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1

Accounting for variability in soil microbial communities of temperate upland grassland ecosystems  

Microsoft Academic Search

This study aimed to determine the factors which regulate soil microbial community organisation and function in temperate upland grassland ecosystems. Soil microbial biomass (Cmic), activity (respiration and potential carbon utilisation) and community structure (phospholipid fatty acid (PLFA) analysis, culturing and community level physiological profiles (CLPP) (Biolog®)) were measured across a gradient of three upland grassland types; Festuca–Agrostis–Galium grassland (unimproved grassland,

S. J. Grayston; G. S. Griffith; J. L. Mawdsley; C. D. Campbell; R. D. Bardgett

2001-01-01

2

Carbon Dioxide and Energy Exchanges in a Temperate Grassland Ecosystem  

Microsoft Academic Search

A micrometeorological study was conducted from May to October in 1987 to evaluate the surface exchanges of carbon dioxide and energy at a temperate grassland site in northeastern Kansas. The fluxes of CO_2 (F_{rm c}), latent heat (LE), sensible heat (H) and momentum were measured using the eddy correlation technique. Pertinent microclimatic, plant and soil variables were also monitored through

Joon Kim

1990-01-01

3

Carbon Dioxide and Energy Exchanges in a Temperate Grassland Ecosystem.  

NASA Astrophysics Data System (ADS)

A micrometeorological study was conducted from May to October in 1987 to evaluate the surface exchanges of carbon dioxide and energy at a temperate grassland site in northeastern Kansas. The fluxes of CO_2 (F_{rm c}), latent heat (LE), sensible heat (H) and momentum were measured using the eddy correlation technique. Pertinent microclimatic, plant and soil variables were also monitored through the season. The prairie was dominated by three C_4 grass species: Andropogon gerardii, Sorghastrum nutans, Panicum virgatum. The energy partitioning was controlled mainly by net radiation (R_{rm n} ) and by soil water availability. On sunny days with no moisture stress, about 58 to 83% of R_ {rm n} was consumed in evapotranspiration during midday. The midday canopy surface conductance averaged about 15 mm s^{-1}. Under moisture stress conditions the magnitude of midday LE/R _{rm n} ranged from 0.35 to 0.45 whereas the canopy surface conductance was less than 3 mm s^{-1}. Considerable daily and seasonal variability of Co_2 flux was observed. The midday F_{rm c} reached a seasonal peak of 1.3 mg m^{-2} (ground area) s^{-1} in early July and was near zero during a dry period in late July. The dependence of the daytime F_ {rm c} on pertinent controlling variables (e.g., light, temperature, vapor pressure deficit, soil water availability, and canopy surface conductance) was investigated. The magnitude of nocturnal F _{rm c}(soil plus plant respiration) averaged 0.4 mg m^{-2}s ^{-1} under well-watered conditions and was about 0.2 mg m^{ -2}s^{-1} during the dry period. A leaf stomatal conductance model was developed for the major grass species in this ecosystem, and was scaled up to a canopy level using a canopy radiative transfer model. Comparisons with field measurements indicated that the model provided reasonable estimates of canopy stomatal conductance for well-watered conditions. The modelled half-hourly values of LE agreed well(generally within 5%) with those measured, under these conditions. A biochemical leaf photosynthesis model was adapted to the major grass species studied here, and was scaled up to a canopy level. Comparisons with field measurements showed that the model realistically simulated the magnitudes and the diurnal variations of canopy photosynthesis under well-watered conditions. Although the modelled canopy photosynthesis overestimated the measured values by 0.2 -0.3 mg m^{-2}s ^{-1} under moisture stress conditions, the model did simulate the diurnal patterns adequately.

Kim, Joon

1990-01-01

4

Net ecosystem productivity of temperate grasslands in northern China: An upscaling study  

USGS Publications Warehouse

Grassland is one of the widespread biome types globally, and plays an important role in the terrestrial carbon cycle. We examined net ecosystem production (NEP) for the temperate grasslands in northern China from 2000 to 2010. We combined flux observations, satellite data, and climate data to develop a piecewise regression model for NEP, and then used the model to map NEP for grasslands in northern China. Over the growing season, the northern China's grassland had a net carbon uptake of 158 ± 25 g C m?2 during 2000–2010 with the mean regional NEP estimate of 126 Tg C. Our results showed generally higher grassland NEP at high latitudes (northeast) than at low latitudes (central and west) because of different grassland types and environmental conditions. In the northeast, which is dominated by meadow steppes, the growing season NEP generally reached 200–300 g C m?2. In the southwest corner of the region, which is partially occupied by alpine meadow systems, the growing season NEP also reached 200–300 g C m?2. In the central part, which is dominated by typical steppe systems, the growing season NEP generally varied in the range of 100–200 g C m?2. The NEP of the northern China's grasslands was highly variable through years, ranging from 129 (2001) to 217 g C m?2 growing season?1 (2010). The large interannual variations of NEP could be attributed to the sensitivity of temperate grasslands to climate changes and extreme climatic events. The droughts in 2000, 2001, and 2006 reduced the carbon uptake over the growing season by 11%, 29%, and 16% relative to the long-term (2000–2010) mean. Over the study period (2000–2010), precipitation was significantly correlated with NEP for the growing season (R2 = 0.35, p-value < 0.1), indicating that water availability is an important stressor for the productivity of the temperate grasslands in semi-arid and arid regions in northern China. We conclude that northern temperate grasslands have the potential to sequester carbon, but the capacity of carbon sequestration depends on grassland types and environmental conditions. Extreme climate events like drought can significantly reduce the net carbon uptake of grasslands.

Zhang, Li; Guo, Huadong; Jia, Gensuo; Wylie, Bruce; Gilmanov, Tagir; Howard, Danny; Ji, Lei; Xiao, Jingfeng; Li, Jing; Yuan, Wenping; Zhao, Tianbao; Chen, Shiping; Zhou, Guangsheng; Kato, Tomomichi

2014-01-01

5

Summertime elemental mercury exchange of temperate grasslands on an ecosystem-scale  

NASA Astrophysics Data System (ADS)

In order to estimate the air-surface mercury exchange of grasslands in temperate climate regions, fluxes of gaseous elemental mercury (GEM) were measured at two sites in Switzerland and one in Austria during summer 2006. Two classic micrometeorological methods (aerodynamic and modified Bowen ratio) have been applied to estimate net GEM exchange rates and to determine the response of the GEM flux to changes in environmental conditions (e.g. heavy rain, summer ozone) on an ecosystem-scale. Both methods proved to be appropriate to estimate fluxes on time scales of a few hours and longer. Average dry deposition rates up to 4.3 ng m-2 h-1 and mean deposition velocities up to 0.10 cm s-1 were measured, which indicates that during the active vegetation period temperate grasslands are a small net sink for atmospheric mercury. With increasing ozone concentrations depletion of GEM was observed, but could not be quantified from the flux signal. Night-time deposition fluxes of GEM were measured and seem to be the result of mercury co-deposition with condensing water. Effects of grass cuts could also be observed, but were of minor magnitude.

Fritsche, J.; Wohlfahrt, G.; Ammann, C.; Zeeman, M.; Hammerle, A.; Obrist, D.; Alewell, C.

2008-12-01

6

Summertime elemental mercury exchange of temperate grasslands on an ecosystem-scale  

NASA Astrophysics Data System (ADS)

In order to estimate the air-surface mercury exchange of grasslands in temperate climate regions, fluxes of gaseous elemental mercury (GEM) were measured at two sites in Switzerland and one in Austria during summer 2006. Two classic micrometeorological methods (aerodynamic and modified Bowen ratio) have been applied to estimate net GEM exchange rates and to determine the response of the GEM flux to changes in environmental conditions (e.g. heavy rain, summer ozone) on an ecosystem-scale. Both methods proved to be appropriate to estimate fluxes on time scales of a few hours and longer. Average dry deposition rates up to 4.3 ng m-2 h-1 and mean deposition velocities up to 0.10 cm s-1 were measured, which indicates that during the active vegetation period temperate grasslands are a small net sink for atmospheric mercury. With increasing ozone concentrations depletion of GEM was observed, but could not be quantified from the flux signal. Night-time deposition fluxes of GEM were measured and seem to be the result of mercury co-deposition with condensing water. Effects of rain and of grass cuts could also be observed, but were of minor magnitude.

Fritsche, J.; Wohlfahrt, G.; Ammann, C.; Zeeman, M.; Hammerle, A.; Obrist, D.; Alewell, C.

2008-02-01

7

Declining Birds in Grassland Ecosystems  

NSDL National Science Digital Library

This United States Geological Survey (USGS) publication discusses the grassland ecosystem with respect to declining bird species. This report is the effort of a number of agencies to develop a strategy for addressing grassland bird information needs. Grasslands are the most imperiled ecosystem worldwide, and birds associated with this ecosystem are on a decline. This report addresses monitoring issues, species in concern, and the effects of habitat and landscape on grassland birds.

8

Relation of Chlorophyll Fluorescence Sensitive Reflectance Ratios to Carbon Flux Measurements of Montanne Grassland and Norway Spruce Forest Ecosystems in the Temperate Zone  

PubMed Central

We explored ability of reflectance vegetation indexes (VIs) related to chlorophyll fluorescence emission (R686/R630, R740/R800) and de-epoxidation state of xanthophyll cycle pigments (PRI, calculated as (R531 ? R570)/(R531 ? R570)) to track changes in the CO2 assimilation rate and Light Use Efficiency (LUE) in montane grassland and Norway spruce forest ecosystems, both at leaf and also canopy level. VIs were measured at two research plots using a ground-based high spatial/spectral resolution imaging spectroscopy technique. No significant relationship between VIs and leaf light-saturated CO2 assimilation (AMAX) was detected in instantaneous measurements of grassland under steady-state irradiance conditions. Once the temporal dimension and daily irradiance variation were included into the experimental setup, statistically significant changes in VIs related to tested physiological parameters were revealed. ?PRI and ?(R686/R630) of grassland plant leaves under dark-to-full sunlight transition in the scale of minutes were significantly related to AMAX (R2 = 0.51). In the daily course, the variation of VIs measured in one-hour intervals correlated well with the variation of Gross Primary Production (GPP), Net Ecosystem Exchange (NEE), and LUE estimated via the eddy-covariance flux tower. Statistical results were weaker in the case of the grassland ecosystem, with the strongest statistical relation of the index R686/R630 with NEE and GPP. PMID:22701368

Ac, Alexander; Malenovsky, Zbynek; Urban, Otmar; Hanus, Jan; Zitova, Martina; Navratil, Martin; Vrablova, Martina; Olejnickova, Julie; Spunda, Vladimir; Marek, Michal

2012-01-01

9

The measurement of soil fungal:bacterial biomass ratios as an indicator of ecosystem self-regulation in temperate meadow grasslands  

Microsoft Academic Search

There is much interest in the development of agricultural land management strategies aimed at enhancing reliance on ecosystem\\u000a self-regulation rather than on artificial inputs such as fertilisers and pesticides. This study tested the usefulness of measures\\u000a of soil microbial biomass and fungal:bacterial biomass ratios as indicators of effective conversion from an intensive grassland\\u000a system, reliant mainly on fertilisers for crop

Richard D. Bardgett; Erica McAlister

1999-01-01

10

Nitrogen loading levels affect abundance and composition of soil ammonia oxidizing prokaryotes in semiarid temperate grassland  

Microsoft Academic Search

Purpose  Global nitrogen deposition has profound impact on the terrestrial ecosystem including the semiarid temperate grassland, causing\\u000a vegetation community shifts and soil acidification. Little is known regarding the effect of nitrogen (N) deposition on the\\u000a belowground microbial communities. This study aimed to examine the response of ammonia-oxidizing bacteria (AOB) and archaea\\u000a (AOA) to added N in semiarid temperate grassland.\\u000a \\u000a \\u000a \\u000a \\u000a Materials and

Xin-Yi Shen; Li-Mei Zhang; Ju-Pei Shen; Ling-Hao Li; Chao-Lei Yuan; Ji-Zheng He

11

How generalist herbivores exploit belowground plant diversity in temperate grasslands.  

PubMed

Belowground herbivores impact plant performance, thereby inducing changes in plant community composition, which potentially leads to cascading effects onto higher trophic levels and ecosystem processes and productivity. Among soil-living insects, external root-chewing generalist herbivores have the strongest impact on plants. However, the lack of knowledge on their feeding behaviour under field conditions considerably hampers achieving a comprehensive understanding of how they affect plant communities. Here, we address this gap of knowledge by investigating the feeding behaviour of Agriotes click beetle larvae, which are common generalist external root-chewers in temperate grassland soils. Utilizing diagnostic multiplex PCR to assess the larval diet, we examined the seasonal patterns in feeding activity, putative preferences for specific plant taxa, and whether species identity and larval instar affect food choices of the herbivores. Contrary to our hypothesis, most of the larvae were feeding-active throughout the entire vegetation period, indicating that the grassland plants are subjected to constant belowground feeding pressure. Feeding was selective, with members of Plantaginaceae and Asteraceae being preferred; Apiaceae were avoided. Poaceae, although assumed to be most preferred, had an intermediate position. The food preferences exhibited seasonal changes, indicating a fluctuation in plant traits important for wireworm feeding choice. Species- and instar-specific differences in dietary choice of the Agriotes larvae were small, suggesting that species and larval instars occupy the same trophic niche. According to the current findings, the food choice of these larvae is primarily driven by plant identity, exhibiting seasonal changes. This needs to be considered when analysing soil herbivore-plant interactions. PMID:24188592

Wallinger, Corinna; Staudacher, Karin; Schallhart, Nikolaus; Mitterrutzner, Evi; Steiner, Eva-Maria; Juen, Anita; Traugott, Michael

2014-08-01

12

Nitrogen relationships in intensively managed temperate grasslands  

Microsoft Academic Search

Summary Most studies of N relationships in grassland have used cut swards. These have shown that for annual inputs of 200 to 400 kg N\\/ha from fertilizer or fixation, 55 to 80% of the N is recovered in harvested herbage. Generally, no more than 5 to 15% is lost through leaching and denitrification with most of the remaining N incorporated

P. Roger Ball; J. C. Ryden

1984-01-01

13

Soil community composition and the regulation of grazed temperate grassland.  

PubMed

The effect of the community composition of soil microbes on ecosystem processes has received relatively little attention. Here we examined the variation in soil microbial composition in a Yellowstone National Park grassland and the effect of that variation on the growth, in a greenhouse, of the dominant grass in the community. Plants and their rhizospheric soil were collected from paired, Poa pratensis-dominated grassland plots located inside and outside a 40-year-old exclosure. P. pratensis aboveground, belowground, and whole plant growth were greater in pots with soil communities from grazed grassland compared to fenced grassland, indicating (1) soil microbial communities differed, and (2) this difference influenced the growth of the plant that dominated both grasslands. Treating pots with fungicide (benomyl) suppressed the soil community influence, indicating that different fungal communities caused the soil microbe effect. In addition, two lines of evidence are consistent with the hypothesis that arbuscular mycorrhizal fungal (AMF) species composition affected P. pratensis: (1) a divergence in AMF spore communities in the two field soils, and (2) little evidence of pathogenic fungi. These findings emphasize the need to examine the role that the composition of the soil microbial community plays in controlling terrestrial ecosystems. PMID:14513350

Frank, Douglas A; Gehring, Catherine A; Machut, Leonard; Phillips, Mark

2003-12-01

14

Soil Respiration and Organic Carbon Dynamics with Grassland Conversions to Woodlands in Temperate China  

PubMed Central

Soils are the largest terrestrial carbon store and soil respiration is the second-largest flux in ecosystem carbon cycling. Across China's temperate region, climatic changes and human activities have frequently caused the transformation of grasslands to woodlands. However, the effect of this transition on soil respiration and soil organic carbon (SOC) dynamics remains uncertain in this area. In this study, we measured in situ soil respiration and SOC storage over a two-year period (Jan. 2007–Dec. 2008) from five characteristic vegetation types in a forest-steppe ecotone of temperate China, including grassland (GR), shrubland (SH), as well as in evergreen coniferous (EC), deciduous coniferous (DC) and deciduous broadleaved forest (DB), to evaluate the changes of soil respiration and SOC storage with grassland conversions to diverse types of woodlands. Annual soil respiration increased by 3%, 6%, 14%, and 22% after the conversion from GR to EC, SH, DC, and DB, respectively. The variation in soil respiration among different vegetation types could be well explained by SOC and soil total nitrogen content. Despite higher soil respiration in woodlands, SOC storage and residence time increased in the upper 20 cm of soil. Our results suggest that the differences in soil environmental conditions, especially soil substrate availability, influenced the level of annual soil respiration produced by different vegetation types. Moreover, shifts from grassland to woody plant dominance resulted in increased SOC storage. Given the widespread increase in woody plant abundance caused by climate change and large-scale afforestation programs, the soils are expected to accumulate and store increased amounts of organic carbon in temperate areas of China. PMID:24058408

Wang, Wei; Zeng, Wenjing; Chen, Weile; Zeng, Hui; Fang, Jingyun

2013-01-01

15

Temperate mountain grasslands: a climate-herbivore hypothesis for origins and persistence.  

PubMed

Temperate montane grasslands and their unique biotas are declining worldwide as they are increasingly being invaded by forests. The origin and persistence of these landscapes have been the focus of such controversy that in many areas their conservation is in doubt. In the USA some biologists have largely dismissed the grass balds of the Southern Appalachians as human artifacts or anomalous and transitory elements of regional geography, worthy of only limited preservation efforts. On the basis of information from biogeography, community ecology, regional history and palaeontology and from consideration of two other montane grassland ecosystems-East Carpathian poloninas and Oregon Coast Range grass balds-we hypothesize that these landscapes are more widespread than was formerly recognized; they are, in many cases, natural and ancient and largely owe their origin and persistence to past climatic extremes and the activities of large mammalian herbivores. PMID:24118866

Weigl, Peter D; Knowles, Travis W

2014-05-01

16

Temperate mountain grasslands: a climate-herbivore hypothesis for origins and persistence  

PubMed Central

Temperate montane grasslands and their unique biotas are declining worldwide as they are increasingly being invaded by forests. The origin and persistence of these landscapes have been the focus of such controversy that in many areas their conservation is in doubt. In the USA some biologists have largely dismissed the grass balds of the Southern Appalachians as human artifacts or anomalous and transitory elements of regional geography, worthy of only limited preservation efforts. On the basis of information from biogeography, community ecology, regional history and palaeontology and from consideration of two other montane grassland ecosystems—East Carpathian poloninas and Oregon Coast Range grass balds—we hypothesize that these landscapes are more widespread than was formerly recognized; they are, in many cases, natural and ancient and largely owe their origin and persistence to past climatic extremes and the activities of large mammalian herbivores. PMID:24118866

Weigl, Peter D; Knowles, Travis W

2014-01-01

17

Agricultural management affects communities of culturable root-endophytic fungi in temperate grasslands  

E-print Network

grasslands E.M. Wilberforcea,b , Lynne Boddyc , R. Griffithsb , G.W. Griffitha,* a Institute of Biological March 2002; received in revised form 10 April 2003; accepted 15 April 2003 Abstract Three grassland; Dark septate endophytes; Fusarium; Agricultural disturbance; Diversity index; Temperate grasslands

Griffith, Gareth

18

The Effects of Warming and Nitrogen Addition on Soil Nitrogen Cycling in a Temperate Grassland, Northeastern China  

PubMed Central

Background Both climate warming and atmospheric nitrogen (N) deposition are predicted to affect soil N cycling in terrestrial biomes over the next century. However, the interactive effects of warming and N deposition on soil N mineralization in temperate grasslands are poorly understood. Methodology/Principal Findings A field manipulation experiment was conducted to examine the effects of warming and N addition on soil N cycling in a temperate grassland of northeastern China from 2007 to 2009. Soil samples were incubated at a constant temperature and moisture, from samples collected in the field. The results showed that both warming and N addition significantly stimulated soil net N mineralization rate and net nitrification rate. Combined warming and N addition caused an interactive effect on N mineralization, which could be explained by the relative shift of soil microbial community structure because of fungal biomass increase and strong plant uptake of added N due to warming. Irrespective of strong intra- and inter-annual variations in soil N mineralization, the responses of N mineralization to warming and N addition did not change during the three growing seasons, suggesting independence of warming and N responses of N mineralization from precipitation variations in the temperate grassland. Conclusions/Significance Interactions between climate warming and N deposition on soil N cycling were significant. These findings will improve our understanding on the response of soil N cycling to the simultaneous climate change drivers in temperate grassland ecosystem. PMID:22096609

Ma, Lin-Na; Lu, Xiao-Tao; Liu, Yang; Guo, Ji-Xun; Zhang, Nan-Yi; Yang, Jian-Qin; Wang, Ren-Zhong

2011-01-01

19

Climate forcings and the nonlinear dynamics of grassland ecosystems  

E-print Network

The nonlinear interaction of climate forcings and ecosystem variables is instrumental in creating the temporal and spatial heterogeneity of grasslands. Ecosystem processes are a product of these interactions and vary in sensitivity to them across...

Petrie, Matthew D.

2010-04-28

20

Grassland ecosystems and climate change: Insights from experiments  

E-print Network

Grassland ecosystems and climate change: Insights from experiments Alan K. KnappAlan K. Knapp Ecosystem Process & Function #12;Sala et al. 1988 NA Grasslands (most) are water limited systems was not predictable when it started." ~Former Defense Secretary Donald Rumsfeld #12;Resources Biota A. Disturbance

21

Patterns of Plant Biomass Allocation in Temperate Grasslands across a 2500-km Transect in Northern China  

PubMed Central

Plant biomass allocation between below- and above-ground parts can actively adapt to the ambient growth conditions and is a key parameter for estimating terrestrial ecosystem carbon (C) stocks. To investigate how climatic variations affect patterns of plant biomass allocation, we sampled 548 plants belonging to four dominant genera (Stipa spp., Cleistogenes spp., Agropyron spp., and Leymus spp.) along a large-scale (2500 km) climatic gradient across the temperate grasslands from west to east in northern China. Our results showed that Leymus spp. had the lowest root/shoot ratios among the each genus. Root/shoot ratios of each genera were positively correlated with mean annual temperature (MAT), and negatively correlated with mean annual precipitation (MAP) across the transect. Temperature contributed more to the variation of root/shoot ratios than precipitation for Cleistogenes spp. (C4 plants), whereas precipitation exerted a stronger influence than temperature on their variations for the other three genera (C3 plants). From east to west, investment of C into the belowground parts increased as precipitation decreased while temperature increased. Such changes in biomass allocation patterns in response to climatic factors may alter the competition regimes among co-existing plants, resulting in changes in community composition, structure and ecosystem functions. Our results suggested that future climate change would have great impact on C allocation and storage, as well as C turnover in the grassland ecosystems in northern China. PMID:23977135

Luo, Wentao; Jiang, Yong; Lu, Xiaotao; Wang, Xue; Li, Mai-He; Bai, Edith; Han, Xingguo; Xu, Zhuwen

2013-01-01

22

Mapping vegetation cover of grassland ecosystem for desertification monitoring in Hulun Buir of Inner Mongolia, China  

NASA Astrophysics Data System (ADS)

Grassland ecosystem degradation and desertification has been highly concerned in China for years because such degradation is perceived to directly relate with the occurrence of sandstorms invading into north China. In this study we intend to map the spatial-temporal variation of vegetation cover density from remote sensing data in Hulun Buir, a typical grassland ecosystem with the highest biomass productivity in Inner Mongolia of China. Since NDVI is a good indicator of vegetation, a practical approach had been developed in the study to map the spatial-temporal variation of the vegetation cover. The MODIS satellite data were used for the mapping. Results from our study indicated that the vegetation cover rate had been steadily decreasing in recent years, with relatively high spatial and temporal variation. Our study reveals that the rate on average has a trend of steadily decreasing in recent years. In 2000 the rate was above 80.6% on average, while it decreased to below 76.5% in 2006. Generally the west part of the region had much lower vegetation cover rate than the east part, probably due to the fact that the east part was dominated with forest ecosystem while the west part with fragile grassland. The counties of Xinbaerhuyou Banner and Manzhouli in the west part had the lowest vegetation cover rate among the 13 counties. As to the grassland types, lowland meadow had the highest vegetation cover rate while the temperate meadow and steppe had the lowest, indicating that ecosystem degradation was very serious in the temperate meadow and steppe, which were mainly distributed in the west part of the region. Though many factors might contribute to the decrease of vegetation cover, annual precipitation vibration had very good correspondence with the up-and-down change of vegetation cover in the region. In addition, overgrazing also played an important role in accelerating the degradation under the drought year. Therefore, we were able to conclude that the grassland ecosystem in Hulun Buir was under a very serious situation of degradation and desertification. Our study suggested that the change of vegetation cover rate could be an applicable indicator for grassland ecosystem monitoring required urgently to combat grassland degradation and desertification in arid and semiarid region.

Qin, Zhihao; Zhu, Yuxia; Li, Wenjuan; Xu, Bin

2008-10-01

23

Acetaldehyde exchange above a managed temperate mountain grassland  

PubMed Central

An overview of acetaldehyde exchange above a managed temperate mountain grassland in Austria over four growing seasons is presented. The meadow acted as a net source of acetaldehyde in all four years, emitting between 7 and 28 mg C m?2 over the whole growing period. The cutting of the meadow resulted in huge acetaldehyde emission bursts on the day of harvesting or one day later. During undisturbed conditions, both uptake and emission fluxes were recorded. The bidirectional nature of acetaldehyde fluxes was also reflected by clear diurnal cycles during certain time periods, indicating strong deposition processes before the 1st cut and emission towards the end of the growing season. The analysis of acetaldehyde compensation points revealed a complex relationship between ambient acetaldehyde mixing ratios and respective fluxes, significantly influenced by multiple environmental parameters and variable throughout the year. As a major finding of this study, we identified both a positive and negative correlation between concentration and flux on a daily scale, where soil temperature and soil water content were the most significant factors in determining the direction of the slope. In turn, this bidirectional relationship on a daily scale resulted in compensation points between 0.40 ppbv and 0.54 ppbv, which could be well explained by collected ancillary data. We conclude that in order to model acetaldehyde fluxes at the site in Neustift on a daily scale over longer time periods, it is crucial to know the type of relationship, i.e. the direction of the slope, between mixing ratios and fluxes on a given day. PMID:24363666

Hörtnagl, L.; Bamberger, I.; Graus, M.; Ruuskanen, T. M.; Schnitzhofer, R.; Walser, M.; Unterberger, A.; Hansel, A.; Wohlfahrt, G.

2013-01-01

24

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

PubMed Central

Methanol (CH3OH) fluxes were quantified above a managed temperate mountain grassland in the Stubai Valley (Tyrol, Austria) during the growing seasons 2008 and 2009. Half-hourly methanol fluxes were calculated by means of the virtual disjunct eddy covariance (vDEC) method using 3-dimensional wind data from a sonic anemometer and methanol volume mixing ratios measured with a proton-transfer-reaction mass spectrometer (PTR-MS). During (undisturbed) mature and growing phases methanol fluxes exhibited a clear diurnal cycle with close-to-zero fluxes during nighttime and emissions, up to 10 nmol m?2 s?1, which followed the diurnal course of radiation and air temperature. Management events were found to represent the largest perturbations of methanol exchange at the studied grassland ecosystem: Peak emissions of 144.5 nmol m?2 s?1 were found during/after cutting of the meadow reflecting the wounding of the plant material and subsequent depletion of the leaf internal aqueous methanol pools. After the application of organic fertilizer, elevated methanol emissions of up to 26.7 nmol m?2 s?1 were observed, likely reflecting enhanced microbial activity associated with the applied manure. Simple and multiple linear regression analyses revealed air temperature and radiation as the dominant abiotic controls, jointly explaining 47 % and 70 % of the variability in half-hourly and daily methanol fluxes. In contrast to published leaf-level laboratory studies, the surface conductance and the daily change in the amount of green plant area, used as ecosystem-scale proxies for stomatal conductance and growth, respectively, were found to exert only minor biotic controls on methanol exchange. PMID:24349901

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

2013-01-01

25

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

NASA Astrophysics Data System (ADS)

Methanol (CH3OH) fluxes were quantified above a managed temperate mountain grassland in the Stubai Valley (Tyrol, Austria) during the growing seasons 2008 and 2009. Half-hourly methanol fluxes were calculated by means of the virtual disjunct eddy covariance (vDEC) method using three-dimensional wind data from a sonic anemometer and methanol volume mixing ratios measured with a proton transfer reaction mass spectrometer (PTR-MS). During (undisturbed) mature and growing phases, methanol fluxes exhibited a clear diurnal cycle with close-to-zero fluxes during nighttime and emissions, up to 10 nmol m-2 s-1, which followed the diurnal course of radiation and air temperature. Management events were found to represent the largest perturbations of methanol exchange at the studied grassland ecosystem: Peak emissions of 144.5 nmol m-2 s-1 were found during/after cutting of the meadow, reflecting the wounding of the plant material and subsequent depletion of the leaf internal aqueous methanol pools. After the application of organic fertilizer, elevated methanol emissions of up to 26.7 nmol m-2 s-1 were observed, likely reflecting enhanced microbial activity associated with the applied manure. Simple and multiple linear regression analyses revealed air temperature and radiation as the dominant abiotic controls, jointly explaining 47% and 70% of the variability in half-hourly and daily methanol fluxes. In contrast to published leaf-level laboratory studies, the surface conductance and the daily change in the amount of green plant area, used as ecosystem-scale proxies for stomatal conductance and growth, respectively, were found to exert only minor biotic controls on methanol exchange.

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

2011-09-01

26

[Effects of artificial Ulmus pumila forest on plant diversity of temperate grassland in Inner Mongolia].  

PubMed

Based on field survey, the effects of artificial Ulmus pumila forest on the species diversity of temperate grassland in Siziwang Banner of Inner Mongolia were studied. The results showed that U. pumila forest had obvious effects on the species diversity of grassland. With increasing density of U. pumila, the Patrick's richness, Pielou's evenness and Shannon-Wiener index of grass species under the forest had a decreasing trend, and were higher nearby the forest than far from the forest. The habitat inside the forest was favorable to Silene jenisseensis, while that nearby the forest was favorable to Heteropappus altaicus, Pocockia ruthenia, Potentilla bifurca, Leymus secalinus and Cleistogenes squarrosa, suggesting that to blindly exclude forestation on grassland could be less scientific, while properly afforesting U. pumila on the sides with relatively abundant soil moisture should be available to the conservation of plant diversity in temperate grassland regions. PMID:18808008

Yang, Hong-Xiao; Wang, Xue-Quan; Yang, Wen-Bin; Lu, Qi

2008-06-01

27

Drought Experiment of a Mongolian Grassland Ecosystem  

NASA Astrophysics Data System (ADS)

Recent large-scale climate change including global warming has likely been manifested as frequent and/or intensive drought occurrences in inland, arid Asia such as Mongolia. In order to investigate the response of a Mongolian grassland ecosystem to such a drought, an artificial drought experiment was conducted at Bayan Unjuul (105.95E, 47.04N) in the Mongolian typical steppe region during the growing season of 2005. The climatological (1995-2004) annul precipitation is 172.9mm, concentrated on the summer months of May- August, while the annual mean temperature is 0.1degC, with soil freezing during the winter. This study site is codominated by perennial grasses such as Stipa krylovii, Agropyron cristatum, and Cleistogenes squarrosa and annual forbs such as Artemisia adamsii and Chenopodium album. An area of 300m w300m in size was surrounded by a fence for protecting this area from grazing. The plots inside and outside of the area are referred to as no-grazing (NG) and grazing (G) plots, respectively. In the NG plot, two plots of 30m w30m with drought (D plot) and mowing (M plot) manipulations are allocated in the southwest part of the NG plot. The drought manipulation was conducted using a rainout shelter with a transparent polyethylene roof, open on all sides during the major growing season from late May to early August 2005. The total precipitation of 60.3mm in the annual total of 96.9mm (that is, a severe drought year) was excluded from the D plot. Thus, natural severe drought and artificial very severe drought conditions were produced in this year. To study the vegetation impact on thermal and moisture conditions at the ground surface, the mowing has been carried out on a monthly basis during the growing season. The initial conditions for each plot were examined during the late growing seasons of 2003 and 2004, showing no significant difference in terms of vegetation (above-/below-ground biomass and species diversity) and physical and chemical soil properties. Comprehensive observations including meteorological, vegetation, and soil elements for each plot have been made to examine two hypothetical processes of how the vegetation-soil system responds to the drought; that is, positive or negative feedback to atmosphere.

Shinoda, M.; Tsunekawa, A.; Nemoto, M.; Nachinshonhor, G. U.; Nakano, T.; Tamura, K.; Asano, M.; Erdenetsetseg, D.

2006-12-01

28

Competitive advantage of Rumex obtusifolius L. might increase in intensively managed temperate grasslands under drier climate  

Microsoft Academic Search

Climate models predict decreasing amounts of precipitation for future summers in Switzerland. Since grasslands cover about one quarter of the area, severe consequences might be expected for Swiss agriculture, ranging from loss of grassland productivity to changes in vegetation composition. Since stressed ecosystems are also more susceptible to invasion, future drier conditions might favour the emergence of weeds. However, the

Anna K. Gilgen; Constant Signarbieux; Urs Feller; Nina Buchmann

2010-01-01

29

Carbon dioxide and water vapor exchange in a warm temperate grassland  

Microsoft Academic Search

Grasslands cover about 40% of the ice-free global terrestrial surface, but their contribution to local and regional water and carbon fluxes and sensitivity to climatic perturbations such as drought remains uncertain. Here, we assess the direction and magnitude of net ecosystem carbon exchange (NEE) and its components, ecosystem carbon assimilation ( A c) and ecosystem respiration ( R E), in

K. A. Novick; P. C. Stoy; G. G. Katul; D. S. Ellsworth; M. B. S. Siqueira; J. Juang; R. Oren

2004-01-01

30

Large Uncertainties in Estimating Grassland Carbon Fluxes: Can Net Ecosystem Production Be Inferred?  

NASA Astrophysics Data System (ADS)

Despite interest in estimating ecosystem carbon budgets based on easily collected field data, no previous study to our knowledge has compared various methods of estimating total above- and belowground net primary production (NPP) and net ecosystem production (NEP, the annual carbon accumulated by an ecosystem) from commonly measured biomass and soil surface CO2 flux data in grasslands. Here we used field data from two grassland restorations and a row-crop agriculture treatment enrolled in the Conservation Reserve Program as a model for an analysis of methodological uncertainty in estimating ecosystem carbon budgets over a short time period. The goal of this study was to investigate how a range of methods for estimating NPP and NEP suggested in the literature might be used to predict ecosystem carbon budgets based on short-term field measurements. We conclude that it is extremely difficult to close the carbon budget of a temperate grassland using flux-based methods that account for plant-derived carbon inputs and soil surface CO2 losses. Current uncertainties in (1) estimating aboveground NPP, (2) determining belowground NPP, and (3) splitting soil respiration into heterotrophic and autotrophic components strongly affect the magnitude, and even the sign, of NEP. A comparison of these estimates, across a treatment of different plant species mixes and land management, cannot reliably distinguish differences in NEP, nor the absolute sign of the overall carbon budget. These uncertainties likely exist in all grassland carbon budget studies using this approach, so conclusions about whether these systems are truly carbon sinks, or how they should be managed to sequester carbon, must be made with extreme care. Longer-term stocks methods, periodically linked to flux-based measurements of individual processes, may be the only way to close the carbon budget in these systems with any reasonable degree of certainty at the present time.

Cahill, K. N.; Foley, J. A.; Kucharik, C. J.

2003-12-01

31

Ecosystem Consequences of Exotic Earthworm Invasion of North Temperate Forests  

Microsoft Academic Search

The invasion of north temperate forests by exotic species of earthworms is an important issue that has been overlooked in the study and management of these forests. We initiated research to address the hypothesis that earthworm invasion will have large consequences for nutrient retention and uptake in these ecosystems. In this special feature of Ecosystems, we present five papers describing

Patrick J. Bohlen; Peter M. Groffman; Timothy J. Fahey; Melany C. Fisk; Esteban Suarez; Derek M. Pelletier; Robert T. Fahey

2004-01-01

32

Factors Controlling Decomposition Rates of Fine Root Litter in Temperate Forests and Grasslands  

NASA Astrophysics Data System (ADS)

Fine root decomposition contributes significantly to biogeochemical cycling in terrestrial ecosystems. Recent studies suggest that root litter is stabilized preferentially compared to shoot litter, contributing in high amounts to soil organic matter. Land use and management may affect root litter decomposition through changes in plant species composition, effects on the decomposer community and differences in soil nutrient availability. We established a large scale root litter decomposition study in three German study regions using a combination of litterbags deployed in forest and grassland sites under different management and soil types. In all three study regions, we compared site-level differences in decomposition by deploying bags containing standardized forest litter in a total of 150 forest plots (50 in each of the three study regions). Bags with standardized grass litter, which had lower lignin content and lignin:N than standardized forest root litter, were similarly distributed across 50 grassland sites in each of the three regions. Standardized fine grass roots decomposed on average faster 23.5 × 6.3% compared to forest roots 11.7 × 4.4% (p < 0.001) when deployed in their respective land use. Fine root decomposition of standardized litter was affected by study region with higher mass losses in northern Germany followed by mass loss rates in central and southern Germany (p < 0.05). Given the standardized litter chemistry, these differences mainly reflect the influence of climate and soil differences between study regions. Within the central German region (Hainich-Dün), we also compared rates of mass loss of root litter collected on-site as part of a second, parallel litterbag deployment to tease apart the influences of litter quality from other factors (such as soil properties and climate) that affect mass loss rates. Despite differences in the initial fine root litter quality, the average mass lost during 12 months for on-site litter was similar to that of standardized root material for respective grasslands and forests. The main predictors of fine root decomposition for on-site litter in the HAI forest sites were the roots' initial lignin:N ratios followed by soil moisture and soil temperature. In addition to these factors, soil C:N ratios influenced on-site litter decomposition in the HAI grasslands. While in forests the lignin:N seems to be mainly related to the type and abundance of tree species, in grasslands it appears to be influenced by land management, especially fertilization, which acts to lower lignin:N ratios. These results, together with previous results showing the standing root biomass is made of older C on average in forests compared to grasslands, confirm that grasslands are cycling C faster belowground than forests in temperate regions.

Solly, E.; Schöning, I.; Trumbore, S.; Michalzik, B.; Schrumpf, M.

2013-12-01

33

INTERACTIONS BETWEEN FIRE AND INVASIVE PLANTS IN TEMPERATE GRASSLANDS OF NORTH AMERICA  

Microsoft Academic Search

A substantial number of invasive grasses, forbs and woody plants have invaded temperate grasslands in North America. Among the invading species are winter annuals, biennials, cool-season perennials, warm-season perennials, vines, shrubs, and trees. Many of these species have been deliberately introduced and widely planted; some are still used for range improvement, pastures, lawns, and as ornamentals, though many are listed

James B. Grace; Melinda D. Smith; Susan L. Grace; Scott L. Collins; Thomas J. Stohlgren

2002-01-01

34

Effects of recurring summer droughts on ecosystem photosynthesis and respiration in a mountain grassland  

NASA Astrophysics Data System (ADS)

Climatic changes in mountain regions play a key role in current and future grassland ecosystem processes. It is currently expected that droughts and heatwaves will become more frequent in a changing climate. All around the world mountain regions have been labelled as sensitive zones, where declining water availability and increasing temperature are expected to increase the vulnerability of these ecosystems. However, the effects of such extreme events on ecosystem carbon (C) fluxes and their coupling in temperate and so far non-water limited Alpine grasslands are not yet well understood. We studied effects of recurring summer drought on the C dynamics of a mountain meadow at 1820 m and an abandoned grassland at 2000 m in the Austrian Central Alps. The aim of the study was (1) to analyse the multiannual effect of drought on net ecosystem CO2 exchange (NEE) and its major component processes, i.e. gross primary productivity (GPP) and ecosystem respiration (Reco), and (2) to trace drought effects on the use of recent C in soil respiration. We tested the hypothesis that drought reduces NEE, GPP and Reco and the ratio of GPP / Reco and causes a reduction in the use of recent photoassimilates in belowground respiration. At each study site, exclusion of rainfall was achieved by establishing rain-out shelters for a period of two months (June, July), while control plots remained exposed to natural precipitation. To trace the fate of recent C from assimilation to respiration 13CO2 pulse-labelling was carried out at the meadow site, and the carbon isotope composition of soil respired CO2 was continuously monitored with an open dynamic-chamber system coupled with a quantum cascade laser. Our results showed that at both sites NEE, GPP and Reco showed a consistent reduction with reduction in soil water level. Drought reduced ecosystem respiration to a lesser extent than photosynthesis. We observed memory effects on all flux processes after 3 years of recurring drought on the mountain meadow, which was likely due to shifts in the abundance of dominant species. Within the first 30 days after labelling, the contribution of recent C to the main component process of ecosystem respiration (soil respiration) was slightly reduced in the drought plots. We conclude that 1) a summer drought may potentially alter the carbon balance of mountain grasslands towards decreasing photosynthesis and assimilation area, whereas 2) repeated drought may lead to adaptation of the ecosystem which reduces the drought response of C fluxes, and 3) summer drought may reduce the contribution of recent C to belowground respiration.

Schmitt, Michael; Ingrisch, Johannes; Sturm, Patrick; Ladreiter-Knauss, Thomas; Hasibeder, Roland; Bramboeck, Peter; Berger, Vanessa; Bahn, Michael

2013-04-01

35

Trophic diversity in two grassland ecosystems  

PubMed Central

The roles of consumers (top-down forces) versus resources (bottom-up forces) as determinants of alpha diversity in a community are not well studied. Numerous community ecology models and empirical studies have provided a framework for understanding how density at various trophic levels responds to variation in the relative strength of top-down and bottom-up forces. The resulting trophic theory can be applied to understanding variation in insect diversity at different trophic levels. The objective of this research was to elucidate the strengths of direct and indirect interactions between plants and entire arthropod communities to determine the effects of trophic interactions on arthropod diversity. Grassland plant and insect diversity was measured in July 2001 to document patterns of diversity at multiple trophic levels. The study site includes riparian grasslands in North-Central Colorado on the Carpenter Ranch, owned and managed by The Nature Conservancy. This pastureland consists of sites with different management regimes: unmanaged pasture intermixed along riparian forest, and cattle grazed pasture with flood irrigation. Plant abundance and richness were higher on the grazed-irrigated pasture versus the unmanaged field. Path analysis revealed strong effects of herbivore diversity on diversity of other trophic levels. For the managed fields, top-down forces were important, with increases in enemy diversity depressing herbivore diversity, which in turn depressed plant abundance. For the unmanaged fields, bottom-up forces dominated, with increases in plant diversity causing increased herbivore diversity, which in turn increased enemy diversity. These results support hypotheses from other empirical studies, demonstrating that changes in diversity of a single trophic level can cascade to effect diversity at other, nonadjacent trophic levels. PMID:19537996

Pearson, Clark V.; Dyer, Lee A.

2006-01-01

36

Plant Functional Group Composition Modifies the Effects of Precipitation Change on Grassland Ecosystem Function  

PubMed Central

Temperate grassland ecosystems face a future of precipitation change, which can alter community composition and ecosystem functions through reduced soil moisture and waterlogging. There is evidence that functionally diverse plant communities contain a wider range of water use and resource capture strategies, resulting in greater resistance of ecosystem function to precipitation change. To investigate this interaction between composition and precipitation change we performed a field experiment for three years in successional grassland in southern England. This consisted of two treatments. The first, precipitation change, simulated end of century predictions, and consisted of a summer drought phase alongside winter rainfall addition. The second, functional group identity, divided the plant community into three groups based on their functional traits- broadly described as perennials, caespitose grasses and annuals- and removed these groups in a factorial design. Ecosystem functions related to C, N and water cycling were measured regularly. Effects of functional groupidentity were apparent, with the dominant trend being that process rates were higher under control conditions where a range of perennial species were present. E.g. litter decomposition rates were significantly higher in plots containing several perennial species, the group with the highest average leaf N content. Process rates were also very strongly affected by the precipitation change treatmentwhen perennial plant species were dominant, but not where the community contained a high abundance of annual species and caespitose grasses. This contrasting response could be attributable to differing rooting patterns (shallower structures under annual plants, and deeper roots under perennials) and faster nutrient uptake in annuals compared to perennials. Our results indicate that precipitation change will have a smaller effect on key process rates in grasslandscontaining a range of perennial and annual species, and that maintaining the presence of key functional groups should be a crucial consideration in future grassland management. PMID:23437300

Fry, Ellen L.; Manning, Pete; Allen, David G. P.; Hurst, Alex; Everwand, Georg; Rimmler, Martin; Power, Sally A.

2013-01-01

37

Ecosystem Carbon and Nitrogen Accumulation after Grazing Exclusion in Semiarid Grassland  

PubMed Central

The grazing exclusion in degraded grassland has been extensively used to prevent the loss of grassland resources and to improve grassland services. The effects of grazing exclusion on C and N balance, however, have not been well addressed but are essential for assessing grassland C sinks, the sustainable use of grassland resources and the support of grassland services. To understand the response of ecosystem C and N to grazing exclusion in semiarid grassland, we determined the C and N in litter, aboveground biomass, roots and soils from ungrazed grassland fenced at different times in northwest China. Our results showed that the aboveground biomass, root biomass and plant litter were 70–92%, 56–151% and 59–141% higher, respectively, in grazer excluded grassland than in grazed grassland. Grazing exclusion significantly increased C and N stored in plant biomass and litter and increased the concentrations and stocks of C and N in soils. Grazing exclusion thus significantly increased the C and N stored in grassland ecosystems. The increase in C and N stored in soil contributed to more than 95% and 97% of the increases in ecosystem C and N storage. The highest C and N stocks in ecosystems were observed in 17-year grazer excluded grassland. The results from this study indicate that grazing exclusion has the potential to increase C and N storage in degraded semiarid grassland and that the recovery of ecosystem C and N was mainly due to the accumulation of C and N in soils. PMID:23383191

Qiu, Liping; Wei, Xiaorong; Zhang, Xingchang; Cheng, Jimin

2013-01-01

38

Monitoring Change in Temperate Coniferous Forest Ecosystems  

NASA Technical Reports Server (NTRS)

The primary goal of this research was to improve monitoring of temperate forest change using remote sensing. In this context, change includes both clearing of forest due to effects such as fire, logging, or land conversion and forest growth and succession. The Landsat 7 ETM+ proved an extremely valuable research tool in this domain. The Landsat 7 program has generated an extremely valuable transformation in the land remote sensing community by making high quality images available for relatively low cost. In addition, the tremendous improvements in the acquisition strategy greatly improved the overall availability of remote sensing images. I believe that from an historical prespective, the Landsat 7 mission will be considered extremely important as the improved image availability will stimulate the use of multitemporal imagery at resolutions useful for local to regional mapping. Also, Landsat 7 has opened the way to global applications of remote sensing at spatial scales where important surface processes and change can be directly monitored. It has been a wonderful experience to have participated on the Landsat 7 Science Team. The research conducted under this project led to contributions in four general domains: I. Improved understanding of the information content of images as a function of spatial resolution; II. Monitoring Forest Change and Succession; III. Development and Integration of Advanced Analysis Methods; and IV. General support of the remote sensing of forests and environmental change. This report is organized according to these topics. This report does not attempt to provide the complete details of the research conducted with support from this grant. That level of detail is provided in the 16 peer reviewed journal articles, 7 book chapters and 5 conference proceedings papers published as part of this grant. This report attempts to explain how the various publications fit together to improve our understanding of how forests are changing and how to monitor forest change with remote sensing. There were no new inventions that resulted from this grant.

Williams, Darrel (Technical Monitor); Woodcock, Curtis E.

2004-01-01

39

Evidence of Physiological Decoupling from Grassland Ecosystem Drivers by an Encroaching Woody Shrub  

E-print Network

Evidence of Physiological Decoupling from Grassland Ecosystem Drivers by an Encroaching Woody Shrub of America Abstract Shrub encroachment of grasslands is a transformative ecological process by which native assessments of shrub physiology. In a mesic grassland in North America, we measured inter- and intra

Nippert, Jesse

40

Monitoring grassland ecosystem degradation using EOS\\/MODIS data in North China  

Microsoft Academic Search

Several sandstorms invading the capital of China in recent years cause many concerns to the issues of grassland ecosystem degradation in arid and semiarid grassland region of north China. Actually the degradation can be viewed as the decrease of primary productivity in the grassland. This provides the possibility to monitoring the degradation using satellite remote sensing technology. In the study

Lipeng Jiang; Zhihao Qin; Liping Lu; Wen Xie; Wenjuan Li

2006-01-01

41

Carbon dioxide budget in a temperature grassland ecosystem  

NASA Technical Reports Server (NTRS)

Eddy correlation measurements of CO2 flux made during May-October 1987 and June-August 1989 were employed, in conjunction with simulated data, to examine the net exchange of CO2 in a temperature grassland ecosystem. Simulated estimates of CO2 uptake were used when flux measurements were not available. These estimates were based on daily intercepted photosynthetically active radiation, air temperature, and extractable soil water. Soil CO2 flux and dark respiration of the aerial part of plants were estimated using the relationships developed by Norman et al. (1992) and Polley et al. (1992) at the study site. The results indicate that the CO2 exchange between this ecosystem and the atmosphere is highly variable. The net ecosystem CO2 exchange reached its peak value (12-18 g/sq m d) during the period when the leaf area index was maximum. Drought, a frequent occurrence in this region, can change this ecosystem from a sink to a source for atmospheric CO2. Comparison with data on dry matter indicated that the aboveground biomass accounted for about 45-70 percent of the net carbon uptake, suggesting the importance of the below ground biomass in estimating net primary productivity in this ecosystem.

Kim, Joon; Verma, Shashi B.; Clement, Robert J.

1992-01-01

42

Belowground nematode herbivores are resistant to elevated atmospheric CO 2 concentrations in grassland ecosystems  

Microsoft Academic Search

Grasslands are considered to be one of the most sensitive ecosystems to rising atmospheric CO2 concentrations, since, in addition to direct effects of elevated CO2 on plant growth, indirect increases in water availability as an effect of elevated CO2 may enhance primary production and alter plant community composition in these typically dry ecosystems. Moreover, grasslands support large populations of belowground

Edward Ayres; Diana H. Wall; Breana L. Simmons; Christopher B. Field; Daniel G. Milchunas; Jack A. Morgan; Jacques Roy

2008-01-01

43

Biochar application reduces N2O emission in intensively managed temperate grassland  

NASA Astrophysics Data System (ADS)

Biochar, a pyrolysis product of organic residues, is seen as an amendment for agricultural soils to improve soil fertility, sequester CO2 and reduce N2O emissions. Mainly used in highly weathered tropical soils, the interest of using biochar in intensively managed temperate soils is increasing. Our previous laboratory incubations have shown N2O reduction potentials of between 20 and 100% for temperate soils after biochar application (Felber et al., Biogeosciences Discuss, 2012). To assess the effect of biochar application under field conditions, a plot experiment (3 control vs. 3 biochar amended plots of 3x3 m size at a rate of 15 t ha-1) was set up in a temperate intensively managed grassland soil. N2O and CO2 emissions were quasi-continuously measured by static chambers under standard management practice over 8 months. In parallel soil samples were taken monthly from all plots and their N2O and CO2 productions were measured under controlled conditions in the lab. At the beginning of the field measurements (April 2011) cumulative N2O fluxes from biochar amended plots were above those of control plots, but the pattern reversed towards reduced fluxes from biochar plots after 3 months and the reduction reached about 15% by the end of 2011. The biochar effect on reducing N2O emissions in the laboratory was two times that of the field measurements, indicating that results from laboratory experiments are not directly transferable to field conditions. The experiments indicate a substantial N2O emission reduction potential of biochar in temperate grassland fields.

Felber, R.; Leifeld, J.; Neftel, A.

2012-04-01

44

Effects of Water and Nitrogen Addition on Species Turnover in Temperate Grasslands in Northern China  

PubMed Central

Global nitrogen (N) deposition and climate change have been identified as two of the most important causes of current plant diversity loss. However, temporal patterns of species turnover underlying diversity changes in response to changing precipitation regimes and atmospheric N deposition have received inadequate attention. We carried out a manipulation experiment in a steppe and an old-field in North China from 2005 to 2009, to test the hypothesis that water addition enhances plant species richness through increase in the rate of species gain and decrease in the rate of species loss, while N addition has opposite effects on species changes. Our results showed that water addition increased the rate of species gain in both the steppe and the old field but decreased the rates of species loss and turnover in the old field. In contrast, N addition increased the rates of species loss and turnover in the steppe but decreased the rate of species gain in the old field. The rate of species change was greater in the old field than in the steppe. Water interacted with N to affect species richness and species turnover, indicating that the impacts of N on semi-arid grasslands were largely mediated by water availability. The temporal stability of communities was negatively correlated with rates of species loss and turnover, suggesting that water addition might enhance, but N addition would reduce the compositional stability of grasslands. Experimental results support our initial hypothesis and demonstrate that water and N availabilities differed in the effects on rate of species change in the temperate grasslands, and these effects also depend on grassland types and/or land-use history. Species gain and loss together contribute to the dynamic change of species richness in semi-arid grasslands under future climate change. PMID:22768119

Xu, Zhuwen; Wan, Shiqiang; Ren, Haiyan; Han, Xingguo; Li, Mai-He; Cheng, Weixin; Jiang, Yong

2012-01-01

45

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

NASA Astrophysics Data System (ADS)

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.

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

2010-05-01

46

Soil respiration flux in northern coastal temperate rainforest ecosystems  

NASA Astrophysics Data System (ADS)

Forest carbon budgets are of increasing concern because of their linkages with changing climate. The potential source strength of northern forested ecosystems is of great interest due to the large carbon stock of these systems, especially the extensive peatlands. Where very few long-term measurements of soil carbon cycles have been made, such as the North Pacific coastal temperate margin, peatlands have potentially large but largely unknown source strengths, particularly through soil respiration. The easily and widely measured factors that influence the metabolism of plants and microorganisms in soils, such as temperature, moisture and substrate quality, must be coupled with a network of plot-scale measurements of soil respiration fluxes in this region in order to produce reasonable models of soil respiration flux across gradients of climate, vegetation and soil types. We designed a study to address this issue and measured soil respiration across a hydrologic gradient to quantify the influence of soil temperature and moisture on the magnitude and seasonality of carbon fluxes in the coastal temperate rainforest biome. Replicated study sites were established in three common ecosystem types (peatlands, forested wetlands, and upland forest) within three coastal watersheds. In total, nine sites of the three ecosystem types were measured at monthly intervals during the snow-free period between May and November for two years. Soil respiration fluxes during the six-month measurement period were used to construct a respiration flux model for each landscape type. Soil respiration fluxes followed the seasonal temperature pattern in all ecosystem types and also varied with soil saturation as well in uplands. Temperature dependent models of soil respiration flux were best fit to intermediate drainage conditions in forested wetlands and explained up to 85% of the variation in this ecosystem type. Modeled soil respiration estimates were better at low temperatures with high water tables and increased in variability with increasing temperature and lower water tables, confirming an interaction with soil moisture.Despite this variability, we were able to predict soil respiration rates within 10% of the actual flux using temperature-dependent models. The soil respiration models we developed will be used to calibrate larger scale estimates of soil respiration flux and populate global change models to reduce the uncertainty in outcomes of ecosystem response to global change in the north pacific coastal temperate rainforest.

