased water use efficiency (WUE), the ratio of carbon dioxide assimilation (canopy photosynthesis, Pc) to water transpired (canopy evaporation, Ec), is assumed to be an adaptive strategy for sclerophyll shrublands to improve productivity and stress resistance in water-limited environments. However, the real complexity of WUE lies in its dependence on both plant physiological traits (e.g. stomatal resistance, photosynthetic capacity, leaf chemical composition, structure) and on environmental conditions (e.g. atmospheric CO2 concentration, vapour pressure deficit, temperature, light, soil water availability). We used a transient-state closed canopy-chamber to characterise CO2 and water vapour exchanges at the whole plant scale under different environmental conditions and phenological stages. Diurnal and seasonal variations in Pc, Ec and WUE were explained by both physiological and environmental variables. All species showed symmetric patterns in both Pc and Ec when not water limited, but asymmetry during summer drought when leaf water potential was low. During drought, grasses (Festuca sp.) showed a marked decline in functioning (Pc and Ec), whereas shrubs (Genista sp., Hormathophylla sp.) maintained spring-like assimilation rates all morning until stomatal controls shut down gas exchanges. While grasses showed the highest WUE when not water limited, their near senescence during summer drought yielded the lowest WUE. Shrubs showed reduced WUE under moderate drought stress, in contradiction to the assumptions made in global ecosystem models. The importance of the appropriate time-scale for calculating WUE (daily versus hourly), together with water use strategies and ecological functions of individual species, will be further discussed.

Biotic, abiotic and management controls on methanol fluxes above a temperate mountain grassland

NASA Astrophysics Data System (ADS)

Hörtnagl, Lukas; Bamberger, Ines; Graus, Martin; Ruuskanen, Taina; Schnitzhofer, Ralf; Müller, Markus; Hansel, Armin; Wohlfahrt, Georg

2010-05-01

It was previously hypothesised that (i) stomatal conductance and plant growth play a key role in the emission of methanol (Hüve et al. 2007, Niinemets et al. 2004), (ii) methanol fluxes increase with air temperature (Niinemets and Reichstein 2003), and (iii) during cutting (leaf wounding) events and during drying high amounts of methanol are emitted into the atmosphere (Davison et al. 2008). Methanol fluxes were measured above a managed, temperate mountain grassland in Stubai Valley (Tyrol, Austria) during two growing seasons (2008 and 2009). Half-hourly flux values were calculated by means of the disjunct eddy covariance method using 3-dimensional wind-data of a sonic anemometer and mixing ratios of methanol measured with a proton-transfer-reaction-mass-spectrometer (PTR-MS). The surface conductance to water vapour was derived from measured evapotranspiration by inverting the Penman-Monteith combination equation (Wohlfahrt et al., 2009) for dry canopy conditions and used as a proxy for canopyscale stomatal conductance. Methanol fluxes exhibited a clear diurnal cycle with closetozero fluxes during nighttime and emissions, up to 10 nmol m-2 s-1, which followed the diurnal course of radiation and air temperature during daytime. Higher emissions of up to 30 nmol m-2 s-1were observed during cut events and spreading of organic manure. Methanol fluxes showed positive correlations with air temperature, stomatal conductance, and photosynthetically active radiation (PAR), confirming previous studies (e.g. Niinemets and Reichstein 2003). All three previously mentioned factors combined together were able to explain 40% of the observed flux variability. The influence of rapid changes in stomatal conductance on methanol fluxes, pointed out in earlier studies at the leaf-level (e.g. Niinemets and Reichstein 2003), could not be confirmed on ecosystem scale, possibly due to within-canopy gradients in stomatal conductance and the fact that fluxes were determined as half-hourly averages. As methanol is produced in expanding cell walls, the change in the measured green area index (?GAI) was used as a proxy for plant growth. However ?GAI was poorly correlated with methanol fluxes, possible explanations will be discussed. References: Davison, B., Brunner, A., Amman, C., Spirig, C., Jocher, M., Neftel, A. Cut-induced VOC emissions from agricultural grasslands. Plant Biol. 10, 76-85, 2008. Harley, P., Greenberg, J., Niinemets, Ü., and Guenther, A..: Environmental controls over methanol emission from leaves. Biogeosciences, 4, 1083-1099, 2007. Hüve, K., Christ, M., Kleist, E., Uerlings, R., Niinemets, Ü., Walter, A. and Wildt, J.: Simultaneous growth and emission measurements demonstrate an interactive control of methanol release by leaf expansion and stomata. doi:10.1093/jxb/erm038, Journal of Experimental Botany, 2007. Niinemets, Ü. and Reichstein, M.: Controls on the emission of plant volatiles through stomata: A sensitivity analysis. J. Geophys. Res., 108, 4211, doi:10.1029/2002JD002626, 2003. Niinemets, Ü., Loreto, F. and Reichstein, M.: Physiological and physicochemical controls on foliar volatile organic compound emissions. Trends in Plant Science,9, 2004. Wohlfahrt G., Haslwanter A., Hörtnagl L., Jasoni R.L., Fenstermaker L.F., Arnone J.A. III, Hammerle A. (2009) On the consequences of the energy imbalance for calculating surface conductance to water vapour. Agricultural and Forest Meteorology 149, 15561559.

Growth of soybean at future tropospheric ozone concentrations decreases canopy evapotranspiration and soil water depletion.

PubMed

Bernacchi, Carl J; Leakey, Andrew D B; Kimball, Bruce A; Ort, Donald R

2011-06-01

Tropospheric ozone is increasing in many agricultural regions resulting in decreased stomatal conductance and overall biomass of sensitive crop species. These physiological effects of ozone forecast changes in evapotranspiration and thus in the terrestrial hydrological cycle, particularly in intercontinental interiors. Soybean plots were fumigated with ozone to achieve concentrations above ambient levels over five growing seasons in open-air field conditions. Mean season increases in ozone concentrations ([O₃]) varied between growing seasons from 22 to 37% above background concentrations. The objective of this experiment was to examine the effects of future [O₃] on crop ecosystem energy fluxes and water use. Elevated [O₃] caused decreases in canopy evapotranspiration resulting in decreased water use by as much as 15% in high ozone years and decreased soil water removal. In addition, ozone treatment resulted in increased sensible heat flux in all years indicative of day-time increase in canopy temperature of up to 0.7 °C. Published by Elsevier Ltd.

Long-term and direct measurements of CO[sub 2] and water vapor exchange over a deciduous forest canopy

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

Greco, S.; Baldocchi, D.D.

1994-06-01

Long-term monitoring of CO[sub 2] and water vapor exchange is needed to determine components of the carbon and hydrologic cycles and to provide data for parameterizing and testing assessment models. Responding to this need we initiated a continous field measurement campaign in April 1993 in a deciduous forest growing near Oak Ridge, TN. The micrometerological eddy correlation method was used to measure flux densities of CO[sub 2] and water vapor over the canopy. Periodic measurements were made of stomatal resistence and pre-dawn water potential to characterize the photosynthetic capacity of the canopy. Three factors accounted for a disproportionate amount ofmore » seasonal variance in CO[sub 2] flux densities: photon flux densities, leaf area and the occurrence of drought. Positive and increasing magnitudes of carbon gain were observed between April and June as leaves expanded, the canopy closed and daily insolation increased. At midsummer a drought and heat spell were experienced. This period caused CO[sub 2] flux densities to decline. By late summer adequate precipitation and replenishment of soil water resurrected carbon uptake rates until autumnal leaf senescence and leaf fall.« less

Forest Restoration in a Fog Oasis: Evidence Indicates Need for Cultural Awareness in Constructing the Reference

PubMed Central

Balaguer, Luís; Arroyo-García, Rosa; Jiménez, Percy; Jiménez, María Dolores; Villegas, Luís; Cordero, Irene; Rubio de Casas, Rafael; Fernández-Delgado, Raúl; Ron, María Eugenia; Manrique, Esteban; Vargas, Pablo; Cano, Emilio; Pueyo, José J.; Aronson, James

2011-01-01

Background In the Peruvian Coastal Desert, an archipelago of fog oases, locally called lomas, are centers of biodiversity and of past human activity. Fog interception by a tree canopy, dominated by the legume tree tara (Caesalpinia spinosa), enables the occurrence in the Atiquipa lomas (southern Peru) of an environmental island with a diverse flora and high productivity. Although this forest provides essential services to the local population, it has suffered 90% anthropogenic reduction in area. Restoration efforts are now getting under way, including discussion as to the most appropriate reference ecosystem to use. Methodology/Principal Findings Genetic diversity of tara was studied in the Atiquipa population and over a wide geographical and ecological range. Neither exclusive plastid haplotypes to loma formations nor clear geographical structuring of the genetic diversity was found. Photosynthetic performance and growth of seedlings naturally recruited in remnant patches of loma forest were compared with those of seedlings recruited or planted in the adjacent deforested area. Despite the greater water and nitrogen availability under tree canopy, growth of forest seedlings did not differ from that of those recruited into the deforested area, and was lower than that of planted seedlings. Tara seedlings exhibited tight stomatal control of photosynthesis, and a structural photoprotection by leaflet closure. These drought-avoiding mechanisms did not optimize seedling performance under the conditions produced by forest interception of fog moisture. Conclusions/Significance Both weak geographic partitioning of genetic variation and lack of physiological specialization of seedlings to the forest water regime strongly suggest that tara was introduced to lomas by humans. Therefore, the most diverse fragment of lomas is the result of landscape management and resource use by pre-Columbian cultures. We argue that an appropriate reference ecosystem for ecological restoration of lomas should include sustainable agroforestry practices that emulate the outcomes of ancient uses. PMID:21829680

Response of leaf and whole-tree canopy conductance to wet conditions within a mature premontane tropical forest in Costa Rica

NASA Astrophysics Data System (ADS)

Aparecido, L. M. T.; Miller, G. R.; Cahill, A. T.; Andrews, R.; Moore, G. W.

2017-12-01

Tropical water recycling and carbon storage are dependent on canopy-atmosphere dynamics, which are substantially altered when rainfall occurs. However, models only indirectly consider leaf wetness as a driving factor for carbon and water fluxes. To better understand how leaf wetness condition affects stomatal and canopy conductance to water vapor, we tested a set of widely used models for a mature tropical forest of Costa Rica with prolonged periods of wet leaves. We relied on a year of sap flux measurements from 26 trees to estimate transpiration (Ec) and multiple micrometeorological profile measurements from a 40-m tower to be used in the models. Stomatal conductance (gs) models included those proposed by Jones (1992) (gs-J), using shaded and sunlit leaf temperatures, and Monteith and Unsworth (1990) (gs-MU), using air temperature. Canopy conductance (gc) models included those proposed by McNaughton and Jarvis (1983) (gc-MJ) and Penman-Monteith (gc-PM). Between gs and gc, gc had the largest differences within models during dry periods; while estimates were most similar during wet periods. Yet, all gc and gs estimates on wet days were at least as high as on dry days, indicative of their insensitivity to leaf wetness. Shaded leaf gs averaged 26% higher than in sunlit leaves. Additionally, the highly decoupled interface (Ω>0.90) reflected multiple environmental drivers that may influence conductance (e.g. vapor pressure deficit and leaf temperature). This was also seen through large shifts of diurnal peaks of gs and gc (up to 2 hours earlier than Ec) associated with the daily variation of air temperature and net radiation. Overall, this study led to three major insights: 1) gc and gs cannot accurately be predicted under wet conditions without accounting for leaf wetness, 2) even during dry days, low vapor pressure deficits interfere with model accuracy, and 3) intermittent rain during semi-dry and wet days cause large fluctuations in gc and gs estimates. Thus, it is advised that sub-daily scale (5- or 10-min intervals) and direct physiological measurements of conductance under wet conditions should be adopted. While methodologically challenging, improved estimates of conductance of water vapor at leaf-to-canopy scales are critical for improving the mechanistic understanding of plant water fluxes in wet environments.

Limitations on gas exchange recovery following natural drought in Californian oak woodlands.

NASA Astrophysics Data System (ADS)

Ackerly, D.; Skelton, R. P.; Dawson, T.; Thompson, S.; Feng, X.; Weitz, A.; McLaughlin, B.

2017-12-01

Abstract Background/Question/Methods Drought can cause major damage to plant communities, but species damage thresholds and post-drought recovery of forest productivity are not yet predictable. We asked the question how should forest net primary productivity recover following exposure to severe drought? We used a natural drought period to investigate whether drought responses and post-drought recovery of canopy health could be predicted by properties of the water transport system. We aimed to test the hypothesis that recovery of gas exchange and canopy health would be most severely limited by xylem embolism in stems. To do this we monitored leaf level gas exchange and water status for multiple individuals of two deciduous and two evergreen species for four years spanning a severe drought event and following subsequent rehydration. Results/Discussion Severe drought caused major declines in leaf water potential, reduced stomatal conductance and assimilation rates and increased canopy bareness in our four canopy species. Water potential surpassed levels associated with incipient embolism in leaves of most trees. In contrast, due to hydraulic segmentation, water potential only rarely surpassed critical thresholds in the stems of the study trees. Individuals that surpassed critical thresholds of embolism in the stem displayed significant canopy dieback and mortality. Thus, recovery of plant gas exchange and canopy health was predicted by xylem safety margin in stems, but not leaves, providing strong support for stem cavitation vulnerability as an index of damage under natural drought conditions.

Coupled carbon-water exchange of the Amazon rain forest, II. Comparison of predicted and observed seasonal exchange of energy, CO2, isoprene and ozone at a remote site in Rondônia

NASA Astrophysics Data System (ADS)

Simon, E.; Meixner, F. X.; Rummel, U.; Ganzeveld, L.; Ammann, C.; Kesselmeier, J.

2005-04-01

A one-dimensional multi-layer scheme describing the coupled exchange of energy and CO2, the emission of isoprene and the dry deposition of ozone is applied to a rain forest canopy in southwest Amazonia. The model was constrained using mean diel cycles of micrometeorological quantities observed during two periods in the wet and dry season 1999. Predicted net fluxes and concentration profiles for both seasonal periods are compared to observations made at two nearby towers.

The predicted day- and nighttime thermal stratification of the canopy layer is consistent with observations in dense canopies. The observed and calculated net fluxes above and H2O and CO2 concentration profiles within the canopy show a good agreement. The predicted net carbon sink decreases from 2.5 t C ha-1yr-1 for wet season conditions to 1 t C ha-1yr-1 for dry season conditions, whereas observed and predicted midday Bowen ratio increases from 0.5 to 0.8. The evaluation results confirmed a seasonal variability of leaf physiological parameters, as already suggested in the companion study. The predicted midday canopy net flux of isoprene increased from 7.1 mg C m-2h-1 during the wet season to 11.4 mg C m-2h-1 during the late dry season. Applying a constant emission capacity in all canopy layers, resulted in a disagreement between observed and simulated profiles of isoprene concentrations, suggesting a smaller emission capacity of shade adapted leaves and deposition to the soil or leaf surfaces. Assuming a strong light acclimation of emission capacity, equivalent to a 66% reduction of the standard emission factor for leaves in the lower canopy, resulted in a better agreement of observed and calculated concentration profiles and a 30% reduction of the canopy net flux. The mean calculated ozone flux for dry season condition at noontime was ≍12 nmol m-2s-1, agreeing well with observed values. The corresponding deposition velocity increased from 0.8 cm s-1 to >1.6 cm s-1 in the wet season, which can not be explained by increased stomatal uptake. Considering reasonable physiological changes in stomatal regulation, the predicted value was not larger than 1.05 cm s-1. Instead, the observed fluxes could be explained with the model by decreasing the cuticular resistance to ozone deposition from 5000 to 1000 s m-1. For doubled atmospheric CO2 concentrations the model predicts a strong increase of surface temperatures (0.1-1°C) and net assimilation (22%), a considerable shift in the energy budget (≍25% decreasing transpiration and increasing sensible heat), a slight increase of isoprene emissions (10%) and a strong decrease of ozone deposition (35%).

Within-catchment variation in regulation of water use by eucalypts, and the roles of stomatal anatomy and physiology

NASA Astrophysics Data System (ADS)

Gharun, Mana; Turnbull, Tarryn; Adams, Mark

2014-05-01

Understanding how environmental cues impact water use of forested catchments is crucial for accurate calculation of water balance and effective catchment management in terrestrial ecosystems. We characterised structural and physiological properties of leaves and canopies of Eucalyptus delegatensis, E. pauciflora and E. radiata, the most common species in high-country catchments in temperate Australia. These properties were related to whole-tree water transport to assess differences in water use strategies among the three species. Stomatal conductance, instantaneous transpiration efficiency, stomatal occlusion (through cuticular ledges) and leaf area index differed significantly among species. Whole-tree water use of all species was strongly coupled to changes in vapour pressure deficit (VPD) and photosynthetically active radiation (Q), yet stomatal closure reduced water transport at VPD > 1 kPa in all species, even when soil water was not limiting. The observed differences in leaf traits and related water use strategies reflect species-specific adaptations to dominant environmental conditions within the landscape matrix of catchments. The generalist E. radiata seems to follow an opportunistic, while the two more spatially restricted species have adopted a pessimistic water use strategy. Catchment-scale models of carbon and water fluxes will need to reflect such variation in structure and function, if they are to fully capture species effects on water balance and yield.

A photosynthesis-based two-leaf canopy stomatal ...

EPA Pesticide Factsheets

A coupled photosynthesis-stomatal conductance model with single-layer sunlit and shaded leaf canopy scaling is implemented and evaluated in a diagnostic box model with the Pleim-Xiu land surface model (PX LSM) and ozone deposition model components taken directly from the meteorology and air quality modeling system—WRF/CMAQ (Weather Research and Forecast model and Community Multiscale Air Quality model). The photosynthesis-based model for PX LSM (PX PSN) is evaluated at a FLUXNET site for implementation against different parameterizations and the current PX LSM approach with a simple Jarvis function (PX Jarvis). Latent heat flux (LH) from PX PSN is further evaluated at five FLUXNET sites with different vegetation types and landscape characteristics. Simulated ozone deposition and flux from PX PSN are evaluated at one of the sites with ozone flux measurements. Overall, the PX PSN simulates LH as well as the PX Jarvis approach. The PX PSN, however, shows distinct advantages over the PX Jarvis approach for grassland that likely result from its treatment of C3 and C4 plants for CO2 assimilation. Simulations using Moderate Resolution Imaging Spectroradiometer (MODIS) leaf area index (LAI) rather than LAI measured at each site assess how the model would perform with grid averaged data used in WRF/CMAQ. MODIS LAI estimates degrade model performance at all sites but one site having exceptionally old and tall trees. Ozone deposition velocity and ozone flux along with LH

Improving representation of canopy temperatures for modeling subcanopy incoming longwave radiation to the snow surface

NASA Astrophysics Data System (ADS)

Webster, Clare; Rutter, Nick; Jonas, Tobias

2017-09-01

A comprehensive analysis of canopy surface temperatures was conducted around a small and large gap at a forested alpine site in the Swiss Alps during the 2015 and 2016 snowmelt seasons (March-April). Canopy surface temperatures within the small gap were within 2-3°C of measured reference air temperature. Vertical and horizontal variations in canopy surface temperatures were greatest around the large gap, varying up to 18°C above measured reference air temperature during clear-sky days. Nighttime canopy surface temperatures around the study site were up to 3°C cooler than reference air temperature. These measurements were used to develop a simple parameterization for correcting reference air temperature for elevated canopy surface temperatures during (1) nighttime conditions (subcanopy shortwave radiation is 0 W m-2) and (2) periods of increased subcanopy shortwave radiation >400 W m-2 representing penetration of shortwave radiation through the canopy. Subcanopy shortwave and longwave radiation collected at a single point in the subcanopy over a 24 h clear-sky period was used to calculate a nighttime bulk offset of 3°C for scenario 1 and develop a multiple linear regression model for scenario 2 using reference air temperature and subcanopy shortwave radiation to predict canopy surface temperature with a root-mean-square error (RMSE) of 0.7°C. Outside of these two scenarios, reference air temperature was used to predict subcanopy incoming longwave radiation. Modeling at 20 radiometer locations throughout two snowmelt seasons using these parameterizations reduced the mean bias and RMSE to below 10 W m s-2 at all locations.

Investigating Polyploidy: Using Marigold Stomates and Fingernail Polish.

ERIC Educational Resources Information Center

Hunter, Kimberly L.; Leone, Rebecca S.; Kohlhepp, Kimberly; Hunter, Richard B.

2002-01-01

Describes a science activity on polyploidy targeting middle and high school students which can be used to discuss topics such as chromosomes, cells, plant growth, and functions of stomates. Integrates mathematics in data collection. (Contains 13 references.) (YDS)

FACE: Free-Air CO{sub 2} Enrichment for plant research in the field

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

Hendrey, G.R.

1992-08-01

Research programs concerning the effects of Carbon Dioxide(CO){sub 2} on cotton plants are described. Biological responses studied include foliage response to CO{sub 2} fluctuations; yield of cotton exposed to CO{sub 2} enrichment; responses of photosynthesis and stomatal conductance to elevated CO{sub 2} in field-grown cotton; cotton leaf and boll temperatures; root response to CO{sub 2} enrichment; and evaluations of cotton response to CO{sub 2} enrichment with canopy reflectance observations.

FACE: Free-Air CO[sub 2] Enrichment for plant research in the field

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

Hendrey, G.R.

1992-08-01

Research programs concerning the effects of Carbon Dioxide(CO)[sub 2] on cotton plants are described. Biological responses studied include foliage response to CO[sub 2] fluctuations; yield of cotton exposed to CO[sub 2] enrichment; responses of photosynthesis and stomatal conductance to elevated CO[sub 2] in field-grown cotton; cotton leaf and boll temperatures; root response to CO[sub 2] enrichment; and evaluations of cotton response to CO[sub 2] enrichment with canopy reflectance observations.

Growth, biomass production and photosynthesis of Cenchrus ciliaris L. under Acacia tortilis (Forssk.) Hayne based silvopastoral systems in semi arid tropics.

PubMed

Mishra, A K; Tiwari, H S; Bhatt, R K

2010-11-01

The growth, biomass production and photosynthesis of Cenchrus ciliaris was studied under the canopies of 17 yr old Acacia tortilis trees in semi arid tropical environment. On an average the full grown canopy of A. tortilis at the spacing of 4 x 4 m allowed 55% of total Photosynthetically Active Radiation (PAR) which in turn increased Relative Humidity (RH) and reduced under canopy temperature to -1.75 degrees C over the open air temperature. C. ciliaris attained higher height under the shade of A. tortilis. The tiller production and leaf area index decreased marginally under the shade of tree canopies as compared to the open grown grasses. C. ciliaris accumulated higher chlorophyll a and b under the shade of tree canopies indicating its shade adaptation potential. The assimilatory functions such as rate of photosynthesis, transpiration, stomatal conductance, photosynthetic water use efficiency (PN/TR) and carboxylation efficiency (PN/CINT) decreased under the tree canopies due to low availability of PAR. The total biomass production in term of fresh and dry weight decreased under the tree canopies. On average of 2 yr C. ciliaris had produced 12.78 t ha(-1) green and 3.72 -t ha(-1) dry biomass under the tree canopies of A. tortilis. The dry matter yield reduced to 38% under the tree canopies over the open grown grasses. The A. tortilis + C. ciliaris maintained higher soil moisture, organic carbon content and available N P K for sustainable biomass production for the longer period. The higher accumulation of crude protein, starch, sugar and nitrogen in leaves and stem of C. ciliaris indicates that this grass species also maintained its quality under A. tortilis based silvopastoral system. The photosynthesis and dry matter accumulation are closely associated with available PAR indicating that for sustainable production of this grass species in the silvopasture systems for longer period about 55% or more PAR is required.

High but not dry: diverse epiphytic bromeliad adaptations to exposure within a seasonally dry tropical forest community.

PubMed

Reyes-García, C; Mejia-Chang, M; Griffiths, H

2012-02-01

• Vascular epiphytes have developed distinct lifeforms to maximize water uptake and storage, particularly when delivered as pulses of precipitation, dewfall or fog. The seasonally dry forest of Chamela, Mexico, has a community of epiphytic bromeliads with Crassulacean acid metabolism showing diverse morphologies and stratification within the canopy. We hypothesize that niche differentiation may be related to the capacity to use fog and dew effectively to perform photosynthesis and to maintain water status. • Four Tillandsia species with either 'tank' or 'atmospheric' lifeforms were studied using seasonal field data and glasshouse experimentation, and compared on the basis of water use, leaf water δ(18) O, photosynthetic and morphological traits. • The atmospheric species, Tillandsia eistetteri, with narrow leaves and the lowest succulence, was restricted to the upper canopy, but displayed the widest range of physiological responses to pulses of precipitation and fog, and was a fog-catching 'nebulophyte'. The other atmospheric species, Tillandsia intermedia, was highly succulent, restricted to the lower canopy and with a narrower range of physiological responses. Both upper canopy tank species relied on tank water and stomatal closure to avoid desiccation. • Niche differentiation was related to capacity for water storage, dependence on fog or dewfall and physiological plasticity. © 2011 The Authors. New Phytologist © 2011 New Phytologist Trust.

Tropospheric ozone fluxes in Norway spruce forest during the transition period from autumn to winter

NASA Astrophysics Data System (ADS)

Juran, Stanislav; Fares, Silvano; Zapletal, Miloš; Cudlín, Pavel; Večeřa, Zbyněk; Urban, Otmar

2017-04-01

Norway spruce exhibits seasonal variations in stomatal conductance and photosynthetic activity typical for overwintering plants, with a decline during autumn and a complete recovery during spring. We investigated ozone fluxes during this transient period (November 2016). Fluxes of tropospheric ozone, the major phytotoxic near-ground pollutant causing injuries to plant tissues, were measured at Bily Kriz experimental station in Beskydy Mountains, the Czech Republic. Dry chemiluminescence fast-response ozone sensor coupled with sonic anemometer was used to measure fast fluctuations in ozone concentration and three-dimensional wind speed, respectively. Apart from this eddy covariance technique, within-canopy ozone concentration gradient was simultaneously measured by UV-absorption based slow-response ozone analysers. Ozone fluxes were subsequently modelled by an Inverse Lagrangian Transport Model (ILTM). A comparison of measured and calculated fluxes is thus available. Moreover, stomatal ozone flux was calculated based on Evaporative/Resistive method assuming stomata are the most relevant sink in the spruce forest. The low NOx concentration throughout the year and low concentrations of volatile organic compounds (VOCs) during the transition period led to hypothesize that non-stomatal flux here estimated by difference between total ozone flux and stomatal ozone flux is represented mainly by dry soil deposition and wet deposition during the snow period. We discuss here the ILTM parameterisation with comparison to measured ozone fluxes. Correct estimation of stomatal ozone flux is essential, especially in transition periods, where main scientific emphasis is put rarely. In addition, this research should help to develop metrics for ozone-risk assessment and advance our knowledge in biosphere-atmosphere exchange over Norway spruce forest. Acknowledgement This work was supported by the Ministry of Education, Youth and Sports within the National Programme for Sustainability (grant No. LO1415) and project CzeCOS (grant No. LM2015061).

Modeling canopy-level productivity: is the "big-leaf" simplification acceptable?

NASA Astrophysics Data System (ADS)

Sprintsin, M.; Chen, J. M.

2009-05-01

The "big-leaf" approach to calculating the carbon balance of plant canopies assumes that canopy carbon fluxes have the same relative responses to the environment as any single unshaded leaf in the upper canopy. Widely used light use efficiency models are essentially simplified versions of the big-leaf model. Despite its wide acceptance, subsequent developments in the modeling of leaf photosynthesis and measurements of canopy physiology have brought into question the assumptions behind this approach showing that big leaf approximation is inadequate for simulating canopy photosynthesis because of the additional leaf internal control on carbon assimilation and because of the non-linear response of photosynthesis on leaf nitrogen and absorbed light, and changes in leaf microenvironment with canopy depth. To avoid this problem a sunlit/shaded leaf separation approach, within which the vegetation is treated as two big leaves under different illumination conditions, is gradually replacing the "big-leaf" strategy, for applications at local and regional scales. Such separation is now widely accepted as a more accurate and physiologically based approach for modeling canopy photosynthesis. Here we compare both strategies for Gross Primary Production (GPP) modeling using the Boreal Ecosystem Productivity Simulator (BEPS) at local (tower footprint) scale for different land cover types spread over North America: two broadleaf forests (Harvard, Massachusetts and Missouri Ozark, Missouri); two coniferous forests (Howland, Maine and Old Black Spruce, Saskatchewan); Lost Creek shrubland site (Wisconsin) and Mer Bleue petland (Ontario). BEPS calculates carbon fixation by scaling Farquhar's leaf biochemical model up to canopy level with stomatal conductance estimated by a modified version of the Ball-Woodrow-Berry model. The "big-leaf" approach was parameterized using derived leaf level parameters scaled up to canopy level by means of Leaf Area Index. The influence of sunlit/shaded leaf separation on GPP prediction was evaluated accounting for the degree of the deviation of 3-dimensional leaf spatial distribution from the random case. More specifically, we compared and evaluated the behavior of both models showing the advantages of sunlit/shaded leaf separation strategy over a simplified big-leaf approach. Keywords: canopy photosynthesis, leaf area index, clumping index, remote sensing.

Monitoring tree health with a dual-wavelength terrestrial laser scanner

NASA Astrophysics Data System (ADS)

Hancock, S.

2013-12-01

Steven Hancock1, Rachel Gaulton1, Mark Danson2 1School of Civil Engineering and Geosciences, Newcastle University, UK, steven.hancock@ncl.ac.uk, rachel.gaulton@ncl.ac.uk 2 School of Environment and Life Sciences, University of Salford, UK, F.M.Danson@salford.ac.uk Forests are a vital part of the Earth's carbon cycle and drive interactions between the land and atmosphere. Accurate and repeatable measurement of forests is essential for understanding the Earth system. Terrestrial laser scanning can be a powerful tool for characterising forests. However, there are a number of issues that have yet to be resolved. Commercial laser scanners are optimised for measuring buildings and other hard targets. Vegetation canopies are complex and porous, confounding standard interpretation techniques. Commercial systems struggle with partial hits and cannot distinguish leaf from wood (Danson et al 2007). A new generation of terrestrial laser scanners, optimised for vegetation measurement, are in development. The Salford Advanced Laser Canopy Analyser (SALCA, Gaulton et al 2013) aims to overcome these issues using full-waveform analysis and two wavelengths (1064 nm and 1545 nm), allowing the characterisation of a porous canopy, the identification of leaf and wood and derivation of information on leaf biochemistry. Gaulton et al (2013) showed that SALCA is capable of measuring the Equivalent Water Thickness (EWT) of individual leaves in laboratory conditions. In this study, the method was applied to complete tree canopies. A controlled experiment simulating a small 'forest' of potted broadleaved (Tilia cordata) and coniferous trees (Pinus nigra) was established and groups subjected to different moisture stresses over a one month period. Trees were repeatedly scanned by SALCA and regular measurements were made of leaf EWT, stomatal conductance, chlorophyll content, spectral properties (using an ASD field spectroradiometer) and, for a limited number of trees, leaf area (by destructive harvesting). Trees were arranged so that some were clearly visible to the scanner and could be analysed individually (a best case scenario) whilst others were grouped to form a denser, more realistic canopy (a worse case scenario). A method was developed to simultaneously extract canopy structure (leaf area, tree height and clumping) and leaf biochemistry (EWT) from the laser scanner data. These results were compared to ground to assess their accuracy. References Danson, F. M., Hetherington D., Morsdorf F., Koetz B., Allgower B., 2007. Forest canopy gap fraction from terrestrial laser scanning. IEEE Geoscience and Remote Sensing Letters, 4, 157-160. Gaulton R., Danson F. M., Ramirez F. A., Gunawan O., 2013. The potential of dual-wavelength laser scanning for estimating vegetation moisture content. Remote Sensing of Environment, 132, 32-39.

Unexpected Connections between Humidity and Ion Transport Discovered Using a Model to Bridge Guard Cell-to-Leaf Scales.

PubMed

Wang, Yizhou; Hills, Adrian; Vialet-Chabrand, Silvere; Papanatsiou, Maria; Griffiths, Howard; Rogers, Simon; Lawson, Tracy; Lew, Virgilio L; Blatt, Michael R

2017-11-01

Stomatal movements depend on the transport and metabolism of osmotic solutes that drive reversible changes in guard cell volume and turgor. These processes are defined by a deep knowledge of the identities of the key transporters and of their biophysical and regulatory properties, and have been modeled successfully with quantitative kinetic detail at the cellular level. Transpiration of the leaf and canopy, by contrast, is described by quasilinear, empirical relations for the inputs of atmospheric humidity, CO 2 , and light, but without connection to guard cell mechanics. Until now, no framework has been available to bridge this gap and provide an understanding of their connections. Here, we introduce OnGuard2, a quantitative systems platform that utilizes the molecular mechanics of ion transport, metabolism, and signaling of the guard cell to define the water relations and transpiration of the leaf. We show that OnGuard2 faithfully reproduces the kinetics of stomatal conductance in Arabidopsis thaliana and its dependence on vapor pressure difference (VPD) and on water feed to the leaf. OnGuard2 also predicted with VPD unexpected alterations in K + channel activities and changes in stomatal conductance of the slac1 Cl - channel and ost2 H + -ATPase mutants, which we verified experimentally. OnGuard2 thus bridges the micro-macro divide, offering a powerful tool with which to explore the links between guard cell homeostasis, stomatal dynamics, and foliar transpiration. © 2017 American Society of Plant Biologists. All rights reserved.

Dry deposition of O3 and SO2 estimated from gradient measurements above a temperate mixed forest.

PubMed

Wu, Zhiyong; Staebler, Ralf; Vet, Robert; Zhang, Leiming

2016-03-01

Vertical profiles of O3 and SO2 concentrations were monitored at the Borden Forest site in southern Ontario, Canada from May 2008 to April 2013. A modified gradient method (MGM) was applied to estimate O3 and SO2 dry deposition fluxes using concentration gradients between a level above and a level below the canopy top. The calculated five-year mean (median) dry deposition velocity (Vd) were 0.35 (0.27) and 0.59 (0.54) cm s(-1), respectively, for O3 and SO2. Vd(O3) exhibited large seasonal variations with the highest monthly mean of 0.68 cm s(-1) in August and the lowest of 0.09 cm s(-1) in February. In contrast, seasonal variations of Vd(SO2) were smaller with monthly means ranging from 0.48 (May) to 0.81 cm s(-1) (December). The different seasonal variations between O3 and SO2 were caused by the enhanced SO2 uptake by snow surfaces in winter. Diurnal variations showed a peak value of Vd in early morning in summer months for both O3 and SO2. Canopy wetness increased the non-stomatal uptake of O3 while decreasing the stomatal uptake. This also applied to SO2, but additional factors such as surface acidity also played an important role on the overall uptake. Crown Copyright © 2015. Published by Elsevier Ltd. All rights reserved.

Optimization of canopy conductance models from concurrent measurements of sap flow and stem water potential on Drooping Sheoak in South Australia

NASA Astrophysics Data System (ADS)

Wang, H.; Guan, H.; Deng, R.; Simmons, C. T.

2013-12-01

Canopy conductance response to environmental conditions is a critical component in land surface hydrological modeling. This response is often formulated as a combination of response functions of each influencing factor (solar radiation, air temperature, vapor pressure deficit, and soil water availability). These functions are climate and vegetation specific. Thus, it is important to determine the most appropriate combination of response functions and their parameter values for a specific environment. We will present a method for this purpose based on field measurements and an optimization scheme. The study was performed on Drooping Sheoak (Allocasuarina verticillata) in Adelaide South Australia. Sap flow and stem water potential were measured in a year together with microclimate variables. Canopy conductance was calculated from the inversed Penman-Monteith (PM) equation, which was then used to examine the performance of 36 combinations of various response functions. Parameters in the models were optimized using a DiffeRential Evolution Adaptive Metropolis (DREAM) model based on a training dataset. The testing results show that the best combination gave a correlation coefficient of 0.97, and root mean square error of 0.0006 m/s in comparison to the PM-calculated values. The maximum stomatal conductance given by this combination is 0.0075 m/s, equivalent to a minimum stomatal resistance of 133 s/m. This is close to the number (150 s/m) used in Noah land surface model for evergreen needle-leaf trees. It is surprising that for all combinations, the optimized parameter of the temperature response function is against its physical meaning. This is likely related to the inter-dependence between air temperature and vapor pressure deficit. Supported by the results, we suggest that the effects of vapor pressure deficit and air temperature should be represented together, so as to be consistent with the physics.

Comparison of Source Partitioning Methods for CO2 and H2O Fluxes Based on High Frequency Eddy Covariance Data

NASA Astrophysics Data System (ADS)

Klosterhalfen, Anne; Moene, Arnold; Schmidt, Marius; Ney, Patrizia; Graf, Alexander

2017-04-01

Source partitioning of eddy covariance (EC) measurements of CO2 into respiration and photosynthesis is routinely used for a better understanding of the exchange of greenhouse gases, especially between terrestrial ecosystems and the atmosphere. The most frequently used methods are usually based either on relations of fluxes to environmental drivers or on chamber measurements. However, they often depend strongly on assumptions or invasive measurements and do usually not offer partitioning estimates for latent heat fluxes into evaporation and transpiration. SCANLON and SAHU (2008) and SCANLON and KUSTAS (2010) proposed an promising method to estimate the contributions of transpiration and evaporation using measured high frequency time series of CO2 and H2O fluxes - no extra instrumentation necessary. This method (SK10 in the following) is based on the spatial separation and relative strength of sources and sinks of CO2 and water vapor among the sub-canopy and canopy. Assuming that air from those sources and sinks is not yet perfectly mixed before reaching EC sensors, partitioning is estimated based on the separate application of the flux-variance similarity theory to the stomatal and non-stomatal components of the regarded fluxes, as well as on additional assumptions on stomatal water use efficiency (WUE). The CO2 partitioning method after THOMAS et al. (2008) (TH08 in the following) also follows the argument that the dissimilarities of sources and sinks in and below a canopy affect the relation between H2O and CO2 fluctuations. Instead of involving assumptions on WUE, TH08 directly screens their scattergram for signals of joint respiration and evaporation events and applies a conditional sampling methodology. In spite of their different main targets (H2O vs. CO2), both methods can yield partitioning estimates on both fluxes. We therefore compare various sub-methods of SK10 and TH08 including own modifications (e.g., cluster analysis) to each other, to established source partitioning methods, and to chamber measurements at various agroecosystems. Further, profile measurements and a canopy-resolving Large Eddy Simulation model are used to test the assumptions involved in SK10. Scanlon, T.M., Kustas, W.P., 2010. Partitioning carbon dioxide and water vapor fluxes using correlation analysis. Agricultural and Forest Meteorology 150 (1), 89-99. Scanlon, T.M., Sahu, P., 2008. On the correlation structure of water vapor and carbon dioxide in the atmospheric surface layer: A basis for flux partitioning. Water Resources Research 44 (10), W10418, 15 pp. Thomas, C., Martin, J.G., Goeckede, M., Siqueira, M.B., Foken, T., Law, B.E., Loescher H.W., Katul, G., 2008. Estimating daytime subcanopy respiration from conditional sampling methods applied to multi-scalar high frequency turbulence time series. Agricultural and Forest Meteorology 148 (8-9), 1210-1229.

A specific PFT and sub-canopy structure for simulating oil palm in the Community Land Model

NASA Astrophysics Data System (ADS)

Fan, Y.; Knohl, A.; Roupsard, O.; Bernoux, M.; LE Maire, G.; Panferov, O.; Kotowska, M.; Meijide, A.

2015-12-01

Towards an effort to quantify the effects of rainforests to oil palm conversion on land-atmosphere carbon, water and energy fluxes, a specific plant functional type (PFT) and sub-canopy structure are developed for simulating oil palm within the Community Land Model (CLM4.5). Current global land surface models only simulate annual crops beside natural vegetation. In this study, a multilayer oil palm subroutine is developed in CLM4.5 for simulating oil palm's phenology and carbon and nitrogen allocation. The oil palm has monopodial morphology and sequential phenology of around 40 stacked phytomers, each carrying a large leaf and a fruit bunch, forming a natural multilayer canopy. A sub-canopy phenological and physiological parameterization is thus introduced, so that multiple phytomer components develop simultaneously but according to their different phenological steps (growth, yield and senescence) at different canopy layers. This specific multilayer structure was proved useful for simulating canopy development in terms of leaf area index (LAI) and fruit yield in terms of carbon and nitrogen outputs in Jambi, Sumatra (Fan et al. 2015). The study supports that species-specific traits, such as palm's monopodial morphology and sequential phenology, are necessary representations in terrestrial biosphere models in order to accurately simulate vegetation dynamics and feedbacks to climate. Further, oil palm's multilayer structure allows adding all canopy-level calculations of radiation, photosynthesis, stomatal conductance and respiration, beside phenology, also to the sub-canopy level, so as to eliminate scale mismatch problem among different processes. A series of adaptations are made to the CLM model. Initial results show that the adapted multilayer radiative transfer scheme and the explicit represention of oil palm's canopy structure improve on simulating photosynthesis-light response curve. The explicit photosynthesis and dynamic leaf nitrogen calculations per canopy layer also enhance simulated CO2 flux when compared to eddy covariance flux data. More investigations on energy and water fluxes and nitrogen balance are being conducted. These new schemes would hopefully promote the understanding of climatic effects of the tropical land use transformation system.

Calibrating the simple biosphere model for Amazonian tropical forest using field and remote sensing data. I - Average calibration with field data

NASA Technical Reports Server (NTRS)

Sellers, Piers J.; Shuttleworth, W. James; Dorman, Jeff L.; Dalcher, Amnon; Roberts, John M.

1989-01-01

Using meteorological and hydrological measurements taken in and above the central-Amazon-basin tropical forest, calibration of the Sellers et al. (1986) simple biosphere (SiB) model are described. The SiB model is a one-dimensional soil-vegetation-atmosphere model designed for use within GCMs models, representing the vegetation cover by analogy with processes operating within a single representative plant. The experimental systems and the procedures used to obtain field data are described, together with the specification of the physiological parameterization required to provide an average description of data. It was found that some of the existing literature on stomatal behavior for tropical species is inconsistent with the observed behavior of the complete canopy in Amazonia, and that the rainfall interception store of the canopy is considerably smaller than originally specified in the SiB model.

Gas valves, forests and global change: a commentary on Jarvis (1976) ‘The interpretation of the variations in leaf water potential and stomatal conductance found in canopies in the field’

PubMed Central

Beerling, David J.

2015-01-01

Microscopic turgor-operated gas valves on leaf surfaces—stomata—facilitate gas exchange between the plant and the atmosphere, and respond to multiple environmental and endogenous cues. Collectively, stomatal activities affect everything from the productivity of forests, grasslands and crops to biophysical feedbacks between land surface vegetation and climate. In 1976, plant physiologist Paul Jarvis reported an empirical model describing stomatal responses to key environmental and plant conditions that predicted the flux of water vapour from leaves into the surrounding atmosphere. Subsequent theoretical advances, building on this earlier approach, established the current paradigm for capturing the physiological behaviour of stomata that became incorporated into sophisticated models of land carbon cycling. However, these models struggle to accurately predict observed trends in the physiological responses of Northern Hemisphere forests to recent atmospheric CO2 increases, highlighting the need for improved representation of the role of stomata in regulating forest–climate interactions. Bridging this gap between observations and theory as atmospheric CO2 rises and climate change accelerates creates challenging opportunities for the next generation of physiologists to advance planetary ecology and climate science. This commentary was written to celebrate the 350th anniversary of the journal Philosophical Transactions of the Royal Society. PMID:25750234

Impacts of elevated ozone on growth and photosynthesis of Metasequoia glyptostroboides Hu et Cheng.

PubMed

Zhang, Weiwei; Feng, Zhaozhong; Wang, Xiaoke; Niu, Junfeng

2014-09-01

One-year-old Metasequoia glyptostroboides seedlings were exposed to non-filtered ambient air (NF) and elevated ozone (E-O3, NF+60 ppb) in open-top chambers for two years. E-O3 accelerated leaf senescence, as indicated by significant decreases in photosynthetic pigment contents with the elongation of O3 exposure. E-O3 significantly affected gas exchange and carboxylation, inducing reductions in light-saturated photosynthesis (Asat), the maximum activity of Rubisco (Vc,max) and the maximum electron transport rate (Jmax). Chl a/b, Vc,max/Jmax and stomatal limitation (l) were not affected. Stomatal conductance (gs) was significantly decreased by E-O3 in the first year, but remained unchanged in the second year. It can be inferred that the decrease in Asat by E-O3 was mainly attributed to the changes in non-stomatal factors. After two years' exposure, E-O3 caused significant decreases in canopy photosynthesis and leaf mass per area, and a significant increase in the number of branches, but induced slight, not significant decreases in growth and biomass. Therefore, it can be concluded that the carbon accumulation of the species M. glyptostroboides could be negatively affected after long-term exposure to high O3 concentration. Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.

Experimental vs. modeled water use in mature Norway spruce (Picea abies) exposed to elevated CO(2).

PubMed

Leuzinger, Sebastian; Bader, Martin K-F

2012-01-01

Rising levels of atmospheric CO(2) have often been reported to reduce plant water use. Such behavior is also predicted by standard equations relating photosynthesis, stomatal conductance, and atmospheric CO(2) concentration, which form the core of dynamic global vegetation models (DGVMs). Here, we provide first results from a free air CO(2) enrichment (FACE) experiment with naturally growing, mature (35 m) Picea abies (L.) (Norway spruce) and compare them to simulations by the DGVM LPJ-GUESS. We monitored sap flow, stem water deficit, stomatal conductance, leaf water potential, and soil moisture in five 35-40 m tall CO(2)-treated (550 ppm) trees over two seasons. Using LPJ-GUESS, we simulated this experiment using climate data from a nearby weather station. While the model predicted a stable reduction of transpiration of between 9% and 18% (at concentrations of 550-700 ppm atmospheric CO(2)), the combined evidence from various methods characterizing water use in our experimental trees suggest no changes in response to future CO(2) concentrations. The discrepancy between the modeled and the experimental results may be a scaling issue: while dynamic vegetation models correctly predict leaf-level responses, they may not sufficiently account for the processes involved at the canopy and ecosystem scale, which could offset the first-order stomatal response.

Impacts of artificial inundation of ephemeral creek beds on mature riparian eucalypts in semi-arid northwest Australia

NASA Astrophysics Data System (ADS)

Argus, Rachel; Page, Gerald; Grierson, Pauline

2014-05-01

The resilience of riparian ecosystems of intermittent rivers to changes in their hydrological regimes is not well understood. In the Pilbara region of northwest Australia, streams flow only occasionally, reflecting a highly dynamic and extremely variable cycle of prolonged droughts punctuated by occasional floods. However, discharge of ground water pumped from mining activities over recent years has resulted in localised areas with constant surface water. Here we sought to assess impacts of prolonged saturation on the health and functioning of two co-occurring eucalypts (Eucalyptus camaldulensis and Eucalyptus victrix). While riparian vegetation is clearly adapted to partial root-zone hypoxia, we hypothesised that trees in inundated areas experience reduced root function due to an energy crisis, which will be reflected by symptoms in the foliage. We expected that complete saturation of the entire root system for an extended time period reduces physiological function through lower stomatal conductance and more negative water potential, results in canopy sparseness and reduces accumulation of foliar nitrogen and phosphorus. Trees (n=26) were assessed at two sites with artificially permanent surface water (discharge sites) and compared to trees (n=21) at a site with a naturally occurring permanent groundwater fed pool ('reference site'). Trees were sampled from a range of positions including the stream bed, the lower bank and the upper bank, in order to determine the extent of influence of the discharge water. No eucalypts grew in the stream bed at the reference site, indicating either the stream bed conditions were unsuitable for seedling survival or eucalypts were outcompeted by the flood tolerant tree Melaleuca argentea (which was absent from the impact sites). Soil redox potential, an indicator of oxygen availability and other soil chemical conditions, was measured with platinum redox probes at 25 cm depth. Trees were assessed for canopy cover, foliage water potential and gas exchange. Leaves from each tree were also analysed for stable isotope composition (δ13C, δ15N and δ18O) and nutrients (N and P). Bank trees did not differ between the discharge and reference sites by any measure. However, trees positioned in the stream bed at discharge sites were exposed to severely reduced soil redox potential (median = -189 mV) compared to trees growing on the lower (90 mV) or upper bank (188 mV). Trees in the stream bed were clearly separated from upper or lower bank trees using principle components analysis (PCA) for all measured attributes. Canopy cover, δ13C and δ18O contributed most to separating the groups. Canopy cover in stream bed trees was 41% and 52% sparser compared to bank trees at discharge and reference sites, respectively. Stream bed tree leaves had more enriched δ13C values but more depleted δ18O values, indicating leaf gas exchange with the atmosphere was more restricted than for the trees on the bank. Overall, we conclude that artificially constant surface water expression significantly changed environmental conditions in the stream bed and the effect on riparian eucalypt trees was highly localised.

Modelling climate change responses in tropical forests: similar productivity estimates across five models, but different mechanisms and responses

NASA Astrophysics Data System (ADS)

Rowland, L.; Harper, A.; Christoffersen, B. O.; Galbraith, D. R.; Imbuzeiro, H. M. A.; Powell, T. L.; Doughty, C.; Levine, N. M.; Malhi, Y.; Saleska, S. R.; Moorcroft, P. R.; Meir, P.; Williams, M.

2015-04-01

Accurately predicting the response of Amazonia to climate change is important for predicting climate change across the globe. Changes in multiple climatic factors simultaneously result in complex non-linear ecosystem responses, which are difficult to predict using vegetation models. Using leaf- and canopy-scale observations, this study evaluated the capability of five vegetation models (Community Land Model version 3.5 coupled to the Dynamic Global Vegetation model - CLM3.5-DGVM; Ecosystem Demography model version 2 - ED2; the Joint UK Land Environment Simulator version 2.1 - JULES; Simple Biosphere model version 3 - SiB3; and the soil-plant-atmosphere model - SPA) to simulate the responses of leaf- and canopy-scale productivity to changes in temperature and drought in an Amazonian forest. The models did not agree as to whether gross primary productivity (GPP) was more sensitive to changes in temperature or precipitation, but all the models were consistent with the prediction that GPP would be higher if tropical forests were 5 °C cooler than current ambient temperatures. There was greater model-data consistency in the response of net ecosystem exchange (NEE) to changes in temperature than in the response to temperature by net photosynthesis (An), stomatal conductance (gs) and leaf area index (LAI). Modelled canopy-scale fluxes are calculated by scaling leaf-scale fluxes using LAI. At the leaf-scale, the models did not agree on the temperature or magnitude of the optimum points of An, Vcmax or gs, and model variation in these parameters was compensated for by variations in the absolute magnitude of simulated LAI and how it altered with temperature. Across the models, there was, however, consistency in two leaf-scale responses: (1) change in An with temperature was more closely linked to stomatal behaviour than biochemical processes; and (2) intrinsic water use efficiency (IWUE) increased with temperature, especially when combined with drought. These results suggest that even up to fairly extreme temperature increases from ambient levels (+6 °C), simulated photosynthesis becomes increasingly sensitive to gs and remains less sensitive to biochemical changes. To improve the reliability of simulations of the response of Amazonian rainforest to climate change, the mechanistic underpinnings of vegetation models need to be validated at both leaf- and canopy-scales to improve accuracy and consistency in the quantification of processes within and across an ecosystem.

Photosynthetic and Canopy Characteristics of Different Varieties at the Early Elongation Stage and Their Relationships with the Cane Yield in Sugarcane

PubMed Central

Luo, Jun; Pan, Yong-Bao; Xu, Liping; Zhang, Yuye; Zhang, Hua; Chen, Rukai

2014-01-01

During sugarcane growth, the Early Elongation stage is critical to cane yield formation. In this study, parameters of 17 sugarcane varieties were determined at the Early Elongation stage using CI-301 photosynthesis measuring system and CI-100 digital plant canopy imager. The data analysis showed highly significant differences in leaf area index (LAI), mean foliage inclination angle (MFIA), transmission coefficient for diffused light penetration (TD), transmission coefficient for solar beam radiation penetration (TR), leaf distribution (LD), net photosynthetic rate (PN), transpiration rate (E), and stomatal conductance (GS) among sugarcane varieties. Based on the photosynthetic or canopy parameters, the 17 sugarcane varieties were classified into four categories. Through the factor analysis, nine parameters were represented by three principal factors, of which the cumulative rate of variance contributions reached 85.77%. A regression for sugarcane yield, with relative error of yield fitting less than 0.05, was successfully established: sugarcane yield = −27.19 − 1.69 × PN + 0.17 ×  E + 90.43 × LAI − 408.81 × LD + 0.0015 × NSH + 101.38 ×  D (R 2 = 0.928**). This study helps provide a theoretical basis and technical guidance for the screening of new sugarcane varieties with high net photosynthetic rate and ideal canopy structure. PMID:25045742

The effects of elevated CO2 and nitrogen fertilization on stomatal conductance estimated from 11 years of scaled sap flux measurements at Duke FACE.

PubMed

Ward, Eric J; Oren, Ram; Bell, David M; Clark, James S; McCarthy, Heather R; Kim, Hyun-Seok; Domec, Jean-Christophe

2013-02-01

In this study, we employ a network of thermal dissipation probes (TDPs) monitoring sap flux density to estimate leaf-specific transpiration (E(L)) and stomatal conductance (G(S)) in Pinus taeda (L.) and Liquidambar styraciflua L. exposed to +200 ppm atmospheric CO(2) levels (eCO(2)) and nitrogen fertilization. Scaling half-hourly measurements from hundreds of sensors over 11 years, we found that P. taeda in eCO(2) intermittently (49% of monthly values) decreased stomatal conductance (G(S)) relative to the control, with a mean reduction of 13% in both total E(L) and mean daytime G(S). This intermittent response was related to changes in a hydraulic allometry index (A(H)), defined as sapwood area per unit leaf area per unit canopy height, which decreased a mean of 15% with eCO(2) over the course of the study, due mostly to a mean 19% increase in leaf area (A(L)). In contrast, L. styraciflua showed a consistent (76% of monthly values) reduction in G(S) with eCO(2) with a total reduction of 32% E(L), 31% G(S) and 23% A(H) (due to increased A(L) per sapwood area). For L. styraciflua, like P. taeda, the relationship between A(H) and G(S) at reference conditions suggested a decrease in G(S) across the range of A(H). Our findings suggest an indirect structural effect of eCO(2) on G(S) in P. taeda and a direct leaf level effect in L. styraciflua. In the initial year of fertilization, P. taeda in both CO(2) treatments, as well as L. styraciflua in eCO(2), exhibited higher G(S) with N(F) than expected from shifts in A(H), suggesting a transient direct effect on G(S). Whether treatment effects on mean leaf-specific G(S) are direct or indirect, this paper highlights that long-term treatment effects on G(S) are generally reflected in A(H) as well.

Leaf temperature and stomatal influences on sap velocity diurnal hysteresis in the Amazon rainforest

NASA Astrophysics Data System (ADS)

Jardine, K.; Gimenez, B.; Negron Juarez, R. I.; Koven, C.; Powell, T.; Higuchi, N.; Chambers, J.; Varadharajan, C.

2016-12-01

In order to improve our ability to predict terrestrial evapotranspiration fluxes, an understanding of the interactions between plant physiology and environmental conditions is necessary, but remains poorly characterized, especially in tropical ecosystems. In this study we show a tight positive correlation between sap velocity (at 1 m of height) and leaf surface temperature (LST, 20-30 m of height) in canopy dominant trees in two primary rainforest sites in the Amazon basin (Santarém and Manaus, Brazil). As leaf temperatures varied throughout the day, sap velocity responded with little delay (<15 min). Positive sap velocity was often observed at night, but also closely followed night time LSTs. When plotted versus LST, sap velocity showed an exponential increase before reaching a reflection point and a plateau and is characterized as a sigmoidal curve, in all observed trees. Moreover, a clear diurnal hysteresis in sap velocity was evident with morning periods showing higher temperature sensitivities than afternoon and night periods. Diurnal leaf observations showed a morning peak in stomatal conductance ( 10:00-10:30), but a mid-day to afternoon peak in transpiration and leaf temperature (12:00-14:00). Our observations suggest the sap velocity-LST hysteresis pattern arises due to the temporal offset between stomatal conductance and vapor pressure deficits (VPD) and demonstrates the dominating effect of VPD over stomatal conductance in maintaining high transpiration/sap flow rates under elevated temperatures. Our results have important implications for modeling tropical forest transpiration and suggests the possibility of predicting evapotranspiration fluxes at the ecosystem to regional scales based on remote sensed vegetation temperature.

Responses of sap flow, leaf gas exchange and growth of hybrid aspen to elevated atmospheric humidity under field conditions

PubMed Central

Niglas, Aigar; Kupper, Priit; Tullus, Arvo; Sellin, Arne

2014-01-01

An increase in average air temperature and frequency of rain events is predicted for higher latitudes by the end of the 21st century, accompanied by a probable rise in air humidity. We currently lack knowledge on how forest trees acclimate to rising air humidity in temperate climates. We analysed the leaf gas exchange, sap flow and growth characteristics of hybrid aspen (Populus tremula × P. tremuloides) trees growing at ambient and artificially elevated air humidity in an experimental forest plantation situated in the hemiboreal vegetation zone. Humidification manipulation did not affect the photosynthetic capacity of plants, but did affect stomatal responses: trees growing at elevated air humidity had higher stomatal conductance at saturating photosynthetically active radiation (gs sat) and lower intrinsic water-use efficiency (IWUE). Reduced stomatal limitation of photosynthesis in trees grown at elevated air humidity allowed slightly higher net photosynthesis and relative current-year height increments than in trees at ambient air humidity. Tree responses suggest a mitigating effect of higher air humidity on trees under mild water stress. At the same time, trees at higher air humidity demonstrated a reduced sensitivity of IWUE to factors inducing stomatal closure and a steeper decline in canopy conductance in response to water deficit, implying higher dehydration risk. Despite the mitigating impact of increased air humidity under moderate drought, a future rise in atmospheric humidity at high latitudes may be disadvantageous for trees during weather extremes and represents a potential threat in hemiboreal forest ecosystems. PMID:24887000

Inter- and under-canopy soil water, leaf-level and whole-plant gas exchange dynamics of a semi-arid perennial C4 grass.

PubMed

Hamerlynck, Erik P; Scott, Russell L; Susan Moran, M; Schwander, Andrea M; Connor, Erin; Huxman, Travis E

2011-01-01

It is not clear if tree canopies in savanna ecosystems exert positive or negative effects on soil moisture, and how these might affect understory plant carbon balance. To address this, we quantified rooting-zone volumetric soil moisture (θ(25 cm)), plant size, leaf-level and whole-plant gas exchange of the bunchgrass, bush muhly (Muhlenbergia porteri), growing under and between mesquite (Prosopis velutina) in a southwestern US savanna. Across two contrasting monsoon seasons, bare soil θ(25 cm) was 1.0-2.5% lower in understory than in the intercanopy, and was consistently higher than in soils under grasses, where θ(25 cm) was similar between locations. Understory plants had smaller canopy areas and volumes with larger basal diameters than intercanopy plants. During an above-average monsoon, intercanopy and understory plants had similar seasonal light-saturated leaf-level photosynthesis (A(net-sat)), stomatal conductance (g(s-sat)), and whole-plant aboveground respiration (R(auto)), but with higher whole-plant photosynthesis (GEP(plant)) and transpiration (T(plant)) in intercanopy plants. During a below-average monsoon, intercanopy plants had higher diurnally integrated GEP(plant), R(auto), and T(plant). These findings showed little evidence of strong, direct positive canopy effects to soil moisture and attendant plant performance. Rather, it seems understory conditions foster competitive dominance by drought-tolerant species, and that positive and negative canopy effects on soil moisture and community and ecosystem processes depends on a suite of interacting biotic and abiotic factors.

Sources and sinks of carbonyl sulfide in a mountain grassland and relationships to the carbon dioxide exchange

NASA Astrophysics Data System (ADS)

Spielmann, Felix M.; Kitz, Florian; Hammerle, Albin; Gerdel, Katharina; Wohlfahrt, Georg

2016-04-01

The trace gas carbonyl sulfide (COS) has been proposed as a tracer for canopy gross primary production (GPP), canopy transpiration and stomatal conductance of plant canopies in the last few years. COS enters the plant leaf through the stomata and diffuses through the intercellular space, the cell wall, the plasma membrane and the cytosol like CO2. It is then catalyzed by the enzyme carbonic anhydrase (CA) in a one-way reaction to H2S and CO2. This one-way flux into the leaf makes COS a promising tracer for the GPP. However there is growing evidence, that plant leaves aren't the only contributors to the ecosystem flux of COS. Therefor the COS uptake of soil microorganisms also containing CA and abiotic COS production might have to be accounted for when using COS as a tracer at the ecosystem scale. The overarching objective of this study was to quantify the relationship between the ecosystem-scale exchange of COS, CO2 and H2O and thus to test for the potential of COS to be used as a tracer for the plant canopy CO2 and H2O exchange. More specifically we aimed at quantifying the contribution of the soil to the ecosystem-scale COS exchange in order to understand complications that may arise due to a non-negligible soil COS exchange. In May 2015 we set up our quantum cascade laser (QCL) (Aerodyne Research Inc., MA, USA) at a temperate mountain grassland in Stubai Valley close to the village of Neustift, Austria. Our site lies at the valley bottom and is an intensively managed mountain grassland, which is cut 3-4 times a year. With the QCL we were able to measure concurrently the concentrations of COS, CO2, H2O (and CO) at a frequency of 10 Hz with minimal noise. This allowed us to conduct ecosystem-scale eddy covariance measurements. The eddy covariance flux measurements revealed that the COS uptake continues at night, which we confirmed was not caused by soil microorganisms, as the soil exchange was close to neutral during nighttime. Instead, the nocturnal COS uptake appears to be caused by incomplete stomatal closure and continuing catalytic CA activity in the absence of light. The resulting data also revealed a weaker correlation between COS- and CO2-fluxes than expected, which hints to further COS-exchange mechanisms at our site. To disentangle sources and sinks within and below the canopy, we measured vertical within-canopy profiles of COS and CO2 and inferred the vertical distribution of sources and sinks by means of an inverse Lagrangian analysis. The resulting data confirmed that soils at our site are sources for COS during daytime and close to neutral during nighttime and place the major COS/CO2 sink in the central part of the canopy, where a large amount of leaf area still receives enough light. Taken together our results suggest that using COS as a tracer for canopy CO2 and H2O exchange may be less straight forward than previously thought and that further work is required to better understand the ecosystem-scale COS exchange and its drivers.

Effect of canopy architectural variation on transpiration and thermoregulation

NASA Astrophysics Data System (ADS)

Linn, R.; Banerjee, T.

2017-12-01

One of the major scientific questions identified by the NGEE - Tropics campaign is the effect of disturbances such as forest fires, vegetation thinning and land use change on carbon, water and energy fluxes. Answers to such questions can help develop effective forest management strategies and shape policies to mitigate damages under natural and anthropogenic climate change. The absence of horizontal and vertical variation of forest canopy structure in current models is a major source of uncertainty in answering these questions. The current work addresses this issue through a bottom up process based modeling approach to systematically investigate the effect of forest canopy architectural variation on plant physiological response as well as canopy level fluxes. A plant biophysics formulation is used which is based on the following principles: (1) a model for the biochemical demand for CO2 as prescribed by photosynthesis models. This model can differentiate between photosynthesis under light-limited and nutrient-limited scenarios. (2) A Fickian mass transfer model including transfer through the laminar boundary layer on leaves that may be subjected to forced or free convection depending upon the mean velocity and the radiation load; (3) an optimal leaf water use strategy that maximizes net carbon gain for a given transpiration rate to describe the stomatal aperture variation; (4) a leaf-level energy balance to accommodate evaporative cooling. Such leaf level processes are coupled to solutions of atmospheric flow through vegetation canopies. In the first test case, different scenarios of top heavy and bottom heavy (vertical) foliage distributions are investigated within a one-dimensional framework where no horizontal heterogeneity of canopy structure is considered. In another test case, different spatial distributions (both horizontal and vertical) of canopy geometry (land use) are considered, where flow solutions using large eddy simulations (LES) are coupled to the aforementioned leaf level physiological model. The systematic differences observed across these simulated scenarios provide a clear insight of disturbance effects of forest-atmosphere interaction.

A photosynthesis-based two-leaf canopy stomatal conductance model for meteorology and air quality modeling with WRF/CMAQ PX LSM

NASA Astrophysics Data System (ADS)

Ran, Limei; Pleim, Jonathan; Song, Conghe; Band, Larry; Walker, John T.; Binkowski, Francis S.

2017-02-01

A coupled photosynthesis-stomatal conductance model with single-layer sunlit and shaded leaf canopy scaling is implemented and evaluated in a diagnostic box model with the Pleim-Xiu land surface model (PX LSM) and ozone deposition model components taken directly from the meteorology and air quality modeling system - WRF/CMAQ (Weather Research and Forecast model and Community Multiscale Air Quality model). The photosynthesis-based model for PX LSM (PX PSN) is evaluated at a FLUXNET site for implementation against different parameterizations and the current PX LSM approach with a simple Jarvis function (PX Jarvis). Latent heat flux (LH) from PX PSN is further evaluated at five FLUXNET sites with different vegetation types and landscape characteristics. Simulated ozone deposition and flux from PX PSN are evaluated at one of the sites with ozone flux measurements. Overall, the PX PSN simulates LH as well as the PX Jarvis approach. The PX PSN, however, shows distinct advantages over the PX Jarvis approach for grassland that likely result from its treatment of C3 and C4 plants for CO2 assimilation. Simulations using Moderate Resolution Imaging Spectroradiometer (MODIS) leaf area index (LAI) rather than LAI measured at each site assess how the model would perform with grid averaged data used in WRF/CMAQ. MODIS LAI estimates degrade model performance at all sites but one site having exceptionally old and tall trees. Ozone deposition velocity and ozone flux along with LH are simulated especially well by the PX PSN compared to significant overestimation by the PX Jarvis for a grassland site.

Seasonal patterns of leaf gas exchange and water relations in dry rain forest trees of contrasting leaf phenology.

PubMed

Choat, Brendan; Ball, Marilyn C; Luly, Jon G; Donnelly, Christine F; Holtum, Joseph A M

2006-05-01

Diurnal and seasonal patterns of leaf gas exchange and water relations were examined in tree species of contrasting leaf phenology growing in a seasonally dry tropical rain forest in north-eastern Australia. Two drought-deciduous species, Brachychiton australis (Schott and Endl.) A. Terracc. and Cochlospermum gillivraei Benth., and two evergreen species, Alphitonia excelsa (Fenzal) Benth. and Austromyrtus bidwillii (Benth.) Burret. were studied. The deciduous species had higher specific leaf areas and maximum photosynthetic rates per leaf dry mass in the wet season than the evergreens. During the transition from wet season to dry season, total canopy area was reduced by 70-90% in the deciduous species and stomatal conductance (g(s)) and assimilation rate (A) were markedly lower in the remaining leaves. Deciduous species maintained daytime leaf water potentials (Psi(L)) at close to or above wet season values by a combination of stomatal regulation and reduction in leaf area. Thus, the timing of leaf drop in deciduous species was not associated with large negative values of daytime Psi(L) (greater than -1.6 MPa) or predawn Psi(L) (greater than -1.0 MPa). The deciduous species appeared sensitive to small perturbations in soil and leaf water status that signalled the onset of drought. The evergreen species were less sensitive to the onset of drought and g(s) values were not significantly lower during the transitional period. In the dry season, the evergreen species maintained their canopies despite increasing water-stress; however, unlike Eucalyptus species from northern Australian savannas, A and g(s) were significantly lower than wet season values.

Evaluation of Multiple Mechanistic Hypotheses of Leaf Photosynthesis and Stomatal Conductance against Diurnal and Seasonal Data from Two Contrasting Panamanian Tropical Forests

NASA Astrophysics Data System (ADS)

Serbin, S.; Walker, A. P.; Wu, J.; Ely, K.; Rogers, A.; Wolfe, B.

2017-12-01

Tropical forests play a key role in regulating the global carbon (C), water, and energy cycles and stores, as well as influence climate through the exchanges of mass and energy with the atmosphere. However, projected changes in temperature and precipitation patterns are expected to impact the tropics and the strength of the tropical C sink, likely resulting in significant climate feedbacks. Moreover, the impact of stronger, longer, and more extensive droughts not well understood. Critical for the accurate modeling of the tropical C and water cycle in Earth System Models (ESMs) is the representation of the coupled photosynthetic and stomatal conductance processes and how these processes are impacted by environmental and other drivers. Moreover, the parameterization and representation of these processes is an important consideration for ESM projections. We use a novel model framework, the Multi-Assumption Architecture and Testbed (MAAT), together with the open-source bioinformatics toolbox, the Predictive Ecosystem Analyzer (PEcAn), to explore the impact of the multiple mechanistic hypotheses of coupled photosynthesis and stomatal conductance as well as the additional uncertainty related to model parameterization. Our goal was to better understand how model choice and parameterization influences diurnal and seasonal modeling of leaf-level photosynthesis and stomatal conductance. We focused on the 2016 ENSO period and starting in February, monthly measurements of diurnal photosynthesis and conductance were made on 7-9 dominant species at the two Smithsonian canopy crane sites. This benchmark dataset was used to test different representations of stomatal conductance and photosynthetic parameterizations with the MAAT model, running within PEcAn. The MAAT model allows for the easy selection of competing hypotheses to test different photosynthetic modeling approaches while PEcAn provides the ability to explore the uncertainties introduced through parameterization. We found that stomatal choice can play a large role in model-data mismatch and observational constraints can be used to reduce simulated model spread, but can also result in large model disagreements with measurements. These results will be used to help inform the modeling of photosynthesis in tropical systems for the larger ESM community.

Understanding the drivers of Amazonian evapotranspiration (ET) change in response to increased CO2.

NASA Astrophysics Data System (ADS)

Halladay, Kate; Good, Peter

2016-04-01

Earth system models allow us to examine the complex interactions and feedbacks between land surface, vegetation and atmosphere. A more thorough understanding of these interactions is essential in reducing uncertainty surrounding the potential impacts of climate and environmental change on the hydrological cycle and the future state and extent of the Amazon rainforest. With HadGEM2-ES simulations from CMIP5 in which CO2 is increased at 1% per year starting from pre-industrial concentrations and reaching 4 times that after 140 years, we separate the various drivers and processes controlling ET in western Amazonia. The design of these simulations allows for radiative and physiological forcings to be examined separately and in combination, and the degree to which the combination of forcings is additive or non-linear. We consider ET as a product of the moisture gradient between the surface and the boundary layer and a conductance term, which includes terms limiting the evaporation from stomata and from the canopy. We find that aside from the direct effects of radiative and physiological forcing, there are a number of other processes occurring: 1) reductions in ET alter the surface energy budget leading to increases in moisture gradient which drive increases in ET, 2) additional reductions in stomatal conductance when surface temperatures exceed optimum temperature for photosynthesis, leading to greater decreases in ET between 2 and 4 times pre-industrial CO2, 3) negative correlation between moisture gradient and conductance terms leads to additional decreases in ET, 4) decreases in canopy water content increases the importance of stomatal conductance which also drives decreases in ET. A combination of these processes leads to non-linear decreases in ET between 2 and 4 times pre-industrial CO2 when both radiative and physiological forcings are operating. These results indicate a major role physiological forcing in the hydrological cycle of Amazonia, highlight the potential for differences in offline and models in terms of the hydrological cycle and land surface feedbacks, and the need to reduce uncertainty in the modelling the response of stomatal conductance to high temperatures.

Stomatal control of leaf fluxes of carbonyl sulfide and CO2 in a Typha freshwater marsh

NASA Astrophysics Data System (ADS)

Sun, Wu; Maseyk, Kadmiel; Lett, Céline; Seibt, Ulli

2018-06-01

Carbonyl sulfide (COS) is an emerging tracer to constrain land photosynthesis at canopy to global scales, because leaf COS and CO2 uptake processes are linked through stomatal diffusion. The COS tracer approach requires knowledge of the concentration normalized ratio of COS uptake to photosynthesis, commonly known as the leaf relative uptake (LRU). LRU is known to increase under low light, but the environmental controls over LRU variability in the field are poorly understood due to scant leaf scale observations. Here we present the first direct observations of LRU responses to environmental variables in the field. We measured leaf COS and CO2 fluxes at a freshwater marsh in summer 2013. Daytime leaf COS and CO2 uptake showed similar peaks in the mid-morning and late afternoon separated by a prolonged midday depression, highlighting the common stomatal control on diffusion. At night, in contrast to CO2, COS uptake continued, indicating partially open stomata. LRU ratios showed a clear relationship with photosynthetically active radiation (PAR), converging to 1.0 at high PAR, while increasing sharply at low PAR. Daytime integrated LRU (calculated from daytime mean COS and CO2 uptake) ranged from 1 to 1.5, with a mean of 1.2 across the campaign, significantly lower than the previously reported laboratory mean value (˜ 1.6). Our results indicate two major determinants of LRU - light and vapor deficit. Light is the primary driver of LRU because CO2 assimilation capacity increases with light, while COS consumption capacity does not. Superimposed upon the light response is a secondary effect that high vapor deficit further reduces LRU, causing LRU minima to occur in the afternoon, not at noon. The partial stomatal closure induced by high vapor deficit suppresses COS uptake more strongly than CO2 uptake because stomatal resistance is a more dominant component in the total resistance of COS. Using stomatal conductance estimates, we show that LRU variability can be explained in terms of different patterns of stomatal vs. internal limitations on COS and CO2 uptake. Our findings illustrate the stomata-driven coupling of COS and CO2 uptake during the most photosynthetically active period in the field and provide an in situ characterization of LRU - a key parameter required for the use of COS as a photosynthetic tracer.

Ecophysiological responses of three evergreen woody Mediterranean species to water stress

NASA Astrophysics Data System (ADS)

Abril, Mireia; Hanano, Ralph

1998-08-01

The ecophysiological response to drought in three different evergreen Mediterranean species were compared. For a better interpretation of the mechanisms regulating physiological processes, the choice of species was based on evident differences in morphological and structural features (leaf size, leaf specific weight, water-conducting system). Seedlings of Ceanothus thyrsiflorus, Quercus agrifolia and Buxus microphylla grown in pots were subjected to natural stressing conditions during late spring in Southern California. Gas exchange, xylem water potential and abscisic acid concentration in xylem sap were measured in control (irrigated) and water-stressed plants, from predawn to sunset. Environmental, hydraulic and hormonal effects on water control and limitations to photosynthesis were analyzed. Q. agrifolia had the highest maximums of net photosynthesis, stomatal conductance and transpiration, which were significantly different from C. thyrsiflorus and B. microphylla. B. microphylla had the lowest values. Stressed individuals of C. thyrsiflorus and B. microphylla reached absolute minimum water potentials during the day and at predawn. Q. agrifolia plants had a water conservative behaviour and did not show these low values. Control plants from Q. agrifolia had the lowest values of hydraulic resistance with high maximum stomatal conductance, while B. microphylla control plants had the lowest maximum stomatal conductance due to higher hydraulic resistance. Changes in plant hydraulic resistance during soil drying were found, which differed among the species. In general, water-use efficiency was reduced during the day by water stress but increased as seasonal drought proceeded. On a long-term basis, Q. agrifolia was the most efficient species in water use. The results support the hypothesis that information on abscisic acid concentration in xylem sap may be one of the most important physiological keys when modelling stomatal conductance and canopy gas exchange over seasons as drought develops on Mediterranean vegetation. Nevertheless, we believe it is necessary to integrate all known factors that control stomatal behaviour in order to construct general models of the vegetation response to environmental changes.

A novel approach for diagnosing isohydric and anisohydric plant water use during drought

NASA Astrophysics Data System (ADS)

Novick, K. A.; Roman, D. T.; Brzostek, E. R.; Dragoni, D.; Phillips, R.

2014-12-01

Recent years have seen the emergence of a new framework for describing plant water use, whereby species-specific water use strategies during periods of hydrologic stress are classified as falling on a spectrum of isohydric to anisohydric behavior. Trees that regulate water potential to within a relatively narrow range, and thereby reduce the risk of damaging xylem cavitation, are categorized as isohydric. In contrast, anisohydric trees allow their leaf water potential to decrease during drought, which may improve gas exchange rates, but at the cost of a greater risk of cavitation in the xylem. To date, most of the approaches to diagnose and characterize isohydric as compared to anisohydric behavior rely on observations of stem or leaf water potential measurements, which are difficult to collect at a high temporal and spatial frequency and rely on destructive techniques. Here, we use cohesion-tension theory to develop a novel approach for diagnosing isohydric/anisohydric behavior in observations of leaf- or canopy-scale stomatal conductance, which are data that may be collected in situ and with relative ease. The approach is particularly focused on exploring how the relationship between stomatal conductance and vapor pressure deficit changes during dry-down periods. The theoretical predictions suggest that the sensitivity of stomatal conductance to vapor pressure deficit may decrease over the course of the drought event for more anisohydric trees, and increase in the case of more isohydric trees. Species-specific, leaf-level observations of the relevant variables collected during the course of a severe drought event affecting the Morgan-Monroe State Forest in 2012 are shown to confirm the theoretical predictions. Finally, the diagnostic approach is evaluated in the context of other emerging approaches for describing stomatal behavior, including the growing recognition of the role of hydraulic capacitance during drought, and recent advances in stomatal optimization theory. Ultimately, placing species along the isohydric-anisohydric contiuum may advance our understanding of the magnitude of drought-related declines in productivity and other physiological processes in forest ecosystems.

Bowen ratio/energy balance technique for estimating crop net CO2 assimilation, and comparison with a canopy chamber

NASA Astrophysics Data System (ADS)

Held, A. A.; Steduto, P.; Orgaz, F.; Matista, A.; Hsiao, T. C.

1990-12-01

This paper describes a Bowen ratio/energy balance (BREB) system which, in conjunction with an infra-red gas analyzer (IRGA), is referred to as BREB+ and is used to estimate evapotranspiration ( ET) and net CO2 flux ( NCF) over crop canopies. The system is composed of a net radiometer, soil heat flux plates, two psychrometers based on platinum resistance thermometers (PRT), bridge circuits to measure resistances, an IRGA, air pumps and switching valves, and a data logger. The psychrometers are triple shielded and aspirated, and with aspiration also between the two inner shields. High resistance (1 000 ohm) PRT's are used for dry and wet bulbs to minimize errors due to wiring and connector resistances. A high (55 K ohm) fixed resistance serves as one arm of the resistance bridge to ensure linearity in output signals. To minimize gaps in data, to allow measurements at short (e.g., 5 min) intervals, and to simplify operation, the psychrometers were fixed at their upper and lower position over the crop and not alternated. Instead, the PRT's, connected to the bridge circuit and the data logger, were carefully calibrated together. Field tests using a common air source showed appartent effects of the local environment around each psychrometer on the temperatures measured. ET rates estimated with the BREB system were compared to those measured with large lysimeters. Daily totals agreed within 5%. There was a tendency, however, for the lysimeter measurements to lag behind the BREB measurements. Daily patterns of NCF estimated with the BREB+ system are consistent with expectations from theories and data in the literature. Side-by-side comparisons with a stirred Mylar canopy chamber showed similar NCF patterns. On the other hand, discrepancies between the results of the two methods were quite marked in the morning or afternoon on certain dates. Part of the discrepancies may be attributed to inaccuracies in the psychrometric temperature measurements. Other possible causes include the highly artificial air turbulence in the canopy chamber and possible associated stomatal response. More work is necessary to identify conclusively the causes. In spite of these uncertainties, the BREB+ technique appears well suited for the automated and simultaneous tracking of photosynthetic performance and water economy of crops in their virtually undisturbed natural environment.

Change in hydraulic properties and leaf traits in a tall rainforest tree species subjected to long-term throughfall exclusion in the perhumid tropics

NASA Astrophysics Data System (ADS)

Schuldt, B.; Leuschner, C.; Horna, V.; Moser, G.; Köhler, M.; van Straaten, O.; Barus, H.

2011-08-01

A large-scale replicated throughfall exclusion experiment was conducted in a pre-montane perhumid rainforest in Sulawesi (Indonesia) exposing the trees for two years to pronounced soil desiccation. The lack of regularly occurring dry periods and shallow rooting patterns distinguish this experiment from similar experiments conducted in the Amazonian rainforest. We tested the hypotheses that a tree's sun canopy is more affected by soil drought than its shade crown, making tall trees particularly vulnerable even under a perhumid climate, and that extended drought periods stimulate an acclimation in the hydraulic system of the sun canopy. In the abundant and tall tree species Castanopsis acuminatissima (Fagaceae), we compared 31 morphological, anatomical, hydraulic and chemical variables of leaves, branches and the stem together with stem diameter growth between drought and control plots. There was no evidence of canopy dieback. However, the drought treatment led to a 30 % reduction in sapwood-specific hydraulic conductivity of sun canopy branches, possibly caused by the formation of smaller vessels and/or vessel filling by tyloses. Drought caused an increase in leaf size, but a decrease in leaf number, and a reduction in foliar calcium content. The δ13C and δ18O signatures of sun canopy leaves gave no indication of a permanent down-regulation of stomatal conductance during the drought, indicating that pre-senescent leaf shedding may have improved the water status of the remaining leaves. Annual stem diameter growth decreased during the drought, while the density of wood in the recently produced xylem increased in both the stem and sun canopy branches (marginally significant). The sun canopy showed a more pronounced drought response than the shade crown indicating that tall trees with a large sun canopy are more vulnerable to drought stress. We conclude that the extended drought prompted a number of medium- to long-term responses in the leaves, branches and the trunk, which may have reduced drought susceptibility. However, unlike a natural drought, our drought simulation experiment was carried out under conditions of high humidity, which may have dampened drought induced damages.

Experimental vs. modeled water use in mature Norway spruce (Picea abies) exposed to elevated CO2

PubMed Central

Leuzinger, Sebastian; Bader, Martin K.-F.

2012-01-01

Rising levels of atmospheric CO2 have often been reported to reduce plant water use. Such behavior is also predicted by standard equations relating photosynthesis, stomatal conductance, and atmospheric CO2 concentration, which form the core of dynamic global vegetation models (DGVMs). Here, we provide first results from a free air CO2 enrichment (FACE) experiment with naturally growing, mature (35 m) Picea abies (L.) (Norway spruce) and compare them to simulations by the DGVM LPJ-GUESS. We monitored sap flow, stem water deficit, stomatal conductance, leaf water potential, and soil moisture in five 35–40 m tall CO2-treated (550 ppm) trees over two seasons. Using LPJ-GUESS, we simulated this experiment using climate data from a nearby weather station. While the model predicted a stable reduction of transpiration of between 9% and 18% (at concentrations of 550–700 ppm atmospheric CO2), the combined evidence from various methods characterizing water use in our experimental trees suggest no changes in response to future CO2 concentrations. The discrepancy between the modeled and the experimental results may be a scaling issue: while dynamic vegetation models correctly predict leaf-level responses, they may not sufficiently account for the processes involved at the canopy and ecosystem scale, which could offset the first-order stomatal response. PMID:23087696

Improving the Representation of Land in Climate Models by Application of EOS Observations

NASA Technical Reports Server (NTRS)

2004-01-01

The PI's IDS current and previous investigation has focused on the applications of the land data toward the improvement of climate models. The previous IDS research identified the key factors limiting the accuracy of climate models to be the representation of albedos, land cover, fraction of landscape covered by vegetation, roughness lengths, surface skin temperature and canopy properties such as leaf area index (LAI) and average stomatal conductance. Therefore, we assembled a team uniquely situated to focus on these key variables and incorporate the remotely sensed measures of these variables into the next generation of climate models.

Modelling the impact of the light regime on single tree transpiration based on 3D representations of plant architecture

NASA Astrophysics Data System (ADS)

Bittner, S.; Priesack, E.

2012-04-01

We apply a functional-structural model of tree water flow to single old-growth trees in a temperate broad-leaved forest stand. Roots, stems and branches are represented by connected porous cylinder elements further divided into the inner heartwood cylinders surrounded by xylem and phloem. Xylem water flow is simulated by applying a non-linear Darcy flow in porous media driven by the water potential gradient according to the cohesion-tension theory. The flow model is based on physiological input parameters such as the hydraulic conductivity, stomatal response to leaf water potential and root water uptake capability and, thus, can reflect the different properties of tree species. The actual root water uptake is calculated using also a non-linear Darcy law based on the gradient between root xylem water potential and rhizosphere soil water potential and by the simulation of soil water flow applying Richards equation. A leaf stomatal conductance model is combined with the hydrological tree and soil water flow model and a spatially explicit three-dimensional canopy light model. The structure of the canopy and the tree architectures are derived by applying an automatic tree skeleton extraction algorithm from point clouds obtained by use of a terrestrial laser scanner allowing an explicit representation of the water flow path in the stem and branches. The high spatial resolution of the root and branch geometry and their connectivity makes the detailed modelling of the water use of single trees possible and allows for the analysis of the interaction between single trees and the influence of the canopy light regime (including different fractions of direct sunlight and diffuse skylight) on the simulated sap flow and transpiration. The model can be applied at various sites and to different tree species, enabling the up-scaling of the water usage of single trees to the total transpiration of mixed stands. Examples are given to reveal differences between diffuse- and ring-porous tree species and to simulate the diurnal dynamics of transpiration, stem sap flux, and root water uptake observed during the vegetation period in the year 2009.

Do the energy fluxes and surface conductance of boreal coniferous forests in Europe scale with leaf area?

PubMed

Launiainen, Samuli; Katul, Gabriel G; Kolari, Pasi; Lindroth, Anders; Lohila, Annalea; Aurela, Mika; Varlagin, Andrej; Grelle, Achim; Vesala, Timo

2016-12-01

Earth observing systems are now routinely used to infer leaf area index (LAI) given its significance in spatial aggregation of land surface fluxes. Whether LAI is an appropriate scaling parameter for daytime growing season energy budget, surface conductance (G s ), water- and light-use efficiency and surface-atmosphere coupling of European boreal coniferous forests was explored using eddy-covariance (EC) energy and CO 2 fluxes. The observed scaling relations were then explained using a biophysical multilayer soil-vegetation-atmosphere transfer model as well as by a bulk G s representation. The LAI variations significantly alter radiation regime, within-canopy microclimate, sink/source distributions of CO 2 , H 2 O and heat, and forest floor fluxes. The contribution of forest floor to ecosystem-scale energy exchange is shown to decrease asymptotically with increased LAI, as expected. Compared with other energy budget components, dry-canopy evapotranspiration (ET) was reasonably 'conservative' over the studied LAI range 0.5-7.0 m 2 m -2 . Both ET and G s experienced a minimum in the LAI range 1-2 m 2 m -2 caused by opposing nonproportional response of stomatally controlled transpiration and 'free' forest floor evaporation to changes in canopy density. The young forests had strongest coupling with the atmosphere while stomatal control of energy partitioning was strongest in relatively sparse (LAI ~2 m 2 m -2 ) pine stands growing on mineral soils. The data analysis and model results suggest that LAI may be an effective scaling parameter for net radiation and its partitioning but only in sparse stands (LAI <3 m 2 m -2 ). This finding emphasizes the significance of stand-replacing disturbances on the controls of surface energy exchange. In denser forests, any LAI dependency varies with physiological traits such as light-saturated water-use efficiency. The results suggest that incorporating species traits and site conditions are necessary when LAI is used in upscaling energy exchanges of boreal coniferous forests. © 2016 John Wiley & Sons Ltd.

Maximum Entropy Production Modeling of Evapotranspiration Partitioning on Heterogeneous Terrain and Canopy Cover: advantages and limitations.

NASA Astrophysics Data System (ADS)

Gutierrez-Jurado, H. A.; Guan, H.; Wang, J.; Wang, H.; Bras, R. L.; Simmons, C. T.

2015-12-01

Quantification of evapotranspiration (ET) and its partition over regions of heterogeneous topography and canopy poses a challenge using traditional approaches. In this study, we report the results of a novel field experiment design guided by the Maximum Entropy Production model of ET (MEP-ET), formulated for estimating evaporation and transpiration from homogeneous soil and canopy. A catchment with complex terrain and patchy vegetation in South Australia was instrumented to measure temperature, humidity and net radiation at soil and canopy surfaces. Performance of the MEP-ET model to quantify transpiration and soil evaporation was evaluated during wet and dry conditions with independently and directly measured transpiration from sapflow and soil evaporation using the Bowen Ratio Energy Balance (BREB). MEP-ET transpiration shows remarkable agreement with that obtained through sapflow measurements during wet conditions, but consistently overestimates the flux during dry periods. However, an additional term introduced to the original MEP-ET model accounting for higher stomatal regulation during dry spells, based on differences between leaf and air vapor pressure deficits and temperatures, significantly improves the model performance. On the other hand, MEP-ET soil evaporation is in good agreement with that from BREB regardless of moisture conditions. The experimental design allows a plot and tree scale quantification of evaporation and transpiration respectively. This study confirms for the first time that the MEP-ET originally developed for homogeneous open bare soil and closed canopy can be used for modeling ET over heterogeneous land surfaces. Furthermore, we show that with the addition of an empirical function simulating the plants ability to regulate transpiration, and based on the same measurements of temperature and humidity, the method can produce reliable estimates of ET during both wet and dry conditions without compromising its parsimony.

Comparison of LiDAR- and photointerpretation-based estimates of canopy cover

Treesearch

Demetrios Gatziolis

2012-01-01

An evaluation of the agreement between photointerpretation- and LiDARbased estimates of canopy cover was performed using 397 90 x 90 m reference areas in Oregon. It was determined that at low canopy cover levels LiDAR estimates tend to exceed those from photointerpretation and that this tendency reverses at high canopy cover levels. Characteristics of the airborne...

Calibration and Validation of Landsat Tree Cover in the Taiga-Tundra Ecotone

NASA Technical Reports Server (NTRS)

Montesano, Paul Mannix; Neigh, Christopher S. R.; Sexton, Joseph; Feng, Min; Channan, Saurabh; Ranson, Kenneth J.; Townshend, John R.

2016-01-01

Monitoring current forest characteristics in the taiga-tundra ecotone (TTE) at multiple scales is critical for understanding its vulnerability to structural changes. A 30 m spatial resolution Landsat-based tree canopy cover map has been calibrated and validated in the TTE with reference tree cover data from airborne LiDAR and high resolution spaceborne images across the full range of boreal forest tree cover. This domain-specific calibration model used estimates of forest height to determine reference forest cover that best matched Landsat estimates. The model removed the systematic under-estimation of tree canopy cover greater than 80% and indicated that Landsat estimates of tree canopy cover more closely matched canopies at least 2 m in height rather than 5 m. The validation improved estimates of uncertainty in tree canopy cover in discontinuous TTE forests for three temporal epochs (2000, 2005, and 2010) by reducing systematic errors, leading to increases in tree canopy cover uncertainty. Average pixel-level uncertainties in tree canopy cover were 29.0%, 27.1% and 31.1% for the 2000, 2005 and 2010 epochs, respectively. Maps from these calibrated data improve the uncertainty associated with Landsat tree canopy cover estimates in the discontinuous forests of the circumpolar TTE.

Foggy days and dry nights determine crown-level water balance in a seasonal tropical Montane cloud forest.

PubMed

Gotsch, Sybil G; Asbjornsen, Heidi; Holwerda, Friso; Goldsmith, Gregory R; Weintraub, Alexis E; Dawson, Todd E

2014-01-01

The ecophysiology of tropical montane cloud forest (TMCF) trees is influenced by crown-level microclimate factors including regular mist/fog water inputs, and large variations in evaporative demand, which in turn can significantly impact water balance. We investigated the effect of such microclimatic factors on canopy ecophysiology and branch-level water balance in the dry season of a seasonal TMCF in Veracruz, Mexico, by quantifying both water inputs (via foliar uptake, FU) and outputs (day- and night-time transpiration, NT). Measurements of sap flow, stomatal conductance, leaf water potential and pressure-volume relations were obtained in Quercus lanceifolia, a canopy-dominant tree species. Our results indicate that FU occurred 34% of the time and led to the recovery of 9% (24 ± 9.1 L) of all the dry-season water transpired from individual branches. Capacity for FU was independently verified for seven additional common tree species. NT accounted for approximately 17% (46 L) of dry-season water loss. There was a strong correlation between FU and the duration of leaf wetness events (fog and/or rain), as well as between NT and the night-time vapour pressure deficit. Our results show the clear importance of fog and NT for the canopy water relations of Q. lanceifolia. © 2013 John Wiley & Sons Ltd.

Evaluation of hydrologic equilibrium in a mountainous watershed: incorporating forest canopy spatial adjustment to soil biogeochemical processes

NASA Astrophysics Data System (ADS)

Mackay, D. Scott

Hydrologic equilibrium theory has been used to describe both short-term regulation of gas exchange and long-term adjustment of forest canopy density. However, by focusing on water and atmospheric conditions alone a hydrologic equilibrium may impose an oversimplification of the growth of forests adjusted to hydrology. In this study nitrogen is incorporated as a third regulation of catchment level forest dynamics and gas exchange. This was examined with an integrated distributed hydrology and forest growth model in a central Sierra Nevada watershed covered primarily by old-growth coniferous forest. Water and atmospheric conditions reasonably reproduced daily latent heat flux, and predicted the expected catenary trend of leaf area index (LAI). However, it was not until the model was provided a spatially detailed description of initial soil carbon and nitrogen pools that spatial patterns of LAI were generated. This latter problem was attributed to a lack of soil history or memory in the initialization of the simulations. Finally, by reducing stomatal sensitivity to vapor pressure deficit (VPD) the canopy density increased when water and nitrogen limitations were not present. The results support a three-control hydrologic equilibrium in the Sierra Nevada watershed. This has implications for modeling catchment level soil-vegetation-atmospheric interactions over interannual, decade, and century time-scales.

Seasonal carbon fluxes for an old-growth temperate forest inferred from carbonyl sulphide

NASA Astrophysics Data System (ADS)

Rastogi, Bharat; Jiang, Yueyang; Berkelhammer, Maxwell; Wharton, Sonia; Noone, David; Still, Christopher

2017-04-01

Characterizing and quantifying the processes that control terrestrial ecosystem exchanges of carbon and water are critical for understanding how forested ecosystems respond to a changing climate. A small but increasing number of studies has identified carbonyl sulfide (OCS) as a potential tracer of canopy photosynthesis and stomatal function. Here we present seasonal fluxes of OCS from a 60m tall old-growth temperate forest. An off-axis integrated cavity output spectroscopy analyzer (Los Gatos Research Inc.) was deployed at the Wind River Experimental Forest in Washington (45.8205°N, 121.9519°W) in 2014 and 2015. GPP (Gross Primary Production) is inferred from OCS fluxes and compared with estimates derived from measurements of NEE (Net Ecosystem Exchange) from eddy flux data as well as GPP predictions using a process based model. Our findings seek to resolve scientific questions regarding ecosystem carbon exchange from tall old growth forests, which have a complicated vertical leaf area structure, high above ground biomass and amount and aerial cover of epiphytic vegetation. Estimates of canopy conductance calculated using tower flux data are also combined with measurements of stable isotopologues of CO2 to infer emergent ecosystem properties such as canopy ci/ca and water use efficiency.

The transient behavior of whole-canopy fluxes during dynamic light conditions for midlatitude and tropical forests

NASA Astrophysics Data System (ADS)

Fitzjarrald, D. R.; Kivalov, S. N.

2017-12-01

Cloud shadows lead to alternating light and dark periods at the surface. Understanding how clouds affect whole-canopy fluxes suffer from two knowledge gaps that limit scaling from leaf to canopy scales, an effort currently done by assertion alone. First, there is a lack a clear quantitative definition of the incident light time series that occur on specific types of cloudy days. Second, the characteristic time scales for leaves to respond to for stomatal opening and closing is 1-10 minutes, a period too short to allow accurate eddy fluxes. We help to close the first gap by linking the durations of alternating light and dark periods statistically to conventional meteorological sky types at a midlatitude mixed deciduous forest (Harvard Forest, MA, USA: 42.53N, 72.17W) and in a tropical rain forest (Tapajós National Forest, Brazil; 2.86S, 54.96W). The second gap is narrowed by measuring the dynamic response whole canopy exchanges in the flux footprint at intervals of only a few seconds using the classical ensemble average method, keying on step changes in light intensity. Combining light and shadow periods of different lengths we estimate ensemble fluxes sensible heat (H), net ecosystem exchange (NEE), and latent heat (LE) fluxes initiated by abrupt radiation changes at intervals of 30 s over 20 minutes. We present composite results of the transient behavior of whole-canopy fluxes at each forest, showing distinct features of each forest type. Observed time constants and transient flux parameterizations are then used to force a simple model to yield NEE, LE, WUE, and Bowen ratio extrema under periodic shadow-light conditions and given cloud amount. We offer the hypothesis that, at least on certain types of cloudy days, the well-known correlation between diffuse light and WUE does not represent a causal connection at the canopy scale.

The Effect of Increased CO2 Mixing Ratio on Water Use Efficiency, Evapo-transpiration, Soil Moisture Content and Stem Flow in two Long-term Field Experiments

NASA Astrophysics Data System (ADS)

Drake, B.; Powell, T.; Li, J.; Hinkle, R.; Rasse, D.

2007-12-01

Stomatal opening in plant leaves control carbon and water exchange between vegetation and the atmosphere. Closure of these water-gates in response to increased atmospheric CO2 mixing ratio's, reduces transpiration under most laboratory and short term experimental conditions. Does this imply however, as atmospheric CO2 rises, and plant canopies expand, that evapo-transpiration (ETR), soil moisture content (SMC), and ecosystem water use efficiency (WUE) will increase? To test this question, field experiments have been and still are conducted using open top chambers. We have exposed native species in Florida Scrub to a carbon dioxide mixing ratio of nearly 700 ppmv CO2 for the past ten years and in Chesapeake Bay wetlands for 21 years. As a result of this treatment, in both ecosystems there was an increase in net ecosystem CO2 exchange and leaf area but a reduction of stomatal conductance, stem flow, transpiration, and ETR. For Florida scrub oak, these changes were also accompanied by an increase in soil moisture content as well.

An analytical model for the distribution of CO2 sources and sinks, fluxes, and mean concentration within the roughness sub-layer

NASA Astrophysics Data System (ADS)

Siqueira, M. B.; Katul, G. G.

2009-12-01

A one-dimensional analytical model that predicts foliage CO2 uptake rates, turbulent fluxes, and mean concentration throughout the roughness sub-layer (RSL), a layer that extends from the ground surface up to 5 times the canopy height (h), is proposed. The model combines the mean continuity equation for CO2 with first-order closure principles for turbulent fluxes and simplified physiological and radiative transfer schemes for foliage uptake. This combination results in a second-order ordinary differential equation in which it is imposed soil respiration (RE) as lower and CO2 concentration well above the RSL as upper boundary conditions. An inverse version of the model was tested against data sets from two contrasting ecosystems: a tropical forest (TF, h=40 m) and a managed irrigated rice canopy (RC, h=0.7 m) - with good agreement noted between modeled and measured mean CO2 concentration profiles within the entire RSL (see figure). Sensitivity analysis on the model parameters revealed a plausible scaling regime between them and a dimensionless parameter defined by the ratio between external (RE) and internal (stomatal conductance) characteristics controlling the CO2 exchange process. The model can be used to infer the thickness of the RSL for CO2 exchange, the inequality in zero-plane displacement between CO2 and momentum, and its consequences on modeled CO2 fluxes. A simplified version of the solution is well suited for being incorporated into large-scale climate models. Furthermore, the model framework here can be used to a priori estimate relative contributions from the soil surface and the atmosphere to canopy-air CO2 concentration thereby making it synergetic to stable isotopes studies. Panels a) and c): Profiles of normalized measured leaf area density distribution (a) for TF and RC, respectively. Continuous lines are the constant a used in the model and dashed lines represent data-derived profiles. Panels b) and d) are modeled and ensemble-averaged measured CO2 profiles reference to the uppermost measured point for TF and RC, respectively.

Difficulties with estimating city-wide urban forest cover change from national, remotely-sensed tree canopy maps

Treesearch

Jeffrey T. Walton

2008-01-01

Two datasets of percent urban tree canopy cover were compared. The first dataset was based on a 1991 AVHRR forest density map. The second was the US Geological Survey's National Land Cover Database (NLCD) 2001 sub-pixel tree canopy. A comparison of these two tree canopy layers was conducted in 36 census designated places of western New York State. Reference data...

Species-specific transpiration responses to intermediate disturbance in a northern hardwood forest: Transpiration response to disturbance

DOE PAGES

Matheny, Ashley M.; Bohrer, Gil; Vogel, Christoph S.; ...

2014-12-04

Intermediate disturbances shape forest structure and composition, which may in turn alter carbon, nitrogen, and water cycling. We used a large-scale experiment in a forest in northern lower Michigan where we prescribed an intermediate disturbance by stem girdling all canopy-dominant early successional trees to simulate an accelerated age-related senescence associated with natural succession.Using 3 years of eddy covariance and sap flux measurements in the disturbed area and an adjacent control plot, we analyzed disturbance-induced changes to plot level and species-specific transpiration and stomatal conductance. We found transpiration to be ~15% lower in disturbed plots than in unmanipulated control plots. However,more » species-specific responses to changes in microclimate varied. While red oak and white pine showed increases in stomatal conductance during post disturbance (62.5 and 132.2%, respectively), redmaple reduced stomatal conductance by 36.8%. We used the hysteresis between sap flux and vapor pressure deficit to quantify diurnal hydraulic stress incurred by each species in both plots. Red oak, a ring porousanisohydric species, demonstrated the largest mean relative hysteresis, while red maple, bigtooth aspen, andpaper birch, all diffuse porous species, had the lowest relative hysteresis. We employed the Penman-Monteithmodel for LE to demonstrate that these species-specific responses to disturbance are not well captured using current modeling strategies and that accounting for changes to leaf area index and plot microclimate are insufffcient to fully describe the effects of disturbance on transpiration.« less

Biochemical acclimation, stomatal limitation and precipitation patterns underlie decreases in photosynthetic stimulation of soybean (Glycine max) at elevated [CO₂] and temperatures under fully open air field conditions.

PubMed

Rosenthal, David M; Ruiz-Vera, Ursula M; Siebers, Matthew H; Gray, Sharon B; Bernacchi, Carl J; Ort, Donald R

2014-09-01

The net effect of elevated [CO2] and temperature on photosynthetic acclimation and plant productivity is poorly resolved. We assessed the effects of canopy warming and fully open air [CO2] enrichment on (1) the acclimation of two biochemical parameters that frequently limit photosynthesis (A), the maximum carboxylation capacity of Rubisco (Vc,max) and the maximum potential linear electron flux through photosystem II (Jmax), (2) the associated responses of leaf structural and chemical properties related to A, as well as (3) the stomatal limitation (l) imposed on A, for soybean over two growing seasons in a conventionally managed agricultural field in Illinois, USA. Acclimation to elevated [CO2] was consistent over two growing seasons with respect to Vc,max and Jmax. However, elevated temperature significantly decreased Jmax contributing to lower photosynthetic stimulation by elevated CO2. Large seasonal differences in precipitation altered soil moisture availability modulating the complex effects of elevated temperature and CO2 on biochemical and structural properties related to A. Elevated temperature also reduced the benefit of elevated [CO2] by eliminating decreases in stomatal limitation at elevated [CO2]. These results highlight the critical importance of considering multiple environmental factors (i.e. temperature, moisture, [CO2]) when trying to predict plant productivity in the context of climate change. Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.

Numerical Study on the Stomatal Responses to Dry-Hot Wind Episodes and Its Effects on Land-Atmosphere Interactions.

PubMed

Wang, Shu; Zheng, Hui; Liu, Shuhua; Miao, Yucong; Li, Jing

2016-01-01

The wheat production in midland China is under serious threat by frequent Dry-Hot Wind (DHW) episodes with high temperature, low moisture and specific wind as well as intensive heat transfer and evapotranspiration. The numerical simulations of these episodes are important for monitoring grain yield and estimating agricultural water demand. However, uncertainties still remain despite that enormous experiments and modeling studies have been conducted concerning this issue, due to either inaccurate synoptic situation derived from mesoscale weather models or unrealistic parameterizations of stomatal physiology in land surface models. Hereby, we investigated the synoptic characteristics of DHW with widely-used mesoscale model Weather Research and Forecasting (WRF) and the effects of leaf physiology on surface evapotranspiration by comparing two land surface models: The Noah land surface model, and Peking University Land Model (PKULM) with stomata processes included. Results show that the WRF model could well replicate the synoptic situations of DHW. Two types of DHW were identified: (1) prevailing heated dry wind stream forces the formation of DHW along with intense sensible heating and (2) dry adiabatic processes overflowing mountains. Under both situations, the PKULM can reasonably model the stomatal closure phenomena, which significantly decreases both evapotranspiration and net ecosystem exchange of canopy, while these phenomena cannot be resolved in the Noah simulations. Therefore, our findings suggest that the WRF-PKULM coupled method may be a more reliable tool to investigate and forecast DHW as well as be instructive to crop models.

Numerical Study on the Stomatal Responses to Dry-Hot Wind Episodes and Its Effects on Land-Atmosphere Interactions

PubMed Central

Zheng, Hui; Liu, Shuhua; Miao, Yucong; Li, Jing

2016-01-01

The wheat production in midland China is under serious threat by frequent Dry-Hot Wind (DHW) episodes with high temperature, low moisture and specific wind as well as intensive heat transfer and evapotranspiration. The numerical simulations of these episodes are important for monitoring grain yield and estimating agricultural water demand. However, uncertainties still remain despite that enormous experiments and modeling studies have been conducted concerning this issue, due to either inaccurate synoptic situation derived from mesoscale weather models or unrealistic parameterizations of stomatal physiology in land surface models. Hereby, we investigated the synoptic characteristics of DHW with widely-used mesoscale model Weather Research and Forecasting (WRF) and the effects of leaf physiology on surface evapotranspiration by comparing two land surface models: The Noah land surface model, and Peking University Land Model (PKULM) with stomata processes included. Results show that the WRF model could well replicate the synoptic situations of DHW. Two types of DHW were identified: (1) prevailing heated dry wind stream forces the formation of DHW along with intense sensible heating and (2) dry adiabatic processes overflowing mountains. Under both situations, the PKULM can reasonably model the stomatal closure phenomena, which significantly decreases both evapotranspiration and net ecosystem exchange of canopy, while these phenomena cannot be resolved in the Noah simulations. Therefore, our findings suggest that the WRF-PKULM coupled method may be a more reliable tool to investigate and forecast DHW as well as be instructive to crop models. PMID:27648943

Species-specific transpiration responses to intermediate disturbance in a northern hardwood forest

NASA Astrophysics Data System (ADS)

Matheny, Ashley M.; Bohrer, Gil; Vogel, Christoph S.; Morin, Timothy H.; He, Lingli; Frasson, Renato Prata de Moraes; Mirfenderesgi, Golnazalsadat; Schäfer, Karina V. R.; Gough, Christopher M.; Ivanov, Valeriy Y.; Curtis, Peter S.

2014-12-01

Intermediate disturbances shape forest structure and composition, which may in turn alter carbon, nitrogen, and water cycling. We used a large-scale experiment in a forest in northern lower Michigan where we prescribed an intermediate disturbance by stem girdling all canopy-dominant early successional trees to simulate an accelerated age-related senescence associated with natural succession. Using 3 years of eddy covariance and sap flux measurements in the disturbed area and an adjacent control plot, we analyzed disturbance-induced changes to plot level and species-specific transpiration and stomatal conductance. We found transpiration to be 15% lower in disturbed plots than in unmanipulated control plots. However, species-specific responses to changes in microclimate varied. While red oak and white pine showed increases in stomatal conductance during postdisturbance (62.5 and 132.2%, respectively), red maple reduced stomatal conductance by 36.8%. We used the hysteresis between sap flux and vapor pressure deficit to quantify diurnal hydraulic stress incurred by each species in both plots. Red oak, a ring porous anisohydric species, demonstrated the largest mean relative hysteresis, while red maple, bigtooth aspen, and paper birch, all diffuse porous species, had the lowest relative hysteresis. We employed the Penman-Monteith model for LE to demonstrate that these species-specific responses to disturbance are not well captured using current modeling strategies and that accounting for changes to leaf area index and plot microclimate are insufficient to fully describe the effects of disturbance on transpiration.

Separating foliar physiology from morphology reveals the relative roles of vertically structured transpiration factors within red maple crowns and limitations of larger scale models

PubMed Central

Bauerle, William L.; Bowden, Joseph D.

2011-01-01

A spatially explicit mechanistic model, MAESTRA, was used to separate key parameters affecting transpiration to provide insights into the most influential parameters for accurate predictions of within-crown and within-canopy transpiration. Once validated among Acer rubrum L. genotypes, model responses to different parameterization scenarios were scaled up to stand transpiration (expressed per unit leaf area) to assess how transpiration might be affected by the spatial distribution of foliage properties. For example, when physiological differences were accounted for, differences in leaf width among A. rubrum L. genotypes resulted in a 25% difference in transpiration. An in silico within-canopy sensitivity analysis was conducted over the range of genotype parameter variation observed and under different climate forcing conditions. The analysis revealed that seven of 16 leaf traits had a ≥5% impact on transpiration predictions. Under sparse foliage conditions, comparisons of the present findings with previous studies were in agreement that parameters such as the maximum Rubisco-limited rate of photosynthesis can explain ∼20% of the variability in predicted transpiration. However, the spatial analysis shows how such parameters can decrease or change in importance below the uppermost canopy layer. Alternatively, model sensitivity to leaf width and minimum stomatal conductance was continuous along a vertical canopy depth profile. Foremost, transpiration sensitivity to an observed range of morphological and physiological parameters is examined and the spatial sensitivity of transpiration model predictions to vertical variations in microclimate and foliage density is identified to reduce the uncertainty of current transpiration predictions. PMID:21617246

Plant hydraulic controls over ecosystem responses to climate-enhanced disturbances

NASA Astrophysics Data System (ADS)

Mackay, D. S.; Ewers, B. E.; Reed, D. E.; Pendall, E.; McDowell, N. G.

2012-12-01

Climate-enhanced disturbances such as drought and insect infestation range in severity, contributing minor to severe stress to forests including forest mortality. While neither form of disturbance has been unambiguously implicated as a mechanism of mortality, both induce changes in water, carbon, and nutrient cycling that are key to understanding forest ecosystem response to, and recovery from, disturbance. Each disturbance type has different biophysical, ecohydrological, and biogeochemical signatures that potentially complicate interpretation and development of theory. Plant hydraulic function is arguably a unifying control over these responses to disturbance because it regulates stomatal conductance, leaf biochemistry, carbon (C) uptake and utilization, and nutrient cycling. We demonstrated this idea by focusing on water and C, including non-structural (NSC), resources, and nitrogen (N) uptake across a spectrum of forest ecosystems (e.g., northern temperate mixed forests, lodgepole pine forests in the Rocky Mountains, and pinon pine - juniper woodlands in New Mexico) using the Terrestrial Regional Ecosystem Exchange Simulator (TREES). TREES is grounded in the biophysics of water movement through soil and plants, respectively via hydraulic conductivity of the soil and cavitation of xylem. It combines this dynamic plant hydraulic conductance with canopy biochemical controls over photosynthesis, and the dynamics of structural and non-structural carbon through a carbon budget that responds to plant hydraulic status. As such, the model can be used to develop testable hypotheses on a multitude of disturbance and recovery responses including xylem dysfunction, stomatal and non-stomatal controls on photosynthesis and carbon allocation, respiration, and allocation to defense compounds. For each of the ecosystems we constrained and evaluated the model with allometry, sap flux and/or eddy covariance data, leaf gas exchange measurements, and vulnerability to cavitation data. Disturbances included declining water tables and canopy defoliators (northern temperature forests), bark beetles and associated blue-stain fungi (coniferous forests), and prolonged drought with bark beetles (semi-arid woodland). We show that C dynamics in trees that experience water-limitation, insect attack, or a combination of both disturbance types cannot be explained solely from hydraulic status or NSC, but are better explained by a combination of both in conjunction with N uptake. Results show that the use of plant hydraulics can yield parsimonious explanations of biophysical, ecohydrological, and biogeochemical responses to disturbance.

Improved infiltration series for studying stomatal opening as illustrated with coffee

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

Alvim, P.deT.; Havis, J.R.

1956-01-01

Very satisfactory results have been obtained in estimation of the degree of stomatal opening of several plant species by using infiltration series prepared with Nujol mineral oil diluted with xylol, kerosene, n-dodecane, n-tetradecane, or Bayol-D. All of these materials, except Nujol, infiltrate the leaves when the stomata are only slightly open. Nujol does not penetrate even wide open stomata, except for plants with particularly large stomata. The results with coffee plants show that leaves exposed to direct sunlight decreased their stomatal aperture during periods of strong illumination in the middle of the day (more than about 8000 fc). 9 references,more » 2 figures.« less

The hydraulic limitation hypothesis revisited.

PubMed

Ryan, Michael G; Phillips, Nathan; Bond, Barbara J

2006-03-01

We proposed the hydraulic limitation hypothesis (HLH) as a mechanism to explain universal patterns in tree height, and tree and stand biomass growth: height growth slows down as trees grow taller, maximum height is lower for trees of the same species on resource-poor sites and annual wood production declines after canopy closure for even-aged forests. Our review of 51 studies that measured one or more of the components necessary for testing the hypothesis showed that taller trees differ physiologically from shorter, younger trees. Stomatal conductance to water vapour (g(s)), photosynthesis (A) and leaf-specific hydraulic conductance (K L) are often, but not always, lower in taller trees. Additionally, leaf mass per area is often greater in taller trees, and leaf area:sapwood area ratio changes with tree height. We conclude that hydraulic limitation of gas exchange with increasing tree size is common, but not universal. Where hydraulic limitations to A do occur, no evidence supports the original expectation that hydraulic limitation of carbon assimilation is sufficient to explain observed declines in wood production. Any limit to height or height growth does not appear to be related to the so-called age-related decline in wood production of forests after canopy closure. Future work on this problem should explicitly link leaf or canopy gas exchange with tree and stand growth, and consider a more fundamental assumption: whether tree biomass growth is limited by carbon availability.

The functional dependence of canopy conductance on water vapor pressure deficit revisited

NASA Astrophysics Data System (ADS)

Fuchs, Marcel; Stanghellini, Cecilia

2018-03-01

Current research seeking to relate between ambient water vapor deficit (D) and foliage conductance (g F ) derives a canopy conductance (g W ) from measured transpiration by inverting the coupled transpiration model to yield g W = m - n ln(D) where m and n are fitting parameters. In contrast, this paper demonstrates that the relation between coupled g W and D is g W = AP/D + B, where P is the barometric pressure, A is the radiative term, and B is the convective term coefficient of the Penman-Monteith equation. A and B are functions of g F and of meteorological parameters but are mathematically independent of D. Keeping A and B constant implies constancy of g F . With these premises, the derived g W is a hyperbolic function of D resembling the logarithmic expression, in contradiction with the pre-set constancy of g F . Calculations with random inputs that ensure independence between g F and D reproduce published experimental scatter plots that display a dependence between g W and D in contradiction with the premises. For this reason, the dependence of g W on D is a computational artifact unrelated to any real effect of ambient humidity on stomatal aperture and closure. Data collected in a maize field confirm the inadequacy of the logarithmic function to quantify the relation between canopy conductance and vapor pressure deficit.

Vegetative and Atmospheric Controls on the Bouchet-Morton Complementary Relationship Hypothesis

NASA Astrophysics Data System (ADS)

Pettijohn, J. C.; Salvucci, G. D.; Phillips, N. G.; Daley, M. J.

2006-12-01

The Bouchet-Morton Complementary Relationship (CR) hypothesis is a potentially-powerful analytic tool to help understand the feedback between evapotranspiring land surfaces and the atmospheric boundary layer (ABL), and how potential evaporation reflects this coupling on multiple time and length scales. In spite of advances in our ability to measure and model these processes, the heuristic CR hypothesis remains an unsolved, first-order problem. The leading theoretical models, i.e., Morton, Granger, and Szilagyi, of the coupled land surface atmosphere mechanisms responsible for CR focus primarily on vertical humidity (vapor pressure) profiles while assuming that vegetative and/or atmospheric diffusivities play an insignificant role in regulating CR. Further, whereas Granger and Szilagyi assume almost opposite vertical temperature profile boundary conditions, both derivations appear to validate CR. Contrary to these multiple working hypotheses' assumptions, our recent CR evaluation of 147 days (1987-1989) at the FIFE temperate grassland discovered that canopy conductance was an essential forcing variable in complementarity, and thus improved CR in application when included in the definition of potential evaporation. To isolate the exact forcing mechanisms of canopy and ABL conductances to complementarity, we evaluated CR in a mixed-deciduous forest at Harvard Forest (summers 2005-2006) by comparing daily averaged water-stressed (non-irrigated, regionally stressed soil moisture) and water-unstressed (irrigated, `potential') transpiration. Root-zone soil moisture of a red maple (Acer rubrum L.) sample set was elevated using a pulse-irrigation system. Whole-tree transpiration of the `potential` (water-unstressed) and a reference (water-stressed) set of maples was monitored at high frequency using heat-dissipation Granier-type sap flux sensors. To isolate physiological and/or atmospheric forcing of CR, we estimated isothermal Penman-Monteith transpiration models of both irrigated and non-irrigated time series using a Jarvis type multiplicative stress model of scaled canopy conductance to water vapor transport. Poorly-constrained model parameters (e.g., environmental stress boundary conditions) were estimated using a grid search routine; further, parameter confidence limits were inferred using bootstrap replacement sampling. Preliminary results suggest the following: (1) the absence of an unstressed canopy conductance in the Penman equation results in violation of fundamental CR assumptions (similar to FIFE); and (2) unlimited root-zone water availability does not reduce the leaf-level stomatal resistance enough to yield complementarity, i.e., the typical CR potential signal is also a function of other environmental stresses, e.g., vapor pressure deficit. In summary, our results yield valuable insight into the role of vertical atmospheric and vegetative conductances in CR.

Relationships between SAP-flow measurements, whole-canopy transpiration and reference evapotranspiration in field-grown papaya (Carica papaya L.)

USDA-ARS?s Scientific Manuscript database

Whole-canopy gas exchange measurement in papaya can provide a scientific basis to optimize irrigation, and fruit yield and quality. The objectives of this study were to: 1) verify the relationship between xylem sap flow measured by the heat coefficient method and whole canopy transpiration in ‘Gra...

[Comparison of growth and field microclimate characteristics of broomcorn millet under different fertilization conditions].

PubMed

Zhang, Pan-pan; Zhou, Yu; Song, Hui; Qiao, Zhi-jun; Wang, Hai-gang; Zheng, Dian-feng; Feng, Bai-li

2015-02-01

A field experiment with two broomcorn millet varieties Longmi 8 (strong drought-resistant variety) and Jinmi 4 (drought-sensitive variety) was conducted to compare their differences in growth, field microclimate and photosynthetic capacity from anthesis to maturity under different fertility conditions. The results showed that, fertilization decreased canopy temperature, air temperature, soil temperature, illumination, but improved the relative humidity among broomcorn millet plants compared with the non-fertilization treatment. With an increase of the fertilizer level, the plant height, SPAD, LAI, net photosynthetic rate, transpiration rate, stomatal conductance, intercellular CO2 concentration in broomcorn millet showed an increasing trend, which of the high fertilization treatment were 9.2%, 15.1%, 56.6%, 17.8%, 24.6%, 14.2%, 29.7% higher than those of non-fertilization treatment, respectively. Compared with Jinmi 4, Longmi 8 showed a cold wet characteristic, with lower canopy temperature, air temperature, soil temperature; illumination, and higher plant height, LAI, SPAD and relative humidity during grain filling. Moreover, each photosynthetic index of Longmi 8 slowly decreased and extended the period of leaf photosynthetic function so as to accumulate more photosynthetic products.

A Testbed for Model Development

NASA Astrophysics Data System (ADS)

Berry, J. A.; Van der Tol, C.; Kornfeld, A.

2014-12-01

Carbon cycle and land-surface models used in global simulations need to be computationally efficient and have a high standard of software engineering. These models also make a number of scaling assumptions to simplify the representation of complex biochemical and structural properties of ecosystems. This makes it difficult to use these models to test new ideas for parameterizations or to evaluate scaling assumptions. The stripped down nature of these models also makes it difficult to "connect" with current disciplinary research which tends to be focused on much more nuanced topics than can be included in the models. In our opinion/experience this indicates the need for another type of model that can more faithfully represent the complexity ecosystems and which has the flexibility to change or interchange parameterizations and to run optimization codes for calibration. We have used the SCOPE (Soil Canopy Observation, Photochemistry and Energy fluxes) model in this way to develop, calibrate, and test parameterizations for solar induced chlorophyll fluorescence, OCS exchange and stomatal parameterizations at the canopy scale. Examples of the data sets and procedures used to develop and test new parameterizations are presented.

The Effects of Fine-scale Soil Moisture and Canopy Heterogeneities on Energy and Soil Water Fluxes in a Temperate Mixed Deciduous Forest

NASA Astrophysics Data System (ADS)

He, L.; Ivanov, V. Y.; Bohrer, G.; Maurer, K.; Vogel, C. S.; Moghaddam, M.

2011-12-01

Vegetation is heterogeneous at different scales, influencing spatially variable energy and water exchanges between land-surface and atmosphere. Current land surface parameterizations of large-scale models consider spatial variability at a scale of a few kilometers and treat vegetation cover as aggregated patches with uniform properties. However, the coupling mechanisms between fine-scale soil moisture, vegetation, and energy fluxes such as evapotranspiration are strongly nonlinear; the aggregation of surface variations may produce biased energy fluxes. This study aims to improve the understanding of the scale impact in atmosphere-biosphere-hydrosphere interactions, which affects predictive capabilities of land surface models. The study uses a high-resolution, physically-based ecohydrological model tRIBS + VEGGIE as a data integration tool to upscale the heterogeneity of canopy distribution resolved at a few meters to the watershed scale. The study was carried out for a spatially heterogeneous, temperate mixed forest environment of Northern Michigan located near the University of Michigan Biological Station (UMBS). Energy and soil water dynamics were simulated at the tree-canopy resolution in the horizontal plane for a small domain (~2 sq. km) located within a footprint of the AmeriFlux tower. A variety of observational data were used to constrain and confirm the model, including a 3-m profile continuous soil moisture dataset and energy flux data (measured at the AmeriFlux tower footprint). A scenario with a spatially uniform canopy, corresponding to the commonly used 'big-leaf' scheme in land surface parameterizations was used to infer the effects of coarse-scale averaging. To gain insights on how heterogeneous canopy and soil moisture interact and contribute to the domain-averaged transpiration, several scenarios of tree-scale leaf area and soil moisture spatial variability were designed. Specifically, for the same mean states, the scenarios of variability of canopy biomass account for the spatial distribution of photosynthesis (and thus the stomatal resistance), the aerodynamic and leaf boundary layer resistances as well as the differential radiation forcing due to tall tree exposure and lateral shading of short trees. The numerical experiments show that by transpiring spatially varying amounts of water, heterogeneous canopies adjust the spatial soil water state to the scaled inverse of the canopy biomass regardless of the initial moisture state. Such a spatial distribution can be further wiped out because of the differential water stress. The aggregation of canopy-scale atmosphere-biosphere-hydrosphere interactions demonstrates non-linear relationship between soil moisture and evapotranspiration, influencing domain-averaged energy fluxes.

Impacts of prescribed fire on Pinus rigida Mill. in upland forests of the Atlantic Coastal Plain.

PubMed

Carlo, Nicholas J; Renninger, Heidi J; Clark, Kenneth L; Schäfer, Karina V R

2016-08-01

A comparative analysis of the impacts of prescribed fire on three upland forest stands in the Northeastern Atlantic Plain, NJ, USA, was conducted. Effects of prescribed fire on water use and gas exchange of overstory pines were estimated via sap-flux rates and photosynthetic measurements on Pinus rigida Mill. Each study site had two sap-flux plots, one experiencing prescribed fire and one control (unburned) plot for comparison before and after the fire. We found that photosynthetic capacity in terms of Rubisco-limited carboxylation rate and intrinsic water-use efficiency was unaffected, while light compensation point and dark respiration rate were significantly lower in the burned vs control plots post-fire. Furthermore, quantum yield in pines in the pine-dominated stands was less affected than pines in the mixed oak/pine stand, as there was an increase in quantum yield in the oak/pine stand post-fire compared with the control (unburned) plot. We attribute this to an effect of forest type but not fire per se. Average daily sap-flux rates of the pine trees increased compared with control (unburned) plots in pine-dominated stands and decreased in the oak/pine stand compared with control (unburned) plots, potentially due to differences in fuel consumption and pre-fire sap-flux rates. Finally, when reference canopy stomatal conductance was analyzed, pines in the pine-dominated stands were more sensitive to changes in vapor pressure deficit (VPD), while stomatal responses of pines in the oak/pine stand were less affected by VPD. Therefore, prescribed fire affects physiological functioning and water use of pines, but the effects may be modulated by forest stand type and fuel consumption pattern, which suggests that these factors may need to be taken into account for forest management in fire-dominated systems. © The Author 2016. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Stomatal control and hydraulic conductance, with special reference to tall trees.

PubMed

Franks, Peter J

2004-08-01

A better understanding of the mechanistic basis of stomatal control is necessary to understand why modes of stomatal response differ among individual trees, and to improve the theoretical foundation for predictive models and manipulative experiments. Current understanding of the mechanistic basis of stomatal control is reviewed here and discussed in relation to the plant hydraulic system. Analysis focused on: (1) the relative role of hydraulic conductance in the vicinity of the stomatal apparatus versus whole-plant hydraulic conductance; (2) the influence of guard cell inflation characteristics and the mechanical interaction between guard cells and epidermal cells; and (3) the system requirements for moderate versus dramatic reductions in stomatal conductance with increasing evaporation potential. Special consideration was given to the potential effect of changes in hydraulic properties as trees grow taller. Stomatal control of leaf gas exchange is coupled to the entire plant hydraulic system and the basis of this coupling is the interdependence of guard cell water potential and transpiration rate. This hydraulic feedback loop is always present, but its dynamic properties may be altered by growth or cavitation-induced changes in hydraulic conductance, and may vary with genetically related differences in hydraulic conductances. Mechanistic models should include this feedback loop. Plants vary in their ability to control transpiration rate sufficiently to maintain constant leaf water potential. Limited control may be achieved through the hydraulic feedback loop alone, but for tighter control, an additional element linking transpiration rate to guard cell osmotic pressure may be needed.

Concurrent CO2 and COS fluxes across major biomes in Europe

NASA Astrophysics Data System (ADS)

Spielmann, Felix M.; Kitz, Florian; Hammerle, Albin; Gerdel, Katharina; Ibrom, Andreas; Kolle, Olaf; Migliavacca, Mirco; Moreno, Gerardo; Noe, Steffen M.; Wohlfahrt, Georg

2017-04-01

The trace gas carbonyl sulfide (COS) has been proposed as a tracer for canopy gross primary production (GPP), canopy transpiration and stomatal conductance of plant canopies in the last few years. COS enters the plant leaf through the stomata and diffuses through the intercellular space, the cell wall, the plasma membrane and the cytosol like carbon dioxide (CO2). It is then catalyzed by the enzyme carbonic anhydrase in a one-way reaction to hydrogen sulfide and CO2. This one-way flux into the leaf makes COS a promising tracer for the GPP. However, this approach assumes that the ratio of the deposition velocities between COS and CO2 is constant, which must be determined in field experiments covering a wide variety of ecosystems. The overarching objective of this study was to quantify the relationship between the ecosystem-scale exchange of COS and CO2 and thus, to test for the potential of COS to be used as a universal tracer for the plant canopy CO2 exchange. Between spring 2015 and summer 2016 we set up our quantum cascade laser at different field sites across Europe. These sites included a managed temperate mountain grassland (AUT), a savanna (ESP), a temperate beech forest (DEN) and a hemiboreal forest (EST). On each of these sites, we conducted ecosystem scale eddy covariance and soil chamber measurements. Since the soil COS flux contribution, especially in grass dominated ecosystems, could not be neglected, we had to derive the actual canopy COS fluxes for all the measurement sites. Using these fluxes we compared the ecosystem relative uptake (ERU) of the sites and searched for factors affecting its variability. We then used the influential factors to scale the ERU to be comparable under different field sites and conditions. Furthermore we also calculated the GPP using conventional CO2 flux partitioning and compared the results with the approach of using the leaf relative uptake.

Towards physiologically meaningful water-use efficiency estimates from eddy covariance data.

PubMed

Knauer, Jürgen; Zaehle, Sönke; Medlyn, Belinda E; Reichstein, Markus; Williams, Christopher A; Migliavacca, Mirco; De Kauwe, Martin G; Werner, Christiane; Keitel, Claudia; Kolari, Pasi; Limousin, Jean-Marc; Linderson, Maj-Lena

2018-02-01

Intrinsic water-use efficiency (iWUE) characterizes the physiological control on the simultaneous exchange of water and carbon dioxide in terrestrial ecosystems. Knowledge of iWUE is commonly gained from leaf-level gas exchange measurements, which are inevitably restricted in their spatial and temporal coverage. Flux measurements based on the eddy covariance (EC) technique can overcome these limitations, as they provide continuous and long-term records of carbon and water fluxes at the ecosystem scale. However, vegetation gas exchange parameters derived from EC data are subject to scale-dependent and method-specific uncertainties that compromise their ecophysiological interpretation as well as their comparability among ecosystems and across spatial scales. Here, we use estimates of canopy conductance and gross primary productivity (GPP) derived from EC data to calculate a measure of iWUE (G 1 , "stomatal slope") at the ecosystem level at six sites comprising tropical, Mediterranean, temperate, and boreal forests. We assess the following six mechanisms potentially causing discrepancies between leaf and ecosystem-level estimates of G 1 : (i) non-transpirational water fluxes; (ii) aerodynamic conductance; (iii) meteorological deviations between measurement height and canopy surface; (iv) energy balance non-closure; (v) uncertainties in net ecosystem exchange partitioning; and (vi) physiological within-canopy gradients. Our results demonstrate that an unclosed energy balance caused the largest uncertainties, in particular if it was associated with erroneous latent heat flux estimates. The effect of aerodynamic conductance on G 1 was sufficiently captured with a simple representation. G 1 was found to be less sensitive to meteorological deviations between canopy surface and measurement height and, given that data are appropriately filtered, to non-transpirational water fluxes. Uncertainties in the derived GPP and physiological within-canopy gradients and their implications for parameter estimates at leaf and ecosystem level are discussed. Our results highlight the importance of adequately considering the sources of uncertainty outlined here when EC-derived water-use efficiency is interpreted in an ecophysiological context. © 2017 John Wiley & Sons Ltd.

Ozone decreases soybean productivity and water use efficiency

NASA Astrophysics Data System (ADS)

Betzelberger, A. M.; VanLoocke, A. D.; Ainsworth, E. A.; Bernacchi, C. J.

2011-12-01

The combination of population growth and climate change will increase pressure on agricultural and water resources throughout this century. An additional consequence of this growth is an increase in anthropogenic emissions that lead to the formation of tropospheric ozone (O3), which in concert with climate change, poses a significant threat to human health and nutrition. In addition to being an important greenhouse gas, O3 reduces plant productivity, an effect that has been particularly pronounced in soybean, which provides over half of the world's oilseed production. Plant productivity is linked to feedbacks in the climate system, indirectly through the carbon cycle, as well as directly through the partitioning of radiation into heat and moisture fluxes. Soybean, along with maize, comprises the largest ecosystem in the contiguous U.S. Therefore, changes in productivity and water use under increasing O3 could impact human nutrition as well as the regional climate. Soybean response to increasing O3 concentrations was tested under open-air agricultural conditions at the SoyFACE research site. During the 2009 growing season, eight 20 m diameter FACE plots were exposed to different O3 concentrations, ranging from 40 to 200 ppb. Canopy growth (leaf area index) and physiological measurements of leaf photosynthesis and stomatal conductance were taken regularly throughout the growing season. Canopy fluxes of heat and moisture were measured using the residual energy balance micrometeorological technique. Our results indicate that as O3 increased from 40 to 200 ppb, rates of photosynthesis and stomatal conductance decreased significantly. Further, the seed yield decreased by over 60%, while water use decreased by 30% and the water-use-efficiency (yield/water-use) declined by 50%. The growing season average canopy temperatures increased by 1°C and midday temperatures increased by 2°C compared to the control. Warmer and drier canopies may result in a positive feedback on O3 as temperature and humidity affect the production/destruction rate of O3. In order to broaden these experimental results, time series modeling is being used to evaluate the historical statistical relationship between soybean production and tropospheric O3 variations at the regional level. A multiple linear regression approach is being taken to understand the effects that O3 has had on soybean yields in Illinois, Iowa, and Indiana over the past 30 years. By combining county yield data with EPA and NASA O3 data, and controlling for variation in temperature and moisture, the O3-exposure relationship for the Midwestern U.S. will be determined. Together, these results indicate the critical need to understand the response of other crops to O3 and to put in place policies that mitigate the emissions of O3 precursors.

Plant chlorophyll fluorescence: active and passive measurements at canopy and leaf scales with different nitrogen treatments

PubMed Central

Cendrero-Mateo, M. Pilar; Moran, M. Susan; Papuga, Shirley A.; Thorp, K.R.; Alonso, L.; Moreno, J.; Ponce-Campos, G.; Rascher, U.; Wang, G.

2016-01-01

Most studies assessing chlorophyll fluorescence (ChlF) have examined leaf responses to environmental stress conditions using active techniques. Alternatively, passive techniques are able to measure ChlF at both leaf and canopy scales. However, the measurement principles of both techniques are different, and only a few datasets concerning the relationships between them are reported in the literature. In this study, we investigated the potential for interchanging ChlF measurements using active techniques with passive measurements at different temporal and spatial scales. The ultimate objective was to determine the limits within which active and passive techniques are comparable. The results presented in this study showed that active and passive measurements were highly correlated over the growing season across nitrogen treatments at both canopy and leaf-average scale. At the single-leaf scale, the seasonal relation between techniques was weaker, but still significant. The variability within single-leaf measurements was largely related to leaf heterogeneity associated with variations in CO2 assimilation and stomatal conductance, and less so to variations in leaf chlorophyll content, leaf size or measurement inputs (e.g. light reflected and emitted by the leaf and illumination conditions and leaf spectrum). This uncertainty was exacerbated when single-leaf analysis was limited to a particular day rather than the entire season. We concluded that daily measurements of active and passive ChlF at the single-leaf scale are not comparable. However, canopy and leaf-average active measurements can be used to better understand the daily and seasonal behaviour of passive ChlF measurements. In turn, this can be used to better estimate plant photosynthetic capacity and therefore to provide improved information for crop management. PMID:26482242

Variable conductivity and embolism in roots, trunks and branches of tree species growing under future atmospheric CO2 concentration (DUKE FACE site): impacts on whole-plant hydraulic performance and carbon assimilation

NASA Astrophysics Data System (ADS)

domec, J.; Palmroth, S.; Oren, R.; Johnson, D. M.; Ward, E. J.; McCulloh, K.; Gonzalez, C.; Warren, J.

2013-12-01

Anatomical and physiological acclimation to water stress of the tree hydraulic system involves tradeoffs between maintenance of stomatal conductance and loss of hydraulic conductivity, with short-term impacts on photosynthesis and long-term consequences to survival and growth. Here we study the role of variations in root, trunk and branch maximum hydraulic specific conductivity (Ks-max) under high and low soil moisture in determining whole-tree hydraulic conductance (Ktree) and in mediating stomatal control of gas exchange in loblolly pine trees growing under ambient and elevated CO2 (CO2a and CO2e). We hypothesized that Ktree would adjust to CO2e, through an increase in root and branch Ks-max in response to anatomical adjustments. Embolism in roots explained the loss of Ktree and therefore indirectly constituted a hydraulic signal involved in stomatal regulation and in the reduction of canopy conductance and carbon assimilation. Across roots, trunk and branches, the increase in Ks-max was associated with a decrease resistance to drought, a consequence of structural acclimation such as larger conduits and lower wood density. In loblolly pine, higher xylem dysfunction under CO2e might impact tree performance in a future climate when increased evaporative demand could cause a greater loss of hydraulic function. The results contributed to our knowledge of the physiological and morphological mechanisms underpinning the responses of tree species to drought and more generally to global change.

Coupling gross primary production and transpiration for a consistent estimate of canopy water use efficiency

NASA Astrophysics Data System (ADS)

Yebra, Marta; van Dijk, Albert

2015-04-01

Water use efficiency (WUE, the amount of transpiration or evapotranspiration per unit gross (GPP) or net CO2 uptake) is key in all areas of plant production and forest management applications. Therefore, mutually consistent estimates of GPP and transpiration are needed to analysed WUE without introducing any artefacts that might arise by combining independently derived GPP and ET estimates. GPP and transpiration are physiologically linked at ecosystem level by the canopy conductance (Gc). Estimates of Gc can be obtained by scaling stomatal conductance (Kelliher et al. 1995) or inferred from ecosystem level measurements of gas exchange (Baldocchi et al., 2008). To derive large-scale or indeed global estimates of Gc, satellite remote sensing based methods are needed. In a previous study, we used water vapour flux estimates derived from eddy covariance flux tower measurements at 16 Fluxnet sites world-wide to develop a method to estimate Gc using MODIS reflectance observations (Yebra et al. 2013). We combined those estimates with the Penman-Monteith combination equation to derive transpiration (T). The resulting T estimates compared favourably with flux tower estimates (R2=0.82, RMSE=29.8 W m-2). Moreover, the method allowed a single parameterisation for all land cover types, which avoids artefacts resulting from land cover classification. In subsequent research (Yebra et al, in preparation) we used the same satellite-derived Gc values within a process-based but simple canopy GPP model to constrain GPP predictions. The developed model uses a 'big-leaf' description of the plant canopy to estimate the mean GPP flux as the lesser of a conductance-limited and radiation-limited GPP rate. The conductance-limited rate was derived assuming that transport of CO2 from the bulk air to the intercellular leaf space is limited by molecular diffusion through the stomata. The radiation-limited rate was estimated assuming that it is proportional to the absorbed photosynthetically active radiation (PAR), calculated as the product of the fraction of absorbed PAR (fPAR) and PAR flux. The proposed algorithm performs well when evaluated against flux tower GPP (R2=0.79, RMSE= 1.93 µmol m2 s-1). Here we use GPP and T estimates previously derived at the same 16 Fluxnet sites to analyse WUE. Satellite-derived WUE explained variation in (long-term average) WUE among plant functional types but evergreen needleleaf had higher WUE than predicted. The benefit of our approach is that it uses mutually consistent estimates of GPP and T to derive canopy-level WUE without any land cover classification artefacts. References Baldocchi, D. (2008). Turner Review No. 15: 'Breathing' of the terrestrial biosphere: lessons learned from a global network of carbon dioxide flux measurement systems. Australian Journal of Botany, 56, 26 Kelliher, F.M., Leuning, R., Raupach, M.R., & Schulze, E.D. (1995). Maximum conductances for evaporation from global vegetation types. Agricultural and Forest Meteorology, 73, 1-16 Yebra, M., Van Dijk, A., Leuning, R., Huete, A., & Guerschman, J.P. (2013). Evaluation of optical remote sensing to estimate actual evapotranspiration and canopy conductance. Remote Sensing of Environment, 129, 250-261

Islands in the Sky: Ecophysiological Cloud-Vegetation Linkages in Southern Appalachian Mountain Cloud Forests

NASA Astrophysics Data System (ADS)

Reinhardt, K.; Emanuel, R. E.; Johnson, D. M.

2013-12-01

Mountain cloud forest (MCF) ecosystems are characterized by a high frequency of cloud fog, with vegetation enshrouded in fog. The altitudinal boundaries of cloud-fog zones co-occur with conspicuous, sharp vegetation ecotones between MCF- and non-MCF-vegetation. This suggests linkages between cloud-fog and vegetation physiology and ecosystem functioning. However, very few studies have provided a mechanistic explanation for the sharp changes in vegetation communities, or how (if) cloud-fog and vegetation are linked. We investigated ecophysiological linkages between clouds and trees in Southern Appalachian spruce-fir MCF. These refugial forests occur in only six mountain-top, sky-island populations, and are immersed in clouds on up to 80% of all growing season days. Our fundamental research questions was: How are cloud-fog and cloud-forest trees linked? We measured microclimate and physiology of canopy tree species across a range of sky conditions (cloud immersed, partly cloudy, sunny). Measurements included: 1) sunlight intensity and spectral quality; 2) carbon gain and photosynthetic capacity at leaf (gas exchange) and ecosystem (eddy covariance) scales; and 3) relative limitations to carbon gain (biochemical, stomatal, hydraulic). RESULTS: 1) Midday sunlight intensity ranged from very dark (<30 μmol m-2 s-1, under cloud-immersed conditions) to very bright (>2500 μmol m-2 s-1), and was highly variable on minute-to-minute timescales whenever clouds were present in the sky. Clouds and cloud-fog increased the proportion of blue-light wavelengths 5-15% compared to sunny conditions, and altered blue:red and red:far red ratios, both of which have been shown to strongly affect stomatal functioning. 2) Cloud-fog resulted in ~50% decreased carbon gain at leaf and ecosystem scales, due to sunlight levels below photosynthetic light-saturation-points. However, greenhouse studies and light-response-curve analyses demonstrated that MCF tree species have low light-compensation points (can photosynthesize even at low light levels), and maximum photosynthesis occurs during high-light, diffuse-light conditions such as occurs during diffuse 'sunflecks' inside the cloud fog. Additionally, the capacity to respond to brief, intermittent sunflecks ('photosynthetic induction', e.g., time to maximum photosynthesis) was high in our MCF species. 3) Data quantifying limitations to photosynthesis were contradictory, underscoring complex relationships among photosynthesis, light, carbon and water relations. While stomatal response to atmospheric moisture demand was sensitive (e.g., 80% drop in stomatal conductance in a <1 kPa drop in vapor-pressure-deficit in conifer species), stem xylem hydraulic conductivity suggested strong drought tolerance capabilities. CONCLUSIONS: Clouds and cloud-fog exert strong influence on canopy-tree and ecosystem carbon relations. MCF are dynamic light environments. In these highly variable but ultimately light-limited ecosystems, vegetation must be able to both fix carbon when cloudy and dark but also be able to capitalize on saturating sunlight when possible.