D'Amore, David; Nay, S. Mark; Edwards, Richard; Valentine, David; Hood, Eran

2010-05-01

47

Components of surface energy balance in a temperate grassland ecosystem  

NASA Astrophysics Data System (ADS)

Eddy correlation measurements were made of fluxes of moisture, heat and momentum at a tallgrass prairie site near Manhattan, Kansas, U.S.A. during the First ISLSCP ISLSCP: International Satellite Land Surface Climatology Project (for details, see Sellers et al., 1988). Field Experiment (FIFE) in 1987. The study site is dominated by three C4 grass species: big bluestem ( Andropogon gerardii), indiangrass ( Sorghastrum nutans), and switchgrass ( Panicum virgatum). The stomatal conductance and leaf water potential of these grass species were also measured. In this paper, daily and seasonal variations in the components of the surface energy balance are examined. The aerodynamic and canopy surface conductances for the prairie vegetation are also evaluated.

Kim, Joon; Verma, Shashi B.

1990-06-01

48

Components of surface energy balance in a temperate grassland ecosystem  

Microsoft Academic Search

Eddy correlation measurements were made of fluxes of moisture, heat and momentum at a tallgrass prairie site near Manhattan, Kansas, U.S.A. during the First ISLSCPISLSCP: International Satellite Land Surface Climatology Project (for details, see Sellers et al., 1988). Field Experiment (FIFE) in 1987. The study site is dominated by three C4 grass species: big bluestem (Andropogon gerardii), indiangrass (Sorghastrum nutans),

Joon Kim; Shashi B. Verma

1990-01-01

49

Carbon dioxide exchange in a temperate grassland ecosystem  

NASA Technical Reports Server (NTRS)

Carbon dioxide exchange was measured, using the eddy correlation technique, over a tallgrass prairie in northeastern Kansas, U.S.A., during a six-month period in 1987. The diurnal patterns of daytime and nocturnal CO2 fluxes are presented on eight selected days. These days were distributed throughout most of the growing season and covered a wide range of meteorological and soil water conditions. The midday CO2 flux reached a maximum of 1.3 mg/sq m (ground area)/s during early July and was near zero during the dry period in late July. The dependence of the daytime carbon dioxide exchange on pertinent controlling variables, particularly photosynthetically active radiation, vapor pressure deficit, and soil water content is discussed. The nocturnal CO2 flux (soil plus plant respiration) averaged -0.4 m sq m (ground area)/s during early July and was about -0.2 mg sq/m during the dry period.

Kim, Joon; Verma, Shashi B.

1990-01-01

50

Resistance and resilience of soil respiration to recurring summer drought in temperate mountain grassland  

NASA Astrophysics Data System (ADS)

Mountain grasslands are highly sensitive to climatic changes and soil respiration (Rs) is their largest source for CO2 emissions. As a contribution to the EU-project Carbo-Extreme and a national (FWF) project we studied how experimental summer drought and subsequent rewetting affects soil respiration over five subsequent years. The study site was a temperate mountain meadow at 1820m in the Austrian Central Alps. Drought was simulated with rain-out-shelters keeping off precipitation over a period of ca. 2 months of each year, which reduced the soil water content in the main rooting horizon to less than 20%vol (i.e. 20-30% relative extractable water). Rs measurements were performed with automated chambers and were complemented by episodic manual measurements on shallow and deep collars. Rs and its temperature sensitivity decreased at a soil moisture threshold of 20 - 30%vol, with the threshold increasing to higher values from the first to the last year of drought. Soil CO2 efflux was strongly stimulated after rainfall following drought, where Rs exceeded the flux rates of the control plots. Post-rewetting Rs remained enhanced for weeks in the first three years of the experiment. In the fourth and fifth year rewetting caused only a short pulse of soil CO2 emissions, after which Rs decreased below values in control plots for weeks. We conclude that recurring summer drought may alter the resistance and resilience of soil respiration in temperate grassland, with implications for its annual carbon balance.

Ladreiter-Knauss, Thomas; Walter, Eric; Gruber, Verena; Schmitt, Michael; Ingrisch, Johannes; Hasibeder, Roland; Bahn, Michael

2013-04-01

51

Nitrogen deposition weakens plant-microbe interactions in grassland ecosystems.  

PubMed

Soil carbon (C) and nitrogen (N) stoichiometry is a main driver of ecosystem functioning. Global N enrichment has greatly changed soil C : N ratios, but how altered resource stoichiometry influences the complexity of direct and indirect interactions among plants, soils, and microbial communities has rarely been explored. Here, we investigated the responses of the plant-soil-microbe system to multi-level N additions and the role of dissolved organic carbon (DOC) and inorganic N stoichiometry in regulating microbial biomass in semiarid grassland in northern China. We documented a significant positive correlation between DOC and inorganic N across the N addition gradient, which contradicts the negative nonlinear correlation between nitrate accrual and DOC availability commonly observed in natural ecosystems. Using hierarchical structural equation modeling, we found that soil acidification resulting from N addition, rather than changes in the plant community, was most closely related to shifts in soil microbial community composition and decline of microbial respiration. These findings indicate a down-regulating effect of high N availability on plant-microbe interactions. That is, with the limiting factor for microbial biomass shifting from resource stoichiometry to soil acidity, N enrichment weakens the bottom-up control of soil microorganisms by plant-derived C sources. These results highlight the importance of integratively studying the plant-soil-microbe system in improving our understanding of ecosystem functioning under conditions of global N enrichment. PMID:23925948

Wei, Cunzheng; Yu, Qiang; Bai, Edith; Lü, Xiaotao; Li, Qi; Xia, Jianyang; Kardol, Paul; Liang, Wenju; Wang, Zhengwen; Han, Xingguo

2013-12-01

52

Biochemical properties in managed grassland soils in a temperate humid zone: modifications of soil quality as a consequence of intensive grassland use  

Microsoft Academic Search

Although soil biochemical properties are considered to be good indicators of changes in soil quality, few studies have been\\u000a made of the changes in biochemical properties brought about by anthropogenic disturbance of grassland ecosystems. In the present\\u000a study, several biochemical properties were analysed in 31 grassland soils subjected to a high level of management, and the\\u000a values obtained were compared

J. Paz-Ferreiro; C. Trasar-Cepeda; M. C. Leirós; S. Seoane; F. Gil-Sotres

2009-01-01

53

Grazing effects on belowground C and N stocks along a network of cattle exclosures in temperate and subtropical grasslands  

E-print Network

Grazing effects on belowground C and N stocks along a network of cattle exclosures in temperate 2008; published 4 April 2009. [1] We evaluated the effects of grazing on C and N belowground pools by comparing 15 grazing-exclosure pairs across the Ri´o de la Plata grasslands of Uruguay and Argentina. We

Nacional de San Luis, Universidad

54

Rapid Response of a Grassland Ecosystem to an Experimental Manipulation of a Keystone Rodent and Domestic Livestock  

Microsoft Academic Search

Megaherbivores and small burrowing mammals commonly coexist and play important functional roles in grassland ecosystems worldwide. The interactive effects of these two functional groups of herbivores in shaping the structure and function of grassland ecosystems are poorly understood. In North America's central grasslands, domestic cattle (Bos taurus) have supplanted bison (Bison bison), and now coexist with prairie dogs (Cynomys spp.),

Ed L. Frederickson; Eduardo Ponce; Dave Lightfoot; Ed Fredrickson; James Brown; Juan Cruzado; Sandra Brantley; Rodrigo Sierra; Rurik List; David Toledo; Gerardo Ceballos

2010-01-01

55

Net ecosystem exchange of grassland in contrasting wet and dry years  

E-print Network

Net ecosystem exchange of grassland in contrasting wet and dry years Vesna Jaksic a , Gerard Kiely. We used an eddy covariance (EC) system to measure the net ecosystem exchange (NEE) at a managed overlooked due to the perception that this ecosystem is C neutral (Ham and Knapp, 1998; Hunt et al., 2002

Katul, Gabriel

56

Ecosystem Change in California Grasslands: Impacts of Species Invasion  

NASA Astrophysics Data System (ADS)

Grassland ecosystems of California have undergone dramatic changes, resulting in the almost complete replacement of native perennial grasses by non-native annuals across millions of hectares of grassland habitat. Our research investigates the effects of this community shift on carbon, water and energy cycles at two sites in northern coastal California. Our goal was to understand how changes to California’s grasslands have affected climate through 1. shifting the balance of carbon storage between terrestrial stocks and the atmosphere, and 2. altering the water and energy regimes that heat or cool the earth's surface. To compare the processes that govern material exchange before and after annual grass invasion, we made use of sites where native vegetation is found adjacent to locations that have undergone non-native invasion. In plots of each vegetation type, we monitored whole plant productivity, root and litter decay rates and soil respiration, as well as soil climatic controls on these processes. At one site, we also measured surface albedo and the components of the surface energy balance in each grass community, using the surface renewal method. Although seemingly subtle, the shift in California grassland communities from native perennial to non-native annual grass dominance has had profound consequences for ecosystem biogeochemical, radiative and hydrological cycles. Soil carbon storage was found to be significantly greater in native perennial grass communities. Across both study sites, we found that non-native grass invasion has resulted in the transfer of from 3 to 6 tons of carbon per hectare from the soil to the atmosphere, dependent on site and species. A soil density fractionation and a radiocarbon analysis also revealed the carbon to be more recalcitrant in native grass dominated locations. The primary plant traits that help explain why soil carbon losses follow annual grass invasion are: 1. differences between annual and perennial grasses in above/ belowground allocation, 2. differences in growth plasticity in response to inter-annual precipitation variability, and 3. the effect of differences in rooting depth and aboveground morphology on soil moisture content and soil respiration. Over the years 2004-2006, we found energy partitioning into latent and sensible heat flux to be similar among annual and perennial grass communities during periods of sufficient soil moisture availability. When water becomes scarce in the late spring, however, and annual grasses die, the ratio of latent to sensible heat loss is reduced in annual grass communities relative to perennials. The deep roots of perennial grasses prolong the period over which transpiration occurs. We also found that albedo differs year-round between perennial and annual grasses, tracking differences in grass phenology. Albedo differences are at a maximum during the summer and autumn months. At this time, the lower albedo in non-native annual communities can raise near surface temperatures up to 6 oC midday relative to native perennials.

Koteen, L. E.; Harte, J.; Baldocchi, D. D.

2009-12-01

57

ECOSYSTEM ECOLOGY -ORIGINAL PAPER Form and function of grass ring patterns in arid grasslands  

E-print Network

ECOSYSTEM ECOLOGY - ORIGINAL PAPER Form and function of grass ring patterns in arid grasslands (Schelsinger et al. 1990) that are sensitive to climate fluctuations and prone to anthropogenic disturbances

D'Odorico, Paolo

58

The impact of human-environment interactions on the stability of forest-grassland mosaic ecosystems  

PubMed Central

Forest-grassland mosaic ecosystems can exhibit alternative stables states, whereby under the same environmental conditions, the ecosystem could equally well reside either in one state or another, depending on the initial conditions. We develop a mathematical model that couples a simplified forest-grassland mosaic model to a dynamic model of opinions about conservation priorities in a population, based on perceptions of ecosystem rarity. Weak human influence increases the region of parameter space where alternative stable states are possible. However, strong human influence precludes bistability, such that forest and grassland either co-exist at a single, stable equilibrium, or their relative abundance oscillates. Moreover, a perturbation can shift the system from a stable state to an oscillatory state. We conclude that human-environment interactions can qualitatively alter the composition of forest-grassland mosaic ecosystems. The human role in such systems should be viewed as dynamic, responsive element rather than as a fixed, unchanging entity. PMID:24048359

Innes, Clinton; Anand, Madhur; Bauch, Chris T.

2013-01-01

59

Prairie Dog Decline Reduces the Supply of Ecosystem Services and Leads to Desertification of Semiarid Grasslands  

PubMed Central

Anthropogenic impacts on North American grasslands, a highly endangered ecosystem, have led to declines of prairie dogs, a keystone species, over 98% of their historical range. While impacts of this loss on maintenance of grassland biodiversity have been widely documented, much less is known about the consequences on the supply of ecosystem services. Here we assessed the effect of prairie dogs in the supply of five ecosystem services by comparing grasslands currently occupied by prairie dogs, grasslands devoid of prairie dogs, and areas that used to be occupied by prairie dogs that are currently dominated by mesquite scrub. Groundwater recharge, regulation of soil erosion, regulation of soil productive potential, soil carbon storage and forage availability were consistently quantitatively or qualitatively higher in prairie dog grasslands relative to grasslands or mesquite scrub. Our findings indicate a severe loss of ecosystem services associated to the absence of prairie dogs. These findings suggest that contrary to a much publicize perception, especially in the US, prairie dogs are fundamental in maintaining grasslands and their decline have strong negative impacts in human well – being through the loss of ecosystem services. PMID:24130691

Martinez-Estevez, Lourdes; Balvanera, Patricia; Pacheco, Jesus; Ceballos, Gerardo

2013-01-01

60

Black carbon in grassland ecosystems of the world  

NASA Astrophysics Data System (ADS)

Black carbon (BC) is the product of incomplete burning processes and a significant component of the passive soil organic carbon (SOC) pool. The role of BC in the global carbon cycle is still unclear. This study aimed to quantify and characterize BC in major grassland ecosystems of the world. Twenty-eight representative soil profiles (mainly Mollisols) were sampled in the Russian Steppe, the U.S. Great Plains, the Argentinian Pampa, the Manchurian Plains in China, and the Chernozem region in central Germany. Black carbon contents were estimated using benzene polycarboxylic acids (BPCA) as a molecular marker, and indications about the origin of the BC were derived from bulk and compound-specific ?13C analyses and radiocarbon dating of bulk soil organic matter (SOM). Our findings suggest that between 5% and 30% of SOC stocks consist of BC. Maximum BC contributions to SOC frequently were found at deeper parts of the A horizon with 14C ages younger than 7000 years BP; that is, incorporation of C as charred particles accompanied ecosystem development since the mid-Holocene. Most of this BC formed from local vegetation, as indicated by a 13C isotope signature similar to that of bulk SOM. At some sites, also nonlocal sources contributed to soil BC, e.g., fossil fuel BC inputs at the German sites. Black carbon stocks were highest in Chernozems and lowest in Kastanozems. The Russian Steppe and Chinese Manchurian sites stored about 3-4 times more BC (around 3 kg m-2) than did the other sites because of thicker A horizons that were rich in BC. On a global scale, we estimate that steppe ecosystems contain between 4 and 17 Pg BC.

Rodionov, Andrej; Amelung, Wulf; Peinemann, Norman; Haumaier, Ludwig; Zhang, Xudong; Kleber, Markus; Glaser, Bruno; Urusevskaya, Inga; Zech, Wolfgang

2010-09-01

61

Effect of degradation intensity on grassland ecosystem services in the alpine region of Qinghai-Tibetan Plateau, China.  

PubMed

The deterioration of alpine grassland has great impact on ecosystem services in the alpine region of Qinghai-Tibetan Plateau. However, the effect of grassland degradation on ecosystem services and the consequence of grassland deterioration on economic loss still remains a mystery. So, in this study, we assessed four types of ecosystem services following the Millennium Ecosystem Assessment classification, along a degradation gradient. Five sites of alpine grassland at different levels of degradation were investigated in Guoluo Prefecture of Qinghai Province, China. The species composition, aboveground biomass, soil total organic carbon (TOC), and soil total nitrogen (TN) were tested to evaluate major ecological services of the alpine grassland. We estimated the value of primary production, carbon storage, nitrogen recycling, and plant diversity. The results show the ecosystem services of alpine grassland varied along the degradation gradient. The ecosystem services of degraded grassland (moderate, heavy and severe) were all significantly lower than non-degraded grassland. Interestingly, the lightly degraded grassland provided more economic benefit from carbon maintenance and nutrient sequestration compared to non-degraded. Due to the destruction of the alpine grassland, the economic loss associated with decrease of biomass in 2008 was $198/ha. Until 2008, the economic loss caused by carbon emissions and nitrogen loss on severely degraded grassland was up to $8 033/ha and $13 315/ha, respectively. Urgent actions are required to maintain or promote the ecosystem services of alpine grassland in the Qinghai-Tibetan Plateau. PMID:23469278

Wen, Lu; Dong, Shikui; Li, Yuanyuan; Li, Xiaoyan; Shi, Jianjun; Wang, Yanlong; Liu, Demei; Ma, Yushou

2013-01-01

62

Independent Evolution of Leaf and Root Traits within and among Temperate Grassland Plant Communities  

PubMed Central

In this study, we used data from temperate grassland plant communities in Alberta, Canada to test two longstanding hypotheses in ecology: 1) that there has been correlated evolution of the leaves and roots of plants due to selection for an integrated whole-plant resource uptake strategy, and 2) that trait diversity in ecological communities is generated by adaptations to the conditions in different habitats. We tested the first hypothesis using phylogenetic comparative methods to test for evidence of correlated evolution of suites of leaf and root functional traits in these grasslands. There were consistent evolutionary correlations among traits related to plant resource uptake strategies within leaf tissues, and within root tissues. In contrast, there were inconsistent correlations between the traits of leaves and the traits of roots, suggesting different evolutionary pressures on the above and belowground components of plant morphology. To test the second hypothesis, we evaluated the relative importance of two components of trait diversity: within-community variation (species trait values relative to co-occurring species; ? traits) and among-community variation (the average trait value in communities where species occur; ? traits). Trait diversity was mostly explained by variation among co-occurring species, not among-communities. Additionally, there was a phylogenetic signal in the within-community trait values of species relative to co-occurring taxa, but not in their habitat associations or among-community trait variation. These results suggest that sorting of pre-existing trait variation into local communities can explain the leaf and root trait diversity in these grasslands. PMID:21687704

Kembel, Steven W.; Cahill, James F.

2011-01-01

63

Nitrogen deposition and reduction of terrestrial biodiversity: evidence from temperate grasslands.  

PubMed

Biodiversity is thought to be essential for ecosystem stability, function and long-term sustainability. Since nitrogen is the limiting nutrient for plant growth in many terrestrial ecosystems, reactive nitrogen has the potential to reduce the diversity of terrestrial vegetation and associated biota through favouring species adapted to quickly exploiting available nutrients. Although the potential has long been recognised, only recently has enough evidence come together to show beyond reasonable doubt that these changes are already occurring. Linked together, experimental, regional/empirical, and time-series research provide a powerful argument that enhanced deposition of reactive nitrogen across Great Britain, and potentially the rest of Europe, has resulted in a significant and ongoing decline in grassland species richness and diversity. PMID:16512195

Dise, Nancy B; Stevens, Carly J

2005-12-01

64

Nitrogen deposition and reduction of terrestrial biodiversity: evidence from temperate grasslands.  

PubMed

Biodiversity is thought to be essential for ecosystem stability, function and long-term sustainability. Since nitrogen is the limiting nutrient for plant growth in many terrestrial ecosystems, reactive nitrogen has the potential to reduce the diversity of terrestrial vegetation and associated biota through favouring species adapted to quickly exploiting available nutrients. Although the potential has long been recognised, only recently has enough evidence come together to show beyond reasonable doubt that these changes are already occurring. Linked together, experimental, regional/empirical, and time-series research provide a powerful argument that enhanced deposition of reactive nitrogen across Great Britain, and potentially the rest of Europe, has resulted in a significant and ongoing decline in grassland species richness and diversity. PMID:20549428

Dise, Nancy B; Stevens, Carly J

2005-09-01

65

Water relations in grassland and desert ecosystems exposed to elevated atmospheric CO 2  

Microsoft Academic Search

Atmospheric CO 2 enrichment may stimulate plant growth directly through (1) enhanced photosynthesis or indirectly, through (2) reduced plant water consumption and hence slower soil moisture depletion, or the combination of both. Herein we describe gas exchange, plant biomass and species responses of five native or semi-native temperate and Mediterranean grasslands and three semi-arid systems to CO 2 enrichment, with

J. A. Morgan; D. E. Pataki; C. Körner; H. Clark; S. J. Del Grosso; J. M. Grünzweig; A. K. Knapp; A. R. Mosier; P. C. D. Newton; P. A. Niklaus; J. B. Nippert; R. S. Nowak; W. J. Parton; H. W. Polley; M. R. Shaw

2004-01-01

66

Effects of nitrogen fertilization on soil respiration in temperate grassland in Inner Mongolia, China  

Microsoft Academic Search

Nitrogen addition to soil can play a vital role in influencing the losses of soil carbon by respiration in N-deficient terrestrial\\u000a ecosystems. The aim of this study was to clarify the effects of different levels of nitrogen fertilization (HN, 200 kg N ha?1 year?1; MN, 100 kg N ha?1 year?1; LN, 50 kg N ha?1 year?1) on soil respiration compared with non-fertilization (CK, 0 kg N ha?1 year?1), from July 2007 to September 2008, in temperate

Qin Peng; Yunshe Dong; Yuchun Qi; Shengsheng Xiao; Yating He; Tao Ma

2011-01-01

67

Understanding of Grassland Ecosystems under Climate Change and Economic Development Pressures in the Mongolia Plateau  

NASA Astrophysics Data System (ADS)

The land use and land cover change, especially in the form of grassland degradation, in the Mongolian Plateau, exhibited a unique spatio-temporal pattern that is a characteristic of a mixed stress from economic development and climate change of the region. The social dimension of the region played a key role in shaping the landscape and land use change, including the cultural clashes with economic development, conflicts between indigenous people and business ventures, and exogenous international influences. Various research projects have been conducted in the region to focus on physical degradation of grasslands and/or on economic development but there is a lack of understanding how the social and economic dimensions interact with grassland ecosystems and changes. In this talk, a synthesis report was made based on the most recent workshop held in Hohhot, Inner Mongolia, of China, that specifically focused on climate change and grassland ecosystems. The report analyzed the degree of grassland degradation, its climate and social drivers, and coupling nature of economic development and conservation of traditional grassland values. The goal is to fully understand the socio-ecological-economic interactions that together shape the trajectory of the grassland ecosystems in the Mongolia Plateau.

Qi, J.; Chen, J.; Shan, P.; Pan, X.; Wei, Y.; Wang, M.; Xin, X.

2011-12-01

68

Grazing alters ecosystem functioning and C:N:P stoichiometry of grasslands along a regional  

E-print Network

Grazing alters ecosystem functioning and C:N:P stoichiometry of grasslands along a regional. The Eurasian steppe has long been subject to grazing by domestic ungulates at high levels, resulting that heavy grazing alters the ecosystem structure and function of grass- lands, research on how grazing

Wu, Jianguo "Jingle"

69

Changes in nitrogen resorption traits of six temperate grassland species along a multi-level N addition gradient  

Microsoft Academic Search

Nitrogen (N) resorption from senescing leaves is an important mechanism of N conservation for terrestrial plant species, but\\u000a changes in N-resorption traits over wide-range and multi-level N addition gradients have not been well characterized. Here,\\u000a a 3-year N addition experiment was conducted to determine the effects of N addition on N resorption of six temperate grassland\\u000a species belonging to three

Ju-Ying Huang; Xiao-Guang Zhu; Zhi-You Yuan; Shi-Huan Song; Xin Li; Ling-Hao Li

2008-01-01

70

Representing the effects of alpine grassland vegetation cover on the simulation of soil thermal dynamics by ecosystem  

E-print Network

Representing the effects of alpine grassland vegetation cover on the simulation of soil thermal and atmospheric factors on the estimation of soil surface temperature for alpine grassland ecosystems has the potential to substantially improve our understanding of the vulnerability of alpine grassland

Ickert-Bond, Steffi

71

Coherent assembly of phytoplankton communities in diverse temperate ocean ecosystems  

PubMed Central

The annual cycle of phytoplankton cell abundance is coherent across diverse ecosystems in the temperate North Atlantic Ocean. In Bedford Basin, on the Scotian Shelf and in the Labrador Sea, the numerical abundance of phytoplankton is low in spring and high in autumn, thus in phase with the temperature cycle. Temperature aligns abundance on a common basis, effectively adjusting apparent cell discrepancies in waters that are colder or warmer than the regional norm. As an example of holistic simplicity arising from underlying complexity, the variance in a community variable (total abundance) is explained by a single predictor (temperature) to the extent of 75% in the marginal seas. In the estuarine basin, weekly averages of phytoplankton and temperature computed from a 13 year time-series yield a predictive relationship with 91% explained variance. Temperature-directed assembly of individual phytoplankton cells to form communities is statistically robust, consistent with observed biomass changes, amenable to theoretical analysis, and a sentinel for long-term change. Since cell abundance is a community property in the same units for all marine microbes at any trophic level and at any phylogenetic position, it promises to integrate biological oceanography into general ecology and evolution. PMID:16822757

Li, William K.W; Glen Harrison, W; Head, Erica J.H

2006-01-01

72

Testing a Model of Carbon and Nitrogen Dynamics in Temperate Forests and Grasslands  

NASA Astrophysics Data System (ADS)

In the last two decades, the importance of hydrological processes for ecosystem dynamics and the effects of plants on hydrological processes has become increasingly apparent A better understanding of the relationship between plant growth (carbon and nitrogen distribution) and the hydrologic characteristics of a catchment would improve ecological assessments and management of forests and grasslands. At the same time, better forecasting tools are needed to support ecosystem management, such as managing land cover to preserve biodiversity, watershed protection, nitrogen retention, and carbon sequestration simultaneously. These tools are needed to manage our natural resources in view of the increasing pollution problems, and to investigate the relationship between ecology and hydrology in a scale amenable for testing and calibration of models. We are developing a detailed, quantitative ecohydrological model for understanding carbon and nitrogen dynamics in small catchments. The model establishes an explicit linkage between the biogeochemical processes and the hydrology of catchments, and its level of prediction is assessed using well-known and tested biogeochemical and hydrological models against field-data. This computer model does not require the use of high performance computers or large and expensive datasets, but it allows the investigation in detail of how the locations and spatial patterns of biogeochemical processes shift across watershed topography in response to antecedent conditions on multiple temporal scales. We present tests of model predictions for seasonal variations in soil ammonium and nitrate over a topographic gradient, and also for spatial patterns of soil total nitrogen and total carbon for Walker Branch Watershed, near Oak Ridge, Tennessee. Model predictions for grasslands include annual biomass production for Cedar Creek Natural History Area, Minnesota.

Gomezdelcampo, E.; Huston, M. A.; Reed, G. D.

2002-05-01

73

Alternative states of a semiarid grassland ecosystem: implications for ecosystem services  

USGS Publications Warehouse

Ecosystems can shift between alternative states characterized by persistent differences in structure, function, and capacity to provide ecosystem services valued by society. We examined empirical evidence for alternative states in a semiarid grassland ecosystem where topographic complexity and contrasting management regimes have led to spatial variations in levels of livestock grazing. Using an inventory data set, we found that plots (n = 72) cluster into three groups corresponding to generalized alternative states identified in an a priori conceptual model. One cluster (biocrust) is notable for high coverage of a biological soil crust functional group in addition to vascular plants. Another (grass-bare) lacks biological crust but retains perennial grasses at levels similar to the biocrust cluster. A third (annualized-bare) is dominated by invasive annual plants. Occurrence of grass-bare and annualized-bare conditions in areas where livestock have been excluded for over 30 years demonstrates the persistence of these states. Significant differences among all three clusters were found for percent bare ground, percent total live cover, and functional group richness. Using data for vegetation structure and soil erodibility, we also found large among-cluster differences in average levels of dust emissions predicted by a wind-erosion model. Predicted emissions were highest for the annualized-bare cluster and lowest for the biocrust cluster, which was characterized by zero or minimal emissions even under conditions of extreme wind. Results illustrate potential trade-offs among ecosystem services including livestock production, soil retention, carbon storage, and biodiversity conservation. Improved understanding of these trade-offs may assist ecosystem managers when evaluating alternative management strategies.

Miller, Mark E.; Belote, R. Travis; Bowker, Matthew A.; Garman, Steven L.

2011-01-01

74

China's grazed temperate grasslands are a net source of atmospheric methane  

NASA Astrophysics Data System (ADS)

A budget for the methane (CH 4) cycle in the Xilin River basin of Inner Mongolia is presented. The annual CH 4 budget in this region depends primarily on the sum of atmospheric CH 4 uptake by upland soils, emission from small wetlands, and emission from grazing ruminants (sheep, goats, and cattle). Flux rates for these processes were averaged over multiple years with differing summer rainfall. Although uplands constitute the vast majority of land area, they consume much less CH 4 per unit area than is emitted by wetlands and ruminants. Atmospheric CH 4 uptake by upland soils was -3.3 and -4.8 kg CH 4 ha -1 y -1 in grazed and ungrazed areas, respectively. Average CH 4 emission was 791.0 kg CH 4 ha -1 y -1 from wetlands and 8.6 kg CH 4 ha -1 y -1 from ruminants. The basin area-weighted average of all three processes was 6.8 kg CH 4 ha -1 y -1, indicating that ruminant production has converted this basin to a net source of atmospheric CH 4. The total CH 4 emission from the Xilin River basin was 7.29 Gg CH 4 y -1. The current grazing intensity is about eightfold higher than that which would result in a net zero CH 4 flux. Since grazing intensity has increased throughout western China, it is likely that ruminant production has converted China's grazed temperate grasslands to a net source of atmospheric CH 4 overall.

Wang, Zhi-Ping; Song, Yang; Gulledge, Jay; Yu, Qiang; Liu, Hong-Sheng; Han, Xing-Guo

75

Modeling of nitric oxide emissions from temperate agricultural ecosystems.  

E-print Network

Uncertainties are associated to the calculation of CRF and differences in the types and areas of14 grassland in the various studies. Under cultivated conditions, agricultural soils are subject to15 heavy disturbances

Paris-Sud XI, Université de

76

Monitoring an ecosystem at risk: what is the degree of grassland fragmentation in the Canadian Prairies?  

PubMed

Increasing fragmentation of grassland habitats by human activities is a major threat to biodiversity and landscape quality. Monitoring their degree of fragmentation has been identified as an urgent need. This study quantifies for the first time the current degree of grassland fragmentation in the Canadian Prairies using four fragmentation geometries (FGs) of increasing specificity (i.e. more restrictive grassland classification) and five types of reporting units (7 ecoregions, 50 census divisions, 1,166 municipalities, 17 sub-basins, and 108 watersheds). We evaluated the suitability of 11 datasets based on 8 suitability criteria and applied the effective mesh size (m(eff)) method to quantify fragmentation. We recommend the combination of the Crop Inventory Mapping of the Prairies and the CanVec datasets as the most suitable for monitoring grassland fragmentation. The grassland area remaining amounts to 87,570.45 km(2) in FG4 (strict grassland definition) and 183,242.042 km(2) in FG1 (broad grassland definition), out of 461,503.97 km(2) (entire Prairie Ecozone area). The very low values of m(eff) of 14.23 km(2) in FG4 and 25.44 km(2) in FG1 indicate an extremely high level of grassland fragmentation. The m(eff) method is supported in this study as highly suitable and recommended for long-term monitoring of grasslands in the Canadian Prairies; it can help set measurable targets and/or limits for regions to guide management efforts and as a tool for performance review of protection efforts, for increasing awareness, and for guiding efforts to minimize grassland fragmentation. This approach can also be applied in other parts of the world and to other ecosystems. PMID:24389841

Roch, Laura; Jaeger, Jochen A G

2014-04-01

77

Nitrogen effects on net ecosystem carbon exchange in a temperate steppe  

Microsoft Academic Search

It has widely been documented that nitrogen (N) enrichment stimulates plant growth and net primary production. However, there is still dispute on how N addition affects net ecosystem CO2 exchange (NEE), which represents the balance between ecosystem carbon (C) uptake and release. We conducted an experimental study to examine effects of N addition on NEE in a temperate steppe in

SHULI NIU; J IANGY ANG X IA; HAIJUN YANG; SHIQIANG WAN

2009-01-01

78

Spatial scaling of CO2 efflux in a temperate grazed grassland  

NASA Astrophysics Data System (ADS)

Understanding CO2 efflux from soil at different scales is important when up-scaling CO2 measurements from plot to larger scales, but there have been few studies investigating spatial CO2 efflux in temperate environments. We conducted a nested analysis of variation to explore how the CO2 efflux variation occurs between different spatial scales. Ninety-six manual dynamic chamber flux measurements of CO2 were undertaken during three, four hour surveys within seven grouped sites, each containing an optimised nested design with lag distances of 0.3m, 1m, 3m and 9m across six hectares of grazed hillslope grassland. This design also included continuous logging soil moisture sensors (plus conductivity and temperature) at 10cm soil depth. A previous study showed at this site that the variation of soil moisture is divided relatively equally between the four spatial scales <0.3m, 0.3-3m, 3-9m and >9m. The proportion of large-scale (>9m) variation increased after rainfall. In contrast in the three surveys analysed to date, the vast majority of the variation in CO2 flux occurred over the two smallest scales. No significant correlation between CO2 and soil moisture was observed over any of the spatial scales. All of these three surveys were conducted on relatively dry soils. We also investigated whether there were significant temporal variations in CO2 efflux over a period of three weeks using an automated soil flux system. These data showed there was no significant temporal variability between 10:00 to 16:00 hrs during late summer. There has recently been substantial rainfall at the field site and we are now conducting additional surveys to examine how the total CO2 fluxes and their spatial variation is effected by these wetter conditions.

Archer, Nicole; Rawlins, Barry; Marchand, Benjamin

2014-05-01

79

Environmental effects of oil and gas lease sites in a grassland ecosystem.  

PubMed

The northern Great Plains of Saskatchewan is one of the most significantly modified landscapes in Canada. While the majority of anthropogenic disturbances to Saskatchewan's grasslands are the result of agricultural practices, development of petroleum and natural gas (PNG) resources is of increasing concern for grassland conservation. Although PNG developments require formal assessment and regulatory approval, follow-up and monitoring of the effects of PNG development on grasslands is not common practice. Consequently, the effects of PNG activity on grasslands and the spatial and temporal extent of such impacts are largely unknown. This paper examines the spatial and temporal extent of PNG development infrastructure from 1955 to 2006 in a grassland ecosystem in southwest Saskatchewan. The effects of PNG development on grassland ecology were assessed from measurements of ground cover characteristics, soil properties, and plant community composition at 31 sites in the study area. PNG lease sites were found to have low cover of herbaceous plants, club moss (Lycopodiaceae), litter, and shallow organic (Ah) horizons. Lease sites were also characterized by low diversity of desirable grassland plants and low range health values compared to off-lease reference sites. These impacts were amplified at active and highly productive lease sites. Impacts of PNG development persisted for more than 50 years following well site construction, and extended outward 20 m-25 m beyond the direct physical footprint of PNG well infrastructure. These results have significant implications with regard to the current state of monitoring and follow-up of PNG development, and the cumulative effective of PNG activity on grassland ecosystems over space and time. PMID:20880628

Nasen, Lawrence C; Noble, Bram F; Johnstone, Jill F

2011-01-01

80

Climate and ecosystem 15N natural abundance along a transect of Inner Mongolian grasslands: Contrasting regional patterns and global patterns  

Microsoft Academic Search

Nitrogen isotopes provide integrated information about nitrogen cycling in terrestrial ecosystems. This study explores the regional patterns of ecosystem 15N abundance along a 1200 km transect in Inner Mongolian grasslands and their relationships with climate. Results indicate that climatic variables control approximately 50% of the variation in ecosystem 15N abundance along the transect. Ecosystem 15N abundance decreases as both mean

Weixin Cheng; Quansheng Chen; Yuqing Xu; Xingguo Han; Linghao Li

2009-01-01

81

Relationship between plant diversity andRelationship between plant diversity and AMF diversity in grassland ecosystems  

E-print Network

in grassland ecosystems Liang, Yug, Institute of Botany, Chinese Academy of Sciences coolrain@ibcas ac disturbance hypothesishypothesis Liang Y, SUN XF, Shahid Naeem, BAI YF,MA KPg , , , , #12;Experimental disturbance removal S i i hSpecies richness #12;Species richness of AMF Partial removal #12;AMF species

Bruns, Tom

82

Contrasting responses of terrestrial ecosystem production to hot temperature extreme regimes between grassland and forest  

NASA Astrophysics Data System (ADS)

Observational data during the past several decades show faster increase of hot temperature extremes over land than changes in mean temperature. Towards more extreme temperature is expected to affect terrestrial ecosystem function. However, the ecological impacts of hot extremes on vegetation production remain uncertain across biomes in natural climatic conditions. In this study, we investigated the effects of hot temperature extremes on aboveground net primary production (ANPP) by combining MODIS EVI dataset and in situ climatic records during 2000 to 2009 from 12 long-term experimental sites across biomes and climates. Our results showed that higher mean annual maximum temperatures (Tmax) greatly reduced grassland production, and yet enhanced forest production after removing the effects of precipitation. Relative decreases in ANPP were 16% for arid grassland and 7% for mesic grassland, and the increase were 5% for forest. We also observed a significant positive relationship between interannual ANPP and Tmax for forest biome (R2 = 0.79, P < 0.001). This line of evidence suggests that hot temperature extreme leads to contrasting ecosystem-level response of vegetation production to warming climate between grassland and forest. Given that many terrestrial ecosystem models use average daily temperature as input, predictions of ecosystem production should consider these contrasting responses to more hot temperature extreme regimes associated with climate change.

Zhang, Y.; Voigt, M.; Liu, H.

2014-04-01

83

Perennial grasslands enhance biodiversity and multiple ecosystem services in bioenergy landscapes  

E-print Network

Perennial grasslands enhance biodiversity and multiple ecosystem services in bioenergy landscapes, Michigan State University, East Lansing, MI 48824; b Great Lakes Bioenergy Research Center, US Department of Nebraska at Omaha, Omaha, NE 68182; d Great Lakes Bioenergy Research Center, US Department of Energy

Landis, Doug

84

Regional patterns and controls of ecosystem salinization with grassland afforestation along a rainfall gradient  

Microsoft Academic Search

Vegetation change affects water fluxes and influences the direction and intensity of salt exchange between ecosystems and groundwater. In some conditions it can also lead to an intense accumulation of salts in soils and aquifers, as has been documented for the conversion of native grassland to tree plantations in the plains of Argentina, Hungary and Russia. In this paper we

M. D. Nosetto; E. G. Jobbágy; T. Tóth; R. B. Jackson

2008-01-01

85

MAGE, a dynamic model of alkaline grassland ecosystems with variable soil characteristics  

Microsoft Academic Search

An area-based process model for alkaline grassland ecosystem, MAGE, was developed to address the problems associated with the soil alkalization\\/dealkalization processes coupled with surface vegetation on Songnen Plain, northeast China. The model gave special consideration to the variation of soil characteristics such as water retentivity and hydraulic conductivity as functions of surface vegetation. Soil within 1 m depth was divided

Qiong Gao; Xiusheng Yang; Rui Yun; Chunping Li

1996-01-01

86

Understanding the importance wet, unimproved Culm grasslands have for the provision of multiple ecosystem services  

NASA Astrophysics Data System (ADS)

It is increasingly recognised that catchments must be carefully managed for the provision of multiple, sometimes conflicting ecosystem services. This requires an increased interdisciplinary environmental understanding to inform management policy and practices by government, landowners and stakeholders. The Culm National Character Area (NCA) covers 3,500 square kilometres in South West England with Culm grasslands consisting of wet unimproved, species rich pastures, typically on poorly drained soils. Since the 1960's, policy changes have encouraged the drainage of large areas of land for agricultural improvement and consequently Culm grassland sites have become highly fragmented. There are currently 575 Culm grassland sites in the Culm NCA with a mean area of 7 ha. Traditionally, Culm grasslands have been managed by light grazing and scrub management. Since 2008, Devon Wildlife Trust's Working Wetlands project has been working with farmers and landowners to manage and restore and recreate Culm grasslands. It is part of South West Water's Upstream Thinking initiative and is now augmented by the Northern Devon Nature Improvement Area programme. However, from a hydrological perspective, Culm and similar unimproved grasslands remain poorly understood. In addition to their recognised conservation and biodiversity importance; unimproved grasslands such as Culm are thought to have a high water storage capacity, reducing runoff and therefore flooding during wet periods, whilst slowly releasing and filtering water to help maintain water quality, and base river flows during dry periods. Therefore, if properly understood and managed Culm soils have the potential to play an important role in the management of catchment water resources. Furthermore, Culm grassland soils are thought to have a high potential for the sequestration and storage of carbon, an increasingly valuable ecosystem service. This study aims to increase understanding of the influence Culm grasslands have upon water and soil resources, relative to other land uses and land covers (wet woodland, scrub and intensively managed grassland). Results will be presented demonstrating that relative to intensively managed grassland, Culm soils have a higher water holding capacity, exhibit a more attenuated response to rainfall events and have higher carbon concentrations. Additionally, results show water leaving a Culm dominated sub-catchment is of a higher quality (i.e. exhibiting lower suspended sediment, dissolved organic carbon and phosphate loads) than comparable intensively managed agricultural catchments.

Brazier, Richard; Elliot, Mark; Warren, Susan; Puttock, Alan

2014-05-01

87

An Ecosystem in Transition: Causes and Consequences of the Conversion of Mesic Grassland to Shrubland  

NSDL National Science Digital Library

This peer -reviewed article from BioScience investigates the change from grassland to shrubland in the central US. Woody plant expansion is one of the greatest contemporary threats to mesic grasslands of the central United States. In this article, we synthesize more than 20 years of research to elucidate the causes and consequences of the ongoing transition of C4-dominated grasslands to savanna-like ecosystems codominated by grasses and woody plants. This transition is contingent on fire-free intervals, which provide the opportunity for recruitment both of new individuals and of additional shrub and tree species into this grassland. Once shrubs establish, their cover increases regardless of fire frequency, and infrequent fires accelerate the spread of some shrub species. This process has resulted in a new dynamic state of shrubgrass coexistence in the mesic grasslands of North America. Important consequences of this shift in plant life-form abundance include alterations in plant productivity, species diversity, and carbon storage. Without drastic measures such as mechanical removal of shrubs, it is unlikely that management of fire and grazing regimes alone will be sufficient to restore historic grass dominance in these ecosystems.

JOHN M. BRIGGS, ALAN K. KNAPP, JOHN M. BLAIR, JANA L. HEISLER, GREG A. HOCH, MICHELLE S. LETT, and JAMES K. McCARRON (;)

2005-03-01

88

Evaluating Ecosystem Services Provided by Non-Native Species: An Experimental Test in California Grasslands  

PubMed Central

The concept of ecosystem services – the benefits that nature provides to human's society – has gained increasing attention over the past decade. Increasing global abiotic and biotic change, including species invasions, is threatening the secure delivery of these ecosystem services. Efficient evaluation methods of ecosystem services are urgently needed to improve our ability to determine management strategies and restoration goals in face of these new emerging ecosystems. Considering a range of multiple ecosystem functions may be a useful way to determine such strategies. We tested this framework experimentally in California grasslands, where large shifts in species composition have occurred since the late 1700's. We compared a suite of ecosystem functions within one historic native and two non-native species assemblages under different grazing intensities to address how different species assemblages vary in provisioning, regulatory and supporting ecosystem services. Forage production was reduced in one non-native assemblage (medusahead). Cultural ecosystem services, such as native species diversity, were inherently lower in both non-native assemblages, whereas most other services were maintained across grazing intensities. All systems provided similar ecosystem services under the highest grazing intensity treatment, which simulated unsustainable grazing intensity. We suggest that applying a more comprehensive ecosystem framework that considers multiple ecosystem services to evaluate new emerging ecosystems is a valuable tool to determine management goals and how to intervene in a changing ecosystem. PMID:25222028

Stein, Claudia; Hallett, Lauren M.; Harpole, W. Stanley; Suding, Katharine N.

2014-01-01

89

Evaluating ecosystem services provided by non-native species: an experimental test in California grasslands.  

PubMed

The concept of ecosystem services--the benefits that nature provides to human's society--has gained increasing attention over the past decade. Increasing global abiotic and biotic change, including species invasions, is threatening the secure delivery of these ecosystem services. Efficient evaluation methods of ecosystem services are urgently needed to improve our ability to determine management strategies and restoration goals in face of these new emerging ecosystems. Considering a range of multiple ecosystem functions may be a useful way to determine such strategies. We tested this framework experimentally in California grasslands, where large shifts in species composition have occurred since the late 1700's. We compared a suite of ecosystem functions within one historic native and two non-native species assemblages under different grazing intensities to address how different species assemblages vary in provisioning, regulatory and supporting ecosystem services. Forage production was reduced in one non-native assemblage (medusahead). Cultural ecosystem services, such as native species diversity, were inherently lower in both non-native assemblages, whereas most other services were maintained across grazing intensities. All systems provided similar ecosystem services under the highest grazing intensity treatment, which simulated unsustainable grazing intensity. We suggest that applying a more comprehensive ecosystem framework that considers multiple ecosystem services to evaluate new emerging ecosystems is a valuable tool to determine management goals and how to intervene in a changing ecosystem. PMID:25222028

Stein, Claudia; Hallett, Lauren M; Harpole, W Stanley; Suding, Katharine N

2014-01-01

90

The biogeochemistry of a north-temperate grassland with native ungulates: Nitrogen dynamics in Yellowstone National Park  

Microsoft Academic Search

Nutrient dynamics of large grassland ecosystems possessing abundant migratory grazers are poorly understood. We examined N cycling on the northern winter range of Yellowstone National Park, home for large herds of free-roaming elk (Cervus elaphus) and bison (Bison bison). Plant and soil N, net N mineralization, and the deposition of ungulate fecal-N were measured at five sites, a ridgetop, mid-slope

Douglas A. Frank; Richard S. Inouye; Nancy Huntly; G. WAYNE MINSHALL; Jay E. Anderson

1994-01-01

91

Fluxes of CO 2 , N 2 O and CH 4 from a typical temperate grassland in Inner Mongolia and its daily variation  

Microsoft Academic Search

Using a dark enclosed chamber technique, the fluxes of CO2, N2O and CH4 from nature and disturbed grassland were measured on the spot in Inner Mongolian Temperate Grassland along the annual rainfall\\u000a gradient section ranging from 450 to 200 mm. The results showed that the measured mean fluxes of CO2, N2O and CH4 were (1 180.4 ± 308.7), (0.010 ±

Yunshe Dong; Shen Zhang; Yuchun Qi; Zuozhong Chen; Yuanbo Geng

2000-01-01

92

Diversity Promotes Temporal Stability across Levels of Ecosystem Organization in Experimental Grasslands  

PubMed Central

The diversity–stability hypothesis states that current losses of biodiversity can impair the ability of an ecosystem to dampen the effect of environmental perturbations on its functioning. Using data from a long-term and comprehensive biodiversity experiment, we quantified the temporal stability of 42 variables characterizing twelve ecological functions in managed grassland plots varying in plant species richness. We demonstrate that diversity increases stability i) across trophic levels (producer, consumer), ii) at both the system (community, ecosystem) and the component levels (population, functional group, phylogenetic clade), and iii) primarily for aboveground rather than belowground processes. Temporal synchronization across studied variables was mostly unaffected with increasing species richness. This study provides the strongest empirical support so far that diversity promotes stability across different ecological functions and levels of ecosystem organization in grasslands. PMID:20967213

Proulx, Raphael; Wirth, Christian; Voigt, Winfried; Weigelt, Alexandra; Roscher, Christiane; Attinger, Sabine; Baade, Jussi; Barnard, Romain L.; Buchmann, Nina; Buscot, Francois; Eisenhauer, Nico; Fischer, Markus; Gleixner, Gerd; Halle, Stefan; Hildebrandt, Anke; Kowalski, Esther; Kuu, Annely; Lange, Markus; Milcu, Alex; Niklaus, Pascal A.; Oelmann, Yvonne; Rosenkranz, Stephan; Sabais, Alexander; Scherber, Christoph; Scherer-Lorenzen, Michael; Scheu, Stefan; Schulze, Ernst-Detlef; Schumacher, Jens; Schwichtenberg, Guido; Soussana, Jean-Francois; Temperton, Vicky M.; Weisser, Wolfgang W.; Wilcke, Wolfgang; Schmid, Bernhard

2010-01-01

93

Leaf and ecosystem response to soil water availability in mountain grasslands  

PubMed Central

Climate change is expected to affect the Alps by increasing the frequency and intensity of summer drought events with negative impacts on ecosystem water resources. The response of CO2 and H2O exchange of a mountain grassland to natural fluctuations of soil water content was evaluated during 2001-2009. In addition, the physiological performance of individual mountain forb and graminoid plant species under progressive soil water shortage was explored in a laboratory drought experiment. During the 9-year study period the natural occurrence of moderately to extremely dry periods did not lead to substantial reductions in net ecosystem CO2 exchange and evapotranspiration. Laboratory drought experiments confirmed that all the surveyed grassland plant species were insensitive to progressive soil drying until very low soil water contents (<0.01 m3 m?3) were reached after several days of drought. In field conditions, such a low threshold was never reached. Re-watering after a short-term drought event (5±1 days) resulted in a fast and complete recovery of the leaf CO2 and H2O gas exchange of the investigated plant species. We conclude that the present-day frequency and intensity of dry periods does not substantially affect the functioning of the investigated grassland ecosystem. During dry periods the observed “water spending” strategy employed by the investigated mountain grassland species is expected to provide a cooling feedback on climate warming, but may have negative consequences for down-stream water users. PMID:24465071

Brilli, Federico; Hortnagl, Lukas; Hammerle, Albin; Haslwanter, Alois; Hansel, Armin; Loreto, Francesco; Wohlfahrt, Georg

2014-01-01

94

Soil ecosystem function under native and exotic plant assemblages as alternative states of successional grasslands  

NASA Astrophysics Data System (ADS)

Old fields often become dominated by exotic plants establishing persistent community states. Ecosystem functioning may differ widely between such novel communities and the native-dominated counterparts. We evaluated soil ecosystem attributes in native and exotic (synthetic) grass assemblages established on a newly abandoned field, and in remnants of native grassland in the Inland Pampa, Argentina. We asked whether exotic species alter soil functioning through the quality of the litter they shed or by changing the decomposition environment. Litter decomposition of the exotic dominant Festuca arundinacea in exotic assemblages was faster than that of the native dominant Paspalum quadrifarium in native assemblages and remnant grasslands. Decomposition of a standard litter (Triticum aestivum) was also faster in exotic assemblages than in native assemblages and remnant grasslands. In a common garden, F. arundinacea showed higher decay rates than P. quadrifarium, which reflected the higher N content and lower C:N of the exotic grass litter. Soil respiration rates were higher in the exotic than in the native assemblages and remnant grasslands. Yet there were no significant differences in soil N availability or net N mineralization between exotic and native assemblages. Our results suggest that exotic grass dominance affected ecosystem function by producing a more decomposable leaf litter and by increasing soil decomposer activity. These changes might contribute to the extended dominance of fast-growing exotic grasses during old-field succession. Further, increased organic matter turnover under novel, exotic communities could reduce the carbon storage capacity of the system in the long term.

Spirito, Florencia; Yahdjian, Laura; Tognetti, Pedro M.; Chaneton, Enrique J.

2014-01-01

95

The influence of abiotic controls and management intensity on phosphorus cycling in established grassland and forest ecosystems  

NASA Astrophysics Data System (ADS)

It is commonly assumed that the bioavailability and cycling of phosphorus (P) is mainly controlled by abiotic soil properties including soil pH and the concentrations and reactivities of clay minerals, CaCO3 and Al/Fe oxides In managed ecosystems, kind, timing and duration of P additions and type and amount of harvested biomass are the major input and output fluxes. Our objective was to disentangle the effects of abiotic controls, and type and intensity of management on the P cycle in soils of temperate grasslands and forests of different management intensity in three regions across Germany in the frame of the Biodiversity Exploratories project. The pH value was the most important variable explaining P concentrations and partitioning in soil and changes in pH are the main mechanism how land-use is affecting the P cycle. However, after the influence of pH was accounted for in a sequential statistical approach, land-use intensity, classified according to the extent of annual biomass removal, explained a significant (P < 0.05) part of the variance in the contributions of several P fractions to total P (TP) among all studied regions and land-use types. In grassland soils of highly diverse systems (up to 57 plant species) in one of the study regions, the Schwäbische Alb, a mid-range mountain area on limestone where soils showed a limited variation in pH in the carbonate buffer range, pedogenic Fe oxide concentrations, fertilizer-P application rates, and TP concentrations in soil explained more than half of the variation in bioavailable inorganic (Pi) concentrations extracted with NaHCO3 in soil. Our results demonstrate that mainly soil pH and mineralogical composition, and intensity of management of the managed ecosystems are significant controls of the P cycle determining the size of bioavailable P pool in soil.

Alt, F.; Oelmann, Y.; Wilcke, W.

2011-12-01

96

Partitioning European grassland net ecosystem CO 2 exchange into gross primary productivity and ecosystem respiration using light response function analysis  

Microsoft Academic Search

Tower CO2 flux measurements from 20 European grasslands in the EUROGRASSFLUX data set covering a wide range of environmental and management conditions were analyzed with respect to their ecophysiological characteristics and CO2 exchange (gross primary production, Pg, and ecosystem respiration, Re) using light-response function analysis. Photosynthetically active radiation (Q) and top-soil temperature (Ts) were identified as key factors controlling CO2

T. G. Gilmanov; J. F. Soussana; L. Aires; V. Allard; C. Ammann; M. Balzarolo; Z. Barcza; C. Bernhofer; C. L. Campbell; A. Cernusca; A. Cescatti; J. C. Clifton-Brown; B. O. M. Dirks; S. Dore; W. Eugster; J. Fuhrer; C. Gimeno; T. Gruenwald; L. Haszpra; A. Hensen; A. Ibrom; A. F. G. Jacobs; M. B. Jones; G. Lanigan; T. Laurila; A. Lohila; G. Manca; B. Marcolla; Z. Nagy; K. Pilegaard; K. Pinter; C. Pio; A. Raschi; N. Rogiers; M. J. Sanz; P. Stefani; M. Sutton; Z. Tuba; R. Valentini; M. L. Williams; G. Wohlfahrt

2007-01-01

97

Soil moisture variations and ecosystem-scale fluxes of water and carbon in semiarid grassland and shrubland  

E-print Network

Soil moisture variations and ecosystem-scale fluxes of water and carbon in semiarid grassland 2007; published 20 June 2007. [1] Soil moisture distribution emerges as a key link between hydrologic at both locations. Additionally, the grassland site features six soil moisture profiles and the shrubland

Small, Eric

98

Effects of species evenness and dominant species identity on multiple ecosystem functions in model grassland communities.  