Constraining Ecosystem Gross Primary Production and Transpiration with Measurements of Photosynthetic 13CO2 Discrimination

NASA Astrophysics Data System (ADS)

Blonquist, J. M.; Wingate, L.; Ogeé, J.; Bowling, D. R.

2011-12-01

The stable carbon isotope composition of atmospheric CO2 (δ13Ca) can provide useful information on water use efficiency (WUE) dynamics of terrestrial ecosystems and potentially constrain models of CO2 and water fluxes at the land surface. This is due to the leaf-level relationship between photosynthetic 13CO2 discrimination (Δ), which influences δ13Ca, and the ratio of leaf intercellular to atmospheric CO2 mole fractions (Ci / Ca), which is related to WUE and is determined by the balance between C assimilation (CO2 demand) and stomatal conductance (CO2 supply). We used branch-scale Δ derived from tunable diode laser absorption spectroscopy measurements collected in a Maritime pine forest to estimate Ci / Ca variations over an entire growing season. We combined Ci / Ca estimates with rates of gross primary production (GPP) derived from eddy covariance (EC) to estimate canopy-scale stomatal conductance (Gs) and transpiration (T). Estimates of T were highly correlated to T estimates derived from sapflow data (y = 1.22x + 0.08; r2 = 0.61; slope P < 0.001) and T predictions from an ecosystem model (MuSICA) (y = 0.88x - 0.05; r2 = 0.64; slope P < 0.001). As an alternative to estimating T, Δ measurements can be used to estimate GPP by combining Ci / Ca estimates with Gs estimates from sapflow data. Estimates of GPP were determined in this fashion and were highly correlated to GPP values derived from EC (y = 0.82 + 0.07; r2 = 0.61; slope P < 0.001) and GPP predictions from MuSICA (y = 1.10 + 0.42; r2 = 0.50; slope P < 0.001). Results demonstrate that the leaf-level relationship between Δ and Ci / Ca can be extended to the canopy-scale and that Δ measurements have utility for partitioning ecosystem-scale CO2 and water fluxes.

Modeling the interaction between plant canopies and the planetary boundary layer using a new 1D multi-layer soil- vegetation-atmosphere transfer (SVAT) scheme combined with a non-local turbulence closure model

NASA Astrophysics Data System (ADS)

Yetzer, Kenneth H.

A new one-dimensional (1D) soil-vegetation-atmospheric transport (SVAT) scheme is coupled to a nonlocal turbulence closure model in order to simulate the interactions between a forested canopy and the planetary boundary layer. The SVAT consists of mechanistic models for both physiological (photosynthesis, stomatal conductance and soil/root and bole respiration) and micrometeorological (radiative transfer and surface energy exchanges) processes. The turbulence closure model is a first-order, nonlocal turbulence closure called transilient turbulence theory (Stull, 1993; Inclan et al., 1995) which includes the effects of form drag, wake turbulence, and interference to vertical mixing by the plant elements. The submodel that accounts for radiative transfer inside the forest has been taken from Norman (1979) and Baldocchi (1989). It includes the effect of varying mean leaf inclination angle with height and it also accounts for leaf clumping The photosynthesis submodel is taken from Nikolov and others (1995). It accounts for both differences between shaded and sunlit leaves and the variation of photosynthetic capacity with height. The model was tested with data obtained from a deciduous forest in Pennsylvania. The results show reasonable agreement with the observations. They also demonstrate the model's ability to simulate phenomena that is characteristic of tall canopies like forests, including counter gradient-fluxes and local wind speed maxima in the trunk space.

Effects of CO2 Concentration on Leaf Photosynthesis and Stomatal Conductance of Potatoes Grown Under Different Irradiance Levels and Photoperiods

NASA Technical Reports Server (NTRS)

Wheeler, R. M.; Fitzpatrick, A. H.; Tibbitts, T. W.

2012-01-01

Potato (Solanum tuberosum L.) cvs. Russet Burbank, Denali, and Norland, were grown in environmental rooms controlled at approx 350 micro mol/mol (ambient during years 1987/1988) and 1000 micro mol/mol (enriched) CO2 concentrations. Plants and electric lamps were arranged to provide two irradiance zones, 400 and 800 micro mol/mol/square m/S PPF and studies were repeated using two photoperiods (12-h light / 12-h dark and continuous light). Leaf photosynthetic rates and leaf stomatal conductance were measured using fully expanded, upper canopy leaves at weekly intervals throughout growth (21 through 84 days after transplanting). Increasing the CO2 from approx 350 to 1000 micro mol/mol under the 12-h photoperiod increased leaf photosynthetic rates by 39% at 400 micro mol/mol/square m/S PPF and 27% at 800 micro mol/mol/square m/S PPF. Increasing the CO2 from approx 350 to 1000 micro mol/mol under continuous light decreased leaf photosynthetic rates by 7% at 400 micro mol/mol/square m/S PPF and 13% at 800 micro mol/mol/square m/S PPF. Increasing the CO2 from approx 350 to 1000 micro mol/mol under the 12-h photoperiod plants decreased stomatal conductance by an average of 26% at 400 micro mol/mol/square m/S PPF and 42% at 800 micro mol/mol/square m/S PPF. Under continuous light, CO2 enrichment resulted in a small increase (2%) of stomatal conductance at 400 micro mol/mol/square m/S PPF, and a small decrease (3%) at 800 micro mol/mol/square m/S PPF. Results indicate that CO2 enrichment under the 12-h photoperiod showed the expected increase in photosynthesis and decrease in stomatal conductance for a C3 species like potato, but the decreases in leaf photosynthetic rates and minimal effect on conductance from CO2 enrichment under continuous light were not expected. The plant leaves under continuous light showed more chlorosis and some rusty flecking versus plants under the 12-h photoperiod, suggesting the continuous light was more stressful on the plants. The increased rates of leaf photosynthesis with increased CO2 concentration paralleled trends in biomass production (published previously) but were not proportional to the biomass yields.

The Role of Vegetation Response to Elevated CO2 in Modifying Land-Atmosphere Feedback Across the Central United States Agro-Ecosystem

NASA Astrophysics Data System (ADS)

Drewry, D.; Kumar, P.; Sivapalan, M.; Long, S.; Liang, X.

2009-05-01

Recent local-scale observational studies have demonstrated significant modifications to the partitioning of incident energy by two key mid-west agricultural species, soy and corn, as ambient atmospheric CO2 concentrations are experimentally augmented to projected future levels. The uptake of CO2 by soy, which utilizes the C3 photosynthetic pathway, has likewise been observed to significantly increase under elevated growth CO2 concentrations. Changes to the sensible and latent heat exchanges between the land surface and the atmospheric boundary layer (ABL) across large portions of the mid-western US has the potential to affect ABL growth and composition, and consequently feed-back to the near-surface environment (air temperature and vapor content) experienced by the vegetation. Here we present a simulation analysis that examines the changes in land-atmosphere feedbacks associated with projected increases in ambient CO2 concentrations over extended soy/corn agricultural areas characteristic of the US mid-west. The model canopies are partitioned into several layers, allowing for resolution of the shortwave and longwave radiation regimes that drive photosynthesis, stomatal conductance and leaf energy balance in each layer, along with the canopy microclimate. The canopy component of the model is coupled to a multi-layer soil-root model that computes soil moisture and heat transport and root water uptake. Model skill in capturing the sub-diurnal variability in canopy-atmosphere exchange is evaluated through multi-year records of canopy-top eddy covariance CO2, water vapor and heat fluxes collected at the Bondville (Illinois) FluxNet site. An evaluation of the ability of the model to simulate observed changes in energy balance components (canopy temperature, net radiation and soil heat flux) under elevated CO2 concentrations projected for 2050 (550 ppm) is made using observations collected at the SoyFACE Free Air Carbon Enrichment (FACE) experimental facilities located in central Illinois, by incorporating observed acclimations in leaf biochemsitry and canopy structure. The simulation control volume is then extended by coupling the canopy models to a simple model of daytime mixed-layer (ML) growth and composition, ie. air temperature and vapor content. Through this coupled canopy-ABL model we quantify the impact of elevated CO2 and vegetation acclimation on ML growth, temperature and vapor content and the consequent feedbacks to the land surface by way of the near-surface environment experienced by the vegetation. Particular focus is placed on the role of short-term drought, and possible changes in land cover composition between soy, a C3 crop, and corn, a more water-use efficient C4 crop, on modulating the strength of these CO2-induced feedbacks.

A low-cost infrared thermometry system for use in research and production agriculture

USDA-ARS?s Scientific Manuscript database

Plant canopy temperature is used in many studies of plant/environment interactions. Non-contact measurement of plant canopy temperature is often accomplished through the use of radiometric surface thermometers commonly referred to as infrared thermometers. Industrial-quality infrared thermocouples a...

Thinning effect on photosynthesis depends on needle ages in a Chinese fir (Cunninghamia lanceolata) plantation.

PubMed

Li, Ren-Shan; Yang, Qing-Peng; Zhang, Wei-Dong; Zheng, Wen-Hui; Chi, Yong-Gang; Xu, Ming; Fang, Yun-Ting; Gessler, Arthur; Li, Mai-He; Wang, Si-Long

2017-02-15

Canopies in evergreen coniferous plantations often consist of various-aged needles. However, the effect of needle age on the photosynthetic responses to thinning remains ambiguous. Photosynthetic responses of different-aged needles to thinning were investigated in a Chinese fir (Cunninghamia lanceolata) plantation. A dual isotope approach [simultaneous measurements of stable carbon (δ 13 C) and oxygen (δ 18 O) isotopes] was employed to distinguish between biochemical and stomatal limitations to photosynthesis. Our results showed that increases in net photosynthesis rates upon thinning only occurred in the current-year and one-year-old needles, and not in the two- to four-year-old needles. The increased δ 13 C and declined δ 18 O in current year needles of trees from thinned stands indicated that both the photosynthetic capacity and stomatal conductance resulted in increasing photosynthesis. In one-year-old needles of trees from thinned stands, an increased needle δ 13 C and a constant needle δ 18 O were observed, indicating the photosynthetic capacity rather than stomatal conductance contributed to the increasing photosynthesis. The higher water-soluble nitrogen content in current-year and one-year-old needles in thinned trees also supported that the photosynthetic capacity plays an important role in the enhancement of photosynthesis. In contrast, the δ 13 C, δ 18 O and water-soluble nitrogen in the two- to four-year-old needles were not significantly different between the control and thinned trees. Thus, the thinning effect on photosynthesis depends on needle age in a Chinese fir plantation. Our results highlight that the different responses of different-aged needles to thinning have to be taken into account for understanding and modelling ecosystem responses to management, especially under the expected environmental changes in future. Copyright © 2016 Elsevier B.V. All rights reserved.

Soil Moisture (SMAP) and Vapor Pressure Deficit Controls on Evaporative Fraction over the Continental U.S.

NASA Astrophysics Data System (ADS)

Salvucci, G.; Rigden, A. J.; Gianotti, D.; Entekhabi, D.

2017-12-01

We analyze the control over evapotranspiration (ET) imposed by soil moisture limitations and stomatal closure due to vapor pressure deficit (VPD) across the United States using estimates of satellite-derived soil moisture from SMAP and a meteorological, data-driven ET estimate over a two year period at over 1000 locations. The ET data are developed independent of soil moisture using the emergent relationship between the diurnal cycle of the relative humidity profile and ET based on ETRHEQ (Salvucci and Gentine (2013), PNAS, 110(16): 6287-6291, Rigden and Salvucci, 2015, WRR, 51(4): 2951-2973; Rigden and Salvucci, 2017, GCB, 23(3) 1140-1151). The key advantage of using this approach to estimate ET is that no measurements of surface limiting factors (soil moisture, leaf area, canopy conductance) are required; instead, ET is estimated from only meteorological data. The combination of these two independent datasets allows for a unique spatial analysis of the control on ET imposed by the availability of soil moisture vs. VPD. Spatial patterns of limitations are inferred by fitting the ETRHEQ-inferred surface conductance to a weighted sum of a Jarvis type stomatal conductance model and bare soil evaporation conductance model, with separate moisture-dependent evaporation efficiency relations for bare soil and vegetation. Spatial patterns are visualized by mapping the optimal curve fitting coefficients and by conducting sensitivity analyses of the resulting fitted model across the Unites States. Results indicate regional variations in rate-limiting factors, and suggest that in some areas the VPD effect on stomatal closure is strong enough to induce a decrease in ET under projected climate change, despite an increase in atmospheric drying (and thus evaporative demand).

Overproduction of Abscisic Acid in Tomato Increases Transpiration Efficiency and Root Hydraulic Conductivity and Influences Leaf Expansion1[OA

PubMed Central

Thompson, Andrew J.; Andrews, John; Mulholland, Barry J.; McKee, John M.T.; Hilton, Howard W.; Horridge, Jon S.; Farquhar, Graham D.; Smeeton, Rachel C.; Smillie, Ian R.A.; Black, Colin R.; Taylor, Ian B.

2007-01-01

Overexpression of genes that respond to drought stress is a seemingly attractive approach for improving drought resistance in crops. However, the consequences for both water-use efficiency and productivity must be considered if agronomic utility is sought. Here, we characterize two tomato (Solanum lycopersicum) lines (sp12 and sp5) that overexpress a gene encoding 9-cis-epoxycarotenoid dioxygenase, the enzyme that catalyzes a key rate-limiting step in abscisic acid (ABA) biosynthesis. Both lines contained more ABA than the wild type, with sp5 accumulating more than sp12. Both had higher transpiration efficiency because of their lower stomatal conductance, as demonstrated by increases in δ13C and δ18O, and also by gravimetric and gas-exchange methods. They also had greater root hydraulic conductivity. Under well-watered glasshouse conditions, mature sp5 plants were found to have a shoot biomass equal to the wild type despite their lower assimilation rate per unit leaf area. These plants also had longer petioles, larger leaf area, increased specific leaf area, and reduced leaf epinasty. When exposed to root-zone water deficits, line sp12 showed an increase in xylem ABA concentration and a reduction in stomatal conductance to the same final levels as the wild type, but from a different basal level. Indeed, the main difference between the high ABA plants and the wild type was their performance under well-watered conditions: the former conserved soil water by limiting maximum stomatal conductance per unit leaf area, but also, at least in the case of sp5, developed a canopy more suited to light interception, maximizing assimilation per plant, possibly due to improved turgor or suppression of epinasty. PMID:17277097

Environmental controls on sap flow in a northern hardwood forest.

PubMed

Bovard, B D; Curtis, P S; Vogel, C S; Su, H-B; Schmid, H P

2005-01-01

Our objective was to gain a detailed understanding of how photosynthetically active radiation (PAR), vapor pressure deficit (D) and soil water interact to control transpiration in the dominant canopy species of a mixed hardwood forest in northern Lower Michigan. An improved understanding of how these environmental factors affect whole-tree water use in unmanaged ecosystems is necessary in assessing the consequences of climate change on the terrestrial water cycle. We used continuously heated sap flow sensors to measure transpiration in mature trees of four species during two successive drought events. The measurements were scaled to the stand level for comparison with eddy covariance estimates of ecosystem water flux (Fw). Photosynthetically active radiation and D together explained 82% of the daytime hourly variation in plot-level transpiration, and low soil water content generally resulted in increased stomatal sensitivity to increasing D. There were also species-specific responses to drought. Quercus rubra L. showed low water use during both dry and wet conditions, and during periods of high D. Among the study species, Acer rubrum L. showed the greatest degree of stomatal closure in response to low soil water availability. Moderate increases in stomatal sensitivity to D during dry periods were observed in Populus grandidentata Michx. and Betula papyrifera Marsh. Sap flow scaled to the plot level and Fw demonstrated similar temporal patterns of water loss suggesting that the mechanisms controlling sap flow of an individual tree also control ecosystem evapotranspiration. However, the absolute magnitude of scaled sap flow estimates was consistently lower than Fw. We conclude that species-specific responses to PAR, D and soil water content are key elements to understanding current and future water fluxes in this ecosystem.

The Effect of Drought on Stomatal Conductance in the Biosphere 2 Rainforest

NASA Astrophysics Data System (ADS)

Gay, J. D.; Van Haren, J. L. M.

2015-12-01

Drought is a major climate change concern for the Earth's rainforests; however little is currently known about how these forests and individual plants will respond to water stress. At the individual level, the ability of plants to regulate their stomatal conductance is an important preservation mechanism that helps to cool leaves, regulate water loss, and uptake carbon dioxide. At the ecosystem level, transpiration in rainforests is a major contributor to the positive feedback loop that returns moisture to the atmosphere for continued precipitation cycles. Nearly 60% of atmospheric moisture in the Amazon rain forests has been traced back to origins of transpiration from its plants. In relation to current climatic conditions, stomatal conductance rates are highly variable across rainforest species and environmental conditions. It is still unknown to what extent these rates will decrease at leaf and forest level in response to periods of drought. The University of Arizona's Biosphere 2 (B2) served as the study site for a simulated 4-week long drought because of its ability to mimic the micrometeorology of an Amazonian rainforest. Three species of plants were chosen at various levels in the canopy: Clitoria racemosa, Cissus sicyoides, and Hibiscus elatus. These plants were selected based on their relative abundance and distribution in the B2 forest. It was revealed that two out of the three species exhibited decreases in H20 efflux at each elevation, while one species (C. racemosa) proved much more resistant, at each elevation, to H20 loss. These results may be useful for future integrative modeling of how individual leaf level responses extend to entire ecosystem scales. It will be important to better understand how rainforests conserve, recycle, and lose water to gauge their response to warming climate, and increased periods of drought in the tropics.

Overproduction of abscisic acid in tomato increases transpiration efficiency and root hydraulic conductivity and influences leaf expansion.

PubMed

Thompson, Andrew J; Andrews, John; Mulholland, Barry J; McKee, John M T; Hilton, Howard W; Horridge, Jon S; Farquhar, Graham D; Smeeton, Rachel C; Smillie, Ian R A; Black, Colin R; Taylor, Ian B

2007-04-01

Overexpression of genes that respond to drought stress is a seemingly attractive approach for improving drought resistance in crops. However, the consequences for both water-use efficiency and productivity must be considered if agronomic utility is sought. Here, we characterize two tomato (Solanum lycopersicum) lines (sp12 and sp5) that overexpress a gene encoding 9-cis-epoxycarotenoid dioxygenase, the enzyme that catalyzes a key rate-limiting step in abscisic acid (ABA) biosynthesis. Both lines contained more ABA than the wild type, with sp5 accumulating more than sp12. Both had higher transpiration efficiency because of their lower stomatal conductance, as demonstrated by increases in delta(13)C and delta(18)O, and also by gravimetric and gas-exchange methods. They also had greater root hydraulic conductivity. Under well-watered glasshouse conditions, mature sp5 plants were found to have a shoot biomass equal to the wild type despite their lower assimilation rate per unit leaf area. These plants also had longer petioles, larger leaf area, increased specific leaf area, and reduced leaf epinasty. When exposed to root-zone water deficits, line sp12 showed an increase in xylem ABA concentration and a reduction in stomatal conductance to the same final levels as the wild type, but from a different basal level. Indeed, the main difference between the high ABA plants and the wild type was their performance under well-watered conditions: the former conserved soil water by limiting maximum stomatal conductance per unit leaf area, but also, at least in the case of sp5, developed a canopy more suited to light interception, maximizing assimilation per plant, possibly due to improved turgor or suppression of epinasty.

A New Approach to Extract Forest Water Use Efficiency from Eddy Covariance Data

NASA Astrophysics Data System (ADS)

Scanlon, T. M.; Sulman, B. N.

2016-12-01

Determination of forest water use efficiency (WUE) from eddy covariance data typically involves the following steps: (a) estimating gross primary productivity (GPP) from direct measurements of net ecosystem exchange (NEE) by extrapolating nighttime ecosystem respiration (ER) to daytime conditions, and (b) assuming direct evaporation (E) is minimal several days after rainfall, meaning that direct measurements of evapotranspiration (ET) are identical to transpiration (T). Both of these steps could lead to errors in the estimation of forest WUE. Here, we present a theoretical approach for estimating WUE through the analysis of standard eddy covariance data, which circumvents these steps. Only five statistics are needed from the high-frequency time series to extract WUE: CO2 flux, water vapor flux, standard deviation in CO2 concentration, standard deviation in water vapor concentration, and the correlation coefficient between CO2 and water vapor concentration for each half-hour period. The approach is based on the assumption that stomatal fluxes (i.e. photosynthesis and transpiration) lead to perfectly negative correlations and non-stomatal fluxes (i.e. ecosystem respiration and direct evaporation) lead to perfectly positive correlations within the CO2 and water vapor high frequency time series measured above forest canopies. A mathematical framework is presented, followed by a proof of concept using eddy covariance data and leaf-level measurements of WUE.

Seasonal change in CO2 and H2O exchange between grassland and atmosphere

NASA Astrophysics Data System (ADS)

Saigusa, N.; Liu, S.; Oikawa, T.; Watanabe, T.

1996-03-01

The seasonal change in CO2 flux over an artificial grassland was analyzed from the ecological and meteorological point of view. This grassland contains C3 and C4 plants; the three dominant species belonging to the Gramineae; Festuca elatior (C3) dominated in early spring, and Imperata cylindrica (C4) and Andropogon virginicus (C4) grew during early summer and became dominant in mid-summer. CO2 flux was measured by the gradient method, and the routinely observed data for the surface-heat budget were used to analyze the CO2 and H2O exchange between the grassland and atmosphere. From August to October in 1993, CO2 flux was reduced to around half under the same solar-radiation conditions, while H2O flux decreased 20% during the same period. The monthly values of water use efficiency, i.e., ratio of CO2 flux to H2O flux decreased from 5.8 to 3.3 mg CO2/g H2O from August to October, the Bowen ratio increased from 0.20 to 0.30, and the ratio of the bulk latent heat transfer coefficient CE to the sensible heat transfer coefficient CH was maintained around 0.40-0.50. The increase in the Bowen ratio was explained by the decrease in air temperature from 22.3 °C in August to 16.6 °C in October without considering biological effects such as stomatal closure on the individual leaves. The nearly constant CE/CH ratios suggested that the contribution ratio of canopy resistance to aerodynamic resistance did not change markedly, although the meteorological conditions changed seasonally. The decrease in the water use efficiency, however, suggested that the photosynthetic rate decreased for individual leaves from August to October under the same radiation conditions. Diurnal variations of CO2 exchange were simulated by the multi-layer canopy model taking into account the differences in the stomatal conductance and photosynthetic pathway between C3 and C4 plants. The results suggested that C4 plants played a major role in the CO2 exchange in August, the contribution of C4 plants decreased in September, and daily variations of CO2 exchange were mainly due to C3 plants in October. The results also suggested that the decrease in the net canopy CO2 exchange from August to October was induced partly by the decrease of net photosynthesis on the individual leaves in both C4 and C3 plants, which could be due to aging of the leaves.

Hydraulics and gas exchange recover more rapidly from severe drought stress in small pot-grown grapevines than in field-grown plants.

PubMed

Romero, Pascual; Botía, Pablo; Keller, Markus

2017-09-01

Modifications of plant hydraulics and shoot resistances (R shoot ) induced by water withholding followed by rewatering, and their relationships with plant water status, leaf gas exchange and water use efficiency at the leaf level, were investigated in pot-grown and field-grown, own-rooted Syrah grapevines in an arid climate. Water stress induced anisohydric behavior, gradually reducing stomatal conductance (g s ) and leaf photosynthesis (A) in response to decreasing midday stem water potential (Ψ s ). Water stress also rapidly increased intrinsic water-use efficiency (A/g s ); this effect persisted for many days after rewatering. Whole-plant (K plant ), canopy (K canopy ), shoot (K shoot ) and leaf (K leaf ) hydraulic conductances decreased during water stress, in tune with the gradual decrease in Ψ s , leaf gas exchange and whole plant water use. Water-stressed vines also had a lower Ψ gradient between stem and leaf (ΔΨ l ), which was correlated with lower leaf transpiration rate (E). E and ΔΨ l increased with increasing vapour pressure deficit (VPD) in non-stressed control vines but not in stressed vines. Perfusion of xylem-mobile dye showed that water flow to petioles and leaves was substantially reduced or even stopped under moderate and severe drought stress. Leaf blade hydraulic resistance accounted for most of the total shoot resistance. However, hydraulic conductance of the whole root system (K root ) was not significantly reduced until water stress became very severe in pot-grown vines. Significant correlations between K plant , K canopy and Ψ s , K canopy and leaf gas exchange, K leaf and Ψ s , and K leaf and A support a link between water supply, leaf water status and gas exchange. Upon re-watering, Ψ s recovered faster than gas exchange and leaf-shoot hydraulics. A gradual recovery of hydraulic functionality of plant organs was also observed, the leaves being the last to recover after rewatering. In pot-grown vines, K canopy recovered rather quickly following restoration of Ψ s , although gas exchange recovery did not directly depend on recovery of K canopy . In field-grown vines, recovery of water status, gas exchange and hydraulic functionality was slower than in pot-grown plants, and low g s after rewatering was related to sustained decreased K plant , K canopy and K shoot and lower water transport to leaves. These results suggest that caution should be exercised when scaling up conclusions from experiments with small pot-grown plants to field conditions. Copyright © 2017 Elsevier GmbH. All rights reserved.

Analysis of Grassland Ecosystem Physiology at Multiple Scales Using Eddy Covariance, Stable Isotope and Remote Sensing Techniques

NASA Astrophysics Data System (ADS)

Flanagan, L. B.; Geske, N.; Emrick, C.; Johnson, B. G.

2006-12-01

Grassland ecosystems typically exhibit very large annual fluctuations in above-ground biomass production and net ecosystem productivity (NEP). Eddy covariance flux measurements, plant stable isotope analyses, and canopy spectral reflectance techniques have been applied to study environmental constraints on grassland ecosystem productivity and the acclimation responses of the ecosystem at a site near Lethbridge, Alberta, Canada. We have observed substantial interannual variation in grassland productivity during 1999-2005. In addition, there was a strong correlation between peak above-ground biomass production and NEP calculated from eddy covariance measurements. Interannual variation in NEP was strongly controlled by the total amount of precipitation received during the growing season (April-August). We also observed significant positive correlations between a multivariate ENSO index and total growing season precipitation, and between the ENSO index and annual NEP values. This suggested that a significant fraction of the annual variability in grassland productivity was associated with ENSO during 1999-2005. Grassland productivity varies asymmetrically in response to changes in precipitation with increases in productivity during wet years being much more pronounced than reductions during dry years. Strong increases in plant water-use efficiency, based on carbon and oxygen stable isotope analyses, contribute to the resilience of productivity during times of drought. Within a growing season increased stomatal limitation of photosynthesis, associated with improved water-use efficiency, resulted in apparent shifts in leaf xanthophyll cycle pigments and changes to the Photochemical Reflectance Index (PRI) calculated from hyper-spectral reflectance measurements conducted at the canopy-scale. These shifts in PRI were apparent before seasonal drought caused significant reductions in leaf area index (LAI) and changes to canopy-scale "greenness" based on NDVI values. With further progression of the seasonal drought, LAI and canopy-scale NDVI also declined in strong correlation. In addition, we have observed strong correlation between NDVI calculated from canopy-scale reflectance measurements and NDVI determined by MODIS. Continued reflectance measurements will help to understand and document the response of the grassland to seasonal and annual environmental change.

Reduced plant water status under sub-ambient pCO2 limits plant productivity in the wild progenitors of C3 and C4 cereals

PubMed Central

Cunniff, Jennifer; Charles, Michael; Jones, Glynis; Osborne, Colin P.

2016-01-01

Background and Aims The reduction of plant productivity by low atmospheric CO2 partial pressure (pCO2) during the last glacial period is proposed as a limiting factor for the establishment of agriculture. Supporting this hypothesis, previous work has shown that glacial pCO2 limits biomass in the wild progenitors of C3 and C4 founder crops, in part due to the direct effects of glacial pCO2 on photosynthesis. Here, we investigate the indirect role of pCO2 mediated via water status, hypothesizing that faster soil water depletion at glacial (18 Pa) compared to post-glacial (27 Pa) pCO2, due to greater stomatal conductance, feeds back to limit photosynthesis during drying cycles. Methods We grew four wild progenitors of C3 and C4 crops at glacial and post-glacial pCO2 and investigated physiological changes in gas exchange, canopy transpiration, soil water content and water potential between regular watering events. Growth parameters including leaf area were measured. Key Results Initial transpiration rates were higher at glacial pCO2 due to greater stomatal conductance. However, stomatal conductance declined more rapidly over the soil drying cycle in glacial pCO2 and was associated with decreased intercellular pCO2 and lower photosynthesis. Soil water content was similar between pCO2 levels as larger leaf areas at post-glacial pCO2 offset the slower depletion of water. Instead the feedback could be linked to reduced plant water status. Particularly in the C4 plants, soil–leaf water potential gradients were greater at 18 Pa compared with 27 Pa pCO2, suggesting an increased ratio of leaf evaporative demand to supply. Conclusions Reduced plant water status appeared to cause a negative feedback on stomatal aperture in plants at glacial pCO2, thereby reducing photosynthesis. The effects were stronger in C4 species, providing a mechanism for reduced biomass at 18 Pa. These results have added significance when set against the drier climate of the glacial period. PMID:27578764

Quantification of ozone exposure- and stomatal uptake-yield response relationships for soybean in Northeast China.

PubMed

Zhang, Weiwei; Feng, Zhaozhong; Wang, Xiaoke; Liu, Xiaobing; Hu, Enzhu

2017-12-01

High ground-level O 3 is a new threat to agricultural production in Northeast China with the increasing ambient O 3 concentration. Little is known about its impacts on soybean production in this key agricultural region. Accumulated O 3 exposure-response and stomatal O 3 flux-response relationships were developed during two continuous growing seasons to evaluate O 3 -induced yield reduction of four typical soybean cultivars in Northeast China. Results showed that critical levels of AOT40 (accumulated hourly O 3 concentrations over a threshold of 40nmol·mol -1 ), SUM06 (sum of all hourly average O 3 concentrations over 0.06μmol·mol -1 ) and W126 (sum of O 3 concentrations weighted by a sigmoidal function) in relation to 5% reduction in relative seed yield were 4.2, 7.6 and 6.8μmol·mol -1 ·h, respectively. The effect of O 3 on plants was influenced by leaf position in canopy. An improved Jarvis stomatal conductance model including leaf (node) position fitted well with field measurements. The best linear relationship between stomatal O 3 flux and relative soybean yield was obtained when phytotoxic ozone dose was integrated over a threshold of 9.6nmol·m -2 ·s -1 (POD 9.6 ) to represent the detoxification capacity of soybean. POD 9.6 and the commonly used POD 6 in relation to 5% reduction in relative seed yield of soybean were 0.9mmol·m -2 and 1.8mmol·m -2 , respectively. O 3 concentrations above ~38nmol·mol -1 contributed to POD 9.6 and caused seed yield loss in soybean. Current annual yield loss of soybean at ambient O 3 was estimated to range between 23.4% and 30.2%. The O 3 dose-response relationships and corresponding thresholds obtained here will benefit regional O 3 risk assessment on soybean production in Northeast China. Copyright © 2017 Elsevier B.V. All rights reserved.

A 3-D functional-structural grapevine model that couples the dynamics of water transport with leaf gas exchange.

PubMed

Zhu, Junqi; Dai, Zhanwu; Vivin, Philippe; Gambetta, Gregory A; Henke, Michael; Peccoux, Anthony; Ollat, Nathalie; Delrot, Serge

2017-12-23

Predicting both plant water status and leaf gas exchange under various environmental conditions is essential for anticipating the effects of climate change on plant growth and productivity. This study developed a functional-structural grapevine model which combines a mechanistic understanding of stomatal function and photosynthesis at the leaf level (i.e. extended Farqhuhar-von Caemmerer-Berry model) and the dynamics of water transport from soil to individual leaves (i.e. Tardieu-Davies model). The model included novel features that account for the effects of xylem embolism (fPLC) on leaf hydraulic conductance and residual stomatal conductance (g0), variable root and leaf hydraulic conductance, and the microclimate of individual organs. The model was calibrated with detailed datasets of leaf photosynthesis, leaf water potential, xylem sap abscisic acid (ABA) concentration and hourly whole-plant transpiration observed within a soil drying period, and validated with independent datasets of whole-plant transpiration under both well-watered and water-stressed conditions. The model well captured the effects of radiation, temperature, CO2 and vapour pressure deficit on leaf photosynthesis, transpiration, stomatal conductance and leaf water potential, and correctly reproduced the diurnal pattern and decline of water flux within the soil drying period. In silico analyses revealed that decreases in g0 with increasing fPLC were essential to avoid unrealistic drops in leaf water potential under severe water stress. Additionally, by varying the hydraulic conductance along the pathway (e.g. root and leaves) and changing the sensitivity of stomatal conductance to ABA and leaf water potential, the model can produce different water use behaviours (i.e. iso- and anisohydric). The robust performance of this model allows for modelling climate effects from individual plants to fields, and for modelling plants with complex, non-homogenous canopies. In addition, the model provides a basis for future modelling efforts aimed at describing the physiology and growth of individual organs in relation to water status. © The Author(s) 2017. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

Nitrogen-addition effects on leaf traits and photosynthetic carbon gain of boreal forest understory shrubs.

PubMed

Palmroth, Sari; Bach, Lisbet Holm; Nordin, Annika; Palmqvist, Kristin

2014-06-01

Boreal coniferous forests are characterized by fairly open canopies where understory vegetation is an important component of ecosystem C and N cycling. We used an ecophysiological approach to study the effects of N additions on uptake and partitioning of C and N in two dominant understory shrubs: deciduous Vaccinium myrtillus in a Picea abies stand and evergreen Vaccinium vitis-idaea in a Pinus sylvestris stand in northern Sweden. N was added to these stands for 16 and 8 years, respectively, at rates of 0, 12.5, and 50 kg N ha(-1) year(-1). N addition at the highest rate increased foliar N and chlorophyll concentrations in both understory species. Canopy cover of P. abies also increased, decreasing light availability and leaf mass per area of V. myrtillus. Among leaves of either shrub, foliar N content did not explain variation in light-saturated CO2 exchange rates. Instead photosynthetic capacity varied with stomatal conductance possibly reflecting plant hydraulic properties and within-site variation in water availability. Moreover, likely due to increased shading under P. abies and due to water limitations in the sandy soil under P. sylvestris, individuals of the two shrubs did not increase their biomass or shift their allocation between above- and belowground parts in response to N additions. Altogether, our results indicate that the understory shrubs in these systems show little response to N additions in terms of photosynthetic physiology or growth and that changes in their performance are mostly associated with responses of the tree canopy.

75 FR 32185 - Government-Owned Inventions; Availability for Licensing

Federal Register 2010, 2011, 2012, 2013, 2014

2010-06-07

...: Stuart R. Maudsley et al. (NIA). Patent Status: HHS Reference No. E-143-2010/0--Research Tool. Patent... grilles are moved or accessed. The canopy has an added benefit of reducing heating or cooling loss which.... Also, the canopy controls leakage of heating and cooling, reducing loads on the central building...

Using canopy resistance for infrared heater control when warming open-field plots

USDA-ARS?s Scientific Manuscript database

Several research groups are using or planning to use arrays of infrared heaters to simulate global warming in open-field plots with a control strategy that involves maintaining a constant rise in canopy temperatures of the heated plots above those of un-heated Reference plots. . However, if the warm...

The Use of Sun Elevation Angle for Stereogrammetric Boreal Forest Height in Open Canopies

NASA Technical Reports Server (NTRS)

Montesano, Paul M.; Neigh, Christopher; Sun, Guoqing; Duncanson, Laura Innice; Van Den Hoek, Jamon; Ranson, Kenneth Jon

2017-01-01

Stereogrammetry applied to globally available high resolution spaceborne imagery (HRSI; less than 5 m spatial resolution) yields fine-scaled digital surface models (DSMs) of elevation. These DSMs may represent elevations that range from the ground to the vegetation canopy surface, are produced from stereoscopic image pairs (stereo pairs) that have a variety of acquisition characteristics, and have been coupled with lidar data of forest structure and ground surface elevation to examine forest height. This work explores surface elevations from HRSI DSMs derived from two types of acquisitions in open canopy forests. We (1) apply an automated mass-production stereogrammetry workflow to along-track HRSI stereo pairs, (2) identify multiple spatially coincident DSMs whose stereo pairs were acquired under different solar geometry, (3) vertically co-register these DSMs using coincident spaceborne lidar footprints (from ICESat-GLAS) as reference, and(4) examine differences in surface elevations between the reference lidar and the co-registered HRSI DSMs associated with two general types of acquisitions (DSM types) from different sun elevation angles. We find that these DSM types, distinguished by sun elevation angle at the time of stereo pair acquisition, are associated with different surface elevations estimated from automated stereogrammetry in open canopy forests. For DSM values with corresponding reference ground surface elevation from spaceborne lidar footprints in open canopy northern Siberian Larix forests with slopes less than10, our results show that HRSI DSM acquired with sun elevation angles greater than 35deg and less than 25deg (during snow-free conditions) produced characteristic and consistently distinct distributions of elevation differences from reference lidar. The former include DSMs of near-ground surfaces with root mean square errors less than 0.68 m relative to lidar. The latter, particularly those with angles less than 10deg, show distributions with larger differences from lidar that are associated with open canopy forests whose vegetation surface elevations are captured. Terrain aspect did not have a strong effect on the distribution of vegetation surfaces. Using the two DSM types together, the distribution of DSM-differenced heights in forests (6.0 m, sigma = 1.4 m) was consistent with the distribution of plot-level mean tree heights (6.5m, sigma = 1.2 m). We conclude that the variation in sun elevation angle at time of stereo pair acquisition can create illumination conditions conducive for capturing elevations of surfaces either near the ground or associated with vegetation canopy. Knowledge of HRSI acquisition solar geometry and snow cover can be used to understand and combine stereogrammetric surface elevation estimates to co-register rand difference overlapping DSMs, providing a means to map forest height at fine scales, resolving the vertical structure of groups of trees from spaceborne platforms in open canopy forests.

Linking physiological processes with mangrove forest structure: phosphorus deficiency limits canopy development, hydraulic conductivity and photosynthetic carbon gain in dwarf Rhizophora mangle.

PubMed

Lovelock, Catherine E; Ball, Marilyn C; Choat, Brendan; Engelbrecht, Bettina M J; Holbrook, N Michelle; Feller, Ilka C

2006-05-01

Spatial gradients in mangrove tree height in barrier islands of Belize are associated with nutrient deficiency and sustained flooding in the absence of a salinity gradient. While nutrient deficiency is likely to affect many parameters, here we show that addition of phosphorus (P) to dwarf mangroves stimulated increases in diameters of xylem vessels, area of conductive xylem tissue and leaf area index (LAI) of the canopy. These changes in structure were consistent with related changes in function, as addition of P also increased hydraulic conductivity (Ks), stomatal conductance and photosynthetic assimilation rates to the same levels measured in taller trees fringing the seaward margin of the mangrove. Increased xylem vessel size and corresponding enhancements in stem hydraulic conductivity in P fertilized dwarf trees came at the cost of enhanced mid-day loss of hydraulic conductivity and was associated with decreased assimilation rates in the afternoon. Analysis of trait plasticity identifies hydraulic properties of trees as more plastic than those of leaf structural and physiological characteristics, implying that hydraulic properties are key in controlling growth in mangroves. Alleviation of P deficiency, which released trees from hydraulic limitations, reduced the structural and functional distinctions between dwarf and taller fringing tree forms of Rhizophora mangle.

Seasonal fluxes of carbonyl sulfide in a midlatitude forest

PubMed Central

Commane, Róisín; Meredith, Laura K.; Baker, Ian T.; Berry, Joseph A.; Munger, J. William; Montzka, Stephen A.; Templer, Pamela H.; Juice, Stephanie M.; Zahniser, Mark S.; Wofsy, Steven C.

2015-01-01

Carbonyl sulfide (OCS), the most abundant sulfur gas in the atmosphere, has a summer minimum associated with uptake by vegetation and soils, closely correlated with CO2. We report the first direct measurements to our knowledge of the ecosystem flux of OCS throughout an annual cycle, at a mixed temperate forest. The forest took up OCS during most of the growing season with an overall uptake of 1.36 ± 0.01 mol OCS per ha (43.5 ± 0.5 g S per ha, 95% confidence intervals) for the year. Daytime fluxes accounted for 72% of total uptake. Both soils and incompletely closed stomata in the canopy contributed to nighttime fluxes. Unexpected net OCS emission occurred during the warmest weeks in summer. Many requirements necessary to use fluxes of OCS as a simple estimate of photosynthesis were not met because OCS fluxes did not have a constant relationship with photosynthesis throughout an entire day or over the entire year. However, OCS fluxes provide a direct measure of ecosystem-scale stomatal conductance and mesophyll function, without relying on measures of soil evaporation or leaf temperature, and reveal previously unseen heterogeneity of forest canopy processes. Observations of OCS flux provide powerful, independent means to test and refine land surface and carbon cycle models at the ecosystem scale. PMID:26578759

Seasonal fluxes of carbonyl sulfide in a midlatitude forest.

PubMed

Commane, Róisín; Meredith, Laura K; Baker, Ian T; Berry, Joseph A; Munger, J William; Montzka, Stephen A; Templer, Pamela H; Juice, Stephanie M; Zahniser, Mark S; Wofsy, Steven C

2015-11-17

Carbonyl sulfide (OCS), the most abundant sulfur gas in the atmosphere, has a summer minimum associated with uptake by vegetation and soils, closely correlated with CO2. We report the first direct measurements to our knowledge of the ecosystem flux of OCS throughout an annual cycle, at a mixed temperate forest. The forest took up OCS during most of the growing season with an overall uptake of 1.36 ± 0.01 mol OCS per ha (43.5 ± 0.5 g S per ha, 95% confidence intervals) for the year. Daytime fluxes accounted for 72% of total uptake. Both soils and incompletely closed stomata in the canopy contributed to nighttime fluxes. Unexpected net OCS emission occurred during the warmest weeks in summer. Many requirements necessary to use fluxes of OCS as a simple estimate of photosynthesis were not met because OCS fluxes did not have a constant relationship with photosynthesis throughout an entire day or over the entire year. However, OCS fluxes provide a direct measure of ecosystem-scale stomatal conductance and mesophyll function, without relying on measures of soil evaporation or leaf temperature, and reveal previously unseen heterogeneity of forest canopy processes. Observations of OCS flux provide powerful, independent means to test and refine land surface and carbon cycle models at the ecosystem scale.

Why do genotypes of Picea glauca differ in their growth response to elevated CO₂?

PubMed

Zhang, Junyan; Mycroft, Erin E; Adams, Greg; Reekie, Ed

2011-01-01

Meta-analyses reveal that fast-growing species have a greater growth response to elevated CO(2) than slow-growing species. It is unknown whether this is a direct response or whether inter-specific differences in growth are simply correlated with other physiological or morphological differences among species that affect the growth response to CO(2). Here we use intra-specific variation in Picea glauca to examine the mechanistic basis for this relationship. Relative growth rate (RGR) of 29 genotypes grown at ambient (370 µl l(-1)) or elevated (740 µl 1(-1)) CO(2) was measured. Physiological and morphological traits describing differences in allocation, canopy structure, stomatal function and photosynthesis were determined. Most variation in RGR (74%) was explained by traits associated with canopy structure. Although there was a strong correlation between RGR(740) and RGR(370), we found no evidence that genotypes that grew fast at ambient CO(2) had a greater relative growth response to CO(2). Given that the pattern found at the intra-specific level differed from that reported at the inter-specific level, our results suggest that RGR per se does not affect the growth response to CO(2). Rather, the CO(2) growth response is determined by traits that may or may not be correlated with RGR.

Estimating forest canopy bulk density using six indirect methods

Treesearch

Robert E. Keane; Elizabeth D. Reinhardt; Joe Scott; Kathy Gray; James Reardon

2005-01-01

Canopy bulk density (CBD) is an important crown characteristic needed to predict crown fire spread, yet it is difficult to measure in the field. Presented here is a comprehensive research effort to evaluate six indirect sampling techniques for estimating CBD. As reference data, detailed crown fuel biomass measurements were taken on each tree within fixed-area plots...

The photosynthetic and stomatal response of Medicago sativa cv. saranac to free-air CO{sub 2} enrichment (F.A.C.E.) and nitrogen

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

Bridson, N.P.

1996-08-01

Plots of Medicago sativa cv. saranac were grown in the field at ambient (355 {mu}mol CO{sub 2} mol{sup -1} air) or elevated (600{mu}mol CO{sub 2} mol{sup -1} air) CO{sub 2} concentrations. High (200kg yr{sup -1}) or low (20kg yr{sup -1}) nitrogen levels were applied to two isogeneic lines, one able and one unable to use nitrogen fixing bacteria. Plants were in the second year of field growth. Exposure to elevated CO{sub 2} was via a Free-Air CO{sub 2} Enrichment System (FACE). Elevated CO{sub 2} increased diurnal assimilation by between 12% and 92%. Analysis of A/C{sub i} responses showed that effectivemore » nitrogen fertilisation was more important to rubisCO and RuBP activity than elevated CO{sub 2}. No acclimation was consistently observed. Leaves lower down the canopy were found to have lower Vc{sub max} and J{sub max} values, though age may be the cause of the latter effect. FACE conditions have only a small effect on these responses. There was some evidence found for the down-regulation of photosynthesis in the late afternoon. The FACE conditions had no affect on stomatal density but did increase epidermal cell density.« less

Plant Uptake of Atmospheric Carbonyl Sulfide in Coast Redwood Forests

NASA Astrophysics Data System (ADS)

Campbell, J. E.; Whelan, M. E.; Berry, J. A.; Hilton, T. W.; Zumkehr, A.; Stinecipher, J.; Lu, Y.; Kornfeld, A.; Seibt, U.; Dawson, T. E.; Montzka, S. A.; Baker, I. T.; Kulkarni, S.; Wang, Y.; Herndon, S. C.; Zahniser, M. S.; Commane, R.; Loik, M. E.

2017-12-01

The future resilience of coast redwoods (Sequoia sempervirens) is now of critical concern due to the detection of a 33% decline in California coastal fog over the 20th century. However, ecosystem-scale measurements of photosynthesis and stomatal conductance are challenging in coast redwood forests, making it difficult to anticipate the impacts of future changes in fog. To address this methodological problem, we explore coastal variations in atmospheric carbonyl sulfide (COS or OCS), which could potentially be used as a tracer of these ecosystem processes. We conducted atmospheric flask campaigns in coast redwood sites, sampling at surface heights and in the canopy ( 70 m), at the University of California Landels-Hill Big Creek Reserve and Big Basin State Park. We simulated COS atmosphere-biosphere exchange with a high-resolution 3-D model to interpret these data. Flask measurements indicated a persistent daytime drawdown between the coast and the downwind forest (45 ± 6 ppt COS) that is consistent with the expected relationship between COS plant uptake, stomatal conductance, and gross primary production. Other sources and sinks of COS that could introduce noise to the COS tracer technique (soils, anthropogenic activity, nocturnal plant uptake, and surface hydrolysis on leaves) are likely to be small relative to daytime COS plant uptake. These results suggest that COS measurements may be useful for making ecosystem-scale estimates of carbon, water, and energy exchange in coast redwood forests.

Comparison of leaf gas exchange and stable isotope signature of water-soluble compounds along canopy gradients of co-occurring Douglas-fir and European beech.

PubMed

Bögelein, Rebekka; Hassdenteufel, Martin; Thomas, Frank M; Werner, Willy

2012-07-01

Combined δ(13) C and δ(18) O analyses of water-soluble leaf and twig phloem material were used to determine intrinsic water-use efficiency (iWUE) and variability of stomatal conductance at different crown positions in adult European beech (Fagus sylvatica) and Douglas-fir (Pseudotsuga menziesii) trees. Simultaneous gas exchange measurements allowed evaluation of the differences in calculating iWUE from leaf or phloem water-soluble compounds, and comparison with a semi-quantitative dual isotope model to infer variability of net photosynthesis (A(n) ) between the investigated crown positions. Estimates of iWUE from δ(13) C of leaf water-soluble organic matter (WSOM) outperformed the estimates from phloem compounds. In the beech crown, δ(13) C of leaf WSOM coincided clearly with gas exchange measurements. The relationship was not as reliable in the Douglas-fir. The differences in δ(18) O between leaf and phloem material were found to correlate with stomatal conductance. The semi-quantitative model approach was applicable for comparisons of daily average A(n) between different crown positions and trees. Intracanopy gradients were more pronounced in the beech than in the Douglas-fir, which reached higher values of iWUE at the respective positions, particularly under dry air conditions. © 2012 Blackwell Publishing Ltd.

On the use of phloem sap δ13C to estimate canopy carbon discrimination

NASA Astrophysics Data System (ADS)

Rascher, Katherine; Máguas, Cristina; Werner, Christiane

2010-05-01

Although the carbon stable isotope composition (d13C) of bulk leaf material is a good integrative parameter of photosynthetic discrimination and can be used as a reliable ecological index of plant functioning; it is not a good tracer of short-term changes in photosynthetic discrimination. In contrast, d13C of phloem sap is potentially useful as an indicator of short-term changes in canopy photosynthetic discrimination. However, recent research indicates that d13C signatures may be substantially altered by metabolic processes downstream of initial leaf-level carbon fixation (e.g. post-photosynthetic fractionation). Accordingly, before phloem sap d13C can be used as a proxy for canopy level carbon discrimination an understanding of factors influencing the degree and magnitude of post-photosynthetic fractionation and how these vary between species is of paramount importance. In this study, we measured the d13C signature along the basipetal transport pathway in two co-occurring tree species in the field - an understory invasive exotic legume, Acacia longifolia, and a native pine, Pinus pinaster. We measured d13C of bulk leaf and leaf water soluble organic matter (WSOM), phloem sap sampled at two points along the plant axis and leaf and root dark respiration. In general, species differences in photosynthetic discrimination resulted in more enriched d13C values in the water-conserving P. pinaster relative to the water-spending A. longifolia. Post-photosynthetic fractionation led to differences in d13C of carbon pools along the plant axis with progressively more depleted d13C from the canopy to the trunk (~6.5 per mil depletion in A. longifolia and ~0.8per mil depletion in P. pinaster). Leaf and root respiration, d13C, were consistently enriched relative to putative substrates. We hypothesize that the pronounced enrichment of leaf respired CO2 relative to leaf WSOM may have left behind relatively depleted carbon to be loaded into the phloem resulting in d13C depletion along the canopy to trunk continuum. We further hypothesize that pronounced depletion along the basipetal transport pathway in A. longifolia (more than 6 per mil from leaf water soluble organic matter to trunk phloem sap) may be due to high stem photosynthesis rates in this green-barked legume. Regardless of these fractionation effects, phloem sap d13C correlated well with environmental parameters driving photosynthesis (photosynthetic photon flux density, soil moisture, vapor pressure deficit) for both species indicating that phloem sap d13C is a good integrative tracer of changes in canopy-level carbon discrimination once species-specific differences in post-photosynthetic fractionation are accounted for. Furthermore, we illustrate that combining sap flow estimated canopy stomatal conductance (gs) with measurements of phloem sap d13C (adjusted for post-photosynthetic fractionation) has significant potential as a relatively non-intensive method for estimating canopy-level carbon assimilation rates in field studies.

Estimating the vegetation canopy height using micro-pulse photon-counting LiDAR data.

PubMed

Nie, Sheng; Wang, Cheng; Xi, Xiaohuan; Luo, Shezhou; Li, Guoyuan; Tian, Jinyan; Wang, Hongtao

2018-05-14

The upcoming space-borne LiDAR satellite Ice, Cloud and land Elevation Satellite-2 (ICESat-2) is scheduled to launch in 2018. Different from the waveform LiDAR system onboard the ICESat, ICESat-2 will use a micro-pulse photon-counting LiDAR system. Thus new data processing algorithms are required to retrieve vegetation canopy height from photon-counting LiDAR data. The objective of this paper is to develop and validate an automated approach for better estimating vegetation canopy height. The new proposed method consists of three key steps: 1) filtering out the noise photons by an effective noise removal algorithm based on localized statistical analysis; 2) separating ground returns from canopy returns using an iterative photon classification algorithm, and then determining ground surface; 3) generating canopy-top surface and calculating vegetation canopy height based on canopy-top and ground surfaces. This automatic vegetation height estimation approach was tested to the simulated ICESat-2 data produced from Sigma Space LiDAR data and Multiple Altimeter Beam Experimental LiDAR (MABEL) data, and the retrieved vegetation canopy heights were validated by canopy height models (CHMs) derived from airborne discrete-return LiDAR data. Results indicated that the estimated vegetation canopy heights have a relatively strong correlation with the reference vegetation heights derived from airborne discrete-return LiDAR data (R 2 and RMSE values ranging from 0.639 to 0.810 and 4.08 m to 4.56 m respectively). This means our new proposed approach is appropriate for retrieving vegetation canopy height from micro-pulse photon-counting LiDAR data.

Bidirectional Reflectance Modeling of Non-homogeneous Plant Canopies

NASA Technical Reports Server (NTRS)

Norman, J. M.

1984-01-01

Efforts to develop a three dimensional model to predict canopy, bidirectional reflectance for heterogenous plant stands using incident radiation and canopy structural descriptions as inputs are described. Utility programs were developed to cope with the complex output from the 3 dimensional model. In addition an attempt was made to define leaf and soil properties, which are appropriate to the mode, by measuring leaf and soil bidirectional reflectance distribution functions; since almost no data exist on these distributions. In the process it was realized that most models probably are using the wrong leaf spectral properties, and that off-nadir reflectance measurements are difficult to make because of non-Lambertian properties of reference surfaces. Also, in the visible wavebands, rough soil may not be distinguishable from canopies when viewed from above.

Native root xylem embolism and stomatal closure in stands of Douglas-fir and ponderosa pine: mitigation by hydraulic redistribution.

PubMed

Domec, J-C; Warren, J M; Meinzer, F C; Brooks, J R; Coulombe, R

2004-09-01

Hydraulic redistribution (HR), the passive movement of water via roots from moist to drier portions of the soil, occurs in many ecosystems, influencing both plant and ecosystem-water use. We examined the effects of HR on root hydraulic functioning during drought in young and old-growth Douglas-fir [ Pseudotsuga menziesii (Mirb.) Franco] and ponderosa pine ( Pinus ponderosa Dougl. Ex Laws) trees growing in four sites. During the 2002 growing season, in situ xylem embolism, water deficit and xylem vulnerability to embolism were measured on medium roots (2-4-mm diameter) collected at 20-30 cm depth. Soil water content and water potentials were monitored concurrently to determine the extent of HR. Additionally, the water potential and stomatal conductance ( g(s)) of upper canopy leaves were measured throughout the growing season. In the site with young Douglas-fir trees, root embolism increased from 20 to 55 percent loss of conductivity (PLC) as the dry season progressed. In young ponderosa pine, root embolism increased from 45 to 75 PLC. In contrast, roots of old-growth Douglas-fir and ponderosa pine trees never experienced more than 30 and 40 PLC, respectively. HR kept soil water potential at 20-30 cm depth above -0.5 MPa in the old-growth Douglas-fir site and -1.8 MPa in the old-growth ponderosa pine site, which significantly reduced loss of shallow root function. In the young ponderosa pine stand, where little HR occurred, the water potential in the upper soil layers fell to about -2.8 MPa, which severely impaired root functioning and limited recovery when the fall rains returned. In both species, daily maximum g(s) decreased linearly with increasing root PLC, suggesting that root xylem embolism acted in concert with stomata to limit water loss, thereby maintaining minimum leaf water potential above critical values. HR appears to be an important mechanism for maintaining shallow root function during drought and preventing total stomatal closure.

Effect of elevated atmospheric carbon dioxide and open-top chambers on transpiration in a tallgrass prairie

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

Bremer, D.J.; Ham, J.M.; Owensby, C.E.

1996-07-01

Increasing concentrations of atmospheric carbon dioxide (CO{sub 2}) may influence plant-water relations in natural and agricultural ecosystems. A tallgrass prairie near Manhattan, KS, was exposed to elevated atmospheric CO{sub 2} using open-top chambers (OTCs). Heat balance sap flow gauges were used to measure transpiration in ironweed [Vernonia baldwini var. interior (Small) Schub.], aC{sub 3}forb, and on individual grass culms of big bluestem (Andropogan geradii Vitman) and indiangrass [Sorghastrum nutans (L>) Nash], both C{sub 4} grasses, in each of three treatments: (1) CE (chamber enriched, 2x ambient CO{sub 2}); (2) CA (chamber ambient, no CO{sub 2} enrichment); and (3) NC (nomore » chamber, no CO{sub 2} enrichment). Sap flow data were coupled with measurements of stomatal conductance, plant/canopy resistance, and whole-chamber evapotranspiration (ET) to determine the effect of elevated CO{sub 2} on water use at different scales. Because of frequent rainfall during the study, all data were collected under well-watered conditions. Comparisons of CE and CA showed that sap flow was reduced by 33% in ironweed, 18% in big bluestem, and 22% in indiangrass under CO{sub 2} enrichment. Whole-chamber ET was reduced by 23 to 27% under CO{sub 2} enrichment. Comparisons of CA and NC showed that the environmental effect of the OTCs caused a 21 to 24% reduction in transpiration. Stomatal conductance decreased from 7.9 to 3.6 mm s{sup {minus}1} in big bluestem and from 5.3 to 3.2 mm s{sup {minus}1} in indiangrass under CO{sub 2} enrichment. Soil water was consistently highest under elevated CO{sub 2}, reflecting the large reductions in transpiration. During sap flow measurements, whole-plant stomatal resistance to water vapor flux in big bluestem increased from 103 to 194 s m{sup {minus}1} under elevated CO{sub 2}. 23 refs., 7 figs., 4 tabs.« less

Water and carbon fluxes in rain fed agricultural sites under a changing climate: The role of stomata

NASA Astrophysics Data System (ADS)

Hosseini, A.; Gayler, S.; Streck, T.; Katul, G. G.

2014-12-01

Vegetation models are needed to assess how crop productivity may be altered due to variations in climatic conditions. Stomatal conductance controls both diffusion of CO2 from the atmosphere into the leaf and water losses from the soil-plant system to the atmosphere through transpiration (E). Despite its significance, stomatal conductance and its links to climatic variables remains empirically specified in current crop models thereby challenging their application to future climatic conditions. It has long been conjectured that stomata has evolved so as to allow terrestrial plants to assimilate CO2 in a desiccating atmosphere while minimizing water losses. Hence, the hypothesis that stomata adapt optimally to their environment so as to maximize assimilation (A) for a given amount of water loss has received significant attention over the past 4 decades. Here, a new approach to implement optimization theory of stomatal conductance into a dynamic canopy gas exchange model is introduced. A key variable in this theory is the so-called marginal water use efficiency (MWUE), which is assumed to be constant on time scales commensurate with fluctuations in stomatal aperture. However, on time scales relevant to crop productivity (daily to seasonal), the boundary conditions on the optimization problem evolve in time prompting the question of how to assign MWUE on such time scales. To address this question, MWUE was formulated as a function of time-integrated leaf-water potential and atmospheric CO2. Next, leaf water potential was linked to root and soil pressure using a soil water balance model based on a modified Richards' equation that considers vertical distribution of root water uptake. The adequacy of the new approach was tested by comparing predicted diurnal cycles of A and E as well as variability of soil moisture with long-term observations at a winter wheat (Triticum aestivum cv.Cubus) field in southwest Germany (see Figure), where transpiration and assimilation rates were derived from eddy-covariance measurements of latent heat flux and net ecosystem exchange. To place those results in the broader context of climate change and food security issues, a sensitivity analyses on water and carbon fluxes with respect to climatic variables, soil texture, and root-density distribution is also presented.

Diel trends in plant sensitivity to ozone: Toward parameterization of the defense component of effective flux

NASA Astrophysics Data System (ADS)

Grantz, D. A.; Vu, H.; Heath, R. L.; Burkey, K.

2011-12-01

Ozone (O3) injury to vegetation can be conceptually divided into three stages: 1) O3 entrance into the leaf including fractionation of stomatal vs. non-stomatal deposition; 2) O3 overcoming initial metabolic defenses within individual leaves, and 3) oxidant attack by O3 or derivatives on bioreceptors to produce injury. Ozone deposition at canopy scale and uptake at leaf scale are routinely obtained by observational and modeling techniques (Massman and Grantz, 1995). Injury can be assessed experimentally. However, predictive association between ozone concentration or flux and injury is currently not well characterized. This is due to uncertainties in rates and capacities of ozone detoxification, the nature of plant defense mechanisms, and their temporal (diel and seasonal) variability (Heath et al., 2009; Massman et al., 2000). We have developed a plant sensitivity parameter (SO3) relating injury (I) to the sum of O3 flux and photon flux density (FO3 + PPFD) during exposure. By restricting leaf exposure to O3 to a brief (15 min) pulse, we assess passive defense mechanisms, assuming that the pulse duration provides insufficient time for induction of additional (active) defense capacity during exposure. Greenhouse grown Pima cotton was exposed in chambers to pulsed O3 at a range of concentrations, stomatal conductance was measured directly pre- and post-exposure, and injury was assessed 1 week later using several indicators. SO3, determined at 2 hour intervals, exhibited clear diel trends, with maximal sensitivity shortly after solar noon, and minimal sensitivity early and late in the photoperiod. This diel pattern of SO3 did not support suggestions that plant defense is correlated with instantaneous photosynthetic rate. There was only weak correlation between SO3 and whole leaf ascorbate, ascorbate redox poise, or total antioxidant capacity, though future measurements of apoplastic antioxidants may improve these relationships. The parameter, SO3, may be directly related to the weighting factor commonly used as a surrogate for plant defense in model relationships between injury and O3 flux (e.g. Massman et al. 2000). Diurnally varying SO3 incorporates the combined oxidative stresses of O3 and photochemistry, and can be combined with natural diel cycles of ozone concentration and models of stomatal conductance and photosynthesis, to yield integrated impacts of O3 on injury to vegetation.

Micrometeorological measurements and vapour pressure deficit relations under in-field rainwater harvesting

NASA Astrophysics Data System (ADS)

Tesfuhuney, Weldemichael A.; Walker, Sue; Van Rensburg, Leon D.; Steyn, A. Stephan

2016-08-01

In a cropped field, microclimate and thermal stability conditions depend on the canopy structures and the prevailing weather. The main aim of the study therefore was to characterize the vertical profiles of weather variables within and above a maize (Zea mays L.) canopy and to describe the water vapour pressure deficit (VPD) under different atmospheric and soil surface conditions for both wide and narrow runoff strips with the in-field rainwater harvesting (IRWH) system. Micrometeorological measurements of wind, temperature and relative humidity were performed at eight levels, within canopy (1.8 and 2.1 m), and just above the canopy (2.4, 2.7, 3.0, and 3.3 m) up to reference levels (3.9 and 4.5 m) when the maize reached a maximum height of 2.2 m. Under incomplete canopy cover of the IRWH system, two important factors complicated evapotranspiration estimation, namely the local advection and high temperatures of the bare soil between adjacent plant rows. Diurnal variations of water vapour related to turbulence at each locality and its position in the thermal internal boundary layers. Generally, advection was more pronounced in wide runoff strips than narrow strips. On wide runoff strips the wind was more effective in replacing the air between the rows and maintained a higher driving force for evaporation. The maximum VPD over the narrow strips was observed at reference level during a dry day, at about 2.2 kPa in the afternoon, while wet day VPD reached a maximum of 1.8 kPa. The VPD of the wide runoff strips correlated negatively with wind speed, but showed a fairly positive correlation with some scattered values on wet days after rain. Therefore, profile characteristics within and above plant canopies played a key role in determining the VPD and consequently, could help to explain transpiration rates of crops. Hence, VPD relations enhanced the understanding of the heat energy exchange processes under the heterogeneous nature of maize canopy of the IRWH tillage system.

Predicting plant vulnerability to drought in biodiverse regions using functional traits.

PubMed

Skelton, Robert Paul; West, Adam G; Dawson, Todd E

2015-05-05

Attempts to understand mechanisms underlying plant mortality during drought have led to the emergence of a hydraulic framework describing distinct hydraulic strategies among coexisting species. This framework distinguishes species that rapidly decrease stomatal conductance (gs), thereby maintaining high water potential (Px; isohydric), from those species that maintain relatively high gs at low Px, thereby maintaining carbon assimilation, albeit at the cost of loss of hydraulic conductivity (anisohydric). This framework is yet to be tested in biodiverse communities, potentially due to a lack of standardized reference values upon which hydraulic strategies can be defined. We developed a system of quantifying hydraulic strategy using indices from vulnerability curves and stomatal dehydration response curves and tested it in a speciose community from South Africa's Cape Floristic Region. Degree of stomatal regulation over cavitation was defined as the margin between Px at stomatal closure (Pg12) and Px at 50% loss of conductivity. To assess relationships between hydraulic strategy and mortality mechanisms, we developed proxies for carbon limitation and hydraulic failure using time since Pg12 and loss of conductivity at minimum seasonal Px, respectively. Our approach captured continuous variation along an isohydry/anisohydry axis and showed that this variation was linearly related to xylem safety margin. Degree of isohydry/anisohydry was associated with contrasting predictions for mortality during drought. Merging stomatal regulation strategies that represent an index of water use behavior with xylem vulnerability facilitates a more comprehensive framework with which to characterize plant response to drought, thus opening up an avenue for predicting the response of diverse communities to future droughts.

Quantification of the effects of architectural traits on dry mass production and light interception of tomato canopy under different temperature regimes using a dynamic functional–structural plant model

PubMed Central

Chen, Tsu-Wei; Nguyen, Thi My Nguyet; Kahlen, Katrin; Stützel, Hartmut

2014-01-01

There is increasing interest in evaluating the environmental effects on crop architectural traits and yield improvement. However, crop models describing the dynamic changes in canopy structure with environmental conditions and the complex interactions between canopy structure, light interception, and dry mass production are only gradually emerging. Using tomato (Solanum lycopersicum L.) as a model crop, a dynamic functional–structural plant model (FSPM) was constructed, parameterized, and evaluated to analyse the effects of temperature on architectural traits, which strongly influence canopy light interception and shoot dry mass. The FSPM predicted the organ growth, organ size, and shoot dry mass over time with high accuracy (>85%). Analyses of this FSPM showed that, in comparison with the reference canopy, shoot dry mass may be affected by leaf angle by as much as 20%, leaf curvature by up to 7%, the leaf length:width ratio by up to 5%, internode length by up to 9%, and curvature ratios and leaf arrangement by up to 6%. Tomato canopies at low temperature had higher canopy density and were more clumped due to higher leaf area and shorter internodes. Interestingly, dry mass production and light interception of the clumped canopy were more sensitive to changes in architectural traits. The complex interactions between architectural traits, canopy light interception, dry mass production, and environmental conditions can be studied by the dynamic FSPM, which may serve as a tool for designing a canopy structure which is ‘ideal’ in a given environment. PMID:25183746

Free-air fumigation of mature trees. A novel system for controlled ozone enrichment in grown-up beech and spruce canopies.

PubMed

Werner, Herbert; Fabian, Peter

2002-01-01

A novel system for continuous and controlled free-air fumigation of mature tree canopies with ozone is described. Ozone generated from oxygen is diluted with air in a pressurized tank and conducted into the canopies by a system of 100 PTFE tubes hanging down from a grid fixed above the crowns. With 45 calibrated outlets per tube providing a constant flow of 0.3 l/min each, a total volume of about 10*10*15 m3 comprising 5 beech and 5 spruce canopies is fumigated. The spatial ozone distribution in the fumigated volume as well as surrounding reference tree canopies is controlled by continuous measuring instruments installed at 4 levels and a dense array of passive samplers. The system will later be used for CO2 fumigation as well. Results of the first year of continuous operation, with 2 * ambient ozone levels having been achieved, are reported.

Automatic Detection of Regions in Spinach Canopies Responding to Soil Moisture Deficit Using Combined Visible and Thermal Imagery

PubMed Central

Raza, Shan-e-Ahmed; Smith, Hazel K.; Clarkson, Graham J. J.; Taylor, Gail; Thompson, Andrew J.; Clarkson, John; Rajpoot, Nasir M.

2014-01-01

Thermal imaging has been used in the past for remote detection of regions of canopy showing symptoms of stress, including water deficit stress. Stress indices derived from thermal images have been used as an indicator of canopy water status, but these depend on the choice of reference surfaces and environmental conditions and can be confounded by variations in complex canopy structure. Therefore, in this work, instead of using stress indices, information from thermal and visible light imagery was combined along with machine learning techniques to identify regions of canopy showing a response to soil water deficit. Thermal and visible light images of a spinach canopy with different levels of soil moisture were captured. Statistical measurements from these images were extracted and used to classify between canopies growing in well-watered soil or under soil moisture deficit using Support Vector Machines (SVM) and Gaussian Processes Classifier (GPC) and a combination of both the classifiers. The classification results show a high correlation with soil moisture. We demonstrate that regions of a spinach crop responding to soil water deficit can be identified by using machine learning techniques with a high accuracy of 97%. This method could, in principle, be applied to any crop at a range of scales. PMID:24892284

Effects of rainfall exclusion on leaf gas exchange traits and osmotic adjustment in mature canopy trees of Dryobalanops aromatica (Dipterocarpaceae) in a Malaysian tropical rain forest.

PubMed

Inoue, Yuta; Ichie, Tomoaki; Kenzo, Tanaka; Yoneyama, Aogu; Kumagai, Tomo'omi; Nakashizuka, Tohru

2017-10-01

Climate change exposes vegetation to unusual levels of drought, risking a decline in productivity and an increase in mortality. It still remains unclear how trees and forests respond to such unusual drought, particularly Southeast Asian tropical rain forests. To understand leaf ecophysiological responses of tropical rain forest trees to soil drying, a rainfall exclusion experiment was conducted on mature canopy trees of Dryobalanops aromatica Gaertn.f. (Dipterocarpaceae) for 4 months in an aseasonal tropical rain forest in Sarawak, Malaysia. The rainfall was intercepted by using a soft vinyl chloride sheet. We compared the three control and three treatment trees with respect to leaf water use at the top of the crown, including stomatal conductance (gsmax), photosynthesis (Amax), leaf water potential (predawn: Ψpre; midday: Ψmid), leaf water potential at turgor loss point (πtlp), osmotic potential at full turgor (π100) and a bulk modulus of elasticity (ε). Measurements were taken using tree-tower and canopy-crane systems. During the experiment, the treatment trees suffered drought stress without evidence of canopy dieback in comparison with the control trees; e.g., Ψpre and Ψmid decreased with soil drying. Minimum values of Ψmid in the treatment trees decreased during the experiment, and were lower than πtlp in the control trees. However, the treatment trees also decreased their πtlp by osmotic adjustment, and the values were lower than the minimum values of their Ψmid. In addition, the treatment trees maintained gs and Amax especially in the morning, though at midday, values decreased to half those of the control trees. Decreasing leaf water potential by osmotic adjustment to maintain gs and Amax under soil drying in treatment trees was considered to represent anisohydric behavior. These results suggest that D. aromatica may have high leaf adaptability to drought by regulating leaf water consumption and maintaining turgor pressure to improve its leaf water relations. © The Author 2017. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Uncertainties in estimates of fAPAR for photosynthesis (fAPARPSN) in tropical, Arctic/boreal, coastal, and wetland-dominant regions when approximated with fAPARcanopy and NDVI

NASA Astrophysics Data System (ADS)

Zhang, Q.; Yao, T.

2016-12-01

The climate is affected by the land surface through regulating the exchange of mass and energy with the atmosphere. The energy that reaches the land surface has three pathways: (1) reflected into atmosphere; (2) absorbed for photosynthesis; and (3) discarded as latent and sensible heat or emitted as fluorescence. Vegetation removes CO2 from the atmosphere during the process of photosynthesis, but also releases CO2 back into the atmosphere through the process of respiration. The complex set of vegetation-soil-atmosphere interactions requires that a realistic land-surface parameterization be included in any climate model or general circulation model (GCM) to accurately simulate canopy photosynthesis and stomatal conductance.We retrieve fraction of PAR absorbed by chlorophyll (fAPARchl) with an advanced canopy-leaf-soil-snow-water coupled radiative transfer model. Most ecological models and land-surface models that simulate vegetation GPP with remote sensing data utilize fraction of PAR absorbed by the whole canopy (fAPARcanopy). However, only the PAR absorbed by chlorophyll is potentially available for photosynthesis since the PAR absorbed by non-photosynthetic vegetation section (NPV) of the canopy is not used for photosynthesis. Therefore, fAPARchl (rather than fAPARcanopy) should be utilized to estimate fAPAR for photosynthesis (fAPARPSN), and thus in GPP simulation. Globally selected sites include those sites in tropical, Arctic/boreal, coastal, and wetland-dominant regions. The fAPARchl and fAPARcanopy products for a surrounding area 50 km x 50 km of each site are mapped. The fAPARchl is utilized to estimate GPP, and compared to tower flux GPP for validation. The GPP estimation performance with fAPARchl is also compared with the GPP estimation performance with MOD15A2 FPAR. The fAPARchl product is further implemented into ecological models and land-surface models to simulate vegetation GPP. NDVI is the other proxy of fAPARPSN in GPP estimation. We quantify the uncertainties in estimates of fAPARPSN when approximated with fAPARcanopy and NDVI. The uncertainties are significant and vary spatially, temporally, and with plant functional types.

Forest Canopy Cover and Height from MISR in Topographically Complex Southwestern US Landscape Assessed with High Quality Reference Data

NASA Technical Reports Server (NTRS)

Chopping, Mark; North, Malcolm; Chen, Jiquan; Schaaf, Crystal B.; Blair, J. Bryan; Martonchik, John V.; Bull, Michael A.

2012-01-01

This study addresses the retrieval of spatially contiguous canopy cover and height estimates in southwestern USforests via inversion of a geometric-optical (GO) model against surface bidirectional reflectance factor (BRF) estimates from the Multi-angle Imaging SpectroRadiometer (MISR). Model inversion can provide such maps if good estimates of the background bidirectional reflectance distribution function (BRDF) are available. The study area is in the Sierra National Forest in the Sierra Nevada of California. Tree number density, mean crown radius, and fractional cover reference estimates were obtained via analysis of QuickBird 0.6 m spatial resolution panchromatic imagery usingthe CANopy Analysis with Panchromatic Imagery (CANAPI) algorithm, while RH50, RH75 and RH100 (50, 75, and 100 energy return) height data were obtained from the NASA Laser Vegetation Imaging Sensor (LVIS), a full waveform light detection and ranging (lidar) instrument. These canopy parameters were used to drive a modified version of the simple GO model (SGM), accurately reproducing patterns ofMISR 672 nm band surface reflectance (mean RMSE 0.011, mean R2 0.82, N 1048). Cover and height maps were obtained through model inversion against MISR 672 nm reflectance estimates on a 250 m grid.The free parameters were tree number density and mean crown radius. RMSE values with respect to reference data for the cover and height retrievals were 0.05 and 6.65 m, respectively, with of 0.54 and 0.49. MISR can thus provide maps of forest cover and height in areas of topographic variation although refinements are required to improve retrieval precision.

Interactions between light and growing season temperatures on, growth and development and gas exchange of Semillon (Vitis vinifera L.) vines grown in an irrigated vineyard.

PubMed

Greer, Dennis H; Weedon, Mark M

2012-05-01

High-light intensities and temperatures of the warm climate regions of Australia and elsewhere have a major effect on the growth and development of grapevines (Vitis vinifera L.). The objective of this research was to assess interactions between the light and seasonal temperatures by shading some vines and comparing these with vines exposed to high-light intensities. Canopy temperatures were monitored using infrared radiometers and budbreak, phenology, growth, yield, berry ripening and gas exchange determined over three growing seasons. Results showed canopies were generally about 4 °C cooler than air and shading extended this cooling. Irradiance, irrespective of seasonal temperatures, had no effect on time of budbreak, shoot phenology, stem growth, yield and bunch fresh weights while bunch and leaf dry weights were reduced in low-light. Bunch ripening was initially delayed by low-light but thereafter the ripening process was highly temperature-dependent. Rates increased linearly with increasing temperature in both low and high-light and were optimal at about 35 °C. Maximum photosynthetic capacity was impaired by low irradiance, in accordance with shade leaf attributes, and attributable to stomatal closure. No effects of the low photosynthetic capacity apparently carried-over to sugar accumulation, consistent with the strong sink capacity of bunches. Crown Copyright © 2012. Published by Elsevier Masson SAS. All rights reserved.

Evapotranspiration and canopy resistance at an undeveloped prairie in a humid subtropical climate

USGS Publications Warehouse

Bidlake, W.R.

2002-01-01

Reliable estimates of evapotranspiration from areas of wildland vegetation are needed for many types of water-resource investigations. However, little is known about surface fluxes from many areally important vegetation types, and relatively few comparisons have been made to examine how well evapotranspiration models can predict evapotranspiration for soil-, climate-, or vegetation-types that differ from those under which the models have been calibrated. In this investigation at a prairie site in west-central Florida, latent heat flux (??E) computed from the energy balance and alternatively by eddy covariance during a 15-month period differed by 4 percent and 7 percent on hourly and daily time scales, respectively. Annual evapotranspiration computed from the energy balance and by eddy covariance were 978 and 944 mm, respectively. An hourly Penman-Monteith (PM) evapotranspiration model with stomatal control predicated on water-vapor-pressure deficit at canopy level, incoming solar radiation intensity, and soil water deficit was developed and calibrated using surface fluxes from eddy covariance. Model-predicted ??E agreed closely with ??E computed from the energy balance except when moisture from dew or precipitation covered vegetation surfaces. Finally, an hourly PM model developed for an Amazonian pasture predicted ??E for the Florida prairie with unexpected reliability. Additional comparisons of PM-type models that have been developed for differing types of short vegetation could aid in assessing interchangeability of such models.

Modeling ozone uptake by urban and peri-urban forest: a case study in the Metropolitan City of Rome.

PubMed

Fusaro, Lina; Mereu, Simone; Salvatori, Elisabetta; Agliari, Elena; Fares, Silvano; Manes, Fausto

2018-03-01

Urban and peri-urban forests are green infrastructures (GI) that play a substantial role in delivering ecosystem services such as the amelioration of air quality by the removal of air pollutants, among which is ozone (O 3 ), which is the most harmful pollutant in Mediterranean metropolitan areas. Models may provide a reliable estimate of gas exchanges between vegetation and atmosphere and are thus a powerful tool to quantify and compare O 3 removal in different contexts. The present study modeled the O 3 stomatal uptake at canopy level of an urban and a peri-urban forest in the Metropolitan City of Rome in two different years. Results show different rates of O 3 fluxes between the two forests, due to different exposure to the pollutant, management practice effects on forest structure and functionality, and environmental conditions, namely, different stressors affecting the gas exchange rates of the two GIs. The periodic components of the time series calculated by means of the spectral analysis show that seasonal variation of modeled canopy transpiration is driven by precipitation in peri-urban forests, whereas in the urban forest seasonal variations are driven by vapor pressure deficit of ambient air. Moreover, in the urban forest high water availability during summer months, owing to irrigation practice, leads to an increase in O 3 uptake, thus suggesting that irrigation may enhance air phytoremediation in urban areas.

An evaluation of ozone exposure metrics for a seasonally drought-stressed ponderosa pine ecosystem.

PubMed

Panek, Jeanne A; Kurpius, Meredith R; Goldstein, Allen H

2002-01-01

Ozone stress has become an increasingly significant factor in cases of forest decline reported throughout the world. Current metrics to estimate ozone exposure for forest trees are derived from atmospheric concentrations and assume that the forest is physiologically active at all times of the growing season. This may be inaccurate in regions with a Mediterranean climate, such as California and the Pacific Northwest, where peak physiological activity occurs early in the season to take advantage of high soil moisture and does not correspond to peak ozone concentrations. It may also misrepresent ecosystems experiencing non-average climate conditions such as drought years. We compared direct measurements of ozone flux into a ponderosa pine canopy with a suite of the most common ozone exposure metrics to determine which best correlated with actual ozone uptake by the forest. Of the metrics we assessed, SUM0 (the sum of all daytime ozone concentrations > 0) best corresponded to ozone uptake by ponderosa pine, however the correlation was only strong at times when the stomata were unconstrained by site moisture conditions. In the early growing season (May and June). SUM0 was an adequate metric for forest ozone exposure. Later in the season, when stomatal conductance was limited by drought. SUM0 overestimated ozone uptake. A better metric for seasonally drought-stressed forests would be one that incorporates forest physiological activity, either through mechanistic modeling, by weighting ozone concentrations by stomatal conductance, or by weighting concentrations by site moisture conditions.

A simple biosphere model (SiB) for use within general circulation models

NASA Technical Reports Server (NTRS)

Sellers, P. J.; Mintz, Y.; Sud, Y. C.; Dalcher, A.

1986-01-01

A simple realistic biosphere model for calculating the transfer of energy, mass and momentum between the atmosphere and the vegetated surface of the earth has been developed for use in atmospheric general circulation models. The vegetation in each terrestrial model grid is represented by an upper level, representing the perennial canopy of trees and shrubs, and a lower level, representing the annual cover of grasses and other heraceous species. The vegetation morphology and the physical and physiological properties of the vegetation layers determine such properties as: the reflection, transmission, absorption and emission of direct and diffuse radiation; the infiltration, drainage, and storage of the residual rainfall in the soil; and the control over the stomatal functioning. The model, with prescribed vegetation parameters and soil interactive soil moisture, can be used for prediction of the atmospheric circulation and precipitaion fields for short periods of up to a few weeks.

Utilizing Chamber Data for Developing and Validating Climate Change Models

NASA Technical Reports Server (NTRS)

Monje, Oscar

2012-01-01

Controlled environment chambers (e.g. growth chambers, SPAR chambers, or open-top chambers) are useful for measuring plant ecosystem responses to climatic variables and CO2 that affect plant water relations. However, data from chambers was found to overestimate responses of C fluxes to CO2 enrichment. Chamber data may be confounded by numerous artifacts (e.g. sidelighting, edge effects, increased temperature and VPD, etc) and this limits what can be measured accurately. Chambers can be used to measure canopy level energy balance under controlled conditions and plant transpiration responses to CO2 concentration can be elucidated. However, these measurements cannot be used directly in model development or validation. The response of stomatal conductance to CO2 will be the same as in the field, but the measured response must be recalculated in such a manner to account for differences in aerodynamic conductance, temperature and VPD between the chamber and the field.

A Comparison of Mangrove Canopy Height Using Multiple Independent Measurements from Land, Air, and Space.

PubMed

Lagomasino, David; Fatoyinbo, Temilola; Lee, SeungKuk; Feliciano, Emanuelle; Trettin, Carl; Simard, Marc

2016-04-01

Canopy height is one of the strongest predictors of biomass and carbon in forested ecosystems. Additionally, mangrove ecosystems represent one of the most concentrated carbon reservoirs that are rapidly degrading as a result of deforestation, development, and hydrologic manipulation. Therefore, the accuracy of Canopy Height Models (CHM) over mangrove forest can provide crucial information for monitoring and verification protocols. We compared four CHMs derived from independent remotely sensed imagery and identified potential errors and bias between measurement types. CHMs were derived from three spaceborne datasets; Very-High Resolution (VHR) stereophotogrammetry, TerraSAR-X add-on for Digital Elevation Measurement, and Shuttle Radar Topography Mission (TanDEM-X), and lidar data which was acquired from an airborne platform. Each dataset exhibited different error characteristics that were related to spatial resolution, sensitivities of the sensors, and reference frames. Canopies over 10 m were accurately predicted by all CHMs while the distributions of canopy height were best predicted by the VHR CHM. Depending on the guidelines and strategies needed for monitoring and verification activities, coarse resolution CHMs could be used to track canopy height at regional and global scales with finer resolution imagery used to validate and monitor critical areas undergoing rapid changes.

Seasonal variation of volatile organic compounds exchange above a periurban Holm oak forest on the Mediterranean coast

NASA Astrophysics Data System (ADS)

Savi, Flavia; Juráň, Stanislav; Fares, Silvano

2015-04-01

Bi-directional exchanges of Volatile Organic Compounds (VOCs) were investigated on a Mediterranean Holm oak forest in Castelporziano presidential estate, a peri-urban forest near the coast of Tyrrhenian sea, 20 Km from Rome downtown, Italy. Two field campaigns were carried out in January and August 2014 to explore VOCs fluxes in two seasons with different climate conditions and physiological activity of plants. Concentration of 23 compounds was measured using a proton transfer reaction - mass spectrometer (PTR-MS). These included biogenic products (BVOC - isoprene, monoterpenes), oxygenated BVOC (OVOC - methanol, acetaldehyde acetone) and VOC of anthropogenic origin (AVOC - acetonitrile, benzene, hexenal, toluene, xylenes). Each half-hour, we switched between measurement at high frequency above the canopy and sampling through a 5-levels gradient from soil to above the canopy. We used the eddy covariance technique to calculate fluxes above the canopy, while gradient measurements were used to estimate in-canopy source and sink distribution by applying an Inverse Lagrangian Transport Model (Karl et al., 2004, J.Geophys.Res). Ozone and NOx concentrations were also measured to better correlate VOCs exchanges with this important secondary pollutant. Low temperatures lead to almost negligible BVOC fluxes during Winter. Summer fluxes were largely represented by BVOC (mainly monoterpenes). The highest fluxes (up to 2.4 nmol m-2 s-1) were recorded in the central hour of the day in response to high light and temperature. Oxygenated compounds (methanol and acetone) showed different behaviour during the two seasons: in Winter a net release of these compounds was observed, while in Summer the canopy acted as a sink for OVOC except for the hottest hours when we observed significant emissions. OVOC source-sink distribution analysis helped identifying the canopy layers which mostly contributed to VOCs exchanges, thus underlining the importance of forest canopies in VOCs exchanges in the soil-plant-atmosphere continuum. AVOC (xylene, toluene and benzene) concentration in Winter was double than in Summer, despite the intense vehicular traffic towards the beach nearby the forest stand in August. Both in Winter and Summer, emission of AVOC from the forest were measured, although we excluded a biogenic source but rather a resuspension of compounds previously accumulated at night under shallow atmospheric boundary layer. Photochemically produced ozone was high during the central hours of the day (up to 40 and 70 ppb in Winter and Summer, respectively), while nocturnal concentration went down to less than 20 ppb. Stomata explained almost the totality of ozone fluxes during day (Fares et al., 2014, Agr.Forest.Meteorol), while other non-stomatal sinks including chemical reactions with VOcs were responsible for nocturnal ozone removal. We discuss here the importance of forest canopies in the interaction between VOC and secondary pollutants, such as ozone and NOx in a peculiar Mediterranean site where the sea-land breeze circulation allows a strong mixing between contaminated air from the city and cleaner air from the sea under high UV radiations and air temperatures.

Analysis of the effect of evergreen and deciduous trees on urban nitrogen dioxide levels in the U.S. using land-use regression

NASA Astrophysics Data System (ADS)

Rao, M.; George, L. A.

2012-12-01

Nitrogen dioxide (NO2), an atmospheric pollutant generated primarily by anthropogenic combustion processes, is typically found at higher concentrations in urban areas compared to non-urbanized environments. Elevated NO2 levels have multiple ecosystem effects at different spatial scales. At the local scale, elevated levels affect human health directly and through the formation of secondary pollutants such as ozone and aerosols; at the regional scale secondary pollutants such as nitric acid and organic nitrates have deleterious effects on non-urbanized areas; and, at the global scale, nitrogen oxide emissions significantly alter the natural biogeochemical nitrogen cycle. As cities globally become larger and larger sources of nitrogen oxide emissions, it is important to assess possible mitigation strategies to reduce the impact of emissions locally, regionally and globally. In this study, we build a national land-use regression (LUR) model to compare the impacts of deciduous and evergreen trees on urban NO2 levels in the United States. We use the EPA monitoring network values of NO2 levels for 2006, the 2006 NLCD tree canopy data for deciduous and evergreen canopies, and the US Census Bureau's TIGER shapefiles for roads, railroads, impervious area & population density as proxies for NO2 sources on-road traffic, railroad traffic, off-road and area sources respectively. Our preliminary LUR model corroborates previous LUR studies showing that the presence of trees is associated with reduced urban NO2 levels. Additionally, our model indicates that deciduous and evergreen trees reduce NO2 to different extents, and that the amount of NO2 reduced varies seasonally. The model indicates that every square kilometer of deciduous canopy within a 2km buffer is associated with a reduction in ambient NO2 levels of 0.64 ppb in summer and 0.46ppb in winter. Similarly, every square kilometer of evergreen tree canopy within a 2 km buffer is associated with a reduction in ambient NO2 by 0.53 ppb in summer and 0.84 ppb in winter. Thus, the model indicates that deciduous trees are associated with a 30% smaller reduction in NO2 in winter as compared to summer, while evergreens are associated with a 60% increase in the reduction of NO2 in winter, for every square kilometer of deciduous or evergreen canopy within a 2 km buffer. Leaf- and local canopy-level studies have shown that trees are a sink for urban NO2 through deposition as well as stomatal and cuticular uptake. The winter time versus summer time effects suggest that leaf-level deposition may not be the only uptake mechanism and points to the need for a more holistic analysis of tree and canopy-level deposition for urban air pollution models. Since deposition velocities for NO2 vary by tree species, the reduction may also vary by species. These findings have implications for designing cities to reduce the impact of air pollution.

Scaling up carbonyl sulfide (COS) fluxes from leaf and soil to the canopy

NASA Astrophysics Data System (ADS)

Yang, Fulin; Yakir, Dan

2016-04-01

Carbonyl sulfide (COS) with atmospheric concentrations around 500 ppt is an analog of CO2 which can potentially serve as powerful and much needed tracer of photosynthetic CO2 uptake, and global gross primary production (GPP). However, questions remain regarding the application of this approach due to uncertainties in the contributions of different ecosystem components to the canopy scale fluxes of COS. We used laser quantum cascade spectroscopy in combination with soil and branch chambers, and eddy covariance measurements of net ecosystem exchange fluxes of COS and CO2 (NEE) in citrus orchard during the driest summer month to test our ability to integrate the chamber measurements into the ecosystem fluxes. The results indicated that: 1) Soil fluxes showed clear gradient from continuous uptake under the trees in wet soil of up to -4 pmol m-2s-1 (CO2 emission of ~0.5 umol m-2s-1) to emission in dry hot and exposed soil between rows of trees of up to +3 pmol m-2s-1 (CO2 emission of ~11 umol m-2s-1). In all cases a clear correlation between fluxes and soil temperature was observed. 2) At the leaf scale, midday uptake was ~5.5 pmol m-2s-1 (CO2 uptake of ~1.8 umol m-2s-1). Some nighttime COS uptake was observed in the citrus leaves consistent with nocturnal leaf stomatal conductance. Leaf relative uptake (LRU) of COS vs. CO2 was not constant over the diurnal cycle, but showed exponential correlation with photosynthetically active radiation (PAR) during the daytime. 3) At the canopy scale mid-day summer flux reached -12.0 pmol m-2s-1 (NEE ~6 umol m-2s-1) with the diurnal patterns of COS fluxes following those of CO2 fluxes during the daytime, but with small COS uptake fluxes maintained also during the night when significant CO2 emission fluxes were observed. The canopy-scale fluxes always indicated COS uptake, irrespective of the soil emission effects. GPP estimates were consistent with conventional indirect estimates based on NEE and nocturnal measurements. Scaling up from soil and leaf chamber to canopy scale was possible by estimating LAI, and differential consideration of soil surface components (shaded vs. exposed fractions). 4) Diurnal changes in the atmospheric concentrations of COS and CO2 above the canopy showed complex patterns with opposite trends after sunrise that could be explain by the development of the planetary boundary layer 5) COS-based estimate of GPP can be improved by adopting light dependent LRU, around the mean value of ~1.6, and correcting for soil COS fluxes based on soil temperature and canopy cover estimates, and coupled COS/CO2 concentration measurements provide useful information on boundary layer dynamics.

Simulating Carbon Flux Dynamics with the Product of PAR Absorbed by Chlorophyll (fAPARchl)

NASA Astrophysics Data System (ADS)

Yao, T.; Zhang, Q.

2016-12-01

A common way to estimate the gross primary production (GPP) is to use the fraction of photosynthetically radiation (PAR) absorbed by vegetation (FPAR). However, only the PAR absorbed by chlorophyll of the canopy, not the PAR absorbed by the foliage or by the entire canopy, is used for photosynthesis. MODIS fAPARchl product, which refers to the fraction of PAR absorbed by chlorophyll of the canopy, is derived from Moderate Resolution Imaging Spectroradiometer (MODIS) surface reflectance by using an advanced leaf-canopy-soil-water-snow coupled radiative transfer model PROSAIL4. PROSAIL4 can retrieve surface water cover fraction, snow cover fraction, and physiologically active canopy chemistry components (chlorophyll concentration and water content), fraction of photosynthetically active radiation (PAR) absorbed by a canopy (fAPARcanopy), fraction of PAR absorbed by photosynthetic vegetation (PV) component (mainly chlorophyll) throughout the canopy (fAPARPV, i.e., fAPARchl) and fraction of PAR absorbed by non-photosynthetic vegetation (NPV) component of the canopy (fAPARNPV). We have successfully retrieved these vegetation parameters for selected areas with PROSAIL4 and the MODIS images, or simulated spectrally MODIS-like images. In this study, the product of PAR absorbed by chlorophyll (fAPARchl) has been used to simulate carbon flux over different kinds of vegetation types. The results show that MODIS fAPARchl product has the ability to better characterize phenology than current phenology model in the Community Land Model and it also will likely be able to increase the accuracy of carbon fluxes simulations.

Water Relations and Foliar Isotopic Composition of Prosopis tamarugo Phil., an Endemic Tree of the Atacama Desert Growing at Three Levels of Water Table Depth.

PubMed

Garrido, Marco; Silva, Paola; Acevedo, Edmundo

2016-01-01

Prosopis tamarugo Phil. is a strict phreatophyte tree species endemic to the "Pampa del Tamarugal", Atacama Desert. The extraction of water for various uses has increased the depth of the water table in the Pampa aquifers threatening its conservation. This study aimed to determine the effect of the groundwater table depth on the water relations of P. tamarugo and to present thresholds of groundwater depth (GWD) that can be used in the groundwater management of the P. tamarugo ecosystem. Three levels of GWD, 11.2 ± 0.3 m, 10.3 ± 0.3 m, and 7.1 ± 0.1 m, (the last GWD being our reference) were selected and groups of four individuals per GWD were studied in the months of January and July of the years 2011 through 2014. When the water table depth exceeded 10 m, P. tamarugo had lower pre-dawn and mid-day water potential but no differences were observed in minimum leaf stomatal resistance when compared to the condition of 7.1 m GWD; the leaf tissue increased its δ(13)C and δ(18)O composition. Furthermore, a smaller green canopy fraction of the trees and increased foliage loss in winter with increasing water table depth was observed. The differences observed in the physiological behavior of P. tamarugo trees, attributable to the ground water depth; show that increasing the depth of the water table from 7 to 11 m significantly affects the water status of P. tamarugo. The results indicate that P. tamarugo has an anisohydric stomatal behavior and that given a reduction in water supply it regulates the water demand via foliage loss. The growth and leaf physiological activities are highly sensitive to GWD. The foliage loss appears to prevent the trees from reaching water potentials leading to complete loss of hydraulic functionality by cavitation. The balance achieved between water supply and demand was reflected in the low variation of the water potential and of the variables related to gas exchange over time for a given GWD. This acclimation capacity of P. tamarugo after experiencing increases in GWD has great value for the implementation of conservation strategies. The thresholds presented in this paper should prove useful for conservation purposes of this unique species.

Water Relations and Foliar Isotopic Composition of Prosopis tamarugo Phil., an Endemic Tree of the Atacama Desert Growing at Three Levels of Water Table Depth

PubMed Central

Garrido, Marco; Silva, Paola; Acevedo, Edmundo

2016-01-01

Prosopis tamarugo Phil. is a strict phreatophyte tree species endemic to the “Pampa del Tamarugal”, Atacama Desert. The extraction of water for various uses has increased the depth of the water table in the Pampa aquifers threatening its conservation. This study aimed to determine the effect of the groundwater table depth on the water relations of P. tamarugo and to present thresholds of groundwater depth (GWD) that can be used in the groundwater management of the P. tamarugo ecosystem. Three levels of GWD, 11.2 ± 0.3 m, 10.3 ± 0.3 m, and 7.1 ± 0.1 m, (the last GWD being our reference) were selected and groups of four individuals per GWD were studied in the months of January and July of the years 2011 through 2014. When the water table depth exceeded 10 m, P. tamarugo had lower pre-dawn and mid-day water potential but no differences were observed in minimum leaf stomatal resistance when compared to the condition of 7.1 m GWD; the leaf tissue increased its δ13C and δ18O composition. Furthermore, a smaller green canopy fraction of the trees and increased foliage loss in winter with increasing water table depth was observed. The differences observed in the physiological behavior of P. tamarugo trees, attributable to the ground water depth; show that increasing the depth of the water table from 7 to 11 m significantly affects the water status of P. tamarugo. The results indicate that P. tamarugo has an anisohydric stomatal behavior and that given a reduction in water supply it regulates the water demand via foliage loss. The growth and leaf physiological activities are highly sensitive to GWD. The foliage loss appears to prevent the trees from reaching water potentials leading to complete loss of hydraulic functionality by cavitation. The balance achieved between water supply and demand was reflected in the low variation of the water potential and of the variables related to gas exchange over time for a given GWD. This acclimation capacity of P. tamarugo after experiencing increases in GWD has great value for the implementation of conservation strategies. The thresholds presented in this paper should prove useful for conservation purposes of this unique species. PMID:27064665

Use of Plant Hydraulic Theory to Predict Ecosystem Fluxes Across Mountainous Gradients in Environmental Controls and Insect Disturbances

NASA Astrophysics Data System (ADS)

Ewers, B. E.; Pendall, E.; Reed, D. E.; Barnard, H. R.; Whitehouse, F.; Frank, J. M.; Massman, W. J.; Brooks, P. D.; Biederman, J. A.; Harpold, A. A.; Naithani, K. J.; Mitra, B.; Mackay, D. S.; Norton, U.; Borkhuu, B.

2011-12-01

While mountainous areas are critical for providing numerous ecosystem benefits at the regional scale, the strong gradients in environmental controls make predictions difficult. A key part of the problem is quantifying and predicting the feedback between mountain gradients and plant function which then controls ecosystem cycling. The emerging theory of plant hydraulics provides a rigorous yet simple platform from which to generate testable hypotheses and predictions of ecosystem pools and fluxes. Plant hydraulic theory predicts that plant controls over carbon, water, energy and nutrient fluxes can be derived from the limitation of plant water transport from the soil through xylem and out of stomata. In addition, the limit to plant water transport can be predicted by combining plant structure (e.g. xylem diameters or root-to-shoot ratios) and plant function (response of stomatal conductance to vapor pressure deficit or root vulnerability to cavitation). We evaluate the predictions of the plant hydraulic theory by testing it against data from a mountain gradient encompassing sagebrush steppe through subalpine forests (2700 to 3400 m). We further test the theory by predicting the carbon, water and nutrient exchanges from several coniferous trees in the same gradient that are dying from xylem dysfunction caused by blue-stain fungi carried by bark beetles. The common theme of both of these data sets is a change in water limitation caused by either changing precipitation along the mountainous gradient or lack of access to soil water from xylem-occluding fungi. Across all of the data sets which range in scale from individual plants to hillslopes, the data fit the predictions of plant hydraulic theory. Namely, there was a proportional tradeoff between the reference canopy stomatal conductance to water vapor and the sensitivity of that conductance to vapor pressure deficit that quantitatively fits the predictions of plant hydraulic theory. Incorporating this result into whole plant mass and energy exchange models allows prediction of plant carbon, energy and nitrogen exchange that fits recently collected data including plant sap flux, leaf gas exchange, eddy covariance towers and stand and watershed-scale biogeochemistry measurements. The results of our work will allow the next generation of ecosystem to regional scale coupled-biogeochemistry models to incorporate a simple plant hydraulic mechanism that will enable defensible predictions of carbon, water, energy and nutrient cycling with changing climate and land use.

Algorithm for retrieving vegetative canopy and leaf parameters from multi- and hyperspectral imagery

NASA Astrophysics Data System (ADS)

Borel, Christoph

2009-05-01

In recent years hyper-spectral data has been used to retrieve information about vegetative canopies such as leaf area index and canopy water content. For the environmental scientist these two parameters are valuable, but there is potentially more information to be gained as high spatial resolution data becomes available. We developed an Amoeba (Nelder-Mead or Simplex) based program to invert a vegetative canopy radiosity model coupled with a leaf (PROSPECT5) reflectance model and modeled for the background reflectance (e.g. soil, water, leaf litter) to a measured reflectance spectrum. The PROSPECT5 leaf model has five parameters: leaf structure parameter Nstru, chlorophyll a+b concentration Cab, carotenoids content Car, equivalent water thickness Cw and dry matter content Cm. The canopy model has two parameters: total leaf area index (LAI) and number of layers. The background reflectance model is either a single reflectance spectrum from a spectral library() derived from a bare area pixel on an image or a linear mixture of soil spectra. We summarize the radiosity model of a layered canopy and give references to the leaf/needle models. The method is then tested on simulated and measured data. We investigate the uniqueness, limitations and accuracy of the retrieved parameters on canopy parameters (low, medium and high leaf area index) spectral resolution (32 to 211 band hyperspectral), sensor noise and initial conditions.

Experimental investigation of the effect of Reynolds number on flow structures in the wake of a circular parachute canopy

NASA Astrophysics Data System (ADS)

Jin, Zhe-Yan; Pasqualini, Sylvio; Qin, Bo

2014-06-01

In the present study, an experimental study was conducted to characterize the effect of Reynolds number on flow structures in the turbulent wake of a circular parachute canopy by utilizing stereoscopic particle image velocimetry (Stereo-PIV) technique. The parachute model tested in the present study was attached by 28 nylon suspension lines and placed horizontally at the test section center of the wind tunnel. The obtained results showed that with the increase of Reynolds number, the intensities of the vortices near the downstream region of the canopy skirt were found to increase accordingly. However, the increase of Reynolds number did not result in a significant change in ensembleaveraged normalized x-component of the velocity, ensembleaveraged normalized vorticity, normalized Reynolds stress, and normalized turbulent kinetic energy distributions in the turbulent wake of the circular parachute canopy. The obtained results are very useful to further our understanding about the unsteady aerodynamics in the wake of flexible circular parachute canopies and to constitute a reference for CFD computation.

Effects of groundwater abstraction on two keystone tree species in an arid savanna national park.

PubMed

Shadwell, Eleanor; February, Edmund

2017-01-01

In arid systems with no surface water, deep boreholes in ephemeral river beds provide for humans and animals. With continually increasing infrastructure development for tourism in arid wildlife parks such as the Kgalagadi Transfrontier Park in southern Africa, we ask what effects increased abstraction may have on large trees. Large trees in arid savannas perform essential ecosystem services by providing food, shade, nesting sites and increased nutrients for many other plant and animal species and for this are regarded as keystone species. We determine seasonal fluctuations in the water table while also determining the water source for the dominant large tree species in the Auob and Nossob rivers in the Park. We also determine the extent to which these trees are physiologically stressed using leaf δ 13 C, xylem pressure potentials, specific leaf area and an estimate of canopy death. We do this both upstream and downstream of a low water use borehole in the Auob River and a high water use borehole in the Nossob River. Our results show that the trees are indeed using deep groundwater in the wet season and that this is the same water used by people. In the dry season, trees in the Auob downstream of the active borehole become detached from the aquifer and use more isotopically enriched soil water. In the Nossob in the dry season, all trees use isotopically enriched soil water, and downstream of the active borehole use stomatal regulation to maintain leaf water potentials. These results suggest that trees in the more heavily utilised Nossob are under more water stress than those trees in the Auob but that trees in both rivers demonstrate physiological adaptation to the changes in available water with smaller heavier leaves, no significant canopy dieback and in the dry season in the Nossob stomatal regulation of leaf water potentials. An increase in abstraction of groundwater particularly at the Nossob borehole may cause an additional draw down of the water table adding to the physiological stress demonstrated in our study. The managers of the Kgalagadi Transfrontier Park have a mandate that includes biodiversity conservation. To fulfil this mandate, upper and lower thresholds for groundwater abstraction that allow for an adequate ecological reserve have to be determined.

Effects of groundwater abstraction on two keystone tree species in an arid savanna national park

PubMed Central

2017-01-01

Background In arid systems with no surface water, deep boreholes in ephemeral river beds provide for humans and animals. With continually increasing infrastructure development for tourism in arid wildlife parks such as the Kgalagadi Transfrontier Park in southern Africa, we ask what effects increased abstraction may have on large trees. Large trees in arid savannas perform essential ecosystem services by providing food, shade, nesting sites and increased nutrients for many other plant and animal species and for this are regarded as keystone species. Methods We determine seasonal fluctuations in the water table while also determining the water source for the dominant large tree species in the Auob and Nossob rivers in the Park. We also determine the extent to which these trees are physiologically stressed using leaf δ13C, xylem pressure potentials, specific leaf area and an estimate of canopy death. We do this both upstream and downstream of a low water use borehole in the Auob River and a high water use borehole in the Nossob River. Results Our results show that the trees are indeed using deep groundwater in the wet season and that this is the same water used by people. In the dry season, trees in the Auob downstream of the active borehole become detached from the aquifer and use more isotopically enriched soil water. In the Nossob in the dry season, all trees use isotopically enriched soil water, and downstream of the active borehole use stomatal regulation to maintain leaf water potentials. These results suggest that trees in the more heavily utilised Nossob are under more water stress than those trees in the Auob but that trees in both rivers demonstrate physiological adaptation to the changes in available water with smaller heavier leaves, no significant canopy dieback and in the dry season in the Nossob stomatal regulation of leaf water potentials. Discussion An increase in abstraction of groundwater particularly at the Nossob borehole may cause an additional draw down of the water table adding to the physiological stress demonstrated in our study. The managers of the Kgalagadi Transfrontier Park have a mandate that includes biodiversity conservation. To fulfil this mandate, upper and lower thresholds for groundwater abstraction that allow for an adequate ecological reserve have to be determined. PMID:28149693

Effects of stomatal development on stomatal conductance and on stomatal limitation of photosynthesis in Syringa oblata and Euonymus japonicus Thunb.

PubMed

Wu, Bing-Jie; Chow, Wah Soon; Liu, Yu-Jun; Shi, Lei; Jiang, Chuang-Dao

2014-12-01

During leaf development, the increase in stomatal conductance cannot meet photosynthetic demand for CO2, thus leading to stomatal limitation of photosynthesis (Ls). Considering the crucial influences of stomatal development on stomatal conductance, we speculated whether stomatal development limits photosynthesis to some extent. To test this hypothesis, stomatal development, stomatal conductance and photosynthesis were carefully studied in both Syringa oblata (normal greening species) and Euonymus japonicus Thunb (delayed greening species). Our results show that the size of stomata increased gradually with leaf expansion, resulting in increased stomatal conductance up to the time of full leaf expansion. During this process, photosynthesis also increased steadily. Compared to that in S. oblata, the development of chloroplasts in E. japonicus Thunb was obviously delayed, leading to a delay in the improvement of photosynthetic capacity. Further analysis revealed that before full leaf expansion, stomatal limitation increased rapidly in both S. oblata and E. japonicus Thunb; after full leaf expansion, stomatal limitation continually increased in E. japonicus Thunb. Accordingly, we suggested that the enhancement of photosynthetic capacity is the main factor leading to stomatal limitation during leaf development but that stomatal development can alleviate stomatal limitation with the increase of photosynthesis by controlling gas exchange. Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.

Quantification of Lyssavirus-Neutralizing Antibodies Using Vesicular Stomatitis Virus Pseudotype Particles.

PubMed

Moeschler, Sarah; Locher, Samira; Conzelmann, Karl-Klaus; Krämer, Beate; Zimmer, Gert

2016-09-16

Rabies is a highly fatal zoonotic disease which is primarily caused by rabies virus (RABV) although other members of the genus Lyssavirus can cause rabies as well. As yet, 14 serologically and genetically diverse lyssaviruses have been identified, mostly in bats. To assess the quality of rabies vaccines and immunoglobulin preparations, virus neutralization tests with live RABV are performed in accordance with enhanced biosafety standards. In the present work, a novel neutralization test is presented which takes advantage of a modified vesicular stomatitis virus (VSV) from which the glycoprotein G gene has been deleted and replaced by reporter genes. This single-cycle virus was trans-complemented with RABV envelope glycoprotein. Neutralization of this pseudotype virus with RABV reference serum or immune sera from vaccinated mice showed a strong correlation with the rapid fluorescent focus inhibition test (RFFIT). Importantly, pseudotype viruses containing the envelope glycoproteins of other lyssaviruses were neutralized by reference serum to a significantly lesser extent or were not neutralized at all. Taken together, a pseudotype virus system has been successfully developed which allows the safe, fast, and sensitive detection of neutralizing antibodies directed against different lyssaviruses.

Flow adjustment inside homogeneous canopies after a leading edge – An analytical approach backed by LES

DOE PAGES

Kroniger, Konstantin; Banerjee, Tirtha; De Roo, Frederik; ...

2017-10-06

A two-dimensional analytical model for describing the mean flow behavior inside a vegetation canopy after a leading edge in neutral conditions was developed and tested by means of large eddy simulations (LES) employing the LES code PALM. The analytical model is developed for the region directly after the canopy edge, the adjustment region, where one-dimensional canopy models fail due to the sharp change in roughness. The derivation of this adjustment region model is based on an analytic solution of the two-dimensional Reynolds averaged Navier–Stokes equation in neutral conditions for a canopy with constant plant area density (PAD). The main assumptionsmore » for solving the governing equations are separability of the velocity components concerning the spatial variables and the neglection of the Reynolds stress gradients. These two assumptions are verified by means of LES. To determine the emerging model parameters, a simultaneous fitting scheme was applied to the velocity and pressure data of a reference LES simulation. Furthermore a sensitivity analysis of the adjustment region model, equipped with the previously calculated parameters, was performed varying the three relevant length, the canopy height ( h), the canopy length and the adjustment length ( Lc), in additional LES. Even if the model parameters are, in general, functions of h/ Lc, it was found out that the model is capable of predicting the flow quantities in various cases, when using constant parameters. Subsequently the adjustment region model is combined with the one-dimensional model of Massman, which is applicable for the interior of the canopy, to attain an analytical model capable of describing the mean flow for the full canopy domain. As a result, the model is tested against an analytical model based on a linearization approach.« less

Flow adjustment inside homogeneous canopies after a leading edge – An analytical approach backed by LES

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

Kroniger, Konstantin; Banerjee, Tirtha; De Roo, Frederik

A two-dimensional analytical model for describing the mean flow behavior inside a vegetation canopy after a leading edge in neutral conditions was developed and tested by means of large eddy simulations (LES) employing the LES code PALM. The analytical model is developed for the region directly after the canopy edge, the adjustment region, where one-dimensional canopy models fail due to the sharp change in roughness. The derivation of this adjustment region model is based on an analytic solution of the two-dimensional Reynolds averaged Navier–Stokes equation in neutral conditions for a canopy with constant plant area density (PAD). The main assumptionsmore » for solving the governing equations are separability of the velocity components concerning the spatial variables and the neglection of the Reynolds stress gradients. These two assumptions are verified by means of LES. To determine the emerging model parameters, a simultaneous fitting scheme was applied to the velocity and pressure data of a reference LES simulation. Furthermore a sensitivity analysis of the adjustment region model, equipped with the previously calculated parameters, was performed varying the three relevant length, the canopy height ( h), the canopy length and the adjustment length ( Lc), in additional LES. Even if the model parameters are, in general, functions of h/ Lc, it was found out that the model is capable of predicting the flow quantities in various cases, when using constant parameters. Subsequently the adjustment region model is combined with the one-dimensional model of Massman, which is applicable for the interior of the canopy, to attain an analytical model capable of describing the mean flow for the full canopy domain. As a result, the model is tested against an analytical model based on a linearization approach.« less

Influence of irrigation and fertilization on transpiration and hydraulic properties of Populus deltoides.

PubMed

Samuelson, Lisa J; Stokes, Thomas A; Coleman, Mark D

2007-05-01

Long-term hydraulic acclimation to resource availability was explored in 3-year-old Populus deltoides Bartr. ex Marsh. clones by examining transpiration, leaf-specific hydraulic conductance (G(L)), canopy stomatal conductance (G(S)) and leaf to sapwood area ratio (A(L):A(S)) in response to irrigation (13 and 551 mm year(-1) in addition to ambient precipitation) and fertilization (0 and 120 kg N ha(-1) year(-1)). Sap flow was measured continuously over one growing season with thermal dissipation probes. Fertilization had a greater effect on growth and hydraulic properties than irrigation, and fertilization effects were independent of irrigation treatment. Transpiration on a ground area basis (E) ranged between 0.3 and 1.8 mm day(-1), and increased 66% and 90% in response to irrigation and fertilization, respectively. Increases in G(L), G(S) at a reference vapor pressure deficit of 1 kPa, and transpiration per unit leaf area in response to increases in resource availability were associated with reductions in A(L):A(S) and consequently a minimal change in the water potential gradient from soil to leaf. Irrigation and fertilization increased leaf area index similarly, from an average 1.16 in control stands to 1.45, but sapwood area was increased from 4.0 to 6.3 m(2) ha(-1) by irrigation and from 3.7 to 6.7 m(2) ha(-1) by fertilization. The balance between leaf area and sapwood area was important in understanding long-term hydraulic acclimation to resource availability and mechanisms controlling maximum productivity in Populus deltoides.

Watershed Land Use and Seasonal Variation Constrain the ...

EPA Pesticide Factsheets

While watershed and local scale controls on stream metabolism have been independently investigated, little is known about how controls exerted at these different scales interact to determine stream metabolic rates, or how these interactions vary across seasons. To address this knowledge gap, we measured ecosystem metabolism in four urban and four reference streams in northern Kentucky, USA, with paired closed and open riparian canopies, during each of the four seasons of the year. Gross primary production (GPP), ecosystem respiration (ER), and net ecosystem production (NEP) were all best predicted by models with season as a main effect, but interactions between season, canopy and watershed varied for each response. Urban streams exhibited higher GPP during most seasons, likely due to elevated nutrient loads. Open canopy reaches in both urban and forested streams supported higher rates of GPP than the closed canopy reaches during the summer and fall when the overhead vegetation shaded the closed reaches. Surprisingly, the effect of canopy cover on GPP was similar among urban and forested streams. The combination of watershed and local-scale controls resulted in urban streams that alternated between net heterotrophy (NEP 0) between seasons with and without dense canopy cover. This finding has management relevance because net production can lead to accumulation of algal biomass and associated issues like dissolved oxygen sags at night. Our study reinforces

A Comparison of Mangrove Canopy Height Using Multiple Independent Measurements from Land, Air, and Space

NASA Technical Reports Server (NTRS)

Lagomasino, David; Fatoyinbo, Temilola; Lee, SeungKuk; Feliciano, Emanuelle; Trettin, Carl; Simard, Marc

2016-01-01

Canopy height is one of the strongest predictors of biomass and carbon in forested ecosystems. Additionally, mangrove ecosystems represent one of the most concentrated carbon reservoirs that are rapidly degrading as a result of deforestation, development, and hydrologic manipulation. Therefore, the accuracy of Canopy Height Models (CHM) over mangrove forest can provide crucial information for monitoring and verification protocols. We compared four CHMs derived from independent remotely sensed imagery and identified potential errors and bias between measurement types. CHMs were derived from three spaceborne datasets; Very-High Resolution (VHR) stereophotogrammetry, TerraSAR-X add-on for Digital Elevation Measurement (DEM), and Shuttle Radar Topography Mission (TanDEM-X), and lidar data which was acquired from an airborne platform. Each dataset exhibited different error characteristics that were related to spatial resolution, sensitivities of the sensors, and reference frames. Canopies over 10 meters were accurately predicted by all CHMs while the distributions of canopy height were best predicted by the VHR CHM. Depending on the guidelines and strategies needed for monitoring and verification activities, coarse resolution CHMs could be used to track canopy height at regional and global scales with finer resolution imagery used to validate and monitor critical areas undergoing rapid changes.

Weak trophic interactions among birds, insects and white oak saplings (Quercus alba)

USGS Publications Warehouse

Lichtenberg, J.S.; Lichtenberg, D.A.

2002-01-01

We examined the interactions among insectivorous birds, arthropods and white oak saplings (Quercus alba L.) in a temperate deciduous forest under 'open' and 'closed' canopy environments. For 2 y, we compared arthropod densities, leaf damage and sapling growth. Saplings from each canopy environment were assigned to one of four treatments: (1) reference, (2) bird exclosure, (3) insecticide and (4) exclosure + insecticide. Sap-feeding insects were the most abundant arthropod feeding guild encountered and birds reduced sap-feeder densities in 1997, but not in 1998. Although there was no detectable influence of birds on leaf-chewer densities in either year, leaf damage to saplings was greater within bird exclosures than outside of bird exclosures in 1997. Insecticide significantly reduced arthropod densities and leaf damage to saplings, but there was no corresponding increase in sapling growth. Growth and biomass were greater for saplings in more open canopy environments for both years. Sap-feeder densities were higher on closed canopy than open canopy saplings in 1997, but canopy environment did not influence the effects of birds on lower trophic levels. Although previous studies have found birds to indirectly influence plant growth and biomass, birds did not significantly influence the growth or biomass of white oak saplings during our study.

A Comparison of Mangrove Canopy Height Using Multiple Independent Measurements from Land, Air, and Space

PubMed Central

Lagomasino, David; Fatoyinbo, Temilola; Lee, SeungKuk; Feliciano, Emanuelle; Trettin, Carl; Simard, Marc

2017-01-01

Canopy height is one of the strongest predictors of biomass and carbon in forested ecosystems. Additionally, mangrove ecosystems represent one of the most concentrated carbon reservoirs that are rapidly degrading as a result of deforestation, development, and hydrologic manipulation. Therefore, the accuracy of Canopy Height Models (CHM) over mangrove forest can provide crucial information for monitoring and verification protocols. We compared four CHMs derived from independent remotely sensed imagery and identified potential errors and bias between measurement types. CHMs were derived from three spaceborne datasets; Very-High Resolution (VHR) stereophotogrammetry, TerraSAR-X add-on for Digital Elevation Measurement, and Shuttle Radar Topography Mission (TanDEM-X), and lidar data which was acquired from an airborne platform. Each dataset exhibited different error characteristics that were related to spatial resolution, sensitivities of the sensors, and reference frames. Canopies over 10 m were accurately predicted by all CHMs while the distributions of canopy height were best predicted by the VHR CHM. Depending on the guidelines and strategies needed for monitoring and verification activities, coarse resolution CHMs could be used to track canopy height at regional and global scales with finer resolution imagery used to validate and monitor critical areas undergoing rapid changes. PMID:29629207

Mechanistic modelling of Middle Eocene atmospheric carbon dioxide using fossil plant material

NASA Astrophysics Data System (ADS)

Grein, Michaela; Roth-Nebelsick, Anita; Wilde, Volker; Konrad, Wilfried; Utescher, Torsten

2010-05-01

Various proxies (such as pedogenic carbonates, boron isotopes or phytoplankton) and geochemical models were applied in order to reconstruct palaeoatmospheric carbon dioxide, partially providing conflicting results. Another promising proxy is the frequency of stomata (pores on the leaf surface used for gaseous exchange). In this project, fossil plant material from the Messel Pit (Hesse, Germany) is used to reconstruct atmospheric carbon dioxide concentration in the Middle Eocene by analyzing stomatal density. We applied the novel mechanistic-theoretical approach of Konrad et al. (2008) which provides a quantitative derivation of the stomatal density response (number of stomata per leaf area) to varying atmospheric carbon dioxide concentration. The model couples 1) C3-photosynthesis, 2) the process of diffusion and 3) an optimisation principle providing maximum photosynthesis (via carbon dioxide uptake) and minimum water loss (via stomatal transpiration). These three sub-models also include data of the palaeoenvironment (temperature, water availability, wind velocity, atmospheric humidity, precipitation) and anatomy of leaf and stoma (depth, length and width of stomatal porus, thickness of assimilation tissue, leaf length). In order to calculate curves of stomatal density as a function of atmospheric carbon dioxide concentration, various biochemical parameters have to be borrowed from extant representatives. The necessary palaeoclimate data are reconstructed from the whole Messel flora using Leaf Margin Analysis (LMA) and the Coexistence Approach (CA). In order to obtain a significant result, we selected three species from which a large number of well-preserved leaves is available (at least 20 leaves per species). Palaeoclimate calculations for the Middle Eocene Messel Pit indicate a warm and humid climate with mean annual temperature of approximately 22°C, up to 2540 mm mean annual precipitation and the absence of extended periods of drought. Mean relative air humidity was probably rather high, up to 77%. The combined results of the three selected plant taxa indicate values for atmospheric carbon dioxide concentration between 700 and 1100 ppm (probably about 900 ppm). Reference: Konrad, W., Roth-Nebelsick, A., Grein, M. (2008). Modelling of stomatal density response to atmospheric CO2. Journal of Theoretical Biology 253(4): 638-658.

Regional Mapping of Coupled Fluxes of Carbon and Water Using Multi-Sensor Fusion Techniques

NASA Astrophysics Data System (ADS)

Schull, M. A.; Anderson, M. C.; Semmens, K. A.; Yang, Y.; Gao, F.; Hain, C.; Houborg, R.

2014-12-01

In an ever-changing climate there is an increasing need to measure the fluxes of water, energy and carbon for decision makers to implement policies that will help mitigate the effects of climate change. In an effort to improve drought monitoring, water resource management and agriculture assessment capabilities, a multi-scale and multi-sensor framework for routine mapping of land-surface fluxes of water and energy at field to regional scales has been established. The framework uses the ALEXI (Atmosphere Land Exchange Inverse)/DisALEXI (Disaggregated ALEXI) suite of land-surface models forced by remotely sensed data from Landsat, MODIS (MODerate resolution Imaging Spectroradiometer), and GOES (Geostationary Operational Environmental Satellite). Land-surface temperature (LST) can be an effective substitute for in-situ surface moisture observations and a valuable metric for constraining land-surface fluxes at sub-field scales. The adopted multi-scale thermal-based land surface modeling framework facilitates regional to local downscaling of water and energy fluxes by using a combination of shortwave reflective and thermal infrared (TIR) imagery from GOES (4-10 km; hourly), MODIS (1 km; daily), and Landsat (30-100 m; bi-weekly). In this research the ALEXI/DisALEXI modeling suite is modified to incorporate carbon fluxes using a stomatal resistance module, which replaces the Priestley-Taylor latent heat approximation. In the module, canopy level nominal light-use-efficiency (βn) is the parameter that modulates the flux of water and carbon in and out of the canopy. Leaf chlorophyll (Chl) is a key parameter for quantifying variability in photosynthetic efficiency to facilitate the spatial distribution of coupled carbon and water retrievals. Spatial distribution of Chl are retrieved from Landsat (30 m) using a surface reflectance dataset as input to the REGularized canopy reFLECtance (REGFLEC) tool. The modified ALEXI/DisALEXI suite is applied to regions of rain fed and irrigated soybean and maize agricultural landscapes within the continental U.S. and flux estimates are compared with flux tower observations.

Mapping a region within the 1RS.1BL translocation in common wheat affecting grain yield and canopy water status.

PubMed

Howell, Tyson; Hale, Iago; Jankuloski, Ljupcho; Bonafede, Marcos; Gilbert, Matthew; Dubcovsky, Jorge

2014-12-01

This study identifies a small distal region of the 1RS chromosome from rye that has a positive impact on wheat yield. The translocation of the short arm of rye (Secale cereale L.) chromosome one (1RS) onto wheat (Triticum aestivum L.) chromosome 1B (1RS.1BL) is used in wheat breeding programs worldwide due to its positive effect on yield, particularly under abiotic stress. Unfortunately, this translocation is associated with poor bread-making quality. To mitigate this problem, the 1RS arm was engineered by the removal and replacement of two interstitial rye segments with wheat chromatin: a distal segment to introduce the Glu-B3/Gli-B1 loci from wheat, and a proximal segment to remove the rye Sec-1 locus. We used this engineered 1RS chromosome (henceforth 1RS(WW)) to develop and evaluate two sets of 1RS/1RS(WW) near isogenic lines (NILs). Field trials showed that standard 1RS lines had significantly higher yield and better canopy water status than the 1RS(WW) NILs in both well-watered and water-stressed environments. We intercrossed the 1RS and 1RS(WW) lines and generated two additional NILs, one carrying the distal (1RS(RW)) and the other carrying the proximal (1RS(WR)) wheat segment. Lines not carrying the distal wheat region (1RS and 1RS(WR)) showed significant improvements in grain yield and canopy water status compared to NILs carrying the distal wheat segment (1RS(WW) and 1RS(RW)), indicating that the 1RS region replaced by the distal wheat segment carries the beneficial allele(s). NILs without the distal wheat segment also showed higher carbon isotope discrimination and increased stomatal conductance, suggesting that these plants had improved access to water. The 1RS(WW), 1RS(WR) and 1RS(RW) NILs have been deposited in the National Small Grains Collection.

Carbonyl sulfide exchange in a temperate loblolly pine forest grown under ambient and elevated CO2

NASA Astrophysics Data System (ADS)

White, M. L.; Zhou, Y.; Russo, R. S.; Mao, H.; Talbot, R.; Varner, R. K.; Sive, B. C.

2009-08-01

Vegetation, soil and ecosystem level carbonyl sulfide (COS) exchange was observed at Duke Forest, a temperate loblolly pine forest, grown under ambient (Ring 1, R1) and elevated (Ring 2, R2) carbon dioxide (CO2). During calm meteorological conditions, ambient COS mixing ratios at the top of the forest canopy followed a distinct diurnal pattern in both CO2 growth regimes, with maximum COS mixing ratios during the day (R1=380±4 pptv and R2=373±3 pptv, daytime mean ±standard error) and minimums at night (R1=340±6 pptv and R2=346±5 pptv, nighttime mean ±standard error) reflecting a significant nighttime sink. Nocturnal vegetative uptake (-11 to -21 pmol m-2 s-1, negative values indicate uptake from the atmosphere) dominated nighttime net ecosystem COS flux estimates (-10 to -30 pmol m-2 s-1) in both CO2 regimes. In comparison, soil uptake (-0.8 to -1.7 pmol m-2 s-1) was a minor component of net ecosystem COS flux. In both CO2 regimes, loblolly pine trees exhibited substantial COS consumption overnight (50% of daytime rates) that was independent of CO2 assimilation. This suggests current estimates of the global vegetative COS sink, which assume that COS and CO2 are consumed simultaneously, may need to be reevaluated. Ambient COS mixing ratios, species specific diurnal patterns of stomatal conductance, temperature and canopy position were the major factors influencing the vegetative COS flux at the branch level. While variability in branch level vegetative COS consumption measurements in ambient and enhanced CO2 environments could not be attributed to CO2 enrichment effects, estimates of net ecosystem COS flux based on ambient canopy mixing ratio measurements suggest less nighttime uptake of COS in R2, the CO2 enriched environment.

Carbonyl sulfide exchange in a temperate loblolly pine forest grown under ambient and elevated CO2

NASA Astrophysics Data System (ADS)

White, M. L.; Zhou, Y.; Russo, R. S.; Mao, H.; Talbot, R.; Varner, R. K.; Sive, B. C.

2010-01-01

Vegetation, soil and ecosystem level carbonyl sulfide (COS) exchange was observed at Duke Forest, a temperate loblolly pine forest, grown under ambient (Ring 1, R1) and elevated (Ring 2, R2) CO2. During calm meteorological conditions, ambient COS mixing ratios at the top of the forest canopy followed a distinct diurnal pattern in both CO2 growth regimes, with maximum COS mixing ratios during the day (R1=380±4 pptv and R2=373±3 pptv, daytime mean ± standard error) and minimums at night (R1=340±6 pptv and R2=346±5 pptv, nighttime mean ± standard error) reflecting a significant nighttime sink. Nocturnal vegetative uptake (-11 to -21 pmol m-2s-1, negative values indicate uptake from the atmosphere) dominated nighttime net ecosystem COS flux estimates (-10 to -30 pmol m-2s-1) in both CO2 regimes. In comparison, soil uptake (-0.8 to -1.7 pmol m-2 s-1) was a minor component of net ecosystem COS flux. In both CO2 regimes, loblolly pine trees exhibited substantial COS consumption overnight (50% of daytime rates) that was independent of CO2 assimilation. This suggests current estimates of the global vegetative COS sink, which assume that COS and CO2 are consumed simultaneously, may need to be reevaluated. Ambient COS mixing ratios, species specific diurnal patterns of stomatal conductance, temperature and canopy position were the major factors influencing the vegetative COS flux at the branch level. While variability in branch level vegetative COS consumption measurements in ambient and enhanced CO2 environments could not be attributed to CO2 enrichment effects, estimates of net ecosystem COS flux based on ambient canopy mixing ratio measurements suggest less nighttime uptake of COS in R2, the CO2 enriched environment.

Stem and leaf gas exchange and their responses to fire in a north Australian tropical savanna.

PubMed

Cernusak, Lucas A; Hutley, Lindsay B; Beringer, Jason; Tapper, Nigel J

2006-04-01

We measured stem CO2 efflux and leaf gas exchange in a tropical savanna ecosystem in northern Australia, and assessed the impact of fire on these processes. Gas exchange of mature leaves that flushed after a fire showed only slight differences from that of mature leaves on unburned trees. Expanding leaves typically showed net losses of CO2 to the atmosphere in both burned and unburned trees, even under saturating irradiance. Fire caused stem CO2 efflux to decline in overstory trees, when measured 8 weeks post-fire. This decline was thought to have resulted from reduced availability of C substrate for respiration, due to reduced canopy photosynthesis caused by leaf scorching, and to priority allocation of fixed C towards reconstruction of a new canopy. At the ecosystem scale, we estimated the annual above-ground woody-tissue CO2 efflux to be 275 g C m(-2) ground area year(-1) in a non-fire year, or approximately 13% of the annual gross primary production. We contrasted the canopy physiology of two co-dominant overstory tree species, one of which has a smooth bark on its branches capable of photosynthetic re-fixation (Eucalyptus miniata), and the other of which has a thick, rough bark incapable of re-fixation (Eucalyptus tetrodonta). Eucalyptus miniata supported a larger branch sapwood cross-sectional area in the crown per unit subtending leaf area, and had higher leaf stomatal conductance and photosynthesis than E. tetrodonta. Re-fixation by photosynthetic bark reduces the C cost of delivering water to evaporative sites in leaves, because it reduces the net C cost of constructing and maintaining sapwood. We suggest that re-fixation allowed leaves of E. miniata to photosynthesize at higher rates than those of E. tetrodonta, while the two invested similar amounts of C in the maintenance of branch sapwood.

Photosynthesis-dependent isoprene emission from leaf to planet in a global carbon-chemistry-climate model

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

Unger, N.; Harper, K.; Zheng, Y.

2013-10-22

We describe the implementation of a biochemical model of isoprene emission that depends on the electron requirement for isoprene synthesis into the Farquhar/Ball- Berry leaf model of photosynthesis and stomatal conductance that is embedded within a global chemistry-climate simulation framework. The isoprene production is calculated as a function of electron transport-limited photosynthesis, intercellular carbon dioxide concentration, and canopy temperature. The vegetation biophysics module computes the photosynthetic uptake of carbon dioxide coupled with the transpiration of water vapor and the isoprene emission rate at the 30 min physical integration time step of the global chemistry-climate model. In the model, the ratemore » of carbon assimilation provides the dominant control on isoprene emission variability over canopy temperature. A control simulation representative of the present day climatic state that uses plant functional types (PFTs), prescribed phenology and generic PFT-specific isoprene emission potentials (fraction of electrons available for isoprene synthesis) reproduces 50% of the variability across different ecosystems and seasons in a global database of measured campaign-average fluxes. Compared to time-varying isoprene flux measurements at select sites, the model authentically captures the observed variability in the 30 min average diurnal cycle (R 2 = 64-96 %) and simulates the flux magnitude to within a factor of 2. The control run yields a global isoprene source strength of 451 TgC yr -1 that increases by 30% in the artificial absence of plant water stress and by 55% for potential natural vegetation.« less

Photosynthesis-dependent Isoprene Emission from Leaf to Planet in a Global Carbon-chemistry-climate Model

NASA Technical Reports Server (NTRS)

Unger, N.; Harper, K.; Zeng, Y.; Kiang, N. Y.; Alienov, I.; Arneth, A.; Schurgers, G.; Amelynck, C.; Goldstein, A.; Guenther, A.;

Estimating evapotranspiration and drought stress with ground-based thermal remote sensing in agriculture: a review.

PubMed

Maes, W H; Steppe, K

2012-08-01

As evaporation of water is an energy-demanding process, increasing evapotranspiration rates decrease the surface temperature (Ts) of leaves and plants. Based on this principle, ground-based thermal remote sensing has become one of the most important methods for estimating evapotranspiration and drought stress and for irrigation. This paper reviews its application in agriculture. The review consists of four parts. First, the basics of thermal remote sensing are briefly reviewed. Second, the theoretical relation between Ts and the sensible and latent heat flux is elaborated. A modelling approach was used to evaluate the effect of weather conditions and leaf or vegetation properties on leaf and canopy temperature. Ts increases with increasing air temperature and incoming radiation and with decreasing wind speed and relative humidity. At the leaf level, the leaf angle and leaf dimension have a large influence on Ts; at the vegetation level, Ts is strongly impacted by the roughness length; hence, by canopy height and structure. In the third part, an overview of the different ground-based thermal remote sensing techniques and approaches used to estimate drought stress or evapotranspiration in agriculture is provided. Among other methods, stress time, stress degree day, crop water stress index (CWSI), and stomatal conductance index are discussed. The theoretical models are used to evaluate the performance and sensitivity of the most important methods, corroborating the literature data. In the fourth and final part, a critical view on the future and remaining challenges of ground-based thermal remote sensing is presented.

Photosynthesis-dependent isoprene emission from leaf to planet in a global carbon-chemistry-climate model

NASA Astrophysics Data System (ADS)

Unger, N.; Harper, K.; Zheng, Y.; Kiang, N. Y.; Aleinov, I.; Arneth, A.; Schurgers, G.; Amelynck, C.; Goldstein, A.; Guenther, A.; Heinesch, B.; Hewitt, C. N.; Karl, T.; Laffineur, Q.; Langford, B.; McKinney, K. A.; Misztal, P.; Potosnak, M.; Rinne, J.; Pressley, S.; Schoon, N.; Serça, D.

2013-10-01

We describe the implementation of a biochemical model of isoprene emission that depends on the electron requirement for isoprene synthesis into the Farquhar-Ball-Berry leaf model of photosynthesis and stomatal conductance that is embedded within a global chemistry-climate simulation framework. The isoprene production is calculated as a function of electron transport-limited photosynthesis, intercellular and atmospheric carbon dioxide concentration, and canopy temperature. The vegetation biophysics module computes the photosynthetic uptake of carbon dioxide coupled with the transpiration of water vapor and the isoprene emission rate at the 30 min physical integration time step of the global chemistry-climate model. In the model, the rate of carbon assimilation provides the dominant control on isoprene emission variability over canopy temperature. A control simulation representative of the present-day climatic state that uses 8 plant functional types (PFTs), prescribed phenology and generic PFT-specific isoprene emission potentials (fraction of electrons available for isoprene synthesis) reproduces 50% of the variability across different ecosystems and seasons in a global database of 28 measured campaign-average fluxes. Compared to time-varying isoprene flux measurements at 9 select sites, the model authentically captures the observed variability in the 30 min average diurnal cycle (R2 = 64-96%) and simulates the flux magnitude to within a factor of 2. The control run yields a global isoprene source strength of 451 TgC yr-1 that increases by 30% in the artificial absence of plant water stress and by 55% for potential natural vegetation.

Photosynthesis-dependent isoprene emission from leaf to planet in a global carbon-chemistry-climate model

NASA Astrophysics Data System (ADS)

Unger, N.; Harper, K.; Zheng, Y.; Kiang, N. Y.; Aleinov, I.; Arneth, A.; Schurgers, G.; Amelynck, C.; Goldstein, A.; Guenther, A.; Heinesch, B.; Hewitt, C. N.; Karl, T.; Laffineur, Q.; Langford, B.; McKinney, K. A.; Misztal, P.; Potosnak, M.; Rinne, J.; Pressley, S.; Schoon, N.; Serça, D.

2013-07-01

We describe the implementation of a biochemical model of isoprene emission that depends on the electron requirement for isoprene synthesis into the Farquhar/Ball-Berry leaf model of photosynthesis and stomatal conductance that is embedded within a global chemistry-climate simulation framework. The isoprene production is calculated as a function of electron transport-limited photosynthesis, intercellular carbon dioxide concentration, and canopy temperature. The vegetation biophysics module computes the photosynthetic uptake of carbon dioxide coupled with the transpiration of water vapor and the isoprene emission rate at the 30 min physical integration time step of the global chemistry-climate model. In the model, the rate of carbon assimilation provides the dominant control on isoprene emission variability over canopy temperature. A control simulation representative of the present day climatic state that uses 8 plant functional types (PFTs), prescribed phenology and generic PFT-specific isoprene emission potentials (fraction of electrons available for isoprene synthesis) reproduces 50% of the variability across different ecosystems and seasons in a global database of 28 measured campaign-average fluxes. Compared to time-varying isoprene flux measurements at 9 select sites, the model authentically captures the observed variability in the 30 min average diurnal cycle (R2= 64-96%) and simulates the flux magnitude to within a factor of 2. The control run yields a global isoprene source strength of 451 Tg C yr-1 that increases by 30% in the artificial absence of plant water stress and by 55% for potential natural vegetation.

Can We Monitor Ecosystem Function Using Keeling Plot Analyses of Nocturnal Cold-Air Drainage?

NASA Astrophysics Data System (ADS)

Bond, B. J.; Ocheltree, T.; Pypker, T.; Unsworth, M. H.; Mix, A. C.; William, R.

2003-12-01

The carbon isotope signature of ecosystem respiration, δ 13CR, as measured by the Keeling Plot approach, has been related to short-term variations in weather and ecosystem function in several recent studies. In order to obtain an adequate range of [CO2] and to sample a consistent vegetation type, investigators typically select sampling locations in relatively flat terrain and uniform canopy cover, but these are unusual conditions for many forested ecosystems. In a pilot study, we are collecting samples for Keeling Plot analyses in cold-air drainage systems in small (60-100 ha), deeply-incised watersheds, one covered with old-growth (ca 450-years-old) Douglas-fir/hemlock forest and one covered with young (ca 45-years-old) Douglas-fir forest. We found that the nightly range of [CO2] was typically 380-460 ppm, sufficient to develop good estimates of δ 13CR. At any point in time there was little variation in [CO2] with height through the canopy (0.5-30m), so the required range was obtained by sampling over several hours. There was no indication that samples taken from different heights or at different times of night represented sources with different isotopic signatures. The isotopic signature of respired CO2 in the older watershed averaged about 1 per mil greater than that of the young watershed, and δ 13CR of both locations correlated with modeled stomatal conductance 6 days prior to flask sampling.

Assessing the effect of marginal water use efficiency on water use of loblolly pine and sweetgum in ambient and elevated CO2 conditions

NASA Astrophysics Data System (ADS)

Kim, D.; Medvigy, D.; Xu, X.; Oren, R.; Ward, E. J.

2017-12-01

Stomata are the common pathways through which diffusion of CO2 and water vapor take place in a plant. Therefore, the responses of stomatal conductance to environmental conditions are important to quantify carbon assimilation and water use of plants. In stomatal optimality theory, plants may adjust the stomatal conductance to maximize carbon assimilation for a given water availability. The carbon cost for unit water loss, marginal water use efficiency (λ), depends on changes in atmospheric CO2 concentration and pre-dawn leaf water potential. The relationship can be described by λ with no water stress (λ0) and the sensitivity of λ to pre-dawn leaf water potential (β0), which may vary by plant functional type. Assessment of sensitivity of tree and canopy water use to those parameters and the estimation of the parameters for individual plant functional type or species are needed. We modeled tree water use of loblolly pine (Pinus taeda) and sweetgum (Liquidambar styraciflua) in ambient and elevated CO2 (+200 µmol mol-1) at the Duke Forest free-air CO2 enrichment (FACE) site with Ecosystem Demography model 2 (ED2), a demographic terrestrial biosphere model that scales up individual-level competition for light, water and nutrients to the ecosystem-level. Simulated sap flux density for different tree size classes and species was compared to observations. The sensitivity analysis with respect to the model's hydraulic parameters was performed. The initial results showed that the impacts of λ on tree water use were greater than other hydraulic traits in the model, such as vertical hydraulic conductivity and leaf and stem capacitance. With 10% increase in λ, modeled water flow from root to leaf decreased by 2.5 and 1.6% for P. taeda and by 7.9 and 5.1% for L. styraciflua in ambient and elevated CO2 conditions, respectively. Values of hydraulic traits (λ0 and β0) for P. taeda and L. styraciflua in ambient an elevated CO2 conditions were also suggested.

The fourth radiation transfer model intercomparison (RAMI-IV): Proficiency testing of canopy reflectance models with ISO-13528

NASA Astrophysics Data System (ADS)

Widlowski, J.-L.; Pinty, B.; Lopatka, M.; Atzberger, C.; Buzica, D.; Chelle, M.; Disney, M.; Gastellu-Etchegorry, J.-P.; Gerboles, M.; Gobron, N.; Grau, E.; Huang, H.; Kallel, A.; Kobayashi, H.; Lewis, P. E.; Qin, W.; Schlerf, M.; Stuckens, J.; Xie, D.