PubMed

Ecosystems provide multiple services upon which humans depend. Understanding the drivers of the ecosystem functions that support these services is therefore important. Much research has investigated how species richness influences functioning, but we lack knowledge of how other community attributes affect ecosystem functioning. Species evenness, species spatial arrangement, and the identity of dominant species are three attributes that could affect ecosystem functioning, by altering the relative abundance of functional traits and the probability of synergistic species interactions such as facilitation and complementary resource use. We tested the effect of these three community attributes and their interactions on ecosystem functions over a growing season, using model grassland communities consisting of three plant species from three functional groups: a grass (Anthoxanthum odoratum), a forb (Plantago lanceolata), and a N-fixing forb (Lotus corniculatus). We measured multiple ecosystem functions that support ecosystem services, including ecosystem gas exchange, water retention, C and N loss in leachates, and plant biomass production. Species evenness and dominant species identity strongly influenced the ecosystem functions measured, but spatial arrangement had few effects. By the end of the growing season, evenness consistently enhanced ecosystem functioning and this effect occurred regardless of dominant species identity. The identity of the dominant species under which the highest level of functioning was attained varied across the growing season. Spatial arrangement had the weakest effect on functioning, but interacted with dominant species identity to affect some functions. Our results highlight the importance of understanding the role of multiple community attributes in driving ecosystem functioning. PMID:24213721

Orwin, Kate H; Ostle, Nick; Wilby, Andrew; Bardgett, Richard D

2014-03-01

99

Effects of management of ecosystem carbon pools and fluxes in grassland ecosystems  

NASA Astrophysics Data System (ADS)

Grasslands represent a large land-use footprint and have considerable potential to sequester carbon (C) in soil. Climate policies and C markets may provide incentives for land managers to pursue strategies that optimize soil C storage, yet we lack robust understanding of C sequestration in grasslands. Previous research has shown that management approaches such as organic amendments or vertical subsoiling can lead to larger soil C pools. These management approaches can both directly and indirectly affect soil C pools. We used well-replicated field experiments to explore the effects of these management strategies on ecosystem C pools and fluxes in two bioclimatic regions of California (Sierra Foothills Research and Extension Center (SFREC) and Nicasio Ranch). Our treatments included an untreated control, compost amendments, plowed (vertical subsoil), and compost + plow. The experiment was conducted over two years allowing us to compare dry (360 mm) and average (632 mm) rainfall conditions. Carbon dioxide (CO2) fluxes were measured weekly using a LI-8100 infrared gas analyzer. Methane (CH4) and nitrous oxide (N2O) fluxes were measured monthly using static flux chambers. Aboveground and belowground biomass were measured at the end of the growing season as an index of net primary productivity (NPP) in the annual plant dominated system. Soil moisture and temperature were measured continuously and averaged on hourly and daily timescales. Soil organic C and N concentrations were measured prior to the application of management treatments and at the ends of each growing season. Soils were collected to a 10 cm depth in year one and at four depth increments (0-10, 10-30, 30-50, and 50-100 cm) in year two. Soil C and N concentrations were converted to content using bulk density values for each plot. During both growing seasons, soil respiration rates were higher in the composted plots and lower in the plowed plots relative to controls at both sites. The effects on C loss via soil respiration were stronger in the first year, with compost soils experiencing a 21 ± 1 % greater cumulative loss at SFREC and 16 ± 3 % more at Nicasio. The second year showed a similar trend, but with a lower magnitude loss. Aboveground NPP responded positively to compost additions and negatively to plowing at both sites. At SFREC, we measured 58 % more ANPP in composted relative to control plots in year one (369 vs 230 g C/m2) and 56 % more in year two (327 vs 209 g C/m2). Aboveground NPP on plowed plots was 129 g C/m2 in year one, and 185 g C/m2 in year two. Plowed soils also showed a significant decline in soil C and N concentrations (C= 2.67 ± 0.13%, N = 0.20 ± 0.01%). Compost additions increased soil C and N concentrations (C= 3.92 ± 0.29%, N = 0.32 ± 0.02%) relative to control soils (C= 3.52 ± 0.20%, N = 0.27 ± 0.07%). Throughout the experiment, we did not detect significant treatment differences in CH4 or N2O fluxes, nor did we detect significant differences at any individual sampling point. These results suggest that compost addition can lead to an increase in ecosystem C storage, with a small offset from elevated soil respiration.

Ryals, R.; Silver, W. L.

2010-12-01

100

SOIL MICROBES COMPETE EFFECTIVELY WITH PLANTS FOR ORGANIC-NITROGEN INPUTS TO TEMPERATE GRASSLANDS  

Microsoft Academic Search

Although agricultural grassland soils have inherently high rates of net ni- trogen (N) mineralization, they often have soil concentrations of soluble organic N that are comparable to inorganic N. We set out to examine in situ the significance of organic N for plant nutrition in grasslands of differing management intensity and soil fertility. Using in situ dual-labeling techniques (glycine-2-13C-15N) we

Richard D. Bardgett; Tania C. Streeter; Roland Bol

2003-01-01

101

A hierarchical perspective on the ecology of biological invasions:: impact of red imported fire ants on grassland ecosystems  

E-print Network

A HIERARCHICAL PERSPECTIVE ON THE ECOLOGY OF BIOLOGICAL INVASIONS: IMPACT OF RED IMPORTED FIRE ANTS ON GRASSLAND ECOSYSTEMS A Thesis REVIN LEE STOKER Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment... of the requirements for the degree of MASTER OF SCIENCE December 1992 Major Subject: Wildlife and Fisheries Sciences A HIERARCHICAL PERSPECTIVE ON THE ECOLOGY OF BIOLOGICAL INVASIONS: IMPACT OF RED IMPORTED FIRE ANTS ON GRASSLAND ECOSYSTEMS A Thesis Revin Lee...

Stoker, Revin Lee

2012-06-07

102

Net ecosystem CO 2 exchange in a temperate cattail marsh in relation to biophysical properties  

Microsoft Academic Search

Net ecosystem exchange (NEE) of carbon dioxide (CO2) was measured at a temperate cattail marsh using the eddy covariance technique in order to examine the relationships between NEE, weather, and vegetation properties. Analyses of CO2 fluxes for a complete year (May 9, 2005 to May 30, 2006) showed that the marsh wetland was a net CO2 sink for each month

Marie-Claude Bonneville; Ian B. Strachan; Elyn R. Humphreys; Nigel T. Roulet

2008-01-01

103

Effects of mowing on N2O emission from a temperate grassland in Inner Mongolia, Northern China  

NASA Astrophysics Data System (ADS)

Grazing and mowing are two common practices for grassland management. Mowing is now recommended as an alternative to traditional grazing for grassland conservation in Inner Mongolia, northern China. Many studies have revealed that both mowing and grazing may alter ecosystem properties in various ways. However, little attention has been paid to the effect of mowing on trace gas emissions, especially on N2O flux. In this study, we conducted an experiment to investigate the effects of mowing on N2O fluxes from a semiarid grassland in Inner Mongolia. The mowing experiment, which started in 2003, comprised four mowing intensity treatments, i.e. mowing heights at 2, 5, 10 and 15 cm above the soil surface, respectively, and a control of non-mowing, with five replicates. Gas fluxes were measured through a closed static chamber technique during the growing seasons (usually from May to September, depending on local climate at the time) of 2008 and 2009, respectively. Our results showed that mowing decreased N2O emissions, above-ground biomass and total litter production. N2O emissions were greater in May and June than in other sampling periods, regardless of treatments. A co-relationship analysis suggested that variations in seasonal N2O fluxes were mainly driven by variations in soil moisture and microbial biomass nitrogen, except in July and August. In July and August, above-ground plant biomass and soil total nitrogen became the major drivers of N2O fluxes under the soil temperatures between 16 °C and 18 °C. Overall, our study indicated that the introduction of mowing as a management practice might decrease N2O emissions in grasslands, and both mowing height and soil properties affected the magnitude of the reduction. Our findings imply that grasslands, along with proper management practices, can be a N2O sink mitigating the rise of N2O in the atmosphere.

Zhang, L.; Wang, Q.; Laanbroek, H. J.; Wang, C.; Guo, D.; Li, L.

2013-12-01

104

Watershed and ecosystem responses to invasive grass establishment and dominance across a desert grassland watershed  

NASA Astrophysics Data System (ADS)

Compared to aridland systems that have undergone rapid change in dominant vegetation growth form, the consequences to watershed and ecosystem processes following a shift in dominance between similar growth forms have not been well-studied. Following a five year drought period, strong summer monsoon rains in 2006 across the USDA-ARS Walnut Gulch Experimental Watershed near Tombstone, AZ, were accompanied by widespread native perennial grass mortality, a transient increase in annual forbs, followed by establishment and sustained dominance by the invasive South African bunchgrass, Lehmann lovegrass (Eragrostis lehmanniana) across a semiarid grassland watershed (Kendall grassland, WS#112). This loss of ecological diversity occurred across a watershed already instrumented for quantifying long-term climate, watershed, hill-slope, and ecosystem-level gas exchange. Salient findings from these data sets were: 1) annual watershed sediment discharge rapidly returned to pre-invasion levels following a large spike in 2006 that accounted for 65% of the total sediment yield summed over 35 years, 2) plot-level experimental runoff studies showed hill-slope sediment yields consistently doubled, as did growing season soil evaporation contributions to ET, and 3) the grassland was a carbon sink during dry conditions under lovegrass dominance. These findings show that while some aspects of watershed and ecosystem function rapidly re-established (i.e. sediment yield and net primary productivity), processes acting at lower spatial and temporal scales have been negatively impacted by lovegrass dominance. We believe these lower-order processes underlie the strong ecological effects associated with Lehmann lovegrass invasion, and may also accelerate landform processes and change the basic ecohydrological characteristics of semi-arid grassland watersheds.

Hamerlynck, E.; Scott, R.; Polyakov, V.; Sugg, Z.; Moran, M. S.; Stone, J.; Nearing, M.

2012-04-01

105

Effects of repeated fires on ecosystem C and N stocks along a fire induced forest/grassland gradient  

NASA Astrophysics Data System (ADS)

Repeated fires might have different effect on ecosystem carbon storage than a single fire event, but information on repeated fires and their effects on forest ecosystems and carbon storage is scarce. However, changes in climate, vegetation composition, and human activities are expected to make forests more susceptible to fires that recur with relatively high frequency. In this study, the effects of repeated fires on ecosystem carbon and nitrogen stocks were examined along a fire-induced forest/grassland gradient wherein the fire events varied from an unburned forest to repeatedly burned grassland. Results from the study show repeated fires drastically decreased ecosystem carbon and nitrogen stocks along the forest/grassland gradient. The reduction began with the disappearance of living tree biomass, and followed by the loss of soil carbon and nitrogen. Within 4 years of the onset of repeated fires on the unburned forest, the original ecosystem carbon and nitrogen stocks were reduced by 42% and 21%, respectively. Subsequent fires caused cumulative reductions in ecosystem carbon and nitrogen stocks by 68% and 44% from the original ecosystem carbon and nitrogen stocks, respectively. The analyses of carbon budgets calculated by vegetation composition and stable isotopic ?13C values indicate that 84% of forest-derived carbon is lost at grassland, whereas the gain of grass-derived carbon only compensates 18% for this loss. Such significant losses in ecosystem carbon and nitrogen stocks suggest that the effects of repeated fires have substantial impacts on ecosystem and soil carbon and nitrogen cycling.

Cheng, Chih-Hsin; Chen, Yung-Sheng; Huang, Yu-Hsuan; Chiou, Chyi-Rong; Lin, Chau-Chih; Menyailo, Oleg V.

2013-03-01

106

Interannual Variability in Net Ecosystem Exchange in United States Great Plains Grasslands  

NASA Astrophysics Data System (ADS)

The grasslands in the United States Great Plains occupy about 1.5 million km2 and span considerable moisture and temperature gradients. The grasslands are characterized by different photosynthetic pathways, from C3 dominance in the north to C4 dominance in the south. The contributions of grasslands to local and regional carbon budgets remain uncertain due to the lack of carbon flux data for these extensive and diverse grassland ecosystems and local variances in climate variability, land use changes, and varying land management practices. There are limited studies on the seasonal, spatial, and interannual variabilities in carbon exchange as well as responses to climatic change across the Great Plains. Our objective was to quantify how the grassland ecosystems will respond to climate under a variety of environmental conditions. Net ecosystem exchange (NEE) was measured at 15 flux towers distributed throughout the Great Plains. These sites represent the wide spatial, ecological, and climatological ranges of grasslands found in this region. We developed a remote sensing-based piecewise regression (PWR) model to estimate grassland carbon fluxes from 2000 to 2008 using flux-tower data and remotely sensed data (250-m resolution) input at 7-day intervals. The model integrated MODIS-derived vegetation indices, weather data, and phenological parameters with the observed NEE data. The correlation coefficient (r) for the independent tests between tower-measured NEE and PWR-estimated NEE were 0.61 to 0.98 for the individual tower sites withheld and 0.81 to 0.92 for the individual years withheld. We mapped 7-day interval NEE at 250-m resolution for the years 2000 to 2008 and evaluated the interannual variability of NEE and its response to climatic variation. NEE varied in space and time across the 9 years (from 0.3 in 2002 to 47.7 g C • m-2 • yr-1 in 2005) with an average annual NEE of 24 ± 14 g C • m-2 • yr-1 and a cumulative flux of 214 g C • m-2. On average, the entire Great Plains grassland region was a carbon sink during the 9 years. However, three ecoregions were sources for carbon because of frequent droughts during 2000-2009 with a cumulative flux of -10 g C • m-2 for the Northwestern Great Plains, -438 g C • m-2 for the Western High Plains, and -696 g C • m-2 for the Southwestern Tablelands. NEE exhibited large spatial variation in the drier west (carbon sources) and in the wetter east (carbon sinks). In addition, large temporal variations in annual NEE were observed over the Great Plains during the 9 year period, especially in the western and southern portion of the region. These results suggest that Great Plains grassland ecosystems are potentially large carbon sinks but may turn to carbon sources during drought periods or upon conversion to agriculture.

Zhang, Li; Wylie, Bruce; Ji, Lei; Gilmanov, Tagir; Howard, Danny

2010-05-01

107

Land use change in a temperate grassland soil: afforestation effects on chemical properties and their ecological and mineralogical implications.  

PubMed

The current change in land use of grassland in the temperate region of South America is a process associated with the worldwide expansion of annual crops and afforestation with fast growing exotic species. This last cultivation has particularly been the subject of numerous studies showing its negative effects on soil (acidification, loss of organic matter and base cations, among others). However its effects on the mineral fraction are not yet known, as it is generally considered as one of the slowest responses to changes. This stimulated the present study in order to assess whether the composition of clay minerals could be altered together with some of the physicochemical parameters affected by afforestation. This study compares the mineralogical composition of clays by X-ray diffraction (XRD) in a grassland soil (Argiudolls) under natural coverage and under Eucalyptus grandis cultivation implanted 25 years ago in a sector of the same grassland. The tendency of some physicochemical parameters, common to other studies was also compared. XRD results showed, as a most noticeable difference in A(11) and A(12) subhorizons (~20 cm) under eucalyptus, the fall of the 10Å spectrum minerals (illite-like minerals), which are the main reservoir of K in the soil. Meanwhile, the physicochemical parameters showed significant changes (p<0.01) to highly significant ones under eucalyptus, particularly in these subhorizons, where on average soil organic matter decreased by 43%; K(+) by 34%; Ca(2+) by 44%, while the pH dropped to this level by half a point. Our results show that the exportation of some nutrients is not compensated due to the turnover of organic forestry debris; the process of soil acidification was not directly associated with the redistribution of cations, but with an incipient podzolization process; the loss of potassium together with soil acidification, leads to a drastic change in clay mineralogy, which would be irreversible. PMID:23064181

Céspedes-Payret, Carlos; Piñeiro, Gustavo; Gutiérrez, Ofelia; Panario, Daniel

2012-11-01

108

Haloorganics in Temperate Forest Ecosystems: Sources, Transport and Degradation  

Microsoft Academic Search

\\u000a The halogens, most importantly fluorine, chlorine, bromine, and iodine, occur in nature as ions and compounds, including organic\\u000a compounds. Halogenated organic substances (haloorganics) were long considered purely anthropogenic products; however, they\\u000a are in addition a commonly occurring and important part of natural ecosystems. Natural haloorganics are produced largely by\\u000a living organisms, although abiotic production occurs as well. A survey is

Nicholas Clarke; Milan Gryndler; Hans-Holger Liste; Reiner Schroll; Peter Schröder; Miroslav Matucha

109

Comparison of seasonal soil microbial process in snow-covered temperate ecosystems of northern China.  

PubMed

More than half of the earth's terrestrial surface currently experiences seasonal snow cover and soil frost. Winter compositional and functional investigations in soil microbial community are frequently conducted in alpine tundra and boreal forest ecosystems. However, little information on winter microbial biogeochemistry is known from seasonally snow-covered temperate ecosystems. As decomposer microbes may differ in their ability/strategy to efficiently use soil organic carbon (SOC) within different phases of the year, understanding seasonal microbial process will increase our knowledge of biogeochemical cycling from the aspect of decomposition rates and corresponding nutrient dynamics. In this study, we measured soil microbial biomass, community composition and potential SOC mineralization rates in winter and summer, from six temperate ecosystems in northern China. Our results showed a clear pattern of increased microbial biomass C to nitrogen (N) ratio in most winter soils. Concurrently, a shift in soil microbial community composition occurred with higher fungal to bacterial biomass ratio and gram negative (G-) to gram positive (G+) bacterial biomass ratio in winter than in summer. Furthermore, potential SOC mineralization rate was higher in winter than in summer. Our study demonstrated a distinct transition of microbial community structure and function from winter to summer in temperate snow-covered ecosystems. Microbial N immobilization in winter may not be the major contributor for plant growth in the following spring. PMID:24667929

Zhang, Xinyue; Wang, Wei; Chen, Weile; Zhang, Naili; Zeng, Hui

2014-01-01

110

Comparison of Seasonal Soil Microbial Process in Snow-Covered Temperate Ecosystems of Northern China  

PubMed Central

More than half of the earth's terrestrial surface currently experiences seasonal snow cover and soil frost. Winter compositional and functional investigations in soil microbial community are frequently conducted in alpine tundra and boreal forest ecosystems. However, little information on winter microbial biogeochemistry is known from seasonally snow-covered temperate ecosystems. As decomposer microbes may differ in their ability/strategy to efficiently use soil organic carbon (SOC) within different phases of the year, understanding seasonal microbial process will increase our knowledge of biogeochemical cycling from the aspect of decomposition rates and corresponding nutrient dynamics. In this study, we measured soil microbial biomass, community composition and potential SOC mineralization rates in winter and summer, from six temperate ecosystems in northern China. Our results showed a clear pattern of increased microbial biomass C to nitrogen (N) ratio in most winter soils. Concurrently, a shift in soil microbial community composition occurred with higher fungal to bacterial biomass ratio and gram negative (G-) to gram positive (G+) bacterial biomass ratio in winter than in summer. Furthermore, potential SOC mineralization rate was higher in winter than in summer. Our study demonstrated a distinct transition of microbial community structure and function from winter to summer in temperate snow-covered ecosystems. Microbial N immobilization in winter may not be the major contributor for plant growth in the following spring. PMID:24667929

Zhang, Xinyue; Wang, Wei; Chen, Weile; Zhang, Naili; Zeng, Hui

2014-01-01

111

Perennial grasslands enhance biodiversity and multiple ecosystem services in bioenergy landscapes  

PubMed Central

Agriculture is being challenged to provide food, and increasingly fuel, for an expanding global population. Producing bioenergy crops on marginal lands—farmland suboptimal for food crops—could help meet energy goals while minimizing competition with food production. However, the ecological costs and benefits of growing bioenergy feedstocks—primarily annual grain crops—on marginal lands have been questioned. Here we show that perennial bioenergy crops provide an alternative to annual grains that increases biodiversity of multiple taxa and sustain a variety of ecosystem functions, promoting the creation of multifunctional agricultural landscapes. We found that switchgrass and prairie plantings harbored significantly greater plant, methanotrophic bacteria, arthropod, and bird diversity than maize. Although biomass production was greater in maize, all other ecosystem services, including methane consumption, pest suppression, pollination, and conservation of grassland birds, were higher in perennial grasslands. Moreover, we found that the linkage between biodiversity and ecosystem services is dependent not only on the choice of bioenergy crop but also on its location relative to other habitats, with local landscape context as important as crop choice in determining provision of some services. Our study suggests that bioenergy policy that supports coordinated land use can diversify agricultural landscapes and sustain multiple critical ecosystem services. PMID:24474791

Werling, Ben P.; Dickson, Timothy L.; Isaacs, Rufus; Gaines, Hannah; Gratton, Claudio; Gross, Katherine L.; Liere, Heidi; Malmstrom, Carolyn M.; Meehan, Timothy D.; Ruan, Leilei; Robertson, Bruce A.; Robertson, G. Philip; Schmidt, Thomas M.; Schrotenboer, Abbie C.; Teal, Tracy K.; Wilson, Julianna K.; Landis, Douglas A.

2014-01-01

112

Linking the Response of Annual Grasslands to Warming and Altered Rainfall Across Scales of Gene Expression, Species, and Ecosystem  

Microsoft Academic Search

Climate change can influence terrestrial ecosystems at multiple biological levels: gene expression, species, and ecosystem. We are studying California grassland mesocosms with seven annual species (five grasses, two forbs) that were started in 2005. In the 2006-2007 growing season, they were exposed to three rainfall treatments (297, 552, and 867 mm y-1) and soil and air temperature (ambient and elevated

M. S. Torn; S. M. Bernard; C. Castanha; M. L. Fischer; F. M. Hopkins; S. A. Placella; S. B. St. Clair; R. Salve; E. Sudderth; D. Herman; D. Ackerly; M. K. Firestone

2007-01-01

113

Following The Money: Characterizing the Dynamics of Microbial Ecosystems and Labile Organic Matter in Grassland Soils  

NASA Astrophysics Data System (ADS)

The dynamics of soil microbial ecosystems and labile fractions of soil organic matter in grasslands have important implications for the response of these critical ecosystems to perturbations. Organic, inorganic and genetic biomarkers in the solid (e.g. lipids, microbial DNA), liquid (e.g. porewater ions) or gaseous phases (e.g. carbon dioxide) have been used to characterize carbon cycling and soil microbial ecology. These proxies are generally limited in the amount of temporal information that they can provide (i.e., solid-phase proxies) or the amount of specific information they can provide about carbon sources or microbial community processes (e.g. inorganic gases). It is the aim of this research to validate the use of soil volatile organic carbon emissions (VOCs) as useful indicators of subsurface microbial community shifts and processes as a function of ecosystem perturbations. We present results of method validation using laboratory microcosm, where VOC metabolites as characterized by gas chromatography and mass spectrometry (GC-MS), were related to other proxies including carbon dioxide (CO2) via infra-red technology, and microbial community shifts as measured by Biolog© and fatty acid methyl ester (FAME) techniques. Experiments with soil collected from grasslands along the coastal margin region in southern Texas were preformed where environmental factors such as soil water content, soil type, and charcoal content are manipulated. Results indicate that over fifty identifiable VOC metabolites are produced from the soils, where many (~15) can be direct indicators of microbial ecology. Principle component analysis (PCA) evidences these trends through similar cluster patterns for the VOC results, the Biolog© results, and FAME. Regression analysis further shows that VOCs are significant (p < 0.05) indicators of microbial stress. Our results are encouraging that characterizing VOCs production in grassland soils are easy to measure, relatively inexpensive method, and useful proxies of subsurface microbial ecosystems and the dynamics of labile carbon in these systems.

Herbert, B. E.; McNeal, K. S.

2006-12-01

114

Ecosystem performance assessment for grasslands in the Greater Platte River Basin: implications for cellulosic biofuel development  

NASA Astrophysics Data System (ADS)

This study identifies lands suitable for cellulosic biofuel (e.g., switchgrass) development across the Northern Great Plains, with an initial emphasis on the Greater Platte River Basin (GPRB), using satellite observations, climate data, and ecosystem models. Our approach is based on previous successful ecosystem performance (EP) studies in the Yukon River Basin and the Upper Colorado River Basin. We hypothesize that areas with fairly consistent high grassland productivity (i.e., high site potential) in fair to good range condition (persistent ecosystem overperformance or normal performance with few ecological disturbances) are potentially suitable for cellulosic biofuel (switchgrass) development. Ecosystem site potential was calculated using a 9-year (2000-2008) average of annually integrated growing season Normalized Difference Vegetation Index (GSN), geophysical and biophysical data, climate data, and a rule-based piecewise regression tree model. The GSN derived from eMODIS (expedited Moderate Resolution Imaging Spectroradiometer) observations was used as a proxy for the actual ecosystem performance. The weather-based expected EP (EEP) was computed using site potential, yearly seasonal climate variables, and piecewise regression tree models. The ecosystem performance anomaly (EPA) for a specific year was estimated based on the difference between the actual EP and the EEP during that year. The final EPA maps were categorized as normal performance, underperformance, and overperformance at the 90% confidence levels. Pixels that either overperformed or normally performed for three of four years from 2005 to 2008 and that have moderate or high site potential within the GPRB are identified as probable areas for future cellulosic biofuel development. Results from this study will help land managers and decision makers make optimal land use decisions for cellulosic biofuel development and sustainability within the grassland regions of the GPRB.

Gu, Y.; Boyte, S. P.; Wylie, B. K.; Tieszen, L. L.

2010-12-01

115

Dormancy patterns, germination ecology, and seed-bank types of twenty temperate fen grassland species  

Microsoft Academic Search

The germination ecology, including primary and secondary dormancy, mortality of seeds, and seed-bank type, of 20 fen grassland\\u000a species from Northern Germany was investigated using a combination of burial and germination experiments. To analyze primary\\u000a dormancy and effects of after-ripening (dry storage for 28 days) on freshly matured seeds, germination was measured at two\\u000a fluctuating temperature regimes (15\\/25°C and 5\\/15°C)

Kai Jensen

2004-01-01

116

Photosynthesis of a temperate fallow C3 herbaceous ecosystem: measurements and model simulations at the leaf and canopy levels  

E-print Network

- 1 - Photosynthesis of a temperate fallow C3 herbaceous ecosystem: measurements and model, 31057 Toulouse Cedex 1, France Abstract The objectives of the study were to characterize photosynthesis of temperate fallow C3 herbaceous species and examine the performance of a simple photosynthesis model (based

Boyer, Edmond

117

Cyanobacterial blooms in a temperate river-floodplain ecosystem: the importance of hydrological extremes  

Microsoft Academic Search

In the past decade, extreme hydrological events were expressed with extreme droughts and floods in temperate regions. The\\u000a aim of this paper is to explain how such changes in hydrology can influence cyanobacterial populations in floodplain ecosystems.\\u000a We therefore analyzed a 6-year (2003–2008) study of the phytoplankton in the Kopa?ki Rit floodplain, one of the largest natural\\u000a floodplains in the

Melita Mihaljevi?; Filip Stevi?

2011-01-01

118

Net ecosystem production in a temperate pine plantation in southeastern Canada  

Microsoft Academic Search

Eddy covariance measurements of carbon dioxide (CO2) and water vapour fluxes were made from June 2002 to May 2003 over a 65-year-old temperate conifer plantation forest in southern Ontario, Canada. This site is part of a newly initiated long-term tower flux measurement program over a chronosequence of white pine plantation forests, known as the Turkey Point Flux Station. Net ecosystem

M. Altaf Arain; Natalia Restrepo-Coupe

2005-01-01

119

Characterizing forest fragments in boreal, temperate, and tropical ecosystems.  

PubMed

An increased ability to analyze landscapes in a spatial manner through the use of remote sensing leads to improved capabilities for quantifying human-induced forest fragmentation. Developments of spatially explicit methods in landscape analyses are emerging. In this paper, the image delineation software program eCognition and the spatial pattern analysis program FRAGSTATS were used to quantify patterns of forest fragments on six landscapes across three different climatic regions characterized by different moisture regimes and different influences of human pressure. Our results support the idea that landscapes with higher road and population density are more fragmented; however, there are other, equally influential factors contributing to fragmentation, such as moisture regime, historic land use, and fire dynamics. Our method provided an objective means to characterize landscapes and assess patterns of forest fragments across different forested ecosystems by addressing the limitations of pixel-based classification and incorporating image objects. PMID:19205180

Meddens, Arjan J H; Hudak, Andrew T; Evans, Jeffrey S; Gould, William A; González, Grizelle

2008-12-01

120

Estimating Daytime Ecosystem Respiration to Improve Estimates of Gross Primary Production of a Temperate Forest  

PubMed Central

Leaf respiration is an important component of carbon exchange in terrestrial ecosystems, and estimates of leaf respiration directly affect the accuracy of ecosystem carbon budgets. Leaf respiration is inhibited by light; therefore, gross primary production (GPP) will be overestimated if the reduction in leaf respiration by light is ignored. However, few studies have quantified GPP overestimation with respect to the degree of light inhibition in forest ecosystems. To determine the effect of light inhibition of leaf respiration on GPP estimation, we assessed the variation in leaf respiration of seedlings of the dominant tree species in an old mixed temperate forest with different photosynthetically active radiation levels using the Laisk method. Canopy respiration was estimated by combining the effect of light inhibition on leaf respiration of these species with within-canopy radiation. Leaf respiration decreased exponentially with an increase in light intensity. Canopy respiration and GPP were overestimated by approximately 20.4% and 4.6%, respectively, when leaf respiration reduction in light was ignored compared with the values obtained when light inhibition of leaf respiration was considered. This study indicates that accurate estimates of daytime ecosystem respiration are needed for the accurate evaluation of carbon budgets in temperate forests. In addition, this study provides a valuable approach to accurately estimate GPP by considering leaf respiration reduction in light in other ecosystems. PMID:25419844

Sun, Jinwei; Wu, Jiabing; Guan, Dexin; Yao, Fuqi; Yuan, Fenghui; Wang, Anzhi; Jin, Changjie

2014-01-01

121

Responses of soil respiration to elevated CO[sub 2] in two California grassland ecosystems  

SciTech Connect

Estimates of soil respiration (SR) in current and elevated CO[sub 2] are critical for predicting future global carbon budgets. We measured SR in two California grassland ecosystems (sandstone and serpentine) growing at ambient and ambient+350 ppm CO[sub 2]. SR was higher in elevated CO[sub 2] for both ecosystems in the field, but differences were not significant. At peak plant growth, SR was approximately 6 [mu]mol m[sup [minus]2]s[sup [minus]1] in elevated CO[sub 2] and 5 [mu]mol m[sup [minus]2] s[sup [minus]1] in ambient CO[sub 2] for both ecosystems. We also examined soil respiration in monocultures of 7 grassland species grown in microecosystems (10-cm diameter by 1-m deep tubes). SR was approximately 2 [mu]mol m[sup [minus]2]s[sup [minus]1] for Plantago, Bromus, Hemizona, and Calycadenia and 7 [minus] 8 [mu]mol m[sup [minus]2]s[sup [minus]2] for Lolium, Avena, and Vulpia. Elevated CO[sub 2] significantly increased soil respiration by 20-30% in Bromus, Hemizonia and Lolium monocultures. SR was significantly correlated with total plant biomass as averaged across all species.

Luo, Y.; Jackson, R.B.; Field, C.B.; Mooney, H.A. (Stanford Univ., CA (United States))

1994-06-01

122

The Effects of Warming-Shifted Plant Phenology on Ecosystem Carbon Exchange Are Regulated by Precipitation in a Semi-Arid Grassland  

PubMed Central

Background The longer growing season under climate warming has served as a crucial mechanism for the enhancement of terrestrial carbon (C) sink over the past decades. A better understanding of this mechanism is critical for projection of changes in C cycling of terrestrial ecosystems. Methodology/Principal Findings A 4-year field experiment with day and night warming was conducted to examine the responses of plant phenology and their influences on plant coverage and ecosystem C cycling in a temperate steppe in northern China. Greater phenological responses were observed under night than day warming. Both day and night warming prolonged the growing season by advancing phenology of early-blooming species but without changing that of late-blooming species. However, no warming response of vegetation coverage was found for any of the eight species. The variances in species-level coverage and ecosystem C fluxes under different treatments were positively dependent upon the accumulated precipitation within phenological duration but not the length of phenological duration. Conclusions/Significance These plants' phenology is more sensitive to night than day warming, and the warming effects on ecosystem C exchange via shifting plant phenology could be mediated by precipitation patterns in semi-arid grasslands. PMID:22359660

Xia, Jianyang; Wan, Shiqiang

2012-01-01

123

A review of nitrous oxide mitigation by farm nitrogen management in temperate grassland-based agriculture.  

PubMed

Nitrous oxide (N2O) emission from grassland-based agriculture is an important source of atmospheric N2O. It is hence crucial to explore various solutions including farm nitrogen (N) management to mitigate N2O emissions without sacrificing farm profitability and food supply. This paper reviews major N management practices to lower N2O emission from grassland-based agriculture. Restricted grazing by reducing grazing time is an effective way to decrease N2O emissions from excreta patches. Balancing the protein-to-energy ratios in the diets of ruminants can also decrease N2O emissions from excreta patches. Among the managements of synthetic fertilizer N application, only adjusting fertilizer N rate and slow-released fertilizers are proven to be effective in lowering N2O emissions. Use of bedding materials may increase N2O emissions from animal houses. Manure storage as slurry, manipulating slurry pH to values lower than 6 and storage as solid manure under anaerobic conditions help to reduce N2O emissions during manure storage stage. For manure land application, N2O emissions can be mitigated by reducing manure N inputs to levels that satisfy grass needs. Use of nitrification inhibitors can substantially lower N2O emissions associated with applications of fertilizers and manures and from urine patches. N2O emissions from legume based grasslands are generally lower than fertilizer-based systems. In conclusion, effective measures should be taken at each step during N flow or combined options should be used in order to mitigate N2O emission at the farm level. PMID:23880433

Li, Dejun; Watson, Catherine J; Yan, Ming Jia; Lalor, Stan; Rafique, Rashid; Hyde, Bernard; Lanigan, Gary; Richards, Karl G; Holden, Nicholas M; Humphreys, James

2013-10-15

124

Nitrogen deposition and reduction of terrestrial biodiversity: Evidence from temperate grasslands  

Microsoft Academic Search

Biodiversity is thought to be essential for ecosystem stability, function and long-term sustainability. Since nitrogen is\\u000a the limiting nutrient for plant growth in many terrestrial ecosystems, reactive nitrogen has the potential to reduce the diversity\\u000a of terrestrial vegetation and associated biota through favouring species adapted to quickly exploiting available nutrients.\\u000a Although the potential has long been recognised, only recently has

Nancy B. Dise; J. Stevens

2005-01-01

125

Ground-based grasslands data to support remote sensing and ecosystem modeling of terrestrial primary production  

NASA Technical Reports Server (NTRS)

Estimating terrestrial net primary production (NPP) using remote-sensing tools and ecosystem models requires adequate ground-based measurements for calibration, parameterization, and validation. These data needs were strongly endorsed at a recent meeting of ecosystem modelers organized by the International Geosphere-Biosphere Program's (IGBP's) Data and Information System (DIS) and its Global Analysis, Interpretation, and Modelling (GAIM) Task Force. To meet these needs, a multinational, multiagency project is being coordinated by the IGBP DIS to compile existing NPP data from field sites and to regionalize NPP point estimates to various-sized grid cells. Progress at Oak Ridge National Laboratory (ORNL) on compiling NPP data for grasslands as part of the IGBP DIS data initiative is described. Site data and associated documentation from diverse field studies are being acquired for selected grasslands and are being reviewed for completeness, consistency, and adequacy of documentation, including a description of sampling methods. Data are being compiled in a database with spatial, temporal, and thematic characteristics relevant to remote sensing and global modeling. NPP data are available from the ORNL Distributed Active Archive Center (DAAC) for biogeochemical dynamics. The ORNL DAAC is part of the Earth Observing System Data and Information System, of the US National Aeronautics and Space Administration.

Olson, R. J.; Scurlock, J. M. O.; Turner, R. S.; Jennings, S. V.

1995-01-01

126

Ground-based grasslands data to support remote sensing and ecosystem modeling of terrestrial primary production  

SciTech Connect

Estimating terrestrial net primary production (NPP) using remote- sensing tools and ecosystem models requires adequate ground-based measurements for calibration, parameterization, and validation. These data needs were strongly endorsed at a recent meeting of ecosystem modelers organized by the International Geosphere-Biosphere Programme`s (IGBP`s) Data and Information System (DIS) and its Global Analysis, Interpretation, and Modelling (GAIM) Task Force. To meet these needs, a multinational, multiagency project is being coordinated by the IGBP DIS to compile existing NPP data from field sites and to regionalize NPP point estimates to various-sized grid cells. Progress at Oak Ridge National Laboratory (ORNL) on compiling NPP data for grasslands as part of the IGBP DIS data initiative is described. Site data and associated documentation from diverse field studies are being acquired for selected grasslands and are being reviewed for completeness, consistency, and adequacy of documentation, including a description of sampling methods. Data are being compiled in a database with spatial, temporal, and thematic characteristics relevant to remote sensing and global modeling. NPP data are available from the ORNL Distributed Active Archive Center (DAAC) for biogeochemical dynamics. The ORNL DAAC is part of the Earth Observing System Data and Information System, of the US National Aeronautics and Space Administration.

Olson, R.J.; Turner, R.S. [Oak Ridge National Lab., TN (United States); Scurlock, J.M.O. [King`s College London, (England); Jennings, S.V. [Tennessee Univ., Knoxville, TN (United States)

1995-12-31

127

How plant functional traits cascade to microbial function and ecosystem services in mountain grasslands  

NASA Astrophysics Data System (ADS)

1. There is growing evidence that plant functional diversity and microbial communities of soil are tightly coupled, and that this coupling influences a range of ecosystem functions. Moreover, it has been hypothesized that changes in the nature of interactions between plant functional diversity and microbial communities along environmental gradients contributes to variation in the delivery of ecosystem services. Although there is empirical support for such relationships using broad plant and microbial functional classifications, or from studies of plant monocultures, such relationships and their consequences for ecosystem services have not been quantified under complex field conditions with diverse plant communities. 2. We aimed to provide an explicit quantification of how plant and microbial functional properties interplay to determine key ecosystem functions underlying ecosystem services provided by grasslands. At three mountain grassland sites in the French Alps, Austrian Tyrol and northern England, we quantified, along gradients of management intensity, (i) plant functional diversity, (ii) soil microbial community composition and parameters associated with nitrogen cycling, and (iii) key ecosystem processes related to the carbon and nitrogen cycles including aboveground biomass production, standing litter, litter decomposition, soil organic matter and nitrate and ammonium leaching . Considering that plants strongly determine microbial communities, we used a hierarchical approach that considered first direct effects of plant traits and then effects of soil microorganisms on processes, to determine the relative effects of plant and microbial functional parameters on key ecosystem properties. 3. We identified a gradient of relative effects of plant and microbial traits from properties controlled mostly by aboveground processes, such as plant biomass production and standing litter, to properties controlled mostly by microbial processes, such as soil leaching of inorganic N (NO3 or NH4). Soil organic matter illustrated an intermediate situations with joint control by plant and microbial traits. 4. Across all sites, we found that increasing management intensity, and concomitant changes in soil fertility, was associated with more exploitative plant strategies (high Specific Leaf Area and Leaf Nitrogen Concentration) and taller vegetation. These vegetation functional properties provided the benefit of greater production, but at the cost of poor carbon and nutrient retention, notably because they were associated with microbial communities dominated by bacteria and with rapid rates of nitrification. Conversely, decreasing management intensity resulted in dominance by plants with conservative strategies (high Leaf Dry Matter Content and C/N ratio), usually low production, but benefits for carbon sequestration and soil nutrient retention by favouring microbial communities dominated by fungi co-occuring with bacteria with slow activities.

Lavorel, S.; Grigulis, K.; Krainer, U.; Legay, N.; Turner, C.; Dumont, M.; Kastl, E.; Arnoldi, C.; Bardgett, R.; Poly, F.; Pommier, T.; Schloter, M.; Tappeiner, U.; Bahn, M.; Clément, J.-C.

2012-04-01

128

Influence of warming on soil water potential controls seedling mortality in perennial but not annual species in a temperate grassland.  

PubMed

In a water-limited system, the following hypotheses are proposed: warming will increase seedling mortality; elevated atmospheric CO2 will reduce seedling mortality by reducing transpiration, thereby increasing soil water availability; and longevity (i.e. whether a species is annual or perennial) will affect the response of a species to global changes. Here, these three hypotheses are tested by assessing the impact of elevated CO2 (550 micromol mol(-1) and warming (+2 degrees C) on seedling emergence, survivorship and establishment in an Australian temperate grassland from autumn 2004 to autumn 2007. Warming impacts on seedling survivorship were dependent upon species longevity. Warming reduced seedling survivorship of perennials through its effects on soil water potential but the seedling survivorship of annuals was reduced to a greater extent than could be accounted for by treatment effects on soil water potential. Elevated CO2 did not significantly affect seedling survivorship in annuals or perennials. These results show that warming will alter recruitment of perennial species by changing soil water potential but will reduce recruitment of annual species independent of any effects on soil moisture. The results also show that exposure to elevated CO2 does not make seedlings more resistant to dry soils. PMID:18631296

Hovenden, Mark J; Newton, Paul C D; Wills, Karen E; Janes, Jasmine K; Williams, Amity L; Vander Schoor, Jacqueline K; Nolan, Michaela J

2008-01-01

129

Transfer of a cyanobacterial neurotoxin within a temperate aquatic ecosystem suggests pathways for human exposure.  

PubMed

beta-methylamino-L-alanine (BMAA), a neurotoxic nonprotein amino acid produced by most cyanobacteria, has been proposed to be the causative agent of devastating neurodegenerative diseases on the island of Guam in the Pacific Ocean. Because cyanobacteria are widespread globally, we hypothesized that BMAA might occur and bioaccumulate in other ecosystems. Here we demonstrate, based on a recently developed extraction and HPLC-MS/MS method and long-term monitoring of BMAA in cyanobacterial populations of a temperate aquatic ecosystem (Baltic Sea, 2007-2008), that BMAA is biosynthesized by cyanobacterial genera dominating the massive surface blooms of this water body. BMAA also was found at higher concentrations in organisms of higher trophic levels that directly or indirectly feed on cyanobacteria, such as zooplankton and various vertebrates (fish) and invertebrates (mussels, oysters). Pelagic and benthic fish species used for human consumption were included. The highest BMAA levels were detected in the muscle and brain of bottom-dwelling fishes. The discovery of regular biosynthesis of the neurotoxin BMAA in a large temperate aquatic ecosystem combined with its possible transfer and bioaccumulation within major food webs, some ending in human consumption, is alarming and requires attention. PMID:20439734

Jonasson, Sara; Eriksson, Johan; Berntzon, Lotta; Spácil, Zdenek; Ilag, Leopold L; Ronnevi, Lars-Olof; Rasmussen, Ulla; Bergman, Birgitta

2010-05-18

130

Transfer of a cyanobacterial neurotoxin within a temperate aquatic ecosystem suggests pathways for human exposure  

PubMed Central

?-methylamino-L-alanine (BMAA), a neurotoxic nonprotein amino acid produced by most cyanobacteria, has been proposed to be the causative agent of devastating neurodegenerative diseases on the island of Guam in the Pacific Ocean. Because cyanobacteria are widespread globally, we hypothesized that BMAA might occur and bioaccumulate in other ecosystems. Here we demonstrate, based on a recently developed extraction and HPLC-MS/MS method and long-term monitoring of BMAA in cyanobacterial populations of a temperate aquatic ecosystem (Baltic Sea, 2007–2008), that BMAA is biosynthesized by cyanobacterial genera dominating the massive surface blooms of this water body. BMAA also was found at higher concentrations in organisms of higher trophic levels that directly or indirectly feed on cyanobacteria, such as zooplankton and various vertebrates (fish) and invertebrates (mussels, oysters). Pelagic and benthic fish species used for human consumption were included. The highest BMAA levels were detected in the muscle and brain of bottom-dwelling fishes. The discovery of regular biosynthesis of the neurotoxin BMAA in a large temperate aquatic ecosystem combined with its possible transfer and bioaccumulation within major food webs, some ending in human consumption, is alarming and requires attention. PMID:20439734

Jonasson, Sara; Eriksson, Johan; Berntzon, Lotta; Spacil, Zdenek; Ilag, Leopold L.; Ronnevi, Lars-Olof; Rasmussen, Ulla; Bergman, Birgitta

2010-01-01

131

Plant and soil microbial responses to defoliation in temperate semi-natural grassland  

Microsoft Academic Search

There is much interest in understanding the nature of feedback mechanisms between plants and soil organisms in grazed ecosystems.\\u000a In this study, we examine the effects of different intensities of defoliation on the growth of three dominant grass species,\\u000a and observe how these plant responses relate to the biomass and activity of the microbial community in the root zone. Our

Ramon Guitian; Richard D. Bardgett

2000-01-01

132

Connecting Soil Organic Carbon and Root Biomass with Land-Use and Vegetation in Temperate Grassland  

PubMed Central

Soils contain much of Earth's terrestrial organic carbon but are sensitive to land-use. Rangelands are important to carbon dynamics and are among ecosystems most widely impacted by land-use. While common practices like grazing, fire, and tillage affect soil properties directly related to soil carbon dynamics, their magnitude and direction of change vary among ecosystems and with intensity of disturbance. We describe variability in soil organic carbon (SOC) and root biomass—sampled from 0–170?cm and 0–100?cm, respectively—in terms of soil properties, land-use history, current management, and plant community composition using linear regression and multivariate ordination. Despite consistency in average values of SOC and root biomass between our data and data from rangelands worldwide, broad ranges in root biomass and SOC in our data suggest these variables are affected by other site-specific factors. Pastures with a recent history of severe grazing had reduced root biomass and greater bulk density. Ordination suggests greater exotic species richness is associated with lower root biomass but the relationship was not apparent when an invasive species of management concern was specifically tested. We discuss how unexplained variability in belowground properties can complicate measurement and prediction of ecosystem processes such as carbon sequestration.

McGranahan, Devan Allen; Daigh, Aaron L.; Veenstra, Jessica J.; Engle, David M.; Miller, James R.; Debinski, Diane M.

2014-01-01

133

Rapid response of a grassland ecosystem to an experimental manipulation of a keystone rodent and domestic livestock.  

PubMed

Megaherbivores and small burrowing mammals commonly coexist and play important functional roles in grassland ecosystems worldwide. The interactive effects of these two functional groups of herbivores in shaping the structure and function of grassland ecosystems are poorly understood. In North America's central grasslands, domestic cattle (Bos taurus) have supplanted bison (Bison bison), and now coexist with prairie dogs (Cynomys spp.), a keystone burrowing rodent. Understanding the ecological relationships between cattle and prairie dogs and their independent and interactive effects is essential to understanding the ecology and important conservation issues affecting North American grassland ecosystems. To address these needs, we established a long-term manipulative experiment that separates the independent and interactive effects of prairie dogs and cattle using a 2 x 2 factorial design. Our study is located in the Janos-Casas Grandes region of northwestern Chihuahua, Mexico, which supports one of the largest remaining complexes of black-tailed prairie dogs (C. ludovicianus). Two years of posttreatment data show nearly twofold increases in prairie dog abundance on plots grazed by cattle compared to plots without cattle. This positive effect of cattle on prairie dogs resulted in synergistic impacts when they occurred together. Vegetation height was significantly lower on the plots where both species co-occurred compared to where either or both species was absent. The treatments also significantly affected abundance and composition of other grassland animal species, including grasshoppers and banner-tailed kangaroo rats (Dipodomys spectabilis). Our results demonstrate that two different functional groups of herbivorous mammals, burrowing mammals and domestic cattle, have distinctive and synergistic impacts in shaping the structure and function of grassland ecosystems. PMID:21141180

Davidson, Ana D; Ponce, Eduardo; Lightfoot, David C; Fredrickson, Ed L; Brown, James H; Cruzado, Juan; Brantley, Sandra L; Sierra-Corona, Rodrigo; List, Rurik; Toledo, David; Ceballos, Gerardo

2010-11-01

134

Satellite-Based Analysis of Evapotranspiration and Water Balance in the Grassland Ecosystems of Dryland East Asia  

E-print Network

of Applied Meteorology, Nanjing University of Information Science and Technology, Nanjing, China, 5 State Key University of Forestry and Technology, Changsha, Hunan, China, 7 State Key Laboratory of VegetationSatellite-Based Analysis of Evapotranspiration and Water Balance in the Grassland Ecosystems

Chen, Jiquan

135

Study on the strategies of sustainable development with the grassland ecosystem environment and yak industry in Ganzi prefecture  

Microsoft Academic Search

Summary This paper introduces the basic circumstance of Ganzi prefecture, the position and present condition of grassland ecosystem environment. It also discusses the process of transforming light energy (sun energy) into plant energy (grass) from photosynthesis of green plant and then transforming plant energy into animal energy (yak products). Finally, it puts forward the countermeasures of sustained development with yak.

Li Ping; Ye Zhongming; Yu Qing

136

Dual isotope and isotopomer ratios of N2O emitted from a temperate grassland soil after fertiliser application.  

PubMed

The N2O and N2 fluxes emitted from a temperate UK grassland soil after fertiliser application (equivalent to 25 and 75 kg N ha(-1)) were simultaneously measured, using a new automated soil incubation system, which replaces soil atmosphere (N2 dominated) with a He+O2 mixture. Dual isotope and isotopomer ratios of the emitted N2O were also determined. Total N2O and N2 fluxes were significantly lower (P<0.001) in the control (0 kg N) than in the 25 and 75 kg N treatments. The total N2O flux was significantly higher (P<0.001) in the 75 kg N than in the 25 kg N treatment. The general patterns of N2O and N2 fluxes were similar for both fertiliser treatments. The total gaseous N loss in the control treatment was nearly all N2, whereas in the fertiliser treatment more N2O than N2 was emitted from the soil. The ratio N2O/N2 fluxes as measured during the experiment suggested three phases in N2O production, in phase 1 nitrification>denitrification, in phase 2 denitrification>nitrification, and in phase 3 denitrification (and total denitrification)>nitrification. Dual delta15N and delta18O isotope and isotopomer (delta15Nalpha and delta15Nbeta) value ratios of emitted N2O also pointed towards an increasing dominance of the production of N2O by denitrification and total denitrification. The site preference value from the soil-emitted N2O was lower than the troposphere value. This confirmed that the enhanced troposphere N2O site preference could result from back injection of N2O from the stratosphere. The measurements of N2O/N2 flux ratio and the isotopic content of emitted N2O pointed, independently, to similar temporal trends in N2O production processes after fertiliser application to grassland soil. This confirmed that both measurements are suitable diagnostic tools to study the N2O production process in soils. PMID:14608627

Bol, R; Toyoda, S; Yamulki, S; Hawkins, J M B; Cardenas, L M; Yoshida, N

2003-01-01

137

[Differences in soil respiration between cropland and grassland ecosystems and factors influencing soil respiration on the Loess Plateau].  

PubMed

Understanding the effect of land-use change on soil respiration rates becomes critical in predicting soil carbon cycling under conversion of arable into grassland on the Loess Plateau. From July 2010 to December 2011, CO2 efflux from the soil surface was measured between 08:00 to 10:00 am in clear days by a Licor-8100 closed chamber system (Li-COR, Lincoln, NE, US). Also, soil temperature and soil moisture at the 5-cm depth was measured using a Li-Cor thermocouple and a hand-held frequency-domain reflectometer (ML2x, Delta-T Devices Ltd, UK) at each PVC collar, respectively. We found marked differences (P < 0.05) in soil respiration related to different land-use: the mean cropland soil respiration [1.35 micromol x (m2 x s)(-1)] was 24% (P < 0.05) less than the paired grassland soil respiration [1.67 micromol x (m2 x s)(-1)] (P < 0.05) during the period of experiment and the cumulative CO2-C emissions in grassland (856 g x m(-2)) was 23% (P < 0.05) higher than that in cropland (694 g x m(-2)). Soil moisture from 0-5 cm depth was much drier in cropland and significantly different between cropland and grassland except for winter. However, there were no clear relationships between soil moisture and soil respiration. Soil temperature at 5-cm depth was 2.5 degress C higher in grassland during the period of experiment (P < 0.05). Regression of soil temperature vs. soil respiration indicated significant exponential relationships both in grassland and cropland. Besides, there were intrinsic differences in response of soil respiration to temperature between the cropland and grassland ecosystems: grassland and cropland respiration response was significantly different at the alpha = 0.05 level, also expressed by a higher temperature sensitivity of soil respiration (Q10) in cropland (2.30) relative to grassland (1.74). Soil temperature of cropland and grassland can explain 79% of the variation in the soil respiration in grassland, compared to 82% in cropland. Therefore, land-use change can alter soil CO2 efflux under similar edaphic and climate conditions in the gully region of the Loess Plateau. The soil temperature difference between cropland and grassland can explain the soil respiration difference caused by land-use change, which was confirmed by the validation results. PMID:23745411

Zhou, Xiao-Gang; Zhang, Yan-Jun; Nan, Ya-Fang; Liu, Qing-Fang; Guo, Sheng-Li

2013-03-01

138

Elevated carbon dioxide and ozone alter productivity and ecosystem carbon content in northern temperate forests.  

PubMed

Three young northern temperate forest communities in the north-central United States were exposed to factorial combinations of elevated carbon dioxide (CO2 ) and tropospheric ozone (O3 ) for 11 years. Here, we report results from an extensive sampling of plant biomass and soil conducted at the conclusion of the experiment that enabled us to estimate ecosystem carbon (C) content and cumulative net primary productivity (NPP). Elevated CO2 enhanced ecosystem C content by 11%, whereas elevated O3 decreased ecosystem C content by 9%. There was little variation in treatment effects on C content across communities and no meaningful interactions between CO2 and O3 . Treatment effects on ecosystem C content resulted primarily from changes in the near-surface mineral soil and tree C, particularly differences in woody tissues. Excluding the mineral soil, cumulative NPP was a strong predictor of ecosystem C content (r(2) = 0.96). Elevated CO2 enhanced cumulative NPP by 39%, a consequence of a 28% increase in canopy nitrogen (N) content (g N m(-2) ) and a 28% increase in N productivity (NPP/canopy N). In contrast, elevated O3 lowered NPP by 10% because of a 21% decrease in canopy N, but did not impact N productivity. Consequently, as the marginal impact of canopy N on NPP (?NPP/?N) decreased through time with further canopy development, the O3 effect on NPP dissipated. Within the mineral soil, there was less C in the top 0.1 m of soil under elevated O3 and less soil C from 0.1 to 0.2 m in depth under elevated CO2 . Overall, these results suggest that elevated CO2 may create a sustained increase in NPP, whereas the long-term effect of elevated O3 on NPP will be smaller than expected. However, changes in soil C are not well-understood and limit our ability to predict changes in ecosystem C content. PMID:24604779

Talhelm, Alan F; Pregitzer, Kurt S; Kubiske, Mark E; Zak, Donald R; Campany, Courtney E; Burton, Andrew J; Dickson, Richard E; Hendrey, George R; Isebrands, J G; Lewin, Keith F; Nagy, John; Karnosky, David F

2014-08-01

139

Arbuscular mycorrhizal community composition associated with two plant species in a grassland ecosystem.  