2013-07-01

The radiation transfer model intercomparison (RAMI) activity aims at assessing the reliability of physics-based radiative transfer (RT) models under controlled experimental conditions. RAMI focuses on computer simulation models that mimic the interactions of radiation with plant canopies. These models are increasingly used in the development of satellite retrieval algorithms for terrestrial essential climate variables (ECVs). Rather than applying ad hoc performance metrics, RAMI-IV makes use of existing ISO standards to enhance the rigor of its protocols evaluating the quality of RT models. ISO-13528 was developed "to determine the performance of individual laboratories for specific tests or measurements." More specifically, it aims to guarantee that measurement results fall within specified tolerance criteria from a known reference. Of particular interest to RAMI is that ISO-13528 provides guidelines for comparisons where the true value of the target quantity is unknown. In those cases, "truth" must be replaced by a reliable "conventional reference value" to enable absolute performance tests. This contribution will show, for the first time, how the ISO-13528 standard developed by the chemical and physical measurement communities can be applied to proficiency testing of computer simulation models. Step by step, the pre-screening of data, the identification of reference solutions, and the choice of proficiency statistics will be discussed and illustrated with simulation results from the RAMI-IV "abstract canopy" scenarios. Detailed performance statistics of the participating RT models will be provided and the role of the accuracy of the reference solutions as well as the choice of the tolerance criteria will be highlighted.

Stomatal and non-stomatal factors regulated the photosynthesis of soybean seedlings in the present of exogenous bisphenol A.

PubMed

Jiao, Liya; Wang, Lihong; Zhou, Qing; Huang, Xiaohua

2017-11-01

Bisphenol A (BPA) is an emerging environmental endocrine disruptor that has toxic effects on plants growth. Photosynthesis supplies the substances and energy required for plant growth, and regulated by stomatal and non-stomatal factors. Therefore, in this study, to reveal how BPA affects photosynthesis in soybean seedlings (Glycine max L.) from the perspective of stomatal and non-stomatal factors, the stomatal factors (stomatal conductance and behaviours) and non-stomatal factors (Hill reaction, apparent quantum efficiency, Rubisco activity, carboxylation efficiency, the maximum Rubisco carboxylation velocity, ribulose-1,5-bisphospate regeneration capacities mediated by maximum electron transport rates, and triose phosphate utilization rate) were investigated using a portable photosynthesis system. Moreover, the pollution of BPA in the environment was simulated. The results indicate that low-dose BPA enhanced net photosynthetic rate (P n ) primarily by promoting stomatal factors, resulting in increased relative growth rates and accelerated soybean seedling growth. High-dose BPA decreases the P n by simultaneously inhibiting stomatal and non-stomatal factors, and this inhibition decreases the relative growth rates further reducing soybean seedling growth. Following the withdrawal of BPA, all of the indices were restored to varying degrees. In conclusion, low-dose BPA increased the P n by promoting stomatal factors while high-dose BPA decreased the P n by simultaneously inhibiting stomatal and non-stomatal factors. These findings provide a model (or, hypothesis) for the effects of BPA on plant photosynthesis. Copyright © 2017 Elsevier Inc. All rights reserved.

Soybean leaf hydraulic conductance does not acclimate to growth at elevated [CO2] or temperature in growth chambers or in the field.

PubMed

Locke, Anna M; Sack, Lawren; Bernacchi, Carl J; Ort, Donald R

2013-09-01

Leaf hydraulic properties are strongly linked with transpiration and photosynthesis in many species. However, it is not known if gas exchange and hydraulics will have co-ordinated responses to climate change. The objective of this study was to investigate the responses of leaf hydraulic conductance (Kleaf) in Glycine max (soybean) to growth at elevated [CO2] and increased temperature compared with the responses of leaf gas exchange and leaf water status. Two controlled-environment growth chamber experiments were conducted with soybean to measure Kleaf, stomatal conductance (gs) and photosynthesis (A) during growth at elevated [CO2] and temperature relative to ambient levels. These results were validated with field experiments on soybean grown under free-air elevated [CO2] (FACE) and canopy warming. In chamber studies, Kleaf did not acclimate to growth at elevated [CO2], even though stomatal conductance decreased and photosynthesis increased. Growth at elevated temperature also did not affect Kleaf, although gs and A showed significant but inconsistent decreases. The lack of response of Kleaf to growth at increased [CO2] and temperature in chamber-grown plants was confirmed with field-grown soybean at a FACE facility. Leaf hydraulic and leaf gas exchange responses to these two climate change factors were not strongly linked in soybean, although gs responded to [CO2] and increased temperature as previously reported. This differential behaviour could lead to an imbalance between hydraulic supply and transpiration demand under extreme environmental conditions likely to become more common as global climate continues to change.

Instantaneous-to-daily GPP upscaling schemes based on a coupled photosynthesis-stomatal conductance model: correcting the overestimation of GPP by directly using daily average meteorological inputs.

PubMed

Wang, Fumin; Gonsamo, Alemu; Chen, Jing M; Black, T Andrew; Zhou, Bin

2014-11-01

Daily canopy photosynthesis is usually temporally upscaled from instantaneous (i.e., seconds) photosynthesis rate. The nonlinear response of photosynthesis to meteorological variables makes the temporal scaling a significant challenge. In this study, two temporal upscaling schemes of daily photosynthesis, the integrated daily model (IDM) and the segmented daily model (SDM), are presented by considering the diurnal variations of meteorological variables based on a coupled photosynthesis-stomatal conductance model. The two models, as well as a simple average daily model (SADM) with daily average meteorological inputs, were validated using the tower-derived gross primary production (GPP) to assess their abilities in simulating daily photosynthesis. The results showed IDM closely followed the seasonal trend of the tower-derived GPP with an average RMSE of 1.63 g C m(-2) day(-1), and an average Nash-Sutcliffe model efficiency coefficient (E) of 0.87. SDM performed similarly to IDM in GPP simulation but decreased the computation time by >66%. SADM overestimated daily GPP by about 15% during the growing season compared to IDM. Both IDM and SDM greatly decreased the overestimation by SADM, and improved the simulation of daily GPP by reducing the RMSE by 34 and 30%, respectively. The results indicated that IDM and SDM are useful temporal upscaling approaches, and both are superior to SADM in daily GPP simulation because they take into account the diurnally varying responses of photosynthesis to meteorological variables. SDM is computationally more efficient, and therefore more suitable for long-term and large-scale GPP simulations.

Seasonal variability of the parameters of the Ball-Berry model of stomatal conductance in maize (Zea mays L.) and sunflower (Helianthus annuus L.) under well-watered and water-stressed conditions.

PubMed

Miner, Grace L; Bauerle, William L

2017-09-01

The Ball-Berry (BB) model of stomatal conductance (g s ) is frequently coupled with a model of assimilation to estimate water and carbon exchanges in plant canopies. The empirical slope (m) and 'residual' g s (g 0 ) parameters of the BB model influence transpiration estimates, but the time-intensive nature of measurement limits species-specific data on seasonal and stress responses. We measured m and g 0 seasonally and under different water availability for maize and sunflower. The statistical method used to estimate parameters impacted values nominally when inter-plant variability was low, but had substantial impact with larger inter-plant variability. Values for maize (m = 4.53 ± 0.65; g 0  = 0.017 ± 0.016 mol m -2 s -1 ) were 40% higher than other published values. In maize, we found no seasonal changes in m or g 0 , supporting the use of constant seasonal values, but water stress reduced both parameters. In sunflower, inter-plant variability of m and g 0 was large (m = 8.84 ± 3.77; g 0  = 0.354 ± 0.226 mol m -2 s -1 ), presenting a challenge to clear interpretation of seasonal and water stress responses - m values were stable seasonally, even as g 0 values trended downward, and m values trended downward with water stress while g 0 values declined substantially. © 2017 John Wiley & Sons Ltd.

Stomatal Density and Responsiveness of Banana Fruit Stomates

PubMed Central

Johnson, Barbara E.; Brun, W. A.

1966-01-01

Determination of stomatal densities of the banana peel (Musa acuminata L. var Hort. Valery) by microscopic observations showed 30 times fewer stomates on fruit epidermis than found on the banana leaf. Observations also showed that peel stomates were not laid down in a linear pattern as on the leaf. It was demonstrated that stomatal responses occurred in banana fruit. Specific conditions of high humidity and light were necessary for stomatal opening: low humidity and darkness were necessary for closure. Responsiveness of the stomates continued for a considerable length of time after the fruit had been severed from the host. Images PMID:16656239

Nutrient and chlorophyll relations in selected streams of the New England Coastal Basins in Massachusetts and New Hampshire, June-September 2001

USGS Publications Warehouse

Riskin, Melissa L.; Deacon, J.R.; Liebman, M.L.; Robinson, K.W.

2003-01-01

The U.S. Environmental Protection Agency is developing guidance to assist states with defining nutrient criteria for rivers and streams and to better describe nutrient-algal relations. As part of this effort, 13 wadeable stream sites were selected, primarily in eastern Massachusetts, for a nutrient-assessment study during the summer of 2001. The sites represent a range of water-quality impairment conditions (reference, moderately impaired, impaired) based on state regulatory agency assessments and previously assessed nitrogen, phosphorus, and dissolved-oxygen data. In addition, a combination of open- and closed-canopy locations were sampled at six of the sites to investigate the effect of sunlight on algal growth. Samples for nutrients and for chlorophyll I from phytoplankton and periphyton were collected at all stream sites. Total nitrogen (dissolved nitrite + nitrate + total ammonia + organic nitrogen) and total phosphorus (phosphorus in an unfiltered water sample) concentrations were lowest at reference sites and highest at impaired sites. There were statistically significant differences (p < 0.05) among reference, moderately impaired, and impaired sites for total nitrogen and total phosphorus. Chlorophyll a concentrations from phytoplankton were not significantly different among site impairment designations. Concentrations of chlorophyll a from periphyton were highest at nutrient-impaired open-canopy sites. Chlorophyll a concentrations from periphyton samples were positively correlated with total nitrogen and total phosphorus at the open- and closed-canopy sites. Correlations were higher at open-canopy sites (p < 0.05, rho = 0.64 to 0.71) than at closed-canopy sites (p < 0.05, rho = 0.36 to 0.40). Statistically significant differences in the median concentrations of chlorophyll a from periphyton samples were observed between the open- and closed-canopy sites (p < 0.05). Total nitrogen and total phosphorus data from moderately impaired and impaired sites in this study exceeded the preliminary U.S. Environmental Protection Agency nutrient criteria values for the coastal region of New England. In an effort to establish more appropriate nutrient and chlorophyll criteria for streams in the New England coastal region, relations between total nitrogen and total phosphorus to periphyton chlorophyll a in wadeable streams from this study were quantified to present potential techniques for determining nutrient concentrations. Linear regression was used to estimate the total nitrogen and total phosphorus concentrations that corresponded to various chlorophyll a concentrations. On the basis of this relation, a median concentration for moderately enriched streams of 21 milligrams per square meter (mg/m2) of periphyton chlorophyll a from the literature corresponded to estimated concentrations of 1.3 milligrams per liter (mg/L) for total nitrogen and 0.12 mg/L for total phosphorus. The median concentration for periphyton chlorophyll a from the literature is similar to the 50th-percentile concentration of periphyton chlorophyll a (17 mg/m2) calculated with the data from open-canopy sites in this study. The 25th-percentile concentration for periphyton chlorophyll a of all open-canopy sites (5.2 mg/m2) and the 75th-percentile concentration for periphyton chlorophyll a of open-canopy reference sites (16 mg/m2) also were plotted to provide additional estimates and methods for developing total nitrogen and total phosphorus criteria. The 25th-percentile concentrations of total nitrogen and total phosphorus were calculated based on all sites in this study and were used as another potential criteria estimation. A concentration of 0.64 mg/L for total nitrogen and 0.030 mg/L for total phosphorus were calculated. As another possible method to develop threshold concentrations, the 10th-percentile concentrations of total nitrogen and total phosphorus were calculated based on all the impaired sites in this study. A concentration threshold of 0

Monitoring Forest Degradation for a Case Study in Cambodia: Comparison of Landsat 8 and Sentinel-2 Imagery

NASA Astrophysics Data System (ADS)

Langner, Andreas; Miettinen, Jukka; Stibig, Hans-Jurgen

2016-08-01

We use a Normalized Burned Ratio (NBR) differential approach for detecting forest canopy disturbance caused by selective logging in evergreen tropical moist forests of central Cambodia. The general disturbance pattern obtained from Landsat 8 (30 m) imagery is largely compatible to Sentinel-2 (10 m), showing good conformity to high resolution RapidEye reference data. However, the 10 m spatial resolution of Sentinel-2 provides notably higher spatial detail and purer pixel values, increasing the potential for detecting fine and subtle forest canopy changes as indicators for potential forest degradation. We can expect further improvement for detecting short-lived disturbance signals in tropical forest canopies due to an increased revisit frequency (5 days) after the Sentinel-2B launch.

OnGuard, a Computational Platform for Quantitative Kinetic Modeling of Guard Cell Physiology1[W][OA

PubMed Central

Hills, Adrian; Chen, Zhong-Hua; Amtmann, Anna; Blatt, Michael R.; Lew, Virgilio L.

2012-01-01

Stomatal guard cells play a key role in gas exchange for photosynthesis while minimizing transpirational water loss from plants by opening and closing the stomatal pore. Foliar gas exchange has long been incorporated into mathematical models, several of which are robust enough to recapitulate transpirational characteristics at the whole-plant and community levels. Few models of stomata have been developed from the bottom up, however, and none are sufficiently generalized to be widely applicable in predicting stomatal behavior at a cellular level. We describe here the construction of computational models for the guard cell, building on the wealth of biophysical and kinetic knowledge available for guard cell transport, signaling, and homeostasis. The OnGuard software was constructed with the HoTSig library to incorporate explicitly all of the fundamental properties for transporters at the plasma membrane and tonoplast, the salient features of osmolite metabolism, and the major controls of cytosolic-free Ca2+ concentration and pH. The library engenders a structured approach to tier and interrelate computational elements, and the OnGuard software allows ready access to parameters and equations ‘on the fly’ while enabling the network of components within each model to interact computationally. We show that an OnGuard model readily achieves stability in a set of physiologically sensible baseline or Reference States; we also show the robustness of these Reference States in adjusting to changes in environmental parameters and the activities of major groups of transporters both at the tonoplast and plasma membrane. The following article addresses the predictive power of the OnGuard model to generate unexpected and counterintuitive outputs. PMID:22635116

Separating Active and Passive Influences on Stomatal Control of Transpiration[OPEN

PubMed Central

McAdam, Scott A.M.; Brodribb, Timothy J.

2014-01-01

Motivated by studies suggesting that the stomata of ferns and lycophytes do not conform to the standard active abscisic acid (ABA) -mediated stomatal control model, we examined stomatal behavior in a conifer species (Metasequoia glyptostroboides) that is phylogenetically midway between the fern and angiosperm clades. Similar to ferns, daytime stomatal closure in response to moderate water stress seemed to be a passive hydraulic process in M. glyptostroboides immediately alleviated by rehydrating excised shoots. Only after prolonged exposure to more extreme water stress did active ABA-mediated stomatal closure become important, because foliar ABA production was triggered after leaf turgor loss. The influence of foliar ABA on stomatal conductance and stomatal aperture was highly predictable and additive with the passive hydraulic influence. M. glyptostroboides thus occupies a stomatal behavior type intermediate between the passively controlled ferns and the characteristic ABA-dependent stomatal closure described in angiosperm herbs. These results highlight the importance of considering phylogeny as a major determinant of stomatal behavior. PMID:24488969

Separating active and passive influences on stomatal control of transpiration.

PubMed

McAdam, Scott A M; Brodribb, Timothy J

2014-04-01

Motivated by studies suggesting that the stomata of ferns and lycophytes do not conform to the standard active abscisic acid (ABA) -mediated stomatal control model, we examined stomatal behavior in a conifer species (Metasequoia glyptostroboides) that is phylogenetically midway between the fern and angiosperm clades. Similar to ferns, daytime stomatal closure in response to moderate water stress seemed to be a passive hydraulic process in M. glyptostroboides immediately alleviated by rehydrating excised shoots. Only after prolonged exposure to more extreme water stress did active ABA-mediated stomatal closure become important, because foliar ABA production was triggered after leaf turgor loss. The influence of foliar ABA on stomatal conductance and stomatal aperture was highly predictable and additive with the passive hydraulic influence. M. glyptostroboides thus occupies a stomatal behavior type intermediate between the passively controlled ferns and the characteristic ABA-dependent stomatal closure described in angiosperm herbs. These results highlight the importance of considering phylogeny as a major determinant of stomatal behavior.

Ozone-induced stomatal sluggishness changes carbon and water balance of temperate deciduous forests.

PubMed

Hoshika, Yasutomo; Katata, Genki; Deushi, Makoto; Watanabe, Makoto; Koike, Takayoshi; Paoletti, Elena

2015-05-06

Tropospheric ozone concentrations have increased by 60-100% in the Northern Hemisphere since the 19(th) century. The phytotoxic nature of ozone can impair forest productivity. In addition, ozone affects stomatal functions, by both favoring stomatal closure and impairing stomatal control. Ozone-induced stomatal sluggishness, i.e., a delay in stomatal responses to fluctuating stimuli, has the potential to change the carbon and water balance of forests. This effect has to be included in models for ozone risk assessment. Here we examine the effects of ozone-induced stomatal sluggishness on carbon assimilation and transpiration of temperate deciduous forests in the Northern Hemisphere in 2006-2009 by combining a detailed multi-layer land surface model and a global atmospheric chemistry model. An analysis of results by ozone FACE (Free-Air Controlled Exposure) experiments suggested that ozone-induced stomatal sluggishness can be incorporated into modelling based on a simple parameter (gmin, minimum stomatal conductance) which is used in the coupled photosynthesis-stomatal model. Our simulation showed that ozone can decrease water use efficiency, i.e., the ratio of net CO2 assimilation to transpiration, of temperate deciduous forests up to 20% when ozone-induced stomatal sluggishness is considered, and up to only 5% when the stomatal sluggishness is neglected.

Natural variation in stomatal abundance of Arabidopsis thaliana includes cryptic diversity for different developmental processes

PubMed Central

Delgado, Dolores; Alonso-Blanco, Carlos; Fenoll, Carmen; Mena, Montaña

2011-01-01

Background and Aims Current understanding of stomatal development in Arabidopsis thaliana is based on mutations producing aberrant, often lethal phenotypes. The aim was to discover if naturally occurring viable phenotypes would be useful for studying stomatal development in a species that enables further molecular analysis. Methods Natural variation in stomatal abundance of A. thaliana was explored in two collections comprising 62 wild accessions by surveying adaxial epidermal cell-type proportion (stomatal index) and density (stomatal and pavement cell density) traits in cotyledons and first leaves. Organ size variation was studied in a subset of accessions. For all traits, maternal effects derived from different laboratory environments were evaluated. In four selected accessions, distinct stomatal initiation processes were quantitatively analysed. Key Results and Conclusions Substantial genetic variation was found for all six stomatal abundance-related traits, which were weakly or not affected by laboratory maternal environments. Correlation analyses revealed overall relationships among all traits. Within each organ, stomatal density highly correlated with the other traits, suggesting common genetic bases. Each trait correlated between organs, supporting supra-organ control of stomatal abundance. Clustering analyses identified accessions with uncommon phenotypic patterns, suggesting differences among genetic programmes controlling the various traits. Variation was also found in organ size, which negatively correlated with cell densities in both organs and with stomatal index in the cotyledon. Relative proportions of primary and satellite lineages varied among the accessions analysed, indicating that distinct developmental components contribute to natural diversity in stomatal abundance. Accessions with similar stomatal indices showed different lineage class ratios, revealing hidden developmental phenotypes and showing that genetic determinants of primary and satellite lineage initiation combine in several ways. This first systematic, comprehensive natural variation survey for stomatal abundance in A. thaliana reveals cryptic developmental genetic variation, and provides relevant relationships amongst stomatal traits and extreme or uncommon accessions as resources for the genetic dissection of stomatal development. PMID:21447490

Simulation of ICESat-2 canopy height retrievals for different ecosystems

NASA Astrophysics Data System (ADS)

Neuenschwander, A. L.

2016-12-01

Slated for launch in late 2017 (or early 2018), the ICESat-2 satellite will provide a global distribution of geodetic measurements from a space-based laser altimeter of both the terrain surface and relative canopy heights which will provide a significant benefit to society through a variety of applications ranging from improved global digital terrain models to producing distribution of above ground vegetation structure. The ATLAS instrument designed for ICESat-2, will utilize a different technology than what is found on most laser mapping systems. The photon counting technology of the ATLAS instrument onboard ICESat-2 will record the arrival time associated with a single photon detection. That detection can occur anywhere within the vertical distribution of the reflected signal, that is, anywhere within the vertical distribution of the canopy. This uncertainty of where the photon will be returned from within the vegetation layer is referred to as the vertical sampling error. Preliminary simulation studies to estimate vertical sampling error have been conducted for several ecosystems including woodland savanna, montane conifers, temperate hardwoods, tropical forest, and boreal forest. The results from these simulations indicate that the canopy heights reported on the ATL08 data product will underestimate the top canopy height in the range of 1 - 4 m. Although simulation results indicate the ICESat-2 will underestimate top canopy height, there is, however, a strong correlation between ICESat-2 heights and relative canopy height metrics (e.g. RH75, RH90). In tropical forest, simulation results indicate the ICESat-2 height correlates strongly with RH90. Similarly, in temperate broadleaf forest, the simulated ICESat-2 heights were also strongly correlated with RH90. In boreal forest, the simulated ICESat-2 heights are strongly correlated with RH75 heights. It is hypothesized that the correlations between simulated ICESat-2 heights and canopy height metrics are a function of both canopy cover and vegetation physiology (e.g. leaf size/shape) which contributes to the horizontal and vertical structure of the vegetation.

Quantification of Lyssavirus-Neutralizing Antibodies Using Vesicular Stomatitis Virus Pseudotype Particles

PubMed Central

Moeschler, Sarah; Locher, Samira; Conzelmann, Karl-Klaus; Krämer, Beate; Zimmer, Gert

2016-01-01

Rabies is a highly fatal zoonotic disease which is primarily caused by rabies virus (RABV) although other members of the genus Lyssavirus can cause rabies as well. As yet, 14 serologically and genetically diverse lyssaviruses have been identified, mostly in bats. To assess the quality of rabies vaccines and immunoglobulin preparations, virus neutralization tests with live RABV are performed in accordance with enhanced biosafety standards. In the present work, a novel neutralization test is presented which takes advantage of a modified vesicular stomatitis virus (VSV) from which the glycoprotein G gene has been deleted and replaced by reporter genes. This single-cycle virus was trans-complemented with RABV envelope glycoprotein. Neutralization of this pseudotype virus with RABV reference serum or immune sera from vaccinated mice showed a strong correlation with the rapid fluorescent focus inhibition test (RFFIT). Importantly, pseudotype viruses containing the envelope glycoproteins of other lyssaviruses were neutralized by reference serum to a significantly lesser extent or were not neutralized at all. Taken together, a pseudotype virus system has been successfully developed which allows the safe, fast, and sensitive detection of neutralizing antibodies directed against different lyssaviruses. PMID:27649230

The potential of detecting intermediate-scale biomass and canopy interception in a coniferous forest using cosmic-ray neutron intensity measurements and neutron transport modeling

NASA Astrophysics Data System (ADS)

Andreasen, M.; Looms, M. C.; Bogena, H. R.; Desilets, D.; Zreda, M. G.; Sonnenborg, T. O.; Jensen, K. H.

2014-12-01

The water stored in the various compartments of the terrestrial ecosystem (in snow, canopy interception, soil and litter) controls the exchange of the water and energy between the land surface and the atmosphere. Therefore, measurements of the water stored within these pools are critical for the prediction of e.g. evapotranspiration and groundwater recharge. The detection of cosmic-ray neutron intensity is a novel non-invasive method for the quantification of continuous intermediate-scale soil moisture. The footprint of the cosmic-ray neutron probe is a hemisphere of a few hectometers and subsurface depths of 10-70 cm depending on wetness. The cosmic-ray neutron method offers measurements at a scale between the point-scale measurements and large-scale satellite retrievals. The cosmic-ray neutron intensity is inversely correlated to the hydrogen stored within the footprint. Overall soil moisture represents the largest pool of hydrogen and changes in the soil moisture clearly affect the cosmic-ray neutron signal. However, the neutron intensity is also sensitive to variations of hydrogen in snow, canopy interception and biomass offering the potential to determine water content in such pools from the signal. In this study we tested the potential of determining canopy interception and biomass using cosmic-ray neutron intensity measurements within the framework of the Danish Hydrologic Observatory (HOBE) and the Terrestrial Environmental Observatories (TERENO). Continuous measurements at the ground and the canopy level, along with profile measurements were conducted at towers at forest field sites. Field experiments, including shielding the cosmic-ray neutron probes with cadmium foil (to remove lower-energy neutrons) and measuring reference intensity rates at complete water saturated conditions (on the sea close to the HOBE site), were further conducted to obtain an increased understanding of the physics controlling the cosmic-ray neutron transport and the equipment used. Additionally, neutron transport modeling, using the extended version of the Monte Carlo N-Particle Transport Code, was conducted. The responses of the reference condition, different amounts of biomass, soil moisture and canopy interception on the cosmic-ray neutron intensity were simulated and compared to the measurements.

Interannual variability in ozone removal by a temperate deciduous forest

NASA Astrophysics Data System (ADS)

Clifton, O. E.; Fiore, A. M.; Munger, J. W.; Malyshev, S.; Horowitz, L. W.; Shevliakova, E.; Paulot, F.; Murray, L. T.; Griffin, K. L.

2017-01-01

The ozone (O3) dry depositional sink and its contribution to observed variability in tropospheric O3 are both poorly understood. Distinguishing O3 uptake through plant stomata versus other pathways is relevant for quantifying the O3 influence on carbon and water cycles. We use a decade of O3, carbon, and energy eddy covariance (EC) fluxes at Harvard Forest to investigate interannual variability (IAV) in O3 deposition velocities (vd,O3). In each month, monthly mean vd,O3 for the highest year is twice that for the lowest. Two independent stomatal conductance estimates, based on either water vapor EC or gross primary productivity, vary little from year to year relative to canopy conductance. We conclude that nonstomatal deposition controls the substantial observed IAV in summertime vd,O3 during the 1990s over this deciduous forest. The absence of obvious relationships between meteorology and vd,O3 implies a need for additional long-term, high-quality measurements and further investigation of nonstomatal mechanisms.

Fluxes of ozone and Biogenic Volatile Organic Compounds in a mixed Mediterranean forest over a transition period between summer and fall

NASA Astrophysics Data System (ADS)

Fares, S.; Schnitzhofer, R.; Hansel, A.; Petersson, F.; Matteucci, G.; Scarascia Mugnozza, G.; Jiang, X.; Guenther, A. B.; Loreto, F.

2012-12-01

Mediterranean plant ecosystems are exposed to abiotic stressors that may be exacerbated by climate change dynamics. Moreover, plants need now to cope with increasing anthropogenic pressures, often associated with expanding impacts of urbanization. Anthropogenic stressors include harmful gases (e.g. ozone,) that are transported from anthropogenic pollution sources to the vegetation. They may alter ecophysiology and compromise metabolism of Mediterranean plants. A disproportionate number of Mediterranean ecosystems, many dominated by forest trees, are being transformed into "urban or pre-urban forests". This is in particular the case for Castelporziano Estate, a 6,000 ha Mediterranean forest located just 25 km from Rome downtown at the coast of the Mediterranean Sea. In September 2011 an intensive field campaign was performed in Castelporziano to investigate ozone deposition and biogenic emissions of volatile organic compounds (BVOC) from a mixed Mediterranean forest, mainly composed by Quercus suber, Quercus ilex, Pinus pinea. Measurements were performed at canopy level with fast real-time instruments (a fast ozone analyzer and a Proton Transfer Reaction-Time of Flight Mass Spectrometer) that allowed eddy covariant flux measurements of ozone and BVOC. In the transitional period from a warm and dry summer to a wet and moderately cool fall we typically observed tropospheric ozone volume mixing ratios (VMR) of 60 ppb at around noon, with high deposition fluxes (up to -10 nmol m-2 s-1) into the forest canopy. Canopy models were used to to calculate that up to 90% of ozone uptake can be attributed to non-stomatal sinks, suggesting that chemical reactions between ozone and reactive BVOC may have played an important role. The concentrations of reactive isoprenoids (e.g. sesquiterpenes) were indeed observed to decrease during the central hours of the day, in coincidence with increased ozone concentrations. Concentrations and fluxes of isoprenoid-ozone-oxidation-(methyl-vinyl-ketone and methacrolein) were found to increase during the day time hours, matching the dynamic pattern of non-stomatal ozone uptake. Monoterpenes were the most abundant BVOC emitted by the forest with fluxes up to 10 nmol m-2 s-1 in the warm days, followed by the oxygenated BVOCs: methanol, acetone, acetaldehyde. Isoprene was emitted at a low rate (less than 1 nmol m-2 s-1), and observations used to develop a new parameterization data for modelling activity. MEGAN was used to predict biogenic emissions from Mediterranean ecosystems. Model results using new basal emission factors (BEF) estimated from the collected data-set revealed considerable differences in the emission estimates compared with the standard parameterization, thus suggesting the importance of including basal emission factors from monoterpene-emitting Mediterranean ecosystems to obtain an accurate estimate in the global model. Future research by chemical transport modelling and smog chamber experiments are planned to investigate the "ex-situ" ozone-forming potential of emitted BVOC, to fully understand the role of Mediterranean urban forests in the complex interactions between biosphere and atmosphere over large Mediterranean conurbations.

A Simplified Biosphere Model for Global Climate Studies.

NASA Astrophysics Data System (ADS)

Xue, Y.; Sellers, P. J.; Kinter, J. L.; Shukla, J.

1991-03-01

The Simple Biosphere Model (SiB) as described in Sellers et al. is a bio-physically based model of land surface-atmosphere interaction. For some general circulation model (GCM) climate studies, further simplifications are desirable to have greater computation efficiency, and more important, to consolidate the parametric representation. Three major reductions in the complexity of SiB have been achieved in the present study.The diurnal variation of surface albedo is computed in SiB by means of a comprehensive yet complex calculation. Since the diurnal cycle is quite regular for each vegetation type, this calculation can be simplified considerably. The effect of root zone soil moisture on stomatal resistance is substantial, but the computation in SiB is complicated and expensive. We have developed approximations, which simulate the effects of reduced soil moisture more simply, keeping the essence of the biophysical concepts used in SiB.The surface stress and the fluxes of heat and moisture between the top of the vegetation canopy and an atmospheric reference level have been parameterized in an off-line version of SiB based upon the studies by Businger et al. and Paulson. We have developed a linear relationship between Richardson number and aero-dynamic resistance. Finally, the second vegetation layer of the original model does not appear explicitly after simplification. Compared to the model of Sellers et al., we have reduced the number of input parameters from 44 to 21. A comparison of results using the reduced parameter biosphere with those from the original formulation in a GCM and a zero-dimensional model shows the simplified version to reproduce the original results quite closely. After simplification, the computational requirement of SiB was reduced by about 55%.

Towards a more detailed representation of the energy balance in a coupled land surface model

NASA Astrophysics Data System (ADS)

Ryder, J.; Polcher, J.; Luyssaert, S.

2012-04-01

Currently, the land-surface region sequesters 25% of global CO2 emissions. In addition to climate change, increasing atmospheric CO2 concentrations, fertilisation and nitrogen deposition, this sink is thought to be largely due to land management. When applied deliberately to enhance the terrestrial carbon sink strength, this land management may have unintended effects on the energy budget, potentially offsetting the radiative effect of carbon sequestration. As with other land surface models, the present release of ORCHIDEE (the land surface model of the IPSL Earth system model) has difficulties in reproducing consistently observed energy balances (Pitman et al., 2009; Jimenez et al., 2011; de Noblet-Ducoudré et al., 2011). Hence, the model must be improved to be better able to study the radiative effect of forest management and land use change. This observation serves as a starting point in this research - improving the level of detail in energy balance simulations of the surface layer. We here outline the structure of a new detailed and practical simulation of the energy budget that is currently under development within the surface model ORCHIDEE, and will be coupled to the atmospheric model LMDZ. The most detailed simulations of the surface layer energy budget are detailed iterative multi-layer canopy models, such as Ogeé et al. (2003), which are linked to specific measurement sites and do not interact with the atmosphere. In this current project, we aim to create a model that will implement the insights obtained in those previous studies and improve upon the present ORCHIDEE parameterisation, but will run stably and efficiently when coupled to an atmospheric model. This work involves a replacement of the existing allocation of 14 different types of vegetation within each surface tile (the 'Plant Functional Types') by a more granular scheme that can be modified to reflect changes in attributes such as vegetation density, leaf type, distribution (clumping factors), age and height of vegetation within the surface tile. There will be the implementation of more than one canopy vegetation layer to simulate the effects of scalar gradients within the canopy for determining, more accurately, the net sensible and latent heat fluxes that are passed to the atmosphere. The model will include representation of characteristics such as in-canopy transport, coupling with sensible heat flux from the soil, a multilayer radiation budget and stomatal resistance, and interaction with the bare soil flux within the canopy space (and also with snow pack). We present how the implicit coupling approach of Polcher et al. (1998) and Best et al. (2004) is to be extended to a multilayer scenario, present initial sensitivity studies and outline future testing scenarios and validation plans.

The potential of biomonitoring of air quality using leaf characteristics of white willow (Salix alba L.).

PubMed

Wuytack, Tatiana; Verheyen, Kris; Wuyts, Karen; Kardel, Fatemeh; Adriaenssens, Sandy; Samson, Roeland

2010-12-01

In this study, we assess the potential of white willow (Salix alba L.) as bioindicator for monitoring of air quality. Therefore, shoot biomass, specific leaf area, stomatal density, stomatal pore surface, and stomatal resistance were assessed from leaves of stem cuttings. The stem cuttings were introduced in two regions in Belgium with a relatively high and a relatively low level of air pollution, i.e., Antwerp city and Zoersel, respectively. In each of these regions, nine sampling points were selected. At each sampling point, three stem cuttings of white willow were planted in potting soil. Shoot biomass and specific leaf area were not significantly different between Antwerp city and Zoersel. Microclimatic differences between the sampling points may have been more important to plant growth than differences in air quality. However, stomatal pore surface and stomatal resistance of white willow were significantly different between Zoersel and Antwerp city. Stomatal pore surface was 20% lower in Antwerp city due to a significant reduction in both stomatal length (-11%) and stomatal width (-14%). Stomatal resistance at the adaxial leaf surface was 17% higher in Antwerp city because of the reduction in stomatal pore surface. Based on these results, we conclude that stomatal characteristics of white willow are potentially useful indicators for air quality.

Denture plaque--past and recent concerns.

PubMed

Nikawa, H; Hamada, T; Yamamoto, T

1998-05-01

This paper critically reviews the history of denture plaque and identifies some concerns with the presence of Candida in the mouth. This review covers literature sources related to Candida albicans and its relationship to denture plaque. The articles selected for this review are from referred journals and describe C. albicans and its relationship to oral, gastrointestinal and pleuropulmonary infections. The relationship to caries, root caries and periodontal disease is also covered. Denture plaque containing Candida could cause not only oral candidiasis, like oral thrush or denture-induced stomatitis, but also caries, root caries and periodontitis of abutment teeth. However, there is only limited experimental evidence or information available on the cariogenicity of Candida. The continuous swallowing or aspiration of micro-organisms from denture plaque exposes patients, particularly the immunocompromised host or medicated elderly, to the risks of unexpected infections. The term, 'denture plaque' has been used throughout the review. However, the term 'plaque on denture' should be used because the microbial flora and its pathogenicity of denture plaque resembles those of plaque formed on the tooth surface, so called dental plaque. In addition, the term 'denture related stomatitis' would be preferable to 'denture induced stomatitis', since the inflammation of (palatal) mucosa is not induced by the denture, but by wearing the denture or by plaque on the denture.

Canopy reflectance modeling in a tropical wooded grassland

NASA Technical Reports Server (NTRS)

Simonett, David; Franklin, Janet

1986-01-01

Geometric/optical canopy reflectance modeling and spatial/spectral pattern recognition is used to study the form and structure of savanna in West Africa. An invertible plant canopy reflectance model is tested for its ability to estimate the amount of woody vegetation from remotely sensed data in areas of sparsely wooded grassland. Dry woodlands and wooded grasslands, commonly referred to as savannas, are important ecologically and economically in Africa, and cover approximately forty percent of the continent by some estimates. The Sahel and Sudan savannas make up the important and sensitive transition zone between the tropical forests and the arid Sahara region. The depletion of woody cover, used for fodder and fuel in these regions, has become a very severe problem for the people living there. LANDSAT Thematic Mapper (TM) data is used to stratify woodland and wooded grassland into areas of relatively homogeneous canopy cover, and then an invertible forest canopy reflectance model is applied to estimate directly the height and spacing of the trees in the stands. Because height and spacing are proportional to biomass in some cases, a successful application of the segmentation/modeling techniques will allow direct estimation of tree biomass, as well as cover density, over significant areas of these valuable and sensitive ecosystems. The model being tested in sites in two different bioclimatic zones in Mali, West Africa, will be used for testing the canopy model. Sudanian zone crop/woodland test sites were located in the Region of Segou, Mali.

In situ temperature response of photosynthesis of 42 tree and liana species in the canopy of two Panamanian lowland tropical forests with contrasting rainfall regimes.

PubMed

Slot, Martijn; Winter, Klaus

2017-05-01

Tropical forests contribute significantly to the global carbon cycle, but little is known about the temperature response of photosynthetic carbon uptake in tropical species, and how this varies within and across forests. We determined in situ photosynthetic temperature-response curves for upper canopy leaves of 42 tree and liana species from two tropical forests in Panama with contrasting rainfall regimes. On the basis of seedling studies, we hypothesized that species with high photosynthetic capacity - light-demanding, fast-growing species - would have a higher temperature optimum of photosynthesis (T Opt ) than species with low photosynthetic capacity - shade-tolerant, slow-growing species - and that, therefore, T Opt would scale with the position of a species on the slow-fast continuum of plant functional traits. T Opt was remarkably similar across species, regardless of their photosynthetic capacity and other plant functional traits. Community-average T Opt was almost identical to mean maximum daytime temperature, which was higher in the dry forest. Photosynthesis above T Opt appeared to be more strongly limited by stomatal conductance in the dry forest than in the wet forest. The observation that all species in a community shared similar T Opt values suggests that photosynthetic performance is optimized under current temperature regimes. These results should facilitate the scaling up of photosynthesis in relation to temperature from leaf to stand level in species-rich tropical forests. © 2017 The Authors. New Phytologist © 2017 New Phytologist Trust.

Investigating the Sustainability of Perennial Agriculture

NASA Astrophysics Data System (ADS)

Sutherlin, C. E.; Brunsell, N. A.; De Oliveira, G.; Crews, T.; Vico, G.

2017-12-01

The changing climate leads to uncertainties concerning the sustainability of certain agricultural resources, and with the additional stresses of an increasing global population, uncertainty in food security will greatly increase. To adhere to future food demands in the face of this changing climate, perennial agriculture has been a proposed solution. However, it is equally important to assure that perennial agriculture is not negatively affecting the climate in exchange for this proposed more robust food source. We chose to examine the interactions between perennial and annual agricultural crops by focusing on the efficiency of exchanges with the atmosphere. This is done using the omega decoupling factor for 4 different sites as a way of quantifying the contributions of radiation and stomatal conductance over the resulting water and carbon cycles. This gives us an indication of how the plant canopy is interacting with, and influencing the local microclimate. Ultimately, this should give us an indication of the ability of perennial crops to aid in the climate mitigation process. We hypothesized that the perennial site chosen would have omega values more similar to the omega values of a natural grassland rather than an annual crop site. Using AmeriFlux towers to determine the canopy values needed to calculate the omega decoupling factor, we focused on the Kernza perennial crops being grown at the Land Institute in Salina, Kansas (KLS), in comparison to a natural grassland in Manhattan, Kansas (KON), a typical land cover model in Lawrence, Kansas (KFS), and an annual crop site in Lamont, Oklahoma (ARM). These results will allow us to move forward in the investigation of perennial crops as a sustainable food source.

Leaf physiology and biomass allocation of backcross hybrid American chestnut (Castanea dentata) seedlings in response to light and water availability.

PubMed

Brown, Caleb E; Mickelbart, Michael V; Jacobs, Douglass F

2014-12-01

Partial canopy cover promotes regeneration of many temperate forest trees, but the consequences of shading on seedling drought resistance are unclear. Reintroduction of blight-resistant American chestnut (Castanea dentata (Marsh.) Borkh.) into eastern North American forests will often occur on water-limited sites and under partial canopy cover. We measured leaf pre-dawn water potential (Ψpd), leaf gas exchange, and growth and biomass allocation of backcross hybrid American chestnut seedlings from three orchard sources grown under different light intensities (76, 26 and 8% full photosynthetically active radiation (PAR)) and subjected to well-watered or mid-season water-stressed conditions. Seedlings in the water-stress treatment were returned to well-watered conditions after wilting to examine recovery. Seedlings growing under medium- and high-light conditions wilted at lower leaf Ψpd than low-light seedlings. Recovery of net photosynthesis (Anet) and stomatal conductance (gs) was greater in low and medium light than in high light. Seed source did not affect the response to water stress or light level in most cases. Between 26 and 8% full PAR, light became limiting to the extent that the effects of water stress had no impact on some growth and morphological traits. We conclude that positive and negative aspects of shading on seedling drought tolerance and recovery are not mutually exclusive. Partial shade may help American chestnut tolerate drought during early establishment through effects on physiological conditioning. © The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Ground and canopy soil N2O fluxes from smallholder oil palm plantations following deforestation in Sumatra, Indonesia

NASA Astrophysics Data System (ADS)

Hassler, Evelyn; Corre, Marife D.; Kurniawan, Syahrul; Allen, Kara; Veldkamp, Edzo

2017-04-01

Due to an increasing global demand in cheap oils and biofuels, forest conversion to oil palm plantations is rapidly increasing in Indonesia. Although forest conversion is known to influence soil N2O fluxes, measurements from oil palm are scarce. Our study aimed to (1) quantify changes in soil N2O fluxes with forest conversion to oil palm plantations, (2) quantify the contribution of oil-palm canopy soil (lodged between the stems and leaf axils) to N2O fluxes, and (3) determine their controlling factors. In Jambi, Sumatra, we selected two landscapes that mainly differed in soil texture but both on heavily weathered soils: loam and clay Acrisol soils. Within each landscape, we investigated lowland forest, jungle rubber (rubber trees interspersed in secondary forest), both as the reference (previous) land uses, and the converted oil palm plantations by smallholders. Each land use had four replicate plots within each landscape. Each replicate plot had four permanently placed chambers, and soil N2O fluxes were measured monthly from December 2012 to December 2013 by placing vented static covers on chamber bases for 30 minutes for gas flux measurement. For oil-palm canopy soil, each replicate plot was represented by five oil palms, and each oil palm stem was delineated into three 1-m sections (low, middle, and top) in order to represent possible gradients of canopy soil conditions that influence N2O fluxes. Measurements were conducted from February 2013 to May 2014 by collecting canopy soil from each stem section and incubating it in-situ in an air-tight glass jar. Land-use conversion to smallholder plantations had no effect on soil N-oxide fluxes (P = 0.58 to 0.76) due to the inherently low soil N availability and the low N fertilization rates (commonly 48 to 88 kg N ha-1 yr-1) of smallholder oil palm plantations. Soil N2O fluxes (kg N ha-1 yr-1) were: 0.6 ± 0.1 to 1.2 ± 0.6 from the reference land uses and 1.0 ± 0.2 to 1.1 ± 0.5 from the smallholder oil palm plantations. N fertilizer-induced N2O emissions were 0.2 - 0.7 % of the applied N. Oil-palm canopy soil N2O emissions per soil mass were large, but on a hectare basis these emissions were small due to the low amount of canopy soil per hectare (170 kg ha-1). Canopy soil N2O emission was 10.7 ± 3.3 g N2O-N ha-1 yr-1, which contributed only 1% of the total soil (canopy soil + ground soil) N2O fluxes. Over one-year measurements, the temporal patterns of ground and canopy soil N2O fluxes were controlled by soil mineral N and water contents. To improve estimate of soil N-oxide fluxes from oil palm plantations in this region, studies should focus on large-scale plantations (which usually have two to four times higher N fertilization rates than smallholders) with frequent measurements following fertilizer application.

Plant water potential improves prediction of empirical stomatal models.

PubMed

Anderegg, William R L; Wolf, Adam; Arango-Velez, Adriana; Choat, Brendan; Chmura, Daniel J; Jansen, Steven; Kolb, Thomas; Li, Shan; Meinzer, Frederick; Pita, Pilar; Resco de Dios, Víctor; Sperry, John S; Wolfe, Brett T; Pacala, Stephen

2017-01-01

Climate change is expected to lead to increases in drought frequency and severity, with deleterious effects on many ecosystems. Stomatal responses to changing environmental conditions form the backbone of all ecosystem models, but are based on empirical relationships and are not well-tested during drought conditions. Here, we use a dataset of 34 woody plant species spanning global forest biomes to examine the effect of leaf water potential on stomatal conductance and test the predictive accuracy of three major stomatal models and a recently proposed model. We find that current leaf-level empirical models have consistent biases of over-prediction of stomatal conductance during dry conditions, particularly at low soil water potentials. Furthermore, the recently proposed stomatal conductance model yields increases in predictive capability compared to current models, and with particular improvement during drought conditions. Our results reveal that including stomatal sensitivity to declining water potential and consequent impairment of plant water transport will improve predictions during drought conditions and show that many biomes contain a diversity of plant stomatal strategies that range from risky to conservative stomatal regulation during water stress. Such improvements in stomatal simulation are greatly needed to help unravel and predict the response of ecosystems to future climate extremes.

Responses of leaf stomatal density to water status and its relationship with photosynthesis in a grass.

PubMed

Xu, Zhenzhu; Zhou, Guangsheng

2008-01-01

Responses of plant leaf stomatal conductance and photosynthesis to water deficit have been extensively reported; however, little is known concerning the relationships of stomatal density with regard to water status and gas exchange. The responses of stomatal density to leaf water status were determined, and correlation with specific leaf area (SLA) in a photosynthetic study of a perennial grass, Leymus chinensis, subjected to different soil moisture contents. Moderate water deficits had positive effects on stomatal number, but more severe deficits led to a reduction, described in a quadratic parabolic curve. The stomatal size obviously decreased with water deficit, and stomatal density was positively correlated with stomatal conductance (g(s)), net CO(2) assimilation rate (A(n)), and water use efficiency (WUE). A significantly negative correlation of SLA with stomatal density was also observed, suggesting that the balance between leaf area and its matter may be associated with the guard cell number. The present results indicate that high flexibilities in stomatal density and guard cell size will change in response to water status, and this process may be closely associated with photosynthesis and water use efficiency.

Evaluating the Community Land Model (CLM4.5) at a coniferous forest site in northwestern United States using flux and carbon-isotope measurements

DOE PAGES

Duarte, Henrique F.; Raczka, Brett M.; Ricciuto, Daniel M.; ...

2017-09-28

Droughts in the western United States are expected to intensify with climate change. Thus, an adequate representation of ecosystem response to water stress in land models is critical for predicting carbon dynamics. The goal of this study was to evaluate the performance of the Community Land Model (CLM) version 4.5 against observations at an old-growth coniferous forest site in the Pacific Northwest region of the United States (Wind River AmeriFlux site), characterized by a Mediterranean climate that subjects trees to water stress each summer. CLM was driven by site-observed meteorology and calibrated primarily using parameter values observed at the site ormore » at similar stands in the region. Key model adjustments included parameters controlling specific leaf area and stomatal conductance. Default values of these parameters led to significant underestimation of gross primary production, overestimation of evapotranspiration, and consequently overestimation of photosynthetic 13C discrimination, reflected in reduced 13C: 12C ratios of carbon fluxes and pools. Adjustments in soil hydraulic parameters within CLM were also critical, preventing significant underestimation of soil water content and unrealistic soil moisture stress during summer. After calibration, CLM was able to simulate energy and carbon fluxes, leaf area index, biomass stocks, and carbon isotope ratios of carbon fluxes and pools in reasonable agreement with site observations. Overall, the calibrated CLM was able to simulate the observed response of canopy conductance to atmospheric vapor pressure deficit (VPD) and soil water content, reasonably capturing the impact of water stress on ecosystem functioning. Both simulations and observations indicate that stomatal response from water stress at Wind River was primarily driven by VPD and not soil moisture. The calibration of the Ball–Berry stomatal conductance slope ( m bb) at Wind River aligned with findings from recent CLM experiments at sites characterized by the same plant functional type (needleleaf evergreen temperate forest), despite significant differences in stand composition and age and climatology, suggesting that CLM could benefit from a revised m bb value of 6, rather than the default value of 9, for this plant functional type. Conversely, Wind River required a unique calibration of the hydrology submodel to simulate soil moisture, suggesting that the default hydrology has a more limited applicability. Here, this study demonstrates that carbon isotope data can be used to constrain stomatal conductance and intrinsic water use efficiency in CLM, as an alternative to eddy covariance flux measurements. It also demonstrates that carbon isotopes can expose structural weaknesses in the model and provide a key constraint that may guide future model development.« less

Evaluating the Community Land Model (CLM4.5) at a coniferous forest site in northwestern United States using flux and carbon-isotope measurements

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

Duarte, Henrique F.; Raczka, Brett M.; Ricciuto, Daniel M.

Droughts in the western United States are expected to intensify with climate change. Thus, an adequate representation of ecosystem response to water stress in land models is critical for predicting carbon dynamics. The goal of this study was to evaluate the performance of the Community Land Model (CLM) version 4.5 against observations at an old-growth coniferous forest site in the Pacific Northwest region of the United States (Wind River AmeriFlux site), characterized by a Mediterranean climate that subjects trees to water stress each summer. CLM was driven by site-observed meteorology and calibrated primarily using parameter values observed at the site ormore » at similar stands in the region. Key model adjustments included parameters controlling specific leaf area and stomatal conductance. Default values of these parameters led to significant underestimation of gross primary production, overestimation of evapotranspiration, and consequently overestimation of photosynthetic 13C discrimination, reflected in reduced 13C: 12C ratios of carbon fluxes and pools. Adjustments in soil hydraulic parameters within CLM were also critical, preventing significant underestimation of soil water content and unrealistic soil moisture stress during summer. After calibration, CLM was able to simulate energy and carbon fluxes, leaf area index, biomass stocks, and carbon isotope ratios of carbon fluxes and pools in reasonable agreement with site observations. Overall, the calibrated CLM was able to simulate the observed response of canopy conductance to atmospheric vapor pressure deficit (VPD) and soil water content, reasonably capturing the impact of water stress on ecosystem functioning. Both simulations and observations indicate that stomatal response from water stress at Wind River was primarily driven by VPD and not soil moisture. The calibration of the Ball–Berry stomatal conductance slope ( m bb) at Wind River aligned with findings from recent CLM experiments at sites characterized by the same plant functional type (needleleaf evergreen temperate forest), despite significant differences in stand composition and age and climatology, suggesting that CLM could benefit from a revised m bb value of 6, rather than the default value of 9, for this plant functional type. Conversely, Wind River required a unique calibration of the hydrology submodel to simulate soil moisture, suggesting that the default hydrology has a more limited applicability. Here, this study demonstrates that carbon isotope data can be used to constrain stomatal conductance and intrinsic water use efficiency in CLM, as an alternative to eddy covariance flux measurements. It also demonstrates that carbon isotopes can expose structural weaknesses in the model and provide a key constraint that may guide future model development.« less

Evaluating the Community Land Model (CLM4.5) at a coniferous forest site in northwestern United States using flux and carbon-isotope measurements

NASA Astrophysics Data System (ADS)

Duarte, Henrique F.; Raczka, Brett M.; Ricciuto, Daniel M.; Lin, John C.; Koven, Charles D.; Thornton, Peter E.; Bowling, David R.; Lai, Chun-Ta; Bible, Kenneth J.; Ehleringer, James R.

2017-09-01

Droughts in the western United States are expected to intensify with climate change. Thus, an adequate representation of ecosystem response to water stress in land models is critical for predicting carbon dynamics. The goal of this study was to evaluate the performance of the Community Land Model (CLM) version 4.5 against observations at an old-growth coniferous forest site in the Pacific Northwest region of the United States (Wind River AmeriFlux site), characterized by a Mediterranean climate that subjects trees to water stress each summer. CLM was driven by site-observed meteorology and calibrated primarily using parameter values observed at the site or at similar stands in the region. Key model adjustments included parameters controlling specific leaf area and stomatal conductance. Default values of these parameters led to significant underestimation of gross primary production, overestimation of evapotranspiration, and consequently overestimation of photosynthetic 13C discrimination, reflected in reduced 13C : 12C ratios of carbon fluxes and pools. Adjustments in soil hydraulic parameters within CLM were also critical, preventing significant underestimation of soil water content and unrealistic soil moisture stress during summer. After calibration, CLM was able to simulate energy and carbon fluxes, leaf area index, biomass stocks, and carbon isotope ratios of carbon fluxes and pools in reasonable agreement with site observations. Overall, the calibrated CLM was able to simulate the observed response of canopy conductance to atmospheric vapor pressure deficit (VPD) and soil water content, reasonably capturing the impact of water stress on ecosystem functioning. Both simulations and observations indicate that stomatal response from water stress at Wind River was primarily driven by VPD and not soil moisture. The calibration of the Ball-Berry stomatal conductance slope (mbb) at Wind River aligned with findings from recent CLM experiments at sites characterized by the same plant functional type (needleleaf evergreen temperate forest), despite significant differences in stand composition and age and climatology, suggesting that CLM could benefit from a revised mbb value of 6, rather than the default value of 9, for this plant functional type. Conversely, Wind River required a unique calibration of the hydrology submodel to simulate soil moisture, suggesting that the default hydrology has a more limited applicability. This study demonstrates that carbon isotope data can be used to constrain stomatal conductance and intrinsic water use efficiency in CLM, as an alternative to eddy covariance flux measurements. It also demonstrates that carbon isotopes can expose structural weaknesses in the model and provide a key constraint that may guide future model development.

Changes in whole-tree water relations during ontogeny of Pinus flexilis and Pinus ponderosa in a high-elevation meadow.

PubMed

Fischer, Dylan G; Kolb, Thomas E; DeWald, Laura E

2002-07-01

We measured sap flux in Pinus ponderosa Laws. and Pinus flexilis James trees in a high-elevation meadow in northern Arizona that has been invaded by conifers over the last 150 years. Sap flux and environmental data were collected from July 1 to September 1, 2000, and used to estimate leaf specific transpiration rate (El), canopy conductance (Gc) and whole-plant hydraulic conductance (Kh). Leaf area to sapwood area ratio (LA/SA) increased with increasing tree size in P. flexilis, but decreased with increasing tree size in P. ponderosa. Both Gc and Kh decreased with increasing tree size in P. flexilis, and showed no clear trends with tree size in P. ponderosa. For both species, Gc was lower in the summer dry season than in the summer rainy season, but El did not change between wet and dry summer seasons. Midday water potential (Psi(mid)) did not change across seasons for either species, whereas predawn water potential (Psi(pre)) tracked variation in soil water content across seasons. Pinus flexilis showed greater stomatal response to vapor pressure deficit (VPD) and maintained higher Psi(mid) than P. ponderosa. Both species showed greater sensitivity to VPD at high photosynthetically active radiation (PAR; > 2500 micromol m-2 s-1) than at low PAR (< 2500 micromol m-2 s-1). We conclude that the direction of change in Gc and Kh with increasing tree size differed between co-occurring Pinus species, and was influenced by changes in LA/SA. Whole-tree water use and El were similar between wet and dry summer seasons, possibly because of tight stomatal control over water loss. 2002 Heron Publishing--Victoria, Canada

Supraoptimal carbon dioxide effects on growth of soybean [Glycine max (L.) Merr.

NASA Technical Reports Server (NTRS)

Wheeler, R. M.; Mackowiak, C. L.; Siegriest, L. M.; Sager, J. C.; Knott, W. M. (Principal Investigator)

1993-01-01

In tightly closed environments used for human life support in space, carbon dioxide (CO2) partial pressures can reach 500 to 1000 Pa, which may be supraoptimal or toxic to plants used for life support. To study this, soybeans [Glycine max (L.) Merr. cvs. McCall and Pixie] were grown for 90 days at 50, 100, 200, and 500 Pa partial pressure CO2 (500, 1000, 2000, and 5000 ppm). Plants were grown using recirculating nutrient film technique with a 12-h photoperiod, a 26 degrees C/20 degrees C thermoperiod, and approximately 300 micromoles m-2 s-1 photosynthetic photon flux (PPF). Seed yield and total biomass were greatest at 100 Pa for cv. McCall, suggesting that higher CO2 levels were supraoptimal. Seed yield and total biomass for cv. Pixie showed little difference between CO2 treatments. Average stomatal conductance of upper canopy leaves at 50 Pa CO2 approximately 500 Pa > 200 Pa > 100 Pa. Total water use over 90 d for both cultivars (combined on one recirculating system) equalled 822 kg water for 100 Pa CO2, 845 kg for 50 Pa, 879 kg for 200 Pa, and 1194 kg for 500 Pa. Water use efficiences for both cultivars combined equalled 3.03 (g biomass kg-1 water) for 100 Pa CO2, 2.54 g kg-1 for 200 Pa, 2.42 g kg-1 for 50 Pa, and 1.91 g kg-1 for 500 Pa. The increased stomatal conductance and stand water use at the highest CO2 level (500 Pa) were unexpected and pose interesting considerations for managing plants in a tightly closed system where CO2 concentrations may reach high levels.

Response of central Siberian Scots pine to soil water deficit and long-term trends in atmospheric CO2 concentration

NASA Astrophysics Data System (ADS)

Arneth, A.; Lloyd, J.; Šantrůčková, H.; Bird, M.; Grigoryev, S.; Kalaschnikov, Y. N.; Gleixner, G.; Schulze, E.-D.

2002-01-01

Twenty tree ring 13C / 12C ratio chronologies from Pinus sylvestris (Scots pine) trees were determined from five locations sampled along the Yenisei River, spaced over a total distance of ~1000 km between the cities of Turuhansk (66°N) and Krasnoyarsk (56°N). The transect covered the major part of the natural distribution of Scots pine in the region with median growing season temperatures and precipitation varying from 12.2°C and 218 mm to 14.0°C and 278 mm for Turuhansk and Krasnoyarsk, respectively. A key focus of the study was to investigate the effects of variations in temperature, precipitation, and atmospheric CO2 concentration on long- and short-term variation in photosynthetic 13C discrimination during photosynthesis and the marginal cost of tree water use, as reflected in the differences in the historical records of the 13C / 12C ratio in wood cellulose compared to that of the atmosphere (Δ13Cc). In 17 of the 20 samples, trees Δ13Cc has declined during the last 150 years, particularly so during the second half of the twentieth century. Using a model of stomatal behaviour combined with a process-based photosynthesis model, we deduce that this trend indicates a long-term decrease in canopy stomatal conductance, probably in response to increasing atmospheric CO2 concentrations. This response being observed for most trees along the transect is suggestive of widespread decreases in Δ13Cc and increased water use efficiency for Scots pine in central Siberia over the last century. Overlying short-term variations in Δ13Cc were also accounted for by the model and were related to variations in growing season soil water deficit and atmospheric humidity.

Soybean leaf hydraulic conductance does not acclimate to growth at elevated [CO2] or temperature in growth chambers or in the field

PubMed Central

Locke, Anna M.; Sack, Lawren; Bernacchi, Carl J.; Ort, Donald R.

2013-01-01

Background and Aims Leaf hydraulic properties are strongly linked with transpiration and photosynthesis in many species. However, it is not known if gas exchange and hydraulics will have co-ordinated responses to climate change. The objective of this study was to investigate the responses of leaf hydraulic conductance (Kleaf) in Glycine max (soybean) to growth at elevated [CO2] and increased temperature compared with the responses of leaf gas exchange and leaf water status. Methods Two controlled-environment growth chamber experiments were conducted with soybean to measure Kleaf, stomatal conductance (gs) and photosynthesis (A) during growth at elevated [CO2] and temperature relative to ambient levels. These results were validated with field experiments on soybean grown under free-air elevated [CO2] (FACE) and canopy warming. Key results In chamber studies, Kleaf did not acclimate to growth at elevated [CO2], even though stomatal conductance decreased and photosynthesis increased. Growth at elevated temperature also did not affect Kleaf, although gs and A showed significant but inconsistent decreases. The lack of response of Kleaf to growth at increased [CO2] and temperature in chamber-grown plants was confirmed with field-grown soybean at a FACE facility. Conclusions Leaf hydraulic and leaf gas exchange responses to these two climate change factors were not strongly linked in soybean, although gs responded to [CO2] and increased temperature as previously reported. This differential behaviour could lead to an imbalance between hydraulic supply and transpiration demand under extreme environmental conditions likely to become more common as global climate continues to change. PMID:23864003

Flight Tests of a 40-Foot Nominal Diameter Modified Ringsail Parachute Deployed at Mach 1.64 and Dynamic Pressure of 9.1 Pounds Per Square Foot

NASA Technical Reports Server (NTRS)

Eckstrom, Clinton V.; Murrow, Harold N.; Preisser, John S.

1967-01-01

A ringsail parachute, which had a nominal diameter of 40 feet (12.2 meters) and reference area of 1256 square feet (117 m(exp 2)) and was modified to provide a total geometric porosity of 15 percent of the reference area, was flight tested as part of the rocket launch portion of the NASA Planetary Entry Parachute Program. The payload for the flight test was an instrumented capsule from which the test parachute was ejected by a deployment mortar when the system was at a Mach number of 1.64 and a dynamic pressure of 9.1 pounds per square foot (43.6 newtons per m(exp 2)). The parachute deployed to suspension line stretch in 0.45 second with a resulting snatch force of 1620 pounds (7200 newtons). Canopy inflation began 0.07 second later and the parachute projected area increased slowly to a maximum of 20 percent of that expected for full inflation. During this test, the suspension lines twisted, primarily because the partially inflated canopy could not restrict the twisting to the attachment bridle and risers. This twisting of the suspension lines hampered canopy inflation at a time when velocity and dynamic-pressure conditions were more favorable.

Bayesian estimation of seasonal course of canopy leaf area index from hyperspectral satellite data

NASA Astrophysics Data System (ADS)

Varvia, Petri; Rautiainen, Miina; Seppänen, Aku

2018-03-01

In this paper, Bayesian inversion of a physically-based forest reflectance model is investigated to estimate of boreal forest canopy leaf area index (LAI) from EO-1 Hyperion hyperspectral data. The data consist of multiple forest stands with different species compositions and structures, imaged in three phases of the growing season. The Bayesian estimates of canopy LAI are compared to reference estimates based on a spectral vegetation index. The forest reflectance model contains also other unknown variables in addition to LAI, for example leaf single scattering albedo and understory reflectance. In the Bayesian approach, these variables are estimated simultaneously with LAI. The feasibility and seasonal variation of these estimates is also examined. Credible intervals for the estimates are also calculated and evaluated. The results show that the Bayesian inversion approach is significantly better than using a comparable spectral vegetation index regression.

Evolutionary Association of Stomatal Traits with Leaf Vein Density in Paphiopedilum, Orchidaceae

PubMed Central

Sun, Mei; Zhang, Juan-Juan; Cao, Kun-Fang; Hu, Hong

2012-01-01

Background Both leaf attributes and stomatal traits are linked to water economy in land plants. However, it is unclear whether these two components are associated evolutionarily. Methodology/Principal Findings In characterizing the possible effect of phylogeny on leaf attributes and stomatal traits, we hypothesized that a correlated evolution exists between the two. Using a phylogenetic comparative method, we analyzed 14 leaf attributes and stomatal traits for 17 species in Paphiopedilum. Stomatal length (SL), stomatal area (SA), upper cuticular thickness (UCT), and total cuticular thickness (TCT) showed strong phylogenetic conservatism whereas stomatal density (SD) and stomatal index (SI) were significantly convergent. Leaf vein density was correlated with SL and SD whether or not phylogeny was considered. The lower epidermal thickness (LET) was correlated positively with SL, SA, and stomatal width but negatively with SD when phylogeny was not considered. When this phylogenetic influence was factored in, only the significant correlation between SL and LET remained. Conclusion/Significance Our results support the hypothesis for correlated evolution between stomatal traits and vein density in Paphiopedilum. However, they do not provide evidence for an evolutionary association between stomata and leaf thickness. These findings lend insight into the evolution of traits related to water economy for orchids under natural selection. PMID:22768224

The BIG protein distinguishes the process of CO2 -induced stomatal closure from the inhibition of stomatal opening by CO2.

PubMed

He, Jingjing; Zhang, Ruo-Xi; Peng, Kai; Tagliavia, Cecilia; Li, Siwen; Xue, Shaowu; Liu, Amy; Hu, Honghong; Zhang, Jingbo; Hubbard, Katharine E; Held, Katrin; McAinsh, Martin R; Gray, Julie E; Kudla, Jörg; Schroeder, Julian I; Liang, Yun-Kuan; Hetherington, Alistair M

2018-04-01

We conducted an infrared thermal imaging-based genetic screen to identify Arabidopsis mutants displaying aberrant stomatal behavior in response to elevated concentrations of CO 2 . This approach resulted in the isolation of a novel allele of the Arabidopsis BIG locus (At3g02260) that we have called CO 2 insensitive 1 (cis1). BIG mutants are compromised in elevated CO 2 -induced stomatal closure and bicarbonate activation of S-type anion channel currents. In contrast with the wild-type, they fail to exhibit reductions in stomatal density and index when grown in elevated CO 2 . However, like the wild-type, BIG mutants display inhibition of stomatal opening when exposed to elevated CO 2 . BIG mutants also display wild-type stomatal aperture responses to the closure-inducing stimulus abscisic acid (ABA). Our results indicate that BIG is a signaling component involved in the elevated CO 2 -mediated control of stomatal development. In the control of stomatal aperture by CO 2 , BIG is only required in elevated CO 2 -induced closure and not in the inhibition of stomatal opening by this environmental signal. These data show that, at the molecular level, the CO 2 -mediated inhibition of opening and promotion of stomatal closure signaling pathways are separable and BIG represents a distinguishing element in these two CO 2 -mediated responses. © 2018 The Authors. New Phytologist © 2018 New Phytologist Trust.

CO2 sensing and CO2 regulation of stomatal conductance: advances and open questions

PubMed Central

Engineer, Cawas; Hashimoto-Sugimoto, Mimi; Negi, Juntaro; Israelsson-Nordstrom, Maria; Azoulay-Shemer, Tamar; Rappel, Wouter-Jan; Iba, Koh; Schroeder, Julian

2015-01-01

Guard cells form epidermal stomatal gas exchange valves in plants and regulate the aperture of stomatal pores in response to changes in the carbon dioxide (CO2) concentration in leaves. Moreover, the development of stomata is repressed by elevated CO2 in diverse plant species. Evidence suggests that plants can sense CO2 concentration changes via guard cells and via mesophyll tissues in mediating stomatal movements. We review new discoveries and open questions on mechanisms mediating CO2-regulated stomatal movements and CO2 modulation of stomatal development, which together function in CO2-regulation of stomatal conductance and gas exchange in plants. Research in this area is timely in light of the necessity of selecting and developing crop cultivars which perform better in a shifting climate. PMID:26482956

Mapping forest canopy fuels in Yellowstone National Park using lidar and hyperspectral data

NASA Astrophysics Data System (ADS)

Halligan, Kerry Quinn

The severity and size of wildland fires in the forested western U.S have increased in recent years despite improvements in fire suppression efficiency. This, along with increased density of homes in the wildland-urban interface, has resulted in high costs for fire management and increased risks to human health, safety and property. Crown fires, in comparison to surface fires, pose an especially high risk due to their intensity and high rate of spread. Crown fire models require a range of quantitative fuel parameters which can be difficult and costly to obtain, but advances in lidar and hyperspectral sensor technologies hold promise for delivering these inputs. Further research is needed, however, to assess the strengths and limitations of these technologies and the most appropriate analysis methodologies for estimating crown fuel parameters from these data. This dissertation focuses on retrieving critical crown fuel parameters, including canopy height, canopy bulk density and proportion of dead canopy fuel, from airborne lidar and hyperspectral data. Remote sensing data were used in conjunction with detailed field data on forest parameters and surface reflectance measurements. A new method was developed for retrieving Digital Surface Model (DSM) and Digital Canopy Models (DCM) from first return lidar data. Validation data on individual tree heights demonstrated the high accuracy (r2 0.95) of the DCMs developed via this new algorithm. Lidar-derived DCMs were used to estimate critical crown fire parameters including available canopy fuel, canopy height and canopy bulk density with linear regression model r2 values ranging from 0.75 to 0.85. Hyperspectral data were used in conjunction with Spectral Mixture Analysis (SMA) to assess fuel quality in the form of live versus dead canopy proportions. Severity and stage of insect-caused forest mortality were estimated using the fractional abundance of green vegetation, non-photosynthetic vegetation and shade obtained from SMA. Proportion of insect attack was estimated with a linear model producing an r2 of 0.6 using SMA and bark endmembers from image and reference libraries. Fraction of red attack, with a possible link to increased crown fire risk, was estimated with an r2 of 0.45.

Co-ordination of physiological and morphological responses of stomata to elevated [CO2] in vascular plants.

PubMed

Haworth, Matthew; Elliott-Kingston, Caroline; McElwain, Jennifer C

2013-01-01

Plant stomata display a wide range of short-term behavioural and long-term morphological responses to atmospheric carbon dioxide concentration ([CO(2)]). The diversity of responses suggests that plants may have different strategies for controlling gas exchange, yet it is not known whether these strategies are co-ordinated in some way. Here, we test the hypothesis that there is co-ordination of physiological (via aperture change) and morphological (via stomatal density change) control of gas exchange by plants. We examined the response of stomatal conductance (G(s)) to instantaneous changes in external [CO(2)] (C(a)) in an evolutionary cross-section of vascular plants grown in atmospheres of elevated [CO(2)] (1,500 ppm) and sub-ambient [O(2)] (13.0 %) compared to control conditions (380 ppm CO(2), 20.9 % O(2)). We found that active control of stomatal aperture to [CO(2)] above current ambient levels was not restricted to angiosperms, occurring in the gymnosperms Lepidozamia peroffskyana and Nageia nagi. The angiosperm species analysed appeared to possess a greater respiratory demand for stomatal movement than gymnosperm species displaying active stomatal control. Those species with little or no control of stomatal aperture (termed passive) to C(a) were more likely to exhibit a reduction in stomatal density than species with active stomatal control when grown in atmospheres of elevated [CO(2)]. The relationship between the degree of stomatal aperture control to C(a) above ambient and the extent of any reduction in stomatal density may suggest the co-ordination of physiological and morphological responses of stomata to [CO(2)] in the optimisation of water use efficiency. This trade-off between stomatal control strategies may have developed due to selective pressures exerted by the costs associated with passive and active stomatal control.