PubMed

Arbuscular mycorrhizal (AM) fungi are biotrophic symbionts colonizing about two-thirds of land plant species and found in all ecosystems. They are of major importance in plant nutrient supply and their diversity is suggested to be an important determinant of plant community composition. The diversity of the AM fungal community composition in the roots of two plant species (Agrostis capillaris and Trifolium repens) that co-occurred in the same grassland ecosystem was characterized using molecular techniques. We analysed the small subunit (SSU) ribosomal RNA gene amplified from a total root DNA extract using AM fungal-specific primers. A total of 2001 cloned fragments from 47 root samples obtained on four dates were analysed by restriction fragment length polymorphism, and 121 of them were sequenced. The diversity found was high: a total of 24 different phylotypes (groups of phylogenetically related sequences) colonized the roots of the two host species. Phylogenetic analyses demonstrate that 19 of these phylotypes belonged to the Glomaceae, three to the Acaulosporaceae and two to the Gigasporaceae. Our study reveals clearly that the AM fungal community colonizing T. repens differed from that colonizing A. capillaris, providing evidence for AM fungal host preference. In addition, our results reveal dynamic changes in the AM fungal community through time. PMID:12144674

Vandenkoornhuyse, P; Husband, R; Daniell, T J; Watson, I J; Duck, J M; Fitter, A H; Young, J P W

2002-08-01

140

Assessing shifts in microbial community structure across a range of grasslands of differing management intensity using CLPP, PLFA and community DNA techniques  

Microsoft Academic Search

This study aimed to characterise soil microbial community structure and function in temperate upland grassland ecosystems. We compared the use of community level physiological profiles (CLPP), phospholipid fatty acid (PLFA) profiles and community DNA (%G+C base distribution) approaches to quantify soil microbial community structure and potential activity across a gradient of three upland grassland types at 10 geographically distinct sites

S. J Grayston; C. D Campbell; R. D Bardgett; J. L Mawdsley; C. D Clegg; K Ritz; B. S Griffiths; J. S Rodwell; S. J Edwards; W. J Davies; D. J Elston; P Millard

2004-01-01

141

Carbon balance of surfaces vs. ecosystems: advantages of measuring eddy covariance and soil respiration simultaneously in dry grassland ecosystems  

NASA Astrophysics Data System (ADS)

An automated open system for measurement of soil CO2 efflux (Rsc) was developed and calibrated against known fluxes and tested in the field, while measuring soil respiration also by the gradient method (Rsg) at a dry sandy grassland (Bugac, Hungary). Ecosystem respiration (Reco) was measured by the eddy covariance technique. Small chamber size (5 cm in diameter) of the chamber system made it possible to use the chambers also in vegetation gaps, thereby avoiding the necessity of removing shoots, the disturbance of the spatial structure of vegetation and the upper soil layer. Low air flow rates associated with small chamber volume and chamber design allowed the overpressure range to stabilize between 0.05-0.12 Pa. While the correlation between ecosystem and soil CO2 efflux rates as measured by the independent methods was significant, Reco rates were similar or even lower than Rsc in the low flux (up to 2 ?mol CO2 m-2 s-1) range, probably due to the larger than assumed storage flux. The gradient method showed both up and downward CO2 fluxes originating from the main rooting zone after rains. Downward fluxes within the soil profile amounted to 15% of the simultaneous upward fluxes and to ~ 7.6% of the total (upward) effluxes during the 3 months study. The upper 5 cm soil layer contributed to ~ 50% of the total soil CO2 efflux. The continuously operated automatic open chamber system and the gradient system makes possible the detection of situations when the eddy system underestimates Reco, gives the lower limit of underestimation (chamber system) and helps in quantifying the downward flux component of soil respiration (gradient method) between the soil layers. These latter (downward) fluxes are expected to seriously affect (1) the Reco vs. temperature response functions and (2) the net ecosystem exchange of CO2 (NEE) vs. photon flux density response functions, therefore potentially affecting also the gap filling procedures and to led to a situation (3) when the measured surface and the real time ecosystem fluxes will necessarily differ in the short term. Simultaneous measurements of Reco and soil CO2 effluxes may reveal the time and degree of the above decoupling, thereby contributing to decrease uncertainty, associated with eddy flux measurements over flat terrains. While the correlation between chamber fluxes and gradient fluxes was strong, gradient fluxes were generally larger than the flux from chambers. Calibration of gradient flux system by chamber effluxes is proposed.

Nagy, Z.; Pintér, K.; Pavelka, M.; Darenová, E.; Balogh, J.

2011-02-01

142

Carbon fluxes of surfaces vs. ecosystems: advantages of measuring eddy covariance and soil respiration simultaneously in dry grassland ecosystems  

NASA Astrophysics Data System (ADS)

An automated open system for measurement of soil CO2 efflux (Rsc) was developed and calibrated against known fluxes. The system was tested in the field, while estimating soil respiration simultaneously by the gradient method (Rsg) at a dry, sandy grassland site (Bugac, Hungary). Ecosystem respiration (Rego) was measured using the eddy covariance technique. The small chamber size (5 cm in diameter) made it possible to use the chambers in vegetation gaps, thereby avoiding the necessity of removing shoots and disturbing the spatial structure of vegetation and the upper soil layer. Low air flow rates associated with small chamber volume and chamber design allowed the overpressure range to stabilize between 0.05-0.12 Pa. The correlation between ecosystem and soil CO2 efflux rates as measured by the independent methods was significant, Reco rates were similar or even lower than Rsc in the low flux (up to 2 ?mol CO2 m-2 s-1) range but the differences were within the uncertainty limits for the two fluxes. Rsc from trenched and non-trenched plots amounted to 16 % and 44 % of Reco, respectively. The gradient method showed both up and downward CO2 fluxes originating from the main rooting zone after rains. Diffusive retardation played a smaller role than CO2 production considering the soil air CO2 concentration increase after rains in a given layer. Downward fluxes within the soil profile amounted to 15 % of the simultaneous upward fluxes and to ~7.6 % of the total (upward) effluxes during the 3-month study. The upper 5 cm soil layer contributed to ~50 % of the total soil CO2 efflux. Downward fluxes are expected to seriously affect (1) the Reco vs. temperature response functions and (2) the net ecosystem exchange of CO2 (NEE) vs. photon flux density response functions, therefore potentially affecting the gap filling procedures and to lead to a situation (3) when the measured surface and the real time ecosystem fluxes will necessarily differ in the short term. Simultaneous measurements of Reco and soil CO2 effluxes may reveal the timing and magnitude of the decoupling, thereby contributing to decreasing uncertainty associated with eddy flux measurements over flat terrains. While the correlations between CO2 effluxes measured by independent systems are strong, Rsg was generally larger than Rsc or Reco, mainly due to overestimation of effective diffusivity in the soil.

Nagy, Z.; Pintér, K.; Pavelka, M.; Darenová, E.; Balogh, J.

2011-09-01

143

Using Elemental Budgets to Determine Effects of Simulated Climate Change on Phosphorus Cycling in a Grassland Ecosystem  

NASA Astrophysics Data System (ADS)

The purpose of the Jasper Ridge Global Change Experiment is to find out the effects of climate change on a terrestrial grassland ecosystem. The different treatments include increased carbon dioxide, nitrogen deposition, temperature, and precipitation. A portion of the above ground biomass of each plot was harvested, and an abundant species chosen to analyze. The goal of this project was to investigate the effects of climate change on phosphorus cycling in the grassland vegetation. Total phosphorus content of each sample was determined by combustion and acid digestion along with optical emission spectrometry. Total nitrogen and carbon was determined via flash combustion in an isotope ratio mass spectrometer. This information was combined to evaluate the limitation of phosphorus in each treatment and better understand how climate change may affect phosphorus cycling in terrestrial grasslands.

Yoo, S.; Paytan, A.; Mellett, T.

2013-12-01

144

Climate change impacts on stream carbon export from coastal temperate rainforest ecosystems in Alaska (Invited)  

NASA Astrophysics Data System (ADS)

Coastal temperate rainforests (CTR) in Alaska contain about 10% of the total carbon in the forests of the conterminous United States. CTR ecosystems span a large environmental gradient that ranges from icefields mantling the Coast Mountains to carbon-rich conifer forests along the coastal margin and within the islands of the Alexander Archipelago in the Gulf of Alaska. Riverine dissolved organic carbon (DOC) export from Alaskan CTR ecosystems, which can exceed 2 Tg C yr-1, is large relative to other northern ecosystems as a result of high rates of specific discharge (~2.5 m yr-1) and an abundance of organic soils found in peatlands and forested wetlands. Runoff from glaciers, which are rapidly thinning and retreating, has also been shown to an important contributor to land-to-ocean fluxes of DOC in this region. Downscaled regional climate models suggest that CTR ecosystems in Alaska will become warmer and wetter in coming decades, with uncertain effects on riverine organic matter (OM) export. Changes in watershed OM export are likely to be driven by changes in both hydrology and the availability of OM in terrestrial source pools. However, the impacts of these climate driven changes will vary with watershed landcover across the continuum from icefields to coastal temperate forests. Expected hydrological perturbations include changes in the timing and magnitude of streamflow associated with shifts in: 1) the extent and duration of seasonal snowcover and 2) the mass balance of glaciers and icefields in the Coast Mountains. The availability of OM for export along hydrologic flowpaths will likely be altered by increased soil temperatures and shifts in water table elevations during the summer/fall runoff season. This will be particularly true for organic carbon export from peatlands in which changes in temperature and oxygen availability can strongly impact rates of organic matter decomposition. This talk will explore how climate-driven changes in hydrology and terrestrial organic matter stocks are expected to interact and modify riverine organic carbon export from CTR watersheds to near-shore marine ecosystems along the Gulf of Alaska.

Hood, E. W.

2013-12-01

145

Wind and water erosion and transport in semi-arid shrubland, grassland and forest ecosystems: quantifying dominance of horizontal wind-driven transport  

Microsoft Academic Search

Soil erosion is an important process in dryland ecosystems, yet measurements and comparisons of wind and water erosion within and among such ecosystems are lacking. Here we compare wind erosion and transport field measurements with water erosion and transport from rainfall-simulation for three different semi-arid ecosystems: a shrubland near Carlsbad, New Mexico; a grassland near Denver, Colorado; and a forest

David D. Breshears; Jeffrey J. Whicker; Mathew P. Johansen; John E. Pinder

2003-01-01

146

Will anticipated future climatic conditions affect belowground C utilization? - Insights into the role of microbial functional groups in a temperate heath/grassland.  

NASA Astrophysics Data System (ADS)

The global terrestrial soil organic matter stock is the biggest terrestrial carbon pool (1500 Pg C) of which about 4 % is turned over annually. Thus, terrestrial ecosystems have the potential to accelerate or diminish atmospheric climate change effects via belowground carbon processes. We investigated the effect of elevated CO2 (510 ppm), prolonged spring/summer droughts and increased temperature (1 ?C) on belowground carbon allocation and on the recovery of carbon by the soil microbial community. An in-situ 13C-carbon pulse-labeling experiment was carried out in a temperate heath/grassland (Denmark) in May 2011. Recently assimilated 13C-carbon was traced into roots, soil and microbial biomass 1, 2 and 8 days after pulse-labeling. The importance of the microbial community in C utilization was investigated using 13C enrichment patterns in microbial functional groups on the basis of phospholipid fatty acids (PLFAs) in roots. Gram-negative and gram-positive bacteria were distinguished from the decomposer groups of actinomycetes (belonging to the group of gram-positive bacteria) and saprophytic fungi. Mycorrhizal fungi specific PLFAs were not detected probably due to limited sample size in combination with restricted sensitivity of the used GC-c-IRMS setup. Climate treatments did not affect 13C allocation into roots, soil and microbial biomass carbon and also the total microbial biomass size stayed unchanged as frequently observed. However, climate treatments changed the composition of the microbial community: elevated CO2 significantly reduced the abundance of gram-negative bacteria (17:0cy) but did not affect the abundance of decomposers. Drought favored the bacterial community whereas increased temperatures showed reduced abundance of gram-negative bacteria (19:0cy) and changed the actinomycetes community (10Me16:0, 10Me18:0). However, not only the microbial community composition was affected by the applied climatic conditions, but also the activity of microbial functional groups in their utilization of recently assimilated carbon. Particularly the negative effect of the future treatment combination (CO2×T×D) on actinomycetes activity was surprising. By means of activity patterns of gram-negative bacteria, we observed the fastest carbon turnover rate under elevated CO2, and the slowest under extended drought conditions. A changed soil microbial community in combination with altered activities of different microbial functional groups leads to the conclusion that carbon allocation belowground was different under ambient and future climatic conditions and indicated reduced utilization of soil organic matter in the future due to a change of actinomycetes abundance and activity.

Reinsch, Sabine; Michelsen, Anders; Sárossy, Zsuzsa; Egsgaard, Helge; Kappel Schmidt, Inger; Jakobsen, Iver; Ambus, Per

2013-04-01

147

Litter decomposition and nutrient release as affected by soil nitrogen availability and litter quality in a semiarid grassland ecosystem  

Microsoft Academic Search

Nitrogen availability is critically important to litter decomposition, especially in arid and semiarid areas where N is limiting.\\u000a We studied the relative contributions of litter quality and soil N to litter decomposition of two dominant grassland species,\\u000a Stipa krylovii and Artemisia frigida, in a semiarid typical steppe ecosystem in Inner Mongolia, China. The study had four different rates of N

Ping Liu; Jianhui Huang; Osbert Jianxin Sun; Xingguo Han

2010-01-01

148

Altering Rainfall Timing and Quantity in a Mesic Grassland Ecosystem: Design and Performance of Rainfall Manipulation Shelters  

Microsoft Academic Search

Global climate change is predicted to alter growing season rainfall patterns, potentially reducing total amounts of growing\\u000a season precipitation and redistributing rainfall into fewer but larger individual events. Such changes may affect numerous\\u000a soil, plant, and ecosystem properties in grasslands and ultimately impact their productivity and biological diversity. Rainout\\u000a shelters are useful tools for experimental manipulations of rainfall patterns, and

Philip A. Fay; Jonathan D. Carlisle; Alan K. Knapp; John M. Blair; Scott L. Collins

2000-01-01

149

FUNCTIONAL AND STRUCTURAL CONVERGENCE OF TEMPERATE GRASSLAND AND SHRUBLAND ECOSYSTEMS. (R824993)  

EPA Science Inventory

The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Concl...

150

Influence of ozone pollution and climate variability on net primary productivity and carbon storage in China's grassland ecosystems from 1961 to 2000.  

PubMed

Our simulations with the Dynamic Land Ecosystem Model (DLEM) indicate that the combined effect of ozone, climate, carbon dioxide and land use have caused China's grasslands to act as a weak carbon sink during 1961-2000. This combined effect on national grassland net primary productivity (NPP) and carbon storage was small, but changes in annual NPP and total carbon storage across China's grasslands showed substantial spatial variation, with the maximum total carbon uptake reduction of more than 400gm(-2) in some places of northeastern China. The grasslands in the central northeastern China were more sensitive and vulnerable to elevated ozone pollution than other regions. The combined effect excluding ozone could potentially lead to an increase of 14Tg C in annual NPP and 0.11Pg C in total carbon storage for the same time period. This implies that improvement in air quality could significantly increase productivity and carbon storage in China's grassland ecosystems. PMID:17618716

Ren, Wei; Tian, Hanqin; Chen, Guangsheng; Liu, Mingliang; Zhang, Chi; Chappelka, Arthur H; Pan, Shufen

2007-10-01

151

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

NASA Astrophysics Data System (ADS)

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.

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

2006-12-01

152

Satellite-Based Analysis of Evapotranspiration and Water Balance in the Grassland Ecosystems of Dryland East Asia  

PubMed Central

The regression tree method is used to upscale evapotranspiration (ET) measurements at eddy-covariance (EC) towers to the grassland ecosystems over the Dryland East Asia (DEA). The regression tree model was driven by satellite and meteorology datasets, and explained 82% and 76% of the variations of ET observations in the calibration and validation datasets, respectively. The annual ET estimates ranged from 222.6 to 269.1 mm yr?1 over the DEA region with an average of 245.8 mm yr?1 from 1982 through 2009. Ecosystem ET showed decreased trends over 61% of the DEA region during this period, especially in most regions of Mongolia and eastern Inner Mongolia due to decreased precipitation. The increased ET occurred primarily in the western and southern DEA region. Over the entire study area, water balance (the difference between precipitation and ecosystem ET) decreased substantially during the summer and growing season. Precipitation reduction was an important cause for the severe water deficits. The drying trend occurring in the grassland ecosystems of the DEA region can exert profound impacts on a variety of terrestrial ecosystem processes and functions. PMID:24845063

Xia, Jiangzhou; Liang, Shunlin; Chen, Jiquan; Yuan, Wenping; Liu, Shuguang; Li, Linghao; Cai, Wenwen; Zhang, Li; Fu, Yang; Zhao, Tianbao; Feng, Jinming; Ma, Zhuguo; Ma, Mingguo; Liu, Shaomin; Zhou, Guangsheng; Asanuma, Jun; Chen, Shiping; Du, Mingyuan; Davaa, Gombo; Kato, Tomomichi; Liu, Qiang; Liu, Suhong; Li, Shenggong; Shao, Changliang; Tang, Yanhong; Zhao, Xiang

2014-01-01

153

Ecosystem water use efficiency in a warm-temperate mixed plantation in the North China  

NASA Astrophysics Data System (ADS)

Water use efficiency (WUE) at the ecosystem level is an important ecophysiological index reflecting the coupling relationship between water and carbon cycles. CO2 and water vapor fluxes were measured by the eddy covariance method during the period 2006-2010 over a warm-temperate mixed plantation in the North China. The seasonal and interannual variations of gross primary productivity (GPP), evapotranspiration (ET) and ecosystem WUE were analyzed, and the impacts of climatic variables and soil moisture on GPP, ET and WUE were discussed. At the monthly scale, GPP and ET had similar relations with solar radiation, air temperature, vapor pressure deficit (VPD) and precipitation. It is suggested that photosynthesis and evapotranspiration were driven by climatic variables at the approximately equal strength. During the growing season, WUE decreased significantly with the increase of VPD and solar radiation. Cloudiness can improve photosynthesis and enhance WUE. GPP was 9-39% greater but ET was 8-26% lower under cloudy sky conditions than that under sunny sky conditions. Therefore, WUE was 29-72% higher under cloudy skies in comparison with that under sunny skies. Annual average WUE ranged from 1.76 to 2.41 g C kg-1 H2O. The major driver of interannual variability in WUE was soil water content in May.

Tong, Xiaojuan; Zhang, Jinsong; Meng, Ping; Li, Jun; Zheng, Ning

2014-05-01

154

Interactive effects of changes in climate and management on yield and CO2 source/sink strength of grassland ecosystems in the Alps  

NASA Astrophysics Data System (ADS)

Grassland farming (cutting for fodder and grazing) is the major agricultural practise in the European Alps, with grasslands covering >85% of the area of 75% of the municipalities. Climate change projections for this area, in particular increases in temperature and reductions in summer precipitation, are expected to influence grassland yields. Higher temperatures are thought to reduce snow cover duration and thus increase the period available for grassland growth and through more intensive management (more frequent cuttings and longer grazing periods) yields. In contrast, lower summer precipitation and associated reduced soil water availability is expected to negatively affect grassland growth and yields. Climate change and adaptations of grassland management in response to climate change are in turn expected to affect the carbon dioxide (CO2) source/sink strength of grassland ecosystems, thus providing feedback to climate change. Longer growing periods are expected to increase the sink activity, while summer soil water shortage and more frequent cutting or longer grazing are thought to decrease the sink strength for carbon dioxide. Here we report on a project, GrassClim, within which the interactive effects of changes in climate and management on grassland yield and the CO2 source/sink strength are investigated. To this end a process-oriented model of carbon cycling in a managed grassland ecosystem is forced with scenarios of regional climate change and associated changes in management. The latter are derived from questionnaires of farmers confronted with regional climate change scenarios. The grassland carbon cycling model is parameterised in a Bayesian framework using eddy covariance net ecosystem CO2 flux measurements and periodic analyses of the amount of above-ground plant matter from several grassland study sites in the Alps. In particular, we aim at answering the following questions:

  1. What are the management scenarios that result from the regional climate scenarios?
  2. How do management and climate scenarios, in isolation and combined, affect the yield and CO2 source/sink strength of grassland ecosystems?
  3. Do management strategies that optimise yield and the CO2 source/sink strength at the same time exist (so-called win-win situations)?
  4. How sensitive are yields and the CO2 source sink strength to projected climatic changes as opposed to changes in management and how do uncertainties inherent to both climate and management scenarios relate to uncertainties in predicted yields and the CO2 sink/strength of grassland ecosystems?

Irschick, C.; Carli, E.; Eliskases, C.; Frischmann, S.; Fritsch, U.; Gobiet, A.; Haas, J.; Kapelari, S.; Norz, J.; Themessl, M. J.; Zebisch, M.; Wohlfahrt, G.

2011-12-01

155

Evidence for non-diffusive transport as an important mechanism determining the soil CO2 efflux in a temperate grassland  

NASA Astrophysics Data System (ADS)

Research on soil respiration has largely focused on the emission of CO2 from soils and far less on the production and subsequent transport of CO2 from soil to atmosphere. The limited knowledge of CO2 transport through the soil, restricts our understanding of the various abiotic and biotic processes underlying emissions of CO2 from terrestrial ecosystems. Soil CO2 efflux is most often measured using soil chambers, but since the early 2000s, solid-state CO2 sensors that measure soil CO2 concentrations at different depths, are becoming more popular. From these continuous high-frequency measurements of the CO2 gradient, the flux can easily be calculated in a very cost-efficient way with minimal disturbance of the natural conditions. This so-called flux-gradient method is based on Fick's law, assuming diffusion to be the only transport mechanism. To test to what extend diffusion is indeed the governing transport process, we compared the CO2 efflux from chamber measurements with the CO2 efflux calculated from soil CO2 concentration profiles for a grassland site in the Austrian Alps. The four commonly used models for diffusivity that we tested, all underestimated the soil chamber effluxes and their amplitudes. What is more, we observed that transport rates correlated well with irradiation (PAR) and -below a certain soil moisture content- with wind speed. Indeed, correlation coefficients of the fits of observed transport rate versus PAR were consistently positive, and those of observed transport rate versus wind speed were positive on days that were not extremely wet (soil water content below 33%). Also, we found that the coupling of transport rate and PAR became stronger as wind speed increased. Our results suggest that non-diffusive bulk air transport mechanisms, such as advective mass transport and pressure pumping, could considerably contribute to soil CO2 transport at this site. We therefore emphasize the importance of investigating alternative transport processes before using solid-state CO2 concentration measurements to estimate soil CO2 emissions at any given site.

Roland, Marilyn; Vicca, Sara; Bahn, Michael; Schmitt, Michael; Janssens, Ivan

2013-04-01

156

Use of Eddy Covariance Data to Calibrate the PhotoCent Model for Grassland and Forest Ecosystems  

NASA Astrophysics Data System (ADS)

Eddy Covariance data sets have been used to calibrate the photosynthesis version of the DayCent ecosystem model (PhotoCent). Data simulation techniques were used to determine the parameters in the photosynthesis submodel for deciduous and coniferous forests, and arid and humid grasslands. A comparison of the seasonal patterns of gross primary production (GPP) and net ecosystem exchange (NEE) for grassland and forest sites showed that maximum NEE and GPP values were observed in the spring (May and June) with NEE and GPP declining until the end of the growing season at different rates for the different biomes. The model results and observed daily GPP and NEE data sets suggest the major factor which controls this seasonal pattern is the decline in maximum photosynthesis rate during the growing season. This analysis suggests that grasslands, coniferous forests and deciduous forests have biome specific patterns in the rate of decline of maximum photosynthesis rates which are supported by observed field data showing similar declines in maximum photosynthesis rates. A comparison of model simulated GPP, NEE and respiration (RESP) rates with observed data shows that the observed biome specific seasonal patterns in these variables are well represented by the PhotoCent model. A comparison of observed vs. simulated daily GPP, NEE , and RESP shows that GPP has the highest correlation with observed data (r2 ranging from 0.70 to 0.90), and somewhat lower correlations for NEE and RESP (0.5 to 0.7).

Del Grosso, S.; Parton, W. J.; Straube, J.; Asao, S.

2012-12-01

157

Environmental effects of oil and gas lease sites in a grassland ecosystem  

Microsoft Academic Search

The northern Great Plains of Saskatchewan is one of the most significantly modified landscapes in Canada. While the majority of anthropogenic disturbances to Saskatchewan’s grasslands are the result of agricultural practices, development of petroleum and natural gas (PNG) resources is of increasing concern for grassland conservation. Although PNG developments require formal assessment and regulatory approval, follow-up and monitoring of the

Lawrence C. Nasen; Bram F. Noble; Jill F. Johnstone

2011-01-01

158

Partitioning Evapotranspiration in Semiarid Grassland and Shrubland Ecosystems Using Diurnal Surface Temperature Variation  

NASA Technical Reports Server (NTRS)

The encroachment of woody plants in grasslands across the Western U.S. will affect soil water availability by altering the contributions of evaporation (E) and transpiration (T) to total evapotranspiration (ET). To study this phenomenon, a network of flux stations is in place to measure ET in grass- and shrub-dominated ecosystems throughout the Western U.S. A method is described and tested here to partition the daily measurements of ET into E and T based on diurnal surface temperature variations of the soil and standard energy balance theory. The difference between the mid-afternoon and pre-dawn soil surface temperature, termed Apparent Thermal Inertia (I(sub A)), was used to identify days when E was negligible, and thus, ET=T. For other days, a three-step procedure based on energy balance equations was used to estimate Qe contributions of daily E and T to total daily ET. The method was tested at Walnut Gulch Experimental Watershed in southeast Arizona based on Bowen ratio estimates of ET and continuous measurements of surface temperature with an infrared thermometer (IRT) from 2004- 2005, and a second dataset of Bowen ratio, IRT and stem-flow gage measurements in 2003. Results showed that reasonable estimates of daily T were obtained for a multi-year period with ease of operation and minimal cost. With known season-long daily T, E and ET, it is possible to determine the soil water availability associated with grass- and shrub-dominated sites and better understand the hydrologic impact of regional woody plant encroachment.

Moran, M. Susan; Scott, Russell L.; Keefer, Timothy O.; Paige, Ginger B.; Emmerich, William E.; Cosh, Michael H.; O'Neill, Peggy E.

2007-01-01

159

Drivers of long-term variability in CO2 net ecosystem exchange in a temperate peatland  

NASA Astrophysics Data System (ADS)

Land-atmosphere exchange of carbon dioxide (CO2) in peatlands exhibits marked seasonal and inter-annual variability, which subsequently affects the carbon sink strength of catchments across multiple temporal scales. Long-term studies are needed to fully capture the natural variability and therefore identify the key hydrometeorological drivers in the net ecosystem exchange (NEE) of CO2. NEE has been measured continuously by eddy-covariance at Auchencorth Moss, a temperate lowland peatland in central Scotland, since 2002. Hence this is one of the longest peatland NEE studies to date. For 11 yr, the site was a consistent, yet variable, atmospheric CO2 sink ranging from -5.2 to -135.9 g CO2-C m-2 yr-1 (mean of -64.1 ± 33.6 g CO2-C m-2 yr-1). Inter-annual variability in NEE was positively correlated to the length of the growing season. Mean winter air temperature explained 87% of the inter-annual variability in the sink strength of the following summer, indicating a phenological memory-effect. Plant productivity exhibited a marked hysteresis with respect to photosynthetically active radiation (PAR) over the growing season, indicative of two separate growth regimes. Ecosystem respiration (Reco) and gross primary productivity (GPP) were closely correlated (ratio 0.74), suggesting that autotrophic processes were dominant. Whilst the site was wet most of the year (water table depth <5 cm) there were indications that heterotrophic respiration was enhanced by drought, which also depressed GPP. NEE was compared to 5 other peatland sites which have published long-term NEE records. The CO2 uptake rate during the growing season was comparable to 3 other European sites, however the emission rate during the dormant season was significantly higher.

Helfter, C.; Campbell, C.; Dinsmore, K. J.; Drewer, J.; Coyle, M.; Anderson, M.; Skiba, U.; Nemitz, E.; Billett, M. F.; Sutton, M. A.

2014-10-01

160

A Transmission Model for the Ecology of an Avian Blood Parasite in a Temperate Ecosystem  

PubMed Central

Most of our knowledge about avian haemosporidian parasites comes from the Hawaiian archipelago, where recently introduced Plasmodiumrelictum has contributed to the extinction of many endemic avian species. While the ecology of invasive malaria is reasonably understood, the ecology of endemic haemosporidian infection in mainland systems is poorly understood, even though it is the rule rather than the exception. We develop a mathematical model to explore and identify the ecological factors that most influence transmission of the common avian parasite, Leucocytozoonfringillinarum (Apicomplexa). The model was parameterized from White-crowned Sparrow (Zonotrichialeucophrys) and S. silvestre / craigi black fly populations breeding in an alpine ecosystem. We identify and examine the importance of altricial nestlings, the seasonal relapse of infected birds for parasite persistence across breeding seasons, and potential impacts of seasonal changes in black fly emergence on parasite prevalence in a high elevation temperate system. We also use the model to identify and estimate the parameters most influencing transmission dynamics. Our analysis found that relapse of adult birds and young of the year birds were crucial for parasite persistence across multiple seasons. However, distinguishing between nude nestlings and feathered young of the year was unnecessary. Finally, due to model sensitivity to many black fly parameters, parasite prevalence and sparrow recruitment may be most affected by seasonal changes in environmental temperature driving shifts in black fly emergence and gonotrophic cycles. PMID:24073288

Murdock, Courtney C.; Foufopoulos, Johannes; Simon, Carl P.

2013-01-01

161

A transmission model for the ecology of an avian blood parasite in a temperate ecosystem.  

PubMed

Most of our knowledge about avian haemosporidian parasites comes from the Hawaiian archipelago, where recently introduced Plasmodiumrelictum has contributed to the extinction of many endemic avian species. While the ecology of invasive malaria is reasonably understood, the ecology of endemic haemosporidian infection in mainland systems is poorly understood, even though it is the rule rather than the exception. We develop a mathematical model to explore and identify the ecological factors that most influence transmission of the common avian parasite, Leucocytozoonfringillinarum (Apicomplexa). The model was parameterized from White-crowned Sparrow (Zonotrichialeucophrys) and S. silvestre / craigi black fly populations breeding in an alpine ecosystem. We identify and examine the importance of altricial nestlings, the seasonal relapse of infected birds for parasite persistence across breeding seasons, and potential impacts of seasonal changes in black fly emergence on parasite prevalence in a high elevation temperate system. We also use the model to identify and estimate the parameters most influencing transmission dynamics. Our analysis found that relapse of adult birds and young of the year birds were crucial for parasite persistence across multiple seasons. However, distinguishing between nude nestlings and feathered young of the year was unnecessary. Finally, due to model sensitivity to many black fly parameters, parasite prevalence and sparrow recruitment may be most affected by seasonal changes in environmental temperature driving shifts in black fly emergence and gonotrophic cycles. PMID:24073288

Murdock, Courtney C; Foufopoulos, Johannes; Simon, Carl P

2013-01-01

162

Arsenic concentrations and speciation in a temperateArsenic concentrations and speciation in a temperate mangrove ecosystem, NSW, Australiamangrove ecosystem, NSW, Australia  

E-print Network

Arsenic concentrations and speciation in a temperateArsenic concentrations and speciation, Australia Received 4 September 2001; Accepted 17 December 2001 Total arsenic concentrations and species were. Mean arsenic concentrations ranged from 0.3 to 55 mg gÃ?1 dry mass. Epiphytic algae/fungi associated

Canberra, University of

163

Rapid top-down regulation of plant C:N:P stoichiometry by grasshoppers in an Inner Mongolia grassland ecosystem.  

PubMed

Understanding how food web interactions alter the processing of limiting nutrient elements is an important goal of ecosystem ecology. An experiment manipulating densities of the grasshopper Oedaleus asiaticus was performed to assess top-down effects of grasshoppers on C:N:P stoichiometry of plants and soil in a grassland ecosystem in Inner Mongolia (China). With increased grasshopper feeding, plant biomass declined fourfold, litter abundance increased 30%, and the plant community became dominated by non-host plant taxa. Plant stoichiometric response depended on whether or not the plant was a grasshopper host food species: C:N and C:P ratios increased with increasing grasshopper density (GD) for host plants but decreased in non-host plants. These data suggest either a direct transfer of grasshopper-recycled nutrients from host to non-host plants or a release of non-host plants from nutrient competition with heavily grazed host plants. Litterfall C:N and C:P decreased across moderate levels of grasshopper density but no effects on C:N:P stoichiometry in the surface soil were observed, possibly due to the short experimental period. Our observations of divergent C:N:P stoichiometric response among plant species highlight the important role of grasshopper herbivory in regulating plant community structure and nutrient cycling in grassland ecosystems. PMID:21267596

Zhang, Guangming; Han, Xingguo; Elser, James J

2011-05-01

164

Cell Turnover and Detritus Production in Marine Sponges from Tropical and Temperate Benthic Ecosystems  

PubMed Central

This study describes in vivo cell turnover (the balance between cell proliferation and cell loss) in eight marine sponge species from tropical coral reef, mangrove and temperate Mediterranean reef ecosystems. Cell proliferation was determined through the incorporation of 5-bromo-2?-deoxyuridine (BrdU) and measuring the percentage of BrdU-positive cells after 6 h of continuous labeling (10 h for Chondrosia reniformis). Apoptosis was identified using an antibody against active caspase-3. Cell loss through shedding was studied quantitatively by collecting and weighing sponge-expelled detritus and qualitatively by light microscopy of sponge tissue and detritus. All species investigated displayed substantial cell proliferation, predominantly in the choanoderm, but also in the mesohyl. The majority of coral reef species (five) showed between 16.1±15.9% and 19.0±2.0% choanocyte proliferation (mean±SD) after 6 h and the Mediterranean species, C. reniformis, showed 16.6±3.2% after 10 h BrdU-labeling. Monanchora arbuscula showed lower choanocyte proliferation (8.1±3.7%), whereas the mangrove species Mycale microsigmatosa showed relatively higher levels of choanocyte proliferation (70.5±6.6%). Choanocyte proliferation in Haliclona vansoesti was variable (2.8–73.1%). Apoptosis was negligible and not the primary mechanism of cell loss involved in cell turnover. All species investigated produced significant amounts of detritus (2.5–18% detritus bodyweight?1·d?1) and cell shedding was observed in seven out of eight species. The amount of shed cells observed in histological sections may be related to differences in residence time of detritus within canals. Detritus production could not be directly linked to cell shedding due to the degraded nature of expelled cellular debris. We have demonstrated that under steady-state conditions, cell turnover through cell proliferation and cell shedding are common processes to maintain tissue homeostasis in a variety of sponge species from different ecosystems. Cell turnover is hypothesized to be the main underlying mechanism producing sponge-derived detritus, a major trophic resource transferred through sponges in benthic ecosystems, such as coral reefs. PMID:25289641

Alexander, Brittany E.; Liebrand, Kevin; Osinga, Ronald; van der Geest, Harm G.; Admiraal, Wim; Cleutjens, Jack P. M.; Schutte, Bert; Verheyen, Fons; Ribes, Marta; van Loon, Emiel; de Goeij, Jasper M.

2014-01-01

165

Cell turnover and detritus production in marine sponges from tropical and temperate benthic ecosystems.  

PubMed

This study describes in vivo cell turnover (the balance between cell proliferation and cell loss) in eight marine sponge species from tropical coral reef, mangrove and temperate Mediterranean reef ecosystems. Cell proliferation was determined through the incorporation of 5-bromo-2'-deoxyuridine (BrdU) and measuring the percentage of BrdU-positive cells after 6 h of continuous labeling (10 h for Chondrosia reniformis). Apoptosis was identified using an antibody against active caspase-3. Cell loss through shedding was studied quantitatively by collecting and weighing sponge-expelled detritus and qualitatively by light microscopy of sponge tissue and detritus. All species investigated displayed substantial cell proliferation, predominantly in the choanoderm, but also in the mesohyl. The majority of coral reef species (five) showed between 16.1±15.9% and 19.0±2.0% choanocyte proliferation (mean±SD) after 6 h and the Mediterranean species, C. reniformis, showed 16.6±3.2% after 10 h BrdU-labeling. Monanchora arbuscula showed lower choanocyte proliferation (8.1±3.7%), whereas the mangrove species Mycale microsigmatosa showed relatively higher levels of choanocyte proliferation (70.5±6.6%). Choanocyte proliferation in Haliclona vansoesti was variable (2.8-73.1%). Apoptosis was negligible and not the primary mechanism of cell loss involved in cell turnover. All species investigated produced significant amounts of detritus (2.5-18% detritus bodyweight-1·d-1) and cell shedding was observed in seven out of eight species. The amount of shed cells observed in histological sections may be related to differences in residence time of detritus within canals. Detritus production could not be directly linked to cell shedding due to the degraded nature of expelled cellular debris. We have demonstrated that under steady-state conditions, cell turnover through cell proliferation and cell shedding are common processes to maintain tissue homeostasis in a variety of sponge species from different ecosystems. Cell turnover is hypothesized to be the main underlying mechanism producing sponge-derived detritus, a major trophic resource transferred through sponges in benthic ecosystems, such as coral reefs. PMID:25289641

Alexander, Brittany E; Liebrand, Kevin; Osinga, Ronald; van der Geest, Harm G; Admiraal, Wim; Cleutjens, Jack P M; Schutte, Bert; Verheyen, Fons; Ribes, Marta; van Loon, Emiel; de Goeij, Jasper M

2014-01-01

166

Plant and arthropod community sensitivity to rainfall manipulation but not nitrogen enrichment in a successional grassland ecosystem.  

PubMed

Grasslands provide many ecosystem services including carbon storage, biodiversity preservation and livestock forage production. These ecosystem services will change in the future in response to multiple global environmental changes, including climate change and increased nitrogen inputs. We conducted an experimental study over 3 years in a mesotrophic grassland ecosystem in southern England. We aimed to expose plots to rainfall manipulation that simulated IPCC 4th Assessment projections for 2100 (+15 % winter rainfall and -30 % summer rainfall) or ambient climate, achieving +15 % winter rainfall and -39 % summer rainfall in rainfall-manipulated plots. Nitrogen (40 kg ha(-1) year(-1)) was also added to half of the experimental plots in factorial combination. Plant species composition and above ground biomass were not affected by rainfall in the first 2 years and the plant community did not respond to nitrogen enrichment throughout the experiment. In the third year, above-ground plant biomass declined in rainfall-manipulated plots, driven by a decline in the abundances of grass species characteristic of moist soils. Declining plant biomass was also associated with changes to arthropod communities, with lower abundances of plant-feeding Auchenorrhyncha and carnivorous Araneae indicating multi-trophic responses to rainfall manipulation. Plant and arthropod community composition and plant biomass responses to rainfall manipulation were not modified by nitrogen enrichment, which was not expected, but may have resulted from prior nitrogen saturation and/or phosphorus limitation. Overall, our study demonstrates that climate change may in future influence plant productivity and induce multi-trophic responses in grasslands. PMID:25224801

Lee, Mark A; Manning, Pete; Walker, Catherine S; Power, Sally A

2014-12-01

167

Synthesis of Watershed and Ecosystem Responses to Lehmann Lovegrass Invasion in a SE Arizona Desert Grassland Watershed  

NASA Astrophysics Data System (ADS)

Compared to aridland systems that have undergone rapid change in dominant vegetation growth form, the responses of watershed and ecosystem processes to a shift in dominance of similar growth forms have not been well-studied. Following a prolonged drought period (2000-2005) at the Walnut Gulch Experimental Watershed's Kendall grassland site (WS#112), near Tombstone, AZ, strong summer monsoon rains in 2006 were accompanied by widespread mortality most native perennial grasses, a transient increase in annual forbs, followed by establishment and sustained dominance by a single perennial grass, the invasive bunchgrass, Lehmann lovegrass (Eragrostis lehmanniana). This loss of ecological diversity occurred across a watershed already instrumented for quantifying long-term climate, watershed, hill-slope, and ecosystem-level gas exchange processes. Salient findings from these data sets were: 1) annual watershed sediment discharge rapidly returned to pre-invasion levels following a large spike in 2006 that accounted for 65% of the total sediment yield summed over 35 years, 2) plot-level experimental runoff studies showed hill-slope sediment yields consistently doubled, as did growing season soil evaporation contributions to ET, and 3) the grassland was a carbon sink during dry conditions under lovegrass dominance. These findings show that while some aspects of overall watershed and ecosystem function were not strongly affected (i.e. sediment yield and net primary productivity), processes acting at lower spatial and temporal scales have been negatively impacted by lovegrass dominance. We believe these lower-order processes underlie the strong ecological effects associated with Lehmann lovegrass invasion, and will also eventually alter landform processes and change the basic ecohydrological characteristics of desert grassland watersheds.

Hamerlynck, E. P.; Scott, R. L.; Polyakov, V.; Sugg, Z.; Moran, S. M.; Stone, J.; Nearing, M.

2011-12-01

168

Identifying grasslands suitable for cellulosic feedstock crops in the Greater Platte River Basin: dynamic modeling of ecosystem performance with 250 m eMODIS  

USGS Publications Warehouse

This study dynamically monitors ecosystem performance (EP) to identify grasslands potentially suitable for cellulosic feedstock crops (e.g., switchgrass) within the Greater Platte River Basin (GPRB). We computed grassland site potential and EP anomalies using 9-year (2000–2008) time series of 250 m expedited moderate resolution imaging spectroradiometer Normalized Difference Vegetation Index data, geophysical and biophysical data, weather and climate data, and EP models. We hypothesize that areas with fairly consistent high grassland productivity (i.e., high grassland site potential) in fair to good range condition (i.e., persistent ecosystem overperformance or normal performance, indicating a lack of severe ecological disturbance) are potentially suitable for cellulosic feedstock crop development. Unproductive (i.e., low grassland site potential) or degraded grasslands (i.e., persistent ecosystem underperformance with poor range condition) are not appropriate for cellulosic feedstock development. Grassland pixels with high or moderate ecosystem site potential and with more than 7 years ecosystem normal performance or overperformance during 2000–2008 are identified as possible regions for future cellulosic feedstock crop development (ca. 68 000 km2 within the GPRB, mostly in the eastern areas). Long-term climate conditions, elevation, soil organic carbon, and yearly seasonal precipitation and temperature are important performance variables to determine the suitable areas in this study. The final map delineating the suitable areas within the GPRB provides a new monitoring and modeling approach that can contribute to decision support tools to help land managers and decision makers make optimal land use decisions regarding cellulosic feedstock crop development and sustainability.

Gu, Yingxin; Boyte, Stephen P.; Wylie, Bruce K.; Tieszen, Larry L.

2012-01-01

169

Bromus tectorum invasion alters nitrogen dynamics in an undisturbed arid grassland ecosystem  

USGS Publications Warehouse

The nonnative annual grass Bromus tectorum has successfully replaced native vegetation in many arid and semiarid ecosystems. Initial introductions accompanied grazing and agriculture, making it difficult to separate the effects of invasion from physical disturbance. This study examined N dynamics in two recently invaded, undisturbed vegetation associations (C3 and C4). The response of these communities was compared to an invaded/disturbed grassland. The invaded/disturbed communities had higher surface NH4+ input in spring, whereas there were no differences for surface input of NO3-. Soil inorganic N was dominated by NH4+, but invaded sites had greater subsurface soil NO3-. Invaded sites had greater total soil N at the surface four years post-invasion in undisturbed communities, but total N was lower in the invaded/disturbed communities. Soil ??15N increased with depth in the noninvaded and recently invaded communities, whereas the invaded/disturbed communities exhibited the opposite pattern. Enriched foliar ??15N values suggest that Bromus assimilated subsurface NO3-, whereas the native grasses were restricted to surface N. A Rayleigh distillation model accurately described decomposition patterns in the noninvaded communities where soil N loss is accompanied by increasing soil ??15N; however, the invaded/disturbed communities exhibited the opposite pattern, suggesting redistribution of N within the soil profile. This study suggests that invasion has altered the mechanisms driving nitrogen dynamics. Bromus litter decomposition and soil NO3- concentrations were greater in the invaded communities during periods of ample precipitation, and NO3- leached from the surface litter, where it was assimilated by Bromus. The primary source of N input in these communities is a biological soil crust that is removed with disturbance, and the lack of N input by the biological soil crust did not balance N loss, resulting in reduced total N in the invaded/disturbed communities. Bromus produced a positive feedback loop by leaching NO3- from decomposing Bromus litter to subsurface soil layers, accessing that deep-soil N pool with deep roots and returning that N to the surface as biomass and subsequent litter. Lack of new inputs combined with continued loss will result in lower total soil N, evidenced by the lower total soil N in the invaded/disturbed communities. ?? 2006 by the Ecological Society of America.

Sperry, L. J.; Belnap, J.; Evans, R. D.

2006-01-01

170

Short-term bioavailability of carbon in soil organic matter fractions of different particle sizes and densities in grassland ecosystems.  

PubMed

The quality, stability and availability of organic carbon (OC) in soil organic matter (SOM) can vary widely between differently managed ecosystems. Several approaches have been developed for isolating SOM fractions to examine their ecological roles, but links between the bioavailability of the OC of size-density fractions and soil microbial communities have not been previously explored. Thus, in the presented laboratory study we investigated the potential bioavailability of OC and the structure of associated microbial communities in different particle-size and density fractions of SOM. For this we used samples from four grassland ecosystems with contrasting management intensity regimes and two soil types: a Haplic Cambisol and a typical Chernozem. A combined size-density fractionation protocol was applied to separate clay-associated SOM fractions (CF1, <1?m; CF2, 1-2?m) from light SOM fractions (LF1, <1.8gcm(-3); LF2, 1.8-2.0gcm(-3)). These fractions were used as carbon sources in a respiration experiment to determine their potential bioavailability. Measured CO2-release was used as an index of substrate accessibility and linked to the soil microbial community structure, as determined by phospholipid fatty acids (PLFA) analysis. Several key factors controlling decomposition processes, and thus the potential bioavailability of OC, were identified: management intensity and the plant community composition of the grasslands (both of which affect the chemical composition and turnover of OC) and specific properties of individual SOM fractions. The PLFA patterns highlighted differences in the composition of microbial communities associated with the examined grasslands, and SOM fractions, providing the first broad insights into their active microbial communities. From observed interactions between abiotic and biotic factors affecting the decomposition of SOM fractions we demonstrate that increasing management intensity could enhance the potential bioavailability of OC, not only in the active and intermediate SOM pools, but also in the passive pool. PMID:25112822

Breulmann, Marc; Masyutenko, Nina Petrovna; Kogut, Boris Maratovich; Schroll, Reiner; Dörfler, Ulrike; Buscot, François; Schulz, Elke

2014-11-01

171

The role of fire in Miocene to Pliocene C4 grassland and ecosystem evolution  

NASA Astrophysics Data System (ADS)

Modern savannah grasslands were established during the late Miocene and Pliocene (8-3 million years ago). In the tropics, grasslands are dominated by grasses that use the C4 photosynthetic pathway, rather than the C3 pathway. The C4 pathway is better adapted to warm, dry and low-CO2 conditions, leading to suggestions that declining atmospheric CO2 levels, increasing aridity and enhanced rainfall seasonality allowed grasses using this pathway to expand during this interval. The role of fire in C4 expansion may have been underestimated. Here we use analyses of pollen, microscopic charcoal and the stable isotopic composition of plant waxes from a marine sediment core off the coast of Namibia to reconstruct the relative timing of changes in plant composition and fire activity for the late Miocene and Pliocene. We find that in southwestern Africa, the expansion of C4 grasses occurred alongside increasing aridity and enhanced fire activity. During further aridification in the Pliocene, the proportion of C4 grasses in the grasslands increased, while the grassland contracted and deserts and semi-deserts expanded. Our results are consistent with the hypothesis that ecological disturbance by fire was an essential feedback mechanism leading to the establishment of C4 grasslands in the Miocene and Pliocene.

Hoetzel, Sebastian; Dupont, Lydie; Schefuß, Enno; Rommerskirchen, Florian; Wefer, Gerold

2013-12-01

172

Stakeholder perceptions of grassland ecosystem services in relation to knowledge on soil fertility and biodiversity  

Microsoft Academic Search

The concept of ecosystem services is increasingly being used by scientists and policy makers. However, most studies in this\\u000a area have focussed on factors that regulate ecosystem functions (i.e. the potential to deliver ecosystem services) or the\\u000a supply of ecosystem services. In contrast, demand for ecosystem services (i.e. the needs of beneficiaries) or understanding\\u000a of the concept and the relative

Pénélope Lamarque; Ulrike Tappeiner; Catherine Turner; Melanie Steinbacher; Richard D. Bardgett; Ute Szukics; Markus Schermer; Sandra Lavorel

173

Evidence of physiological decoupling from grassland ecosystem drivers by an encroaching woody shrub.  

PubMed

Shrub encroachment of grasslands is a transformative ecological process by which native woody species increase in cover and frequency and replace the herbaceous community. Mechanisms of encroachment are typically assessed using temporal data or experimental manipulations, with few large spatial assessments of shrub physiology. In a mesic grassland in North America, we measured inter- and intra-annual variability in leaf ?(13)C in Cornus drummondii across a grassland landscape with varying fire frequency, presence of large grazers and topographic variability. This assessment of changes in individual shrub physiology is the largest spatial and temporal assessment recorded to date. Despite a doubling of annual rainfall (in 2008 versus 2011), leaf ?(13)C was statistically similar among and within years from 2008-11 (range of -28 to -27‰). A topography*grazing interaction was present, with higher leaf ?(13)C in locations that typically have more bare soil and higher sensible heat in the growing season (upland topographic positions and grazed grasslands). Leaf ?(13)C from slopes varied among grazing contrasts, with upland and slope leaf ?(13)C more similar in ungrazed locations, while slopes and lowlands were more similar in grazed locations. In 2011, canopy greenness (normalized difference vegetation index - NDVI) was assessed at the centroid of individual shrubs using high-resolution hyperspectral imagery. Canopy greenness was highest mid-summer, likely reflecting temporal periods when C assimilation rates were highest. Similar to patterns seen in leaf ?(13)C, NDVI was highest in locations that typically experience lowest sensible heat (lowlands and ungrazed). The ability of Cornus drummondii to decouple leaf physiological responses from climate variability and fire frequency is a likely contributor to the increase in cover and frequency of this shrub species in mesic grassland and may be generalizable to other grasslands undergoing woody encroachment. PMID:24339950

Nippert, Jesse B; Ocheltree, Troy W; Orozco, Graciela L; Ratajczak, Zak; Ling, Bohua; Skibbe, Adam M

2013-01-01

174

Plant trait-based models identify direct and indirect effects of climate change on bundles of grassland ecosystem services  

PubMed Central

Land use and climate change are primary causes of changes in the supply of ecosystem services (ESs). Although the consequences of climate change on ecosystem properties and associated services are well documented, the cascading impacts of climate change on ESs through changes in land use are largely overlooked. We present a trait-based framework based on an empirical model to elucidate how climate change affects tradeoffs among ESs. Using alternative scenarios for mountain grasslands, we predicted how direct effects of climate change on ecosystems and indirect effects through farmers’ adaptations are likely to affect ES bundles through changes in plant functional properties. ES supply was overall more sensitive to climate than to induced management change, and ES bundles remained stable across scenarios. These responses largely reflected the restricted extent of management change in this constrained system, which was incorporated when scaling up plot level climate and management effects on ecosystem properties to the entire landscape. The trait-based approach revealed how the combination of common driving traits and common responses to changed fertility determined interactions and tradeoffs among ESs. PMID:25225382

Lamarque, Penelope; Lavorel, Sandra; Mouchet, Maud; Quetier, Fabien

2014-01-01

175

Comparison of Carbon Sequestration Rates and Energy Balance of Turf in the Denver Urban Ecosystem and an Adjacent Native Grassland  

NASA Astrophysics Data System (ADS)

Urban ecosystems are currently characterized by rapid growth, are expected to continually expand and, thus, represent an important driver of land use change. A significant component of urban ecosystems is lawns, potentially the single largest irrigated "crop" in the U.S. Beginning in March of 2011 (ahead of the growing season), eddy covariance measurements of net carbon exchange and evapotranspiration along with energy balance fluxes were conducted for a well-watered, fertilized lawn (rye-bluegrass-mix) in metropolitan Denver and for a nearby tallgrass prairie (big bluestem, switchgrass, cheatgrass, blue grama). Due to the semi-arid climate conditions of the Denver region, differences in management (i.e., irrigation and fertilization) are expected to have a discernible impact on ecosystem productivity and thus on carbon sequestration rates, evapotranspiration, and the sensible and latent heat partitioning of the energy balance. By mid-July, preliminary data indicated that cumulative evapotranspiration was approximately 270 mm and 170 mm for urban and native grasslands, respectively, although cumulative carbon sequestration at that time was similar for both (approximately 40 mg/m2). However, the pattern of carbon exchange differed between the grasslands. Both sites showed daily net uptake of carbon starting in late May, but the urban lawn displayed greater diurnal variability as well as greater uptake rates in general, especially following fertilization in mid-June. In contrast, the trend of carbon uptake at the prairie site was occasionally reversed following strong convective precipitation events, resulting in a temporary net release of carbon. The continuing acquisition of data and investigation of these relations will help us assess the potential impact of urban growth on regional carbon sequestration.

Thienelt, T. S.; Anderson, D. E.; Powell, K. M.

2011-12-01

176

Conservation genetics of two co-dominant grass species in an endangered grassland ecosystem  

Microsoft Academic Search

Summary 1. Global habitat fragmentation and loss of undisturbed grasslands has led to the use of non-local seed and cultivars in restoration. There is concern that these sources may be genetically depauperate and their introduction may lead to loss of unique local gen- otypes. Within this context we considered the issue with regard to the once widespread but now highly

D. J. Gustafson; D. J. Gibson; D. L. Nickrent

2004-01-01

177

Anatomical and Eco-Physiological Changes in Leaves of Couch-Grass ( Elymus repens L.), a Temperate Loess Grassland Species, after 7 Years Growth Under Elevated CO 2 Concentration  

Microsoft Academic Search

Leaf anatomy and eco-physiology of Elymus repens, a temperate loess grassland species, were determined after seven years of exposure to 700 ?mol (CO2) mol?1 (EC). EC treatment resulted in significant reduction of stomatal density on both surfaces of couch-grass leaves. Thickness\\u000a of leaves and that of the sclerenchyma tissues between the vessels and the adaxial surfaces, the area of vascular

A. I. Engloner; D. Kovács; J. Balogh; Z. Tuba

2003-01-01

178

Trace metal mobility and microbial community structure in tropical soils: examples from adjacent forest and grassland ecosystems  

NASA Astrophysics Data System (ADS)

Many factors determine the quality and sustainability of a soil environment and changes in land use can impact significantly soil geochemistry and the associated soil microbial communities. Native tropical forests and human-constructed grasslands on Barro Colorado Island provide an excellent setting for comparing changes in soil ecosystems in undisturbed and altered landscapes. The goals of this study were to examine biological, chemical, and mineralogical changes in soil properties as a function of land use changes during the wet and dry seasons. Soil pits were excavated at two study sites, a tropical forest and an adjacent plot that has been converted to grassland, during March 2002 and August 2003. The 1 meter deep pits were sampled at 5 cm intervals and characterized for soil organic matter content, soil moisture, community structure and total lipid biomass of the soil microbial community, mineralogy, and trace metal distribution using a sequential extraction method. Results demonstrate that forested soils exhibit higher organic matter content than grassland soils regardless of soil moisture content. Total lipid biomass of the active soil microbial population decreases with depth in both soils, but is elevated in the forested soil, likely correlating with the organic matter content in this system. Diversity of the soil microbial community, determined by PLFA analysis, decreases sharply at the base of the root zone and general trends in community structure are similar in both soils. XRD analysis of the soils reveal that the weathering profile in the forest has extended to a greater depth, but these differences in the mineralogy profile do not exert significant control on trace element mobility. Vanadium, copper, zinc, and aluminum show strong affinities for the organically bound fraction in both soils.

Wilson, A. D.; Roberts, J. A.; MacPherson, G. L.; Mauck, B. S.; Stallard, R. F.

2004-12-01

179

The effects of global climate change on the species composition and ecosystem function in the central grasslands  

SciTech Connect

Alterations to the Earth`s environment are projected to be of an amplitude not experienced in the recent biological history. How ecosystems will respond to these changes is a matter of great uncertainty. Using the ecosystem model CENTURY, we evaluated the responses of five grass species, common to the Central Grasslands Region to changing climates. The altered climates used in this simulation, based on CCC GCM outputs, were 2.5 - 4{degrees}C increase in mean annual temperature and a 1% increase in mean annual precipitation with significant variation in seasonal distribution. The species included Agrostis scabra (C{sub 3} grass), Agropyron repens (C{sub 3} grass), Poa pratensis (C{sub 3} grass), Schizachyrium scoparium (C{sub 4} grass), and Andropogon gerardii (C{sub 4} grass). Soil carbon decreased for all five species under the modified climate scenario. Annual production varied among species. Agropyron repens showed a slight increase, A. scabra showed a slight decrease, while the two C{sub 4} species, S. scoparium and A. gerardii, and the C{sub 3} invasive grass Poa pratensis showed larger increases in annual production. The increased annual production of P. pratensis under the modified climate scenario may indicate the potential for this species to further expand its range. What impact a range expansion of P. pratensis will have on ecosystem function and overall species composition is unclear.

Falkner, M.B.; Ojima, D.S.; Parton, W.J. [Colorado State Univ., Fort Collins, CO (United States)

1995-06-01

180

Linking the Response of Annual Grasslands to Warming and Altered Rainfall Across Scales of Gene Expression, Species, and Ecosystem  

NASA Astrophysics Data System (ADS)

Climate change can influence terrestrial ecosystems at multiple biological levels: gene expression, species, and ecosystem. We are studying California grassland mesocosms with seven annual species (five grasses, two forbs) that were started in 2005. In the 2006-2007 growing season, they were exposed to three rainfall treatments (297, 552, and 867 mm y-1) and soil and air temperature (ambient and elevated +4oC) in replicated greenhouses. This presentation will combine plant and ecosystem level results with transcript level analyses associated with key enzymes, such as rubisco and glutamine synthetase (GS). Because rainfall is the dominant climate variable for most processes in this Mediterranean ecosystem, the effect of warming was strongly mediated by rainfall. In fact, we saw significant interactions between temperature and rainfall treatments at all three biological levels. For example, at the ecosystem level, warming led to a decrease in aboveground and total NPP under low rainfall, and an increase under high rainfall. For the dominant species, Avena barbata, warming had no effect under high rainfall, but suppressed Avena NPP in low rainfall. At the same time, warmer, wetter conditions accelerated Avena flowering by almost 15 days. This shift in phenology was presaged by observations at the transcript level. Specifically, in the high temperature, high rainfall treatment, the levels of mRNAs for RbcS and GS2 (encoding the small subunit of rubisco and the chloroplastic isoform of GS, respectively) declined while GS1 (encoding the cytosolic isoform of GS) was upregulated several weeks before heading. The transcript level response (along with soil and plant nitrogen data) indicated the leaf had switched from a carbon and nitrogen sink to a source - consistent with more mature plant function and earlier flowering. Soil CO2 respiration also showed strong rain-by-temperature interactions that were due mainly to changes in root response (respiration and/or exudates) rather than in microbial respiration. Overall, the pervasive rain-by-temperature interactions mean that it may be very difficult to predict the effect of warming alone, without accounting for changes in precipitation (in our Mediterranean system). While predictions of warming of 3-6°C in the next 100 years are fairly certain, changes in precipitation are much more uncertain, with some forecasts drier and others wetter for a given location. We suggest that uncertainty about future precipitation and the interacting influences of temperature and moisture on ecosystems are currently key limitations in predicting ecosystem response to climate change, particularly in Mediterranean ecosystems such as the one studied here.

Torn, M. S.; Bernard, S. M.; Castanha, C.; Fischer, M. L.; Hopkins, F. M.; Placella, S. A.; St. Clair, S. B.; Salve, R.; Sudderth, E.; Herman, D.; Ackerly, D.; Firestone, M. K.

2007-12-01

181

On the relationship between ecosystem-scale hyperspectral reflectance and CO2 exchange in European mountain grasslands  

NASA Astrophysics Data System (ADS)

In this paper we explore the use of hyperspectral reflectance measurements and vegetation indices (VIs) derived therefrom in estimating carbon dioxide (CO2) fluxes (net ecosystem exchange - NEE; gross primary production - GPP), and some key ecophysiological variables related to NEE and GPP (light use efficiency - ?; initial quantum yield - ?; and GPP at saturating light - GPPmax) for grasslands. Hyperspectral reflectance data (400-1000 nm), CO2 fluxes and biophysical parameters were measured at three grassland sites located in European mountain regions. The relationships between CO2 fluxes, ecophysiological variables and VIs derived using all two-band combinations of wavelengths available from the whole hyperspectral data space were analysed. We found that hyperspectral VIs generally explained a large fraction of the variability in the investigated dependent variables and that they generally exhibited more skill in estimating midday and daily average GPP and NEE, as well as GPPmax, than ? and ?. Relationships between VIs and CO2 fluxes and ecophysiological parameters were site-specific, likely due to differences in soils, vegetation parameters and environmental conditions. Chlorophyll and water content related VIs (e.g. CI, NPCI, WI), reflecting seasonal changes in biophysical parameters controlling the photosynthesis process, explained the largest fraction of variability in most of the dependent variables. A limitation of the hyperspectral sensors is that their cost is still high and the use laborious. At the eddy covariance with a limited budget and without technical support, we suggest to use at least dual or four channels low cost sensors in the the following spectral regions: 400-420 nm; 500-530 nm; 750-770 nm; 780-800 nm and 880-900 nm. In addition, our findings have major implications for up-scaling terrestrial CO2 fluxes to larger regions and for remote and proximal sensing sampling and analysis strategies and call for more cross-site synthesis studies linking ground-based spectral reflectance with ecosystem-scale CO2 fluxes.

Balzarolo, M.; Vescovo, L.; Hammerle, A.; Gianelle, D.; Papale, D.; Wohlfahrt, G.

2014-07-01

182

Testing functional trait-based mechanisms underpinning plant responses to grazing and linkages to ecosystem functioning in grasslands  

NASA Astrophysics Data System (ADS)

Abundant evidence has shown that grazing alters plant functional traits, ecological strategies, community structure, and ecosystem functioning of grasslands. Few studies, however, have examined how plant responses to grazing are mediated by resource availability and functional group identity. We test functional trait-based mechanisms underlying the responses of different life forms to grazing and linkages to ecosystem functioning along a soil moisture gradient in the Inner Mongolia grassland. A principal component analysis (PCA) based on 9 traits × 276 species matrix showed that the plant size spectrum (i.e., individual biomass), leaf economics spectrum (leaf N content and leaf density), and light competition spectrum (height and stem-leaf biomass ratio) distinguished plant species responses to grazing. The three life forms exhibited differential strategies as indicated by trait responses to grazing. The annuals and biennials adopted grazing-tolerant strategies associated with high growth rate, reflected by high leaf N content and specific leaf area. The perennial grasses exhibited grazing-tolerant strategies associated with great regrowth capacity and high palatability scores, whereas perennial forbs showed grazing-avoidant strategies with short stature and low palatability scores. In addition, the dominant perennial bunchgrasses exhibited mixed tolerance-resistance strategies to grazing and mixed acquisitive-conservative strategies in resource utilization. Grazing increased the relative abundance of perennial forbs with low palatability in the wet and fertile meadow, but it promoted perennial grasses with high palatability in the dry and infertile typical steppe. Our findings suggest that the effects of grazing on plant functional traits are dependent on both the abiotic (e.g., soil moisture) and biotic (e.g., plant functional group identity and composition) factors. Grazing-induced shifts in functional group composition are largely dependent on resource availability, particularly water availability.

Zheng, S. X.; Li, W. H.; Lan, Z. C.; Ren, H. Y.; Wang, K. B.; Bai, Y. F.

2014-09-01

183

Biodiversity and ecosystem stability in a decade-long grassland experiment.  

PubMed

Human-driven ecosystem simplification has highlighted questions about how the number of species in an ecosystem influences its functioning. Although biodiversity is now known to affect ecosystem productivity, its effects on stability are debated. Here we present a long-term experimental field test of the diversity-stability hypothesis. During a decade of data collection in an experiment that directly controlled the number of perennial prairie species, growing-season climate varied considerably, causing year-to-year variation in abundances of plant species and in ecosystem productivity. We found that greater numbers of plant species led to greater temporal stability of ecosystem annual aboveground plant production. In particular, the decadal temporal stability of the ecosystem, whether measured with intervals of two, five or ten years, was significantly greater at higher plant diversity and tended to increase as plots matured. Ecosystem stability was also positively dependent on root mass, which is a measure of perenniating biomass. Temporal stability of the ecosystem increased with diversity, despite a lower temporal stability of individual species, because of both portfolio (statistical averaging) and overyielding effects. However, we found no evidence of a covariance effect. Our results indicate that the reliable, efficient and sustainable supply of some foods (for example, livestock fodder), biofuels and ecosystem services can be enhanced by the use of biodiversity. PMID:16738658

Tilman, David; Reich, Peter B; Knops, Johannes M H

2006-06-01

184

Ecosystem performance assessment for grasslands in the Greater Platte River Basin: implications for cellulosic biofuel development  

Microsoft Academic Search

This study identifies lands suitable for cellulosic biofuel (e.g., switchgrass) development across the Northern Great Plains, with an initial emphasis on the Greater Platte River Basin (GPRB), using satellite observations, climate data, and ecosystem models. Our approach is based on previous successful ecosystem performance (EP) studies in the Yukon River Basin and the Upper Colorado River Basin. We hypothesize that

Y. Gu; S. P. Boyte; B. K. Wylie; L. L. Tieszen

2010-01-01

185

Changes in grassland ecosystem function due to extreme rainfall events: implications for responses to climate change  

Microsoft Academic Search

Climate change is causing measurable changes in rainfall patterns, and will likely cause increases in extreme rainfall events, with uncertain implications for key processes in ecosystem function and carbon cycling. We examined how variation in rainfall total quantity (Q), the interval between rainfall events (I), and individual event size (SE) affected soil water content (SWC) and three aspects of ecosystem

PHILIP A. FAY; D AW N M. K AUF; JESSE B. N IPPERT; J ONAT; HAN D. CARLISLE

186

Annual Cycle and Interannual Variability of Ecosystem Metabolism in a Temperate Climate Embayment  

Microsoft Academic Search

We have studied the net and gross metabolism of Tomales Bay, a temperate climate estuary in northern California. Tomales Bay has proved to be heterotrophic, im- plying that the bay oxidizes a subsidy of organic carbon from outside the system, in excess of inorganic nutrients supplied to it from outside and in addition to material cycling within it. Net organic

S. V. Smith; J. T. Hollibaugh

1997-01-01

187

Exploring mobilisation and transport of diffuse substances using multiple sediment and colloid tracers applied to a temperate grassland catchment.  

NASA Astrophysics Data System (ADS)

The mobilisation and transport of diffuse substances from livestock grassland systems to surface water bodies is known to impact aquatic ecology and human health. Diffuse substances include sediment and colloidal material detached from the soil surface and subsurface and colloidal material solubilised by water travelling across and through the soil matrix. Improving understanding of the dominant processes controlling the mobilisation and transport of sediment and colloid associated materials requires the application of established and novel tracing methods. In this study our objective was to link mobilisation from the plot to head water catchment scales by tracing the movement of slurry material delivered to a first order stream through the application of natural and artificial fluorescence and rare earth oxide (REO) tracing techniques. Slurry treated with fluorescent beads or REO's was applied to a hydrologically isolated field within a ~40 ha catchment. Novel natural fluorescence techniques were used to assess the presence of dissolved slurry material through the distinctive signature of samples in drainage waters. The particulate phase of slurry was traced using artificial fluorescent beads manufactured to represent two particulate phases of slurry: organic and mineral. The bead treated slurry was applied homogeneously across the entire field. REO treated slurry was applied in five 1 ha contour zones across the field, each zone receiving slurry labelled with different REOs. Surface drainage was monitored and sampled at a v-notch weir placed at the hydrological outlet of the field and at a trapezoidal flume at the catchment outlet.

Granger, S.; Hawkins, J.

2009-04-01

188

Aeolian process effects on vegetation communities in an arid grassland ecosystem  

PubMed Central

Many arid grassland communities are changing from grass dominance to shrub dominance, but the mechanisms involved in this conversion process are not completely understood. Aeolian processes likely contribute to this conversion from grassland to shrubland. The purpose of this research is to provide information regarding how vegetation changes occur in an arid grassland as a result of aeolian sediment transport. The experimental design included three treatment blocks, each with a 25 × 50 m area where all grasses, semi-shrubs, and perennial forbs were hand removed, a 25 × 50 m control area with no manipulation of vegetation cover, and two 10 × 25 m plots immediately downwind of the grass-removal and control areas in the prevailing wind direction, 19° north of east, for measuring vegetation cover. Aeolian sediment flux, soil nutrients, and soil seed bank were monitored on each treatment area and downwind plot. Grass and shrub cover were measured on each grass-removal, control, and downwind plot along continuous line transects as well as on 5 × 10 m subplots within each downwind area over four years following grass removal. On grass-removal areas, sediment flux increased significantly, soil nutrients and seed bank were depleted, and Prosopis glandulosa shrub cover increased compared to controls. Additionally, differential changes for grass and shrub cover were observed for plots downwind of vegetation-removal and control areas. Grass cover on plots downwind of vegetation-removal areas decreased over time (2004–2007) despite above average rainfall throughout the period of observation, while grass cover increased downwind of control areas; P. glandulosa cover increased on plots downwind of vegetation-removal areas, while decreasing on plots downwind of control areas. The relationships between vegetation changes and aeolian sediment flux were significant and were best described by a logarithmic function, with decreases in grass cover and increases in shrub cover occurring with small increases in aeolian sediment flux. PMID:22837828

Alvarez, Lorelei J; Epstein, Howard E; Li, Junran; Okin, Gregory S

2012-01-01

189

Complex facilitation and competition in a temperate grassland: loss of plant diversity and elevated CO2 have divergent and opposite effects on oak establishment.  

PubMed

Encroachment of woody vegetation into grasslands is a widespread phenomenon that alters plant community composition and ecosystem function. Woody encroachment is often the result of fire suppression, but it may also be related to changes in resource availability associated with global environmental change. We tested the relative strength of three important global change factors (CO(2) enrichment, nitrogen deposition, and loss of herbaceous plant diversity) on the first 3 years of bur oak (Quercus macrocarpa) seedling performance in a field experiment in central Minnesota, USA. We found that loss of plant diversity decreased initial oak survival but increased overall oak growth. Conversely, elevated CO(2) increased initial oak seedling survival and reduced overall growth, especially at low levels of diversity. Nitrogen deposition surprisingly had no net effect on survival or growth. The magnitude of these effects indicates that long-term woody encroachment trends may be most strongly associated with those few individuals that survive, but grow much larger in lower diversity patches. Further, while the CO(2) results and the species richness results appear to describe opposing trends, this is due only to the fact that the natural drivers are moving in opposite directions (decreasing species richness and increasing CO(2)). Interestingly, the mechanisms that underlie both patterns are very similar, increased CO(2) and increased species richness both increase herbaceous biomass which (1) increases belowground competition for resources and (2) increases facilitation of early plant survival under a more diverse plant canopy; in other words, both competition and facilitation help determine community composition in these grasslands. PMID:22865092

Wright, Alexandra; Schnitzer, Stefan A; Dickie, Ian A; Gunderson, Alex R; Pinter, Gabriella A; Mangan, Scott A; Reich, Peter B

2013-02-01

190

Can ectomycorrhizal fungi circumvent the nitrogen mineralization for plant nutrition in temperate forest ecosystems?  

Microsoft Academic Search

Nitrogen (N) limits plant growth in many forest ecosystems. The largest N pool in the plant–soil system is typically organic, contained primarily within the living plants and in the humus and litter layers of the soil. Understanding the pathways by which plants obtain N is a priority for clarifying N cycling processes in forest ecosystems. In this review, the interactions

Tiehang Wu

2011-01-01

191

Changes in grassland ecosystem function due to extreme rainfall events: implications for responses to  

E-print Network

soil water content (SWC) and three aspects of ecosystem function: leaf photo- synthetic carbon gain the effects of Q, and shifted the system towards increased net carbon uptake. Variation in SE at shorter I

Nippert, Jesse

192

Changes in grassland ecosystem function due to extreme rainfall events: implications for responses to climate change  

Microsoft Academic Search

Abstract Climate change is causing measurable changes in rainfall patterns, and will likely cause increases in extreme rainfall events, with uncertain implications for key processes in ecosystem,function,and,carbon,cycling. We,examined,how,variation,in rainfall,total quantity (Q), the interval between rainfall events (I), and individual event size (SE) affected,soil water,content,(SWC) and,three aspects,of ecosystem,function: leaf photo- synthetic carbon gain (ACO2 ), aboveground net primary productivity (ANPP), and

Philip A. Fay; Jesse B. N Ippertw; J Onat Han D. Carlisle; C Hristopher; W. Harper

193

rizona's grassland ecosystems are an integral part of the regional ecology, and they provide important social and economic values  

E-print Network

, wildlife watching and camping. · AGRICULTURE Grasslands supply forage for grazing animals and areas owners and consumers of downstream groundwater and intrinsic value to vegetation and wildlife for growing wine grapes. · BIODIVERSITY Grasslands support critical habitat, wildlife migration corridors

194

Seasonal variation in leaf properties and ecosystem carbon budget in a cool-temperate deciduous broad-leaved forest: simulation analysis at Takayama site, Japan  

Microsoft Academic Search

Seasonal changes in gross primary production (GPP) and net ecosystem production (NEP) in temperate deciduous forests are mostly driven by environmental conditions and the phenology of leaf demography. This study addresses another factor, temporal changes in leaf properties, i.e., leaf aging from emergence to senescence. A process-based model was used to link the ecosystem-scale carbon budget with leaf-level properties on

Akihiko Ito; Hiroyuki Muraoka; Hiroshi Koizumi; Nobuko Saigusa; Shohei Murayama; Susumu Yamamoto

2006-01-01

195

Conversion of temperate forests into heaths: Role of ecosystem disturbance and ericaceous plants  

NASA Astrophysics Data System (ADS)

Fire and logging in nutrient-poor temperate forests with certain ericaceous understory plants may convert the forests into heaths. The process of disturbance-induced heath formation is documented by using examples of Calluna in western Europe, Kalmia in Newfoundland, and Gaultheria (salal) in coastal British Columbia. In a cool, temperate climate, rapid vegetative growth of Calluna, Kalmia, and salal following disturbance results in increasing organic accumulation (paludification), nutrient sequestration, soil acidification, and allelochemicals. These are thought to be the main reasons to conifer regeneration failure in disturbed habitats. If continuation in forest is a land-use objective, then temperate forests with an ericaceous understory should not be logged unless effective silvicultural methods are devised to control the ericaceous plants and restore forest regeneration. Preharvest vegetation control may be considered as an option. Failure to control the understory plants may lead to a long-term vegetation shift, from forest to heathland, particularly in nutrient-poor sites. Successful methods of controlling Kalmia and Gaultheria, however, have yet to be developed. While the Kalmia- and Gaultheria- dominated heathlands are undesirable in Canada and the Pacific Northwest, a wide range of Calluna heathlands of western Europe are being conserved as natural and seminatural vegetation.

Mallik, A. U.

1995-09-01

196

Litter decomposition and nutrient release as affected by soil nitrogen availability and litter quality in a semiarid grassland ecosystem.  

PubMed

Nitrogen availability is critically important to litter decomposition, especially in arid and semiarid areas where N is limiting. We studied the relative contributions of litter quality and soil N to litter decomposition of two dominant grassland species, Stipa krylovii and Artemisia frigida, in a semiarid typical steppe ecosystem in Inner Mongolia, China. The study had four different rates of N addition (0, 8, 32, and 64 g N m(-2) year(-1)), and litter samples were decomposed under varying site conditions and by litter types. Litter-mixing effects of the two species were also examined. We found that N addition increased litter N concentration and thus enhanced litter decomposition by improving substrate quality. This increase, however, was offset by the negative effect of increased soil N, resulting in a diminished effect of increased soil N availability on in situ litter decomposition. The positive effects of improved litter quality slightly out-performed the negative effects of increased soil N. Our further analysis revealed that the negative effect of increasing soil N on litter decomposition could be partially explained by reduced soil microbial biomass and activity. Decomposition was significantly faster for litters of a two-species mixture than litters of the single species, but the rate of litter decomposition did not differ much between the two species, suggesting that compositional balance, rather than changes in the dominance between Stipa and Artemisia, is more critical for litter decomposition, hence nutrient cycling in this ecosystem. This semiarid steppe ecosystem may become more conservative in nutrient use with switching of dominance from Artemisia to Stipa with increasing soil N, because Stipa has a slower decomposition rate and a higher nutrient retention rate than Artemisia. PMID:19921269

Liu, Ping; Huang, Jianhui; Sun, Osbert Jianxin; Han, Xingguo

2010-03-01

197

Effects of Elevated CO2 and N Addition on Growth and N2 Fixation of a Legume Subshrub (Caragana microphylla Lam.) in Temperate Grassland in China  

PubMed Central

It is well demonstrated that the responses of plants to elevated atmospheric CO2 concentration are species-specific and dependent on environmental conditions. We investigated the responses of a subshrub legume species, Caragana microphylla Lam., to elevated CO2 and nitrogen (N) addition using open-top chambers in a semiarid temperate grassland in northern China for three years. Measured variables include leaf photosynthetic rate, shoot biomass, root biomass, symbiotic nitrogenase activity, and leaf N content. Symbiotic nitrogenase activity was determined by the C2H2 reduction method. Elevated CO2 enhanced photosynthesis and shoot biomass by 83% and 25%, respectively, and the enhancement of shoot biomass was significant only at a high N concentration. In addition, the photosynthetic capacity of C. microphylla did not show down-regulation under elevated CO2. Elevated CO2 had no significant effect on root biomass, symbiotic nitrogenase activity and leaf N content. Under elevated CO2, N addition stimulated photosynthesis and shoot biomass. By contrast, N addition strongly inhibited symbiotic nitrogenase activity and slightly increased leaf N content of C. microphylla under both CO2 levels, and had no significant effect on root biomass. The effect of elevated CO2 and N addition on C. microphylla did not show interannual variation, except for the effect of N addition on leaf N content. These results indicate that shoot growth of C. microphylla is more sensitive to elevated CO2 than is root growth. The stimulation of shoot growth of C. microphylla under elevated CO2 or N addition is not associated with changes in N2-fixation. Additionally, elevated CO2 and N addition interacted to affect shoot growth of C. microphylla with a stimulatory effect occurring only under combination of these two factors. PMID:22046376

Zhang, Lin; Wu, Dongxiu; Shi, Huiqiu; Zhang, Canjuan; Zhan, Xiaoyun; Zhou, Shuangxi

2011-01-01

198

Climate extreme effects on the chemical composition of temperate grassland species under ambient and elevated CO2: a comparison of fructan and non-fructan accumulators.  

PubMed

Elevated CO2 concentrations and extreme climate events, are two increasing components of the ongoing global climatic change factors, may alter plant chemical composition and thereby their economic and ecological characteristics, e.g. nutritional quality and decomposition rates. To investigate the impact of climate extremes on tissue quality, four temperate grassland species: the fructan accumulating grasses Lolium perenne, Poa pratensis, and the nitrogen (N) fixing legumes Medicago lupulina and Lotus corniculatus were subjected to water deficit at elevated temperature (+3°C), under ambient CO2 (392 ppm) and elevated CO2 (620 ppm). As a general observation, the effects of the climate extreme were larger and more ubiquitous in combination with elevated CO2. The imposed climate extreme increased non-structural carbohydrate and phenolics in all species, whereas it increased lignin in legumes and decreased tannins in grasses. However, there was no significant effect of climate extreme on structural carbohydrates, proteins, lipids and mineral contents and stoichiometric ratios. In combination with elevated CO2, climate extreme elicited larger increases in fructan and sucrose content in the grasses without affecting the total carbohydrate content, while it significantly increased total carbohydrates in legumes. The accumulation of carbohydrates in legumes was accompanied by higher activity of sucrose phosphate synthase, sucrose synthase and ADP-Glc pyrophosphorylase. In the legumes, elevated CO2 in combination with climate extreme reduced protein, phosphorus (P) and magnesium (Mg) contents and the total element:N ratio and it increased phenol, lignin, tannin, carbon (C), nitrogen (N) contents and C:N, C:P and N:P ratios. On the other hand, the tissue composition of the fructan accumulating grasses was not affected at this level, in line with recent views that fructans contribute to cellular homeostasis under stress. It is speculated that quality losses will be less prominent in grasses (fructan accumulators) than legumes under climate extreme and its combination with elevated CO2 conditions. PMID:24670435

AbdElgawad, Hamada; Peshev, Darin; Zinta, Gaurav; Van den Ende, Wim; Janssens, Ivan A; Asard, Han

2014-01-01

199

The likely impact of elevated [CO2], nitrogen deposition, increased temperature, and management on carbon sequestration in temperate and boreal forest ecosystems. A literature review  

Microsoft Academic Search

Temperate and Boreal forest ecosystems contain a large part of the carbon stored on land, both in the form of biomass and soil organic matter. Increasing atmospheric carbon dioxide concentration, increasing temperatures, elevated nitrogen deposition, and intensified management will change this carbon store. We review current literature and conclude that northern forests will acquire extra carbon as a result of

Norby; Richard J; Sune Linder; Tryggve Persson; M. Francesca Cotrufo; Alf Ekblad; Michael Freeman; Achim Grelle; Ivan A. Janssens; Paul G. Jarvis; Seppo Kellomäki; Anders Lindroth; Denis Loustau; Tomas Lundmark; Richard J. Norby; Ram Oren; Kim Pilegaard; Michael G. Ryan; Bjarni D. Sigurdsson; Monika Strömgren; Marcel Van Oijen; Göran Wallin

2007-01-01

200

Mercury bioaccumulation along food webs in temperate aquatic ecosystems colonized by aquatic macrophytes in south western France.  

PubMed

Mercury (Hg) is considered as an important pollutant for aquatic systems as its organic form, methylmercury (MeHg), is easily bioaccumulated and bioamplified along food webs. In various ecosystems, aquatic periphyton associated with macrophyte was identified as an important place for Hg storage and methylation by microorganisms. Our study concerns temperate aquatic ecosystems (South Western France) colonized by invasive macrophytes and characterized by high mercury methylation potentials. This work establishes original data concerning Hg bioaccumulation in organisms (plants, crustaceans, molluscs and fish) from five contrasting ecosystems. For low trophic level species, total Hg (THg) concentrations were low (from 27±2ngTHgg(-1)dw in asiatic clam Corbicula fluminea to 418±114ngTHgg(-1)dw in crayfish Procambarus clarkii). THg concentrations in some carnivorous fish (high trophic level) were close to or exceeded the International Marketing Level (IML) with values ranging from 1049±220ngTHgg(-1)dw in pike perch muscle (Sander lucioperca) to 3910±1307ngTHgg(-1)dw in eel muscle (Anguilla Anguilla). Trophic levels for the individuals were also evaluated through stable isotope analysis, and linked to Hg concentrations of organisms. A significant Hg biomagnification (r(2)= 0.9) was observed in the Aureilhan lake, despite the absence of top predator fish. For this site, Ludwigia sp. periphyton, as an entry point of Hg into food webs, is a serious hypothesis which remains to be confirmed. This study provides a first investigation of Hg transfer in the ecosystems of south western France and allows the assessment of the risk associated with the presence of Hg in aquatic food webs. PMID:23466146

Gentès, Sophie; Maury-Brachet, Régine; Guyoneaud, Rémy; Monperrus, Mathilde; André, Jean-Marc; Davail, Stéphane; Legeay, Alexia

2013-05-01

201

Influence of local air pollution on the deposition of peroxyacteyl nitrate to a nutrient-poor natural grassland ecosystem  

NASA Astrophysics Data System (ADS)

Dry deposition of peroxyacetyl nitrate (PAN) is known to have a phytotoxic impact on plants under photochemical smog conditions, but it may also lead to higher productivity and threaten species richness of vulnerable ecosystems in remote regions. However, underlying mechanisms or controlling factors for PAN deposition are not well understood and studies on dry deposition of PAN are limited. In this study, we investigate the impact of PAN deposition on a nutrient-poor natural grassland ecosystem situated at the edge of an urban and industrialized region in Germany. PAN mixing ratios were measured within a 3.5 months summer to early autumn period. In addition, PAN fluxes were determined with the modified Bowen ratio technique for a selected period. The evaluation of both stomatal and non-stomatal deposition pathways was used to model PAN deposition over the entire summer-autumn period. We found that air masses at the site were influenced by two contrasting pollution regimes, which lead to median diurnal PAN mixing ratios ranging between 50 and 300 ppt during unpolluted and between 200 and 600 ppt during polluted episodes. The measured PAN fluxes showed a clear diurnal cycle with maximal deposition fluxes of ~ -0.1 nmol m-2 s-1 (corresponding to a deposition velocity of 0.3 cm s-1) during daytime and a significant non-stomatal contribution was found. The ratio of PAN to ozone deposition velocities was found to be ~0.1, which is much larger than assumed by current deposition models. The modelled PAN flux over the entire period revealed that PAN deposition over an entire day was 333 ?g m-2 d-1 under unpolluted and 518 ?g m-2 d-1 under polluted episodes. Besides, thermochemical decomposition PAN deposition accounted for 32% under unpolluted episodes and 22% under polluted episodes of the total atmospheric PAN loss. However, the impact of PAN deposition as a nitrogen source to the nutrient-poor grassland was estimated to be only minor, under both unpolluted and polluted episodes.

Moravek, A.; Stella, P.; Foken, T.; Trebs, I.

2014-08-01

202

BROMUS TECTORUMINVASION ALTERS NITROGEN DYNAMICS IN AN UNDISTURBED ARID GRASSLAND ECOSYSTEM  

Microsoft Academic Search

The nonnative annual grass Bromus tectorumhas successfully replaced native vegetation in many arid and semiarid ecosystems. Initial introductions accompanied grazing and agriculture, making it difficult to separate the effects of invasion from physical dis- turbance. This study examined N dynamics in two recently invaded, undisturbed vegetation associations (C3 and C4). The response of these communities was compared to an invaded\\/

L. J. SPERRY; J. BELNAP; R. D. EVANS

2006-01-01

203

Trajectories of grassland ecosystem change in response to experimental manipulations of precipitation  

Microsoft Academic Search

Understanding and predicting the dynamics of ecological systems has always been central to Ecology. Today, ecologists recognize that in addition to natural and human-caused disturbances, a fundamentally different type of ecosystem change is being driven by the combined and cumulative effects of anthropogenic activities affecting earth's climate and biogeochemical cycles. This type of change is historically unprecedented in magnitude, and

Alan Knapp; Melinda Smith; Scott Collins; John Blair; John Briggs

2010-01-01

204

Growth, water and nitrogen relations in grassland model ecosystems of the semi-arid Negev of Israel exposed to elevated CO 2  

Microsoft Academic Search

Are ecosystems in dry regions particularly responsive to atmospheric CO2 enrichment? We studied responses of semi-arid grassland assemblages from the northern Negev (Israel) to CO2 concentrations representative of the pre-industrial era, and early and mid to late 21st century (280, 440, and 600 µl l-1, respectively). Communities of 32 mostly annual species were grown for a full season in large

José M. Grünzweig; Christian Körner

2001-01-01

205

Diverse responses of phenology to global changes in a grassland ecosystem  

PubMed Central

Shifting plant phenology (i.e., timing of flowering and other developmental events) in recent decades establishes that species and ecosystems are already responding to global environmental change. Earlier flowering and an extended period of active plant growth across much of the northern hemisphere have been interpreted as responses to warming. However, several kinds of environmental change have the potential to influence the phenology of flowering and primary production. Here, we report shifts in phenology of flowering and canopy greenness (Normalized Difference Vegetation Index) in response to four experimentally simulated global changes: warming, elevated CO2, nitrogen (N) deposition, and increased precipitation. Consistent with previous observations, warming accelerated both flowering and greening of the canopy, but phenological responses to the other global change treatments were diverse. Elevated CO2 and N addition delayed flowering in grasses, but slightly accelerated flowering in forbs. The opposing responses of these two important functional groups decreased their phenological complementarity and potentially increased competition for limiting soil resources. At the ecosystem level, timing of canopy greenness mirrored the flowering phenology of the grasses, which dominate primary production in this system. Elevated CO2 delayed greening, whereas N addition dampened the acceleration of greening caused by warming. Increased precipitation had no consistent impacts on phenology. This diversity of phenological changes, between plant functional groups and in response to multiple environmental changes, helps explain the diversity in large-scale observations and indicates that changing temperature is only one of several factors reshaping the seasonality of ecosystem processes. PMID:16954189

Cleland, Elsa E.; Chiariello, Nona R.; Loarie, Scott R.; Mooney, Harold A.; Field, Christopher B.

2006-01-01

206

An Integrated Mercury Monitoring Program for Temperate Estuarine and Marine Ecosystems on the North American Atlantic Coast  

PubMed Central

During the past century, anthropogenic activities have altered the distribution of mercury (Hg) on the earth’s surface. The impacts of such alterations to the natural cycle of Hg can be minimized through coordinated management, policy decisions, and legislative regulations. An ability to quantitatively measure environmental Hg loadings and spatiotemporal trends of their fate in the environment is critical for science-based decision making. Here, we outline a Hg monitoring program for temperate estuarine and marine ecosystems on the Atlantic Coast of North America. This framework follows a similar, previously developed plan for freshwater and terrestrial ecosystems in the United States. Methylmercury (MeHg) is the toxicologically relevant form of Hg, and its ability to bioaccumulate in organisms and biomagnify in food webs depends on numerous biological and physicochemical factors that affect its production, transport, and fate. Therefore, multiple indicators are needed to fully characterize potential changes of Hg loadings in the environment and MeHg bioaccumulation through the different marine food webs. In addition to a description of how to monitor environmental Hg loads for air, sediment, and water, we outline a species-specific matrix of biotic indicators that include shellfish and other invertebrates, fish, birds and mammals. Such a Hg monitoring template is applicable to coastal areas across the Northern Hemisphere and is transferable to arctic and tropical marine ecosystems. We believe that a comprehensive approach provides an ability to best detect spatiotemporal Hg trends for both human and ecological health, and concurrently identify food webs and species at greatest risk to MeHg toxicity. PMID:19294469

Evers, David C.; Mason, Robert P.; Kamman, Neil C.; Chen, Celia Y.; Bogomolni, Andrea L.; Taylor, David L.; Hammerschmidt, Chad R.; Jones, Stephen H.; Burgess, Neil M.; Munney, Kenneth; Parsons, Katharine C.

2008-01-01

207

Predicting the effect of climate change on temperate shallow lakes with the ecosystem model PCLake  

Microsoft Academic Search

Global average surface temperatures are expected to rise by about 1.4-5.8°C from the present until the year 2100. This temperature\\u000a increase will affect all ecosystems on earth. For shallow lakes-which can be either in a clear water or a turbid state-this\\u000a climate change will expectedly negatively affect water transparency though the prediction is far from conclusive and experimental\\u000a investigations elucidating

W. M. Mooij; J. H. Janse; L. N. Senerpont Domis; S. Hülsmann; B. W. Ibelings

208

Predicting the effect of climate change on temperate shallow lakes with the ecosystem model PCLake  

Microsoft Academic Search

Global average surface temperatures are expected to rise by about 1.4–5.8°C from the present until the year 2100. This temperature\\u000a increase will affect all ecosystems on earth. For shallow lakes—which can be either in a clear water or a turbid state—this\\u000a climate change will expectedly negatively affect water transparency though the prediction is far from conclusive and experimental\\u000a investigations elucidating

W. M. Mooij; J. H. Janse; L. N. De Senerpont Domis; S. Hülsmann; B. W. Ibelings

2007-01-01

209

Forest and grassland ecosystem studies using the advanced solid-state array spectroradiometer  

NASA Technical Reports Server (NTRS)

The advanced solid-state array spectroradiometer (ASAS) is an airborne, off-nadir pointing imaging spectroradiometer used to acquire bidirectional radiance data for terrestrial targets. As its platform aircraft flies over a target the sensor can image the target through a sequence of at least seven fore-to-aft view directions ranging up to 45 deg on either side of nadir. ASAS acquires data for 29 spectral bands in the visible and near-infrared portions of the spectrum with a resolution of 15 nm. ASAS data were recently acquired for a prairie ecosystem and a northern forest ecosystem. The data demonstrate the combined effects of reflectance anisotropy and increased atmospheric path length on off-nadir observations. One result of these effects is a variation in vegetation indices as a function of view direction. Normalized-difference-vegetation-indices for prairie grass, coniferous, and deciduous canopies varied up to 14 percent, 23 percent, and 6 percent, respectively, relative to nadir as a function of view zenith angle along the solar principal plane.

Irons, James R.; Ranson, K. Jon; Williams, Darrel L.; Irish, Richard R.

1989-01-01

210

Ecosystem Phenology from Eddy-covariance Measurements: Spring Photosynthesis in a Cool Temperate Bog  

NASA Astrophysics Data System (ADS)

The onset and increase of spring photosynthetic flux of carbon dioxide is an important attribute of the carbon budget of northern ecosystems and we used eddy-covariance measurements from March to May over 5 years at the Mer Bleue ombrotrophic bog to establish the important controls. The onset of ecosystem photosynthesis (day-of-year from 86 to 101) was associated with the disappearance on the snow cover and there is evidence that photosynthesis can continue after a thin new snowfall. The growth of photosynthesis during the spring period was partially associated with light (daily photosynthetically active radiation) but primarily with temperature, with the strongest correlation being observed with peat temperature at a depth of 5 and 10 cm, except in one year in which there was a long snow cover. The vegetation comprises mosses, which are able to photosynthesize very early, evergreen shrubs, which appear dependent on soil warming, and deciduous shrubs, which leaf-out only in late spring. We observed changes in shrub leaf colour from brown to green and concomitant increases in foliar nitrogen and chlorophyll concentrations during the spring in this "evergreen" system. We analyzed MODIS images for periods of overlap of tower and satellite data and found a generally strong correlation, though the infrequent satellite measurements were unable to pick out the onset and timing of rapid growth of photosynthesis in this ecosystem.

Lafleur, P.; Moore, T. R.; Poon, D.; Seaquist, J.

2005-12-01

211

Reducing Greenhouse Gas Emissions in Grassland Ecosystems of the Central Lithuania: Multi-Criteria Evaluation on a Basis of the ARAS Method  

PubMed Central

N2O, CH4, and CO2 are potential greenhouse gas (GHG) contributing to climate change; therefore, solutions have to be sought to reduce their emission from agriculture. This work evaluates GHG emission from grasslands submitted to different mineral fertilizers during vegetation period (June–September) in two experimental sites, namely, seminatural grassland (8 treatments of mineral fertilizers) and cultural pasture (intensively managed) in the Training Farm of the Lithuanian University of Agriculture. Chamber method was applied for evaluation of GHG emissions on the field scale. As a result, soil chemical composition, compactness, temperature, and gravimetric moisture as well as biomass yield of fresh and dry biomass and botanical composition, were assessed during the research. Furthermore, a simulation of multi-criteria assessment of sustainable fertilizers management was carried out on a basis of ARAS method. The multicriteria analysis of different fertilizing regimes was based on a system of environmental and productivity indices. Consequently, agroecosystems of cultural pasture (N180P120K150) and seminatural grassland fertilizing rates N180P120K150 and N60P40K50 were evaluated as the most sustainable alternatives leading to reduction of emissions between biosphere-atmosphere and human-induced biogenic pollution in grassland ecosystems, thus contributing to improvement of countryside environment. PMID:22645463

Balezentiene, Ligita; Kusta, Albinas

2012-01-01

212

Soil Environmental Conditions and Microbial Build-Up Mediate the Effect of Plant Diversity on Soil Nitrifying and Denitrifying Enzyme Activities in Temperate Grasslands  

PubMed Central

Random reductions in plant diversity can affect ecosystem functioning, but it is still unclear which components of plant diversity (species number – namely richness, presence of particular plant functional groups, or particular combinations of these) and associated biotic and abiotic drivers explain the observed relationships, particularly for soil processes. We assembled grassland communities including 1 to 16 plant species with a factorial separation of the effects of richness and functional group composition to analyze how plant diversity components influence soil nitrifying and denitrifying enzyme activities (NEA and DEA, respectively), the abundance of nitrifiers (bacterial and archaeal amoA gene number) and denitrifiers (nirK, nirS and nosZ gene number), and key soil environmental conditions. Plant diversity effects were largely due to differences in functional group composition between communities of identical richness (number of sown species), though richness also had an effect per se. NEA was positively related to the percentage of legumes in terms of sown species number, the additional effect of richness at any given legume percentage being negative. DEA was higher in plots with legumes, decreased with increasing percentage of grasses, and increased with richness. No correlation was observed between DEA and denitrifier abundance. NEA increased with the abundance of ammonia oxidizing bacteria. The effect of richness on NEA was entirely due to the build-up of nitrifying organisms, while legume effect was partly linked to modified ammonium availability and nitrifier abundance. Richness effect on DEA was entirely due to changes in soil moisture, while the effects of legumes and grasses were partly due to modified nitrate availability, which influenced the specific activity of denitrifiers. These results suggest that plant diversity-induced changes in microbial specific activity are important for facultative activities such as denitrification, whereas changes in microbial abundance play a major role for non-facultative activities such as nitrification. PMID:23613785

Le Roux, Xavier; Schmid, Bernhard; Poly, Franck; Barnard, Romain L.; Niklaus, Pascal A.; Guillaumaud, Nadine; Habekost, Maike; Oelmann, Yvonne; Philippot, Laurent; Salles, Joana Falcao; Schloter, Michael; Steinbeiss, Sibylle; Weigelt, Alexandra

2013-01-01

213

Use of historical logging patterns to identify disproportionately logged ecosystems within temperate rainforests of southeastern Alaska.  

PubMed

The forests of southeastern Alaska remain largely intact and contain a substantial proportion of Earth's remaining old-growth temperate rainforest. Nonetheless, industrial-scale logging has occurred since the 1950s within a relatively narrow range of forest types that has never been quantified at a regional scale. We analyzed historical patterns of logging from 1954 through 2004 and compared the relative rates of change among forest types, landform associations, and biogeographic provinces. We found a consistent pattern of disproportionate logging at multiple scales, including large-tree stands and landscapes with contiguous productive old-growth forests. The highest rates of change were among landform associations and biogeographic provinces that originally contained the largest concentrations of productive old growth (i.e., timber volume >46.6 m³/ha). Although only 11.9% of productive old-growth forests have been logged region wide, large-tree stands have been reduced by at least 28.1%, karst forests by 37%, and landscapes with the highest volume of contiguous old growth by 66.5%. Within some island biogeographic provinces, loss of rare forest types may place local viability of species dependent on old growth at risk of extirpation. Examination of historical patterns of change among ecological forest types can facilitate planning for conservation of biodiversity and sustainable use of forest resources. PMID:23866037

Albert, David M; Schoen, John W

2013-08-01

214

Whole-Ecosystem Labile Carbon Production in a North Temperate Deciduous Forest  

NASA Astrophysics Data System (ADS)

Management for forest carbon (C) sequestration requires knowledge of the fate of photosynthetic C. Labile C is an essential intermediary between C assimilation and growth in deciduous forests, accumulating when photosynthetic C supply exceeds demand and later depleting when reallocated to growth during periods of depressed photosynthesis. We developed a new approach that combined meteorological and biometric C cycling data for a mixed deciduous forest in Michigan, USA, to provide novel estimates of whole-ecosystem labile C production (PLC) and reallocation to growth inferred from the temporal imbalance between carbon supply from canopy net C assimilation (Ac) and C demand for net primary production (NPP). We substantiated these estimates with measurements of Populus grandidentata and Quercus rubra wood non-structural carbohydrate (NSC) concentration and mass over two years. Our analysis showed that half of annual Ac was allocated to PLC rather than to immediate growth. Labile C produced during the latter half of summer later supported dormant-season growth and respiration, with 35% of NPP in a given year requiring labile C stored during previous years. Seasonal changes in wood NSC concentration and mass generally corroborated patterns of labile C production and reallocation to growth. We observed a negative relationship between current-year PLC and NPP, indicating that disparities between same-year meteorological and biometric net ecosystem production (NEP) estimates can arise when C assimilated via photosynthesis, a flux incorporated into meteorological NEP estimates, is diverted away from NPP, a flux included in biometric NEP estimates, and instead allocated to PLC. A large, annually recharging pool of labile C also may buffer growth from climate conditions that immediately affect Ac. We conclude that a broader understanding of labile C production and reallocation across ecosystems may be important to interpreting lagged canopy C cycling and growth processes.

Gough, C. M.; Flower, C. E.; Vogel, C. S.; Dragoni, D.; Curtis, P. S.

2008-12-01

215

Tree-ring ? 13C tracks flux tower ecosystem productivity estimates in a NE temperate forest  

NASA Astrophysics Data System (ADS)

We investigated relationships between tree-ring ?13C and growth, and flux tower estimates of gross primary productivity (GPP) at Harvard Forest from 1992 to 2010. Seasonal variations of derived photosynthetic isotope discrimination (?13C) and leaf intercellular CO2 concentration (c i ) showed significant increasing trends for the dominant deciduous and coniferous species. ?13C was positively correlated to growing-season GPP and is primarily controlled by precipitation and soil moisture indicating that site conditions maintained high stomatal conductance under increasing atmospheric CO2 levels. Increasing ?13C over the 1992–2010 period is attributed to increasing annual and summer water availability identified at Harvard Forest and across the region. Higher ?13C is coincident with an enhancement in growth and ecosystem-level net carbon uptake. This work suggests that tree-ring ?13C could serve as a measure of forest GPP and be used to improve the calibration and predictive skill of ecosystem and carbon cycle models.

Belmecheri, Soumaya; Stockton Maxwell, R.; Taylor, Alan H.; Davis, Kenneth J.; Freeman, Katherine H.; Munger, William J.

2014-07-01

216

Cascading effects of fishing can alter carbon flow through a temperate coastal ecosystem.  

PubMed

Mounting evidence suggests that fishing can trigger trophic cascades and alter food web dynamics, yet its effects on ecosystem function remain largely unknown. We used the large-scale experimental framework of four marine reserves, spanning an oceanographic gradient in northeastern New Zealand, to test the extent to which the exploitation of reef predators can alter kelp carbon flux and secondary production. We provide evidence that the reduction of predatory snapper (Pagrus auratus) and lobster (Jasus edwardsii) can lead to an increase in sea urchins (Evechinus chloroticus) and indirect declines in kelp biomass in some locations but not others. Stable carbon isotope ratios (delta13C) of oysters (Crassostrea gigas) and mussels (Perna canaliculus) transplanted in reserve and fished sites within four locations revealed that fishing indirectly reduced the proportion of kelp-derived organic carbon assimilated by filter feeders in two locations where densities of actively grazing sea urchins were 23.7 and 8.3 times higher and kelp biomass was an order of magnitude lower than in non-fished reserve sites. In contrast, in the two locations where fishing had no effect on urchin density or kelp biomass, we detected no effect of fishing on the carbon signature of filter feeders. We show that the effects of fishing on nearshore trophic structure and carbon flux are context-dependent and hinge on large-scale, regional oceanographic factors. Where cascading effects of fishing on kelp biomass were documented, enhanced assimilation of kelp carbon did not result in the magnification of secondary production. Instead, a strong regional gradient in filter feeder growth emerged, best predicted by chlorophyll a. Estimates of kelp contribution to the diet of transplanted consumers averaged 56.9% +/- 6.2% (mean +/- SE) for mussels and 33.8% +/- 7.3% for oysters, suggesting that organic carbon fixed by kelp is an important food source fueling northeastern New Zealand's nearshore food webs. The importance of predators in mediating benthic primary production and organic carbon flux suggests that overfishing can have profound consequences on ecosystem functioning particularly where pelagic primary production is limiting. Our results underscore the broader ecosystem repercussions of overfishing and its context-dependent effects. PMID:19263885

Salomon, Anne K; Shears, Nick T; Langlois, Timothy J; Babcock, Russell C

2008-12-01

217

Applicability of the flood-pulse concept in a temperate floodplain river ecosystem: Thermal and temporal components  

USGS Publications Warehouse

Annual growth increments were calculated for blue catfish (Ictalurus furcatus) and flathead catfish (Pylodictis olivaris) from the lower Mississippi River (LMR) to assess hypothesized relationships between fish growth and floodplain inundation as predicted by the Flood-Pulse Concept. Variation in catfish growth increment was high for all age classes of both species, and growth increments were not consistently related to various measures of floodplain inundation. However, relationships became stronger, and usually direct, when water temperature was integrated with area and duration of floodplain inundation. Relationships were significant for four of six age classes for blue catfish, a species known to utilize floodplain habitats. Though similar in direction, relationships were weaker for flathead catfish, which is considered a more riverine species. Our results indicate the Flood-Pulse Concept applies more strongly to temperate floodplain-river ecosystems when thermal aspects of flood pulses are considered. We recommend that future management of the LMR should consider ways to 'recouple' the annual flood and thermal cycles. An adaptive management approach will allow further determination of important processes affecting fisheries production in the LMR. Copyright ?? John Wiley & Sons, Ltd.

Schramm, H.L., Jr.; Eggleton, M.A.

2006-01-01

218

The importance of phenology for the evaluation of impact of climate change on growth of boreal, temperate and Mediterranean forests ecosystems: an overview  

Microsoft Academic Search

An overview is presented of the phenological models relevant for boreal coniferous, temperate-zone deciduous and Mediterranean\\u000a coniferous forest ecosystems. The phenology of the boreal forests is mainly driven by temperature, affecting the timing of\\u000a the start of the growing season and thereby its duration, and the level of frost hardiness and thereby the reduction of foliage\\u000a area and photosynthetic capacity

K. Kramer; I. Leinonen; D. Loustau

2000-01-01

219

Predicting invasion in grassland ecosystems: is exotic dominance the real embarrassment of richness?  

PubMed

Invasions have increased the size of regional species pools, but are typically assumed to reduce native diversity. However, global-scale tests of this assumption have been elusive because of the focus on exotic species richness, rather than relative abundance. This is problematic because low invader richness can indicate invasion resistance by the native community or, alternatively, dominance by a single exotic species. Here, we used a globally replicated study to quantify relationships between exotic richness and abundance in grass-dominated ecosystems in 13 countries on six continents, ranging from salt marshes to alpine tundra. We tested effects of human land use, native community diversity, herbivore pressure, and nutrient limitation on exotic plant dominance. Despite its widespread use, exotic richness was a poor proxy for exotic dominance at low exotic richness, because sites that contained few exotic species ranged from relatively pristine (low exotic richness and cover) to almost completely exotic-dominated ones (low exotic richness but high exotic cover). Both exotic cover and richness were predicted by native plant diversity (native grass richness) and land use (distance to cultivation). Although climate was important for predicting both exotic cover and richness, climatic factors predicting cover (precipitation variability) differed from those predicting richness (maximum temperature and mean temperature in the wettest quarter). Herbivory and nutrient limitation did not predict exotic richness or cover. Exotic dominance was greatest in areas with low native grass richness at the site- or regional-scale. Although this could reflect native grass displacement, a lack of biotic resistance is a more likely explanation, given that grasses comprise the most aggressive invaders. These findings underscore the need to move beyond richness as a surrogate for the extent of invasion, because this metric confounds monodominance with invasion resistance. Monitoring species' relative abundance will more rapidly advance our understanding of invasions. PMID:24038796

Seabloom, Eric W; Borer, Elizabeth T; Buckley, Yvonne; Cleland, Elsa E; Davies, Kendi; Firn, Jennifer; Harpole, W Stanley; Hautier, Yann; Lind, Eric; MacDougall, Andrew; Orrock, John L; Prober, Suzanne M; Adler, Peter; Alberti, Juan; Anderson, T Michael; Bakker, Jonathan D; Biederman, Lori A; Blumenthal, Dana; Brown, Cynthia S; Brudvig, Lars A; Caldeira, Maria; Chu, Chengjin; Crawley, Michael J; Daleo, Pedro; Damschen, Ellen I; D'Antonio, Carla M; DeCrappeo, Nicole M; Dickman, Chris R; Du, Guozhen; Fay, Philip A; Frater, Paul; Gruner, Daniel S; Hagenah, Nicole; Hector, Andrew; Helm, Aveliina; Hillebrand, Helmut; Hofmockel, Kirsten S; Humphries, Hope C; Iribarne, Oscar; Jin, Virginia L; Kay, Adam; Kirkman, Kevin P; Klein, Julia A; Knops, Johannes M H; La Pierre, Kimberly J; Ladwig, Laura M; Lambrinos, John G; Leakey, Andrew D B; Li, Qi; Li, Wei; McCulley, Rebecca; Melbourne, Brett; Mitchell, Charles E; Moore, Joslin L; Morgan, John; Mortensen, Brent; O'Halloran, Lydia R; Pärtel, Meelis; Pascual, Jesús; Pyke, David A; Risch, Anita C; Salguero-Gómez, Roberto; Sankaran, Mahesh; Schuetz, Martin; Simonsen, Anna; Smith, Melinda; Stevens, Carly; Sullivan, Lauren; Wardle, Glenda M; Wolkovich, Elizabeth M; Wragg, Peter D; Wright, Justin; Yang, Louie

2013-12-01

220

Predicting invasion in grassland ecosystems: is exotic dominance the real embarrassment of richness?  