Acclimation of leaf hydraulic conductance and stomatal conductance of Pinus taeda (loblolly pine) to long-term growth in elevated CO2 (free-air CO2 enrichment) and N-fertilizationpce

Treesearch

Jean-Christophe Domec; Sari Palmroth; Eric Ward; Chris Maier; M. Therezien; Ram Oren

2009-01-01

We investigated how leaf hydraulic conductance (Kleaf) of loblolly pine trees is influenced by soil nitrogen amendment (N) in stands subjected to ambient or elevated CO2 concentrations CO2 a and CO2 e, respectively). We also examined how Kleaf varies with changes in reference leaf water potential (...

Accuracy Assessment of Lidar-Derived Digital Terrain Model (dtm) with Different Slope and Canopy Cover in Tropical Forest Region

NASA Astrophysics Data System (ADS)

Salleh, M. R. M.; Ismail, Z.; Rahman, M. Z. A.

2015-10-01

Airborne Light Detection and Ranging (LiDAR) technology has been widely used recent years especially in generating high accuracy of Digital Terrain Model (DTM). High density and good quality of airborne LiDAR data promises a high quality of DTM. This study focussing on the analysing the error associated with the density of vegetation cover (canopy cover) and terrain slope in a LiDAR derived-DTM value in a tropical forest environment in Bentong, State of Pahang, Malaysia. Airborne LiDAR data were collected can be consider as low density captured by Reigl system mounted on an aircraft. The ground filtering procedure use adaptive triangulation irregular network (ATIN) algorithm technique in producing ground points. Next, the ground control points (GCPs) used in generating the reference DTM and these DTM was used for slope classification and the point clouds belong to non-ground are then used in determining the relative percentage of canopy cover. The results show that terrain slope has high correlation for both study area (0.993 and 0.870) with the RMSE of the LiDAR-derived DTM. This is similar to canopy cover where high value of correlation (0.989 and 0.924) obtained. This indicates that the accuracy of airborne LiDAR-derived DTM is significantly affected by terrain slope and canopy caver of study area.

Dry Season Impact on Physiological Functioning of Two Tropical Tree Species in the Daintree Rainforest, Northeast Australia

NASA Astrophysics Data System (ADS)

Cernusak, L. A.; Dempsey, R.; Cheesman, A.; Meir, P.; Laurance, S.

2016-12-01

We measured leaf gas exchange, leaf biochemistry, and stem growth in two tropical tree species in the Daintree rainforest. The site experiences an average dry season length of three months, with global climate change predictions indicating that this could increase. Of the two studied species, Elaeocarpus angustifolius is wide-spread and early-successional, whereas Endiandra microneura is locally endemic and late-successional. Measurements started in 2014 and ended in 2015, thus encompassing the 2014 dry season. Upper canopy foliage was accessed from a 48 m tall canopy crane. Photosynthetic rates were higher during the wet season in Elaeocarpus than in Endiandra, consistent with its pioneering habit. Elaeocarpus showed larger reductions in both photosynthesis and stomatal conductance in response to the dry season than did Endiandra. Dry season depression of photosynthesis was associated with reduced intercellular carbon dioxide concentrations in Endiandra, but not in Elaeocarpus, indicating a role for photo-inhibition in restricting photosynthesis during the dry season in the early successional species, but not in the late successional species. Consistently, Endiandra invested more heavily in photoprotective and anti-oxidative compounds in its upper canopy foliage than did Elaeocarpus. Stem growth rates were four-fold higher in Elaeocarpus than in Endiandra during the wet season, reflecting the successional status of the two species. Stem growth slowed in both species in response to the dry season, and all but ceased by the late dry season. With the onset of the early wet season, stem growth increased markedly, and Elaeocarpus again maintained much faster growth than Endiandra. Overall, our results indicate that at the leaf level, biochemical and physiological processes associated with photosynthesis were more vulnerable to dry season stress in Elaeocarpus than in Endiandra; however, at the whole-plant level, our measurements and the geographic distribution of Elaeocarpus suggest that its overall performance is robust in the face of the dry season. The difference between insights at the leaf-level and those at the whole-plant level presumably reflects a strategy in Elaeocarpus of investing in cheaper, shorter lived, and more easily replaced leaves than does the late successional species, Endiandra.

Organ-specific effects of brassinosteroids on stomatal production coordinate with the action of Too Many Mouths.

PubMed

Wang, Ming; Yang, Kezhen; Le, Jie

2015-03-01

In Arabidopsis, stomatal development initiates after protodermal cells acquire stomatal lineage cell fate. Stomata or their precursors communicate with their neighbor epidermal cells to ensure the "one cell spacing" rule. The signals from EPF/EPFL peptide ligands received by Too Many Mouths (TMM) and ERECTA-family receptors are supposed to be transduced by YODA MAPK cascade. A basic helix-loop-helix transcription factor SPEECHLESS (SPCH) is another key regulator of stomatal cell fate determination and asymmetric entry divisions, and SPCH activity is regulated by YODA MAPK cascade. Brassinosteroid (BR) signaling, one of the most well characterized signal transduction pathways in plants, contributes to the control of stomatal production. But opposite organ-specific effects of BR on stomatal production were reported. Here we confirm that stomatal production in hypocotyls is controlled by BR levels. YODA and CYCD4 are not essential for BR stomata-promoting function. Furthermore, we found that BR could confer tmm hypocotyls clustered stomatal phenotype, indicating that the BR organ-specific effects on stomatal production might coordinate with the TMM organ-specific actions. © 2014 Institute of Botany, Chinese Academy of Sciences.

On the theory of gaseous transport to plant canopies

NASA Astrophysics Data System (ADS)

Bache, D. H.

Solutions of the convection-diffusion equations are developed to show the relationship between bulk transport parameters affecting gaseous transfer to plant canopies and local rates of transfer within the canopy. Foliage density is considered to be uniform and the drag coefficient of elements is specified by cd = γu- n with u as the local wind-speed and γ and n constants. Under conditions of high surface resistance, the bulk deposition velocity at the top of the canopy vg( h) approaches a limit defined by v g(h) = v̂gL p(1-ψ v̂gL p/u ∗) , where v̂g is the local deposition rate, Lp the effective foliage area, u ∗ the friction velocity and ψ a structure coefficient. From this, a criterion is proposed for defining the conditions in which the local resistances may be added in parallel. Comparisons with the external model for the bulk transport resistance rp = ra + rb + rc (where r p = 1/v g(h) and ra is a diffusive resistance between the apparent momentum sink and height h) shows that the bulk surface resistance r c = r̂s/L p( r̂s being a local surface resistance due to internal properties of the surface) and r b = overliner̂p-r a, appearing as an excess aerodynamic component; overliner̂p refers to the depth-averaged value of r̂p—the resistance to transfer through the laminar sublayer enveloping individual canopy elements. In conditions of zero surface resistance the bulk transport rate rp, o can be specified by r p,o/r a = E( r̂p/r̂∗) hq with E and q as constants, the term r̂p/r̂∗ referring to the resistances to mass and momentum transfer to canopy elements. A general expression is formulated for the sublayer Stanton number B -1  r bu ∗ at the extremes of high and zero surface resistance. In conditions of low surface resistance, it is shown that the terms rb + rc cannot be conveniently separated into equivalent aerodynamic and surface components as at the limit of high surface resistance. This conclusion is a departure from previous analyses and emphasizes the hidden dangers of adding resistances 'in parallel' in conditions of low surface resistance.

Leaf surface traits and water storage retention affect photosynthetic responses to leaf surface wetness among wet tropical forest and semiarid savanna plants.

PubMed

Aparecido, Luiza M T; Miller, Gretchen R; Cahill, Anthony T; Moore, Georgianne W

2017-10-01

While it is reasonable to predict that photosynthetic rates are inhibited while leaves are wet, leaf gas exchange measurements during wet conditions are challenging to obtain due to equipment limitations and the complexity of canopy-atmosphere interactions in forested environments. Thus, the objective of this study was to evaluate responses of seven tropical and three semiarid savanna plant species to simulated leaf wetness and test the hypotheses that (i) leaf wetness reduces photosynthetic rates (Anet), (ii) leaf traits explain different responses among species and (iii) leaves from wet environments are better adapted for wet leaf conditions than those from drier environments. The two sites were a tropical rainforest in northern Costa Rica with ~4200 mm annual rainfall and a savanna in central Texas with ~1100 mm. Gas exchange measurements were collected under dry and wet conditions on five sun-exposed leaf replicates from each species. Additional measurements included leaf wetness duration and stomatal density. We found that Anet responses varied greatly among species, but all plants maintained a baseline of activity under wet leaf conditions, suggesting that abaxial leaf Anet was a significant percentage of total leaf Anet for amphistomatous species. Among tropical species, Anet responses immediately after wetting ranged from -31% (Senna alata (L.) Roxb.) to +21% (Zamia skinneri Warsz. Ex. A. Dietr.), while all savanna species declined (up to -48%). After 10 min of drying, most species recovered Anet towards the observed status prior to wetting or surpassed it, with the exception of Quercus stellata Wangenh., a savanna species, which remained 13% below Anet dry. The combination of leaf wetness duration and leaf traits, such as stomatal density, trichomes or wax, most likely influenced Anet responses positively or negatively. There was also overlap between leaf traits and Anet responses of savanna and tropical plants. It is possible that these species converge on a relatively conservative response to wetness, each for divergent purposes (cooling, avoiding stomatal occlusion, or by several unique means of rapid drying). A better understanding of leaf wetness inhibiting photosynthesis is vital for accurate modeling of growth in forested environments; however, species adapted for wet environments may possess compensatory traits that mitigate these effects. © The Author 2017. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Stomatal Blue Light Response Is Present in Early Vascular Plants.

PubMed

Doi, Michio; Kitagawa, Yuki; Shimazaki, Ken-ichiro

2015-10-01

Light is a major environmental factor required for stomatal opening. Blue light (BL) induces stomatal opening in higher plants as a signal under the photosynthetic active radiation. The stomatal BL response is not present in the fern species of Polypodiopsida. The acquisition of a stomatal BL response might provide competitive advantages in both the uptake of CO2 and prevention of water loss with the ability to rapidly open and close stomata. We surveyed the stomatal opening in response to strong red light (RL) and weak BL under the RL with gas exchange technique in a diverse selection of plant species from euphyllophytes, including spermatophytes and monilophytes, to lycophytes. We showed the presence of RL-induced stomatal opening in most of these species and found that the BL responses operated in all euphyllophytes except Polypodiopsida. We also confirmed that the stomatal opening in lycophytes, the early vascular plants, is driven by plasma membrane proton-translocating adenosine triphosphatase and K(+) accumulation in guard cells, which is the same mechanism operating in stomata of angiosperms. These results suggest that the early vascular plants respond to both RL and BL and actively regulate stomatal aperture. We also found three plant species that absolutely require BL for both stomatal opening and photosynthetic CO2 fixation, including a gymnosperm, C. revoluta, and the ferns Equisetum hyemale and Psilotum nudum. © 2015 American Society of Plant Biologists. All Rights Reserved.

Stomatal Spacing Safeguards Stomatal Dynamics by Facilitating Guard Cell Ion Transport Independent of the Epidermal Solute Reservoir12[CC-BY

PubMed Central

Papanatsiou, Maria; Amtmann, Anna

2016-01-01

Stomata enable gaseous exchange between the interior of the leaf and the atmosphere through the stomatal pore. Control of the pore aperture depends on osmotic solute accumulation by, and its loss from the guard cells surrounding the pore. Stomata in most plants are separated by at least one epidermal cell, and this spacing is thought to enhance stomatal function, although there are several genera that exhibit stomata in clusters. We made use of Arabidopsis (Arabidopsis thaliana) stomatal patterning mutants to explore the impact of clustering on guard cell dynamics, gas exchange, and ion transport of guard cells. These studies showed that stomatal clustering in the Arabidopsis too many mouths (tmm1) mutant suppressed stomatal movements and affected CO2 assimilation and transpiration differentially between dark and light conditions and were associated with alterations in K+ channel gating. These changes were consistent with the impaired dynamics of tmm1 stomata and were accompanied by a reduced accumulation of K+ ions in the guard cells. Our findings underline the significance of spacing for stomatal dynamics. While stomatal spacing may be important as a reservoir for K+ and other ions to facilitate stomatal movements, the effects on channel gating, and by inference on K+ accumulation, cannot be explained on the basis of a reduced number of epidermal cells facilitating ion supply to the guard cells. PMID:27406168

Contrasting responses of leaf stomatal characteristics to climate change: a considerable challenge to predict carbon and water cycles.

PubMed

Yan, Weiming; Zhong, Yangquanwei; Shangguan, Zhouping

2017-09-01

Stomata control the cycling of water and carbon between plants and the atmosphere; however, no consistent conclusions have been drawn regarding the response of stomatal frequency to climate change. Here, we conducted a meta-analysis of 1854 globally obtained data series to determine the response of stomatal frequency to climate change, which including four plant life forms (over 900 species), at altitudes ranging from 0 to 4500 m and over a time span of more than one hundred thousand years. Stomatal frequency decreased with increasing CO 2 concentration and increased with elevated temperature and drought stress; it was also dependent on the species and experimental conditions. The response of stomatal frequency to climate change showed a trade-off between stomatal control strategies and environmental factors, such as the CO 2 concentration, temperature, and soil water availability. Moreover, threshold effects of elevated CO 2 and temperature on stomatal frequency were detected, indicating that the response of stomatal density to increasing CO 2 concentration will decrease over the next few years. The results also suggested that the stomatal index may be more reliable than stomatal density for determination of the historic CO 2 concentration. Our findings indicate that the contrasting responses of stomata to climate change bring a considerable challenge in predicting future water and carbon cycles. © 2017 John Wiley & Sons Ltd.

Drought limitations to leaf-level gas exchange: results from a model linking stomatal optimization and cohesion-tension theory.

PubMed

Novick, Kimberly A; Miniat, Chelcy F; Vose, James M

2016-03-01

We merge concepts from stomatal optimization theory and cohesion-tension theory to examine the dynamics of three mechanisms that are potentially limiting to leaf-level gas exchange in trees during drought: (1) a 'demand limitation' driven by an assumption of optimal stomatal functioning; (2) 'hydraulic limitation' of water movement from the roots to the leaves; and (3) 'non-stomatal' limitations imposed by declining leaf water status within the leaf. Model results suggest that species-specific 'economics' of stomatal behaviour may play an important role in differentiating species along the continuum of isohydric to anisohydric behaviour; specifically, we show that non-stomatal and demand limitations may reduce stomatal conductance and increase leaf water potential, promoting wide safety margins characteristic of isohydric species. We used model results to develop a diagnostic framework to identify the most likely limiting mechanism to stomatal functioning during drought and showed that many of those features were commonly observed in field observations of tree water use dynamics. Direct comparisons of modelled and measured stomatal conductance further indicated that non-stomatal and demand limitations reproduced observed patterns of tree water use well for an isohydric species but that a hydraulic limitation likely applies in the case of an anisohydric species. Published 2015. This article is a US Government work and is in the public domain in the USA.

Coming of Age: Polarization as a Probe of Plant Canopy Water Status

NASA Astrophysics Data System (ADS)

Vanderbilt, V. C.; Daughtry, C. S. T.; Kupinski, M.; Bradley, C. L.; Dahlgren, R. P.

2015-12-01

We tested the hypothesis that the relative water content (RWC) of the sunlit leaves in a plant canopy may be estimated from polarized canopy imagery. Recently (IGARSS, July 27-31, 2015, Milan, Italy), we reported the results of laboratory polarization measurements of single detached leaves during dry down. We found that RWC was linearly related to the ratio of the reflectance of the interior of the leaf and the leaf transmittance. Here we report application of the laboratory results to estimate RWC for sunlit leaves in a plant canopy. Using a commercial-off-the-shelf (COTS) Nikon 810 camera with Nikkor 300 mm lens and Polaroid type HN-22 linear polarizer, we photographed in the principle plane a plant canopy displaying a gradient of water stress and collected, at each of multiple points along the gradient, two images, one with the polarization filter oriented for maximum scene response and a second with the filter oriented for minimum scene response. We converted the digital values in the two images to reflectance factor with reference to images of a white, flat, horizontal Spectralon surface. We classified the polarization imagery, identifying reflecting leaves, transmitting leaves, other sunlit vegetation and shadows. For each image pair we normalized the leaf internal reflectance by dividing by the cosine of the angle of incidence of the sunlight on the leaf, selected the leaf maximum transmittance in the scene and divided to obtain the ratio reflectance/transmittance, which we compared with leaf RWC. We determined the leaf relative water content by harvesting a section of leaf and immediately placing it in a sealed container in an ice chest. Later in the laboratory the leaf sample was weighed, rehydrated, weighed, dried and again weighed. RWC was determined using the standard formula.Our experimental results support our hypothesis, suggesting that the RWC of sunlit leaves in a plant canopy may be estimated from analysis of polarization imagery collected by a COTS camera system. Unlike remotely sensed estimates of canopy equivalent water thickness, our estimates of the RWC of sunlit canopy leaves provide leaf physiological information. We propose RWC estimates based upon sunlit leaves are more relevant to assessing the water status of a plant canopy than would be RWC estimates based upon large FOV canopy measurements.

Coming of Age: Polarization as a Probe of Plant Canopy Water Status

NASA Technical Reports Server (NTRS)

Vanderbilt, Vern C.; Daughtry, Craig S. T.; Kupinski, Meredith; Bradley, Christine Lavella; Dahlgren, Robert P.

2015-01-01

We tested the hypothesis that the relative water content (RWC) of the sunlit leaves in a plant canopy may be estimated from polarized canopy imagery. Recently (IGARSS, July 27-31, 2015, Milan, Italy), we reported the results of laboratory polarization measurements of single detached leaves during dry down. We found that RWC was linearly related to the ratio of the reflectance of the interior of the leaf and the leaf transmittance. Here we report application of the laboratory results to estimate RWC for sunlit leaves in a plant canopy. Using a commercial-off-the-shelf (COTS) Nikon 810 camera with Nikkor 300 mm lens and Polaroid type HN-22 linear polarizer, we photographed in the principle plane a plant canopy displaying a gradient of water stress and collected, at each of multiple points along the gradient, two images, one with the polarization filter oriented for maximum scene response and a second with the filter oriented for minimum scene response. We converted the digital values in the two images to reflectance factor with reference to images of a white, flat, horizontal Spectralon surface. We classified the polarization imagery, identifying reflecting leaves, transmitting leaves, other sunlit vegetation and shadows. For each image pair we normalized the leaf internal reflectance by dividing by the cosine of the angle of incidence of the sunlight on the leaf, selected the leaf maximum transmittance in the scene and divided to obtain the ratio reflectance/transmittance, which we compared with leaf RWC. We determined the leaf relative water content by harvesting a section of leaf and immediately placing it in a sealed container in an ice chest. Later in the laboratory the leaf sample was weighed, rehydrated, weighed, dried and again weighed. RWC was determined using the standard formula. Our experimental results support our hypothesis, suggesting that the RWC of sunlit leaves in a plant canopy may be estimated from analysis of polarization imagery collected by a COTS camera system. Unlike remotely sensed estimates of canopy equivalent water thickness, our estimates of the RWC of sunlit canopy leaves provide leaf physiological information. We propose RWC estimates based upon sunlit leaves are more relevant to assessing the water status of a plant canopy than would be RWC estimates based upon large FOV canopy measurements.

Stomatal Opening in Isolated Epidermal Strips of Vicia faba. I. Response to Light and to CO2-free Air 1

PubMed Central

Fischer, R. A.

1968-01-01

This paper reports a consistent and large opening response to light + CO2-free air in living stomata of isolated epidermal strips of Vicia faba. The response was compared to that of non-isolated stomata in leaf discs floating on water; stomatal apertures, guard cell solute potentials and starch contents were similar in the 2 situations. To obtain such stomatal behavior, it was necessary to float epidermal strips on dilute KCl solutions. This suggests that solute uptake is necessary for stomatal opening. The demonstration of normal stomatal behavior in isolated epidermal strips provides a very useful system in which to investigate the mechanism of stomatal opening. It was possible to show independent responses in stomatal aperture to light and to CO2-free air. PMID:16656995

Jasmonate-mediated stomatal closure under elevated CO2 revealed by time-resolved metabolomics

USDA-ARS?s Scientific Manuscript database

Foliar stomatal movements are critical for regulating plant water status and gas exchange. Elevated carbon dioxide (CO2) concentrations are known to induce stomatal closure. However, current knowledge on CO2 signal transduction in stomatal guard cells is limited. Here we report the metabolomic respo...

Spray distribution evaluation of different settings of a hand-held-trolley sprayer used in greenhouse tomato crops.

PubMed

Llop, Jordi; Gil, Emilio; Gallart, Montserrat; Contador, Felipe; Ercilla, Mireia

2016-03-01

Hand-held-trolley sprayers have recently been promoted to improve spray application techniques in greenhouses in south-eastern Spain. However, certain aspects remain to be improved. A modified hand-held-trolley sprayer was evaluated under two different canopy conditions (high and low canopy density) and with several sprayer settings (nozzle type, air assistance and spray volume). In this study, the deposition, coverage and uniformity of distribution of the spray on the canopy have been assessed. The deposition on leaves was significantly higher when flat-fan nozzles and air assistance were used at both high and low spray volumes. No differences were detected between the reference system at a high spray volume and the modified trolley at a low spray volume. Flat-fan nozzles with air assistance increased penetrability into the canopy. Air assistance and flat-fan nozzles allow volume rates to be reduced while maintaining or improving spray quality distribution. The working parameters of hand-held sprayers must be considered to reduce environmental risk and increase the efficacy of the spraying process. © 2015 Society of Chemical Industry. © 2015 Society of Chemical Industry.

Got Point Clouds: Characterizing Canopy Structure With Active and Passive Sensors

NASA Astrophysics Data System (ADS)

Popescu, S. C.; Malambo, L.; Sheridan, R.; Putman, E.; Murray, S.; Rooney, W.; Rajan, N.

2016-12-01

Unmanned Aerial Systems (UAS) provide the means to acquire highly customized aerial data at local scale with a multitude of sensors. UAS allow us to obtain affordably repeated observations of canopy structure for agricultural and natural resources applications by using passive optical sensors, such as cameras and photogrammetric techniques, and active sensors, such as lidar (Light Detection and Ranging). The objectives of this presentation are to: (1) offer a brief overview of UAS used for agriculture and natural resources studies, (2) describe experiences in conducting agriculture phenotyping and forest vegetation measurements, and (3) give details on the methodology developed for image and lidar data processing for characterizing the three dimensional structure of plant canopies. The UAS types used for this purpose included rotary platforms, such as quadcopters, hexacopters, and octocopters, with a payload capacity of up to 19 lbs. The sensors that collected data over two crop seasons include multispectral cameras in the visible color spectrum and near infrared, and UAS-lidar. For ground reference data we used terrestrial lidar scanners and field measurements. Results comparing UAS and terrestrial measurements show high correlation and open new areas of scientific investigation of crop canopies previously not possible with affordable techniques.

Measuring and modeling changes in land-atmosphere exchanges and hydrologic response in forests undergoing insect-driven mortality

NASA Astrophysics Data System (ADS)

Gochis, D. J.; Brooks, P. D.; Harpold, A. A.; Ewers, B. E.; Pendall, E.; Barnard, H. R.; Reed, D.; Harley, P. C.; Hu, J.; Biederman, J.

2010-12-01

Given the magnitude and spatial extent of recent forest mortality in the western U.S. there is a pressing need to improve representation of such influences on the exchange of energy, water, biogeochemical and momentum fluxes in land-atmosphere parameterizations coupled to weather and climate models. In this talk we present observational data and model results from a new study aimed at improving understanding the impacts of mountain pine beetle-induced forest mortality in the central Rocky Mountains. Baseline observations and model runs from undisturbed lodgepole pine forest conditions are developed as references against which new observations and model runs from infested stands are compared. We will specifically look at the structure and evolution of sub-canopy energy exchange variables such as shortwave and longwave radiation and sub-canopy turbulence as well as sub-canopy precipitation, sapflow fluxes, canopy-scale fluxes and soil moisture and temperature. In this manner we seek to lay the ground work for evaluating the recent generation of land surface model changes aimed at representing insect-related forest dynamics in the CLM-C/N and Noah land surface models.

Hydraulic Balance of a Eucalyptus urophylla Plantation in Response to Periodic Drought in Low Subtropical China

PubMed Central

Zhang, Zhenzhen; Zhao, Ping; McCarthy, Heather R.; Ouyang, Lei; Niu, Junfeng; Zhu, Liwei; Ni, Guangyan; Huang, Yuqing

2016-01-01

A clear understanding of hydraulic regulation in cultivated plants is crucial for addressing challenges to forest water cycling due to climate changes in low subtropical China. Experiments were conducted to determine the hydrologic balance of a Eucalyptus urophylla plantation in response to periodic drought. Trees displayed lower stomatal conductance (GS) and leaf water potentials (ΨL) during the dry periods. A decrease of 22.4% was found for the maximum reference GS (GS at D = 1 kPa; GSref-max). Accordingly, specific hydraulic conductivity (ks) decreased by 45.3 – 65.6% from the wet to the dry season, depending on the tree size. Fairly stable leaf stomatal conductance (gs) with decreasing ΨL (ΨL < -1.6 MPa) contributed to the high water-use efficiency (WUE) of this Eucalyptus species. Additionally, the lower stomatal sensitivity (-m = 0.53) in the dry season might also be responsible for the high WUE, since we found an anisohydric behavior that was associated with photosynthetically active radiation (Q0). Larger trees were found to use water more efficiently than small trees, due to the higher sensitivity of ks to decreasing ΨL. This was also verified by the decreasing leaf carbon isotope discrimination (Δ13C) with increasing tree diameter. However, further studies are needed to determine the universality of these results for other Eucalyptus species in this region. PMID:27725821

Determination of the Sources of Radar Scattering

NASA Technical Reports Server (NTRS)

Moore, R. K.; Zoughi, R.

1984-01-01

Fine-resolution radar backscattering measurements were proposed to determine the backscattering sources in various vegetation canopies and surface targets. The results were then used to improve the existing theoretical models of terrain scattering, and also to enhance understanding of the radar signal observed by an imaging radar over a vegetated area. Various experiments were performed on targets such as corn, milo, soybeans, grass, asphalt pavements, soil and concrete walkways. Due to the lack of available references on measurements of this type, the obtained results will be used primarily as a foundation or future experiments. The constituent backscattering characteristics of the vegetation canopies was also examined.

Starch Biosynthesis in Guard Cells But Not in Mesophyll Cells Is Involved in CO2-Induced Stomatal Closing1[OPEN

PubMed Central

Stephan, Aaron B.; Schroeder, Julian I.

2016-01-01

Starch metabolism is involved in stomatal movement regulation. However, it remains unknown whether starch-deficient mutants affect CO2-induced stomatal closing and whether starch biosynthesis in guard cells and/or mesophyll cells is rate limiting for high CO2-induced stomatal closing. Stomatal responses to [CO2] shifts and CO2 assimilation rates were compared in Arabidopsis (Arabidopsis thaliana) mutants that were either starch deficient in all plant tissues (ADP-Glc-pyrophosphorylase [ADGase]) or retain starch accumulation in guard cells but are starch deficient in mesophyll cells (plastidial phosphoglucose isomerase [pPGI]). ADGase mutants exhibited impaired CO2-induced stomatal closure, but pPGI mutants did not, showing that starch biosynthesis in guard cells but not mesophyll functions in CO2-induced stomatal closing. Nevertheless, starch-deficient ADGase mutant alleles exhibited partial CO2 responses, pointing toward a starch biosynthesis-independent component of the response that is likely mediated by anion channels. Furthermore, whole-leaf CO2 assimilation rates of both ADGase and pPGI mutants were lower upon shifts to high [CO2], but only ADGase mutants caused impairments in CO2-induced stomatal closing. These genetic analyses determine the roles of starch biosynthesis for high CO2-induced stomatal closing. PMID:27208296

Stomatal Spacing Safeguards Stomatal Dynamics by Facilitating Guard Cell Ion Transport Independent of the Epidermal Solute Reservoir.

PubMed

Papanatsiou, Maria; Amtmann, Anna; Blatt, Michael R

2016-09-01

Stomata enable gaseous exchange between the interior of the leaf and the atmosphere through the stomatal pore. Control of the pore aperture depends on osmotic solute accumulation by, and its loss from the guard cells surrounding the pore. Stomata in most plants are separated by at least one epidermal cell, and this spacing is thought to enhance stomatal function, although there are several genera that exhibit stomata in clusters. We made use of Arabidopsis (Arabidopsis thaliana) stomatal patterning mutants to explore the impact of clustering on guard cell dynamics, gas exchange, and ion transport of guard cells. These studies showed that stomatal clustering in the Arabidopsis too many mouths (tmm1) mutant suppressed stomatal movements and affected CO2 assimilation and transpiration differentially between dark and light conditions and were associated with alterations in K(+) channel gating. These changes were consistent with the impaired dynamics of tmm1 stomata and were accompanied by a reduced accumulation of K(+) ions in the guard cells. Our findings underline the significance of spacing for stomatal dynamics. While stomatal spacing may be important as a reservoir for K(+) and other ions to facilitate stomatal movements, the effects on channel gating, and by inference on K(+) accumulation, cannot be explained on the basis of a reduced number of epidermal cells facilitating ion supply to the guard cells. © 2016 American Society of Plant Biologists. All rights reserved.

Guard cell photosynthesis is critical for stomatal turgor production, yet does not directly mediate CO2- and ABA-induced stomatal closing

PubMed Central

Azoulay-Shemer, Tamar; Palomares, Axxell; Bagheri, Andish; Israelsson-Nordstrom, Maria; Engineer, Cawas B.; Bargmann, Bastiaan O.R.; Stephan, Aaron B.; Schroeder, Julian I.

2015-01-01

SUMMARY Stomata mediate gas exchange between the inter-cellular spaces of leaves and the atmosphere. CO2 levels in leaves (Ci) are determined by respiration, photosynthesis, stomatal conductance and atmospheric [CO2]. [CO2] in leaves mediates stomatal movements. The role of guard-cell photosynthesis in stomatal conductance responses is a matter of debate, and genetic approaches are needed. We have generated transgenic Arabidopsis plants that are chlorophyll-deficient in guard cells only, expressing a constitutively active chlorophyllase in a guard-cell specific enhancer trap-line. Our data show that more than 90% of guard cells were chlorophyll-deficient. Interestingly, approximately ~ 45% of stomata had an unusual, previously not-described, morphology of thin-shaped chlorophyll-less stomata. Nevertheless, stomatal size, stomatal index, plant morphology, and whole-leaf photosynthetic parameters (PSII, qP, qN, FV′/FM′) were comparable to wild-type plants. Time-resolved intact leaf gas exchange analyses showed a reduction in stomatal conductance and carbon assimilation rates of the transgenic plants. Normalization of CO2 responses showed that stomata of transgenic plants respond to [CO2] shifts. Detailed stomatal aperture measurements of normal kidney-shaped stomata, which lack chlorophyll, showed stomatal closing responses to [CO2] elevation and abscisic acid (ABA), while thin-shaped stomata were continuously closed. Our present findings show that stomatal movement responses to [CO2] and ABA are functional in guard cells that lack chlorophyll. These data suggest that guard-cell CO2 and ABA signal transduction are not directly modulated by guard-cell photosynthesis/electron transport. Moreover, the finding that chlorophyll-less stomata cause a “deflated” thin-shaped phenotype, suggests that photosynthesis in guard cells is critical for energization and guard-cell turgor production. PMID:26096271

The acclimation of Tilia cordata stomatal opening in response to light, and stomatal anatomy to vegetational shade and its components.

PubMed

Aasamaa, Krõõt; Aphalo, Pedro José

2017-02-01

Stomatal anatomical traits and rapid responses to several components of visible light were measured in Tilia cordata Mill. seedlings grown in an open, fully sunlit field (C-set), or under different kinds of shade. The main questions were: (i) stomatal responses to which visible light spectrum regions are modified by growth-environment shade and (ii) which separate component of vegetational shade is most effective in eliciting the acclimation effects of the full vegetational shade. We found that stomatal opening in response to red or green light did not differ between the plants grown in the different environments. Stomatal response to blue light was increased (in comparison with that of C-set) in the leaves grown in full vegetational shade (IABW-set), in attenuated UVAB irradiance (AB-set) or in decreased light intensity (neutral shade) plus attenuated UVAB irradiance (IAB-set). In all sets, the addition of green light-two or four times stronger-into induction light barely changed the rate of the blue-light-stimulated stomatal opening. In the AB-set, stomatal response to blue light equalled the strong IABW-set response. In attenuated UVB-grown leaves, stomatal response fell midway between IABW- and C-set results. Blue light response by neutral shade-grown leaves did not differ from that of the C-set, and the response by the IAB-set did not differ from that of the AB-set. Stomatal size was not modified by growth environments. Stomatal density and index were remarkably decreased only in the IABW- and IAB-sets. It was concluded that differences in white light responses between T. cordata leaves grown in different light environments are caused only by their different blue light response. Differences in stomatal sensitivity are not dependent on altered stomatal anatomy. Attenuated UVAB irradiance is the most efficient component of vegetational shade in stimulating acclimation of stomata, whereas decreased light intensity plays a minor role. © The Author 2016. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.

World Reference Center and Arbovirus Diagnosis.

DTIC Science & Technology

1984-02-10

and a bat; a new bunyavirus from a sentinel mouse; 4 new phieboviruses - one from a spiney rat and 3 from sandf lies; 2 new rhabdoviruses from a...virus, a new rhabdovirus from ticks in New England. Previously described viruses were identified from new geographic regions, including Thogoto from ticks... Rhabdoviruses belonging to the vesicular stomatitis virus subgroup, J. Virol. 23:152-166, 1977. Elizan, T.S., Schwartz, J., Yahr, M.D., and Casals, J

Modeling Water and Nutrient Transport through the Soil-Root-Canopy Continuum: Explicitly Linking the Below- and Above-Ground Processes

NASA Astrophysics Data System (ADS)

Kumar, P.; Quijano, J. C.; Drewry, D.

2010-12-01

Vegetation roots provide a fundamental link between the below ground water and nutrient dynamics and above ground canopy processes such as photosynthesis, evapotranspiration and energy balance. The “hydraulic architecture” of roots, consisting of the structural organization of the root system and the flow properties of the conduits (xylem) as well as interfaces with the soil and the above ground canopy, affect stomatal conductance thereby directly linking them to the transpiration. Roots serve as preferential pathways for the movement of moisture from wet to dry soil layers during the night, both from upper soil layer to deeper layers during the wet season (‘hydraulic descent’) and vice-versa (‘hydraulic lift’) as determined by the moisture gradients. The conductivities of transport through the root system are significantly, often orders of magnitude, larger than that of the surrounding soil resulting in movement of soil-moisture at rates that are substantially larger than that through the soil. This phenomenon is called hydraulic redistribution (HR). The ability of the deep-rooted vegetation to “bank” the water through hydraulic descent during wet periods for utilization during dry periods provides them with a competitive advantage. However, during periods of hydraulic lift these deep-rooted trees may facilitate the growth of understory vegetation where the understory scavenges the hydraulically lifted soil water. In other words, understory vegetation with relatively shallow root systems have access to the banked deep-water reservoir. These inter-dependent root systems have a significant influence on water cycle and ecosystem productivity. HR induced available moisture may support rhizosphere microbial and mycorrhizal fungi activities and enable utilization of heterogeneously distributed water and nutrient resources To capture this complex inter-dependent nutrient and water transport through the soil-root-canopy continuum we present modeling results using coupled partial differential equations of transport in soils and roots along with that for nutrient dynamics. We study the feedbkack of HR on the dynamics of water and nitrogen cycling in the soil and how these dynamics influence root water and nitrogen uptake and consequently carbon assimilation by the canopy. The forcing data is obtained from the Ameriflux Tower located in Blodgett Forest, Sierra Nevada, California. We consider single-species (Ponderosa Pine) and multi-species (overstory Ponderosa Pine and understory shrubs) interaction. When single species is considered, the near surface soil-moisture available from HR during dry summer season is an important source of evaporation and contributes significantly to the total ET flux. However, when multi-species interactions are taken into account, the soil-water from the HR becomes an important source of transpiration from the understory. The results also show that passive plant nitrogen uptake is higher when HR is present and it is critical for sustaining expected rates of carbon assimilation.

Height-related changes in leaf photosynthetic traits in diverse Bornean tropical rain forest trees.

PubMed

Kenzo, Tanaka; Inoue, Yuta; Yoshimura, Mitsunori; Yamashita, Megumi; Tanaka-Oda, Ayumi; Ichie, Tomoaki

2015-01-01

Knowledge of variations in morphophysiological leaf traits with forest height is essential for quantifying carbon and water fluxes from forest ecosystems. Here, we examined changes in leaf traits with forest height in diverse tree species and their role in environmental acclimation in a tropical rain forest in Borneo that does not experience dry spells. Height-related changes in leaf physiological and morphological traits [e.g., maximum photosynthetic rate (Amax), stomatal conductance (gs), dark respiration rate (Rd), carbon isotope ratio (δ(13)C), nitrogen (N) content, and leaf mass per area (LMA)] from understory to emergent trees were investigated in 104 species in 29 families. We found that many leaf area-based physiological traits (e.g., A(max-area), Rd, gs), N, δ(13)C, and LMA increased linearly with tree height, while leaf mass-based physiological traits (e.g., A(max-mass)) only increased slightly. These patterns differed from other biomes such as temperate and tropical dry forests, where trees usually show decreased photosynthetic capacity (e.g., A(max-area), A(max-mass)) with height. Increases in photosynthetic capacity, LMA, and δ(13)C are favored under bright and dry upper canopy conditions with higher photosynthetic productivity and drought tolerance, whereas lower R d and LMA may improve shade tolerance in lower canopy trees. Rapid recovery of leaf midday water potential to theoretical gravity potential during the night supports the idea that the majority of trees do not suffer from strong drought stress. Overall, leaf area-based photosynthetic traits were associated with tree height and the degree of leaf drought stress, even in diverse tropical rain forest trees.

Is the WBE model appropriate for semi-arid shrubs subjected to clear cutting?

PubMed

Issoufou, Hassane Bil-Assanou; Rambal, Serge; Le Dantec, Valérie; Oï, Monique; Laurent, Jean-Paul; Saadou, Mahamane; Seghieri, Josiane

2015-02-01

It is crucial to understand the adaptive mechanisms of woody plants facing periodic drought to assess their vulnerability to the increasing climate variability predicted in the Sahel. Guiera senegalensis J.F.Gmel is a semi-evergreen Combretaceae commonly found in Sahelian rangelands, fallows and crop fields because of its value as an agroforestry species. We compared canopy leafing, and allometric measurements of leaf area, stem area and stem length and their relationships with leaf water potential, stomatal conductance (gs) and soil-to-leaf hydraulic conductance (KS-L), in mature and current-year resprouts of G. senegalensis in Sahelian Niger. In mature shrubs, seasonal drought reduced the ratio of leaf area to cross-sectional stem area (AL : AS), mainly due to leaf shedding. The canopy of the current-year resprouts remained permanently leafed as the shrubs produced leaves and stems continuously, and their AL : AS ratio increased throughout the dry season. Their KS-L increased, whereas gs decreased. West, Brown and Enquist's (WBE) model can thus describe allometric trends in the seasonal life cycle of undisturbed mature shrubs, but not that of resprouts. Annual clear cutting drives allometric scaling relationships away from theoretical WBE predictions in the current-year resprouts, with scaling exponents 2.5 times greater than those of mature shrubs. High KS-L (twice that of mature shrubs) supports this intensive regeneration process. The adaptive strategy described here is probably common to many woody species that have to cope with both severe seasonal drought and regular disturbance over the long term. © The Author 2015. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Leaf variations in Elaeagnus angustifolia related to environmental heterogeneity.

PubMed

Klich

2000-11-01

Elaeagnus angustifolia (Russian olive) is a Eurasian tree that has become naturalized and has invaded zones along watercourses in many arid and semiarid regions of the world. These habitats are characterized by vertical environmental gradients, thus trees must develop some plasticity to adapt to the wide range of site conditions. This study was undertaken to test the hypothesis that variations in leaf anatomy and morphology of E. angustifolia reflect their adaptability to the differences in the microclimate that occur within the canopy of single trees. Foliar architecture, blade and petiole epidermal and internal anatomy were examined in leaves at different canopy positions and related to environmental conditions. Upper sun-leaves are exposed to higher solar irradiance and lower air humidity and are smaller, more slender and thicker than the lower, half-exposed and shade-leaves. Color varies between the leaves at different levels, from silvery grey-green in the upper strata, to dark green in the lower one. Bicolor is more evident in half-exposed and shaded leaves. When compared with the lower half-exposed and shade-leaves, the upper leaves of E. angustifolia have a greater areole density, a higher mesophyll proportion and stomatal density. Trichomes are multicellular, pedestalled, stellate-branched or peltate and their form and density can be associated with leaf color and appearance. The slender petioles of the upper leaves have proportionally more epidermis, collenchyma and phloem and less parenchyma and xylem than those of lower leaves, when observed in transverse sections. Foliar morphological and anatomical variability in E. angustifolia may be considered an adaptive advantage that enables leaves to develop and function in habitats marked by strong variations of solar radiation, air temperature and humidity.

Characterizing the Diurnal Cycle of Land Surface Temperature and Evapotranspiration at High Spatial Resolution Using Thermal Observations from sUAS.

NASA Astrophysics Data System (ADS)

Dutta, D.; Drewry, D.; Johnson, W. R.

2017-12-01

The surface temperature of plant canopies is an important indicator of the stomatal regulation of plant water use and the associated water flux from plants to atmosphere (evapotranspiration (ET)). Remotely sensed thermal observations using compact, low-cost, lightweight sensors from small unmanned aerial systems (sUAS) have the potential to provide surface temperature (ST) and ET estimates at unprecedented spatial and temporal resolutions, allowing us to characterize the intra-field diurnal variations in canopy ST and ET for a variety of vegetation systems. However, major challenges exist for obtaining accurate surface temperature estimates from low-cost uncooled microbolometer-type sensors. Here we describe the development of calibration methods using thermal chamber experiments, taking into account the ambient optics and sensor temperatures, and applying simple models of spatial non-uniformity correction to the sensor focal-plane-array. We present a framework that can be used to derive accurate surface temperatures using radiometric observations from low-cost sensors, and demonstrate this framework using a sUAS-mounted sensor across a diverse set of calibration and vegetation targets. Further, we demonstrate the use of the Surface Temperature Initiated Closure (STIC) model for computing spatially explicit, high spatial resolution ET estimates across several well-monitored agricultural systems, as driven by sUAS acquired surface temperatures. STIC provides a physically-based surface energy balance framework for the simultaneous retrieval of the surface and atmospheric vapor conductances and surface energy fluxes, by physically integrating radiometric surface temperature information into the Penman-Monteith equation. Results of our analysis over agricultural systems in Ames, IA and Davis, CA demonstrate the power of this approach for quantifying the intra-field spatial variability in the diurnal cycle of plant water use at sub-meter resolutions.

Evaluation of Morpho-Physiological Traits Adjustment of Prosopis tamarugo Under Long-Term Groundwater Depletion in the Hyper-Arid Atacama Desert

PubMed Central

Garrido, Marco; Silva, Herman; Franck, Nicolás; Arenas, Jorge; Acevedo, Edmundo

2018-01-01

Water extraction from the underground aquifers of the Pampa del Tamarugal (Atacama Desert, Chile) reduced the growing area of Prosopis tamarugo, a strict phreatic species endemic to northern Chile. The objective of this work was to evaluate the effect of various architectural and morpho-physiological traits adjustment of P. tamarugo subjected to three groundwater depletion intervals (GWDr): <1 m (control), 1–4 m and 6–9 m. The traits were evaluated at three levels, plant [height, trunk cross-section area, leaf fraction (fGCC), and crown size], organ [length of internodes, leaf mass per unit area (LMA), leaflet mass and area], and tissue level [wood density (WD), leaf 13C, 18O isotope composition (δ), and intrinsic water use efficiency (iWUE)]. In addition, soil water content (VWC) to 1.3 m soil depth, pre-dawn and midday water potential difference (ΔΨ), and stomatal conductance (gs) were evaluated. At the deeper GWDr, P. tamarugo experienced significant growth restriction and reduced fGCC, the remaining canopy had a significantly higher LMA associated with smaller leaflets. No differences in internode length and WD were observed. Values for δ13C and δ18O indicated that as GWDr increased, iWUE increased as a result of partial stomata closure with no significant effect on net assimilation over time. The morpho-physiological changes experienced by P. tamarugo allowed it to acclimate and survive in a condition of groundwater depletion, keeping a functional but diminished canopy. These adjustments allowed maintenance of a relatively high gs; ΔΨ was not different among GWDrs despite smaller VWC at greater GWDr. Although current conservation initiatives of this species are promising, forest deterioration is expected continue as groundwater depth increases. PMID:29686691

Evaluation of Morpho-Physiological Traits Adjustment of Prosopis tamarugo Under Long-Term Groundwater Depletion in the Hyper-Arid Atacama Desert.

PubMed

Garrido, Marco; Silva, Herman; Franck, Nicolás; Arenas, Jorge; Acevedo, Edmundo

2018-01-01

Water extraction from the underground aquifers of the Pampa del Tamarugal (Atacama Desert, Chile) reduced the growing area of Prosopis tamarugo , a strict phreatic species endemic to northern Chile. The objective of this work was to evaluate the effect of various architectural and morpho-physiological traits adjustment of P. tamarugo subjected to three groundwater depletion intervals (GWDr): <1 m (control), 1-4 m and 6-9 m. The traits were evaluated at three levels, plant [height, trunk cross-section area, leaf fraction ( f GCC), and crown size], organ [length of internodes, leaf mass per unit area (LMA), leaflet mass and area], and tissue level [wood density (WD), leaf 13 C, 18 O isotope composition (δ), and intrinsic water use efficiency (iWUE)]. In addition, soil water content (VWC) to 1.3 m soil depth, pre-dawn and midday water potential difference (ΔΨ), and stomatal conductance (g s ) were evaluated. At the deeper GWDr, P. tamarugo experienced significant growth restriction and reduced f GCC, the remaining canopy had a significantly higher LMA associated with smaller leaflets. No differences in internode length and WD were observed. Values for δ 13 C and δ 18 O indicated that as GWDr increased, iWUE increased as a result of partial stomata closure with no significant effect on net assimilation over time. The morpho-physiological changes experienced by P. tamarugo allowed it to acclimate and survive in a condition of groundwater depletion, keeping a functional but diminished canopy. These adjustments allowed maintenance of a relatively high g s ; ΔΨ was not different among GWDrs despite smaller VWC at greater GWDr. Although current conservation initiatives of this species are promising, forest deterioration is expected continue as groundwater depth increases.

Environmental drivers of spatial variation in whole-tree transpiration in an aspen-dominated upland-to-wetland forest gradient

NASA Astrophysics Data System (ADS)

Loranty, Michael M.; Mackay, D. Scott; Ewers, Brent E.; Adelman, Jonathan D.; Kruger, Eric L.

2008-02-01

Assumed representative center-of-stand measurements are typical inputs to models that scale forest transpiration to stand and regional extents. These inputs do not consider gradients in transpiration at stand boundaries or along moisture gradients and therefore potentially bias the large-scale estimates. We measured half-hourly sap flux (JS) for 173 trees in a spatially explicit cyclic sampling design across a topographically controlled gradient between a forested wetland and upland forest in northern Wisconsin. Our analyses focused on three dominant species in the site: quaking aspen (Populus tremuloides Michx), speckled alder (Alnus incana (DuRoi) Spreng), and white cedar (Thuja occidentalis L.). Sapwood area (AS) was used to scale JS to whole tree transpiration (EC). Because spatial patterns imply underlying processes, geostatistical analyses were employed to quantify patterns of spatial autocorrelation across the site. A simple Jarvis type model parameterized using a Monte Carlo sampling approach was used to simulate EC (EC-SIM). EC-SIM was compared with observed EC(EC-OBS) and found to reproduce both the temporal trends and spatial variance of canopy transpiration. EC-SIM was then used to examine spatial autocorrelation as a function of environmental drivers. We found no spatial autocorrelation in JS across the gradient from forested wetland to forested upland. EC was spatially autocorrelated and this was attributed to spatial variation in AS which suggests species spatial patterns are important for understanding spatial estimates of transpiration. However, the range of autocorrelation in EC-SIM decreased linearly with increasing vapor pressure deficit, implying that consideration of spatial variation in the sensitivity of canopy stomatal conductance to D is also key to accurately scaling up transpiration in space.

Applying the concept of ecohydrological equilibrium to predict steady-state leaf area index for Australian ecosystems

NASA Astrophysics Data System (ADS)

Yang, J.; Medlyn, B.; De Kauwe, M. G.; Duursma, R.

2017-12-01

Leaf Area Index (LAI) is a key variable in modelling terrestrial vegetation, because it has a major impact on carbon, water and energy fluxes. However, LAI is difficult to predict: several recent intercomparisons have shown that modelled LAI differs significantly among models, and between models and satellite-derived estimates. Empirical studies show that long-term mean LAI is strongly related to mean annual precipitation. This observation is predicted by the theory of ecohydrological equilibrium, which provides a promising alternative means to predict steady-state LAI. We implemented this theory in a simple optimisation model. We hypothesized that, when water availability is limited, plants should adjust long-term LAI and stomatal behavior (g1) to maximize net canopy carbon export, under the constraint that canopy transpiration is a fixed fraction of total precipitation. We evaluated the predicted LAI (Lopt) for Australia against ground-based observations of LAI at 135 sites, and continental-scale satellite-derived estimates. For the site-level data, the RMSE of predicted Lopt was 0.14 m2 m-2, which was similar to the RMSE of a comparison of the data against nine-year mean satellite-derived LAI at those sites. Continentally, Lopt had a R2 of over 70% when compared to satellite-derived LAI, which is comparable to the R2 obtained when different satellite products are compared against each other. The predicted response of Lopt to the increase in atmospheric CO2 over the last 30 years also agreed with the estimate based on satellite-derivatives. Our results indicate that long-term equilibrium LAI can be successfully predicted from a simple application of ecohydrological theory. We suggest that this theory could be usefully incorporated into terrestrial vegetation models to improve their predictions of LAI.

[Observation of ozone dry deposition in the field of winter wheat.

PubMed

Li, Shuo; Zheng, You Fei; Wu, Rong Jun; Yin, Ji Fu; Xu, Jing Xin; Zhao, Hui; Sun, Jian

2016-06-01

Ozone is one of the main atmospheric pollutants over surface layer, and its increasing surface ozone concentration and its impact on main crops have become the focus of the public. In order to explore ozone deposition law and environmental factors influencing ozone deposition process, this study used the micrometeorological methods and carried out the experiment under natural conditions. The results showed that during the observational period (the vigorously growing season of wheat), the mean value of ozone flux was -0.35 μg·m -2 ·s -1 (the negative sign indicated that the deposition direction was toward the ground). The mean rate of ozone deposition was 0.55 cm·s -1 . The mean value of aerodynamic resistance was 30 s·m -1 , the mean value of sub-layer resistance was 257 s·m -1 , and that of the canopy layer stomatic resistance was 163 s·m -1 . All the test parameters presented distinct diurnal fluctuation. The ozone deposition resistance was influenced by friction velocity, solar radiation velocity, temperature, relative humidity and other factors.

Tracking diurnal changes of photosynthesis and evapotranspiration using fluorescence, gas exchange and hyperspectral remote sensing measurements

NASA Astrophysics Data System (ADS)

Wang, S.; Zhang, L.; Guanter, L.; Huang, C.

2017-12-01

Photosynthesis and evapotranspiration (ET) are the two most important activities of vegetation and make a great contribution to carbon, water and energy exchanges. Remote sensing provides opportunities for monitoring these processes across time and space. This study focuses on tracking diurnal changes of photosynthesis and evapotranspiration over soybean using multiple measurement techniques. Diurnal changes of both remote sensing-based indicators, including active and passive chlorophyll fluorescence and biophysical-related parameters, including photosynthesis rate (photo) and leaf stomatal conductance (cond), were observed. Results showed that both leaf-level steady-state fluorescence (Fs) and canopy-level solar-induced chlorophyll fluorescence were linearly correlated to photosynthetically active radiation (PAR) during the daytime. A double-peak diurnal change curve was observed for leaf-level photo and cond but not for Fs or SIF. Photo and cond showed a strong nonlinear (second-order) correlation, indicating that photosynthesis, which might be remotely sensed by SIF, has the opportunity to track short-term changes of ET. Results presented in this report will be helpful for better understanding the relationship between remote-sensing-based indices and vegetation's biophysical processes.

Canopy reflectance modeling in a tropical wooded grassland

NASA Technical Reports Server (NTRS)

Simonett, D.; Franklin, J.

1986-01-01

Geometric/optical canopy reflectance modeling and spatial/spectral pattern recognition are used to study the form and structure of savanna in West Africa. An invertible plant canopy reflectance model is tested for its ability to estimate the amount of woody vegetation cover in areas of sparsely wooded grassland from remotely sensed data. Dry woodlands and wooded grasslands, commonly referred to as savannas, are important ecologically and economically in Africa, and cover approximately forty percent of the continent by some estimates. The Sahelian and Sudanian savanna make up the important and sensitive transition zone between the tropical forests and the arid Saharan region. The depletion of woody cover, used for fodder and fuel in these regions, has become a very severe problem for the people living there. LANDSAT Thematic Mapper (TM) data is used to stratify woodland and wooded grassland into areas of relatively homogeneous canopy cover, and then by applying an invertible forest canopy reflectance model to estimate directly the height and spacing of the trees in the stands. Since height and spacing are proportional to biomass in some cases, a successful application of the segmentation/modeling techniques will allow direct estimation of woody biomass, as well as cover density, over significant areas of these valuable and sensitive ecosystems. Sahelian savanna sites in the Gourma area of Mali being used by the NASA/GIMMS project (Global Inventory Modeling and Monitoring System, at Goddard Space Flight Center), in conjunction with CIPEA/Mali (Centre International pour l'Elevage en Afrique) will be used for testing the canopy model. The model will also be tested in a Sudanian zone crop/woodland area in the Region of Segou, Mali.

Effect of canopy and topography induced wakes on land-atmosphere fluxes of momentum and scalars

NASA Astrophysics Data System (ADS)

Markfort, C. D.; Zhang, W.; Porté-Agel, F.; Stefan, H. G.

2012-04-01

Wakes shed from natural and anthropogenic landscape features affect land-atmosphere fluxes of momentum and scalars, including water vapor and trace gases (e.g. CO2). Canopies and bluff bodies, such as forests, buildings and topography, cause boundary layer flow separation, and lead to a break down of standard Monin-Obukhov similarity relationships in the atmospheric boundary layer (ABL). Wakes generated by these land surface features persist for significant distances (>100 typical length scales) and affect a large fraction of the Earth's terrestrial surface. This effect is currently not accounted for in land-atmosphere models, and little is known about how heterogeneity of wake-generating features affect land surface fluxes. Additionally flux measurements, made in wake-affected regions, do not satisfy the homogeneous flow requirements for the standard eddy correlation (EC) method. This phenomenon, often referred to as wind sheltering, has been shown to affect momentum and kinetic energy fluxes at the lake-atmosphere interface (Markfort et al. 2010). This presentation will highlight results from controlled wind tunnel experiments of neutral and thermally stratified boundary layers, using particle image velocimetry (PIV) and custom x-wire/cold-wire anemometry, to understand how the physical structure of upstream bluff bodies and porous canopies as well as how thermal stability affect the flow separation zone, boundary layer recovery and surface fluxes. We have found that there is a nonlinear relationship between canopy length/porosity and flow separation downwind of a canopy to clearing transition. Results will provide the basis for new parameterizations to account for wake effects on land-atmosphere fluxes and corrections for the EC measurements over open fields, lakes, and wetlands. Key words: Atmospheric boundary layer; Wakes; Stratification; Land-Atmosphere Parameterization; Canopy

Local environmental context conditions the impact of Russian olive in a heterogeneous riparian ecosystem

USGS Publications Warehouse

Tuttle, Graham M.; Katz, Gabrielle L.; Friedman, Jonathan M.; Norton, Andrew P.

2016-01-01

Local abiotic and biotic conditions can alter the strength of exotic species impacts. To better understand the effects of exotic species on invaded ecosystems and to prioritize management efforts, it is important that exotic species impacts are put in local environmental context. We studied how differences in plant community composition, photosynthetically active radiation (PAR), and available soil N associated with Russian olive presence are conditioned by local environmental variation within a western U.S. riparian ecosystem. In four sites along the South Fork of the Republican River in Colorado, we established 200 pairs of plots (underneath and apart from Russian olive) to measure the effects of invasion across the ecosystem. We used a series of a priori mixed models to identify environmental variables that altered the effects of Russian olive. For all response variables, models that included the interaction of environmental characteristics, such as presence/absence of an existing cottonwood canopy, with the presence/absence of Russian olive canopy were stronger candidate models than those that just included Russian olive canopy presence as a factor. Compared with reference plots outside of Russian olive canopy, plots underneath Russian olive had higher relative exotic cover (exotic/total cover), lower perennial C4 grass cover, and higher perennial forb cover. These effects were reduced, however, in the presence of a cottonwood canopy. As expected, Russian olive was associated with reduced PAR and increased N, but these effects were reduced under cottonwood canopy. Our results demonstrate that local abiotic and biotic environmental factors condition the effects of Russian olive within a heterogeneous riparian ecosystem and suggest that management efforts should be focused in open areas where Russian olive impacts are strongest.

The Ecophysiology Of A Pinus Ponderosa Ecosystem Exposed To High Tropospheric Ozone: Implications For Stomatal And Non-Stomatal Ozone Fluxes

NASA Astrophysics Data System (ADS)

Fares, S.; McKay, M.; Goldstein, A.

2008-12-01

Ecosystems remove ozone from the troposphere through both stomatal and non-stomatal deposition. The portion of ozone taken up through stomata has an oxidative effect causing damage. We used a multi-year dataset to assess the physiological controls over ozone deposition. Environmental parameters, CO2 and ozone fluxes were measured continuously from January 2001 to December 2006 above a ponderosa pine plantation near Blodgett Forest, Georgetown, California. We studied the dynamic of NEE (Net Ecosystem Exchange, -838 g C m-2 yr-1) and water evapotranspiration on an annual and daily basis. These processes are tightly coupled to stomatal aperture which also controlled ozone fluxes. High levels of ozone concentrations (~ 100 ppb) were observed during the spring-summer period, with corresponding high levels of ozone fluxes (~ 30 μmol m-2 h-1). During the summer season, a large portion of the total ozone flux was due to non-stomatal processes, and we propose that a plant physiological control, releasing BVOC (Biogenic Volatile Organic Compounds), is mainly responsible. We analyzed the correlations of common ozone exposure metrics based on accumulation of concentrations (AOT40 and SUM0) with ozone fluxes (total, stomatal and non-stomatal). Stomatal flux showed poorer correlation with ozone concentrations than non-stomatal flux during summer and fall seasons, which largely corresponded to the growing period. We therefore suggest that AOT40 and SUM0 are poor predictors of ozone damage and that a physiologically based metric would be more effective.

Functional analysis of cellulose and xyloglucan in the walls of stomatal guard cells of Arabidopsis thaliana

DOE PAGES

Rui, Yue; Anderson, Charles T.

2016-01-04

Here, stomatal guard cells are pairs of specialized epidermal cells that control water and CO 2 exchange between the plant and the environment. To fulfill the functions of stomatal opening and closure that are driven by changes in turgor pressure, guard cell walls must be both strong and flexible, but how the structure and dynamics of guard cell walls enable stomatal function remains poorly understood. To address this question, we applied cell biological and genetic analyses to investigate guard cell walls and their relationship to stomatal function in Arabidopsis ( Arabidopsis thaliana). Using live-cell spinning disk confocal microscopy, we measuredmore » the motility of cellulose synthase (CESA)-containing complexes labeled by green fluorescent protein (GFP)-CESA3 and observed a reduced proportion of GFP-CESA3 particles colocalizing with microtubules upon stomatal closure. Imaging cellulose organization in guard cells revealed a relatively uniform distribution of cellulose in the open state and a more fibrillar pattern in the closed state, indicating that cellulose microfibrils undergo dynamic reorganization during stomatal movements. In cesa3 je5 mutants defective in cellulose synthesis and xxt1 xxt2 mutants lacking the hemicellulose xyloglucan, stomatal apertures, changes in guard cell length, and cellulose reorganization were aberrant during fusicoccin-induced stomatal opening or abscisic acid-induced stomatal closure, indicating that sufficient cellulose and xyloglucan are required for normal guard cell dynamics. Together, these results provide new insights into how guard cell walls allow stomata to function as responsive mediators of gas exchange at the plant surface.« less

Functional Analysis of Cellulose and Xyloglucan in the Walls of Stomatal Guard Cells of Arabidopsis1[OPEN

PubMed Central

Rui, Yue; Anderson, Charles T.

2016-01-01

Stomatal guard cells are pairs of specialized epidermal cells that control water and CO2 exchange between the plant and the environment. To fulfill the functions of stomatal opening and closure that are driven by changes in turgor pressure, guard cell walls must be both strong and flexible, but how the structure and dynamics of guard cell walls enable stomatal function remains poorly understood. To address this question, we applied cell biological and genetic analyses to investigate guard cell walls and their relationship to stomatal function in Arabidopsis (Arabidopsis thaliana). Using live-cell spinning disk confocal microscopy, we measured the motility of cellulose synthase (CESA)-containing complexes labeled by green fluorescent protein (GFP)-CESA3 and observed a reduced proportion of GFP-CESA3 particles colocalizing with microtubules upon stomatal closure. Imaging cellulose organization in guard cells revealed a relatively uniform distribution of cellulose in the open state and a more fibrillar pattern in the closed state, indicating that cellulose microfibrils undergo dynamic reorganization during stomatal movements. In cesa3je5 mutants defective in cellulose synthesis and xxt1 xxt2 mutants lacking the hemicellulose xyloglucan, stomatal apertures, changes in guard cell length, and cellulose reorganization were aberrant during fusicoccin-induced stomatal opening or abscisic acid-induced stomatal closure, indicating that sufficient cellulose and xyloglucan are required for normal guard cell dynamics. Together, these results provide new insights into how guard cell walls allow stomata to function as responsive mediators of gas exchange at the plant surface. PMID:26729799

A steady-state stomatal model of balanced leaf gas exchange, hydraulics and maximal source-sink flux.

PubMed

Hölttä, Teemu; Lintunen, Anna; Chan, Tommy; Mäkelä, Annikki; Nikinmaa, Eero

2017-07-01

Trees must simultaneously balance their CO2 uptake rate via stomata, photosynthesis, the transport rate of sugars and rate of sugar utilization in sinks while maintaining a favourable water and carbon balance. We demonstrate using a numerical model that it is possible to understand stomatal functioning from the viewpoint of maximizing the simultaneous photosynthetic production, phloem transport and sink sugar utilization rate under the limitation that the transpiration-driven hydrostatic pressure gradient sets for those processes. A key feature in our model is that non-stomatal limitations to photosynthesis increase with decreasing leaf water potential and/or increasing leaf sugar concentration and are thus coupled to stomatal conductance. Maximizing the photosynthetic production rate using a numerical steady-state model leads to stomatal behaviour that is able to reproduce the well-known trends of stomatal behaviour in response to, e.g., light, vapour concentration difference, ambient CO2 concentration, soil water status, sink strength and xylem and phloem hydraulic conductance. We show that our results for stomatal behaviour are very similar to the solutions given by the earlier models of stomatal conductance derived solely from gas exchange considerations. Our modelling results also demonstrate how the 'marginal cost of water' in the unified stomatal conductance model and the optimal stomatal model could be related to plant structural and physiological traits, most importantly, the soil-to-leaf hydraulic conductance and soil moisture. © The Author 2017. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Positive and negative peptide signals control stomatal density.

PubMed

Shimada, Tomoo; Sugano, Shigeo S; Hara-Nishimura, Ikuko

2011-06-01

The stoma is a micro valve found on aerial plant organs that promotes gas exchange between the atmosphere and the plant body. Each stoma is formed by a strict cell lineage during the early stages of leaf development. Molecular genetics research using the model plant Arabidopsis has revealed the genes involved in stomatal differentiation. Cysteine-rich secretory peptides of the EPIDERMAL PATTERNING FACTOR-LIKE (EPFL) family play crucial roles as extracellular signaling factors. Stomatal development is orchestrated by the positive factor STOMAGEN/EPFL9 and the negative factors EPF1, EPF2, and CHALLAH/EPFL6 in combination with multiple receptors. EPF1 and EPF2 are produced in the stomatal lineage cells of the epidermis, whereas STOMAGEN and CHALLAH are derived from the inner tissues. These findings highlight the complex cell-to-cell and intertissue communications that regulate stomatal development. To optimize gas exchange, particularly the balance between the uptake of carbon dioxide (CO(2)) and loss of water, plants control stomatal activity in response to environmental conditions. The CO(2) level and light intensity influence stomatal density. Plants sense environmental cues in mature leaves and adjust the stomatal density of newly forming leaves, indicating the involvement of long-distance systemic signaling. This review summarizes recent research progress in the peptide signaling of stomatal development and discusses the evolutionary model of the signaling machinery.

A prospective randomized controlled trial to determine if cryotherapy can reduce the pain of patients with minor form of recurrent aphthous stomatitis.

PubMed

Arikan, Osman Kursat; Birol, Ahu; Tuncez, Fatma; Erkek, Emel; Koc, Can

2006-01-01

Tissue cooling has long been used in the management of both acute and chronic pain. To determine whether the application of cryotherapy can reduce the pain of patients with minor form of recurrent aphthous stomatitis. Twenty adult patients who had 2 discrete aphthous stomatitides in the labial mucosa at the same time were included in this prospective, randomized, and placebo-controlled study. One of the 2 aphthous stomatitides was treated with cryotherapy, the other serving as a control. The pain of aphthous stomatitis was scored by the patient on a 6-point scale (from 0 to 5). The size of the aphthous stomatitis was also measured. At any interval, no statistical difference was found between the cryotherapy-treated aphthous stomatitis and the control in the change in the value of pain severity, nor was any statistical difference found in the change in the size of the aphthous stomatitis. However, a trend toward less pain in the aphthous stomatitis receiving cryotherapy was noted. These results suggest that application of cryotherapy on minor form of recurrent oral aphthous stomatitis has no beneficial analgesic effect compared to placebo.

Carbonic anhydrases, EPF2 and a novel protease mediate CO2 control of stomatal development.

PubMed

Engineer, Cawas B; Ghassemian, Majid; Anderson, Jeffrey C; Peck, Scott C; Hu, Honghong; Schroeder, Julian I

2014-09-11

Environmental stimuli, including elevated carbon dioxide levels, regulate stomatal development; however, the key mechanisms mediating the perception and relay of the CO2 signal to the stomatal development machinery remain elusive. To adapt CO2 intake to water loss, plants regulate the development of stomatal gas exchange pores in the aerial epidermis. A diverse range of plant species show a decrease in stomatal density in response to the continuing rise in atmospheric CO2 (ref. 4). To date, one mutant that exhibits deregulation of this CO2-controlled stomatal development response, hic (which is defective in cell-wall wax biosynthesis, ref. 5), has been identified. Here we show that recently isolated Arabidopsis thaliana β-carbonic anhydrase double mutants (ca1 ca4) exhibit an inversion in their response to elevated CO2, showing increased stomatal development at elevated CO2 levels. We characterized the mechanisms mediating this response and identified an extracellular signalling pathway involved in the regulation of CO2-controlled stomatal development by carbonic anhydrases. RNA-seq analyses of transcripts show that the extracellular pro-peptide-encoding gene EPIDERMAL PATTERNING FACTOR 2 (EPF2), but not EPF1 (ref. 9), is induced in wild-type leaves but not in ca1 ca4 mutant leaves at elevated CO2 levels. Moreover, EPF2 is essential for CO2 control of stomatal development. Using cell-wall proteomic analyses and CO2-dependent transcriptomic analyses, we identified a novel CO2-induced extracellular protease, CRSP (CO2 RESPONSE SECRETED PROTEASE), as a mediator of CO2-controlled stomatal development. Our results identify mechanisms and genes that function in the repression of stomatal development in leaves during atmospheric CO2 elevation, including the carbonic-anhydrase-encoding genes CA1 and CA4 and the secreted protease CRSP, which cleaves the pro-peptide EPF2, in turn repressing stomatal development. Elucidation of these mechanisms advances the understanding of how plants perceive and relay the elevated CO2 signal and provides a framework to guide future research into how environmental challenges can modulate gas exchange in plants.

Carbonic anhydrases, EPF2 and a novel protease mediate CO2 control of stomatal development

PubMed Central

Engineer, Cawas B.; Ghassemian, Majid; Anderson, Jeffrey C.; Peck, Scott C.; Hu, Honghong; Schroeder, Julian I.

2014-01-01

Environmental stimuli, including elevated carbon dioxide levels, regulate stomatal development1–3; however, the key mechanisms mediating the perception and relay of the CO2 signal to the stomatal development machinery remain elusive. To adapt CO2 intake to water loss, plants regulate the development of stomatal gas exchange pores in the aerial epidermis. A diverse range of plant species show a decrease in stomatal density in response to the continuing rise in atmospheric CO2 (ref. 4). To date, one mutant that exhibits deregulation of this CO2-controlled stomatal development response, hic (which is defective in cell-wall wax biosynthesis, ref. 5), has been identified. Here we show that recently isolated Arabidopsis thaliana β-carbonic anhydrase double mutants (ca1 ca4)6 exhibit aninversion in their response to elevated CO2, showing increased stomatal development at elevated CO2 levels. We characterized the mechanisms mediating this response and identified an extracellular signalling pathway involved in the regulation of CO2-controlled stomatal development by carbonic anhydrases. RNA-seq analyses of transcripts show that the extracellular pro-peptide-encoding gene EPIDERMAL PATTERNING FACTOR 2 (EPF2)7,8, but not EPF1 (ref. 9), is induced in wild-type leaves but not inca1 ca4 mutant leaves at elevated CO2 levels. Moreover, EPF2 is essential for CO2 control of stomatal development. Using cell-wall proteomic analyses and CO2-dependent transcriptomic analyses, we identified a novel CO2-induced extracellular protease, CRSP (CO2 RESPONSE SECRETED PROTEASE), as a mediator of CO2-controlled stomatal development. Our results identify mechanisms and genes that function in the repression of stomatal development in leaves during atmospheric CO2 elevation, including the carbonic-anhydrase-encoding genes CA1 and CA4 and the secreted protease CRSP, which cleaves the pro-peptide EPF2, in turn repressing stomatal development. Elucidation of these mechanisms advances the understanding of how plants perceive and relay the elevated CO2 signal and provides a framework to guide future research into how environmental challenges can modulate gas exchange in plants. PMID:25043023

Guard cell photosynthesis is critical for stomatal turgor production, yet does not directly mediate CO2 - and ABA-induced stomatal closing.