USGS Publications Warehouse

Invasions have increased the size of regional species pools, but are typically assumed to reduce native diversity. However, global-scale tests of this assumption have been elusive because of the focus on exotic species richness, rather than relative abundance. This is problematic because low invader richness can indicate invasion resistance by the native community or, alternatively, dominance by a single exotic species. Here, we used a globally replicated study to quantify relationships between exotic richness and abundance in grass-dominated ecosystems in 13 countries on six continents, ranging from salt marshes to alpine tundra. We tested effects of human land use, native community diversity, herbivore pressure, and nutrient limitation on exotic plant dominance. Despite its widespread use, exotic richness was a poor proxy for exotic dominance at low exotic richness, because sites that contained few exotic species ranged from relatively pristine (low exotic richness and cover) to almost completely exotic-dominated ones (low exotic richness but high exotic cover). Both exotic cover and richness were predicted by native plant diversity (native grass richness) and land use (distance to cultivation). Although climate was important for predicting both exotic cover and richness, climatic factors predicting cover (precipitation variability) differed from those predicting richness (maximum temperature and mean temperature in the wettest quarter). Herbivory and nutrient limitation did not predict exotic richness or cover. Exotic dominance was greatest in areas with low native grass richness at the site- or regional-scale. Although this could reflect native grass displacement, a lack of biotic resistance is a more likely explanation, given that grasses comprise the most aggressive invaders. These findings underscore the need to move beyond richness as a surrogate for the extent of invasion, because this metric confounds monodominance with invasion resistance. Monitoring species' relative abundance will more rapidly advance our understanding of invasions

Seabloom, Eric; Borer, Elizabeth; Buckley, Yvonne; Cleland, Elsa E.; Davies, Kendi; Firn, Jennifer; Harpole, W. Stanley; Hautier, Yann; Lind, Eric; MacDougall, Andrew; Orrock, John L.; Prober, Suzanne M.; Adler, Peter; Alberti, Juan; Anderson, T. Michael; Bakker, Jonathan D.; Biederman, Lori A.; Blumenthal, Dana; Brown, Cynthia S.; Brudvig, Lars A.; Caldeira, Maria; Chu, Cheng-Jin; Crawley, Michael J.; Daleo, Pedro; Damschen, Ellen I.; D'Antonio, Carla M.; DeCrappeo, Nicole M.; Dickman, Chris R.; Du, Guozhen; Fay, Philip A.; Frater, Paul; Gruner, Daniel S.; Hagenah, Nicole; Hector, Andrew; Helm, Aveliina; Hillebrand, Helmut; Hofmockel, Kirsten S.; Humphries, Hope C.; Iribarne, Oscar; Jin, Virginia L.; Kay, Adam; Kirkman, Kevin P.; Klein, Julia A.; Knops, Johannes M.H.; La Pierre, Kimberly J.; Ladwig, Laura M.; John, G.; Leakey, Andrew D.B.; Li, Qi; Li, Wei; McCulley, Rebecca; Melbourne, Brett; Charles, E.; Moore, Joslin L.; Morgan, John; Mortensen, Brent; O'Halloran, Lydia R.; Pärtel, Meelis; Pascual, Jesús; Pyke, David A.; Risch, Anita C.; Salguero-Gómez, Roberto; Sankaran, Mahesh; Schuetz, Martin; Simonsen, Anna; Smith, Melinda; Stevens, Carly; Sullivan, Lauren; Wardle, Glenda M.; Wolkovich, Elizabeth M.; Wragg, Peter D.; Wright, Justin; Yang, Louie

2013-01-01

221

GPP/RE Partitioning of Long-term Network Flux Data as a Tool for Estimating Ecosystem-scale Ecophysiological Parameters of Grasslands and Croplands  

NASA Astrophysics Data System (ADS)

The physiologically based model of canopy CO2 exchange by Thornly and Johnson (2000) modified to incorporate vapor pressure deficit (VPD) limitation of photosynthesis is a robust tool for partitioning tower network net CO2 exchange data into gross photosynthesis (GPP) and ecosystem respiration (RE) (Gilmanov et al. 2013a, b). In addition to 30-min and daily photosynthesis and respiration values, the procedure generates daily estimates and uncertainties of essential ecosystem-scale parameters such as apparent quantum yield ALPHA, photosynthetic capacity AMAX, convexity of light response THETA, gross ecological light-use efficiency LUE, daytime ecosystem respiration rate RDAY, and nighttime ecosystem respiration rate RNIGHT. These ecosystem-scale parameters are highly demanded by the modeling community and open opportunities for comparison with the rich data of leaf-level estimates of corresponding parameters available from physiological studies of previous decades. Based on the data for 70+ site-years of flux tower measurements at the non-forest sites of the Ameriflux network and the non-affiliated sites, we present results of the comparative analysis and multi-site synthesis of the magnitudes, uncertainties, patterns of seasonal and yearly dynamics, and spatiotemporal distribution of these parameters for grasslands and croplands of the conterminous United States (CONUS). Combining this site-level parameter data set with the rich spatiotemporal data sets of a remotely sensed vegetation index, weather and climate conditions, and site biophysical and geophysical features (phenology, photosynthetically active radiation, and soil water holding capacity) using methods of multivariate analysis (e.g., Cubist regression tree) offers new opportunities for predictive modeling and scaling-up of ecosystem-scale parameters of carbon cycling in grassland and agricultural ecosystems of CONUS (Zhang et al. 2011; Gu et al. 2012). REFERENCES Gilmanov TG, Baker JM, Bernacchi CJ, Billesbach DP, Burba GG, et al. (2013a). Productivity and CO2 exchange of the leguminous crops: Estimates from flux tower measurements. Agronomy J (submitted). Gilmanov TG, Wylie BK, Tieszen LL, Meyers TP, Baron VS, et al. (2013b). CO2 uptake and ecophysiological parameters of the grain crops of midcontinent North America: Estimates from flux tower measurements. Agric Ecosyst Environm 164: 162-175 Gu Y, Howard DM, Wylie BK, and Zhang L (2012). Mapping carbon flux uncertainty and selecting optimal locations for future flux towers in the Great Plains: Landscape Ecology, 27: 319-326. Thornley JHM., Johnson IR (2000). Plant and crop modelling. A mathematical approach to plant and crop physiology. The Blackburn Press, Caldwell, New Jersey. Zhang L, Wylie BK, Ji L, Gilmanov TG, Tieszen LL, Howard DM (2011). Upscaling carbon fluxes over the Great Plains grasslands: Sinks and sources. J Geophys Res G: Biogeosciences 116: G00J3

Gilmanov, T. G.; Wylie, B. K.; Gu, Y.; Howard, D. M.; Zhang, L.

2013-12-01

222

Interactive effects of elevated CO2, warming, and drought on photosynthesis of Deschampsia flexuosa in a temperate heath ecosystem  

PubMed Central

Global change factors affect plant carbon uptake in concert. In order to investigate the response directions and potential interactive effects, and to understand the underlying mechanisms, multifactor experiments are needed. The focus of this study was on the photosynthetic response to elevated CO2 [CO2; free air CO2 enrichment (FACE)], drought (D; water-excluding curtains), and night-time warming (T; infrared-reflective curtains) in a temperate heath. A/Ci curves were measured, allowing analysis of light-saturated net photosynthesis (Pn), light- and CO2-saturated net photosynthesis (Pmax), stomatal conductance (gs), the maximal rate of Rubisco carboxylation (Vcmax), and the maximal rate of ribulose bisphosphate (RuBP) regeneration (Jmax) along with leaf ?13C, and carbon and nitrogen concentration on a monthly basis in the grass Deschampsia flexuosa. Seasonal drought reduced Pn via gs, but severe (experimental) drought decreased Pn via a reduction in photosynthetic capacity (Pmax, Jmax, and Vcmax). The effects were completely reversed by rewetting and stimulated Pn via photosynthetic capacity stimulation. Warming increased early and late season Pn via higher Pmax and Jmax. Elevated CO2 did not decrease gs, but stimulated Pn via increased Ci. The T×CO2 synergistically increased plant carbon uptake via photosynthetic capacity up-regulation in early season and by better access to water after rewetting. The effects of the combination of drought and elevated CO2 depended on soil water availability, with additive effects when the soil water content was low and D×CO2 synergistic stimulation of Pn after rewetting. The photosynthetic responses appeared to be highly influenced by growth pattern. The grass has opportunistic water consumption, and a biphasic growth pattern allowing for leaf dieback at low soil water availability followed by rapid re-growth of active leaves when rewetted and possibly a large resource allocation capability mediated by the rhizome. This growth characteristic allowed for the photosynthetic capacity up-regulations that mediated the T×CO2 and D×CO2 synergistic effects on photosynthesis. These are clearly advantageous characteristics when exposed to climate changes. In conclusion, after 1 year of experimentation, the limitations by low soil water availability and stimulation in early and late season by warming clearly structure and interact with the photosynthetic response to elevated CO2 in this grassland species. PMID:21586430

Albert, K. R.; Ro-Poulsen, H.; Mikkelsen, T. N.; Michelsen, A.; van der Linden, L.; Beier, C.

2011-01-01

223

Gnawing damage by rodents to the seedlings of Fagus crenata and Quercus mongolica var. grosseserrata in a temperate Sasa grassland-deciduous forest series in southwestern Japan  

Microsoft Academic Search

The effects of dwarf bamboo,Sasa, cover on the initial morrality of hardwood seedlings were investigated by transplanting 1-year-old beech (Fagus crenata) and current-year oak (Quercus mongolica var.grosseserrata) seedling to three different stands; old-growth beech and secondary oak forests withSasa undergrowth, and aSasa grassland in a grassland-forest series near the top of Mt Jippo, southwestern Japan. The most frequent cause of

Hideyuki Ida; Nobukazu Nakagoshi

1996-01-01

224

Inter-annual Variability in Net Ecosystem Exchange of Carbon Dioxide and Methane Emissions in a Temperate Freshwater Marsh  

NASA Astrophysics Data System (ADS)

There exists very little information on greenhouse gas (GHG) exchange in marsh wetlands, especially in temperate climates. Measurements of carbon dioxide (CO2) and methane (CH4) fluxes were made from May 2005 to June 2008 in a temperate freshwater cattail marsh in Eastern Ontario, Canada. The net ecosystem exchange (NEE) of CO2 was measured continuously using the eddy covariance technique, and closed chambers were used to measure CH4 emissions from open water, soil, and vegetated portions of the marsh. Based on NEE, we found that the marsh accumulated 264 g C m-2 from May 2005 to April 2006 and 185 g C m-2 and 308 g C m-2 in 2006-2007 and 2007-2008, respectively. Lower spring temperature in 2005 seems to have delayed the initial growth of cattails and therefore led to a later switchover time from a net CO2 source to a net CO2 sink compared to spring 2006 and 2007. The lower cumulative NEE measured in 2006-2007 is mainly due to the cloudy conditions (i.e. low average incoming photosynthetically active radiation) that occurred through late summer and early fall 2006, which greatly decreased cattail photosynthesis and induced an earlier death of the pants, which in turn resulted in a lower average CO2 uptake compared to the other years. During the 2005, 2006 and 2007 growing seasons, the carbon uptake period was 109, 104, and 116 days in length, which is consistent with the inter-annual variability in NEE observed. The results suggest that the timing of the fall switchover from a net CO2 sink to a net CO2 source is probably the main factor influencing the annual CO2 accumulation. The average CH4 flux measured from open water was 658 mg CH4 m-2 d-1 in 2005, 381 mg CH4 m-2 d-1 in 2006, and 352 mg CH4 m-2 d-1 in 2008. The average CH4 flux from vegetation was 1001 mg CH4 m-2 d-1 in 2005, 1640 mg CH4 m-2 d-1 in 2006, and 1260 mg CH4 m-2 d-1 in 2008. The CH4 flux from soil was only measured in 2006 (255 mg CH4 m-2 d-1) and 2008 (224 mg CH4 m-2 d-1). It is known that the presence of the aerenchyma tissue that runs through the cattail's roots, stem and leaves facilitates the transport of gases such as CH4 from the production site (i.e. soil) to the atmosphere, which explains the higher fluxes measured from vegetated portions of the marsh. Knowing that CH4 is produced under anaerobic waterlogged conditions, the higher CH4 fluxes measured from plants in 2006 may be related to the higher rainfall observed during that year. This long-term record of CO2 and CH4 fluxes combined with continuous measurements of meteorological and ecosystem properties allows us to investigate the overall carbon budget of this marsh wetland as well as the major controls on the GHG fluxes for this type of ecosystem. This study provides valuable knowledge that can complement the existing information on other wetlands types and may be useful for predicting the impacts of climate change on CO2 and CH4 fluxes and for estimating national carbon stocks.

Bonneville, M.; Strachan, I.

2009-05-01

225

Ecosystem loss of soil inorganic carbon from agricultural conversion of native grasslands and woodlands  

NASA Astrophysics Data System (ADS)

Soil carbonates represent a quarter of the terrestrial carbon pool and are considered to be relatively stable, with fluxes significant only at geologic timescales. However, given the potential importance of water on carbonate chemistry, we propose that increased soil water fluxes from recent land-use changes may enhance dissolution of soil carbonates. To test rapid changes in soil carbonates with land-use changes, we assessed soil carbonate storage to 7.2 m depth in 4 triplets of native vegetation and rain-fed and irrigated cropland plots and 2 additional pairs of native vegetation and rain-fed cultivation plots across the southern Great Plains of United States and Pampas of Argentina, where large scale agricultural conversion typically increases soil water flux. Rain-fed and irrigated croplands had 513 and 906 Mg/ha less soil carbonate storage compared to their native vegetation pairs on average (P<0.0002), which were more than an order of magnitude larger than changes in ecosystem organic carbon at the sites. The eventual fate of the lost carbon (i.e. sequestration or emission of CO2), however, is unclear. Average soil carbonate contents from individual boreholes were negatively related to groundwater recharge estimates (site-specific; 0.00004

Kim, J. H.; Jobbagy, E. G.; Richter, D.; Jackson, R. B.

2013-12-01

226

Grassland/atmosphere response to changing climate: Coupling regional and local scales. Final report  

SciTech Connect

The objectives of the study were: to evaluate the response of grassland ecosystems to atmospheric change at regional and site scales, and to develop multiscaled modeling systems to relate ecological and atmospheric models with different spatial and temporal resolutions. A menu-driven shell was developed to facilitate use of models at different temporal scales and to facilitate exchange information between models at different temporal scales. A detailed ecosystem model predicted that C{sub 3} temperate grasslands wig respond more strongly to elevated CO{sub 2} than temperate C{sub 4} grasslands in the short-term while a large positive N-PP response was predicted for a C{sub 4} Kenyan grassland. Long-term climate change scenarios produced either decreases or increases in Colorado plant productivity (NPP) depending on rainfall, but uniform increases in N-PP were predicted in Kenya. Elevated CO{sub 2} is likely to have little effect on ecosystem carbon storage in Colorado while it will increase carbon storage in Kenya. A synoptic climate classification processor (SCP) was developed to evaluate results of GCM climate sensitivity experiments. Roughly 80% agreement was achieved with manual classifications. Comparison of lx and 2xCO{sub 2} GCM Simulations revealed relatively small differences.

Coughenour, M.B.; Kittel, T.G.F.; Pielke, R.A.; Eastman, J.

1993-10-01

227

Bacterial weathering and its contribution to nutrient cycling in temperate forest ecosystems.  

PubMed

Unlike farmland, forests growing on acidic soils are among the terrestrial ecosystems that are the least influenced or amended by man. Forests which developed on acidic soils are characterized by an important stock of inorganic nutrients entrapped in poorly weatherable soil minerals. In this context, the mineral-weathering process is of great importance, since such minerals are not easily accessible to tree roots. To date, several bacterial genera have been noted for their ability to weather minerals and, in the case of some of them, to improve tree nutrition. Nevertheless, few studies have focused their analyses on mineral-weathering bacterial communities in relation to geochemical cycles and soil characteristics, their ecological origin, associated tree species and forest management practices. Here we discuss the heterogeneity of the mineral-weathering process in forest soils and present what is known concerning the taxonomic and functional characteristics of mineral-weathering bacteria, as well as the different locations where they have been isolated in forest soils. We also discuss the biotic and abiotic factors that may influence the distribution of these bacteria, such as the effect of tree species or forest management practices. PMID:21315149

Uroz, Stéphane; Oger, Phil; Lepleux, Cendrella; Collignon, Christelle; Frey-Klett, Pascale; Turpault, Marie-Pierre

2011-11-01

228

A semi-mechanistic model of dead fine fuel moisture for Temperate and Mediterranean ecosystems  

NASA Astrophysics Data System (ADS)

Fire is a major disturbance in terrestrial ecosystems globally. It has an enormous economic and social cost, and leads to fatalities in the worst cases. The moisture content of the vegetation (fuel moisture) is one of the main determinants of fire risk. Predicting the moisture content of dead and fine fuel (< 2.5 cm in diameter) is particularly important, as this is often the most important component of the fuel complex for fire propagation. A variety of drought indices, empirical and mechanistic models have been proposed to model fuel moisture. A commonality across these different approaches is that they have been neither validated across large temporal datasets nor validated across broadly different vegetation types. Here, we present the results of a study performed at 6 locations in California, USA (5 sites) and New South Wales, Australia (1 site), where 10-hours fuel moisture content was continuously measured every 30 minutes during one full year at each site. We observed that drought indices did not accurately predict fuel moisture, and that empirical and mechanistic models both needed site-specific calibrations, which hinders their global application as indices of fuel moisture. We developed a novel, single equation and semi-mechanistic model, based on atmospheric vapor-pressure deficit. Across sites and years, mean absolute error (MAE) of predicted fuel moisture was 4.7%. MAE dropped <1% in the critical range of fuel moisture <10%. The high simplicity, accuracy and precision of our model makes it suitable for a wide range of applications: from operational purposes, to global vegetation models.

Resco de Dios, Víctor; Fellows, Aaron; Boer, Matthias; Bradstock, Ross; Nolan, Rachel; Goulden, Michel

2014-05-01

229

Impact of small mammal disturbances on sediment yield from grassland and shrubland ecosystems in the Chihuahuan Desert  

Microsoft Academic Search

This study examines water and sediment movement on Summerford bajada in the Jornada Basin, N.M. Forty-five rainfall simulation experiments were conducted on 1- and 2-m2 runoff plots in grassland, degraded grassland, and shrubland communities. Within the shrubland community separate experiments were conducted in shrub and intershrub environments. Regression analyses indicate that for a 30-min rainfall at approximately 130 mm h?1,

Melissa Neave; Athol D Abrahams

2001-01-01

230

Habitat requirements of weasels Mustela nivalis constrain their impact on prey populations in complex ecosystems of the temperate zone.  

PubMed

Differences in habitat use by prey and predator may lead to a shift of occupied niches and affect dynamics of their populations. The weasel Mustela nivalis specializes in hunting rodents, therefore habitat preferences of this predator may have important consequences for the population dynamics of its prey. We investigated habitat selection by weasels in the Bia?owieza Forest in different seasons at the landscape and local scales, and evaluated possible consequences for the population dynamics of their prey. At the landscape scale, weasels preferred open habitats (both dry and wet) and avoided forest. In open areas they selected habitats with higher prey abundance, except during the low-density phase of the vole cycle, when the distribution of these predators was more uniform. Also in winter, the distribution of weasels at the landscape scale was proportional to available resources. In summer, within open dry and wet habitats, weasels preferred areas characterised by dense vegetation, but avoided poor plant cover. In winter, weasels used wet open areas proportionally to availability of habitats when hunting, but in contrast to summer, they rested only in habitats characterized by a lower water level, which offered better thermal conditions. At the local scale, the abundance of voles was a less important factor affecting the distribution of these predators. Although we were not able to provide direct evidence for the existence of refuges for voles, our results show that they may be located within habitat patches, where availability of dense plant cover and physiological constraints limit the activity of weasels. Our results indicate that in complex ecosystems of the temperate zone, characterized by a mosaic pattern of vegetation types and habitat specific dynamics of rodents, impact of weasels on prey populations might be limited. PMID:18629542

Zub, K; Sönnichsen, L; Szafra?ska, P A

2008-10-01

231

Monitoring of carbon dioxide fluxes in a subalpine grassland ecosystem of the Italian Alps using a multispectral sensor  

NASA Astrophysics Data System (ADS)

The study investigates the potential of a commercially available proximal sensing system - based on a 16-band multispectral sensor - for monitoring mean midday gross ecosystem production (GEPm) in a subalpine grassland of the Italian Alps equipped with an eddy covariance flux tower. Reflectance observations were collected for 5 consecutive years, characterized by different climatic conditions, together with turbulent carbon dioxide fluxes and their meteorological drivers. Different models based on linear regression (vegetation indices approach) and on multiple regression (reflectance approach) were tested to estimateGEPm from optical data. The overall performance of this relatively low-cost system was positive. Chlorophyll-related indices including the red-edge part of the spectrum in their formulation (red-edge normalized difference vegetation index, NDVIred-edge; chlorophyll index, CIred-edge) were the best predictors of GEPm, explaining most of its variability during the observation period. The use of the reflectance approach did not lead to considerably improved results in estimating GEPm: the adjusted R2 (adjR2) of the model based on linear regression - including all the 5 years - was 0.74, while the adjR2 for the multiple regression model was 0.79. Incorporating mean midday photosynthetically active radiation (PARm) into the model resulted in a general decrease in the accuracy of estimates, highlighting the complexity of the GEPm response to incident radiation. In fact, significantly higher photosynthesis rates were observed under diffuse as regards direct radiation conditions. The models which were observed to perform best were then used to test the potential of optical data for GEPm gap filling. Artificial gaps of three different lengths (1, 3 and 5 observation days) were introduced in the GEPm time series. The values of adjR2 for the three gap-filling scenarios showed that the accuracy of the gap filling slightly decreased with gap length. However, on average, the GEPm gaps were filled with an accuracy of 73% with the model fed with NDVIred-edge, and of 76% with the model using reflectance at 681, 720 and 781 nm and PARm data.

Sakowska, K.; Vescovo, L.; Marcolla, B.; Juszczak, R.; Olejnik, J.; Gianelle, D.

2014-09-01

232

Light, Soil Temperature, and VPD as controls of flux-tower NEE partitioning into gross photosynthesis and respiration in grassland and agricultural ecosystems  

NASA Astrophysics Data System (ADS)

Partitioning of the flux-tower net CO2 exchange measurements (NEE) into gross photosynthesis (Pg) and ecosystem respiration (Re) components is an essential step in post-processing flux tower data for analysis and modeling. We have developed a method of NEE = Pg - Re partitioning using photosynthetically active radiation (Q), soil temperature at 5 cm depth (Ts), and vapor pressure deficit at 2 m height (VPD) as factors in a nonrectangular hyperbolic model of net CO2 exchange in terrestrial ecosystems (Gilmanov et al. 2003, Bas. Appl. Ecol. 4: 167-183) modified to include the effect of vapor pressure deficit. In contrast to other VPD-based methods of NEE partitioning suggested in the literature, our method (i) describes combined effect of VPD on photosynthetic capacity (Amax) and apparent quantum yield (ALPHA) due to the special functional properties of the nonrectangular hyperbolic equation; (ii) delivers less biased estimates of light-response parameters due to explicit description of the convexity of the light-response compared to rectangular hyperbolic model, and (iii) generates more numerically robust and statistically significant estimates than methods using highly correlated predictors such as incoming radiation, air temperature and VPD. We demonstrate application of the method to flux-tower NEE data sets from grassland and agro-ecosystems of North America as a tool to estimate numerical values and uncertainty characteristics of productivity, respiration, and ecophysiological parameters (apparent quantum yield ALPHA, photosynthetic capacity Amax, gross ecological light-use efficiency LUE, carbon use efficiency CUE, and others). On a representative statistical material our results confirm earlier findings that gross photosynthesis estimates derived through partitioning of flux-tower NEE are significantly closer related to remote sensing indices (e.g., eMODIS NDVI) than variables directly provided by tower measurements such as day-time net CO2 flux totals. We present diagnostic phenomenological models of gross photosynthesis and ecosystem respiration utilizing weekly NDVI data that explain >80% of the seasonal variability of CO2 exchange at a 7-day time scale over the long (up to six years) periods. The light-soil temperature-VPD-based method of tower-NEE data partitioning provides a robust tool to gap-fill flux tower data series to obtain annual totals of GPP and RE of grasslands and agro-ecosystems. Such data for >25 North American flux-tower sites (>50 site-years) plotted on the H. Odum’s RE vs. GPP scatter diagram clearly demonstrate that according to flux-tower data, crop and grassland ecosystems take from the atmosphere significantly more CO2 through gross photosynthesis than return with respiration. Though considerable amount of the CO2 taken up by NEE of these ecosystems may be later returned to the atmosphere in animal feeding facilities, production and consumption of ethanol and human food, etc., it is presently clear that the role of grasslands and agro-ecosystems as sinks for atmospheric CO2 is much higher that estimated previously from non-flux-based (inventory) data (cf.: The First State of the Carbon Cycle Report, 2007).

Gilmanov, T. G.

2010-12-01

233

Scale-Dependent Effects of Grazing on Plant C: N: P Stoichiometry and Linkages to Ecosystem Functioning in the Inner Mongolia Grassland  

PubMed Central

Background Livestock grazing is the most prevalent land use of grasslands worldwide. The effects of grazing on plant C, N, P contents and stoichiometry across hierarchical levels, however, have rarely been studied; particularly whether the effects are mediated by resource availability and the underpinning mechanisms remain largely unclear. Methodology/Principal Findings Using a multi-organization-level approach, we examined the effects of grazing on the C, N, and P contents and stoichiometry in plant tissues (leaves and roots) and linkages to ecosystem functioning across three vegetation types (meadow, meadow steppe, and typical steppe) in the Inner Mongolia grassland, China. Our results showed that the effects of grazing on the C, N, and P contents and stoichiometry in leaves and roots differed substantially among vegetation types and across different hierarchical levels (species, functional group, and vegetation type levels). The magnitude of positive effects of grazing on leaf N and P contents increased progressively along the hierarchy of organizational levels in the meadow, whereas its negative effect on leaf N content decreased considerably along hierarchical levels in both the typical and meadow steppes. Grazing increased N and P allocation to aboveground in the meadow, while greater N and P allocation to belowground was found in the typical and meadow steppes. The differences in soil properties, plant trait-based resource use strategies, tolerance or defense strategies to grazing, and shifts in functional group composition are likely to be the key mechanisms for the observed patterns among vegetation types. Conclusions/Significance Our findings suggest that the enhanced vegetation-type-level N contents by grazing and species compensatory feedbacks may be insufficient to prevent widespread declines in primary productivity in the Inner Mongolia grassland. Hence, it is essential to reduce the currently high stocking rates and restore the vast degraded steppes for sustainable development of arid and semiarid grasslands. PMID:23272158

Zheng, Shuxia; Ren, Haiyan; Li, Wenhuai; Lan, Zhichun

2012-01-01

234

Differences in plant cover and species composition of semiarid grassland communities of Central Mexico and its effects on net ecosystem exchange  

NASA Astrophysics Data System (ADS)

Changes in land use across the semiarid grasslands of Northern Mexico have driven a decline of plant cover and alteration of plant species composition. A number of different plant communities have resulted from these changes, however, their implications on the carbon cycle and regional carbon balance are still poorly understood. Here, we examined the effects of plant cover loss and changes in species composition on net ecosystem CO2 exchange (NEE) and their biotic and abiotic controls. Five typical plant community types were examined in the semiarid grassland by encasing the entire above-ground ecosystem using the geodesic dome method. Sites included an oat crop (crop), a moderately grazed grassland (moderate grazing), a 28 yr-old grazing exclosure (exclosure), an overgrazed site with low perennial grass cover (overgrazed), and an overgrazed site presenting shrub encroachment (shrub encroachment). For natural vegetation, rates of daytime NEE for sites with a high plant cover (exclosure and moderate grazing) were similar (P>0.05) as compared to sites with low plant cover (overgrazed and shrub encroachment). However, night time NEE (carbon loss) was more than double (P<0.05) for sites with high plant cover compared to sites with low cover, resulting into slight C sinks for the low plant cover sites and neutral or sources for the high plant cover sites on an annual basis. Differences in plant cover and its associated biomass defined the sensitivity to environmental controls. Thus, daytime NEE in low plant cover sites reached light compensation points at lower PPFD values than those from high plant cover sites. Differences in species composition did not influence NEE rates even though there were transient or permanent changes in C3 vs. C4 functional groups.

Delgado-Balbuena, J.; Arredondo, J. T.; Loescher, H. W.; Huber-Sannwald, E.; Chavez-Aguilar, G.; Luna-Luna, M.; Barretero-Hernandez, R.

2012-12-01

235

Grasslands and Grassland Sciences in  

E-print Network

Grasslands and Grassland Sciences in Northern China A Report of the Committee on Scholarly,andsometypographicerrorsmayhavebeenaccidentallyinserted.Pleaseusetheprintversionofthispublicationastheauthoritativeversionforattribution. Copyright © National Academy of Sciences. All rights reserved. Grasslands and Grassland Sciences in Northern steppe (Map 1-3) is one of the few well-preserved areas of the Inner Mongolia grassland region. Although

Wu, Jianguo "Jingle"

236

Testing mechanisms of N-enrichment-induced species loss in a semiarid Inner Mongolia grassland: critical thresholds and implications for long-term ecosystem responses  

PubMed Central

The increase in nutrient availability as a consequence of elevated nitrogen (N) deposition is an important component of global environmental change. This is likely to substantially affect the functioning and provisioning of ecosystem services by drylands, where water and N are often limited. We tested mechanisms of chronic N-enrichment-induced plant species loss in a 10-year field experiment with six levels of N addition rate. Our findings on a semi-arid grassland in Inner Mongolia demonstrated that: (i) species richness (SR) declined by 16 per cent even at low levels of additional N (1.75 g N m–2 yr?1), and 50–70% species were excluded from plots which received high N input (10.5–28 g N m?2 yr?1); (ii) the responses of SR and above-ground biomass (AGB) to N were greater in wet years than dry years; (iii) N addition increased the inter-annual variations in AGB, reduced the drought resistance of production and hence diminished ecosystem stability; (iv) the critical threshold for chronic N-enrichment-induced reduction in SR differed between common and rare species, and increased over the time of the experiment owing to the loss of the more sensitive species. These results clearly indicate that both abundance and functional trait-based mechanisms operate simultaneously on N-induced species loss. The low initial abundance and low above-ground competitive ability may be attributable to the loss of rare species. However, shift from below-ground competition to above-ground competition and recruitment limitation are likely to be the key mechanisms for the loss of abundant species, with soil acidification being less important. Our results have important implications for understanding the impacts of N deposition and global climatic change (e.g. change in precipitation regimes) on biodiversity and ecosystem services of the Inner Mongolian grassland and beyond. PMID:23045710

Lan, Zhichun; Bai, Yongfei

2012-01-01

237

Dynamics of evapotranspiration in semiarid grassland and shrubland ecosystems during the summer monsoon season, central New Mexico  

Microsoft Academic Search

To understand the coupled water and energy cycles in semiarid environments, we measured temporal fluctuations of evapotranspiration (ET) and identified key sources of the observed variability. Flux measurements are made using the Bowen ratio method, accompanied by measurements of soil moisture and radiation. We present data from semiarid grassland and shrubland sites, situated within 2 km of each other in

Shirley A. Kurc; Eric E. Small

2004-01-01

238

Super High Resolution Airborne Remote Sensing for Evaluating the Decomposition Function of Ecosystem of Temperate Forest in Japan  

NASA Astrophysics Data System (ADS)

Forest ecosystem is sustained by nutrients cycle among trees, floor vegetation, litter, and soil etc. One of important driving mechanisms for such nutrients cycle is the decomposition of the fallen trees by fungi, and this process would play an important function in the biogeochemical cycle of the environment. This study challenged to identify the position and size of fallen trees in a temperate forest in Japan based on super high resolution (less than 1cm) visual images taken from a camera aboard a helicopter. Field campaign was carried out on November 29, 2011 at the experimental forest (6 ha, 300m x 200m, 36° 56' 10.5'N, 140° 35' 16.5'E) in Kitaibaraki, Ibaraki, Japan. According to the census survey of the forest, deciduous broad leave trees are dominant. There was almost no leaf in the forest crown on the day of the field campaign, and that brought a high visibility of the floor from the sky. The topography of the forest site is characterized by a small valley with a river flowing north to south at its bottom. An unmanned helicopter (Yamaha RMAX G1) flew over the forest in north-south lines with a speed of 3m/s at height of 30-70m from the ground surface. The interval between adjacent two lines was 20m. A consumer grade camera (Canon EOS Kiss X5 with 55mm lens; 5184 x 3456 pixels) was fixed with the vertically looking down direction on the helicopter. The camera took forest images with 5 seconds interval. The helicopter was also equipped by a laser range finder (LRF) (SkEyesBOX MP-1). Based on the point cloud created by the LRF measurement, 1 x 1m digital elevation model (DEM) of the ground surface was established by finding the lowest point value of the point cloud in each 1 x 1m grid of the forest. The forest was covered by 211 images taken by the camera. Each image was orthorectified by using the DEM and the data of the position and orientations of the helicopter, and then they were mosaicked into one image. Fallen trees with the diameter more than 10cm were targeted for the analysis, and we confirmed that some of fallen tree was easily to identify visually, but some of them was hard to identify because the branch and trunk of trees hided fallen trees. We are going develop the automatic detection algorithm by decision tree and object-based classifications, and then validate the algorithm with in situ information.

Suzuki, R.; Fadaei, H.; Ishii, R.; Nagai, S.; Okabe, K.; Yamashita, S.; Taki, H.; Honda, Y.; Kajiwara, K.

2013-12-01

239

Soil warming effect on net ecosystem exchange of carbon dioxide during the transition from winter carbon source to spring carbon sink in a temperate urban lawn.  

PubMed

The significant warming in urban environment caused by the combined effects of global warming and heat island has stimulated widely development of urban vegetations. However, it is less known of the climate feedback of urban lawn in warmed environment. Soil warming effect on net ecosystem exchange (NEE) of carbon dioxide during the transition period from winter to spring was investigated in a temperate urban lawn in Beijing, China. The NEE (negative for uptake) under soil warming treatment (temperature was about 5 degrees C higher than the ambient treatment as a control) was -0.71 micromol/(m2 x sec), the ecosytem was a CO2 sink under soil warming treatment, the lawn ecosystem under the control was a CO2 source (0.13 micromol/(m2 x sec)), indicating that the lawn ecosystem would provide a negative feedback to global warming. There was no significant effect of soil warming on nocturnal NEE (i.e., ecosystem respiration), although the soil temperature sensitivity (Q10) of ecosystem respiration under soil warming treatment was 3.86, much lower than that in the control (7.03). The CO2 uptake was significantly increased by soil warming treatment that was attributed to about 100% increase of alpha (apparent quantum yield) and Amax (maximum rate of photosynthesis). Our results indicated that the response of photosynthesis in urban lawn is much more sensitive to global warming than respiration in the transition period. PMID:23534206

Zhou, Xiaoping; Wang, Xiaoke; Tong, Lei; Zhang, Hongxing; Lu, Fei; Zheng, Feixiang; Hou, Peiqiang; Song, Wenzhi; Ouyang, Zhiyun

2012-01-01

240

Effect of rainfall patterns on soil surface CO2 efflux, soil moisture, soil temperature and plant growth in a grassland ecosystem of northern Ontario, Canada: implications for climate change  

Microsoft Academic Search

BACKGROUND: The effect of rainfall patterns on soil surface CO2 efflux, soil moisture, soil temperature and plant growth was investigated in a grassland ecosystem of northern Ontario, Canada, where climatic change is predicted to introduce new precipitation regimes. Rain shelters were established in a fallow field consisting mainly of Trifolium hybridum L., Trifolium pratense L., and Phleum pratense L. Daytime

Michael F Laporte; LC Duchesne; S Wetzel

2002-01-01

241

Ecosystem Carbon Storage Across the Grassland–Forest Transition in the High Andes of Manu National Park, Peru  

Microsoft Academic Search

Improved management of carbon storage by terrestrial biomes has significant value for mitigating climate change. The carbon\\u000a value of such management has the potential to provide additional income to rural communities and provide biodiversity and\\u000a climate adaptation co-benefits. Here, we quantify the carbon stores in a 49,300-ha landscape centered on the cloud forest–grassland\\u000a transition of the high Andes in Manu

Adam Gibbon; Miles R. Silman; Yadvinder Malhi; Joshua B. Fisher; Patrick Meir; Michael Zimmermann; Greta C. Dargie; William R. Farfan; Karina C. Garcia

2010-01-01

242

How climate and vegetation type influence evapotranspiration and water use efficiency in Canadian forest, peatland and grassland ecosystems  

Microsoft Academic Search

The effects of climatic factors and vegetation type on evapotranspiration (E) and water use efficiency (WUE) were analyzed using tower-based eddy-covariance (EC) data for nine mature forest sites, two peatland sites and one grassland site across an east–west continental-scale transect in Canada during the period 2003–2006. The seasonal pattern of E was closely linked to growing-season length and rainfall distribution.

Christian Brümmer; T. Andrew Black; Rachhpal S. Jassal; Nicholas J. Grant; David L. Spittlehouse; Baozhang Chen; Zoran Nesic; Brian D. Amiro; M. Altaf Arain; Alan G. Barr; Charles P.-A. Bourque; Carole Coursolle; Allison L. Dunn; Lawrence B. Flanagan; Elyn R. Humphreys; Peter M. Lafleur; Hank A. Margolis; J. Harry McCaughey; Steven C. Wofsy

243

The importance of phenology for the evaluation of impact of climate change on growth of boreal, temperate and Mediterranean forests ecosystems: an overview.  

PubMed

An overview is presented of the phenological models relevant for boreal coniferous, temperate-zone deciduous and Mediterranean coniferous forest ecosystems. The phenology of the boreal forests is mainly driven by temperature, affecting the timing of the start of the growing season and thereby its duration, and the level of frost hardiness and thereby the reduction of foliage area and photosynthetic capacity by severe frost events. The phenology of temperate-zone forests is also mainly driven by temperature. Since temperate-zone forests are mostly mixed-species deciduous forests, differences in phenological response may affect competition between tree species. The phenology of Mediterranean coniferous forests is mainly driven by water availability, affecting the development of leaf area, rather than the timing of phenological events. These phenological models were subsequently coupled to the process-based forest model FORGRO to evaluate the effect of different climate change scenarios on growth. The results indicate that the phenology of each of the forest types significantly affects the growth response to a given climate change scenario. The absolute responses presented in this study should, however, be used with caution as there are still uncertainties in the phenological models, the growth models, the parameter values obtained and the climate change scenarios used. Future research should attempt to reduce these uncertainties. It is recommended that phenological models that describe the mechanisms by which seasonality in climatic drivers affects the phenological aspects of trees should be developed and carefully tested. Only by using such models may we make an assessment of the impact of climate change on the functioning and productivity of different forest ecosystems. PMID:10993560

Kramer, K; Leinonen, I; Loustau, D

2000-08-01

244

Effects of grazing on leaf traits and ecosystem functioning in Inner Mongolia grasslands: scaling from species to community  

Microsoft Academic Search

Understanding the mechanistic links between environmental drivers, human disturbance, plant functional traits, and ecosystem properties is a fundamental aspect of biodiversity-ecosystem functioning research. Recent studies have focused mostly on leaf-level traits or community-level weighted traits to predict species responses to grazing and the consequent change in ecosystem functioning. However, studies of leaf-level traits or community-level weighted traits seldom identify the

S. X. Zheng; H. Y. Ren; Z. C. Lan; W. H. Li; K. B. Wang; Y. F. Bai

2010-01-01

245

Leaf area index drives soil water availability and extreme drought-related mortality under elevated CO2 in a temperate grassland model system.  

PubMed

The magnitude and frequency of climatic extremes, such as drought, are predicted to increase under future climate change conditions. However, little is known about how other factors such as CO2 concentration will modify plant community responses to these extreme climatic events, even though such modifications are highly likely. We asked whether the response of grasslands to repeat extreme drought events is modified by elevated CO2, and if so, what are the underlying mechanisms? We grew grassland mesocosms consisting of 10 co-occurring grass species common to the Cumberland Plain Woodland of western Sydney under ambient and elevated CO2 and subjected them to repeated extreme drought treatments. The 10 species included a mix of C3, C4, native and exotic species. We hypothesized that a reduction in the stomatal conductance of the grasses under elevated CO2 would be offset by increases in the leaf area index thus the retention of soil water and the consequent vulnerability of the grasses to extreme drought would not differ between the CO2 treatments. Our results did not support this hypothesis: soil water content was significantly lower in the mesocosms grown under elevated CO2 and extreme drought-related mortality of the grasses was greater. The C4 and native grasses had significantly higher leaf area index under elevated CO2 levels. This offset the reduction in the stomatal conductance of the exotic grasses as well as increased rainfall interception, resulting in reduced soil water content in the elevated CO2 mesocosms. Our results suggest that projected increases in net primary productivity globally of grasslands in a high CO2 world may be limited by reduced soil water availability in the future. PMID:24632832

Manea, Anthony; Leishman, Michelle R

2014-01-01

246

Soil microbial communities and their feedbacks to simulated climate change: comparisons among terrestrial montane ecosystems  

NASA Astrophysics Data System (ADS)

Microorganisms are well known to be more sensitive to changes in environmental conditions than to other soil chemical and physical parameters. However, the consequences of the on-going warming of montane ecosystems on microorganisms and the processes they mediate are still not well understood. In addition, different terrestrial ecosystems comprise different microbial communities, and their responses to changing environmental conditions require consideration of the complex interactions that occur between microorganisms and other site-specific biotic and abiotic factors. Here, using phospholipid fatty acids (PLFAs) analysis, we investigated short- to medium-term changes in microbial communities among three different montane ecosystems (i.e. temperate limestone alps (forest and grassland), temperate silicate alpine grasslands, and tropical silicate forest) in response to two years of experimental field warming (+ 1.5 to 3°C) simulated by high-to-low elevation soil translocation. We found that changes in substrate quantity and quality in the course of the decomposition (in the temperate limestone alps) affected the microbial community composition and its substrate utilization less than the prevailing environmental site conditions, to which the microbial community adapted quickly upon change. Results from the temperate grassland and tropical forest sites will be presented and discussed in view of multifactorial interactions as well as their importance in feedback responses to climate change.

Djukic, Ika; Zehetner, Franz; Gerzabek, Martin H.; Lair, Georg J.; Hell, Verena; Tappeiner, Ulrike; Niedrist, Georg; Zimmermann, Michael; Bird, Michael I.

2013-04-01

247

Differences in plant cover and species composition of semiarid grassland communities of central Mexico and its effects on net ecosystem exchange  

NASA Astrophysics Data System (ADS)

Changes in land use across the semiarid grasslands of northern Mexico have driven a decline of plant cover and alteration of plant species composition. A number of different plant communities have resulted from these changes. Their implications, however, on the carbon (C) cycle and regional carbon balance are still poorly understood. Here, we examined the effects of plant cover loss and changes in species composition on net ecosystem CO2 exchange (NEE) and their biotic and abiotic controls. NEE was measured in five representative plant community types within a semiarid grassland by temporarily enclosing the entire aboveground ecosystem using a chamber method (i.e., geodesic dome). Sites included an oat crop (crop), a moderately grazed grassland (moderate grazing), a 28 yr-old grazing exclosure (exclosure), an overgrazed site with low perennial grass cover (overgrazed), and an overgrazed site presenting shrub encroachment (shrub encroachment). For natural vegetation, rates of standardized daytime NEE for sites with a high plant cover (exclosure and moderate grazing) were similar (P > 0.05) as compared to sites with low plant cover (overgrazed and shrub encroachment). However, yearly total nighttime NEE (carbon loss) was more than double (P < 0.05) for sites with high plant cover compared to sites with low cover, resulting to slight C sinks for the low plant cover sites, and neutral or sources for the high plant cover sites as accounted by daytime and nighttime NEE annual balance. Differences in plant cover and its associated biomass defined the sensitivity to environmental controls. Thus, daytime NEE in low plant cover sites reached light compensation points at lower photosynthetic photon flux density than those from high plant cover sites. Differences in species composition did not influence NEE rates even though there were transient or permanent changes in C3 vs. C4 functional groups. Our results allowed the detection of the large variability and contribution of different plant communities to regional C balance in patchy landscapes. Identification of the role of landscape patches in the regional C balance as either sinks or sources may provide tools allowing land use management strategies that could favor C uptake in patchy landscapes.

Delgado-Balbuena, J.; Arredondo, J. T.; Loescher, H. W.; Huber-Sannwald, E.; Chavez-Aguilar, G.; Luna-Luna, M.; Barretero-Hernandez, R.

2013-07-01

248

The effects of climatic and CO[sub 2] changes on grassland storage of soil carbon  

SciTech Connect

We present results from analysis of the sensitivity of global grassland ecosystems to modified climate. We assess over 30 grassland sites from around the world under two different GCM double CO[sub 2] climates. The results indicate that soil C losses occur in Ar grassland regions (losses range from 1.6 to 8.8% of current soil C levels for the surface 20 cm). The Eurasian grasslands lost the greatest amount of soil C ([approximately]700 g C/m[sub 2]) and the other temperate grasslands lost approximately half this amount. The tropical grasslands and savannas lost the least amount of soil C per unit area (ranging from no change to 130 g C/m[sub 2] losses). Plant production varies according to modifications in rainfall amounts under the altered climate and to altered nitrogen mineralization rates. The two GCM's differed in predictions of rainfall with a doubling of CO[sub 2], and this difference is reflected in plant production. Soil decomposition rates responded most predictably to changes in temperature. CO[sub 2] fertilization effects on soil C loss and plant production tended to reduce the net impact of climate alterations.

Ojima, D.S.; Parton, W.J. (Colorado State Univ., Fort Collins (United States)); Schimel, D.S. (National Centerfor Atmospheric Research, Boulder, CO (United States)); Scurlock, J.M.O. (Kings College London (United Kingdom))

1993-06-01

249

Community structure, trophic position and reproductive mode of soil and bark-living oribatid mites in an alpine grassland ecosystem  

PubMed Central

The community structure, stable isotope ratios (15N/14N, 13C/12C) and reproductive mode of oribatid mites (Acari, Oribatida) were investigated in four habitats (upper tree bark, lower tree bark, dry grassland soil, forest soil) at two sites in the Central Alps (Tyrol, Austria). We hypothesized that community structure and trophic position of oribatid mites of dry grassland soils and bark of trees are similar since these habitats have similar abiotic characteristics (open, dry) compared with forest soil. Further, we hypothesized that derived taxa of oribatid mites reproducing sexually dominate on the bark of trees since species in this habitat consume living resources such as lichens. In contrast to our hypothesis, the community structure of oribatid mites differed among grassland, forest and bark indicating the existence of niche differentiation in the respective oribatid mite species. In agreement with our hypothesis, sexually reproducing taxa of oribatid mites dominated on the bark of trees whereas parthenogenetic species were more frequent in soil. Several species of bark-living oribatid mites had stable isotope signatures that were similar to lichens indicating that they feed on lichens. However, nine species that frequently occurred on tree bark did not feed on lichens according to their stable isotope signatures. No oribatid mite species could be ascribed to moss feeding. We conclude that sexual reproduction served as preadaptation for oribatid mites allowing them to exploit new habitats and new resources on the bark of trees. Abiotic factors likely are of limited importance for bark-living oribatid mites since harsh abiotic conditions are assumed to favor parthenogenesis. PMID:20490626

Schatz, Heinrich; Maraun, Mark

2010-01-01

250

Different Land Use Intensities in Grassland Ecosystems Drive Ecology of Microbial Communities Involved in Nitrogen Turnover in Soil  

PubMed Central

Understanding factors driving the ecology of N cycling microbial communities is of central importance for sustainable land use. In this study we report changes of abundance of denitrifiers, nitrifiers and nitrogen-fixing microorganisms (based on qPCR data for selected functional genes) in response to different land use intensity levels and the consequences for potential turnover rates. We investigated selected grassland sites being comparable with respect to soil type and climatic conditions, which have been continuously treated for many years as intensely used meadows (IM), intensely used mown pastures (IP) and extensively used pastures (EP), respectively. The obtained data were linked to above ground biodiversity pattern as well as water extractable fractions of nitrogen and carbon in soil. Shifts in land use intensity changed plant community composition from systems dominated by s-strategists in extensive managed grasslands to c-strategist dominated communities in intensive managed grasslands. Along the different types of land use intensity, the availability of inorganic nitrogen regulated the abundance of bacterial and archaeal ammonia oxidizers. In contrast, the amount of dissolved organic nitrogen determined the abundance of denitrifiers (nirS and nirK). The high abundance of nifH carrying bacteria at intensive managed sites gave evidence that the amounts of substrates as energy source outcompete the high availability of inorganic nitrogen in these sites. Overall, we revealed that abundance and function of microorganisms involved in key processes of inorganic N cycling (nitrification, denitrification and N fixation) might be independently regulated by different abiotic and biotic factors in response to land use intensity. PMID:24039974

Meyer, Annabel; Focks, Andreas; Radl, Viviane; Keil, Daniel; Welzl, Gerhard; Schoning, Ingo; Boch, Steffen; Marhan, Sven; Kandeler, Ellen; Schloter, Michael

2013-01-01

251

Spatial and temporal variability of bacterial 16S rDNA-based T-RFLP patterns derived from soil of two Wyoming grassland ecosystems.  

PubMed

Abstract Spatial and temporal variability of soil bacterial 16S rDNA terminal restriction fragment (TRF) size variation was evaluated in a homogeneous grassland (HG) dominated by the turf-forming grass Bouteloua gracilis and in a shrubland (SL) dominated by Artemisia tridentata (Wyoming big sagebrush). Temporal variability was also evaluated on the HG site over a growing season. No trends toward dissimilarity were detected with temporal (180 days) or spatial (up to 100 m) distance in the HG system. Terminal-restriction fragment length polymorphism (T-RFLP) profiles of the SL site exhibited pronounced small-scale spatial variability (<70 cm), although spatial analysis indicated weak spatial autocorrelation to distances greater than 36 cm. While shrub-induced nutrient localization was shown to significantly influence T-RFLP profiles, very little of the variability could be accounted for on the basis of spatial characteristics, suggesting that soil bacterial 16S rDNA composition of this site is predominantly controlled at scales other than those measured. Average dissimilarity values differed greatly between the two sites (0.27 and 0.59 for HG and SL sites, respectively). These results suggest that plant community structure strongly influences bacterial community composition in these semiarid ecosystems, highlighting the importance of considering spatial variability when designing field studies related to bacterial diversity in ecosystems having patchy or heterogeneous plant cover. PMID:19719588

Mummey, Daniel L; Stahl, Peter D

2003-10-01

252

Climate warming increases biodiversity of small rodents by favoring rare or less abundant species in a grassland ecosystem.  

PubMed

Our Earth is facing the challenge of accelerating climate change, which imposes a great threat to biodiversity. Many published studies suggest that climate warming may cause a dramatic decline in biodiversity, especially in colder and drier regions. In this study, we investigated the effects of temperature, precipitation and a normalized difference vegetation index on biodiversity indices of rodent communities in the current or previous year for both detrended and nondetrended data in semi-arid grassland of Inner Mongolia during 1982-2006. Our results demonstrate that temperature showed predominantly positive effects on the biodiversity of small rodents; precipitation showed both positive and negative effects; a normalized difference vegetation index showed positive effects; and cross-correlation function values between rodent abundance and temperature were negatively correlated with rodent abundance. Our results suggest that recent climate warming increased the biodiversity of small rodents by providing more benefits to population growth of rare or less abundant species than that of more abundant species in Inner Mongolia grassland, which does not support the popular view that global warming would decrease biodiversity in colder and drier regions. We hypothesized that higher temperatures might benefit rare or less abundant species (with smaller populations and more folivorous diets) by reducing the probability of local extinction and/or by increasing herbaceous food resources. PMID:23731812

Jiang, Guangshun; Liu, Jun; Xu, Lei; Yu, Guirui; He, Honglin; Zhang, Zhibin

2013-06-01

253

Warmer temperatures stimulate respiration and reduce net ecosystem productivity in a northern Great Plains grassland: Analysis of CO2 exchange in automatic chambers  

NASA Astrophysics Data System (ADS)

The interacting effects of altered temperature and precipitation are expected to have significant consequences for ecosystem net carbon storage. Here I report the results of an experiment that evaluated the effects of elevated temperature and altered precipitation on ecosystem CO2 exchange in a northern Great Plains grassland, near Lethbridge, Alberta Canada. Open-top chambers were used to establish an experiment in 2012 with three treatments (control, warmed, warmed plus 50% of normal precipitation input). A smaller experiment with only the two temperature treatments (control and warmed) was conducted in 2013. Continuous half-hourly net CO2 exchange measurements were made using nine automatic chambers during May-October in both years. My objectives were to determine the sensitivity of the ecosystem carbon budget to temperature and moisture manipulations, and to test for direct and indirect effects of the environmental changes on ecosystem CO2 exchange. The experimental manipulations resulted primarily in a significant increase in air temperature in the warmed treatment plots. A cumulative net loss of carbon or negative net ecosystem productivity (NEP) occurred during May through September in the warmed treatment (NEP = -659 g C m-2), while in the control treatment there was a cumulative net gain of carbon (NEP = +50 g C m-2). An eddy covariance system that operated at the site, over a footprint region that was not influenced by the experimental treatments, also showed a net gain of carbon by the ecosystem. The reduced NEP was due to higher plant and soil respiration rates in the warmed treatment that appeared to be caused by a combination of: (i) higher carbon substrate availability indirectly stimulating soil respiration in the warmed relative to the control treatment, and (ii) a strong increase in leaf respiration likely caused by a shift in electron partitioning to the alternative pathway respiration in the warmed treatment, particularly when exposed to high light intensity. Increased partitioning to the alternative pathway respiration can act to alter redox status in mitochondria and reduce reactive oxygen species that may accumulate during periods of environmental stress.

Flanagan, L. B.

2013-12-01

254

Ecology, stable isotopes, and management of grassland songbirds at National Park Service properties on the Great Plains.  

E-print Network

??Grassland ecosystems have been severely reduced and grassland bird populations have experienced consistent declines. National Park Service (NPS) properties on the Great Plains provide breeding… (more)

Rehme, Sarah E

2010-01-01

255

Effects of Seasonality and Species Diversity on Nitrogen Uptake in Grassland Johanna Jensen  

E-print Network

1 Effects of Seasonality and Species Diversity on Nitrogen Uptake in Grassland Ecosystems Johanna controls on nitrogen cycling in grassland ecosystems than species diversity in fall months. Three grassland growing season and affinity for nitrate, while a senescing, diverse grassland had the least. In addition

Vallino, Joseph J.