PubMed

Azoulay-Shemer, Tamar; Palomares, Axxell; Bagheri, Andisheh; Israelsson-Nordstrom, Maria; Engineer, Cawas B; Bargmann, Bastiaan O R; Stephan, Aaron B; Schroeder, Julian I

2015-08-01

Stomata mediate gas exchange between the inter-cellular spaces of leaves and the atmosphere. CO2 levels in leaves (Ci) are determined by respiration, photosynthesis, stomatal conductance and atmospheric [CO2 ]. [CO2 ] in leaves mediates stomatal movements. The role of guard cell photosynthesis in stomatal conductance responses is a matter of debate, and genetic approaches are needed. We have generated transgenic Arabidopsis plants that are chlorophyll-deficient in guard cells only, expressing a constitutively active chlorophyllase in a guard cell specific enhancer trap line. Our data show that more than 90% of guard cells were chlorophyll-deficient. Interestingly, approximately 45% of stomata had an unusual, previously not-described, morphology of thin-shaped chlorophyll-less stomata. Nevertheless, stomatal size, stomatal index, plant morphology, and whole-leaf photosynthetic parameters (PSII, qP, qN, FV '/FM' ) were comparable with wild-type plants. Time-resolved intact leaf gas-exchange analyses showed a reduction in stomatal conductance and CO2 -assimilation rates of the transgenic plants. Normalization of CO2 responses showed that stomata of transgenic plants respond to [CO2 ] shifts. Detailed stomatal aperture measurements of normal kidney-shaped stomata, which lack chlorophyll, showed stomatal closing responses to [CO2 ] elevation and abscisic acid (ABA), while thin-shaped stomata were continuously closed. Our present findings show that stomatal movement responses to [CO2 ] and ABA are functional in guard cells that lack chlorophyll. These data suggest that guard cell CO2 and ABA signal transduction are not directly modulated by guard cell photosynthesis/electron transport. Moreover, the finding that chlorophyll-less stomata cause a 'deflated' thin-shaped phenotype, suggests that photosynthesis in guard cells is critical for energization and guard cell turgor production. © 2015 The Authors The Plant Journal © 2015 John Wiley & Sons Ltd.

Evapotranspiration and cloud variability at regional sub-grid scales

NASA Astrophysics Data System (ADS)

Vila-Guerau de Arellano, Jordi; Sikma, Martin; Pedruzo-Bagazgoitia, Xabier; van Heerwaarden, Chiel; Hartogensis, Oscar; Ouwersloot, Huug

2017-04-01

In regional and global models uncertainties arise due to our incomplete understanding of the coupling between biochemical and physical processes. Representing their impact depends on our ability to calculate these processes using physically sound parameterizations, since they are unresolved at scales smaller than the grid size. More specifically over land, the coupling between evapotranspiration, turbulent transport of heat and moisture, and clouds lacks a combined representation to take these sub-grid scales interactions into account. Our approach is based on understanding how radiation, surface exchange, turbulent transport and moist convection are interacting from the leaf- to the cloud scale. We therefore place special emphasis on plant stomatal aperture as the main regulator of CO2-assimilation and water transpiration, a key source of moisture source to the atmosphere. Plant functionality is critically modulated by interactions with atmospheric conditions occurring at very short spatiotemporal scales such as cloud radiation perturbations or water vapour turbulent fluctuations. By explicitly resolving these processes, the LES (large-eddy simulation) technique is enabling us to characterize and better understand the interactions between canopies and the local atmosphere. This includes the adaption time of vegetation to rapid changes in atmospheric conditions driven by turbulence or the presence of cumulus clouds. Our LES experiments are based on explicitly coupling the diurnal atmospheric dynamics to a plant physiology model. Our general hypothesis is that different partitioning of direct and diffuse radiation leads to different responses of the vegetation. As a result there are changes in the water use efficiencies and shifts in the partitioning of sensible and latent heat fluxes under the presence of clouds. Our presentation is as follows. First, we discuss the ability of LES to reproduce the surface energy balance including photosynthesis and CO2 soil respiration coupled to the dynamics of a convective boundary layer. LES results are compared with a complete set of surface and upper-air meteorological and carbon-dioxide observations gathered during a representative day at the 213-meter meteorological tall tower at Cabauw. Second, we perform systematic numerical experiments under a wide range of background wind conditions and stomatal aperture response time. Our analysis unravel how thin clouds, characterized by lower values of the cloud optical depth, have a different impact on evapotranspiration compared to thick clouds due to differences in the partitioning between direct and diffuse radiation at canopy level. Related to this detailed simulation, we discuss how new instrumental techniques, e.g. scintillometery, enable us to obtain new observational insight of the coupling between clouds and vegetation. We will close the presentation with open questions regarding the need to include parameterizations for these interactions at short spatiotemporal scales in regional or climate models.

Effects of a Rebamipide Mouthwash on Stomatitis Caused by Cancer Chemotherapy-Evaluation of the Efficacy by Patients Themselves.

PubMed

Ishii, Naoko; Kawano, Yayoi; Sakai, Hideki; Hayashi, Seitaku; Akizuki, Norikazu; Komoda, Masayo; Hanawa, Takehisa

2017-08-01

 Anticancer drug-induced stomatitis develops in 30% to 40% of cancer cases that undergo chemotherapy. However, medications for this condition are not commercially available in Japan. Upon obtaining approval of the ethics committee, a mouthwash containing rebamipide as the active ingredient (rebamipide mouthwash) was administered to one inpatient and four outpatients, who had developed stomatitis caused by cancer chemotherapy. Starting from 14 d after the administration of the rebamipide mouthwash, the patients scored a stomatitis survey on oral state, pain level, and diet and recorded the number of times they gargled, as well as any stomatitis observations, in a stomatitis diary. The total scores for the points for each of the three types of survey sections were classified into Grades 0 to 4 and evaluated as a stomatitis evaluation score (SES). The SES became "0" in three out of the five patients within 14 d of treatment. No change in SES was found in one patient. In the remaining patients, SES became "0" once but increased again later. Using image analysis software (ImageJ), the area at which the stomatitis was observed was measured. When comparing SES and change in the area in patients who agreed to participate, gradual reductions in the extent of stomatitis was observed even during the period when SES did not change. Having patients fill in an observation chart was effective for grasping changes in symptoms in outpatients.

Model-based analysis of avoidance of ozone stress by stomatal closure in Siebold's beech (Fagus crenata)

PubMed Central

Hoshika, Yasutomo; Watanabe, Makoto; Inada, Naoki; Koike, Takayoshi

2013-01-01

Background and Aims Resistance of plants to ozone stress can be classified as either avoidance or tolerance. Avoidance of ozone stress may be explained by decreased stomatal conductance during ozone exposure because stomata are the principal interface for entry of ozone into plants. In this study, a coupled photosynthesis–stomatal model was modified to test whether the presence of ozone can induce avoidance of ozone stress by stomatal closure. Methods The response of Siebold's beech (Fagus crenata), a representative deciduous tree species, to ozone was studied in a free-air ozone exposure experiment in Japan. Photosynthesis and stomatal conductance were measured under ambient and elevated ozone. An optimization model of stomata involving water, CO2 and ozone flux was tested using the leaf gas exchange data. Key Results The data suggest that there are two phases in the avoidance of ozone stress via stomatal closure for Siebold's beech: (1) in early summer ozone influx is efficiently limited by a reduction in stomatal conductance, without any clear effect on photosynthetic capacity; and (2) in late summer and autumn the efficiency of ozone stress avoidance was decreased because the decrease in stomatal conductance was small and accompanied by an ozone-induced decline of photosynthetic capacity. Conclusions Ozone-induced stomatal closure in Siebold's beech during early summer reduces ozone influx and allows the maximum photosynthetic capacity to be reached, but is not sufficient in older leaves to protect the photosynthetic system. PMID:23904447

Origins and Evolution of Stomatal Development1[OPEN

PubMed Central

2017-01-01

The fossil record suggests stomata-like pores were present on the surfaces of land plants over 400 million years ago. Whether stomata arose once or whether they arose independently across newly evolving land plant lineages has long been a matter of debate. In Arabidopsis, a genetic toolbox has been identified that tightly controls stomatal development and patterning. This includes the basic helix-loop-helix (bHLH) transcription factors SPEECHLESS (SPCH), MUTE, FAMA, and ICE/SCREAMs (SCRMs), which promote stomatal formation. These factors are regulated via a signaling cascade, which includes mobile EPIDERMAL PATTERNING FACTOR (EPF) peptides to enforce stomatal spacing. Mosses and hornworts, the most ancient extant lineages to possess stomata, possess orthologs of these Arabidopsis (Arabidopsis thaliana) stomatal toolbox genes, and manipulation in the model bryophyte Physcomitrella patens has shown that the bHLH and EPF components are also required for moss stomatal development and patterning. This supports an ancient and tightly conserved genetic origin of stomata. Here, we review recent discoveries and, by interrogating newly available plant genomes, we advance the story of stomatal development and patterning across land plant evolution. Furthermore, we identify potential orthologs of the key toolbox genes in a hornwort, further supporting a single ancient genetic origin of stomata in the ancestor to all stomatous land plants. PMID:28356502

Regulation of the calcium-sensing receptor in both stomatal movement and photosynthetic electron transport is crucial for water use efficiency and drought tolerance in Arabidopsis.

PubMed

Wang, Wen-Hua; Chen, Juan; Liu, Ting-Wu; Chen, Juan; Han, Ai-Dong; Simon, Martin; Dong, Xue-Jun; He, Jun-Xian; Zheng, Hai-Lei

2014-01-01

Production per amount of water used (water use efficiency, WUE) is closely correlated with drought tolerance. Although stomatal aperture can regulate WUE, the underlying molecular mechanisms are still unclear. Previous reports revealed that stomatal closure was inhibited in the calcium-sensing receptor (CAS) antisense line of Arabidopsis (CASas). Here it is shown that decreased drought tolerance and WUE of CASas was associated with higher stomatal conductance due to improper regulation of stomatal aperture, rather than any change of stomatal density. CASas plants also had a lower CO2 assimilation rate that was attributed to a lower photosynthetic electron transport rate, leading to higher chlorophyll fluorescence. Gene co-expression combined with analyses of chlorophyll content and transcription levels of photosynthesis-related genes indicate that CAS is involved in the formation of the photosynthetic electron transport system. These data suggest that CAS regulates transpiration and optimizes photosynthesis by playing important roles in stomatal movement and formation of photosynthetic electron transport, thereby regulating WUE and drought tolerance.

Mix-and-match: ligand-receptor pairs in stomatal development and beyond.

PubMed

Torii, Keiko U

2012-12-01

Stomata are small valves on the plant epidermis balancing gas exchange and water loss. Stomata are formed according to positional cues. In Arabidopsis, two EPIDERMAL PATTERNING FACTOR (EPF) peptides, EPF1 and EPF2, are secreted from stomatal precursors enforcing proper stomatal patterning. Here, I review recent studies revealing the ligand-receptor pairs and revising the previously predicted relations between receptors specifying stomatal patterning: ERECTA-family and TOO MANY MOUTHS (TMM). Furthermore, EPF-LIKE9 (EPFL9/Stomagen) promotes stomatal differentiation from internal tissues. Two EPFL peptides specify inflorescence architecture, a process beyond stomatal development, as ligands for ERECTA. Thus, broadly expressed receptor kinases may regulate multiple developmental processes through perceiving different peptide ligands, each with a specialized expression pattern. TMM in the epidermis may fine-tune multiple EPF/EPFL signals to prevent signal interference. Copyright © 2012 Elsevier Ltd. All rights reserved.

Stomatal Complex Development and F-Actin Organization in Maize Leaf Epidermis Depend on Cellulose Synthesis.

PubMed

Panteris, Emmanuel; Achlati, Theonymphi; Daras, Gerasimos; Rigas, Stamatis

2018-06-06

Cellulose microfibrils reinforce the cell wall for morphogenesis in plants. Herein, we provide evidence on a series of defects regarding stomatal complex development and F-actin organization in Zea mays leaf epidermis, due to inhibition of cellulose synthesis. Formative cell divisions of stomatal complex ontogenesis were delayed or inhibited, resulting in lack of subsidiary cells and frequently in unicellular stomata, with an atypical stomatal pore. Guard cells failed to acquire a dumbbell shape, becoming rounded, while subsidiary cells, whenever present, exhibited aberrant morphogenesis. F-actin organization was also affected, since the stomatal complex-specific arrays were scarcely observed. At late developmental stages, the overall F-actin network was diminished in all epidermal cells, although thick actin bundles persisted. Taken together, stomatal complex development strongly depends on cell wall mechanical properties. Moreover, F-actin organization exhibits a tight relationship with the cell wall.

Fern Stomatal Responses to ABA and CO2 Depend on Species and Growth Conditions.

PubMed

Hõrak, Hanna; Kollist, Hannes; Merilo, Ebe

2017-06-01

Changing atmospheric CO 2 levels, climate, and air humidity affect plant gas exchange that is controlled by stomata, small pores on plant leaves and stems formed by guard cells. Evolution has shaped the morphology and regulatory mechanisms governing stomatal movements to correspond to the needs of various land plant groups over the past 400 million years. Stomata close in response to the plant hormone abscisic acid (ABA), elevated CO 2 concentration, and reduced air humidity. Whether the active regulatory mechanisms that control stomatal closure in response to these stimuli are present already in mosses, the oldest plant group with stomata, or were acquired more recently in angiosperms remains controversial. It has been suggested that the stomata of the basal vascular plants, such as ferns and lycophytes, close solely hydropassively. On the other hand, active stomatal closure in response to ABA and CO 2 was found in several moss, lycophyte, and fern species. Here, we show that the stomata of two temperate fern species respond to ABA and CO 2 and that an active mechanism of stomatal regulation in response to reduced air humidity is present in some ferns. Importantly, fern stomatal responses depend on growth conditions. The data indicate that the stomatal behavior of ferns is more complex than anticipated before, and active stomatal regulation is present in some ferns and has possibly been lost in others. Further analysis that takes into account fern species, life history, evolutionary age, and growth conditions is required to gain insight into the evolution of land plant stomatal responses. © 2017 American Society of Plant Biologists. All Rights Reserved.

Testing Earth System Models with Earth System Data: using C isotopes in atmospheric CO2 to probe stomatal response to future climate change

NASA Astrophysics Data System (ADS)

Ballantyne, A. P.; Miller, J. B.; Bowling, D. R.; Tans, P. P.; Baker, I. T.

2013-12-01

The global cycles of water and carbon are inextricably linked through photosynthesis. This link is largely governed by stomatal conductance that regulates water loss to the atmosphere and carbon gain to the biosphere. Although extensive research has focused on the response of stomatal conductance to increased atmospheric CO2, much less research has focused on the response of stomatal conductance to concomitant climate change. Here we make use of intensive and extensive measurements of C isotopes in source CO2 to the atmosphere (del-bio) to make inferences about stomatal response to climatic factors at a single forest site and across a network of global observation sites. Based on intensive observations at the Niwot Ridge Ameriflux site we discover that del-bio is an excellent physical proxy of stomatal response during the growing season and this response is highly sensitive to atmospheric water vapor pressure deficit (VPD). We use these intensive single forest site observations to inform our analysis of the global observation network, focusing in on the growing season across an array of terrestrial sites. We find that stomatal response across most of these terrestrial sites is also highly sensitive to VPD. Lastly, we simulate the response of future climate change on stomatal response and discover that future increases in VPD may limit the biosphere's capacity to assimilate future CO2 emissions. These results have direct implications for the benchmarking of Earth System Models as stomatal conductance in many of these models does not vary as a function of VPD.

Fern Stomatal Responses to ABA and CO2 Depend on Species and Growth Conditions1[OPEN

PubMed Central

2017-01-01

Changing atmospheric CO2 levels, climate, and air humidity affect plant gas exchange that is controlled by stomata, small pores on plant leaves and stems formed by guard cells. Evolution has shaped the morphology and regulatory mechanisms governing stomatal movements to correspond to the needs of various land plant groups over the past 400 million years. Stomata close in response to the plant hormone abscisic acid (ABA), elevated CO2 concentration, and reduced air humidity. Whether the active regulatory mechanisms that control stomatal closure in response to these stimuli are present already in mosses, the oldest plant group with stomata, or were acquired more recently in angiosperms remains controversial. It has been suggested that the stomata of the basal vascular plants, such as ferns and lycophytes, close solely hydropassively. On the other hand, active stomatal closure in response to ABA and CO2 was found in several moss, lycophyte, and fern species. Here, we show that the stomata of two temperate fern species respond to ABA and CO2 and that an active mechanism of stomatal regulation in response to reduced air humidity is present in some ferns. Importantly, fern stomatal responses depend on growth conditions. The data indicate that the stomatal behavior of ferns is more complex than anticipated before, and active stomatal regulation is present in some ferns and has possibly been lost in others. Further analysis that takes into account fern species, life history, evolutionary age, and growth conditions is required to gain insight into the evolution of land plant stomatal responses. PMID:28351911

Canopy and seasonal profiles of nitrate reductase in soybeans

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

Harper, J.E.; Hageman, R.H.

1972-01-01

Nitrate reductase activity of soybeans (Glycine max L. Merr.) was evaluated in soil plots and outdoor hydroponic gravel culture systems throughout the growing season. Nitrate reductase profiles within the plant canopy were also established. Mean activity per gram fresh weight per hour of the entire plant canopy was highest in the seedling stage while total activity (activity per gram fresh weight per hour times the total leaf weight) reached a maximum when plants were in the full bloom to midpod fill stage. Nitrate reductase activity per gram fresh weight per hour was highest in the uppermost leaf just prior tomore » full expansion and declined with leaf positions lower in the canopy. Total nitrate reductase activity per leaf was also highest in the uppermost fully expanded leaf during early growth stages. Maximum total activity shifted to leaf positions lower in the plant canopy with later growth stages. Nitrate reductase activity of soybeans grown in hydroponic systems was significantly higher than activity of adjacent soil grown plants at later growth stages, which suggested that under normal field conditions the potential for nitrate utilization may not be realized. Nitrate reductase activity per gram fresh weight per hour and nitrate content were positively correlated over the growing season with plants grown in either soil or solution culture. Computations based upon the nitrate reductase assay of plants grown in hydroponics indicated that from 1.7 to 1.8 grams N could have been supplied to the plant via the nitrate reductase process. 11 references, 9 figures, 3 tables.« less

Does Size Matter? Atmospheric CO2 May Be a Stronger Driver of Stomatal Closing Rate Than Stomatal Size in Taxa That Diversified under Low CO2.

PubMed

Elliott-Kingston, Caroline; Haworth, Matthew; Yearsley, Jon M; Batke, Sven P; Lawson, Tracy; McElwain, Jennifer C

2016-01-01

One strategy for plants to optimize stomatal function is to open and close their stomata quickly in response to environmental signals. It is generally assumed that small stomata can alter aperture faster than large stomata. We tested the hypothesis that species with small stomata close faster than species with larger stomata in response to darkness by comparing rate of stomatal closure across an evolutionary range of species including ferns, cycads, conifers, and angiosperms under controlled ambient conditions (380 ppm CO2; 20.9% O2). The two species with fastest half-closure time and the two species with slowest half-closure time had large stomata while the remaining three species had small stomata, implying that closing rate was not correlated with stomatal size in these species. Neither was response time correlated with stomatal density, phylogeny, functional group, or life strategy. Our results suggest that past atmospheric CO2 concentration during time of taxa diversification may influence stomatal response time. We show that species which last diversified under low or declining atmospheric CO2 concentration close stomata faster than species that last diversified in a high CO2 world. Low atmospheric [CO2] during taxa diversification may have placed a selection pressure on plants to accelerate stomatal closing to maintain adequate internal CO2 and optimize water use efficiency.

Does Size Matter? Atmospheric CO2 May Be a Stronger Driver of Stomatal Closing Rate Than Stomatal Size in Taxa That Diversified under Low CO2

PubMed Central

Elliott-Kingston, Caroline; Haworth, Matthew; Yearsley, Jon M.; Batke, Sven P.; Lawson, Tracy; McElwain, Jennifer C.

2016-01-01

One strategy for plants to optimize stomatal function is to open and close their stomata quickly in response to environmental signals. It is generally assumed that small stomata can alter aperture faster than large stomata. We tested the hypothesis that species with small stomata close faster than species with larger stomata in response to darkness by comparing rate of stomatal closure across an evolutionary range of species including ferns, cycads, conifers, and angiosperms under controlled ambient conditions (380 ppm CO2; 20.9% O2). The two species with fastest half-closure time and the two species with slowest half-closure time had large stomata while the remaining three species had small stomata, implying that closing rate was not correlated with stomatal size in these species. Neither was response time correlated with stomatal density, phylogeny, functional group, or life strategy. Our results suggest that past atmospheric CO2 concentration during time of taxa diversification may influence stomatal response time. We show that species which last diversified under low or declining atmospheric CO2 concentration close stomata faster than species that last diversified in a high CO2 world. Low atmospheric [CO2] during taxa diversification may have placed a selection pressure on plants to accelerate stomatal closing to maintain adequate internal CO2 and optimize water use efficiency. PMID:27605929

Generalized hydromechanical model for stomatal responses to hydraulic perturbations.

PubMed

Kwon, H W; Choi, M Y

2014-01-07

Stomata respond in a common pattern to various hydraulic perturbations on any part of the 'soil-plant-air' system: initial transient 'wrong-way' responses and final stationary 'right-way' responses. In order to describe this pattern on the basis of statistical physics, we propose a simple model where turgor pressure of a cell is taken to be a power function of its volume, and obtain results in qualitative agreement with experimental data for responses to a variety of hydraulic perturbations: Firstly, stationary stomatal conductance as a function of the vapor pressure deficit divides into three regimes characterized by sensitivities of the stomatal conductance and the transpiration rate with respect to vapor pressure deficit; secondly, for every hydraulic perturbation, the initial transient 'wrong-way' responses always appear; thirdly, on condition that water is supplied insufficiently, stomatal oscillations are often observed; finally, stomatal responses following leaf excision exhibit, after the initial transient wrong-way responses, slow relaxation to stomatal closing. In particular, comparison of areoles having different numbers of stomata demonstrates that areoles with small numbers of stomata tend to provoke lack of water in the soil as well as in the plant. In addition, our model also describes well dependence of the stomatal conductance on temperature. It may be extended further to describe stomatal responses to other environmental factors such as carbon dioxide, light, and temperature. © 2013 Elsevier Ltd. All rights reserved.

Arabidopsis ANGUSTIFOLIA3 (AN3) is associated with the promoter of CONSTITUTIVE PHOTOMORPHOGENIC1 (COP1) to regulate light-mediated stomatal development.

PubMed

Meng, Lai-Sheng; Li, Cong; Xu, Meng-Ke; Sun, Xu-Dong; Wan, Wen; Cao, Xiao-Ying; Zhang, Jin-Lin; Chen, Kun-Ming

2018-04-12

Light signals are perceived by multiple photoreceptors that converge to suppress the RING E3 ubiquitin ligase CONSTITUTIVE PHOTOMORPHOGENIC1 (COP1) for the regulation of stomatal development. Thus, COP1 is a point of integration between light signaling and stomatal patterning. However, how light signaling is collected into COP1 for the production and spacing of stomata is still unknown. Here, we report that the loss-of-function mutant of ANGUSTIFOLIA3 (AN3) delays asymmetric cell division, which leads to decreased stomatal index. Furthermore, overexpression of AN3 accelerates asymmetric cell division, which results in clusters of stomata. In addition, the stomatal development through AN3 regulation is mediated by light signaling. Finally, we find that an3 is a light-signaling mutant, and that AN3 protein is light regulated. Self-activation by AN3 contributes to the control of AN3 expression. Thus, AN3 is a point of collection between light signaling and stomatal patterning. Target-gene analysis indicates that AN3 is associated with COP1 promoter for the regulation of light-controlling stomatal development. Together, these components for regulating stomatal development form an AN3-COP1-E3 ubiquitin ligase complex, allowing the integration of light signaling into the production and spacing of stomata. © 2018 John Wiley & Sons Ltd.

[Suitability of four stomatal conductance models in agro-pastoral ecotone in North China: A case study for potato and oil sunflower.

PubMed

Huang, Ming Xia; Wang, Jing; Tang, Jian Zhao; Yu, Qiang; Zhang, Jun; Xue, Qing Yu; Chang, Qing; Tan, Mei Xiu

2016-11-18

The suitability of four popular empirical and semi-empirical stomatal conductance models (Jarvis model, Ball-Berry model, Leuning model and Medlyn model) was evaluated based on para-llel observation data of leaf stomatal conductance, leaf net photosynthetic rate and meteorological factors during the vigorous growing period of potato and oil sunflower at Wuchuan experimental station in agro-pastoral ecotone in North China. It was found that there was a significant linear relationship between leaf stomatal conductance and leaf net photosynthetic rate for potato, whereas the linear relationship appeared weaker for oil sunflower. The results of model evaluation showed that Ball-Berry model performed best in simulating leaf stomatal conductance of potato, followed by Leuning model and Medlyn model, while Jarvis model was the last in the performance rating. The root-mean-square error (RMSE) was 0.0331, 0.0371, 0.0456 and 0.0794 mol·m -2 ·s -1 , the normalized root-mean-square error (NRMSE) was 26.8%, 30.0%, 36.9% and 64.3%, and R-squared (R 2 ) was 0.96, 0.61, 0.91 and 0.88 between simulated and observed leaf stomatal conductance of potato for Ball-Berry model, Leuning model, Medlyn model and Jarvis model, respectively. For leaf stomatal conductance of oil sunflower, Jarvis model performed slightly better than Leuning model, Ball-Berry model and Medlyn model. RMSE was 0.2221, 0.2534, 0.2547 and 0.2758 mol·m -2 ·s -1 , NRMSE was 40.3%, 46.0%, 46.2% and 50.1%, and R 2 was 0.38, 0.22, 0.23 and 0.20 between simulated and observed leaf stomatal conductance of oil sunflower for Jarvis model, Leuning model, Ball-Berry model and Medlyn model, respectively. The path analysis was conducted to identify effects of specific meteorological factors on leaf stomatal conductance. The diurnal variation of leaf stomatal conductance was principally affected by vapour pressure saturation deficit for both potato and oil sunflower. The model evaluation suggested that the stomatal conductance models for oil sunflower are to be improved in further research.

Stomatal closure induced by phytosphingosine-1-phosphate and sphingosine-1-phosphate depends on nitric oxide and pH of guard cells in Pisum sativum.

PubMed

Puli, Mallikarjuna Rao; Rajsheel, Pidakala; Aswani, Vetcha; Agurla, Srinivas; Kuchitsu, Kazuyuki; Raghavendra, Agepati S

2016-10-01

Phyto-S1P and S1P induced stomatal closure in epidermis of pea ( Pisum sativum ) by raising the levels of NO and pH in guard cells. Phosphosphingolipids, such as phytosphingosine-1-phosphate (phyto-S1P) and sphingosine-1-phosphate (S1P), are important signaling components during drought stress. The biosynthesis of phyto-S1P or S1P is mediated by sphingosine kinases (SPHKs). Although phyto-S1P and S1P are known to be signaling components in higher plants, their ability to induce stomatal closure has been ambiguous. We evaluated in detail the effects of phyto-S1P, S1P and SPHK inhibitors on signaling events leading to stomatal closure in the epidermis of Pisum sativum. Phyto-S1P or S1P induced stomatal closure, along with a marked rise in nitric oxide (NO) and cytoplasmic pH of guard cells, as in case of ABA. Two SPHK inhibitors, DL-threo dihydrosphingosine and N',N'-dimethylsphingosine, restricted ABA-induced stomatal closure and prevented the increase of NO or pH by ABA. Modulators of NO or pH impaired both stomatal closure and increase in NO or pH by phyto-S1P/S1P. The stomatal closure by phyto-S1P/S1P was mediated by phospholipase D and phosphatidic acid (PA). When present, PA elevated the levels of pH, but not NO of guard cells. Our results demonstrate that stomatal closure induced by phyto-S1P and S1P depends on rise in pH as well as NO of guard cells. A scheme of signaling events initiated by phyto-S1P/S1P, and converging to cause stomatal closure, is proposed.

Expression of Arabidopsis Hexokinase in Citrus Guard Cells Controls Stomatal Aperture and Reduces Transpiration.

PubMed

Lugassi, Nitsan; Kelly, Gilor; Fidel, Lena; Yaniv, Yossi; Attia, Ziv; Levi, Asher; Alchanatis, Victor; Moshelion, Menachem; Raveh, Eran; Carmi, Nir; Granot, David

2015-01-01

Hexokinase (HXK) is a sugar-phosphorylating enzyme involved in sugar-sensing. It has recently been shown that HXK in guard cells mediates stomatal closure and coordinates photosynthesis with transpiration in the annual species tomato and Arabidopsis. To examine the role of HXK in the control of the stomatal movement of perennial plants, we generated citrus plants that express Arabidopsis HXK1 (AtHXK1) under KST1, a guard cell-specific promoter. The expression of KST1 in the guard cells of citrus plants has been verified using GFP as a reporter gene. The expression of AtHXK1 in the guard cells of citrus reduced stomatal conductance and transpiration with no negative effect on the rate of photosynthesis, leading to increased water-use efficiency. The effects of light intensity and humidity on stomatal behavior were examined in rooted leaves of the citrus plants. The optimal intensity of photosynthetically active radiation and lower humidity enhanced stomatal closure of AtHXK1-expressing leaves, supporting the role of sugar in the regulation of citrus stomata. These results suggest that HXK coordinates photosynthesis and transpiration and stimulates stomatal closure not only in annual species, but also in perennial species.

Expression of Arabidopsis Hexokinase in Citrus Guard Cells Controls Stomatal Aperture and Reduces Transpiration

PubMed Central

Lugassi, Nitsan; Kelly, Gilor; Fidel, Lena; Yaniv, Yossi; Attia, Ziv; Levi, Asher; Alchanatis, Victor; Moshelion, Menachem; Raveh, Eran; Carmi, Nir; Granot, David

2015-01-01

Hexokinase (HXK) is a sugar-phosphorylating enzyme involved in sugar-sensing. It has recently been shown that HXK in guard cells mediates stomatal closure and coordinates photosynthesis with transpiration in the annual species tomato and Arabidopsis. To examine the role of HXK in the control of the stomatal movement of perennial plants, we generated citrus plants that express Arabidopsis HXK1 (AtHXK1) under KST1, a guard cell-specific promoter. The expression of KST1 in the guard cells of citrus plants has been verified using GFP as a reporter gene. The expression of AtHXK1 in the guard cells of citrus reduced stomatal conductance and transpiration with no negative effect on the rate of photosynthesis, leading to increased water-use efficiency. The effects of light intensity and humidity on stomatal behavior were examined in rooted leaves of the citrus plants. The optimal intensity of photosynthetically active radiation and lower humidity enhanced stomatal closure of AtHXK1-expressing leaves, supporting the role of sugar in the regulation of citrus stomata. These results suggest that HXK coordinates photosynthesis and transpiration and stimulates stomatal closure not only in annual species, but also in perennial species. PMID:26734024

Salicaceae Endophytes Modulate Stomatal Behavior and Increase Water Use Efficiency in Rice

PubMed Central

Rho, Hyungmin; Van Epps, Victor; Wegley, Nicholas; Doty, Sharon L.; Kim, Soo-Hyung

2018-01-01

Bacterial and yeast endophytes isolated from the Salicaceae family have been shown to promote growth and alleviate stress in plants from different taxa. To determine the physiological pathways through which endophytes affect plant water relations, we investigated leaf water potential, whole-plant water use, and stomatal responses of rice plants to Salicaceae endophyte inoculation under CO2 enrichment and water deficit. Daytime stomatal conductance and stomatal density were lower in inoculated plants compared to controls. Leaf ABA concentrations increased with endophyte inoculation. As a result, transpirational water use decreased significantly with endophyte inoculation while biomass did not change or slightly increased. This response led to a significant increase in cumulative water use efficiency at harvest. Different endophyte strains produced the same results in host plant water relations and stomatal responses. These stomatal responses were also observed under elevated CO2 conditions, and the increase in water use efficiency was more pronounced under water deficit conditions. The effect on water use efficiency was positively correlated with daily light integrals across different experiments. Our results provide insights on the physiological mechanisms of plant-endophyte interactions involving plant water relations and stomatal functions. PMID:29552021

Post Wildfire Changes in Plant Functioning and Vegetation Dynamics: Implications for Water Fluxes in Re-sprouting Forests

NASA Astrophysics Data System (ADS)

Nolan, R. H.; Lane, P. N.; Mitchell, P. J.; Bradstock, R. A.

2011-12-01

Fire induced changes to the vegetation dynamics in temperate forests have been demonstrated to affect evapotranspiration (Et) rates through increases in plant size and density and stand-level transpiration and interception. In many cases these transient changes in forest structure result in substantial declines in stream flow for protracted periods after the disturbance. However to date research has focused on the wetter 'ash' forests of south-eastern Australia which solely regenerate via seedlings, it is unknown what changes in Et may occur in those forests which re-sprout post-fire. We hypothesize that Et fluxes track post-fire changes in sapwood area and leaf area index (L) in re-sprouting temperate forests, increasing as the forest regenerates. Following the 2009 Black Saturday wildfires in Victoria, we monitored Et rates for over a year in both damp and dry re-sprouting forest, incorporating a range of fire severity classes. Components of Et including overstorey transpiration, rainfall interception loss and forest floor Et were measured in conjunction with changes in L, sapwood area and leaf physiology. The monitoring period began one year post-fire with a typical hot, dry summer, at which stage Et rates in burnt forest were similar or less than those in unburnt forest. During the following summer, which was one of the wettest on record, Et increased across all monitoring plots but particularly so in the burnt forest where seedling regeneration resulted in an understorey L nearly twice that of unburnt forest. Forest floor Et was up to 46% higher in burnt forest, and rainfall interception values accounted for approximately 25% of rainfall compared to 15% in unburnt forest. The greatest increase in canopy transpiration rates over this period occurred in those trees subject to a low intensity fire where most of the canopy remained intact but there was also fire-triggered sprouting of new leaves along the trunk and main branches. In these trees rates of sapflow, standardized by sapwood area, were up to 50% greater than in unburnt trees. Measurements of leaf physiology in mature leaves, regenerating canopy leaves and in seedlings indicate higher rates of stomatal conductance in seedlings, and in the early regeneration phase of canopy leaves, which may be driving higher rates of water use per unit leaf area in the early stages of post-fire regeneration. This research indicates that disturbance-induced changes in vegetation dynamics are dependent on fire severity and can alter forest energy and water balances through changes in stand structure (i.e. L) and adjustments in plant functioning via leaf level increases in water use.

Plant physiological models of heat, water and photoinhibition stress for climate change modelling and agricultural prediction

NASA Astrophysics Data System (ADS)

Nicolas, B.; Gilbert, M. E.; Paw U, K. T.

2015-12-01

Soil-Vegetation-Atmosphere Transfer (SVAT) models are based upon well understood steady state photosynthetic physiology - the Farquhar-von Caemmerer-Berry model (FvCB). However, representations of physiological stress and damage have not been successfully integrated into SVAT models. Generally, it has been assumed that plants will strive to conserve water at higher temperatures by reducing stomatal conductance or adjusting osmotic balance, until potentially damaging temperatures and the need for evaporative cooling become more important than water conservation. A key point is that damage is the result of combined stresses: drought leads to stomatal closure, less evaporative cooling, high leaf temperature, less photosynthetic dissipation of absorbed energy, all coupled with high light (photosynthetic photon flux density; PPFD). This leads to excess absorbed energy by Photosystem II (PSII) and results in photoinhibition and damage, neither are included in SVAT models. Current representations of photoinhibition are treated as a function of PPFD, not as a function of constrained photosynthesis under heat or water. Thus, it seems unlikely that current models can predict responses of vegetation to climate variability and change. We propose a dynamic model of damage to Rubisco and RuBP-regeneration that accounts, mechanistically, for the interactions between high temperature, light, and constrained photosynthesis under drought. Further, these predictions are illustrated by key experiments allowing model validation. We also integrated this new framework within the Advanced Canopy-Atmosphere-Soil Algorithm (ACASA). Preliminary results show that our approach can be used to predict reasonable photosynthetic dynamics. For instances, a leaf undergoing one day of drought stress will quickly decrease its maximum quantum yield of PSII (Fv/Fm), but it won't recover to unstressed levels for several days. Consequently, cumulative effect of photoinhibition on photosynthesis can cause a decrease of about 35% of CO2 uptake. As a result, the incorporation of stress and damage into SVAT models could considerably improve our ability to predict global responses to climate change.

Transmission and pathogenesis of vesicular stomatitis viruses

USDA-ARS?s Scientific Manuscript database

Vesicular Stomatitis (VS) is caused by the Vesicular Stomatitis Virus (VSV), a negative single stranded RNA arthropod-borne virus member of the Family Rhabdoviridae. The virion is composed of the host derived plasma membrane, the envelope, and an internal ribonucleoprotein core. The envelope contain...

O3 flux-related responsiveness of photosynthesis, respiration, and stomatal conductance of adult Fagus sylvatica to experimentally enhanced free-air O3 exposure.

PubMed

Löw, M; Häberle, K-H; Warren, C R; Matyssek, R

2007-03-01

Knowledge of responses of photosynthesis, respiration, and stomatal conductance to cumulative ozone uptake (COU) is still scarce, and this is particularly the case for adult trees. The effect of ozone (O(3)) exposure on trees was examined with 60-year-old beech trees (FAGUS SYLVATICA) at a forest site of southern Germany. Trees were exposed to the ambient O(3) regime (1 x O(3)) or an experimentally elevated twice-ambient O(3) regime (2 x O(3)). The elevated 2 x O (3) regime was provided by means of a free-air O(3) canopy exposure system. The hypotheses were tested that (1) gas exchange is negatively affected by O(3) and (2) the effects of O(3) are dose-dependent and thus the sizes of differences between treatments are positively related to COU. Gas exchange (light-saturated CO(2) uptake rate A(max), stomatal conductance g (s), maximum rate of carboxylation Vc (max), ribulose-1,5-bisphosphate turnover limited rate of photosynthesis J (max), CO(2) compensation point CP, apparent quantum yield of net CO(2) uptake AQ, carboxylation efficiency CE, day- and nighttime respiration) and chlorophyll fluorescence (electron transfer rate, ETR) were measured IN SITU on attached sun and shade leaves. Measurements were made periodically throughout the growing seasons of 2003 (an exceptionally dry year) and 2004 (a year with average rainfall). In 2004 Vc(max), J(max), and CE were lower in trees receiving 2 x O(3) compared with the ambient O(3) regime (1 x O(3)). Treatment differences in Vc (max), J (max), CE were rather small in 2004 (i.e., parameter levels were lower by 10 - 30 % in 2 x O(3) than 1 x O(3)) and not significant in 2003. In 2004 COU was positively correlated with the difference between treatments in A (max), g (s), and ETR (i.e., consistent with the dose-dependence of O(3)'s deleterious effects). However, in 2003, differences in A(max), g (s), and ETR between the two O(3) regimes were smaller at the end of the dry summer 2003 (i.e., when COU was greatest). The relationship of COU with effects on gas exchange can apparently be complex and, in fact, varied between years and within the growing season. In addition, high doses of O(3) did not always have significant effects on leaf gas exchange. In view of the key findings, both hypotheses were to be rejected.

Nonredundant functions of Arabidopsis LecRK-V.2 and LecRK-VII.1 in controlling stomatal immunity and jasmonate-mediated stomatal closure.

PubMed

Yekondi, Shweta; Liang, Fu-Chun; Okuma, Eiji; Radziejwoski, Amandine; Mai, Hsien-Wei; Swain, Swadhin; Singh, Prashant; Gauthier, Mathieu; Chien, Hsiao-Chiao; Murata, Yoshiyuki; Zimmerli, Laurent

2018-04-01

Stomatal immunity restricts bacterial entry to leaves through the recognition of microbe-associated molecular patterns (MAMPs) by pattern-recognition receptors (PRRs) and downstream abscisic acid and salicylic acid signaling. Through a reverse genetics approach, we characterized the function of the L-type lectin receptor kinase-V.2 (LecRK-V.2) and -VII.1 (LecRK-VII.1). Analyses of interactions with the PRR FLAGELLIN SENSING2 (FLS2) were performed by co-immunoprecipitation and bimolecular fluorescence complementation and whole-cell patch-clamp analyses were used to evaluate guard cell Ca 2+ -permeable cation channels. The Arabidopsis thaliana LecRK-V.2 and LecRK-VII.1 and notably their kinase activities were required for full activation of stomatal immunity. Knockout lecrk-V.2 and lecrk-VII.1 mutants were hyper-susceptible to Pseudomonas syringae infection and showed defective stomatal closure in response to bacteria or to the MAMPs flagellin and EF-Tu. By contrast, Arabidopsis over-expressing LecRK-V.2 or LecRK-VII.1 demonstrated a potentiated stomatal immunity. LecRK-V.2 and LecRK-VII.1 are shown to be part of the FLS2 PRR complex. In addition, LecRK-V.2 and LecRK-VII.1 were critical for methyl jasmonate (MeJA)-mediated stomatal closure, notably for MeJA-induced activation of guard cell Ca 2+ -permeable cation channels. This study highlights the role of LecRK-V.2 and LecRK-VII.1 in stomatal immunity at the FLS2 PRR complex and in MeJA-mediated stomatal closure. © 2017 The Authors. New Phytologist © 2017 New Phytologist Trust.

Stomatal VPD Response: There Is More to the Story Than ABA.

PubMed

Merilo, Ebe; Yarmolinsky, Dmitry; Jalakas, Pirko; Parik, Helen; Tulva, Ingmar; Rasulov, Bakhtier; Kilk, Kalle; Kollist, Hannes

2018-01-01

Guard cells shrink and close stomatal pores when air humidity decreases (i.e. when the difference between the vapor pressures of leaf and atmosphere [VPD] increases). The role of abscisic acid (ABA) in VPD-induced stomatal closure has been studied using ABA-related mutants that respond to VPD in some studies and not in others. The importance of ABA biosynthesis in guard cells versus vasculature for whole-plant stomatal regulation is unclear as well. Here, we show that Arabidopsis ( Arabidopsis thaliana ) lines carrying mutations in different steps of ABA biosynthesis as well as pea ( Pisum sativum ) wilty and tomato ( Solanum lycopersicum ) flacca ABA-deficient mutants had higher stomatal conductance compared with wild-type plants. To characterize the role of ABA production in different cells, we generated transgenic plants where ABA biosynthesis was rescued in guard cells or phloem companion cells of an ABA-deficient mutant. In both cases, the whole-plant stomatal conductance, stunted growth phenotype, and leaf ABA level were restored to wild-type values, pointing to the redundancy of ABA sources and to the effectiveness of leaf ABA transport. All ABA-deficient lines closed their stomata rapidly and extensively in response to high VPD, whereas plants with mutated protein kinase OST1 showed stunted VPD-induced responses. Another strongly ABA-insensitive mutant, defective in the six ABA PYR/RCAR receptors, responded to changes in VPD in both directions strongly and symmetrically, indicating that its VPD-induced closure could be passive hydraulic. We discuss that both the VPD-induced passive hydraulic stomatal closure and the stomatal VPD regulation of ABA-deficient mutants may be conditional on the initial pretreatment stomatal conductance. © 2018 American Society of Plant Biologists. All Rights Reserved.

Relating Stomatal Conductance to Leaf Functional Traits.

PubMed

Kröber, Wenzel; Plath, Isa; Heklau, Heike; Bruelheide, Helge

2015-10-12

Leaf functional traits are important because they reflect physiological functions, such as transpiration and carbon assimilation. In particular, morphological leaf traits have the potential to summarize plants strategies in terms of water use efficiency, growth pattern and nutrient use. The leaf economics spectrum (LES) is a recognized framework in functional plant ecology and reflects a gradient of increasing specific leaf area (SLA), leaf nitrogen, phosphorus and cation content, and decreasing leaf dry matter content (LDMC) and carbon nitrogen ratio (CN). The LES describes different strategies ranging from that of short-lived leaves with high photosynthetic capacity per leaf mass to long-lived leaves with low mass-based carbon assimilation rates. However, traits that are not included in the LES might provide additional information on the species' physiology, such as those related to stomatal control. Protocols are presented for a wide range of leaf functional traits, including traits of the LES, but also traits that are independent of the LES. In particular, a new method is introduced that relates the plants' regulatory behavior in stomatal conductance to vapor pressure deficit. The resulting parameters of stomatal regulation can then be compared to the LES and other plant functional traits. The results show that functional leaf traits of the LES were also valid predictors for the parameters of stomatal regulation. For example, leaf carbon concentration was positively related to the vapor pressure deficit (vpd) at the point of inflection and the maximum of the conductance-vpd curve. However, traits that are not included in the LES added information in explaining parameters of stomatal control: the vpd at the point of inflection of the conductance-vpd curve was lower for species with higher stomatal density and higher stomatal index. Overall, stomata and vein traits were more powerful predictors for explaining stomatal regulation than traits used in the LES.

Estimation of canopy water interception of a near-tropical montane cloud forest in Taiwan

NASA Astrophysics Data System (ADS)

Apurva, B.; Huang, C. Y.; Zhang, J.

2017-12-01

Tropical and subtropical montane cloud forests are some of the rarest and least studied ecosystems. Due to the frequent immersion of fog water with high humidity, these zones are major water sources for lowland environments and habitats for many fauna and flora. Their dependence on cloud water leaves them highly susceptible to the effects of climate change. Studies have been conducted to quantify the characteristics of the low altitude clouds such as spatial dynamics, cloud top and base heights, occurrence frequency or immersion duration. In this study, we carried out a field measurement to estimate canopy water interception (CWI), which is directly utilized by the ecosystems. The study site was a 61 ha near-tropical hinoki cypress montane cloud forest plantation in northern Taiwan at 1705 m asl. Leaves of CHOB were clipped, air-dried and attached to trees at three different canopy depths from the top to the base of canopies along a high tower. The samples were weighed before and after the occurrence of a fog event. In addition, a cylinder shaped fog gauge was installed at the ground level next to the tower to assess amount of fog water penetrating the canopy layer. After afternoon fog events with the duration of 60 minutes, we found that there was an apparent trend of decline of CWI from top (mean ± standard deviation = 0.023 g ± 0.0015 g), middle (0.021 g ± 0.0015 g) to the bottom (0.013 g ± 0.0015 g) of the canopies. Since the study site is a coniferous evergreen forest plantation with a relatively homogenous surface through seasons, with the background knowledge of the average leaf area index of 4.4, we estimated that this 61 ha site harvested 28.2 Mg of CWI for a daily fog event. We also found that no clear evidence of CWI was observed below the canopies by referring to bi-weekly records from the cylinder shaded fog gauge. Therefore, we can assume that the majority fog water was intercepted by the hinoki cypress canopy layer. This study demonstrates that a substantial amount of fog water can be harvested by the montane cloud forest, and this horizontal precipitation is not negligible and should be taken into account for ecological research.

Approximating Reflectance and Transmittance of Vegetation Using Multiple Spectral Invariants

NASA Astrophysics Data System (ADS)

Mottus, M.

2011-12-01

Canopy spectral invariants, eigenvalues of the radiative transfer equation and photon recollision probability are some of the new theoretical tools that have been applied in remote sensing of vegetation and atmosphere. The theoretical approach based on spectral invariants, informally also referred to as the p-theory, owns its attractivity to several factors. Firstly, it provides a rapid and physically-based way of describing canopy scattering. Secondly, the p-theory aims at parameterizing canopy structure in reflectance models using a simple and intuitive concept which can be applied at various structural levels, from shoot to tree crown. The theory has already been applied at scales from the molecular level to forest stands. The most important shortcoming of the p-theory lies in its inability to predict the directionality of scattering. The theory is currently based on only one physical parameter, the photon recollision probability p. It is evident that one parameter cannot contain enough information to reasonably predict the observed complex reflectance patterns produced by natural vegetation canopies. Without estimating scattering directionality, however, the theory cannot be compared with even the most simple (and well-tested) two-stream vegetation reflectance models. In this study, we evaluate the possibility to use additional parameters to fit the measured reflectance and transmittance of a vegetation stand. As a first step, the parameters are applied to separate canopy scattering into reflectance and transmittance. New parameters are introduced following the general approach of eigenvector expansion. Thus, the new parameters are coined higher-order spectral invariants. Calculation of higher-order invariants is based on separating first-order scattering from total scattering. Thus, the method explicitly accounts for different view geometries with different fractions of visible sunlit canopy (e.g., hot-spot). It additionally allows to produce different irradiation levels on leaf surfaces for direct and diffuse incidence, thus (in theory) allowing more accurate calculation of potential photosynthesis rates. Similarly to the p-theory, the use of multiple spectral invariants facilitates easy parametrization of canopy structure and scaling between different structural levels (leaf-shoot-stand). Spectral invariant-based remote sensing approaches are well suited for relatively large pixels even when no detailed ground truth information is available. In a case study, the theory of multiple spectral invariants was applied to measured canopy scattering. Spectral reflectance and transmittance measurements were carried out in gray alder (Alnus incana) plantation at Tartu Observatory, Estonia, in August 2006. The equations produced by the theory of spectral invariants were fitted to measured radiation fluxes. Preliminary results indicate that quantities with invariant-like behavior may indeed be used to approximate canopy scattering directionality.

Observations on the Stomatal Control of NO2 Exchange.

NASA Astrophysics Data System (ADS)

Kesselmeier, J.; Chaparro-Suarez, I. G.; Meixner, F. X.

2005-12-01

Nitrogen oxides play a central role in tropospheric chemistry especially in the formation of tropospheric ozone, acid rain and hydroxyl radical as well as in CH4 and CO oxidation processes. NO2 can be assimilated and emitted by the plant leaves as well. We investigated the impact of the stomatal regulation with four tree species (Betula pendula, Fagus sylvatica, Quercus ilex und Pinus sylvestris) by exposure of leaves to the hormone abscisic acid inducing stomatal closure. The results showed that the NO2 uptake was strongly dependent on stomatal aperture. The uptake correlated linearly with stomatal (leaf) conductance in case of all four tree species investigated. In contrast an NO2 emission was observed with beech in the dark when stomata were basically closed.

Drawing the future

PubMed Central

2008-01-01

Gas exchange between the plant and the atmosphere is regulated by controlling both the stomatal density and the aperture of the stomatal pore. Environmental factors such as light, the level of atmospheric CO2 and hormones regulate stomatal development and/or function. Because atmospheric CO2 levels have been rising since the Industrial Revolution, and it is predicted that they will continue doing so in the future, an understanding of the CO2 signalling mechanisms in the stomatal responses will help to know how plants were in the past and will allow predicting how they will respond to climate change in the near future. This article covers the recent knowledge of the CO2 signalling mechanisms that regulate both stomatal function and development. PMID:19513216

Opinion: the red-light response of stomatal movement is sensed by the redox state of the photosynthetic electron transport chain.

PubMed

Busch, Florian A

2014-02-01

Guard cells regulate CO2 uptake and water loss of a leaf by controlling stomatal movement in response to environmental factors such as CO2, humidity, and light. The mechanisms by which stomata respond to red light are actively debated in the literature, and even after decades of research it is still controversial whether stomatal movement is related to photosynthesis or not. This review summarizes the current knowledge of the red-light response of stomata. A comparison of published evidence suggests that stomatal movement is controlled by the redox state of photosynthetic electron transport chain components, in particular the redox state of plastoquinone. Potential consequences for the modeling of stomatal conductance are discussed.

Organised Motion in a Tall Spruce Canopy: Temporal Scales, Structure Spacing and Terrain Effects

NASA Astrophysics Data System (ADS)

Thomas, Christoph; Foken, Thomas

2007-01-01

This study investigates the organised motion near the canopy-atmosphere interface of a moderately dense spruce forest in heterogeneous, complex terrain. Wind direction is used to assess differences in topography and surface properties. Observations were obtained at several heights above and within the canopy using sonic anemometers and fast-response gas analysers over the course of several weeks. Analysed variables include the three-dimensional wind vector, the sonic temperature, and the concentration of carbon dioxide. Wavelet analysis was used to extract the organised motion from time series and to derive its temporal scales. Spectral Fourier analysis was deployed to compute power spectra and phase spectra. Profiles of temporal scales of ramp-like coherent structures in the vertical and longitudinal wind components showed a reversed variation with height and were of similar size within the canopy. Temporal scales of scalar fields were comparable to those of the longitudinal wind component suggesting that the lateral scalar transport dominates. The existence of a 1 power law in the longitudinal power spectra was confirmed for a few cases only, with a majority showing a clear 5/3 decay. The variation of effective scales of organised motion in the longitudinal velocity and temperature were found to vary with atmospheric stability, suggesting that both Kelvin-Helmholtz instabilities and attached eddies dominate the flow with increasing convectional forcing. The canopy mixing-layer analogy was observed to be applicable for ramp-like coherent structures in the vertical wind component for selected wind directions only. Departures from the prediction of m = Λ w L {/s -1} = 8 10 (where Λ w is the streamwise spacing of coherent structures in the vertical wind w and L s is a canopy shear length scale) were caused by smaller shear length scales associated with large-scale changes in the terrain as well as the vertical structure of the canopy. The occurrence of linear gravity waves was related to a rise in local topography and can therefore be referred to as mountain-type gravity waves. Temporal scales of wave motion and ramp-like coherent structures were observed to be comparable.

Genetic and antigenic relationships of veicular stomatitis viruses from South America

USDA-ARS?s Scientific Manuscript database

Vesicular stomatitis (VS) viruses have beenclassified into two serotypes: New Jersey (VSNJV) and Indiana (VSIV). Here, we have characterized field isolates causing vesicular stomatitis in Brazil and Argentina over a 35-year span. Cluster analysis based on either serological relatedness, as inferred ...

A comparison of multi-spectral, multi-angular, and multi-temporal remote sensing datasets for fractional shrub canopy mapping in Arctic Alaska

USGS Publications Warehouse

Selkowitz, D.J.

2010-01-01

Shrub cover appears to be increasing across many areas of the Arctic tundra biome, and increasing shrub cover in the Arctic has the potential to significantly impact global carbon budgets and the global climate system. For most of the Arctic, however, there is no existing baseline inventory of shrub canopy cover, as existing maps of Arctic vegetation provide little information about the density of shrub cover at a moderate spatial resolution across the region. Remotely-sensed fractional shrub canopy maps can provide this necessary baseline inventory of shrub cover. In this study, we compare the accuracy of fractional shrub canopy (> 0.5 m tall) maps derived from multi-spectral, multi-angular, and multi-temporal datasets from Landsat imagery at 30 m spatial resolution, Moderate Resolution Imaging SpectroRadiometer (MODIS) imagery at 250 m and 500 m spatial resolution, and MultiAngle Imaging Spectroradiometer (MISR) imagery at 275 m spatial resolution for a 1067 km2 study area in Arctic Alaska. The study area is centered at 69 ??N, ranges in elevation from 130 to 770 m, is composed primarily of rolling topography with gentle slopes less than 10??, and is free of glaciers and perennial snow cover. Shrubs > 0.5 m in height cover 2.9% of the study area and are primarily confined to patches associated with specific landscape features. Reference fractional shrub canopy is determined from in situ shrub canopy measurements and a high spatial resolution IKONOS image swath. Regression tree models are constructed to estimate fractional canopy cover at 250 m using different combinations of input data from Landsat, MODIS, and MISR. Results indicate that multi-spectral data provide substantially more accurate estimates of fractional shrub canopy cover than multi-angular or multi-temporal data. Higher spatial resolution datasets also provide more accurate estimates of fractional shrub canopy cover (aggregated to moderate spatial resolutions) than lower spatial resolution datasets, an expected result for a study area where most shrub cover is concentrated in narrow patches associated with rivers, drainages, and slopes. Including the middle infrared bands available from Landsat and MODIS in the regression tree models (in addition to the four standard visible and near-infrared spectral bands) typically results in a slight boost in accuracy. Including the multi-angular red band data available from MISR in the regression tree models, however, typically boosts accuracy more substantially, resulting in moderate resolution fractional shrub canopy estimates approaching the accuracy of estimates derived from the much higher spatial resolution Landsat sensor. Given the poor availability of snow and cloud-free Landsat scenes in many areas of the Arctic and the promising results demonstrated here by the MISR sensor, MISR may be the best choice for large area fractional shrub canopy mapping in the Alaskan Arctic for the period 2000-2009.

Ozone risk assessment for agricultural crops in Europe: Further development of stomatal flux and flux-response relationships for European wheat and potato

NASA Astrophysics Data System (ADS)

Pleijel, H.; Danielsson, H.; Emberson, L.; Ashmore, M. R.; Mills, G.

Applications of a parameterised Jarvis-type multiplicative stomatal conductance model with data collated from open-top chamber experiments on field grown wheat and potato were used to derive relationships between relative yield and stomatal ozone uptake. The relationships were based on thirteen experiments from four European countries for wheat and seven experiments from four European countries for potato. The parameterisation of the conductance model was based both on an extensive literature review and primary data. Application of the stomatal conductance models to the open-top chamber experiments resulted in improved linear regressions between relative yield and ozone uptake compared to earlier stomatal conductance models, both for wheat ( r2=0.83) and potato ( r2=0.76). The improvement was largest for potato. The relationships with the highest correlation were obtained using a stomatal ozone flux threshold. For both wheat and potato the best performing exposure index was AF st6 (accumulated stomatal flux of ozone above a flux rate threshold of 6 nmol ozone m -2 projected sunlit leaf area, based on hourly values of ozone flux). The results demonstrate that flux-based models are now sufficiently well calibrated to be used with confidence to predict the effects of ozone on yield loss of major arable crops across Europe. Further studies, using innovations in stomatal conductance modelling and plant exposure experimentation, are needed if these models are to be further improved.

A Modeling Approach to Quantify the Effects of Stomatal Behavior and Mesophyll Conductance on Leaf Water Use Efficiency

PubMed Central

Moualeu-Ngangue, Dany P.; Chen, Tsu-Wei; Stützel, Hartmut

2016-01-01

Water use efficiency (WUE) is considered as a determinant of yield under stress and a component of crop drought resistance. Stomatal behavior regulates both transpiration rate and net assimilation and has been suggested to be crucial for improving crop WUE. In this work, a dynamic model was used to examine the impact of dynamic properties of stomata on WUE. The model includes sub-models of stomatal conductance dynamics, solute accumulation in the mesophyll, mesophyll water content, and water flow to the mesophyll. Using the instantaneous value of stomatal conductance, photosynthesis, and transpiration rate were simulated using a biochemical model and Penman-Monteith equation, respectively. The model was parameterized for a cucumber leaf and model outputs were evaluated using climatic data. Our simulations revealed that WUE was higher on a cloudy than a sunny day. Fast stomatal reaction to light decreased WUE during the period of increasing light (e.g., in the morning) by up to 10.2% and increased WUE during the period of decreasing light (afternoon) by up to 6.25%. Sensitivity of daily WUE to stomatal parameters and mesophyll conductance to CO2 was tested for sunny and cloudy days. Increasing mesophyll conductance to CO2 was more likely to increase WUE for all climatic conditions (up to 5.5% on the sunny day) than modifications of stomatal reaction speed to light and maximum stomatal conductance. PMID:27379150

Stomatal response of swordfern to volcanogenic CO2 and SO2 from Kilauea volcano

NASA Astrophysics Data System (ADS)

Tanner, Lawrence H.; Smith, David L.; Allan, Amanda

2007-08-01

The experimentally determined relationship between atmospheric pCO2 and plant stomata has been used to interpret large but transient changes in atmospheric composition, such as may have resulted from the eruptions of flood basalt. However, this relationship has not been tested in the field, i.e. in the vicinity of active volcanoes, to examine the specific effects of volcanogenic emissions. Moreover, the interpretation of paleoatmospheric pCO2 from fossil stomatal data assumes that the stomatal response resulted solely from variation in pCO2 and ignores the potential effect of outgassed SO2. We hypothesize that volcanogenic SO2 also has a significant effect on leaf stomata and test this hypothesis by measuring the stomatal index of the common swordfern (Nephrolepis exaltata) in the plumes of the actively outgassing vents of Kilauea volcano. We find that, compared to control locations, stomatal index is lowest at sample sites in the plume of Halema'uma'u Crater, where concentrations of both CO2 and SO2 are much higher than background. However, sites located directly in the plume of Pu'u O'o, where SO2 levels are high, but CO2 levels are not, also yield low values of stomatal index. We propose that shifts in the stomatal index of fossil leaves may record transient atmospheric increases in both SO2 and CO2, such as may be caused by eruptions of flood basalts. Calculations of pCO2 based on stomatal frequency are likely to be exaggerated.

Canopy temperature for simulation of heat stress in irrigated wheat in a semi-arid environment: a multi-model comparison

USDA-ARS?s Scientific Manuscript database

Mounting evidence suggests that even brief periods of high temperatures occurring around flowering and during grain filling can severely reduce grain yield in cereals, a phenomenon referred to as heat stress. Recently, ecophysiological models of crops models have begun to represent such phenomena. M...

Conservation importance of early post-disturbance temperate forests

Treesearch

Charles Kwit; David I. King; Beverly Collins; Mark E. Swanson

2014-01-01

The early post-disturbance stage of temperate forest succession (also referred to as 'early-seral' or 'early-successional' forest) has been the subject of interest and debate. Often thought of as an ephemeral (and often disorganized) state of eventual closed-canopy systems, its direct and immediate role in conservation traditionally has been ignored...

Exploring links between greenspace and sudden unexpected death: A spatial analysis.

PubMed

Wu, Jianyong; Rappazzo, Kristen M; Simpson, Ross J; Joodi, Golsa; Pursell, Irion W; Mounsey, J Paul; Cascio, Wayne E; Jackson, Laura E

2018-04-01

Greenspace has been increasingly recognized as having numerous health benefits. However, its effects are unknown concerning sudden unexpected death (SUD), commonly referred to as sudden cardiac death, which constitutes a large proportion of mortality in the United States. Because greenspace can promote physical activity, reduce stress and buffer air pollutants, it may have beneficial effects for people at risk of SUD, such as those with heart disease, hypertension, and diabetes mellitus. Using several spatial techniques, this study explored the relationship between SUD and greenspace. We adjudicated 396 SUD cases that occurred from March 2013 to February 2015 among reports from emergency medical services (EMS) that attended out-of-hospital deaths in Wake County (central North Carolina, USA). We measured multiple greenspace metrics in each census tract, including the percentages of forest, grassland, average tree canopy, tree canopy diversity, near-road tree canopy and greenway density. The associations between SUD incidence and these greenspace metrics were examined using Poisson regression (non-spatial) and Bayesian spatial models. The results from both models indicated that SUD incidence was inversely associated with both greenway density (adjusted risk ratio [RR] = 0.82, 95% credible/ confidence interval [CI]: 0.69-0.97) and the percentage of forest (adjusted RR = 0.90, 95% CI: 0.81-0.99). These results suggest that increases in greenway density by 1 km/km 2 and in forest by 10% were associated with a decrease in SUD risk of 18% and 10%, respectively. The inverse relationship was not observed between SUD incidence and other metrics, including grassland, average tree canopy, near-road tree canopy and tree canopy diversity. This study implies that greenspace, specifically greenways and forest, may have beneficial effects for people at risk of SUD. Further studies are needed to investigate potential causal relationships between greenspace and SUD, and potential mechanisms such as promoting physical activity and reducing stress. Copyright © 2018 Elsevier Ltd. All rights reserved.

Application of 3D triangulations of airborne laser scanning data to estimate boreal forest leaf area index

NASA Astrophysics Data System (ADS)

Majasalmi, Titta; Korhonen, Lauri; Korpela, Ilkka; Vauhkonen, Jari

2017-07-01

We propose 3D triangulations of airborne Laser Scanning (ALS) point clouds as a new approach to derive 3D canopy structures and to estimate forest canopy effective LAI (LAIe). Computational geometry and topological connectivity were employed to filter the triangulations to yield a quasi-optimal relationship with the field measured LAIe. The optimal filtering parameters were predicted based on ALS height metrics, emulating the production of maps of LAIe and canopy volume for large areas. The LAIe from triangulations was validated with field measured LAIe and compared with a reference LAIe calculated from ALS data using logarithmic model based on Beer's law. Canopy transmittance was estimated using All Echo Cover Index (ACI), and the mean projection of unit foliage area (β) was obtained using no-intercept regression with field measured LAIe. We investigated the influence species and season on the triangulated LAIe and demonstrated the relationship between triangulated LAIe and canopy volume. Our data is from 115 forest plots located at the southern boreal forest area in Finland and for each plot three different ALS datasets were available to apply the triangulations. The triangulation approach was found applicable for both leaf-on and leaf-off datasets after initial calibration. Results showed the Root Mean Square Errors (RMSEs) between LAIe from triangulations and field measured values agreed the most using the highest pulse density data (RMSE = 0.63, the coefficient of determination (R2) = 0.53). Yet, the LAIe calculated using ACI-index agreed better with the field measured LAIe (RMSE = 0.53 and R2 = 0.70). The best models to predict the optimal alpha value contained the ACI-index, which indicates that within-crown transmittance is accounted by the triangulation approach. The cover indices may be recommended for retrieving LAIe only, but for applications which require more sophisticated information on canopy shape and volume, such as radiative transfer models, the triangulation approach may be preferred.

Sap flux density and stomatal conductance of European beech and common oak trees in pure and mixed stands during the summer drought of 2003

NASA Astrophysics Data System (ADS)

Jonard, F.; André, F.; Ponette, Q.; Vincke, C.; Jonard, M.

2011-10-01

SummarySap flux density of European beech and common oak trees was determined from sap flow measurements in pure and mixed stands during the summer drought of 2003. Eight trees per species and per stand were equipped with sap flow sensors. Soil water content was monitored in each stand at different depths by using time-domain reflectometry (TDR). Leaf area index and vertical root distribution were also investigated during the growing season. From sap flux density ( SFD) data, mean stomatal conductance of individual trees ( G s) was calculated by inverting the Penman-Monteith equation. Linear mixed models were developed to analyse the effects of species and stand type (pure vs. mixed) on SFD and G s and on their sensitivity to environmental variables (vapour pressure deficit ( D), incoming solar radiation ( R G), and relative extractable water ( REW)). For reference environmental conditions, we did not find any tree species or stand type effects on SFD. The sensitivity of SFD to D was higher for oak than for beech in the pure stands ( P < 0.0001) but the mixing of species reduced it for oak and increased it for beech, so that the sensitivity of SFD to D became higher for beech than for oak in the mixed stand ( P < 0.0001). At reference conditions, G s was significantly higher for beech compared to oak (2.1 and 1.8 times in the pure and mixed stand, respectively). This was explained by a larger beech sapwood-to-leaf area ratio compared to oak. The sensitivity of G s to REW was higher for beech than for oak and was ascribed to a higher vulnerability of beech to air embolism and to a more sensitive stomatal regulation. The sensitivity of beech G s to REW was lower in the mixed than in the pure stand, which could be explained by a better sharing of the resources in the mixture, by facilitation processes (hydraulic lift), and by a rainfall partitioning in favour of beech.

Experimental infection of Didelphis marsupialis with Vesicular Stomatitis New Jersey Virus

USDA-ARS?s Scientific Manuscript database

Although vesicular stomatitis has been present for many years in the Americas, many aspects of its natural history remain undefined. In this study we challenged five adult Virginia opossums (Didelphis marsupialis) with vesicular stomatitis New Jersey serotype virus (VSNJV). Opossums had no detecta...

TOO MANY MOUTHS promotes cell fate progression in stomatal development of Arabidopsis stems.

PubMed

Bhave, Neela S; Veley, Kira M; Nadeau, Jeanette A; Lucas, Jessica R; Bhave, Sanjay L; Sack, Fred D

2009-01-01

Mutations in TOO MANY MOUTHS (TMM), which encodes a receptor-like protein, cause stomatal patterning defects in Arabidopsis leaves but eliminate stomatal formation in stems. Stomatal development in wild-type and tmm stems was analyzed to define TMM function. Epidermal cells in young tmm stems underwent many asymmetric divisions characteristic of entry into the stomatal pathway. The resulting precursor cells, meristemoids, appropriately expressed cell fate markers such as pTMM:GFP. However, instead of progressing developmentally by forming a guard mother cell, the meristemoids arrested, dedifferentiated, and enlarged. Thus asymmetric divisions are necessary but not sufficient for stomatal formation in stems, and TMM promotes the fate and developmental progression of early precursor cells. Comparable developmental and mature stomatal phenotypes were also found in tmm hypocotyls and in the proximal flower stalk. TMM is also a positive regulator of meristemoid division in leaves suggesting that TMM generally promotes meristemoid activity. Our results are consistent with a model in which TMM interacts with other proteins to modulate precursor cell fate and progression in an organ and domain-specific manner. Finally, the consistent presence of a small number of dedifferentiated meristemoids in mature wild-type stems suggests that precursor cell arrest is a normal feature of Arabidopsis stem development.

Phenomics allows identification of genomic regions affecting maize stomatal conductance with conditional effects of water deficit and evaporative demand.

PubMed

Prado, Santiago Alvarez; Cabrera-Bosquet, Llorenç; Grau, Antonin; Coupel-Ledru, Aude; Millet, Emilie J; Welcker, Claude; Tardieu, François

2018-02-01

Stomatal conductance is central for the trades-off between hydraulics and photosynthesis. We aimed at deciphering its genetic control and that of its responses to evaporative demand and water deficit, a nearly impossible task with gas exchanges measurements. Whole-plant stomatal conductance was estimated via inversion of the Penman-Monteith equation from data of transpiration and plant architecture collected in a phenotyping platform. We have analysed jointly 4 experiments with contrasting environmental conditions imposed to a panel of 254 maize hybrids. Estimated whole-plant stomatal conductance closely correlated with gas-exchange measurements and biomass accumulation rate. Sixteen robust quantitative trait loci (QTLs) were identified by genome wide association studies and co-located with QTLs of transpiration and biomass. Light, vapour pressure deficit, or soil water potential largely accounted for the differences in allelic effects between experiments, thereby providing strong hypotheses for mechanisms of stomatal control and a way to select relevant candidate genes among the 1-19 genes harboured by QTLs. The combination of allelic effects, as affected by environmental conditions, accounted for the variability of stomatal conductance across a range of hybrids and environmental conditions. This approach may therefore contribute to genetic analysis and prediction of stomatal control in diverse environments. © 2017 John Wiley & Sons Ltd.

Responses of two semiarid conifer tree species to reduced precipitation and warming reveal new perspectives for stomatal regulation

DOE PAGES

Garcia-Forner, Nuria; Adams, Henry D.; Sevanto, Sanna; ...

2015-08-08

Here, relatively anisohydric species are predicted to be more predisposed to hydraulic failure than relatively isohydric species, as they operate with narrower hydraulic safety margins. We subjected co-occurring anisohydric Juniperus monosperma and isohydric Pinus edulis trees to warming, reduced precipitation, or both, and measured their gas exchange and hydraulic responses. We found that reductions in stomatal conductance and assimilation by heat and drought were more frequent during relatively moist periods, but these effects were not exacerbated in the combined heat and drought treatment. Counter to expectations, both species exhibited similar gs temporal dynamics in response to drought. Further, whereas P.more » edulis exhibited chronic embolism, J. monosperma showed very little embolism due to its conservative stomatal regulation and maintenance of xylem water potential above the embolism entry point. This tight stomatal control and low levels of embolism experienced by juniper refuted the notion that very low water potentials during drought are associated with loose stomatal control and with the hypothesis that anisohydric species are more prone to hydraulic failure than isohydric species. Because direct association of stomatal behaviour with embolism resistance can be misleading, we advocate consideration of stomatal behaviour relative to embolism resistance for classifying species drought response strategies.« less

Sucrose breakdown within guard cells provides substrates for glycolysis and glutamine biosynthesis during light-induced stomatal opening.

PubMed

Medeiros, David B; Perez Souza, Leonardo; Antunes, Werner C; Araújo, Wagner L; Daloso, Danilo M; Fernie, Alisdair R

2018-05-01

Sucrose has long been thought to play an osmolytic role in stomatal opening. However, recent evidence supports the idea that the role of sucrose in this process is primarily energetic. Here we used a combination of stomatal aperture assays and kinetic [U- 13 C]-sucrose isotope labelling experiments to confirm that sucrose is degraded during light-induced stomatal opening and to define the fate of the C released from sucrose breakdown. We additionally show that addition of sucrose to the medium did not enhance light-induced stomatal opening. The isotope experiment showed a consistent 13 C enrichment in fructose and glucose, indicating that during light-induced stomatal opening sucrose is indeed degraded. We also observed a clear 13 C enrichment in glutamate and glutamine (Gln), suggesting a concerted activation of sucrose degradation, glycolysis and the tricarboxylic acid cycle. This is in contrast to the situation for Gln biosynthesis in leaves under light, which has been demonstrated to rely on previously stored C. Our results thus collectively allow us to redraw current models concerning the influence of sucrose during light-induced stomatal opening, in which, instead of being accumulated, sucrose is degraded providing C skeletons for Gln biosynthesis. © 2018 The Authors The Plant Journal © 2018 John Wiley & Sons Ltd.

Responses of two semiarid conifer tree species to reduced precipitation and warming reveal new perspectives for stomatal regulation

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

Garcia-Forner, Nuria; Adams, Henry D.; Sevanto, Sanna

Here, relatively anisohydric species are predicted to be more predisposed to hydraulic failure than relatively isohydric species, as they operate with narrower hydraulic safety margins. We subjected co-occurring anisohydric Juniperus monosperma and isohydric Pinus edulis trees to warming, reduced precipitation, or both, and measured their gas exchange and hydraulic responses. We found that reductions in stomatal conductance and assimilation by heat and drought were more frequent during relatively moist periods, but these effects were not exacerbated in the combined heat and drought treatment. Counter to expectations, both species exhibited similar gs temporal dynamics in response to drought. Further, whereas P.more » edulis exhibited chronic embolism, J. monosperma showed very little embolism due to its conservative stomatal regulation and maintenance of xylem water potential above the embolism entry point. This tight stomatal control and low levels of embolism experienced by juniper refuted the notion that very low water potentials during drought are associated with loose stomatal control and with the hypothesis that anisohydric species are more prone to hydraulic failure than isohydric species. Because direct association of stomatal behaviour with embolism resistance can be misleading, we advocate consideration of stomatal behaviour relative to embolism resistance for classifying species drought response strategies.« less

Drought tolerance, xylem sap abscisic acid and stomatal conductance during soil drying: a comparison of young plants of four temperate deciduous angiosperms.

PubMed

Loewenstein, Nancy J.; Pallardy, Stephen G.

1998-07-01

Patterns of water relations, xylem sap abscisic acid (ABA) concentration ([ABA]) and stomatal aperture were compared in drought-sensitive black walnut (Juglans nigra L.) and black willow (Salix nigra Marsh.), less drought-sensitive sugar maple (Acer saccharum Marsh.) and drought-tolerant white oak (Quercus alba L.). Strong correlations among reduction in predawn water potential, increase in xylem sap [ABA] and stomatal closure were observed in all species. Stomatal response was more highly correlated with xylem [ABA] than with ABA flux. Xylem sap pH and ion concentrations appeared not to play a major role in the stomatal response of these species. Stomata were more sensitive to relative changes in [ABA] in drought-sensitive black walnut and black willow than in sugar maple and white oak. In the early stages of drought, increased [ABA] in the xylem sap of black walnut and black willow was probably of root origin and provided a signal to the shoot of the water status of the roots. In sugar maple and white oak, leaf water potential declined with the onset of stomatal closure, so that stomatal closure also may have occurred in response to the change in leaf water potential.

Intercomparison of clumping index estimates from POLDER, MODIS, and MISR satellite data over reference sites

NASA Astrophysics Data System (ADS)

Pisek, Jan; Govind, Ajit; Arndt, Stefan K.; Hocking, Darren; Wardlaw, Timothy J.; Fang, Hongliang; Matteucci, Giorgio; Longdoz, Bernard

2015-03-01

Clumping index is the measure of foliage grouping relative to a random distribution of leaves in space. It is a key structural parameter of plant canopies that influences canopy radiation regimes and controls canopy photosynthesis and other land-atmosphere interactions. The Normalized Difference between Hotspot and Darkspot (NDHD) index has been previously used to retrieve global clumping index maps from POLarization and Directionality of the Earth's Reflectances (POLDER) data at ˜6 km resolution and the Bidirectional Reflectance Distribution Function (BRDF) product from Moderate Resolution Imaging Spectroradiometer (MODIS) at 500 m resolution. Most recently the algorithm was also applied with Multi-angle Imaging SpectroRadiometer (MISR) data at 275 m resolution over selected areas. In this study for the first time we characterized and compared the three products over a set of sites representing diverse biomes and different canopy structures. The products were also directly validated with both in-situ vertical profiles and available seasonal trajectories of clumping index over several sites. We demonstrated that the vertical distribution of foliage and especially the effect of understory need to be taken into account while validating foliage clumping products from remote sensing products with values measured in the field. Satellite measurements responded to the structural effects near the top of canopies, while ground measurements may be biased by the lower vegetation layers. Additionally, caution should be taken regarding the misclassification in land cover maps as their errors can propagate into the foliage clumping maps. Our results indicate that MODIS data and MISR data, with 275 m in particular, can provide good quality clumping index estimates at spatial scales pertinent for modeling local carbon and energy fluxes.

Increased phytochrome B alleviates density effects on tuber yield of field potato crops.

PubMed

Boccalandro, Hernán E; Ploschuk, Edmundo L; Yanovsky, Marcelo J; Sánchez, Rodolfo A; Gatz, Christiane; Casal, Jorge J

2003-12-01

The possibility that reduced photomorphogenic responses could increase field crop yield has been suggested often, but experimental support is still lacking. Here, we report that ectopic expression of the Arabidopsis PHYB (phytochrome B) gene, a photoreceptor involved in detecting red to far-red light ratio associated with plant density, can increase tuber yield in field-grown transgenic potato (Solanum tuberosum) crops. Surprisingly, this effect was larger at very high densities, despite the intense reduction in the red to far-red light ratios and the concomitant narrowed differences in active phytochrome B levels between wild type and transgenics at these densities. Increased PHYB expression not only altered the ability of plants to respond to light signals, but they also modified the light environment itself. This combination resulted in larger effects of enhanced PHYB expression on tuber number and crop photosynthesis at high planting densities. The PHYB transgenics showed higher maximum photosynthesis in leaves of all strata of the canopy, and this effect was largely due to increased leaf stomatal conductance. We propose that enhanced PHYB expression could be used in breeding programs to shift optimum planting densities to higher levels.

How trees uptake carbon, release water and cool themselves in air: a marriage between biophysics and turbulent fluid dynamics

NASA Astrophysics Data System (ADS)

Banerjee, Tirtha; Linn, Rodman

2017-11-01

Resolving the role of the biosphere as a terrestrial carbon sink and the nature of nonlinear couplings between carbon and water cycles across a very wide range of spatiotemporal scales constitute the scope of this work. To achieve this goal, plant physiology models are coupled with atmospheric turbulence simulations. The plant biophysics code is based on the following principles: (1) a model for photosynthesis; (2) a mass transfer model through the laminar boundary layer on leaves; (3) an optimal leaf water use strategy regulated by stomatal aperture variation; (4) a leaf-level energy balance to accommodate evaporative cooling. Leaf-level outputs are upscaled to plant, canopy and landscape scales using HIGRAD/FIRETEC, a high fidelity large eddy simulation (LES) framework developed at LANL. The coupled biophysics-CFD code can take inputs such as wind speed, light availability, ambient CO2 concentration, air temperature, site characteristics etc. and can deliver predictions for leaf temperature, transpiration, carbon assimilation, sensible and latent heat flux, which is used to illustrate the complex the complex interaction between trees and their surrounding environments. These simulation capabilities are being used to study climate feedbacks of forests and agroecosystems.

Avoiding high relative air humidity during critical stages of leaf ontogeny is decisive for stomatal functioning.

PubMed

Fanourakis, Dimitrios; Carvalho, Susana M P; Almeida, Domingos P F; Heuvelink, Ep

2011-07-01

Plants of several species, if grown at high relative air humidity (RH ≥85%), develop stomata that fail to close fully in case of low leaf water potential. We studied the effect of a reciprocal change in RH, at different stages of leaf expansion of Rosa hybrida grown at moderate (60%) or high (95%) RH, on the stomatal closing ability. This was assessed by measuring the leaf transpiration rate in response to desiccation once the leaves had fully expanded. For leaves that started expanding at high RH but completed their expansion after transfer to moderate RH, the earlier this switch took place the better the stomatal functioning. Leaves initially expanding at moderate RH and transferred to high RH exhibited poor stomatal functioning, even when this transfer occurred very late during leaf expansion. Applying a daily abscisic acid (ABA) solution to the leaves of plants grown at continuous high RH was effective in inducing stomatal closure at low water potential, if done before full leaf expansion (FLE). After FLE, stomatal functioning was no longer affected either by the RH or ABA level. The results indicate that the degree of stomatal adaptation depends on both the timing and duration of exposure to high RH. It is concluded that stomatal functionality is strongly dependent on the humidity at which the leaf completed its expansion. The data also show that the effect of ambient RH and the alleviating role of ABA are restricted to the period of leaf expansion. Copyright © Physiologia Plantarum 2011.

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

Systems Analysis of Guard Cell Membrane Transport for Enhanced Stomatal Dynamics and Water Use Efficiency1[W][OPEN

PubMed Central

Wang, Yizhou; Hills, Adrian; Blatt, Michael R.

2014-01-01

Stomatal transpiration is at the center of a crisis in water availability and crop production that is expected to unfold over the next 20 to 30 years. Global water usage has increased 6-fold in the past 100 years, twice as fast as the human population, and is expected to double again before 2030, driven mainly by irrigation and agriculture. Guard cell membrane transport is integral to controlling stomatal aperture and offers important targets for genetic manipulation to improve crop performance. However, its complexity presents a formidable barrier to exploring such possibilities. With few exceptions, mutations that increase water use efficiency commonly have been found to do so with substantial costs to the rate of carbon assimilation, reflecting the trade-off in CO2 availability with suppressed stomatal transpiration. One approach yet to be explored in detail relies on quantitative systems analysis of the guard cell. Our deep knowledge of transport and homeostasis in these cells gives real substance to the prospect for reverse engineering of stomatal responses, using in silico design in directing genetic manipulation for improved water use and crop yields. Here we address this problem with a focus on stomatal kinetics, taking advantage of the OnGuard software and models of the stomatal guard cell recently developed for exploring stomatal physiology. Our analysis suggests that manipulations of single transporter populations are likely to have unforeseen consequences. Channel gating, especially of the dominant K+ channels, appears the most favorable target for experimental manipulation. PMID:24596330

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.

Vanadate inhibition of stomatal opening in epidermal peels of Commelina communis

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

Schwartz, A.; Illan, N.; Assmann, S.M.

There are conflicting reports on the effectiveness of the plasmamembrane H{sup +} ATPase inhibitor, vanadate, in inhibiting stomatal opening. We have observed that vanadate inhibited light-stimulated stomatal opening in epidermal peels of Commelina communis only at KCl concentrations lower than 50 mM. When KCl was replaced with n-methylglucamine chloride, vanadate was still ineffective at high salt concentrations. However, in the absence of Cl{sup {minus}}, when KOH was buffered with V{sub 2}O{sub 5}, vanadate inhibition of stomatal opening occurred even at high salt concentrations (K{sup +} = 70 mM). An inhibitor of anion uptake, anthracene-9-carboxylic acid (200 {mu}M), partially prevented vanadatemore » inhibition of stomatal opening; other inhibitors (DIDS, SITS, Zn{sup 2+}) were ineffective. These results suggest that inhibition of stomatal opening by vanadate requires its entry into guard cells through an anion uptake system. Decreasing vanadate inhibition at high Cl{sup {minus}}/vanadate ratios may result from competition between vanadate and Cl{sup {minus}} for a common uptake mechanism.« less

Role of nitric oxide in regulating stomatal apertures

PubMed Central

Ribeiro, Dimas M; Bright, Jo; Confraria, Ana; Harrison, Judith; Barros, Raimundo S; Desikan, Radhika; Neill, Steven J; Hancock, John T

2009-01-01

During stomatal closure, nitric oxide (NO) operates as one of the key intermediates in the complex, abscisic acid (ABA)-mediated, guard cell signaling network that regulates this process. However, data concerning the role of NO in stomatal closure that occurs in turgid vs. dehydrated plants is limited. The data presented demonstrate that, while there is a requirement for NO during the ABA-induced stomatal closure of turgid leaves, such a requirement does not exist for ABA-enhanced stomatal closure observed to occur during conditions of rapid dehydration. The data also indicate that the ABA signaling pathway must be both functional and to some degree activated for guard cell NO signaling to occur. These observations are in line with the idea that the effects of NO in guard cells are mediated via a Ca2+-dependent rather than a Ca2+-independent ABA signaling pathway. It appears that there is a role for NO in the fine tuning of the stomatal apertures of turgid leaves that occurs in response to fluctuations in the prevailing environment. PMID:19816112

Metabolomics and Proteomics of Brassica napus Guard Cells in Response to Low CO2

PubMed Central

Geng, Sisi; Yu, Bing; Zhu, Ning; Dufresne, Craig; Chen, Sixue

2017-01-01

Stomatal guard cell response to various stimuli is an important process that balances plant carbon dioxide (CO2) uptake and water transpiration. Elevated CO2 induces stomatal closure, while low CO2 promotes stomatal opening. The signaling process of elevated CO2 induced stomatal closure has been extensively studied in recent years. However, the mechanism of low CO2 induced stomatal opening is not fully understood. Here we report metabolomic and proteomic responses of Brassica napus guard cells to low CO2 using hyphenated mass spectrometry technologies. A total of 411 metabolites and 1397 proteins were quantified in a time-course study of low CO2 effects. Metabolites and proteins that exhibited significant changes are overrepresented in fatty acid metabolism, starch and sucrose metabolism, glycolysis and redox regulation. Concomitantly, multiple hormones that promote stomatal opening increased in response to low CO2. Interestingly, jasmonic acid precursors were diverted to a branch pathway of traumatic acid biosynthesis. These results indicate that the low CO2 response is mediated by a complex crosstalk between different phytohormones. PMID:28791296

Metabolomics and Proteomics of Brassica napus Guard Cells in Response to Low CO2.

PubMed

Geng, Sisi; Yu, Bing; Zhu, Ning; Dufresne, Craig; Chen, Sixue

2017-01-01

Stomatal guard cell response to various stimuli is an important process that balances plant carbon dioxide (CO 2 ) uptake and water transpiration. Elevated CO 2 induces stomatal closure, while low CO 2 promotes stomatal opening. The signaling process of elevated CO 2 induced stomatal closure has been extensively studied in recent years. However, the mechanism of low CO 2 induced stomatal opening is not fully understood. Here we report metabolomic and proteomic responses of Brassica napus guard cells to low CO 2 using hyphenated mass spectrometry technologies. A total of 411 metabolites and 1397 proteins were quantified in a time-course study of low CO 2 effects. Metabolites and proteins that exhibited significant changes are overrepresented in fatty acid metabolism, starch and sucrose metabolism, glycolysis and redox regulation. Concomitantly, multiple hormones that promote stomatal opening increased in response to low CO 2 . Interestingly, jasmonic acid precursors were diverted to a branch pathway of traumatic acid biosynthesis. These results indicate that the low CO 2 response is mediated by a complex crosstalk between different phytohormones.

Do fossil plants signal palaeoatmospheric carbon dioxide concentration in the geological past?

PubMed Central

McElwain, J. C.

1998-01-01

Fossil, subfossil, and herbarium leaves have been shown to provide a morphological signal of the atmospheric carbon dioxide environment in which they developed by means of their stomatal density and index. An inverse relationship between stomatal density/index and atmospheric carbon dioxide concentration has been documented for all the studies to date concerning fossil and subfossil material. Furthermore, this relationship has been demonstrated experimentally by growing plants under elevated and reducedcarbon dioxide concentrations. To date, the mechanism that controls the stomatal density response to atmospheric carbon dioxide concentration remains unknown. However, stomatal parameters of fossil plants have been successfully used as a proxy indicator of palaeo-carbon dioxide levels. This paper presents new estimates of palaeo-atmospheric carbon dioxide concentrations for the Middle Eocene (Lutetian), based on the stomatal ratios of fossil Lauraceae species from Bournemouth in England. Estimates of atmospheric carbon dioxide concentrations derived from stomatal data from plants of the Early Devonian, Late Carboniferous, Early Permian and Middle Jurassic ages are reviewed in the light of new data. Semi-quantitative palaeo-carbon dioxide estimates based on the stomatal ratio (a ratio of the stomatal index of a fossil plant to that of a selected nearest living equivalent) have in the past relied on the use of a Carboniferous standard. The application of a new standard based on the present-day carbon dioxide level is reported here for comparison. The resultant ranges of palaeo-carbon dioxide estimates made from standardized fossil stomatal ratio data are in good agreement with both carbon isotopic data from terrestrial and marine sources and long-term carbon cycle modelling estimates for all the time periods studied. These data indicate elevated atmospheric carbon dioxide concentrations during the Early Devonian, Middle Jurassic and Middle Eocene, and reduced concentrations during the Late Carboniferous and Early Permian. Such data are important in demonstrating the long-term responses of plants to changing carbon dioxide concentrations and in contributing to the database needed for general circulation model climatic analogues.

Intraspecific variation in stomatal traits, leaf traits and physiology reflects adaptation along aridity gradients in a South African shrub

PubMed Central

Carlson, Jane E.; Adams, Christopher A.; Holsinger, Kent E.

2016-01-01

Background and Aims Trait–environment relationships are commonly interpreted as evidence for local adaptation in plants. However, even when selection analyses support this interpretation, the mechanisms underlying differential benefits are often unknown. This study addresses this gap in knowledge using the broadly distributed South African shrub Protea repens. Specifically, the study examines whether broad-scale patterns of trait variation are consistent with spatial differences in selection and ecophysiology in the wild. Methods In a common garden study of plants sourced from 19 populations, associations were measured between five morphological traits and three axes describing source climates. Trait–trait and trait–environment associations were analysed in a multi-response model. Within two focal populations in the wild, selection and path analyses were used to test associations between traits, fecundity and physiological performance. Key Results Across 19 populations in a common garden, stomatal density increased with the source population’s mean annual temperature and decreased with its average amount of rainfall in midsummer. Concordantly, selection analysis in two natural populations revealed positive selection on stomatal density at the hotter, drier site, while failing to detect selection at the cooler, moister site. Dry-site plants with high stomatal density also had higher stomatal conductances, cooler leaf temperatures and higher light-saturated photosynthetic rates than those with low stomatal density, but no such relationships were present among wet-site plants. Leaf area, stomatal pore index and specific leaf area in the garden also co-varied with climate, but within-population differences were not associated with fitness in either wild population. Conclusions The parallel patterns of broad-scale variation, differences in selection and differences in trait–ecophysiology relationships suggest a mechanism for adaptive differentiation in stomatal density. Densely packed stomata may improve performance by increasing transpiration and cooling, but predominately in drier, hotter climates. This study uniquely shows context-dependent benefits of stomatal density – a trait rarely linked to local adaptation in plants. PMID:26424782

Ferns are less dependent on passive dilution by cell expansion to coordinate leaf vein and stomatal spacing than angiosperms

PubMed Central

Jordan, Gregory J.; Brodribb, Timothy J.

2017-01-01

Producing leaves with closely spaced veins is a key innovation linked to high rates of photosynthesis in angiosperms. A close geometric link between veins and stomata in angiosperms ensures that investment in enhanced venous water transport provides the strongest net carbon return to the plant. This link is underpinned by “passive dilution” via expansion of surrounding cells. However, it is not known whether this ‘passive dilution’ mechanism is present in plant lineages other than angiosperms and is another key feature of the angiosperms’ evolutionary success. Consequently, we sought to determine whether the ‘passive dilution’ mechanism is; (i) exclusive to the angiosperms, (ii) a conserved mechanism that evolved in the common ancestor of ferns and angiosperms, or (iii) has evolved continuously over time. To do this we first we assessed the plasticity of vein and stomatal density and epidermal cell size in ferns in response to light environment. We then compared the relationships between these traits found among ferns with modelled relationships that assume vein and stomatal density respond passively to epidermal cell expansion, and with those previously observed in angiosperms. Vein density, stomatal density and epidermal cell size were linked in ferns with remarkably similar relationships to those observed in angiosperms, except that fern leaves had fewer veins per stomata. However, plasticity was limited in ferns and stomatal spacing was dependent on active stomatal differentiation as well as passive cell expansion. Thus, ferns (like angiosperms) appear to coordinate vein and stomatal density with epidermal cell expansion to some extent to maintain a constant ratio between veins and stomata in the leaf. The different general relationships between vein density and stomatal density in ferns and angiosperms suggests the groups have different optimum balances between the production of vein tissue dedicated to water supply and stomatal tissue for gas exchange. PMID:28953931

Transport and coordination in the coupled soil-root-xylem-phloem leaf system

NASA Astrophysics Data System (ADS)

Huang, C. W.; Katul, G. G.; Pockman, W.; Litvak, M. E.; Domec, J. C.; Palmroth, S.

2016-12-01

In response to varying environmental conditions, stomatal pores act as biological valves that dynamically adjust their size thereby determining the rate of CO2 assimilation and water loss (i.e., transpiration) to the dry atmosphere. Although the significance of this biotic control on gas exchange is rarely disputed, representing parsimoniously all the underlying mechanisms responsible for stomatal kinetics remain a subject of some debate. It has been conjectured that stomatal control in seed plants (i.e., angiosperm and gymnosperm) represents a compromise between biochemical demand for CO2 and prevention of excessive water loss. This view has been amended at the whole-plant level, where xylem hydraulics and sucrose transport efficiency in phloem appear to impose additional constraints on gas exchange. If such additional constraints impact stomatal opening and closure, then seed plants may have evolved coordinated photosynthetic-hydraulic-sugar transporting machinery that confers some competitive advantages in fluctuating environmental conditions. Thus, a stomatal optimization model that explicitly considers xylem hydraulics and maximum sucrose transport is developed to explore this coordination in the leaf-xylem-phloem system. The model is then applied to progressive drought conditions. The main findings from the model calculations are that (1) the predicted stomatal conductance from the conventional stomatal optimization theory at the leaf and the newly proposed models converge, suggesting a tight coordination in the leaf-xylem-phloem system; (2) stomatal control is mainly limited by the water supply function of the soil-xylem hydraulic system especially when the water flux through the transpiration stream is significantly larger than water exchange between xylem and phloem; (3) thus, xylem limitation imposed on the supply function can be used to differentiate species with different water use strategy across the spectrum of isohydric to anisohydric behavior. Keywords: leaf-level gas exchange, stomatal control, sucrose transport in phloem, xylem hydraulics

BASL and EPF2 act independently to regulate asymmetric divisions during stomatal development

PubMed Central

Hunt, Lee

2010-01-01

The initiation of stomatal development in the developing Arabidopsis epidermis is characterized by an asymmetric ‘entry’ division in which a small cell, known as a meristemoid, and a larger daughter cell is formed. The meristemoid may undergo further asymmetric divisions, regenerating a meristemoid each time, before differentiating into a guard mother cell which divides symmetrically to form a pair of guard cells surrounding a stomatal pore. Recently EPF2 and BASL have emerged as regulators of these asymmetric divisions and here we present results indicating that these two factors operate independently to control stomatal development PMID:20220310

Subpixel urban land cover estimation: comparing cubist, random forests, and support vector regression

Treesearch

Jeffrey T. Walton

2008-01-01

Three machine learning subpixel estimation methods (Cubist, Random Forests, and support vector regression) were applied to estimate urban cover. Urban forest canopy cover and impervious surface cover were estimated from Landsat-7 ETM+ imagery using a higher resolution cover map resampled to 30 m as training and reference data. Three different band combinations (...

Predicting photosynthesis and transpiration responses to ozone: decoupling modeled photosynthesis and stomatal conductance

NASA Astrophysics Data System (ADS)

Lombardozzi, D.; Levis, S.; Bonan, G.; Sparks, J. P.

2012-08-01

Plants exchange greenhouse gases carbon dioxide and water with the atmosphere through the processes of photosynthesis and transpiration, making them essential in climate regulation. Carbon dioxide and water exchange are typically coupled through the control of stomatal conductance, and the parameterization in many models often predict conductance based on photosynthesis values. Some environmental conditions, like exposure to high ozone (O3) concentrations, alter photosynthesis independent of stomatal conductance, so models that couple these processes cannot accurately predict both. The goals of this study were to test direct and indirect photosynthesis and stomatal conductance modifications based on O3 damage to tulip poplar (Liriodendron tulipifera) in a coupled Farquhar/Ball-Berry model. The same modifications were then tested in the Community Land Model (CLM) to determine the impacts on gross primary productivity (GPP) and transpiration at a constant O3 concentration of 100 parts per billion (ppb). Modifying the Vcmax parameter and directly modifying stomatal conductance best predicts photosynthesis and stomatal conductance responses to chronic O3 over a range of environmental conditions. On a global scale, directly modifying conductance reduces the effect of O3 on both transpiration and GPP compared to indirectly modifying conductance, particularly in the tropics. The results of this study suggest that independently modifying stomatal conductance can improve the ability of models to predict hydrologic cycling, and therefore improve future climate predictions.

ABA-Induced Stomatal Closure Involves ALMT4, a Phosphorylation-Dependent Vacuolar Anion Channel of Arabidopsis[OPEN

PubMed Central

Baetz, Ulrike; Huck, Nicola V.; Zhang, Jingbo

2017-01-01

Stomatal pores are formed between a pair of guard cells and allow plant uptake of CO2 and water evaporation. Their aperture depends on changes in osmolyte concentration of guard cell vacuoles, specifically of K+ and Mal2−. Efflux of Mal2− from the vacuole is required for stomatal closure; however, it is not clear how the anion is released. Here, we report the identification of ALMT4 (ALUMINUM ACTIVATED MALATE TRANSPORTER4) as an Arabidopsis thaliana ion channel that can mediate Mal2− release from the vacuole and is required for stomatal closure in response to abscisic acid (ABA). Knockout mutants showed impaired stomatal closure in response to the drought stress hormone ABA and increased whole-plant wilting in response to drought and ABA. Electrophysiological data show that ALMT4 can mediate Mal2− efflux and that the channel activity is dependent on a phosphorylatable C-terminal serine. Dephosphomimetic mutants of ALMT4 S382 showed increased channel activity and Mal2− efflux. Reconstituting the active channel in almt4 mutants impaired growth and stomatal opening. Phosphomimetic mutants were electrically inactive and phenocopied the almt4 mutants. Surprisingly, S382 can be phosphorylated by mitogen-activated protein kinases in vitro. In brief, ALMT4 likely mediates Mal2− efflux during ABA-induced stomatal closure and its activity depends on phosphorylation. PMID:28874508

Chlorella Induces Stomatal Closure via NADPH Oxidase-Dependent ROS Production and Its Effects on Instantaneous Water Use Efficiency in Vicia faba

PubMed Central

Li, Yan; Xu, Shan-Shan; Gao, Jing; Pan, Sha; Wang, Gen-Xuan

2014-01-01

Reactive oxygen species (ROS) have been established to participate in stomatal closure induced by live microbes and microbe-associated molecular patterns (MAMPs). Chlorella as a beneficial microorganism can be expected to trigger stomatal closure via ROS production. Here, we reported that Chlorella induced stomatal closure in a dose-and time-dependent manner in epidermal peels of Vicia faba. Using pharmacological methods in this work, we found that the Chlorella-induced stomatal closure was almost completely abolished by a hydrogen peroxide (H2O2) scavenger, catalase (CAT), significantly suppressed by an NADPH oxidase inhibitor, diphenylene iodonium chloride (DPI), and slightly affected by a peroxidase inhibitor, salicylhydroxamic acid (SHAM), suggesting that ROS production involved in Chlorella-induced stomatal closure is mainly mediated by DPI-sensitive NADPH oxidase. Additionally, Exogenous application of optimal concentrations of Chlorella suspension improved instantaneous water use efficiency (WUEi) in Vicia faba via a reduction in leaf transpiration rate (E) without a parallel reduction in net photosynthetic rate (Pn) assessed by gas-exchange measurements. The chlorophyll fluorescence and content analysis further demonstrated that short-term use of Chlorella did not influence plant photosynthetic reactions center. These results preliminarily reveal that Chlorella can trigger stomatal closure via NADPH oxidase-dependent ROS production in epidermal strips and improve WUEi in leave levels. PMID:24687099

Chlorella induces stomatal closure via NADPH oxidase-dependent ROS production and its effects on instantaneous water use efficiency in Vicia faba.

PubMed

Li, Yan; Xu, Shan-Shan; Gao, Jing; Pan, Sha; Wang, Gen-Xuan

2014-01-01

Reactive oxygen species (ROS) have been established to participate in stomatal closure induced by live microbes and microbe-associated molecular patterns (MAMPs). Chlorella as a beneficial microorganism can be expected to trigger stomatal closure via ROS production. Here, we reported that Chlorella induced stomatal closure in a dose-and time-dependent manner in epidermal peels of Vicia faba. Using pharmacological methods in this work, we found that the Chlorella-induced stomatal closure was almost completely abolished by a hydrogen peroxide (H2O2) scavenger, catalase (CAT), significantly suppressed by an NADPH oxidase inhibitor, diphenylene iodonium chloride (DPI), and slightly affected by a peroxidase inhibitor, salicylhydroxamic acid (SHAM), suggesting that ROS production involved in Chlorella-induced stomatal closure is mainly mediated by DPI-sensitive NADPH oxidase. Additionally, Exogenous application of optimal concentrations of Chlorella suspension improved instantaneous water use efficiency (WUEi) in Vicia faba via a reduction in leaf transpiration rate (E) without a parallel reduction in net photosynthetic rate (Pn) assessed by gas-exchange measurements. The chlorophyll fluorescence and content analysis further demonstrated that short-term use of Chlorella did not influence plant photosynthetic reactions center. These results preliminarily reveal that Chlorella can trigger stomatal closure via NADPH oxidase-dependent ROS production in epidermal strips and improve WUEi in leave levels.

The alpha-subunit of the Arabidopsis heterotrimeric G protein, GPA1, is a regulator of transpiration efficiency.

PubMed

Nilson, Sarah E; Assmann, Sarah M

2010-04-01

Land plants must balance CO2 assimilation with transpiration in order to minimize drought stress and maximize their reproductive success. The ratio of assimilation to transpiration is called transpiration efficiency (TE). TE is under genetic control, although only one specific gene, ERECTA, has been shown to regulate TE. We have found that the alpha-subunit of the heterotrimeric G protein in Arabidopsis (Arabidopsis thaliana), GPA1, is a regulator of TE. gpa1 mutants, despite having guard cells that are hyposensitive to abscisic acid-induced inhibition of stomatal opening, have increased TE under ample water and drought stress conditions and when treated with exogenous abscisic acid. Leaf-level gas-exchange analysis shows that gpa1 mutants have wild-type assimilation versus internal CO2 concentration responses but exhibit reduced stomatal conductance compared with ecotype Columbia at ambient and below-ambient internal CO2 concentrations. The increased TE and reduced whole leaf stomatal conductance of gpa1 can be primarily attributed to stomatal density, which is reduced in gpa1 mutants. GPA1 regulates stomatal density via the control of epidermal cell size and stomata formation. GPA1 promoter::beta-glucuronidase lines indicate that the GPA1 promoter is active in the stomatal cell lineage, further supporting a function for GPA1 in stomatal development in true leaves.

Xylem vulnerability curves of canopy branches of mature trees from Caxiuana and Tapajos National Forests, Para, Brazil

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

Powell, Thomas; Moorcroft, Paul

Raw data for xylem vulnerability curves measured on upper canopy branches of mature trees from the Caxiuana and Tapajos National Forests, Para, Brazil. Tapajos samples were harvested from km67 transects, which is nearby the decommissioned throughfall-exclusion, drought-experiment plots. Caxiuana samples were harvested from trees growing in the throughfall-exclusion, drought-experiment plots. Data were collected in 2011 and 2012. Dataset includes: date of measurement, site ID, plot ID, tree ID (species, tree tag #), xylem pressure, percent loss of conductivity. Air injection method was used. Data reference: Powell et al. (2017) Differences in xylem cavitation resistance and leaf hydraulic traits explain differencesmore » in drought tolerance among mature Amazon rainforest trees. Global Change Biology.« less

Complete Genome Sequences of Two Vesicular Stomatitis Virus Isolates Collected in Mexico.

PubMed

Velazquez-Salinas, Lauro; Isa, Pavel; Pauszek, Steven J; Rodriguez, Luis L

2017-09-14

We report two full-genome sequences of vesicular stomatitis New Jersey virus (VSNJV) obtained by Illumina next-generation sequencing of RNA isolated from epithelial suspensions of cattle naturally infected in Mexico. These genomes represent the first full-genome sequences of vesicular stomatitis New Jersey viruses circulating in Mexico deposited in the GenBank database.

Comparison of different stomatal conductance algorithms for ozone flux modelling [Proceedings

Treesearch

P. Buker; L. D. Emberson; M. R. Ashmore; G. Gerosa; C. Jacobs; W. J. Massman; J. Muller; N. Nikolov; K. Novak; E. Oksanen; D. De La Torre; J. -P. Tuovinen

2006-01-01

The ozone deposition model (D03SE) that has been developed and applied within the EMEP photooxidant model (Emberson et al., 2000, Simpson et al. 2003) currently estimates stomatal ozone flux using a stomatal conductance (gs) model based on the multiplicative algorithm initially developed by Jarvis (1976). This model links gs to environmental and phenological parameters...

Impacts of tree height on leaf hydraulic architecture and stomatal control in Douglas-fir.

Treesearch

D.R. Woodruff; K.A. McCulloh; J.M. Warren; F.C. Meinzer; B.L. Gartner

2007-01-01

We investigated the mechanisms involved in the regulation of stomatal closure in Douglas-fir and evaluated the potential compensatory adjustments in response to increasing tree height. Stomatal closure was initiated at values of leaf water potential corresponding to nearly complete loss of leaf hydraulic conductance. Cryogenic scanning electron microscopic images...

The Plasma Membrane H+-ATPase AHA1 Plays a Major Role in Stomatal Opening in Response to Blue Light1

PubMed Central

Yamauchi, Shota; Takemiya, Atsushi; Sakamoto, Tomoaki; Kurata, Tetsuya; Tsutsumi, Toshifumi

2016-01-01

Stomata open in response to a beam of weak blue light under strong red light illumination. A blue light signal is perceived by phototropins and transmitted to the plasma membrane H+-ATPase that drives stomatal opening. To identify the components in this pathway, we screened for mutants impaired in blue light-dependent stomatal opening. We analyzed one such mutant, provisionally named blus2 (blue light signaling2), and found that stomatal opening in leaves was impaired by 65%, although the magnitude of red light-induced opening was not affected. Blue light-dependent stomatal opening in the epidermis and H+ pumping in guard cell protoplasts were inhibited by 70% in blus2. Whole-genome resequencing identified a mutation in the AHA1 gene of the mutant at Gly-602. T-DNA insertion mutants of AHA1 exhibited a similar phenotype to blus2; this phenotype was complemented by the AHA1 gene. We renamed blus2 as aha1-10. T-DNA insertion mutants of AHA2 and AHA5 did not show any impairment in stomatal response, although the transcript levels of AHA2 and AHA5 were higher than those of AHA1 in wild-type guard cells. Stomata in ost2, a constitutively active AHA1 mutant, did not respond to blue light. A decreased amount of H+-ATPase in aha1-10 accounted for the reduced stomatal blue light responses and the decrease was likely caused by proteolysis of misfolded AHA1. From these results, we conclude that AHA1 plays a major role in blue light-dependent stomatal opening in Arabidopsis and that the mutation made the AHA1 protein unstable in guard cells. PMID:27261063

The Plasma Membrane H+-ATPase AHA1 Plays a Major Role in Stomatal Opening in Response to Blue Light.

PubMed

Yamauchi, Shota; Takemiya, Atsushi; Sakamoto, Tomoaki; Kurata, Tetsuya; Tsutsumi, Toshifumi; Kinoshita, Toshinori; Shimazaki, Ken-Ichiro

2016-08-01

Stomata open in response to a beam of weak blue light under strong red light illumination. A blue light signal is perceived by phototropins and transmitted to the plasma membrane H(+)-ATPase that drives stomatal opening. To identify the components in this pathway, we screened for mutants impaired in blue light-dependent stomatal opening. We analyzed one such mutant, provisionally named blus2 (blue light signaling2), and found that stomatal opening in leaves was impaired by 65%, although the magnitude of red light-induced opening was not affected. Blue light-dependent stomatal opening in the epidermis and H(+) pumping in guard cell protoplasts were inhibited by 70% in blus2 Whole-genome resequencing identified a mutation in the AHA1 gene of the mutant at Gly-602. T-DNA insertion mutants of AHA1 exhibited a similar phenotype to blus2; this phenotype was complemented by the AHA1 gene. We renamed blus2 as aha1-10 T-DNA insertion mutants of AHA2 and AHA5 did not show any impairment in stomatal response, although the transcript levels of AHA2 and AHA5 were higher than those of AHA1 in wild-type guard cells. Stomata in ost2, a constitutively active AHA1 mutant, did not respond to blue light. A decreased amount of H(+)-ATPase in aha1-10 accounted for the reduced stomatal blue light responses and the decrease was likely caused by proteolysis of misfolded AHA1. From these results, we conclude that AHA1 plays a major role in blue light-dependent stomatal opening in Arabidopsis and that the mutation made the AHA1 protein unstable in guard cells. © 2016 American Society of Plant Biologists. All Rights Reserved.

Stomatal cell wall composition: distinctive structural patterns associated with different phylogenetic groups

PubMed Central

Shtein, Ilana; Shelef, Yaniv; Marom, Ziv; Zelinger, Einat; Schwartz, Amnon; Popper, Zoë A.; Bar-On, Benny

2017-01-01

Background and Aims Stomatal morphology and function have remained largely conserved throughout ∼400 million years of plant evolution. However, plant cell wall composition has evolved and changed. Here stomatal cell wall composition was investigated in different vascular plant groups in attempt to understand their possible effect on stomatal function. Methods A renewed look at stomatal cell walls was attempted utilizing digitalized polar microscopy, confocal microscopy, histology and a numerical finite-elements simulation. The six species of vascular plants chosen for this study cover a broad structural, ecophysiological and evolutionary spectrum: ferns (Asplenium nidus and Platycerium bifurcatum) and angiosperms (Arabidopsis thaliana and Commelina erecta) with kidney-shaped stomata, and grasses (angiosperms, family Poaceae) with dumbbell-shaped stomata (Sorghum bicolor and Triticum aestivum). Key Results Three distinct patterns of cellulose crystallinity in stomatal cell walls were observed: Type I (kidney-shaped stomata, ferns), Type II (kidney-shaped stomata, angiosperms) and Type III (dumbbell-shaped stomata, grasses). The different stomatal cell wall attributes investigated (cellulose crystallinity, pectins, lignin, phenolics) exhibited taxon-specific patterns, with reciprocal substitution of structural elements in the end-walls of kidney-shaped stomata. According to a numerical bio-mechanical model, the end walls of kidney-shaped stomata develop the highest stresses during opening. Conclusions The data presented demonstrate for the first time the existence of distinct spatial patterns of varying cellulose crystallinity in guard cell walls. It is also highly intriguing that in angiosperms crystalline cellulose appears to have replaced lignin that occurs in the stomatal end-walls of ferns serving a similar wall strengthening function. Such taxon-specific spatial patterns of cell wall components could imply different biomechanical functions, which in turn could be a consequence of differences in environmental selection along the course of plant evolution. PMID:28158449

Overexpression of plasma membrane H+-ATPase in guard cells promotes light-induced stomatal opening and enhances plant growth.

PubMed

Wang, Yin; Noguchi, Ko; Ono, Natsuko; Inoue, Shin-ichiro; Terashima, Ichiro; Kinoshita, Toshinori

2014-01-07

Stomatal pores surrounded by a pair of guard cells in the plant epidermis control gas exchange between plants and the atmosphere in response to light, CO2, and the plant hormone abscisic acid. Light-induced stomatal opening is mediated by at least three key components: the blue light receptor phototropin (phot1 and phot2), plasma membrane H(+)-ATPase, and plasma membrane inward-rectifying K(+) channels. Very few attempts have been made to enhance stomatal opening with the goal of increasing photosynthesis and plant growth, even though stomatal resistance is thought to be the major limiting factor for CO2 uptake by plants. Here, we show that transgenic Arabidopsis plants overexpressing H(+)-ATPase using the strong guard cell promoter GC1 showed enhanced light-induced stomatal opening, photosynthesis, and plant growth. The transgenic plants produced larger and increased numbers of rosette leaves, with ∼42-63% greater fresh and dry weights than the wild type in the first 25 d of growth. The dry weights of total flowering stems of 45-d-old transgenic plants, including seeds, siliques, and flowers, were ∼36-41% greater than those of the wild type. In addition, stomata in the transgenic plants closed normally in response to darkness and abscisic acid. In contrast, the overexpression of phototropin or inward-rectifying K(+) channels in guard cells had no effect on these phenotypes. These results demonstrate that stomatal aperture is a limiting factor in photosynthesis and plant growth, and that manipulation of stomatal opening by overexpressing H(+)-ATPase in guard cells is useful for the promotion of plant growth.

Stomatal Function Requires Pectin De-methyl-esterification of the Guard Cell Wall

DOE PAGES

Amsbury, Sam; Hunt, Lee; Elhaddad, Nagat; ...

2016-10-06

Stomatal opening and closure depends on changes in turgor pressure acting within guard cells to alter cell shape. The extent of these shape changes is limited by the mechanical properties of the cells, which will be largely dependent on the structure of the cell walls. Although it has long been observed that guard cells are anisotropic due to differential thickening and the orientation of cellulose microfibrils, our understanding of the composition of the cell wall that allows them to undergo repeated swelling and deflation remains surprisingly poor. Here, we show that the walls of guard cells are rich in un-esterified pectins.more » We identify a pectin methylesterase gene, PME6, which is highly expressed in guard cells and required for stomatal function. pme6-1 mutant guard cells have walls enriched in methyl-esterified pectin and show a decreased dynamic range in response to triggers of stomatal opening/closure, including elevated osmoticum, suggesting that abrogation of stomatal function reflects a mechanical change in the guard cell wall. Altered stomatal function leads to increased conductance and evaporative cooling, as well as decreased plant growth. The growth defect of the  pme6-1 mutant is rescued by maintaining the plants in elevated CO 2, substantiating gas exchange analyses, indicating that the mutant stomata can bestow an improved assimilation rate. Restoration of PME6 rescues guard cell wall pectin methyl-esterification status, stomatal function, and plant growth. Our results establish a link between gene expression in guard cells and their cell wall properties, with a corresponding effect on stomatal function and plant physiology.« less

Stomatal action directly feeds back on leaf turgor: new insights into the regulation of the plant water status from non-invasive pressure probe measurements.

PubMed

Ache, Peter; Bauer, Hubert; Kollist, Hannes; Al-Rasheid, Khaled A S; Lautner, Silke; Hartung, Wolfram; Hedrich, Rainer

2010-06-01

Uptake of CO(2) by the leaf is associated with loss of water. Control of stomatal aperture by volume changes of guard cell pairs optimizes the efficiency of water use. Under water stress, the protein kinase OPEN STOMATA 1 (OST1) activates the guard-cell anion release channel SLOW ANION CHANNEL-ASSOCIATED 1 (SLAC1), and thereby triggers stomatal closure. Plants with mutated OST1 and SLAC1 are defective in guard-cell turgor regulation. To study the effect of stomatal movement on leaf turgor using intact leaves of Arabidopsis, we used a new pressure probe to monitor transpiration and turgor pressure simultaneously and non-invasively. This probe permits routine easy access to parameters related to water status and stomatal conductance under physiological conditions using the model plant Arabidopsis thaliana. Long-term leaf turgor pressure recordings over several weeks showed a drop in turgor during the day and recovery at night. Thus pressure changes directly correlated with the degree of plant transpiration. Leaf turgor of wild-type plants responded to CO(2), light, humidity, ozone and abscisic acid (ABA) in a guard cell-specific manner. Pressure probe measurements of mutants lacking OST1 and SLAC1 function indicated impairment in stomatal responses to light and humidity. In contrast to wild-type plants, leaves from well-watered ost1 plants exposed to a dry atmosphere wilted after light-induced stomatal opening. Experiments with open stomata mutants indicated that the hydraulic conductance of leaf stomata is higher than that of the root-shoot continuum. Thus leaf turgor appears to rely to a large extent on the anion channel activity of autonomously regulated stomatal guard cells.

Stomatal control in tomato with ABA-deficient roots: response of grafted plants to soil drying.

PubMed

Holbrook, N Michele; Shashidhar, V R; James, Richard A; Munns, Rana

2002-06-01

The hypothesis that ABA produced by roots in drying soil is responsible for stomatal closure was tested with grafted plants constructed from the ABA-deficient tomato mutants, sitiens and flacca and their near-isogenic wild-type parent. Three types of experiments were conducted. In the first type, reciprocal grafts were made between the wild type and sitiens or flacca. Stomatal conductance accorded with the genotype of the shoot, not the root. Stomates closed in all of the grafted plants in response to soil drying, regardless of the root genotype, i.e. regardless of the ability of the roots to produce ABA. In the second type of experiment, wild-type shoots were grafted onto a split-root system consisting of one wild-type root grafted to one mutant (flacca or sitiens) root. Water was withheld from one root system, while the other was watered well so that the shoots did not experience any decline in water potential or loss of turgor. Stomates closed to a similar extent when water was withheld from the mutant roots or the wild-type roots. In the third type of experiment, grafted plants with wild-type shoots and either wild-type or sitiens roots were established in pots that could be placed inside a pressure chamber, and the pressure increased as the soil dried so that the shoots remained fully turgid throughout. Stomates closed as the soil dried, regardless of whether the roots were wild type or sitiens. These experiments demonstrate that stomatal closure in response to soil drying can occur in the absence of leaf water deficit, and does not require ABA production by roots. A chemical signal from roots leading to a change in apoplastic ABA levels in leaves may be responsible for the stomatal closure.

Stomatal Function Requires Pectin De-methyl-esterification of the Guard Cell Wall

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

Amsbury, Sam; Hunt, Lee; Elhaddad, Nagat

Stomatal opening and closure depends on changes in turgor pressure acting within guard cells to alter cell shape. The extent of these shape changes is limited by the mechanical properties of the cells, which will be largely dependent on the structure of the cell walls. Although it has long been observed that guard cells are anisotropic due to differential thickening and the orientation of cellulose microfibrils, our understanding of the composition of the cell wall that allows them to undergo repeated swelling and deflation remains surprisingly poor. Here, we show that the walls of guard cells are rich in un-esterified pectins.more » We identify a pectin methylesterase gene, PME6, which is highly expressed in guard cells and required for stomatal function. pme6-1 mutant guard cells have walls enriched in methyl-esterified pectin and show a decreased dynamic range in response to triggers of stomatal opening/closure, including elevated osmoticum, suggesting that abrogation of stomatal function reflects a mechanical change in the guard cell wall. Altered stomatal function leads to increased conductance and evaporative cooling, as well as decreased plant growth. The growth defect of the  pme6-1 mutant is rescued by maintaining the plants in elevated CO 2, substantiating gas exchange analyses, indicating that the mutant stomata can bestow an improved assimilation rate. Restoration of PME6 rescues guard cell wall pectin methyl-esterification status, stomatal function, and plant growth. Our results establish a link between gene expression in guard cells and their cell wall properties, with a corresponding effect on stomatal function and plant physiology.« less

Stomatal vs. genome size in angiosperms: the somatic tail wagging the genomic dog?

PubMed Central

Hodgson, J. G.; Sharafi, M.; Jalili, A.; Díaz, S.; Montserrat-Martí, G.; Palmer, C.; Cerabolini, B.; Pierce, S.; Hamzehee, B.; Asri, Y.; Jamzad, Z.; Wilson, P.; Raven, J. A.; Band, S. R.; Basconcelo, S.; Bogard, A.; Carter, G.; Charles, M.; Castro-Díez, P.; Cornelissen, J. H. C.; Funes, G.; Jones, G.; Khoshnevis, M.; Pérez-Harguindeguy, N.; Pérez-Rontomé, M. C.; Shirvany, F. A.; Vendramini, F.; Yazdani, S.; Abbas-Azimi, R.; Boustani, S.; Dehghan, M.; Guerrero-Campo, J.; Hynd, A.; Kowsary, E.; Kazemi-Saeed, F.; Siavash, B.; Villar-Salvador, P.; Craigie, R.; Naqinezhad, A.; Romo-Díez, A.; de Torres Espuny, L.; Simmons, E.

2010-01-01

Background and Aims Genome size is a function, and the product, of cell volume. As such it is contingent on ecological circumstance. The nature of ‘this ecological circumstance’ is, however, hotly debated. Here, we investigate for angiosperms whether stomatal size may be this ‘missing link’: the primary determinant of genome size. Stomata are crucial for photosynthesis and their size affects functional efficiency. Methods Stomatal and leaf characteristics were measured for 1442 species from Argentina, Iran, Spain and the UK and, using PCA, some emergent ecological and taxonomic patterns identified. Subsequently, an assessment of the relationship between genome-size values obtained from the Plant DNA C-values database and measurements of stomatal size was carried out. Key Results Stomatal size is an ecologically important attribute. It varies with life-history (woody species < herbaceous species < vernal geophytes) and contributes to ecologically and physiologically important axes of leaf specialization. Moreover, it is positively correlated with genome size across a wide range of major taxa. Conclusions Stomatal size predicts genome size within angiosperms. Correlation is not, however, proof of causality and here our interpretation is hampered by unexpected deficiencies in the scientific literature. Firstly, there are discrepancies between our own observations and established ideas about the ecological significance of stomatal size; very large stomata, theoretically facilitating photosynthesis in deep shade, were, in this study (and in other studies), primarily associated with vernal geophytes of unshaded habitats. Secondly, the lower size limit at which stomata can function efficiently, and the ecological circumstances under which these minute stomata might occur, have not been satisfactorally resolved. Thus, our hypothesis, that the optimization of stomatal size for functional efficiency is a major ecological determinant of genome size, remains unproven. PMID:20375204

Stomatal Function Requires Pectin De-methyl-esterification of the Guard Cell Wall.

PubMed

Amsbury, Sam; Hunt, Lee; Elhaddad, Nagat; Baillie, Alice; Lundgren, Marjorie; Verhertbruggen, Yves; Scheller, Henrik V; Knox, J Paul; Fleming, Andrew J; Gray, Julie E

2016-11-07

Stomatal opening and closure depends on changes in turgor pressure acting within guard cells to alter cell shape [1]. The extent of these shape changes is limited by the mechanical properties of the cells, which will be largely dependent on the structure of the cell walls. Although it has long been observed that guard cells are anisotropic due to differential thickening and the orientation of cellulose microfibrils [2], our understanding of the composition of the cell wall that allows them to undergo repeated swelling and deflation remains surprisingly poor. Here, we show that the walls of guard cells are rich in un-esterified pectins. We identify a pectin methylesterase gene, PME6, which is highly expressed in guard cells and required for stomatal function. pme6-1 mutant guard cells have walls enriched in methyl-esterified pectin and show a decreased dynamic range in response to triggers of stomatal opening/closure, including elevated osmoticum, suggesting that abrogation of stomatal function reflects a mechanical change in the guard cell wall. Altered stomatal function leads to increased conductance and evaporative cooling, as well as decreased plant growth. The growth defect of the pme6-1 mutant is rescued by maintaining the plants in elevated CO 2 , substantiating gas exchange analyses, indicating that the mutant stomata can bestow an improved assimilation rate. Restoration of PME6 rescues guard cell wall pectin methyl-esterification status, stomatal function, and plant growth. Our results establish a link between gene expression in guard cells and their cell wall properties, with a corresponding effect on stomatal function and plant physiology. Copyright © 2016 The Authors. Published by Elsevier Ltd.. All rights reserved.

Coordination and transport of water and carbohydrates in the coupled soil-root-xylem-phloem leaf system

NASA Astrophysics Data System (ADS)

Katul, Gabriel; Huang, Cheng-Wei

2017-04-01

In response to varying environmental conditions, stomatal pores act as biological valves that dynamically adjust their size thereby determining the rate of CO2 assimilation and water loss (i.e., transpiration) to the atmosphere. Although the significance of this biotic control on gas exchange is rarely disputed, representing parsimoniously all the underlying mechanisms responsible for stomatal kinetics remain a subject of some debate. It has been conjectured that stomatal control in seed plants (i.e., angiosperm and gymnosperm) represents a compromise between biochemical demand for CO2 and prevention of excessive water loss. This view has been amended at the whole-plant level, where xylem hydraulics and sucrose transport efficiency in phloem appear to impose additional constraints on gas exchange. If such additional constraints impact stomatal opening and closure, then seed plants may have evolved coordinated photosynthetic-hydraulic-sugar transporting machinery that confers some competitive advantages in fluctuating environmental conditions. Thus, a stomatal optimization model that explicitly considers xylem hydraulics and maximum sucrose transport is developed to explore this coordination in the leaf-xylem-phloem system. The model is then applied to progressive drought conditions. The main findings from the model calculations are that (1) the predicted stomatal conductance from the conventional stomatal optimization theory at the leaf and the newly proposed models converge, suggesting a tight coordination in the leaf-xylem-phloem system; (2) stomatal control is mainly limited by the water supply function of the soil-xylem hydraulic system especially when the water flux through the transpiration stream is significantly larger than water exchange between xylem and phloem; (3) thus, xylem limitation imposed on the supply function can be used to differentiate species with different water use strategy across the spectrum of isohydric to anisohydric behavior.

Stomatal movements in laurophyllous plants

NASA Astrophysics Data System (ADS)

Pautov, A. A.; Bauer, S. M.; Ivanova, O. V.; Sapach, Y. O.; Krylova, E. G.

2018-05-01

Stomata are the structural elements of plant epidermis which control transpiration and gas exchange. Each stoma consists of two guard cells divided by the stomatal aperture. These cells are capable of reversible deformations determining the width of aperture. It is known that these deformations depend on the value of turgor pressure in the guard cells and on the structure of their walls. In this work, the influence of the outer tangential wall geometry of the guard cells on stomatal movements is estimated by means of the finite element method in the ANSYS software. The application of modelling has shown that cuticular outgrowths on the tangential walls influence the degree and pattern of guard cell deformations. The outgrowths prevent wide opening of the stomatal aperture and cause its sinking deep into leaf epidermis. The functional significance of such stomatal movements is discussed. It is deduced that the discovered phenomenon had great importance to the survival of laurophyllous plants in conditions of aridization.

Stomatal innovation and the rise of seed plants.

PubMed

McAdam, Scott A M; Brodribb, Timothy J

2012-01-01

Stomatal valves on the leaves of vascular plants not only prevent desiccation but also dynamically regulate water loss to maintain efficient daytime water use. This latter process involves sophisticated active control of stomatal aperture that may be absent from early-branching plant clades. To test this hypothesis, we compare the stomatal response to light intensity in 13 species of ferns and lycophytes with a diverse sample of seed plants to determine whether the capacity to optimise water use is an ancestral or derived feature of stomatal physiology. We found that in seed plants, the ratio of photosynthesis to water use remained high and constant at different light intensities, but fern and lycophyte stomata were incapable of sustaining homeostatic water use efficiency. We conclude that efficient water use in early seed plants provided them with a competitive advantage that contributed to the decline of fern and lycophyte dominated-ecosystems in the late Paleozoic. © 2011 Blackwell Publishing Ltd/CNRS.

Developmental priming of stomatal sensitivity to abscisic acid by leaf microclimate.

PubMed

Pantin, Florent; Renaud, Jeanne; Barbier, François; Vavasseur, Alain; Le Thiec, Didier; Rose, Christophe; Bariac, Thierry; Casson, Stuart; McLachlan, Deirdre H; Hetherington, Alistair M; Muller, Bertrand; Simonneau, Thierry

2013-09-23

Plant water loss and CO2 uptake are controlled by valve-like structures on the leaf surface known as stomata. Stomatal aperture is regulated by hormonal and environmental signals. We show here that stomatal sensitivity to the drought hormone abscisic acid (ABA) is acquired during leaf development by exposure to an increasingly dryer atmosphere in the rosette plant Arabidopsis. Young leaves, which develop in the center of the rosette, do not close in response to ABA. As the leaves increase in size, they are naturally exposed to increasingly dry air as a consequence of the spatial arrangement of the leaves, and this triggers the acquisition of ABA sensitivity. Interestingly, stomatal ABA sensitivity in young leaves is rapidly restored upon water stress. These findings shed new light on how plant architecture and stomatal physiology have coevolved to optimize carbon gain against water loss in stressing environments. Copyright © 2013 Elsevier Ltd. All rights reserved.

Infection of guinea pigs with vesicular stomatitis New Jersey virus Transmitted by Culicoides sonorensis (Diptera: Ceratopogonidae).

PubMed

Pérez De León, Adalberto A; O'Toole, Donal; Tabachnick, Walter J

2006-05-01

Intrathoracically inoculated Culicoides sonorensis Wirth & Jones were capable of transmitting vesicular stomatitis New Jersey virus (family Rhabdoviridae, genus Vesiculovirus, VSNJV) during blood feeding on the abdomen of six guinea pigs. None of the guinea pigs infected in this manner developed clinical signs of vesicular stomatitis despite seroconversion for VSNJV. Guinea pigs infected by intradermal inoculations of VSNJV in the abdomen also failed to develop clinical signs of vesicular stomatitis. Three guinea pigs given intradermal inoculations of VSNJV in the foot pad developed lesions typical of vesicular stomatitis. Transmission by the bite of C. sonorensis may have facilitated guinea pig infection with VSNJV because a single infected C. sonorensis caused seroconversion and all guinea pigs infected by insect bite seroconverted compared with 50% of the guinea pigs infected by intradermal inoculation with a higher titer VSNJV inoculum. The role of C. sonorensis in the transmission of VSNJV is discussed.

Ecohydrological optimality in the Northeast China Transect

NASA Astrophysics Data System (ADS)

Cong, Zhentao; Li, Qinshu; Mo, Kangle; Zhang, Lexin; Shen, Hong

2017-05-01

The Northeast China Transect (NECT) is one of the International Geosphere-Biosphere Program (IGBP) terrestrial transects, where there is a significant precipitation gradient from east to west, as well as a vegetation transition of forest-grassland-desert. It is remarkable to understand vegetation distribution and dynamics under climate change in this transect. We take canopy cover (M), derived from Normalized Difference Vegetation Index (NDVI), as an index to describe the properties of vegetation distribution and dynamics in the NECT. In Eagleson's ecohydrological optimality theory, the optimal canopy cover (M*) is determined by the trade-off between water supply depending on water balance and water demand depending on canopy transpiration. We apply Eagleson's ecohydrological optimality method in the NECT based on data from 2000 to 2013 to get M*, which is compared with M from NDVI to further discuss the sensitivity of M* to vegetation properties and climate factors. The result indicates that the average M* fits the actual M well (for forest, M* = 0.822 while M = 0.826; for grassland, M* = 0.353 while M = 0.352; the correlation coefficient between M and M* is 0.81). Results of water balance also match the field-measured data in the references. The sensitivity analyses show that M* decreases with the increase of leaf area index (LAI), stem fraction and temperature, while it increases with the increase of leaf angle and precipitation amount. Eagleson's ecohydrological optimality method offers a quantitative way to understand the impacts of climate change on canopy cover and provides guidelines for ecorestoration projects.

Reading the Leaves’ Palm: Leaf Traits and Herbivory along the Microclimatic Gradient of Forest Layers

PubMed Central

Entling, Martin H.; Mantilla-Contreras, Jasmin

2017-01-01

Microclimate in different positions on a host plant has strong direct effects on herbivores. But little is known about indirect effects due to changes of leaf traits. We hypothesized that herbivory increases from upper canopy to lower canopy and understory due to a combination of direct and indirect pathways. Furthermore, we hypothesized that herbivory in the understory differs between tree species in accordance with their leaf traits. We investigated herbivory by leaf chewing insects along the vertical gradient of mixed deciduous forest stands on the broad-leaved tree species Fagus sylvatica L. (European beech) with study sites located along a 140 km long transect. Additionally, we studied juvenile Acer pseudoplatanus L. (sycamore maple) and Carpinus betulus L. (hornbeam) individuals within the understory as a reference of leaf traits in the same microclimate. Lowest levels of herbivory were observed in upper canopies, where temperatures were highest. Temperature was the best predictor for insect herbivory across forest layers in our study. However, the direction was opposite to the generally known positive relationship. Herbivory also varied between the three tree species with lowest levels for F. sylvatica. Leaf carbon content was highest for F. sylvatica and probably indicates higher amounts of phenolic defense compounds. We conclude that the effect of temperature must have been indirect, whereby the expected higher herbivory was suppressed due to unfavorable leaf traits (lower nitrogen content, higher toughness and carbon content) of upper canopy leaves compared to the understory. PMID:28099483

Diel trends in stomatal response to ozone and water deficit: a unique relationship of midday values to growth and allometry in Pima cotton?

Treesearch

D. A. Grantz; R. Paudel; H.-B. Vu; A. Shrestha; Nancy Grulke; L. J. De Kok

2015-01-01

Plant responses to ozone (O3) and water deficit (WD) are commonly observed, although less is known about their interaction. Stomatal conductance (gs) is both an impact of these stressors and a protective response to them. Stomatal closure reduces inward flux of O3 and outward flux...

Complete Genome Sequences of Two Vesicular Stomatitis Virus Isolates Collected in Mexico

PubMed Central

Isa, Pavel; Pauszek, Steven J.; Rodriguez, Luis L.

2017-01-01

ABSTRACT We report two full-genome sequences of vesicular stomatitis New Jersey virus (VSNJV) obtained by Illumina next-generation sequencing of RNA isolated from epithelial suspensions of cattle naturally infected in Mexico. These genomes represent the first full-genome sequences of vesicular stomatitis New Jersey viruses circulating in Mexico deposited in the GenBank database. PMID:28912331

Height-related trends in stomatal sensitivity to leaf-to-air vapour pressure deficit in a tall conifer

Treesearch

D.R. Woodruff; F.C. Meinzer; K.A. McCulloh

2010-01-01

Stomatal responses to leaf-to-air vapour pressure deficit (LVPD), leaf water potential components, and cuticular properties were characterized for Douglas-fir (Pseudotsuga menziesii) foliage collected from treetops along a height gradient from 5 m to 58 m in order to explore height-related trends in stomatal sensitivity to LVPD and to investigate...

Daily changes in VPD during leaf development in high air humidity increase the stomatal responsiveness to darkness and dry air.

PubMed

Arve, Louise E; Kruse, Ole Mathis Opstad; Tanino, Karen K; Olsen, Jorunn E; Futsæther, Cecilia; Torre, Sissel

2017-04-01

Previous studies have shown that plants developed under high relative air humidity (RH>85%) develop malfunctioning stomata and therefor have increased transpiration and reduced desiccation tolerance when transferred to lower RH conditions and darkness. In this study, plants developed at high RH were exposed to daily VPD fluctuations created by changes in temperature and/or RH to evaluate the potential improvements in stomatal functioning. Daily periods with an 11°C temperature increase and consequently a VPD increase (vpd: 0.36-2.37KPa) reduced the stomatal apertures and improved the stomatal functionality and desiccation tolerance of the rosette plant Arabidopsis thaliana. A similar experiment was performed with only a 4°C temperature increase and/or a RH decrease on tomato. The results showed that a daily change in VPD (vpd: 0.36-1.43KPa) also resulted in improved stomatal responsiveness and decreased water usage during growth. In tomato, the most effective treatment to increase the stomatal responsiveness to darkness as a signal for closure was daily changes in RH without a temperature increase. Copyright © 2017 Elsevier GmbH. All rights reserved.

Variation in waterlogging-triggered stomatal behavior contributes to changes in the cold acclimation process in prehardened Lolium perenne and Festuca pratensis.

PubMed

Jurczyk, Barbara; Pociecha, Ewa; Janowiak, Franciszek; Kabała, Dawid; Rapacz, Marcin

2016-12-01

According to predicted changes in climate, waterlogging events may occur more frequently in the future during autumn and winter at high latitudes of the Northern Hemisphere. If excess soil water coincides with the process of cold acclimation for plants, winter survival may potentially be affected. The effects of waterlogging during cold acclimation on stomatal aperture, relative water content, photochemical activity of photosystem II, freezing tolerance and plant regrowth after freezing were compared for two prehardened overwintering forage grasses, Lolium perenne and Festuca pratensis. The experiment was performed to test the hypothesis that changes in photochemical activity initiated by waterlogging-triggered modifications in the stomatal aperture contribute to changes in freezing tolerance. Principal component analysis showed that waterlogging activated different adaptive strategies in the two species studied. The increased freezing tolerance of F. pratensis was associated with increased photochemical activity connected with stomatal opening, whereas freezing tolerance of L. perenne was associated with a decrease in stomatal aperture. In conclusion, waterlogging-triggered stomatal behavior contributed to the efficiency of the cold acclimation process in L. perenne and F. pratensis. Copyright © 2016 Elsevier Masson SAS. All rights reserved.

Constitutive activation of a plasma membrane H(+)-ATPase prevents abscisic acid-mediated stomatal closure.

PubMed

Merlot, Sylvain; Leonhardt, Nathalie; Fenzi, Francesca; Valon, Christiane; Costa, Miguel; Piette, Laurie; Vavasseur, Alain; Genty, Bernard; Boivin, Karine; Müller, Axel; Giraudat, Jérôme; Leung, Jeffrey

2007-07-11

Light activates proton (H(+))-ATPases in guard cells, to drive hyperpolarization of the plasma membrane to initiate stomatal opening, allowing diffusion of ambient CO(2) to photosynthetic tissues. Light to darkness transition, high CO(2) levels and the stress hormone abscisic acid (ABA) promote stomatal closing. The overall H(+)-ATPase activity is diminished by ABA treatments, but the significance of this phenomenon in relationship to stomatal closure is still debated. We report two dominant mutations in the OPEN STOMATA2 (OST2) locus of Arabidopsis that completely abolish stomatal response to ABA, but importantly, to a much lesser extent the responses to CO(2) and darkness. The OST2 gene encodes the major plasma membrane H(+)-ATPase AHA1, and both mutations cause constitutive activity of this pump, leading to necrotic lesions. H(+)-ATPases have been traditionally assumed to be general endpoints of all signaling pathways affecting membrane polarization and transport. Our results provide evidence that AHA1 is a distinct component of an ABA-directed signaling pathway, and that dynamic downregulation of this pump during drought is an essential step in membrane depolarization to initiate stomatal closure.

Water limitations to carbon exchange in old-growth and young ponderosa pine stands.

PubMed

Irvine, J; Law, B E; Anthoni, P M; Meinzer, F C

2002-02-01

We investigated the impact of seasonal soil water deficit on the processes driving net ecosystem exchange of carbon (NEE) in old-growth and recently regenerating ponderosa pine (Pinus ponderosa Doug. ex Laws.) stands in Oregon. We measured seasonal patterns of transpiration, canopy conductance and NEE, as well as soil water, soil temperature and soil respiration. The old-growth stand (O) included two primary age classes (50 and 250 years), had a leaf area index (LAI) of 2.1 and had never been logged. The recently regenerating stand (Y) consisted predominantly of 14-year-old ponderosa pine with an LAI of 1.0. Both stands experienced similar meteorological conditions with moderately cold wet winters and hot dry summers. By August, soil volumetric water content within the upper 30 cm had declined to a seasonal minimum of 0.07 at both sites. Between April and June, both stands showed similar rates of transpiration peaking at 0.96 mm day(-1); thereafter, trees at the Y site showed increasing drought stress with canopy stomatal resistance increasing 6-fold by mid-August relative to values for trees at the O site. Over the same period, predawn water potential (psi(pd)) of trees at the Y site declined from -0.54 to -1.24 MPa, whereas psi(pd) of trees at the O site remained greater than -0.8 MPa throughout the season. Soil respiration at the O site showed a strong seasonal correlation with soil temperature with no discernible constraints imposed by declining soil water. In contrast, soil respiration at the Y site peaked before seasonal maximal soil temperatures and declined thereafter with declining soil water. No pronounced seasonal pattern in daytime NEE was observed at either site between April and September. At the Y site this behavior was driven by concurrent soil water limitations on soil respiration and assimilation, whereas there was no evidence of seasonal soil water limitations on either process at the O site.

Withstanding a record drought: Dry season sap flow and safety margins of canopy epiphytes in three sites along an elevation gradient in a tropical montane cloud forest

NASA Astrophysics Data System (ADS)

Gotsch, S. G.; Darby, A.; Glunk, A.; Murray, J.; Draguljic, D.

2016-12-01

Tropical montane cloud forests (TMCFs) are projected to experience shifts in microclimate due to changes in precipitation patterns and cloud base heights. Understanding how the TMCF will be affected by such changes is critical since these forests harbor a great number of endemic species and the intact forest plays an important role in local and regional hydrology. The epiphyte community is one of the characteristic components of this unique ecosystem. Epiphytes contribute greatly to the biomass and diversity of the forest, and play an important role in the TMCF water cycle. The ecosystem role played by the epiphyte community may be lost if these species, which lack roots to the ground, cannot withstand projected changes in climate. We measured dry season sap flow in canopy epiphytes in three sites along an elevation gradient, in Monteverde Costa Rica during an extreme drought event. In addition, we measured predawn and midday leaf water potentials, and dry season pressure-volume curves on focal species. We found that during a month-long dry period, species in all sites reduced transpiration considerably, and for a two-week period, sap flow rates were close to zero. During this time, predawn and midday leaf water potentials remained high (> -1.0 MPa) due to the utilization of stored leaf water and strong stomatal regulation. At the end of the dry season, midday leaf water potentials were approximately 2x lower in the driest versus the wettest site (AVG: -0.94 vs. -0.47 MPa) although hydraulic safety margins were greater at the driest sites. Our results indicate that epiphyte communities vary in their water use strategies and that the epiphyte community in wetter sites is more likely to experience hydraulic failure if there are increases in the number of days without precipitation and/or increases in temperature.