256

Characterization of shrub distribution using high spatial resolution remote sensing: Ecosystem implications for a former Chihuahuan Desert grassland  

Microsoft Academic Search

Patchiness is often considered a defining quality of ecosystems in arid and semiarid regions. The spatial distribution of vegetation patches and soil nutrients coupled with wind and water erosion as well as biotic processes are believed to have an influence on land degradation. A geostatistical measure of spatial “connectivity” is presented to directly measure the size of patches in the

Ian O. McGlynn; Gregory S. Okin

2006-01-01

257

Managing for Habitat Heterogeneity in Grassland Agro-Ecosystems Influences the Abundance of Masked Shrews (Sorex cinereus)  

Microsoft Academic Search

Many agri-environment programs prescribe modified farming practices and provision of heterogeneous habitat types, such as fallow field edges and shelterbelts. The conservation benefit of these actions to biodiversity has been well described. However, the response of insectivorous small mammals to habitat heterogeneity in agro-ecosystems has received little empirical attention. We compared the abundance of the masked shrew (Sorex cinereus) between

Joseph J. Nocera; Kimberly L. Dawe

2008-01-01

258

Effects of grazing on leaf traits and ecosystem functioning in Inner Mongolia grasslands: scaling from species to community  

Microsoft Academic Search

More attention has focused on using some easily measured plant functional traits to predict grazing influence on plant growth and ecosystem functioning. However, there has been much controversy on leaf traits response to grazing, thus more research should be conducted at the species level. Here we investigated the leaf area, leaf mass and specific leaf area (SLA) of 263 species

S. X. Zheng; H. Y. Ren; Z. C. Lan; W. H. Li; Y. F. Bai

2009-01-01

259

Effects of an increase in summer precipitation on leaf, soil, and ecosystem fluxes of CO 2 and H 2 O in a sotol grassland in Big Bend National Park, Texas  

Microsoft Academic Search

Global climate models predict that in the next century precipitation in desert regions of the USA will increase, which is\\u000a anticipated to affect biosphere\\/atmosphere exchanges of both CO2 and H2O. In a sotol grassland ecosystem in the Chihuahuan Desert at Big Bend National Park, we measured the response of leaf-level\\u000a fluxes of CO2 and H2O 1 day before and up to

Lisa Patrick; Jessica Cable; Daniel Potts; Danielle Ignace; Greg Barron-Gafford; Alden Griffith; Holly Alpert; Natasja Van Gestel; Traesha Robertson; Travis E. Huxman; John Zak; Michael E. Loik; David Tissue

2007-01-01

260

Fire effects on ecosystem nitrogen cycling in a Californian bishop pine forest  

Microsoft Academic Search

Fire can cause severe nitrogen (N) losses from grassland, chaparral, and temperate and boreal forest ecosystems. Paradoxically,\\u000a soil ammonium levels are markedly increased by fire, resulting in high rates of primary production in re-establishing plant\\u000a communities. In a manipulative experiment, we examined the influence of wild-fire ash residues on soil, microbial and plant\\u000a N pools in a recently burned Californian

P. Grogan; T. D. Burns; F. S. Chapin III

2000-01-01

261

Spatial and Temporal Dynamics of Flora in Forest, Grassland and Common Land Ecosystems of Western Chitwan, Nepal  

PubMed Central

This paper describes changes of species composition and population of flora in space and time in western Chitwan, Nepal. This paper also discusses on the changes in flora due to flood and human activities. To illustrate these changes, we used survey data collected from January to April of 1996, 2000, and 2007 from the Barandabhar forest, National Park forest and the forests along the Narayani River banks, grasslands of National Park and common lands of western Chitwan as a part of longitudinal study on “reciprocal relation of population and the environment”. From these data, density values were calculated to analyze spatial and temporal changes in flora species composition and population. We also noted the changes of top species in time and space in due course of time. If the species and its rank not changed, their densities (population) values of flora species changed. We found that changes in species composition, population, appearance or disappearance of flora from a particular space (research plot) were noted as a result of natural forces or human activities. PMID:25061414

DANGOL, Dharma Raj; MAHARJAN, Keshav Lall

2013-01-01

262

Herbivore influence on soil microbial biomass and nitrogen mineralization in a northern grassland ecosystem: Yellowstone National Park  

Microsoft Academic Search

Microorganisms are largely responsible for soil nutrient cycling and energy flow in terrestrial ecosystems. Although soil\\u000a microorganisms are affected by topography and grazing, little is known about how these two variables may interact to influence\\u000a microbial processes. Even less is known about how these variables influence microorganisms in systems that contain large populations\\u000a of free-roaming ungulates. In this study, we

Benjamin F. Tracy; Douglas A. Frank

1998-01-01

263

Incorporating grassland management in ORCHIDEE: model description and evaluation at 11 eddy-covariance sites in Europe  

NASA Astrophysics Data System (ADS)

This study describes how management of grasslands is included in the Organizing Carbon and Hydrology in Dynamic Ecosystems (ORCHIDEE) process-based ecosystem model designed for large-scale applications, and how management affects modeled grassland-atmosphere CO2 fluxes. The new model, ORCHIDEE-GM (grassland management) is enabled with a management module inspired from a grassland model (PaSim, version 5.0), with two grassland management practices being considered, cutting and grazing. The evaluation of the results from ORCHIDEE compared with those of ORCHIDEE-GM at 11 European sites, equipped with eddy covariance and biometric measurements, shows that ORCHIDEE-GM can realistically capture the cut-induced seasonal variation in biometric variables (LAI: leaf area index; AGB: aboveground biomass) and in CO2 fluxes (GPP: gross primary productivity; TER: total ecosystem respiration; and NEE: net ecosystem exchange). However, improvements at grazing sites are only marginal in ORCHIDEE-GM due to the difficulty in accounting for continuous grazing disturbance and its induced complex animal-vegetation interactions. Both NEE and GPP on monthly to annual timescales can be better simulated in ORCHIDEE-GM than in ORCHIDEE without management. For annual CO2 fluxes, the NEE bias and RMSE (root mean square error) in ORCHIDEE-GM are reduced by 53% and 20%, respectively, compared to ORCHIDEE. ORCHIDEE-GM is capable of modeling the net carbon balance (NBP) of managed temperate grasslands (37 ± 30 gC m-2 yr-1 (P < 0.01) over the 11 sites) because the management module contains provisions to simulate the carbon fluxes of forage yield, herbage consumption, animal respiration and methane emissions.

Chang, J. F.; Viovy, N.; Vuichard, N.; Ciais, P.; Wang, T.; Cozic, A.; Lardy, R.; Graux, A.-I.; Klumpp, K.; Martin, R.; Soussana, J.-F.

2013-12-01

264

Effects of elevated atmospheric carbon dioxide on amino acid and NH4 1 -N cycling in a temperate pine ecosystem  

Microsoft Academic Search

Rising atmospheric carbon dioxide (CO2) is expected to increase forest productivity, resulting in greater carbon (C) storage in forest ecosystems. Because elevated atmo- spheric CO2 does not increase nitrogen (N) use efficiency in many forest tree species, additional N inputs will be required to sustain increased net primary productivity (NPP) under elevated atmospheric CO2. We investigated the importance of free

KIRSTEN S. H OFMOCKEL; W ILLIAM H. S CHLESINGER; R O B E RT

265

Methane fluxes in wetland and forest soils, beaver ponds, and low-order streams of a temperate forest ecosystem  

NASA Technical Reports Server (NTRS)

This study was conducted to determine whether temperate wetlands and forests play important roles in the global balances of atmospheric methane. Flux measurements for methane in several different wetland, forest, and open-water (e.g., beaver pond and low-order stream) sites were determined using collection chambers placed over the soil- or water-air interface. All of the sites were located in the Appalachian Mountain region of West Virginia and western Maryland. Between June 1987 and April 1989 the wetland sites acted as small sources of atmospheric methane, with emission rates for methane usually lower than 200 mg CH4/sq m per day; consumption of atmospheric methane in the wetland soils was observed frequently.

Yavitt, J. B.; Lang, G. E.; Sexstone, A. J.

1990-01-01

266

Spatial and temporal dynamics of biotic and abiotic features of temperate coastal ecosystems as revealed by a combination of ecological indicators  

NASA Astrophysics Data System (ADS)

Coastal ecosystems exhibit complex spatio-temporal patterns due to their position at the interface between land and sea. This is particularly the case of temperate ecosystems where exploitation of coastal resources (fisheries and aquaculture) and intensive agricultural use of watersheds further complicate our understanding of their dynamics. The aim of the present study was to unravel the spatio-temporal dynamics of contrasted megatidal coastal ecosystems located at the same regional scale (i.e. under the same regional climate), but under different kinds of human pressure. Two kinds of ecological indicators were assessed over a period of four years at 11 locations along the coast of the Cotentin peninsula (Normandy, France). A first set of hydrobiological variables (dissolved nutrients, Chl a, temperature, salinity, etc.) was measured fortnightly in the water column. These data were analysed by principal components analysis (PCA). A second set of variables were the carbon and nitrogen stable isotope ratios of the adductor muscles of cultured Crassostrea gigas introduced every year to typify the bentho-pelagic coupling at each location. Food sources were also investigated using a mixing model with data on the isotopic composition of the food sources obtained previously. To identify which environmental variables played a significant role in determining the oyster diet, the contributions of oyster food sources were combined with environmental variables in a canonical correspondence analysis (CCA). Isotopic values of adductor muscles varied significantly between -20.12‰ and -16.79‰ for ?13C and between 8.28‰ and 11.87‰ for ?15N. The PCA distinguished two groups of coastal ecosystems that differed in their coastal hydrology, nutrient inputs, and the size of their respective watershed, irrespective of the year. In each zone, different spatial patterns in the measured variables were observed depending on the year showing that local impacts differed temporally. As revealed by CCA, food sources used by the oysters were mainly explained by salinity suggesting regional differences between ecosystems. On the west coast of the peninsula, climatic factors act in synergy with anthropogenic factors (i.e. nutrient enrichment) whereas on the east coast, climatic factors appear to be dampened by anthropogenic factors.

Grangeré, K.; Lefebvre, S.; Blin, J.-L.

2012-08-01

267

Whole-farm models to quantify greenhouse gas emissions and their potential use for linking climate change mitigation and adaptation in temperate grassland ruminant-based farming systems.  

PubMed

The farm level is the most appropriate scale for evaluating options for mitigating greenhouse gas (GHG) emissions, because the farm represents the unit at which management decisions in livestock production are made. To date, a number of whole farm modelling approaches have been developed to quantify GHG emissions and explore climate change mitigation strategies for livestock systems. This paper analyses the limitations and strengths of the different existing approaches for modelling GHG mitigation by considering basic model structures, approaches for simulating GHG emissions from various farm components and the sensitivity of GHG outputs and mitigation measures to different approaches. Potential challenges for linking existing models with the simulation of impacts and adaptation measures under climate change are explored along with a brief discussion of the effects on other ecosystem services. PMID:23739478

Del Prado, A; Crosson, P; Olesen, J E; Rotz, C A

2013-06-01

268

Deposition Fluxes of Terpenes over Grassland  

PubMed Central

Eddy covariance flux measurements were carried out for two subsequent vegetation periods above a temperate mountain grassland in an alpine valley using a proton-transfer-reaction – mass spectrometer (PTR-MS) and a PTR-time of flight – mass spectrometer (PTR-TOF). In 2008 and during the first half of the vegetation period 2009 the volume mixing ratios (VMRs) for the sum of monoterpenes (MTs) were typically well below 1 ppbv and neither MT emission nor deposition was observed. After a hailstorm in July 2009 an order of magnitude higher amount of terpenes was transported to the site from nearby coniferous forests causing elevated VMRs. As a consequence, deposition fluxes of terpenes to the grassland, which continued over a time period of several weeks without significant re-emission, were observed. For days without precipitation the deposition occurred at velocities close to the aerodynamic limit. In addition to monoterpene uptake, deposition fluxes of the sum of sesquiterpenes (SQTs) and the sum of oxygenated terpenes (OTs) were detected. Considering an entire growing season for the grassland (i.e., 1st of April to 1st of November), the cumulative carbon deposition of monoterpenes reached 276 mg C m?2. This is comparable to the net carbon emission of methanol (329 mg C m?2), which is the dominant non methane volatile organic compound (VOC) emitted from this site, during the same time period. It is suggested that deposition of monoterpenes to terrestrial ecosystems could play a more significant role in the reactive carbon budget than previously assumed. PMID:24383048

Bamberger, I.; Hörtnagl, L.; Ruuskanen, T. M.; Schnitzhofer, R.; Müller, M.; Graus, M.; Karl, T.; Wohlfahrt, G.; Hansel, A.

2013-01-01

269

Net ecosystem productivity of temperate and boreal forests after clearcutting-a Fluxnet-Canada measurement and modelling synthesis  

NASA Astrophysics Data System (ADS)

ABSTRACT Clearcutting strongly affects subsequent forest net ecosystem productivity (NEP). Hypotheses for ecological controls on NEP in the ecosystem model ecosys were tested with CO2 fluxes measured by eddy covariance (EC) in three post-clearcut conifer chronosequences in different ecological zones across Canada. In the model, microbial colonization of postharvest fine and woody debris drove heterotrophic respiration (Rh), and hence decomposition, microbial growth, N mineralization and asymbiotic N2 fixation. These processes controlled root N uptake, and thereby CO2 fixation in regrowing vegetation. Interactions among soil and plant processes allowed the model to simulate hourly CO2 fluxes and annual NEP within the uncertainty of EC measurements from 2003 to 2007 over forest stands from 1 to 80 yr of age in all three chronosequences without site- or species-specific parameterization. The model was then used to study the impacts of increasing harvest removals on subsequent C stocks at one of the chronosequence sites. Model results indicated that increasing harvest removals would hasten recovery of NEP during the first 30 yr after clearcutting, but would reduce ecosystem C stocks by about 15% of the increased removals at the end of an 80-yr harvest cycle.

Grant, R. F.; Barr, A. G.; Black, T. A.; Margolis, H. A.; McCaughey, J. H.; Trofymow, J. A.

2010-11-01

270

Net Ecosystem Productivity of Temperate and Boreal Forests after Clearcutting - a Fluxnet-Canada Measurement and Modelling Synthesis  

NASA Astrophysics Data System (ADS)

Clearcutting strongly affects subsequent forest net ecosystem productivity (NEP). Hypotheses for ecological controls on NEP in the ecosystem model ecosys were tested with CO2 fluxes measured by eddy covariance (EC) in three post-clearcut conifer chronosequences in different ecological zones across Canada. In the model, microbial growth drove colonization of postharvest fine and woody debris and hence determined the time course of heterotrophic respiration (Rh), and hence decomposition, microbial growth, N mineralization and asymbiotic N2 fixation. These processes controlled the time course of root N uptake, and thereby CO2 fixation in regrowing vegetation. Interactions among soil and plant processes allowed the model to simulate hourly CO2 fluxes and annual NEP within the uncertainty of EC measurements from 2003 through 2007 over forest stands from 1 to 80 years of age in all three chronosequences without site- or species-specific parameterization. The model was then used to study the impacts of increasing harvest removals on subsequent C stocks at one of the chronosequence sites. Model results indicated that increasing harvest removals would hasten recovery of NEP during the first 30 years after clearcutting, but would reduce ecosystem C stocks by about 15% of the increased removals at the end of an 80 year harvest cycle.

Grant, R. F.; Barr, A. G.; Black, T. A.; Margolis, H. A.; McCaughey, J. H.; Trofymow, J. A.

2010-12-01

271

Effects of nitrogen reduction on invasive plants in restored grasslands  

Microsoft Academic Search

Control of invasive plant species is a problem facing ecosystem management officials, especially for disturbed ecosystems and ecosystems with elevated nutrient levels. Disturbed grasslands with elevated nitrogen levels tend to have low species diversity and high numbers of invasive species. I studied the effects of carbon amendments on disturbed grassland with elevated nitrogen levels to see if carbon amendments could

Kimberlly J. Reever

272

Evaluation of grassland dynamics in the northern-tibet plateau of china using remote sensing and climate data  

USGS Publications Warehouse

The grassland ecosystem in the Northern-Tibet Plateau (NTP) of China is very sensitive to weather and climate conditions of the region. In this study, we investigate the spatial and temporal variations of the grassland ecosystem in the NTP using the NOAA/AVHRR ten-day maximum NDVI composite data of 1981-2001. The relationships among Vegetation Peak-Normalized Difference Vegetation Index (VP-NDVI) and climate variables were quantified for six counties within the NTP. The notable and uneven alterations of the grassland in response to variation of climate and human impact in the NTP were revealed. Over the last two decades of the 20th century, the maximum greenness of the grassland has exhibited high increase, slight increase, no-change, slight decrease and high decrease, each occupies 0.27%, 8.71%, 77.27%, 13.06% and 0.69% of the total area of the NTP, respectively. A remarkable increase (decrease) in VP-NDVI occurred in the central-eastern (eastern) NTP whereas little change was observed in the western and northwestern NTP. A strong negative relationship between VP-NDVI and ET 0 was found in sub-frigid, semi-arid and frigid- arid regions of the NTP (i.e., Nakchu, Shantsa, Palgon and Amdo counties), suggesting that the ETo is one limiting factor affecting grassland degradation. In the temperate-humid, sub-frigid and sub-humid regions of the NTP (Chali and Sokshan counties), a significant inverse correlation between VP-NDVI and population indicates that human activities have adversely affected the grassland condition as was previously reported in the literature. Results from this research suggest that the alteration and degradation of the grassland in the lower altitude of the NTP over the last two decades of the 20th century are likely caused by variations of climate and anthropogenic activities. ?? 2007 by MDPI.

Zhang, J.; Yao, F.; Zheng, L.; Yang, L.

2007-01-01

273

Comprehensive ecosystem model-experiment synthesis using multiple datasets at two temperate forest free-air CO2 enrichment experiments: model performance and compensating biases  

SciTech Connect

Free Air CO2 Enrichment (FACE) experiments provide a remarkable wealth of data to test the sensitivities of terrestrial ecosystem models (TEMs). In this study, a broad set of 11 TEMs were compared to 22 years of data from two contrasting FACE experiments in temperate forests of the south eastern US the evergreen Duke Forest and the deciduous Oak Ridge forest. We evaluated the models' ability to reproduce observed net primary productivity (NPP), transpiration and Leaf Area index (LAI) in ambient CO2 treatments. Encouragingly, many models simulated annual NPP and transpiration within observed uncertainty. Daily transpiration model errors were often related to errors in leaf area phenology and peak LAI. Our analysis demonstrates that the simulation of LAI often drives the simulation of transpiration and hence there is a need to adopt the most appropriate of hypothesis driven methods to simulate and predict LAI. Of the three competing hypotheses determining peak LAI (1) optimisation to maximise carbon export, (2) increasing SLA with canopy depth and (3) the pipe model the pipe model produced LAI closest to the observations. Modelled phenology was either prescribed or based on broader empirical calibrations to climate. In some cases, simulation accuracy was achieved through compensating biases in component variables. For example, NPP accuracy was sometimes achieved with counter-balancing biases in nitrogen use efficiency and nitrogen uptake. Combined analysis of parallel measurements aides the identification of offsetting biases; without which over-confidence in model abilities to predict ecosystem function may emerge, potentially leading to erroneous predictions of change under future climates.

Walker, Anthony P [ORNL] [ORNL; Hanson, Paul J [ORNL] [ORNL; DeKauwe, Martin G [Macquarie University] [Macquarie University; Medlyn, Belinda [Macquarie University] [Macquarie University; Zaehle, S [Max Planck Institute for Biogeochemistry] [Max Planck Institute for Biogeochemistry; Asao, Shinichi [Colorado State University, Fort Collins] [Colorado State University, Fort Collins; Dietze, Michael [University of Illinois, Urbana-Champaign] [University of Illinois, Urbana-Champaign; Hickler, Thomas [Goethe University, Frankfurt, Germany] [Goethe University, Frankfurt, Germany; Huntinford, Chris [Centre for Ecology and Hydrology, Wallingford, United Kingdom] [Centre for Ecology and Hydrology, Wallingford, United Kingdom; Iversen, Colleen M [ORNL] [ORNL; Jain, Atul [University of Illinois, Urbana-Champaign] [University of Illinois, Urbana-Champaign; Lomas, Mark [University of Sheffield] [University of Sheffield; Luo, Yiqi [University of Oklahoma] [University of Oklahoma; McCarthy, Heather R [Duke University] [Duke University; Parton, William [Colorado State University, Fort Collins] [Colorado State University, Fort Collins; Prentice, I. Collin [Macquarie University] [Macquarie University; Thornton, Peter E [ORNL] [ORNL; Wang, Shusen [Canada Centre for Remote Sensing (CCRS)] [Canada Centre for Remote Sensing (CCRS); Wang, Yingping [CSIRO Marine and Atmospheric Research] [CSIRO Marine and Atmospheric Research; Warlind, David [Lund University, Sweden] [Lund University, Sweden; Weng, Ensheng [University of Oklahoma, Norman] [University of Oklahoma, Norman; Warren, Jeffrey [ORNL] [ORNL; Woodward, F. Ian [University of Sheffield] [University of Sheffield; Oren, Ram [Duke University] [Duke University; Norby, Richard J [ORNL] [ORNL

2014-01-01

274

Effects of Increased Nitrogen Deposition and Precipitation on Seed and Seedling Production of Potentilla tanacetifolia in a Temperate Steppe Ecosystem  

PubMed Central

Background The responses of plant seeds and seedlings to changing atmospheric nitrogen (N) deposition and precipitation regimes determine plant population dynamics and community composition under global change. Methodology/Principal Findings In a temperate steppe in northern China, seeds of P. tanacetifolia were collected from a field-based experiment with N addition and increased precipitation to measure changes in their traits (production, mass, germination). Seedlings germinated from those seeds were grown in a greenhouse to examine the effects of improved N and water availability in maternal and offspring environments on seedling growth. Maternal N-addition stimulated seed production, but it suppressed seed mass, germination rate and seedling biomass of P. tanacetifolia. Maternal N-addition also enhanced responses of seedlings to N and water addition in the offspring environment. Maternal increased-precipitation stimulated seed production, but it had no effect on seed mass and germination rate. Maternal increased-precipitation enhanced seedling growth when grown under similar conditions, whereas seedling responses to offspring N- and water-addition were suppressed by maternal increased-precipitation. Both offspring N-addition and increased-precipitation stimulated growth of seedlings germinated from seeds collected from the maternal control environment without either N or water addition. Our observations indicate that both maternal and offspring environments can influence seedling growth of P. tanacetifolia with consequent impacts on the future population dynamics of this species in the study area. Conclusion/Significance The findings highlight the importance of the maternal effects on seed and seedling production as well as responses of offspring to changing environmental drivers in mechanistic understanding and projecting of plant population dynamics under global change. PMID:22194863

Li, Yang; Yang, Haijun; Xia, Jianyang; Zhang, Wenhao; Wan, Shiqiang; Li, Linghao

2011-01-01

275

Environmental change in grasslands: Assessment using models  

Microsoft Academic Search

Modeling studies and observed data suggest that plant production, species distribution, disturbance regimes, grassland biome boundaries and secondary production (i.e., animal productivity) could be affected by potential changes in climate and by changes in land use practices. There are many studies in which computer models have been used to assess the impact of climate changes on grassland ecosystems. A global

William J. Parton; Dennis S. Ojima; David S. Schimel

1994-01-01

276

Observed and modeled ecosystem isoprene fluxes from an oak-dominated temperate forest and the influence of drought stress  

NASA Astrophysics Data System (ADS)

Ecosystem fluxes of isoprene emissions were measured during the majority of the 2011 growing season at the University of Missouri's Baskett Wildlife Research and Education Area in central Missouri, USA (38.7° N, 92.2° W). This broadleaf deciduous forest is typical of forests common in the Ozarks region of the central United States. The goal of the isoprene flux measurements was to test our understanding of the controls on isoprene emission from the hourly to the seasonal timescale using a state-of-the-art emission model, MEGAN (Model of Emissions of Gases and Aerosols from Nature). Isoprene emission rates from the forest were very high with a maximum of 53.3 mg m-2 h-1 (217 nmol m-2 s-1), which to our knowledge exceeds all other reports of canopy-scale isoprene emission. The fluxes showed a clear dependence on the previous temperature and light regimes, which was successfully captured by the existing algorithms in MEGAN. During a period of drought, MEGAN was unable to reproduce the time-dependent response of isoprene emission to water stress. Overall, the performance of MEGAN was robust and could explain 90% of the observed variance in the measured fluxes, but the response of isoprene emission to drought stress is a major source of uncertainty.

Potosnak, Mark J.; LeStourgeon, Lauren; Pallardy, Stephen G.; Hosman, Kevin P.; Gu, Lianhong; Karl, Thomas; Geron, Chris; Guenther, Alex B.

2014-02-01

277

Alien species in a brackish water temperate ecosystem: annual-scale dynamics in response to environmental variability.  

PubMed

Alien species contribute to global change in all marine ecosystems. Environmental variability can affect species distribution and population sizes, and is therefore expected to influence alien species. In this study, we have investigated temporal variability of 11 alien species representing different trophic levels and ecological functions in two gulfs of the brackish Baltic Sea in relation to environmental change. Independent of the invasion time, organism group or the life-history stage, abundance and/or biomass of the investigated alien species was either stable or displayed abrupt increases over time. Timing in population shifts was species-specific and exhibited no generic patterns, indicating that the observed large shifts in environmental parameters have no uniform consequences to the alien biota. In general, the inter-annual dynamics of alien and native species was not largely different, though native species tended to exhibit more diverse variability patterns compared to the alien species. There were no key environmental factors that affected most of the alien species, instead, the effects varied among the studied gulfs and species. Non-indigenous species have caused prominent structural changes in invaded communities as a result of exponential increase in the most recent invasions, as well as increased densities of the already established alien species. PMID:21440890

Ojaveer, Henn; Kotta, Jonne; Põllumäe, Arno; Põllupüü, Maria; Jaanus, Andres; Vetemaa, Markus

2011-10-01

278

Biological soil crusts are the main contributor to winter soil respiration in a temperate desert ecosystem of China  

NASA Astrophysics Data System (ADS)

Aims Biological soil crusts (BSCs) are a key biotic component of desert ecosystems worldwide. However, most studies carried out to date on carbon (fluxes) in these ecosystems, such as soil respiration (RS), have neglected them. Also, winter RS is reported to be a significant component of annual carbon budget in other ecosystems, however, we have less knowledge about winter RS of BSCs in winter and its contribution to carbon cycle in desert regions. Therefore, the specific objectives of this study were to: (i) quantify the effects of different BSCs types (moss crust, algae crust, physical crust) on the winter RS; (ii) explore relationships of RS against soil temperature and water content for different BSCs, and (iii) assess the relative contribution of BSCs to the annual amount of C released by RS at desert ecosystem level. Methods Site Description The study sites are located at the southeast fringe of the Tengger Desert in the Shapotou region of the Ningxia Hui Autonomous Region [37°32'N and 105°02'E, at 1340 m above mean sea level (a.m.s.l.)], western China. The mean daily temperature in January is -6.9°C , while it is 24.3°C in July. The mean annual precipitation is 186 mm, approximately 80% of which falls between May and September. The annual potential evaporation is 2800 mm. The landscape of the Shapotou region is characterized by large and dense reticulate barchans chains of sand dunes that migrate south-eastward at a velocity of 3-6 m per year. The soil is loose, infertile and mobile and can thus be classified as orthic sierozem and Aeolian sandy soil. Additionally, the soil has a consistent gravimetric water content that ranges from 3 to 4%. The groundwater in the study area is too deep (>60 m) to support large areas of the native vegetation cover; therefore, precipitation is usually the only source of freshwater. The predominant native plants are Hedysarum scoparium Fisch. and Agriophyllum squarrosum Moq., Psammochloa cillosa Bor, which scattered distribute with cover about 1% of the entire study area. Prior to revegetation, straw-checkerboards approximately 1×1 m2 in area were constructed using wheat or rice straw to stabilize the dune surface and allow time for the planted xerophytic shrubs to adapt to the new environment. In 1956, the following 2-year-old xerophytic shrub seedlings were planted within the checkerboard at a density of 16 individuals per 100 m2 and grown without irrigation: Artemisia ordosica Krasch, H. scoparium Fisch, Calligonum mongolicum Turc'z, Caragana microphylla Lam., Caragana korshinskii Kom, Salix gordejevii and Atraphaxis bracteata A.Los. The stabilized area was then expanded to parallel areas in 1964 and 1982 using the same method and species. As a result, the initial stages of change that have occurred at these sites were similar. After more than fifties years succession, the predominant plants are semi-shrubs, shrubs, forbs, and grasses at present and BSCs formed. The common BSCs in the region may be dominated by cyanobacteria, algae, lichens and mosses, or any combination of these organisms. Cyanobacteria species include Microcolous vaginatus Gom., Hydrocoleus violacens Gom., Lyngbya crytoraginatus Schk., Phormidium amblgum Gom., P. autumnale (Ag.) Gom., P. foveolarum (Mont.) Gom. and Phormidium luridum (Kutz) Gom. etc; algal species mainly include Anabaena azotica Ley, Euglena sp., Hantzschia amphioxys var capitata Grum, Oscillatoria obscura Gom., O. pseudogeminate G. Schm. And Scytonema javanicum (Kutz) Bornet Flash etc; lichen species include Collema tenax (Sw.) Ach., Endocarpon pusillum Hedw.; and moss species are dominated by Bryum argenteum Hedw., Didymodon constrictus (Mitt.) Saito., Tortula bidentata Bai Xue Liang and T. desertorum Broth.. Experimental Design and Rs measurements On October 2010, We selected the moss-dominated BSCs at four revegetation sites and natural vegetation sites, in which 3 replicated plots were selected randomly. In each plot, olyvinyl chloride (PVC) collar (lenth 10 cm, internal diameter 10cm ) were inserted 7 cm into the soil. During the

He, M. Z.

2012-04-01

279

Trace Gas and Carbon Sequestration Dynamics in Temperate Croplands and Successional Ecosystems: A Full-Cost Accounting  

NASA Astrophysics Data System (ADS)

Agriculture is responsible for 21-25% of the global anthropic CO2 flux, 55-60% of the anthropic CH4 flux, and 65-80% of the anthopic flux of N2O. A number of CO2 stabilization strategies target agricultural production practices, and the potential for simultaneously abating fluxes of the non-CO2 greenhouse gases is substantial. But so is the potential for creating greenhouse gas (GHG) liabilities, the unintentional increase in one or more GHGs by activities that mitigate another. Whole-system accounting provides a means for including all GHG-contributing processes in the same cropping system analysis in order to illuminate major liabilities and synergies. We contrast a field crop system in the upper U.S. midwest with unmanaged successional ecosystems in the same landscape, and provide evidence that N2O flux - the major contributor to radiative forcing in row-crop systems - can be abated with little loss of crop productivity.

Robertson, G. P.; McSwiney, C. P.

2003-12-01

280

Effects of cloud optical thickness on net ecosystem exchange in a Northern U.S. temperate forest  

NASA Astrophysics Data System (ADS)

Surface observations show that since the 1950s, the amount of cloud cover has increased over the United States. Changes in cloud properties could affect the degree to which forests act as carbon sinks, since clouds influence the amount and quality of light that reaches and penetrates forest canopies. Canopy photosynthesis can be higher under cloudy conditions than under clear skies because scattered, diffuse light can penetrate deeper into canopies and reach leaves that would otherwise be light-limited. As forests undergo canopy structural modifications during succession, cloud impacts on forest carbon storage may change. Most studies related to this topic use measured sunlight at the Earth's surface as a proxy for cloud cover. To determine a more precise relationship between cloud conditions and forest carbon storage, cloud optical thickness values from 2000-2010 were retrieved from NASA's Moderate Resolution Imaging Spectroradiometer (MODIS). These values are used to evaluate the amount of radiation extinguished by clouds and its impact on net ecosystem exchange (NEE), gross primary production (GPP) and respiration in a regionally representative forest equipped with an Ameriflux eddy co-variance tower at the University of Michigan Biological Station (UMBS). Comparisons of the Ameriflux site with the UMBS Forest Accelerated Succession ExperimenT (FASET) allow testing of how later successional forests may respond to cloud conditions. In the FASET experiment, more than 6,700 early successional aspen and birch trees (~35% leaf area index) were stem-girdled to create a later-successional forest. NEE, GPP and respiration relationships measured by the FASET tower are compared to those seen at the Ameriflux site. The interaction between cloud optical thickness and other environmental factors, such as air temperature and soil moisture, is also examined to determine which conditions result in stronger effects of clouds on forest processes.

Cheng, S. J.; Steiner, A. L.; Nadelhoffer, K.; Bohrer, G.; Curtis, P.

2011-12-01

281

The effect of enhanced ultraviolet-B radiation on germination and seedling development of plant species occurring in a dune grassland ecosystem  

Microsoft Academic Search

The germination of seeds of seven plant species occurring in a dune grassland vegetation of the Netherlands, was studied at four levels of UV-B radiation simulating unto 45% stratospheric ozone reduction during April. With the exception of seeds of Senecio jacobaea, germination of the dune grassland species was not affected by enhanced UV-B irradiance. Although a clear UV-B fluence-response relationship

Marcel Tosserams; Esther Bolink; Jelte Rozema

1997-01-01

282

Equilibrium carbon storage in North American ecosystems as estimated by the Terrestruak Ecosystem Model for pre-industrial CO[sub 2]: Soil C storage along gradients of temperature, moisture, and texture  

SciTech Connect

The Terrestrial Ecosystem Model (TEM), a process-based model, estimates a total C storage of 410 PgC (10[sup 15] gC) for undisturbed North American ecosystems at preindustrial CO[sub 2], of which soil C is 59%. Conifer forests and moist tundra account for the most vegetation and soil C storage, 31% and 18%, respectively. Along a temperature gradient in eastern North America, soil C storage decreases from 16200 to 6200 gC m[sup [minus]2] between the northern limit of moist tundra and the southern limit of temperate forest. Along a moisture gradient at 40[degrees]N, soil C storage increases from 3000 to 11000 gC m[sup [minus]2] between the western end of temperate grasslands and the eastern end of temperate forests. The model estimates that finer textured soils store more carbon under the same climatic conditions.

McGuire, A.D.; Melillo, J.M.; Joyce, L.A.; Kicklighter, D.W. (The Ecosystems Center, Woods Hole, MA (United States) Rocky Mountain Forest and Range Experiment Station, Ft. Colling, CO (United States))

1993-06-01

283

Ecosystems  

NSDL National Science Digital Library

This self-contained module on ecosystems includes a range of fun activities that students can perform in the classroom and at home with family members. They impart important concepts such as observation, identification, measurement, and differentiation.

Science, Houghton M.

284

Disentangling root responses to climate change in a semiarid grassland.  

PubMed

Future ecosystem properties of grasslands will be driven largely by belowground biomass responses to climate change, which are challenging to understand due to experimental and technical constraints. We used a multi-faceted approach to explore single and combined impacts of elevated CO2 and warming on root carbon (C) and nitrogen (N) dynamics in a temperate, semiarid, native grassland at the Prairie Heating and CO2 Enrichment experiment. To investigate the indirect, moisture mediated effects of elevated CO2, we included an irrigation treatment. We assessed root standing mass, morphology, residence time and seasonal appearance/disappearance of community-aggregated roots, as well as mass and N losses during decomposition of two dominant grass species (a C3 and a C4). In contrast to what is common in mesic grasslands, greater root standing mass under elevated CO2 resulted from increased production, unmatched by disappearance. Elevated CO2 plus warming produced roots that were longer, thinner and had greater surface area, which, together with greater standing biomass, could potentially alter root function and dynamics. Decomposition increased under environmental conditions generated by elevated CO2, but not those generated by warming, likely due to soil desiccation with warming. Elevated CO2, particularly under warming, slowed N release from C4-but not C3-roots, and consequently could indirectly affect N availability through treatment effects on species composition. Elevated CO2 and warming effects on root morphology and decomposition could offset increased C inputs from greater root biomass, thereby limiting future net C accrual in this semiarid grassland. PMID:24643718

Carrillo, Yolima; Dijkstra, Feike A; LeCain, Dan; Morgan, Jack A; Blumenthal, Dana; Waldron, Sarah; Pendall, Elise

2014-06-01

285

Comprehensive ecosystem model-data synthesis using multiple data sets at two temperate forest free-air CO2 enrichment experiments: Model performance at ambient CO2 concentration  

NASA Astrophysics Data System (ADS)

CO2 enrichment (FACE) experiments provide a remarkable wealth of data which can be used to evaluate and improve terrestrial ecosystem models (TEMs). In the FACE model-data synthesis project, 11 TEMs were applied to two decadelong FACE experiments in temperate forests of the southeastern U.S.—the evergreen Duke Forest and the deciduous Oak Ridge Forest. In this baseline paper, we demonstrate our approach to model-data synthesis by evaluating the models' ability to reproduce observed net primary productivity (NPP), transpiration, and leaf area index (LAI) in ambient CO2 treatments. Model outputs were compared against observations using a range of goodness-of-fit statistics. Many models simulated annual NPP and transpiration within observed uncertainty. We demonstrate, however, that high goodness-of-fit values do not necessarily indicate a successful model, because simulation accuracy may be achieved through compensating biases in component variables. For example, transpiration accuracy was sometimes achieved with compensating biases in leaf area index and transpiration per unit leaf area. Our approach to model-data synthesis therefore goes beyond goodness-of-fit to investigate the success of alternative representations of component processes. Here we demonstrate this approach by comparing competing model hypotheses determining peak LAI. Of three alternative hypotheses—(1) optimization to maximize carbon export, (2) increasing specific leaf area with canopy depth, and (3) the pipe model—the pipe model produced peak LAI closest to the observations. This example illustrates how data sets from intensive field experiments such as FACE can be used to reduce model uncertainty despite compensating biases by evaluating individual model assumptions.

Walker, Anthony P.; Hanson, Paul J.; De Kauwe, Martin G.; Medlyn, Belinda E.; Zaehle, Sönke; Asao, Shinichi; Dietze, Michael; Hickler, Thomas; Huntingford, Chris; Iversen, Colleen M.; Jain, Atul; Lomas, Mark; Luo, Yiqi; McCarthy, Heather; Parton, William J.; Prentice, I. Colin; Thornton, Peter E.; Wang, Shusen; Wang, Ying-Ping; Warlind, David; Weng, Ensheng; Warren, Jeffrey M.; Woodward, F. Ian; Oren, Ram; Norby, Richard J.

2014-05-01

286

Impacts of Diffuse Radiation on Light Use Efficiency across Terrestrial Ecosystems Based on Eddy Covariance Observation in China  

PubMed Central

Ecosystem light use efficiency (LUE) is a key factor of production models for gross primary production (GPP) predictions. Previous studies revealed that ecosystem LUE could be significantly enhanced by an increase on diffuse radiation. Under large spatial heterogeneity and increasing annual diffuse radiation in China, eddy covariance flux data at 6 sites across different ecosystems from 2003 to 2007 were used to investigate the impacts of diffuse radiation indicated by the cloudiness index (CI) on ecosystem LUE in grassland and forest ecosystems. Our results showed that the ecosystem LUE at the six sites was significantly correlated with the cloudiness variation (0.24?R2?0.85), especially at the Changbaishan temperate forest ecosystem (R2?=?0.85). Meanwhile, the CI values appeared more frequently between 0.8 and 1.0 in two subtropical forest ecosystems (Qianyanzhou and Dinghushan) and were much larger than those in temperate ecosystems. Besides, cloudiness thresholds which were favorable for enhancing ecosystem carbon sequestration existed at the three forest sites, respectively. Our research confirmed that the ecosystem LUE at the six sites in China was positively responsive to the diffuse radiation, and the cloudiness index could be used as an environmental regulator for LUE modeling in regional GPP prediction. PMID:25393629

Huang, Kun; Wang, Shaoqiang; Zhou, Lei; Wang, Huimin; Zhang, Junhui; Yan, Junhua; Zhao, Liang; Wang, Yanfen; Shi, Peili

2014-01-01

287

Community structure and dynamics in desert ecosystems: potential implications for insecticide risk assessment.  

PubMed

Insecticides are increasingly being used in hot arid ecosystems. The evaluation of the ecological risk these insecticides may pose, however, is based largely on data derived from temperate organisms and ecosystems. The major differences in the composition, structure, and functioning of desert animal communities when compared to temperate terrestrial ecosystems are discussed. Desert communities are characterized by a high fraction of ectotherms (both vertebrates and invertebrates);rodents and insectivores appear to dominate the mammalian fauna; and detritivores make up a very large part of the arthropod fauna. Presently available toxicity data cover these groups only to a very limited extent. It is not known if the ranges of insecticide susceptibility observed in temperate species are representative of those in arid organisms. Thus, it is not certain that ecotoxicological assessments based on such data sets adequately protect desert animal communities. It is shown that food web connectance is higher in desert ecosystems than in temperate grasslands or forests. This may to a large extent be due to the high degree of omnivory among desert organisms. Population regulation between predators and prey appears to be weaker in deserts. The same is often, though not always, the case for competition among desert organisms. It is argued that such characteristics will reduce the chance that strong indirect effects of insecticide perturbations will occur. In spite of the fact that many desert organisms are well adapted to cope with high temporal and spatial environmental variability, there is no reason to believe that they will always recover more rapidly from population perturbations caused by insecticides. The relatively large physiological and life-history plasticity encountered in many desert animals may increase tolerance to insecticide stress. Food chains are longer in deserts than in temperate grasslands and forests. The implications of this observation for the risk of biomagnification of contaminants are discussed. PMID:9002430

van der Valk, H C

1997-01-01

288

The impacts of land cover change on surface energy fluxes and radiometric surface temperature in the temperate zone  

NASA Astrophysics Data System (ADS)

Vegetation is an important control on the surface energy balance, but the impacts of land use and land cover change on changes to surface energy fluxes and radiometric surface temperature (Tsurf) in the temperate zone remain the subject of active research. We quantified the mechanisms driving changes in Tsurf following landcover changes using paired ecosystem case studies from the Ameriflux database. A differential analysis of models of varying complexity was used to quantify the change in Tsurf attributable to structural and functional ecosystem changes. Results support previous findings that deciduous and coniferous forests in the Duke Forest, NC, are about 1 °C cooler than an adjacent field on an annual basis because an aerodynamic and ecophysiological cooling of ca. 2 °C outweighs an albedo-related warming of ca. 1 °C upon transition to forest. A 50-70% reduction in the aerodynamic resistance to sensible and latent heat exchange in the forested ecosystems dominated the cooling effect. In northern Arizona, a grassland ecosystem that succeeded a stand-replacing ponderosa pine fire was ca. 1 °C warmer than unburned stands for similar mechanisms to the Duke Forest case study; a 1.5 °C aerodynamic warming offset a slight surface cooling due to greater albedo and soil heat flux. In southern Arizona, ecosystems dominated by mesquite shrub encroachment were nearly 2 °C warmer than a native grassland ecosystem because aerodynamic and albedo-related warming outweighed a small cooling effect due to changes in soil heat flux. Further to these findings, an investigation of over 8 million data points in the FLUXNET database revealed that surface temperature increased less per unit net radiation in forests than in short-statured ecosystems globally. Together, these results suggest that temperate forests tend to cool the land surface in addition to their high CO2 sequestration potential.

Stoy, P. C.; Jammet, M.; Luyssaert, S.; Katul, G. G.; Juang, J.-Y.; Siqueira, M. B. S.; Novick, K. A.; Dore, S.; Kolb, T. E.; Montes-Helu, M. C.; Scott, R. L.

2012-04-01

289

Short communication Land use change patterns in the Rio de la Plata grasslands: The influence of  

E-print Network

Short communication Land use change patterns in the Ri´o de la Plata grasslands: The influence) hold one of the largest area of temperate grasslands of the world, the Ri´o de la Plata grasslands (RPG­387) (Fig. 1). Ri´o de la Plata grasslands have an area of 3.4 � 106 km2 at the center-east of Argentina

Nacional de San Luis, Universidad

290

Ecosystems  

NSDL National Science Digital Library

This "Ecosystems" module has four units of instruction. The units include: natural selection, population balance, exchange cycles, and environmental protection. Each module has a "Hazards" link that leads to a menu of study units on various environmental hazards (such as oil spills, farm runoff, insecticides, and so on).

Klemm, W. R.

2002-01-01

291

March 2005 / Vol. 55 No. 3 BioScience 243 Grasslands and savannas occupy more than 40%  

E-print Network

March 2005 / Vol. 55 No. 3 · BioScience 243 Articles Grasslands and savannas occupy more than 40 and climate can have dramatic ecological and social consequences (Lauenroth et al.1999).Temperate grasslands are important from both agronomic and ecological perspectives. These grasslands are the basis of an extensive

Blair, John

292

Ecosystems  

NSDL National Science Digital Library

This lesson plan is part of the DiscoverySchool.com lesson plan library for grades 6-8. It focuses on biodiversity within ecosystems and within species. Students visit a local area and collect leaves to demonstrate how diverse life can exist within a small area. Included are objectives, materials, procedures, discussion questions, evaluation ideas, suggested readings, and vocabulary. There are videos available to order which complement this lesson, an audio-enhanced vocabulary list, and links to teaching tools for making custom quizzes, worksheets, puzzles and lesson plans.

2007-12-12

293

[Impact of the Beijing and Tianjin Sand Source Control Project on the grassland soil organic carbon storage: a case study of Xilingol League, Inner Mongolia, China].  

PubMed

Understanding the impacts of eco-construction project on grassland soil carbon storage is crucial to assess the effectiveness of the project and its role in carbon cycling of the grassland ecosystems. Using IPCC carbon budget inventory method, this paper analyzed the influence of Beijing and Tianjin Sand Source Control Project (BTSSCP) on the grassland soil carbon storage between 2000 and 2006 in Xilingol League, Inner Mongolia, and evaluated the time needed to reach the maximal soil carbon density for three management practices (i. e. , sown pasture, aerial sowing pasture, and grazing exclosure). Results showed that the BTSSCP significantly increased soil carbon storage, with a carbon sequestration of 59.26 x 10(4) t C from 2000 to 2006. The rate and effectiveness of soil carbon sequestration varied significantly with management practices, with the highest rate in sown pasture (0.25 t C x hm(-2) x a(-1)) while a greater benefit of soil carbon sequestration in the grazing exclosure (63 million yuan). Compared with other grassland vegetations, lowland meadow and temperate meadow steppe both had higher carbon sequestration rates of 0.14 t C x hm(-2) x a(-1). Long time would be needed to reach the maximum soil carbon density in grassland under the three practices, yet shorter for sown pasture with average of 57.75 years. PMID:24830235

Zhang, Liang-Xia; Fan, Jiang-Wen; Zhang, Wen-Yan; Tang, Feng-Pei

2014-02-01

294

Our current understanding of lake ecosystem response to climate change: What have we really learned from the north temperate deep lakes?  

Microsoft Academic Search

Climatic change is recognized as an important factor capable of influencing the structural properties of aquatic ecosystems. Lake ecosystems are particularly sensitive to climate change. Several long time-series studies have shown close coupling between climate, lake thermal properties and individual organism physiology, population abundance, community structure, and food-web structure. Understanding the complex interplay between climate, hydrological variability, and ecosystem structure

Yuko Shimoda; M. Ekram Azim; Gurbir Perhar; Maryam Ramin; Melissa A. Kenney; Somayeh Sadraddini; Alex Gudimov; George B. Arhonditsis

2011-01-01

295

Carbon and Nitrogen Dynamics of Temperate and Subarctic Heath  

E-print Network

-season cycling of carbon and nitrogen in temperate and subarctic heath ecosystems. Over the last three years, I.................................................................................................. 9 2. The carbon cycle.......................................................................................... 12 2.1 Measuring and modeling ecosystem carbon cycling............................... 13 2.2 Results

296

From Imperata cylindrica grasslands to productive agroforestry  

Microsoft Academic Search

Keywords:<\\/strong> Ecosystem, Agroforestry, Imperata cylindrica , pioneer, mycorrhizae, inter-cropping, tree architecture, biomass, functional branching analysisConversion of an Imperata cylindrica ecosystem into an agroforestry ecosystem is a complex process. Integrated control of the I . cylindrica grass is needed in combination with planting deep-rooted pioneer tree species, a legume cover crop and annual food crops. I . cylindrica grasslands are generally

Murniati

2002-01-01

297

Regional variability of grassland CO2 fluxes in Tyrol/Austria  

NASA Astrophysics Data System (ADS)

The FLUXNET project [1] aims at quantifying the magnitude and controls on the CO2, H2O and energy exchange of terrestrial ecosystems. Ideally, the various biomes of the Earth would be sampled in proportion to their spatial extent - in reality, however, study site selection is usually based on other (more practical) criteria so that a bias exists towards certain biomes and ecosystem types. This may be problematic because FLUXNET data are used to calibrate/parameterize models at various scales - if certain ecosystems are poorly replicated this may bias model predictions. Here we present data from a project in Tyrol/Austria where we have been investigating the CO2, H2O and energy exchange of five grassland sites during 2005-2007. The five permanent grassland sites were exposed to similar climate, but differed slightly in management. In a FLUXNET style approach, any of these sites might have been selected for making long-term flux measurements - the aim of this project was to examine the representativeness of these sites and, if evident, elucidate the causes for and controls on differences between sites. To this end we conducted continuous eddy covariance flux measurements at one (anchor) site [2, 3], and episodic, month long flux measurements at the four additional sites using a roving eddy covariance tower. These data were complemented by measurements of environmental drivers, the amount of above ground phytomass and basic data on vegetation and soil type, as well as management. Data are subject to a rigorous statistical analysis in order to quantify significant differences in the CO2, H2O and energy exchange between the sites and to identify the factors which are responsible for these differences. In the present contribution we report results on CO2 fluxes. Our major findings are that (i) site-identity of the surveyed grassland ecosystems was a significant factor for the net ecosystem CO2 exchange (NEE), somewhat less for gross primary production (GPP) and not for ecosystem respiration (RECO), (ii) GPP depended mainly on the amount of incident photosynthetically active radiation and the amount of green plant matter, the scale of influence of these two factors varying fourfold between the sites, and not so much on the available water, (iii) RECO was mainly affected by the soil temperature, but some evidence for priming effects was also found, (iv) the NEE was mainly influenced by GPP and to a lower extent by RECO. Taken together our results indicate that even within the same ecosystem type exposed to similar climate and land use, site selection may strongly affect the resulting NEE estimates. References: [1] D.D. Baldocchi, "Breathing of the terrestrial biosphere: lessons learned from a global network of carbon dioxide flux measurement systems", Australian Journal of Botany vol.56 (2008) pp. 1-26. [2] A. Hammerle, A. Haslwanter, U. Tappeiner, A. Cernusca, G. Wohlfahrt, "Leaf area controls on energy partitioning of a temperate mountain grassland", Biogeosciences vol.5 (2008) pp. 421 431. [3] G. Wohlfahrt, A. Hammerle, A. Haslwanter, M. Bahn, U. Tappeiner, A. Cernusca, "Seasonal and inter-annual variability of the net ecosystem CO2 exchange of a temperate mountain grassland: effects of weather and management", Journal of Geophysical Research 113 (2008) D08110, doi:10.1029/2007JD009286.

Irschick, Christoph; Hammerle, Albin; Haslwanter, Alois; Wohlfahrt, Georg

2010-05-01

298

Parallel Computing for Terrestrial Ecosystem Carbon Modeling  

SciTech Connect

Terrestrial ecosystems are a primary component of research on global environmental change. Observational and modeling research on terrestrial ecosystems at the global scale, however, has lagged behind their counterparts for oceanic and atmospheric systems, largely because the unique challenges associated with the tremendous diversity and complexity of terrestrial ecosystems. There are 8 major types of terrestrial ecosystem: tropical rain forest, savannas, deserts, temperate grassland, deciduous forest, coniferous forest, tundra, and chaparral. The carbon cycle is an important mechanism in the coupling of terrestrial ecosystems with climate through biological fluxes of CO{sub 2}. The influence of terrestrial ecosystems on atmospheric CO{sub 2} can be modeled via several means at different timescales. Important processes include plant dynamics, change in land use, as well as ecosystem biogeography. Over the past several decades, many terrestrial ecosystem models (see the 'Model developments' section) have been developed to understand the interactions between terrestrial carbon storage and CO{sub 2} concentration in the atmosphere, as well as the consequences of these interactions. Early TECMs generally adapted simple box-flow exchange models, in which photosynthetic CO{sub 2} uptake and respiratory CO{sub 2} release are simulated in an empirical manner with a small number of vegetation and soil carbon pools. Demands on kinds and amount of information required from global TECMs have grown. Recently, along with the rapid development of parallel computing, spatially explicit TECMs with detailed process based representations of carbon dynamics become attractive, because those models can readily incorporate a variety of additional ecosystem processes (such as dispersal, establishment, growth, mortality etc.) and environmental factors (such as landscape position, pest populations, disturbances, resource manipulations, etc.), and provide information to frame policy options for climate change impact analysis.

Wang, Dali [ORNL; Post, Wilfred M [ORNL; Ricciuto, Daniel M [ORNL; Berry, Michael [University of Tennessee, Knoxville (UTK)

2011-01-01

299

Research, part of a Special Feature on The influence of human demography and agriculture on natural systems in the Neotropics Land-Use and Land Cover Dynamics in South American Temperate Grasslands  

Microsoft Academic Search

In the Río de la Plata grasslands (RPG) biogeographical region of South America, agricultural activities have undergone important changes during the last 15-18 years because of technological improvements and new national and international market conditions. We characterized changes in the landscape structure between 1985-1989 and 2002-2004 for eight pilot areas distributed across the main regional environmental gradients. These areas incorporated

Germán Baldi; José M. Paruelo

300

Effects of plant diversity on invertebrate herbivory in experimental grassland.  

PubMed

The rate at which a plant species is attacked by invertebrate herbivores has been hypothesized to depend on plant species richness, yet empirical evidence is scarce. Current theory predicts higher herbivore damage in monocultures than in species-rich mixtures. We quantified herbivore damage by insects and molluscs to plants in experimental plots established in 2002 from a species pool of 60 species of Central European Arrhenatherum grasslands. Plots differed in plant species richness (1, 2, 4, 8, 16, 60 species), number of functional groups (1, 2, 3, 4), functional group and species composition. We estimated herbivore damage by insects and molluscs at the level of transplanted plant individuals ("phytometer" species Plantago lanceolata, Trifolium pratense, Rumex acetosa) and of the entire plant community during 2003 and 2004. In contrast to previous studies, our design allows specific predictions about the relative contributions of functional diversity, plant functional identity, and species richness in relation to herbivory. Additionally, the phytometer approach is new to biodiversity-herbivory studies, allowing estimates of species-specific herbivory rates within the larger biodiversity-ecosystem functioning context. Herbivory in phytometers and experimental communities tended to increase with plant species richness and the number of plant functional groups, but the effects were rarely significant. Herbivory in phytometers was in some cases positively correlated with community biomass or leaf area index. The most important factor influencing invertebrate herbivory was the presence of particular plant functional groups. Legume (grass) presence strongly increased (decreased) herbivory at the community level. The opposite pattern was found for herbivory in T. pratense phytometers. We conclude that (1) plant species richness is much less important than previously thought and (2) plant functional identity is a much better predictor of invertebrate herbivory in temperate grassland ecosystems. PMID:16231192

Scherber, Christoph; Mwangi, Peter N; Temperton, Vicky M; Roscher, Christiane; Schumacher, Jens; Schmid, Bernhard; Weisser, Wolfgang W

2006-03-01

301

Interactive Effects of Time, CO 2 , N, and Diversity on Total Belowground Carbon Allocation and Ecosystem Carbon Storage in a Grassland Community  

Microsoft Academic Search

Predicting if ecosystems will mitigate or exacerbate rising CO2 requires understanding how elevated CO2 will interact with coincident changes in diversity and nitrogen (N) availability to affect ecosystem carbon (C) storage.\\u000a Yet achieving such understanding has been hampered by the difficulty of quantifying belowground C pools and fluxes. Thus,\\u000a we used mass balance calculations to quantify the effects of diversity,

E. Carol Adair; Peter B. Reich; Sarah E. Hobbie; Johannes M. H. Knops

2009-01-01

302

Trophic control of grassland production and biomass by pathogens  

E-print Network

REPORT Trophic control of grassland production and biomass by pathogens Charles E. Mitchell. Here, I report the results of an experiment factorially excluding foliar fungal pathogens and insect herbivores from an intact grassland ecosystem. At peak in control plots, 8.9% of community leaf area

Crews, Stephen

303

Carbon-Nitrogen Cycle Model of Terrestrial Ecosystem for Plot Scale: Application to Cool Temperate Deciduous Broad-leaved Forest and Cool Temperate Evergreen Coniferous Forest in Central Japan  

Microsoft Academic Search

By developing a biogeochemical model that fully includes carbon cycle and nitrogen cycle in a single framework, we can consider nitrogen nutrition as a limiting elements in the model and evaluate atmosphere-ecosystem exchange of trace greenhouse gases in addition to carbon dioxide (i.e. methane and nitrous oxide). In this study, a process-based model simulating carbon-nitrogen cycle was developed and applied

A. Ito; M. Inatomi

2007-01-01

304

Impacts of seasonality and surface heterogeneity on water-use efficiency in mesic grasslands  

E-print Network

Impacts of seasonality and surface heterogeneity on water-use efficiency in mesic grasslands N. A encroachment is occurring in grasslands worldwide, with largely unknown effects on local carbon and water evapotranspiration. Here, a was compared among three different grassland ecosystems in eastern KS, USA, by using

Nippert, Jesse

305

Observations and modeling of biomass and soil organic matter dynamics for the grassland biome worldwide  

Microsoft Academic Search

Century is a model of terrestrial biogeochemistry based on relationships between climate, human management (fire, grazing), soil properties, plant productivity, and decomposition. The grassland version of the Century model was tested using observed data from 11 temperate and tropical grasslands around the world. The results show that soil C and N levels can be simulated to within +\\/-25% of the

W. J. Parton; J. M. O. Scurlock; D. S. Ojima; T. G. Gilmanov; R. J. Scholes; D. S. Schimel; T. Kirchner; J.-C. Menaut; T. Seastedt; E. Garcia Moya; Apinan Kamnalrut; J. I. Kinyamario

1993-01-01

306

From fronds to fish: the use of indicators for ecological monitoring in marine benthic ecosystems, with case studies from temperate Western Australia  

Microsoft Academic Search

Ecological indicators are used for monitoring in marine habitats the world over. With the advent of Ecosystem Based Fisheries\\u000a Management (EBFM), the need for cost effective indicators of environmental impacts and ecosystem condition has intensified.\\u000a Here, we review the development, utilisation and analysis of indicators for monitoring in marine benthic habitats, and outline\\u000a important advances made in recent years. We

Dan A. Smale; Timothy J. Langlois; Gary A. Kendrick; Jessica J. Meeuwig; Euan S. Harvey

307

Temper tantrums.  

PubMed

Temper tantrums are a normal response to anger and occur commonly in the child between one and four years of age. They arise from the child's thwarted efforts to exercise mastery and autonomy. Tantrums occur more frequently in the active, determined child who has abundant energy. Parenting practices that may encourage tantrums include inconsistency, unreasonable expectations, excessive strictness, overprotectiveness and overindulgence. Boredom, fatigue, hunger or illness may reduce the child's tolerance for frustration. Management consists of teaching the parents to understand the underlying meaning of tantrums and to modify parental behaviors that may perpetuate or accentuate the problem. Temper tantrums are best handled by ignoring the outburst, offering nurturance to the child after the tantrum has subsided and helping the child learn to express negative feelings in more acceptable ways. PMID:1858612

Leung, A K; Fagan, J E

1991-08-01

308

BVOC fluxes above mountain grassland  

PubMed Central

Grasslands comprise natural tropical savannah over managed temperate fields to tundra and cover one quarter of the Earth’s land surface. Plant growth, maintenance and decay result in volatile organic compound (VOCs) emissions to the atmosphere. Furthermore, biogenic VOCs (BVOCs) are emitted as a consequence of various environmental stresses including cutting and drying during harvesting. Fluxes of BVOCs were measured with a proton-transfer-reaction-mass-spectrometer (PTR-MS) over temperate mountain grassland in Stubai Valley (Tyrol, Austria) over one growing season (2008). VOC fluxes were calculated from the disjunct PTR-MS data using the virtual disjunct eddy covariance method and the gap filling method. Methanol fluxes obtained with the two independent flux calculation methods were highly correlated (y = 0.95×?0.12, R2 = 0.92). Methanol showed strong daytime emissions throughout the growing season – with maximal values of 9.7 nmol m?2 s?1, methanol fluxes from the growing grassland were considerably higher at the beginning of the growing season in June compared to those measured during October (2.5 nmol m?2 s?1). Methanol was the only component that exhibited consistent fluxes during the entire growing periods of the grass. The cutting and drying of the grass increased the emissions of methanol to up to 78.4 nmol m?2 s?1. In addition, emissions of acetaldehyde (up to 11.0 nmol m?2 s?1), and hexenal (leaf aldehyde, up to 8.6 nmol m?2 s?1) were detected during/after harvesting. PMID:24339833

Bamberger, I.; Hortnagl, L.; Schnitzhofer, R.; Graus, M.; Ruuskanen, T. M.; Muller, M.; Dunkl, J.; Wohlfahrt, G.; Hansel, A.

2013-01-01

309

Temper Foam  

NASA Technical Reports Server (NTRS)

Fabricated by Expanded Rubber & Plastics Corporation, Temper Foam provides better impact protection for airplane passengers and enhances passenger comfort on long flights because it distributes body weight and pressure evenly over the entire contact area. Called a "memory foam" it matches the contour of the body pressing against it and returns to its original shape once the pressure is removed. As a shock absorber, a three-inch foam pad has the ability to absorb the impact of a 10-foot fall by an adult. Applications include seat cushioning for transportation vehicles, padding for furniture and a variety of athletic equipment medical applications including wheelchair padding, artificial limb socket lining, finger splint and hand padding for burn patients, special mattresses for the bedridden and dental stools. Production and sales rights are owned by Temper Foam, Inc. Material is manufactured under license by the Dewey and Almy Division of Grace Chemical Corporation. Distributors of the product are Kees Goebel Medical Specialties, Inc. and Alimed, Inc. They sell Temper Foam in bulk to the fabricators who trim it to shapes required by their customers.

1981-01-01

310

Estimation of nitrous oxide emissions from US grasslands  

SciTech Connect

Nitrous oxide (N{sub 2}O) emissions from temperate grasslands are poorly quantified and may be an important part of the atmospheric N{sub 2}O budget. In this study N{sub 2}O emissions were simulated for 1,052 grassland sites in the US using the NGAS model of Parton and others (1996) coupled with an organic matter decomposition model. N{sub 2}O flux was calculated for each site using soil and land use data obtained from the National Resource Inventory (NRI) database and weather data obtained from NASA. The estimates were regionalized based upon temperature and moisture isotherms. Annual N{sub 2}O emissions for each region were based on the grassland area of each region and the mean estimated annual N{sub 2}O flux from NRI grassland sites in the region. The regional fluxes ranged from 0.18 to 1.02 kg N{sub 2}O N/ha/yr with the mean flux for all regions being 0.29 kg N{sub 2}O N/ha/yr. Even though fluxes from the western regions were relatively low, these regions made the largest contribution to total emissions due to their large grassland area. Total US grassland N{sub 2}O emissions were estimated to be about 67 Gg N{sub 2}O N/yr. Emissions from the Great Plains states, which contain the largest expanse of natural grassland in the US, were estimated to average 0.24 kg N{sub 2}O N/ha/yr. Using the annual flux estimate for the temperate Great Plains, the authors estimate that temperate grasslands worldwide may potentially produce 0.27 Tg N{sub 2}O N/yr. Even though the estimate for global temperate grassland N{sub 2}O emissions is less than published estimates for other major temperate grasslands are a significant part of both United States and global atmospheric N{sub 2}O budgets. This study demonstrates the utility of models for regional N{sub 2}O budgets. This study demonstrates the utility of models for regional N{sub 2}O flux estimation although additional data from carefully designed field studies is needed to further validate model results.

Mummey, D.L.; Smith, J.L.; Bluhm, G.

2000-02-01

311

Effect of rainfall patterns on soil surface CO2 efflux, soil moisture, soil temperature and plant growth in a grassland ecosystem of northern Ontario, Canada: implications for climate change  

PubMed Central

Background The effect of rainfall patterns on soil surface CO2 efflux, soil moisture, soil temperature and plant growth was investigated in a grassland ecosystem of northern Ontario, Canada, where climatic change is predicted to introduce new precipitation regimes. Rain shelters were established in a fallow field consisting mainly of Trifolium hybridum L., Trifolium pratense L., and Phleum pratense L. Daytime ambient air temperatures within the shelters increased by an average of 1.9°C similar to predicted future increases in air temperatures for this region. To simulate six precipitation regimes which cover the maximum range to be expected under climate change, a portable irrigation system was designed to modify the frequency of monthly rainfall events with a constant delivery rate of water, while maintaining contemporary average precipitation volumes. Controls consisted of blocks irrigated with frequencies and total monthly precipitation consistent with the 25 year average rainfall for this location. Results Seasonal soil moisture correlated with soil surface CO2 efflux (R = 0.756, P < 0.001) and above ground plant biomass (R = 0.447, P = 0.029). By reducing irrigation frequency, soil surface CO2 efflux decreased by 80%, P < 0.001, while soil moisture content decreased by 42%, P < 0.001. Conclusions Manipulating the number of precipitation events and inter-rainfall intervals, while maintaining monthly rainfall averages impacted CO2 efflux and plant growth. Even with monthly rainfall averages that are similar to contemporary monthly precipitation averages, decreasing the number of monthly rainfall events reduced soil surface CO2 efflux and plant growth through soil moisture deficits. Although many have speculated that climate change will increase ecosystem productivity, our results show that a reduction in the number of monthly rainfall events while maintaining monthly averages will limit carbon dynamics. PMID:12445327

Laporte, Michael F; Duchesne, LC; Wetzel, S

2002-01-01

312

Conversion of grassland to coniferous woodland has limited effects on soil nitrogen cycle processes  

Microsoft Academic Search

In the last century, conversion of native North American grasslands to Juniperus virginiana forests or woodlands has dramatically altered ecosystem structure and significantly increased ecosystem carbon (C) stocks. We compared soils under recently established J. virginiana forests and adjacent native C4-dominated grassland to assess changes in potential soil nitrogen (N) transformations and plant available N. Over a 2-year period, concentrations

Duncan C. McKinley; Charles W. Rice; John M. Blair

2008-01-01

313

Effects of air pollution and acid rain on fish, wildlife, and their habitats - grasslands. Final report  

Microsoft Academic Search

Report 7 of the series synthesizing the results of scientific research related to the effects of air pollution and acid deposition on fish and wildlife resources deals with grasslands. General aspects of grassland ecosystems relevant to a discussion of air pollution effects are presented along with a brief introduction to various other types of ecosystem stresses.

1982-01-01

314

Sensitivity of Temperate Desert Steppe Carbon Exchange to Seasonal Droughts and Precipitation Variations in Inner Mongolia, China  

PubMed Central

Arid grassland ecosystems have significant interannual variation in carbon exchange; however, it is unclear how environmental factors influence carbon exchange in different hydrological years. In this study, the eddy covariance technique was used to investigate the seasonal and interannual variability of CO2 flux over a temperate desert steppe in Inner Mongolia, China from 2008 to 2010. The amounts and times of precipitation varied significantly throughout the study period. The precipitation in 2009 (186.4 mm) was close to the long-term average (183.9±47.6 mm), while the precipitation in 2008 (136.3 mm) and 2010 (141.3 mm) was approximately a quarter below the long-term average. The temperate desert steppe showed carbon neutrality for atmospheric CO2 throughout the study period, with a net ecosystem carbon dioxide exchange (NEE) of ?7.2, ?22.9, and 26.0 g C m?2 yr?1 in 2008, 2009, and 2010, not significantly different from zero. The ecosystem gained more carbon in 2009 compared to other two relatively dry years, while there was significant difference in carbon uptake between 2008 and 2010, although both years recorded similar annual precipitation. The results suggest that summer precipitation is a key factor determining annual NEE. The apparent quantum yield and saturation value of NEE (NEEsat) and the temperature sensitivity coefficient of ecosystem respiration (Reco) exhibited significant variations. The values of NEEsat were ?2.6, ?2.9, and ?1.4 µmol CO2 m?2 s?1 in 2008, 2009, and 2010, respectively. Drought suppressed both the gross primary production (GPP) and Reco, and the drought sensitivity of GPP was greater than that of Reco. The soil water content sensitivity of GPP was high during the dry year of 2008 with limited soil moisture availability. Our results suggest the carbon balance of this temperate desert steppe was not only sensitive to total annual precipitation, but also to its seasonal distribution. PMID:23393576

Yang, Fulin; Zhou, Guangsheng

2013-01-01

315

Sensitivity of temperate desert steppe carbon exchange to seasonal droughts and precipitation variations in Inner Mongolia, China.  

PubMed

Arid grassland ecosystems have significant interannual variation in carbon exchange; however, it is unclear how environmental factors influence carbon exchange in different hydrological years. In this study, the eddy covariance technique was used to investigate the seasonal and interannual variability of CO? flux over a temperate desert steppe in Inner Mongolia, China from 2008 to 2010. The amounts and times of precipitation varied significantly throughout the study period. The precipitation in 2009 (186.4 mm) was close to the long-term average (183.9±47.6 mm), while the precipitation in 2008 (136.3 mm) and 2010 (141.3 mm) was approximately a quarter below the long-term average. The temperate desert steppe showed carbon neutrality for atmospheric CO? throughout the study period, with a net ecosystem carbon dioxide exchange (NEE) of -7.2, -22.9, and 26.0 g C m?² yr?¹ in 2008, 2009, and 2010, not significantly different from zero. The ecosystem gained more carbon in 2009 compared to other two relatively dry years, while there was significant difference in carbon uptake between 2008 and 2010, although both years recorded similar annual precipitation. The results suggest that summer precipitation is a key factor determining annual NEE. The apparent quantum yield and saturation value of NEE (NEE(sat)) and the temperature sensitivity coefficient of ecosystem respiration (R(eco)) exhibited significant variations. The values of NEE(sat) were -2.6, -2.9, and -1.4 µmol CO? m?² s?¹ in 2008, 2009, and 2010, respectively. Drought suppressed both the gross primary production (GPP) and R(eco), and the drought sensitivity of GPP was greater than that of R(eco). The soil water content sensitivity of GPP was high during the dry year of 2008 with limited soil moisture availability. Our results suggest the carbon balance of this temperate desert steppe was not only sensitive to total annual precipitation, but also to its seasonal distribution. PMID:23393576

Yang, Fulin; Zhou, Guangsheng

2013-01-01

316

Quantifying Grassland-to-Woodland Transitions and the Implications for Carbon and Nitrogen Dynamics in the Southwest United States  

NASA Technical Reports Server (NTRS)

Replacement of grasslands and savannas by shrublands and woodlands has been widely reported in tropical, temperate and high-latitude rangelands worldwide (Archer 1994). These changes in vegetation structure may reflect historical shifts in climate and land use; and are likely to influence biodiversity, productivity, above- and below ground carbon and nitrogen sequestration and biophysical aspects of land surface-atmosphere interactions. The goal of our proposed research is to investigate how changes in the relative abundance of herbaceous and woody vegetation affect carbon and nitrogen dynamics across heterogeneous savannas and shrub/woodlands. By linking actual land-cover composition (derived through spectral mixture analysis of AVIRIS, TM, and AVHRR imagery) with a process-based ecosystem model, we will generate explicit predictions of the C and N storage in plants and soils resulting from changes in vegetation structure. Our specific objectives will be to (1) continue development and test applications of spectral mixture analysis across grassland-to-woodland transitions; (2) quantify temporal changes in plant and soil C and N storage and turnover for remote sensing and process model parameterization and verification; and (3) couple landscape fraction maps to an ecosystem simulation model to observe biogeochemical dynamics under changing landscape structure and climatological forcings.

Wessman, Carol A.; Archer, Steven R.; Asner, Gregory P.; Bateson, C. Ann

2004-01-01

317

Stimulation of symbiotic N{sub 2} fixation in trifolium repens L. under elevated atmospheric pCO{sub 2} in a grassland ecosystem  

SciTech Connect

Symbiotic N{sub 2} fixation is one of the main processes that introduces N into terrestrial ecosystems. As such, it may be crucial for the sequestration of the extra C available in a world of continuously increasing atmospheric CO{sub 2} partial pressure (pCO{sub 2}). The effect of elevated pCO{sub 2} (60 Pa) on symbiotic N{sub 2} fixation ({sup 15}N-isotope dilution method) was investigated using Free-Air-CO{sub 2}-Enrichment technology over a period of 3 years. Trifolium repens was cultivated either alone or together with Lolium perenne (a nonfixing reference crop) in mixed swards. Two different N fertilization levels and defoliation frequencies were applied. The total N yield increased consistently and the percentage of plant N derived from symbiotic N{sub 2} fixation increased significantly in T. repens under elevated pCO{sub 2}. All additionally assimilated N was derived from symbiotic N{sub 2} fixation, not from the soil. In the mixtures exposed to elevated pCO{sub 2}, an increased amount of symbiotically fixed N (+7.8, 8.2, and 6.2 g m{sup {minus}2} a {sup {minus}1} in 1993, 1994, and 1995, respectively) was introduced into the system. Increased N{sub 2} fixation is a competitive advantage for T. repens in mixed swards with paster grasses and may be a crucial factor in maintaining the C:N ratio in the ecosystem as a whole. 57 refs., 1 fig., 3 tabs.

Zanetti, S.; Hartwig, U.A.; Luescher, A. [Swiss Federal Institute of Technology, Zurich (Switzerland)] [and others

1996-10-01

318

Long-term resistance to simulated climate change in an infertile grassland  

PubMed Central

Climate shifts over this century are widely expected to alter the structure and functioning of temperate plant communities. However, long-term climate experiments in natural vegetation are rare and largely confined to systems with the capacity for rapid compositional change. In unproductive, grazed grassland at Buxton in northern England (U.K.), one of the longest running experimental manipulations of temperature and rainfall reveals vegetation highly resistant to climate shifts maintained over 13 yr. Here we document this resistance in the form of: (i) constancy in the relative abundance of growth forms and maintained dominance by long-lived, slow-growing grasses, sedges, and small forbs; (ii) immediate but minor shifts in the abundance of several species that have remained stable over the course of the experiment; (iii) no change in productivity in response to climate treatments with the exception of reduction from chronic summer drought; and (iv) only minor species losses in response to drought and winter heating. Overall, compositional changes induced by 13-yr exposure to climate regime change were less than short-term fluctuations in species abundances driven by interannual climate fluctuations. The lack of progressive compositional change, coupled with the long-term historical persistence of unproductive grasslands in northern England, suggests the community at Buxton possesses a stabilizing capacity that leads to long-term persistence of dominant species. Unproductive ecosystems provide a refuge for many threatened plants and animals and perform a diversity of ecosystem services. Our results support the view that changing land use and overexploitation rather than climate change per se constitute the primary threats to these fragile ecosystems. PMID:18606995

Grime, J. Philip; Fridley, Jason D.; Askew, Andrew P.; Thompson, Ken; Hodgson, John G.; Bennett, Chris R.

2008-01-01

319

Interannual Variation in Root Production in Grasslands Affected by Artificially Modified Amount of Rainfall  

PubMed Central

The effect of different amounts of rainfall on the below-ground plant biomass was studied in three grassland ecosystems. Responses of the lowland (dry Festuca grassland), highland (wet Cirsium grassland), and mountain (Nardus grassland) grasslands were studied during five years (2006–2010). A field experiment based on rainout shelters and gravity irrigation simulated three climate scenarios: rainfall reduced by 50% (dry), rainfall increased by 50% (wet), and the natural rainfall of the current growing season (ambient). The interannual variation in root increment and total below-ground biomass reflected the experimentally manipulated amount of precipitation and also the amount of current rainfall of individual years. The effect of year on these below-ground parameters was found significant in all studied grasslands. In comparison with dry Festuca grassland, better adapted to drought, submontane wet Cirsium grassland was more sensitive to the different water inputs forming rather lower amount of below-ground plant matter at reduced precipitation. PMID:22629201

Fiala, Karel; Tuma, Ivan; Holub, Petr

2012-01-01

320

Interannual variation in root production in grasslands affected by artificially modified amount of rainfall.  

PubMed

The effect of different amounts of rainfall on the below-ground plant biomass was studied in three grassland ecosystems. Responses of the lowland (dry Festuca grassland), highland (wet Cirsium grassland), and mountain (Nardus grassland) grasslands were studied during five years (2006-2010). A field experiment based on rainout shelters and gravity irrigation simulated three climate scenarios: rainfall reduced by 50% (dry), rainfall increased by 50% (wet), and the natural rainfall of the current growing season (ambient). The interannual variation in root increment and total below-ground biomass reflected the experimentally manipulated amount of precipitation and also the amount of current rainfall of individual years. The effect of year on these below-ground parameters was found significant in all studied grasslands. In comparison with dry Festuca grassland, better adapted to drought, submontane wet Cirsium grassland was more sensitive to the different water inputs forming rather lower amount of below-ground plant matter at reduced precipitation. PMID:22629201

Fiala, Karel; T?ma, Ivan; Holub, Petr

2012-01-01

321

Effects of nitrogen addition and fire on plant nitrogen use in a temperate steppe.  

PubMed

Plant nitrogen (N) use strategies have great implications for primary production and ecosystem nutrient cycling. Given the increasing atmospheric N deposition received by most of the terrestrial ecosystems, understanding the responses of plant N use would facilitate the projection of plant-mediated N cycling under global change scenarios. The effects of N deposition on plant N use would be affected by both natural and anthropogenic disturbances, such as prescribed fire in the grassland. We examined the effects of N addition (5.25 g N m(-2) yr(-1)) and prescribed fire (annual burning) on plant N concentrations and N use characters at both species and community levels in a temperate steppe of northern China. We found that N addition and fire independently affected soil N availability and plant N use traits. Nitrogen addition increased aboveground net primary productivity (ANPP), inorganic N, and N uptake, decreased N response efficiency (NRE), but did not affect biomass-weighed N concentrations at community level. Prescribed fire did not change the community level N concentrations, but largely decreased N uptake efficiency and NRE. At the species level, the effects of N addition and fire on plant N use were species-specific. The divergent responses of plant N use at community and species levels to N addition and fire highlight the importance of the hierarchical responses of plant N use at diverse biological organization levels to the alteration of soil N availability. This study will improve our understanding of the responses of plant-mediated N cycling to global change factors and ecosystem management strategies in the semiarid grasslands. PMID:24594654

Wei, Hai-Wei; Lü, Xiao-Tao; Lü, Fu-Mei; Han, Xing-Guo

2014-01-01

322

Effects of Nitrogen Addition and Fire on Plant Nitrogen Use in a Temperate Steppe  

PubMed Central

Plant nitrogen (N) use strategies have great implications for primary production and ecosystem nutrient cycling. Given the increasing atmospheric N deposition received by most of the terrestrial ecosystems, understanding the responses of plant N use would facilitate the projection of plant-mediated N cycling under global change scenarios. The effects of N deposition on plant N use would be affected by both natural and anthropogenic disturbances, such as prescribed fire in the grassland. We examined the effects of N addition (5.25 g N m?2 yr?1) and prescribed fire (annual burning) on plant N concentrations and N use characters at both species and community levels in a temperate steppe of northern China. We found that N addition and fire independently affected soil N availability and plant N use traits. Nitrogen addition increased aboveground net primary productivity (ANPP), inorganic N, and N uptake, decreased N response efficiency (NRE), but did not affect biomass-weighed N concentrations at community level. Prescribed fire did not change the community level N concentrations, but largely decreased N uptake efficiency and NRE. At the species level, the effects of N addition and fire on plant N use were species-specific. The divergent responses of plant N use at community and species levels to N addition and fire highlight the importance of the hierarchical responses of plant N use at diverse biological organization levels to the alteration of soil N availability. This study will improve our understanding of the responses of plant-mediated N cycling to global change factors and ecosystem management strategies in the semiarid grasslands. PMID:24594654

Wei, Hai-Wei; Lu, Xiao-Tao; Lu, Fu-Mei; Han, Xing-Guo

2014-01-01

323

[Evaluation of the ecosystem services of artificial landscapes in Beijing].  

PubMed

According to quantitatively evaluating and comparing the ecosystem services of artificial grassland and cultivated trees, artificial pool and constructed wetland in Beijing by the well-accepted method, it was found that the net ecological values of grassland and pool are all negative. It was suggested that cultivated trees are more beneficial than artificial grassland and constructed wetland than artificial pool. PMID:15623013

Tian, Gang; Cai, Bo-feng

2004-09-01

324

Enhancement of Carbon Sequestration in Soil in the Temperature Grasslands of Northern China by Addition of Nitrogen and Phosphorus  

PubMed Central

Increased nitrogen (N) deposition is common worldwide. Questions of where, how, and if reactive N-input influences soil carbon (C) sequestration in terrestrial ecosystems are of great concern. To explore the potential for soil C sequestration in steppe region under N and phosphorus (P) addition, we conducted a field experiment between 2006 and 2012 in the temperate grasslands of northern China. The experiment examined 6 levels of N (0–56 g N m-2 yr-1), 6 levels of P (0–12.4 g P m-2 yr-1), and a control scenario. Our results showed that addition of both N and P enhanced soil total C storage in grasslands due to significant increases of C input from litter and roots. Compared with control plots, soil organic carbon (SOC) in the 0–100 cm soil layer varied quadratically, from 156.8 to 1352.9 g C m-2 with N addition gradient (R2 = 0.99, P < 0.001); and logarithmically, from 293.6 to 788.6 g C m-2 with P addition gradient (R2 = 0.56, P = 0.087). Soil inorganic carbon (SIC) decreased quadratically with N addition. The net C sequestration on grassland (including plant, roots, SIC, and SOC) increased linearly from -128.6 to 729.0 g C m-2 under N addition (R2 = 0.72, P = 0.023); and increased logarithmically, from 248.5 to 698 g C m-2under P addition (R2 = 0.82, P = 0.014). Our study implies that N addition has complex effects on soil carbon dynamics, and future studies of soil C sequestration on grasslands should include evaluations of both SOC and SIC under various scenarios. PMID:24130863

He, Nianpeng; Yu, Qiang; Wang, Ruomeng; Zhang, Yunhai; Gao, Yang; Yu, Guirui

2013-01-01

325

The recovery of ant communities in regenerating temperate conifer forests  

Microsoft Academic Search

Although ants perform many critical functions in forested ecosystems, little is known about how they respond to timber harvesting, especially in temperate systems. We examined ground-foraging ant communities and 11 forest characteristics in temperate conifer forests of southwestern Oregon, USA that ranged in age from 5 to 427 years. Seven forest characteristics were related to stand age and were summarized

Jennifer D. Palladini; Maureen G. Jones; Nathan J. Sanders; Erik S. Jules

2007-01-01

326

Air Pollution and Acid Rain, Report No. 7. Effects of air pollution and acid rain on fish, wildlife, and their habitats: grasslands  

Microsoft Academic Search

This report on grassland ecosystems is part of a series synthesizing the results of scientific research related to the effects of air pollution and acid deposition on fish and wildlife resources. General aspects of grassland ecosystems relevant to a discussion of air pollution effects are presented along with a brief introduction to various other types of ecosystem stresses. The bulk

1982-01-01

327

Restoring biopedturbation in grasslands with anthropogenic focal disturbance  

Microsoft Academic Search

Grassland ecosystems evolved with natural disturbance events on multiple spatial scales in which focal, fine-scale soil disturbance\\u000a by animals often was imbedded within large-scale grazing disturbance. The resulting plant communities adapted to both broad-scale\\u000a and fine-scale disturbance that resulted in species-rich plant communities. These natural disturbance regimes have been largely\\u000a replaced by anthropogenic disturbance. While we generally understand grassland response

Ryan F. Limb; David M. Engle; Terrence G. Bidwell; Donald P. Althoff; Alan B. Anderson; Philip S. Gipson; Heidi R. Howard

2010-01-01

328

Fire and grazing differentially affect aerial biomass and species composition in Andean grasslands  

Microsoft Academic Search

Grazing and fire have been the most common disturbances in many grasslands ecosystems for many centuries. However, some mountain regions are currently experiencing a decrease in land use, and therefore in frequency or intensity of these disturbances. In this study, we evaluated how fire and grazing affect vegetation structure in mountain grasslands of NW Argentina. We hypothesized that they would

Julieta Carilla; Roxana Aragón; Diego E. Gurvich

2011-01-01

329

How Useful are Ant Assemblages for Monitoring Habitat Disturbance on Grasslands in South Eastern Australia?  

Microsoft Academic Search

Native grasslands are one of the most endangered ecosystems in south eastern Australia. Conservation of grassland remnants and development of effective indicator groups to monitor their quality is a high priority. Recent surveys of epigaeic invertebrates have revealed several candidate groups for this. Ants are a popular focal group for invertebrate surveys in the region. The ant species richness and

T. R. New

2000-01-01

330

CONTINGENCY OF GRASSLAND RESTORATION ON YEAR, SITE, AND COMPETITION FROM INTRODUCED GRASSES  

Microsoft Academic Search

Semiarid ecosystems such as grasslands are characterized by high temporal variability in abiotic factors, which has led to suggestions that management actions may be more effective in some years than others. Here we examine this hypothesis in the context of grassland restoration, which faces two major obstacles: the contingency of native grass establishment on unpredictable precipitation, and competition from introduced

Jonathan D. Bakker; Scott D. Wilson; Janice M. Christian; Xingdong Li; Laura G. Ambrose; John Waddington

2003-01-01

331

REPRODUCTIVE SUCCESS OF CHESTNUT-COLLARED LONGSPURS IN NATIVE AND EXOTIC GRASSLAND  

Microsoft Academic Search

Habitat loss and fragmentation have been identified as important factors in the decline of grassland bird populations. However, population declines are apparent even in prairie ecosystems that remain relatively intact suggesting that additional factors are involved. The degradation of breeding habitat may be one such factor, but few studies have examined habitat- specific demography of grassland birds, and thus little

John D. Lloyd; Thomas E. Martin

2005-01-01

332

Land-use intensity modifies spatial distribution and function of soil microorganisms in grasslands  

Microsoft Academic Search

The aim of the present study was to investigate whether land-use intensity (LUI) contributes to spatial variation in microbial abundance and function in grassland ecosystems. At one time point, three sites at low (unfertilized pastures), at intermediate (fertilized mown pastures) and at high (fertilized mown meadows) LUIs were selected in southern Germany. Within each of these nine grassland sites, 54

Doreen Berner; Sven Marhan; Daniel Keil; Christian Poll; André Schützenmeister; Hans-Peter Piepho; Ellen Kandeler

2011-01-01

333

Productivity responses to altered rainfall patterns in a C 4 -dominated grassland  

Microsoft Academic Search

Rainfall variability is a key driver of ecosystem structure and function in grasslands worldwide. Changes in rainfall patterns predicted by global climate models for the central United States are expected to cause lower and increasingly variable soil water availability, which may impact net primary production and plant species composition in native Great Plains grasslands. We experimentally altered the timing and

Philip A. Fay; Jonathan D. Carlisle; Alan K. Knapp; John M. Blair; Scott L. Collins

2003-01-01

334

Rapid transfer of photosynthetic carbon through the plant-soil system in differently managed grasslands  

Microsoft Academic Search

Plant-soil interactions are central to short-term carbon (C) cycling through the rapid transfer of recently assimilated C from plant roots to soil biota. In grassland ecosystems, changes in C cycling are likely to be influenced by land use and management that changes vegetation and the associated soil microbial communities. Here we tested whether changes in grassland vegetation composition resulting from

G. B. de Deyn; H. Quirk; S. Oakley; N. J. Ostle; R. D. Bardgett

2011-01-01

335

Ceballos, G., List, R., Davidson, A., Fredrickson, E.L., Sierra Corona, R., Martinez, L., Herrick, J.E., Pacheco, J. 2009. Grassland in the Borderlands. Understanding coupled  

E-print Network

., Herrick, J.E., Pacheco, J. 2009. Grassland in the Borderlands. Understanding coupled natural-human systems of Arizona Press. p. 188-203. Chapter 12 Grasslands in the borderlands: understanding coupled human, Rodrigo Sierra, Lourdes Martínez, Jeff E. Herrick and Jesús Pacheco In a Nutshell Grassland ecosystems

336

The effect of sulfur and nitrogen additions on nutrient cycling and vegetative cover composition in sandplain grassland restoration plots in Edgartown, MA  

E-print Network

in sandplain grassland restoration plots in Edgartown, MA Fiona Jevon Harvard University Mentor: Chris Neill Ecosystems Center, Marine Biological Laboratories December 19th , 2011 #12;Abstract Sandplain grasslands to be dominated by non-native vegetation. One theory for restoring these systems to native sandplain grassland

Vallino, Joseph J.

337

Residual Characteristics of Picloram In Grassland Ecosystems.  

E-print Network

(Acacia farnesiana (L.) Willd.) (15). A portion of the picloram could be replaced wit11 2,4,5-T and huisache control maintained if 1 pound per acre of each herbicide was applied. Picloram, applied to the soil in granular or pelleted form, controlled...) (Opuntia spp.) Yaupon (Ilex vomitmia Ait.) Whitebrush (Aloysia lycioides Cham.) Blackbrush (Acacia rigidula Benth.) Huisache (Acacia farnesiana (L.) Willd.) Mixed hardwoods Texas persimmon (Diosyfiros texana Scheele) Spiney hackberry (granjeno...

Bovey, R. W.; Scifres, C. J.

1971-01-01

338

[Impacts of Ochotona pallasi disturbance on alpine grassland community characteristics].  

PubMed

Plateau pika is the main fossorial mammal in the alpine grassland in Qinghai Lake Watershed of Northwest China. Based on the field investigation data from 18 alpine grassland quadrats in the Watershed, and by using redundancy analysis (RDA) and the surface fitting offered by 'R-Vegan' , the disturbance intensity of plateau pika (Ochotona pallasi) was classified as four levels. In order to explore the impacts of plateau pika disturbance on the alpine grassland ecosystem and its grazing quality, the community characteristics under different disturbance intensities by plateau pika were analyzed, and a conceptual model about the alpine grassland community succession was proposed. The results showed that with the increase of the disturbance intensity, the dominant species changed from Juncus roemerianus to Poa pratensis and Laux maritima. When the disturbance was small, the community had high quantitative values of coverage, aboveground biomass, biodiversity, and species richness, but the proportion of weeds was also high. When the disturbance was large, the quantitative values were the lowest, while the proportion of weeds was the highest. When the disturbance was moderate, the community had relatively high quantitative values, and the proportion of grasses and sedges was the highest. It was concluded that the community' s characteristic values under low plateau pika disturbance intensity were high but the grazing quality was low, while high disturbance intensity resulted in the grassland degradation. Therefore, the disturbance intensity in the threshold could maintain the stability of alpine grassland ecosystem and improve its grazing quality. PMID:24380328

Zhao, Guo-qin; Li, Guang-yong; Ma, Wen-hu; Zhao, Dian-zhi; Li, Xiao-yan

2013-08-01

339

Effects of grassland succession on communities of small mammals in Illinois, USA  

Microsoft Academic Search

Native grasslands are among the most imperiled of the North American ecosystems, with only ?4% of their pre-settlement area\\u000a remaining, but some grassland habitats are being restored and maintained through such methods as prescribed burning and mowing,\\u000a which may provide habitat for animal species endemic to this ecosystem. I determined how succession of the plant community,\\u000a due to a four-year

Matthew L. Richardson

2010-01-01

340

Conversion of cropland to grassland: increasing or decreasing soil organic carbon?  

NASA Astrophysics Data System (ADS)

Conversion of cropland to permanent grassland is often expected to sequester atmospheric CO2 by increasing soil organic carbon (SOC) stocks. We investigated this possibility under realistic management conditions on the field scale. We compared the development of the carbon (C) balance and SOC stocks of intensively (high nitrogen input and frequent cutting) and extensively (no nitrogen input, infrequent cutting) managed grassland after conversion from an arable rotation. The study was carried out at a site in the northern lowlands of Switzerland with a temperate climate and a soil classified as Eutri-Stagnic Cambisol. As a first approach, C balance was assessed by measuring C fluxes in and out of the ecosystem including net CO2 exchange by eddy flux measurements, as well as C import by organic fertilizer and C export by harvest. In a second approach, SOC stocks (0-45 cm depth) were quantified at the beginning (2001) and at the end (2006) of a 5-year observational period. An equivalent soil mass of 500 kg m-2 was sampled. Results showed very similar SOC stocks in 2001 of 13-14 kg C m-2 for the intensive and extensive field. Over the 5-year period, the observed mean annual increase for the intensive field was small and not significant, whereas for the extensive field a significant decrease of 0.22 kg C m-2 yr-1 was found. The other approach (flux budget) also indicated a generally positive carbon balance (C accumulation) for the intensive field and a negative balance (C loss) for the extensive field, with substantial inter-annual variations in relation to growing season length and soil moisture. Both, stock and flux measurements, revealed a consistent difference between the C balance of the two management types (about 0.25 kg C m-2 yr-1), which also appeared in simulations with the mechanistic grassland model PROGRASS. However, absolute values for the C balance differed between the two experimental approaches. The flux measurements indicated higher gains to the intensive management, whereas the stock approach suggested larger losses due to extensive management. It can be concluded that without continuous nitrogen input, the conversion from arable rotation to permanent grassland may cause a considerable loss of SOC due to increased soil organic matter decomposition.

Ammann, Christof; Leifeld, Jens; Calanca, Pierluigi; Neftel, Albrecht; Fuhrer, Jürg

2010-05-01

341

Soil Warming and Carbon Release: Varying Patterns of Organic Matter Breakdown Across Five Ecosystems  

NASA Astrophysics Data System (ADS)

Our understanding of the mechanisms governing soil organic carbon (SOC) retention vs. loss as CO2 in the future suffers from an inability to predict how mineralization of labile vs. recalcitrant SOC will proceed with warming. Incubation and field studies of soil warming have resulted in conflicting conclusions about how multiple SOC pools will respond to rising temperatures. In this study, we explore SOC transformations in a long-term incubation with warming from five North American ecosystems by assessing respired CO2 and solid state 13C nuclear magnetic resonance (NMR) spectra of non-incubated and cool vs. warm incubated soils. We also quantified extra-cellular enzyme activities (EEA) late in the incubation to assess how relatively slow-turnover SOC pools responded to warming. Soils from a cool temperate forest, a warm temperate forest, and a temperate grassland released an average of 95% more CO2 when warmed by the end of the 200 d incubation. Soils from a boreal forest and acidic arctic tundra released slightly more CO2 with warming during the first 20 d of the incubation, but after day 20 and until day 200 CO2 released by warmed soils was equivalent to the control soils. NMR spectra and EEA data suggest varying responses of these ecosystems' SOC pools to warming. Arctic tundra soils did not experience a change in the kinds of C compounds mineralized with warming, yet EEA data indicate greater acquisition of C from phenolic compounds. Boreal forest soil NMR spectra suggest greater net humification with warming, with only slight increases in enzymatic C acquisition. These soils may have experienced an increase in C use efficiency with warming that resulted in acquired C not being "wasted" on respiration. Cool temperate forest soils exhibited no change in the kinds of C accessed by microbes with warming, as revealed via NMR, in spite of these soils' greater C acquisition and respiration with warming. Grassland soils experienced an increase in humification with warming, associated with an increase in CO2 released. Warm temperate forest soils, in contrast, exhibited less humification with warming. These data suggest that changing microbial C use efficiency with warming is an important and relatively unexplored determinant governing the net influence of warming on SOC transformations and eventual CO2 release.

Billings, S. A.; Barich, D.; Munson, E.

2008-12-01

342

Restoring Native Grasslands  

E-print Network

Much of Texas' native grasslands has been converted to improved pastures and cropland, neither of which is suitable for wildlife habitat. Now, many landowners are interested in restoring native grasses because they are cheaper to produce for forage...

Hays, K. Brian; Wagner, Matthew; Smeins, Fred; Wilkins, Neal

2005-03-23

343

Soil organic carbon dynamics in the forest-grassland limit.  

NASA Astrophysics Data System (ADS)

An upward shift of the treeline at the extent of former grasslands has been observed in the last decades in several regions along the world. Implications of the land use change from grasslands to forests are not clear yet in regard to soil organic carbon stocks, greenhouse gas fluxes and composition of the soil organic matter. In order to investigate the consequences of forest expansion at the regional scale, an extensive grassland—forest comparison was conducted at the altitudinal limit of the forest. We considered two contrasting geographical areas: one Mediterranean -The Sistema Central in Spain- and one temperate area -the Austrian Alps-. Ten and seven sites were investigated, respectively. At each of the sites, the forest floor and the topsoil was sampled in grasslands and adjacent coniferous forest areas. Mineral soils were incubated for 6 months in the laboratory under standardized conditions and both bulk concentration and the isotopic signature of soil organic carbon and nitrogen were determined across the study sites. Grasslands were not consistently different from forests in terms of soil organic carbon concentrations and cumulative soil carbon dioxide effluxes. However, soil C:N ratio was significantly narrower in grasslands than in forests, and this results was consistent for both Spanish and Austrian sites. Isotopic signature of C and N resulted to be significantly different between grasslands and forests for Spanish soils, only, suggesting a combined influence of land use change and climate. In Spain, grasslands soils were enriched in 15N but depleted in 13C as compared to forests soils. Interestingly, mean temperature negatively influenced C concentrations in Spanish grasslands, but had no clear effect on forests. Our results did not show a clear trend of net soil organic carbon gain or loss due to forest expansion, but rather a change in the characteristics of the soil mineralization conditions after vegetation shifted. Changes in transformation processes and therefore in the soil organic matter were dynamically modulated by the aboveground vegetation, but also by the climate. In addition, influence of climate under mediterranean conditions seemed to be more determinant than in temperate, continental environments.

Díaz-Pinés, Eugenio; Vázquez, Eduardo; Ortiz, Carlos; Schindlbacher, Andreas; Jandl, Robert; Kiese, Ralf; Butterbach-Bahl, Klaus; Benito, Marta; Rubio, Agustin

2014-05-01

344

Linkages between land Cover, enzymes, and soil organic matter chemistry following encroachment of leguminous woody plant into grasslands  

NASA Astrophysics Data System (ADS)

In the Rio Grande Plains of southern Texas, subtropical thorn woodlands dominated by the N-fixing tree Prosopis glandulosa have largely replaced native grasslands over the last 150 years as a result of fire suppression and over grazing. This land cover change has resulted in the increase of belowground stocks of C, N, and P, changes to the amount and chemical nature of soil-stabilized plant biopolymers, and the composition and activity of soil microbes. Given that extracellular enzymes produced by plants and microbes are the principal means by which complex compounds are degraded and the production of such enzymes is triggered or suppressed by changes in primary input and nutrient availability we sought to relate how these fundamental changes in this ecosystem are reflected in the activity of soil stabilized extracellular enzymes and soil organic matter (SOM) chemistry in this system. We focused upon a successional chronosequence from C4-dominant grassland to woody patches of up to 86 yrs age since mesquite establishment. We related the molecular composition and concentration of hydrolysable amino acids and amino sugars, as well as CuO extractable lignin and substituted fatty acid to the potential activities of five extracellular enzymes (arylamidase, acid phosphatase, ?-glucosidase, ?-glucosaminidase (NAGase, polyphenoloxidase (PPO)) and a general marker for hydrolytic activity, fluorescein diacetate (FDA). Each of these enzymes, with the exception of PPO, showed higher potential activity in soils from woody clusters than grasslands and had activities generally well correlated to carbon content. PPO, often defined as a proxy for microbial lignin decay activity, showed no statistical difference between grassland and forest sites and no significant relationship to soil C content. Yields of total amino acids and amino sugars all show increases in content with cluster age when normalized to soil mass, as did the enzyme activities targeted to their decomposition, but only weak trends with age when normalized to carbon content. Although, PPO was nearly invariant across the chronosequence, lignin content rose dramatically, normalized both to soil mass and to organic carbon content, indicating oxidase activity was not matched to input and lignin was selectively accruing in the below ground carbon pools. We propose that the dramatic increase in available N in the leguminous system suppressed microbial oxidase production allowing lignin to selectively accrue while microbial activity for the other plant biopolymers has nearly kept pace with input-consistent with recent findings in other temperate deciduous systems. These results have important implications for the modeling of woodland-grassland conversion and the dynamics of biogeochemical cycles in this globally significant land cover change.

Filley, T. R.; Stott, D. E.; Boutton, T. W.; Creamer, C. A.; Olk, D.

2009-12-01

345

[Experimental research on the anti-wind erosion of typical grasslands].  

PubMed

Wind erosion is one of the most important factors influencing the stability and functions of typical grassland ecosystem and one of the main reasons causing grassland degradation. In order to understand the effects of the human disturbances to the ability of anti-wind erosion of the typical grasslands, a wind tunnel experiment was made and the wind erosion rates (WER) and wind erosion amount (WEA) were selected to illustrate the effects. From the experiment, it can be found that banned-grazing reduced the WEA and the WER markedly. At the same wind speed, the longer the banned-grazing period, the less the WEA and the WER; the WEA and the WER in the grassland cultivation are more than those of the natural grasslands and the differences increase with wind speed. There exists a linear relationship between WER and the disturbance intensity. The results show that grazing and cultivation can weaken the ability of anti-wind erosion of typical grassland ecosystem, and banned-grazing can strengthen the ability. Therefore, in typical grassland areas, taking the active banned-grazing measures is the most effective approach to stop the degradation and trigger the rehabilitation of typical grassland ecosystem. PMID:16366492

Xu, Zhong-Qi; Li, Wen-Hua; Min, Qing-Wen; Ao, Qi-Er; Wang, Ying-Shun; Han, Xi; He, Xu-Sheng; He, Jun-Jie

2005-09-01

346

Long-term oscillations in grassland productivity induced by drought  

E-print Network

REPORT Long-term oscillations in grassland productivity induced by drought Nick M. Haddad,1,2 David, USA Abstract Disturbances such as drought have immediate impacts on ecosystem functioning, but little is known about long-term dynamic consequences of disturbance. Here, we show that a major drought perturbed

Minnesota, University of

347

Carbon sequestration in grasslands: grazing versus fire under climate change  

Microsoft Academic Search

We simulated different levels of grazing and frequencies of fire using the biogeochemical model DAYCENT across a climate gradient from Montana to New Mexico to look at their long-term implications on carbon sequestration in grasslands. We also used 3 future climate scenarios and 2 CO2 emission levels to estimate interactions between disturbance and climate. In all cases, total ecosystem carbon

D. M. Bachelet; R. Kelly; W. J. Parton

2009-01-01

348

Exotic Plant Invasion Alters Nitrogen Dynamics in an Arid Grassland  

Microsoft Academic Search

The introduction of nonnative plant species may decrease ecosystem stability by altering the availability of nitrogen (N) for plant growth. Invasive species can impact N availability by changing litter quantity and quality, rates of N 2-fixation, or rates of N loss. We quantified the effects of invasion by the annual grass Bromus tectorum on N cycling in an arid grassland

R. D. Evans; R. Rimer; L. Sperry; J. Belnap

2001-01-01

349

Detecting grassland spatial variation by a wavelet approach  

Microsoft Academic Search

Insight into the spatial variation of an ecosystem can provide better under- standing of ecological processes and patterns in different scales. Detecting these multiple scales of spatial variation in grassland landscapes is valuable for determining management options, designing proper sampling regimes, and selecting suitable resolutions of remote sensing products. The objective of this study is to examine how environmental factors

Yuhong He; Xulin Guo; Bing Cheng Si

2007-01-01

350

Interactions Among Grassland Plant Species, Microbial Communities, and Soil Processes  

Microsoft Academic Search

Plant-microbial interactions are thought to be an important determinant of ecosystem processes, yet we do not know whether impacts of plant species on soil microbial community composition translate to impacts on function. We established field plots in a California annual grassland of five plant monocultures for two years to determine the effects of different plant species on the composition of

V. Eviner; M. Waldrop; E. Schwartz; J. Pett-Ridge; M. Firestone

2002-01-01

351

Multisensor analysis of NDVI, surface temperature and biophysical variables at a mixed grassland site  

Microsoft Academic Search

A unique remotely sensed data set derived for a temperate mixed grassland in the central United States was used to test the comparability of a suite of satellite and aircraft sensors, and to characterize temporal variability in the normalized diÄ erence vegetation index (NDVI), retrieved surface radiant temperature (Ts), and surface biophysical variables. The temporal evolution of atmospherically corrected NDVI

S. J. GOETZ

1997-01-01

352

Response of grassland biomass production to simulated climate change and clipping along an elevation gradient.  

PubMed

Changes in rainfall and temperature regimes are altering plant productivity in grasslands worldwide, and these climate change factors are likely to interact with grassland disturbances, particularly grazing. Understanding how plant production responds to both climate change and defoliation, and how this response varies among grassland types, is important for the long-term sustainability of grasslands. For 4 years, we manipulated temperature [ambient and increased using open-top chambers (OTC)], water (ambient, reduced using rainout shelters and increased using hand watering) and defoliation (clipped, and unclipped) in three grassland types along an elevation gradient. We monitored plant cover and biomass and found that OTC reduced biomass by 15%, but clipping and water treatments interacted with each other and their effects varied in different grassland types. For example, total biomass did not decline in the higher elevation grasslands due to clipping, and water addition mitigated the effects of clipping on subordinate grasses in the lower grasslands. The response of total biomass was driven by dominant plant species while subordinate grasses and forbs showed more variable responses. Overall, our results demonstrate that biomass in the highest elevation grassland was least effected by the treatments and the response of biomass tended to be dependent on interactions between climate change treatments and defoliation. Together, the results suggest that ecosystem function of these grasslands under altered climate patterns will be dependent on site-specific management. PMID:24249117

Carlyle, Cameron N; Fraser, Lauchlan H; Turkington, Roy

2014-03-01

353

Precipitation variability and fire influence the temporal dynamics of soil CO2 efflux in an arid grassland  

E-print Network

- limited ecosystems. Keywords: carbon cycle, climate change, disturbance, extreme pulses, grasslands, net grassland R O D R I G O V A R G A S * , S C O T T L . C O L L I N S , M I C H E L L L . T H O M E Y , J E grassland 2 years before and 2 years after a lightning-caused wildfire. Soil CO2 efflux rates were always

354

Contribution of root to soil respiration and carbon balance in disturbed and undisturbed grassland communities, northeast China  

Microsoft Academic Search

Changes in the composition of plant species induced by grassland degradation may alter soil respiration rates and decrease\\u000a carbon sequestration; however, few studies in this area have been conducted. We used net primary productivity (NPP), microbial\\u000a biomass carbon (MBC), and soil organic carbon (SOC) to examine the changes in soil respiration and carbon balance in two Chinese\\u000a temperate grassland communities

Wei Wang; Jixun Guo; Takehisa Oikawa

2007-01-01

355

4, 36073638, 2007 Grassland energy  

E-print Network

BGD 4, 3607­3638, 2007 Grassland energy partitioning A. Hammerle et al. Title Page Abstract partitioning of a mountain grassland A. Hammerle, A. Haslwanter, U. Tappeiner, A. Cernusca, and G. Wohlfahrt.hammerle@uibk.ac.at) 3607 #12;BGD 4, 3607­3638, 2007 Grassland energy partitioning A. Hammerle et al. Title Page Abstract

Boyer, Edmond

356

Tempered fractional Brownian motion  

NASA Astrophysics Data System (ADS)

Tempered fractional Brownian motion (TFBM) modifies the power law kernel in the moving average representation of a fractional Brownian motion (FBM), adding an exponential tempering. It also has a harmonizable representation. The increments of TFBM are stationary, and the autocovariance of the resulting tempered fractional Gaussian noise (TFGN) has semi-long range dependence, in which the autocorrelations decay like a power law over a moderate length scale, but eventually fall off more rapidly. TFBM can be represented as the linear combination of tempered fractional derivative (or tempered fractional integral) of the indicator functions. This representation and the classical Ito isometry provides to characterize the class of all deterministic functions for which the stochastic integral with respect to TFBM is well defined. Replacing the Gaussian random measure (Brownian motion) in the moving average or harmonizable representation of TFBM by a stable random measure, a linear tempered fractional stable motion (LTFSM), or a real harmonizable tempered fractional stable motion (HTFSM), respectively. Unlike the Gaussian case, LTFSM and HTFSM are two completely different processes. Existence, basic properties, sample path behavior, and dependence structure of both processes will be described.

Sabzikar, Farzad

357

PERSISTENCE OF DESERTIFIED ECOSYSTEMS: EXPLANATIONS AND IMPLICATIONS  

EPA Science Inventory

Studies of rainfall partitioning by shrubs, responses of shrub-dominated ecosystems to herbicide treatment, and experiments using drought and supplemental rainfall were conducted to test the hypothesis that the shrub-dominated ecosystems that have replaced desert grasslands are r...

358

Persistence of desertified ecosystems: Explanations and implications  

Microsoft Academic Search

Studies of rainfall partitioning by shrubs, responses of shrub-dominated ecosystems to herbicide treatment, and experiments using drought and supplemental rainfall were conducted to test the hypothesis that the shrub-dominated ecosystems that have replaced desert grasslands are resistant and resilient to disturbance. Between 16 and 25% of the intercepted rainfall is channelized to deep soil storage by stemflow and root channelization.

Walter G. Whitford; Gustavo Martinez-Turanzas; Ernesto Martinez-Meza

1995-01-01

359

Dynamic interactions between soil animals and microorganisms in upland grassland soils amended with sheep dung: a microcosm experiment  

Microsoft Academic Search

There is presently much discussion over factors regulating soil microbial processes in grazed grassland ecosystems. We examined the relative importance of dung and soil fauna, and their interactions on microbial biomass and activity in two contrasting upland grassland soils. We found that the presence of nematodes and Collembola was associated with significant (P<0.05) increases in microbial biomass in both soil

R. D. Bardgett; S. Keiller; R. Cook; A. S. Gilburn

1998-01-01

360

Scavenging ant foraging behavior and variation in the scale of nutrient redistribution among semi-arid grasslands  

Microsoft Academic Search

The scavenging of arthropod carrion by ants can be an important mechanism of nutrient redistribution in grasslands. By removing materials to nests over different sized areas, scavenging ants may contribute to differences in ecosystem patchiness. We asked how variation in overall ant foraging activity among three desert\\/grassland Long-Term Ecological Research sites creates differences in the distances that scavenged material is

Brandon T. Bestelmeyer; John A. Wiens

2003-01-01

361

Rapid transfer of photosynthetic carbon through the plant-soil system in differently managed species-rich grasslands  

Microsoft Academic Search

Plant-soil interactions are central to short-term carbon (C) cycling through the rapid transfer of recently assimilated C from plant roots to soil biota. In grassland ecosystems, changes in C cycling are likely to be influenced by land use and management that changes vegetation and the associated soil microbial communities. Here we tested whether changes in grassland vegetation composition resulting from

G. B. de Deyn; H. Quirk; S. Oakley; N. J. Ostle; R. D. Bardgett

2011-01-01

362

Incorporating grassland management in a global vegetation model  

NASA Astrophysics Data System (ADS)

Grassland is a widespread vegetation type, covering nearly one-fifth of the world's land surface (24 million km2), and playing a significant role in the global carbon (C) cycle. Most of grasslands in Europe are cultivated to feed animals, either directly by grazing or indirectly by grass harvest (cutting). A better understanding of the C fluxes from grassland ecosystems in response to climate and management requires not only field experiments but also the aid of simulation models. ORCHIDEE process-based ecosystem model designed for large-scale applications treats grasslands as being unmanaged, where C / water fluxes are only subject to atmospheric CO2 and climate changes. Our study describes how management of grasslands is included in the ORCHIDEE, and how management affects modeled grassland-atmosphere CO2 fluxes. The new model, ORCHIDEE-GM (Grassland Management) is capable with a management module inspired from a grassland model (PaSim, version 5.0), of accounting for two grassland management practices (cutting and grazing). The evaluation of the results of ORCHIDEE-GM compared with those of ORCHIDEE at 11 European sites equipped with eddy covariance and biometric measurements, show that ORCHIDEE-GM can capture realistically the cut-induced seasonal variation in biometric variables (LAI: Leaf Area Index; AGB: Aboveground Biomass) and in CO2 fluxes (GPP: Gross Primary Productivity; TER: Total Ecosystem Respiration; and NEE: Net Ecosystem Exchange). But improvements at grazing sites are only marginal in ORCHIDEE-GM, which relates to the difficulty in accounting for continuous grazing disturbance and its induced complex animal-vegetation interactions. Both NEE and GPP on monthly to annual timescales can be better simulated in ORCHIDEE-GM than in ORCHIDEE without management. At some sites, the model-observation misfit in ORCHIDEE-GM is found to be more related to ill-constrained parameter values than to model structure. Additionally, ORCHIDEE-GM is able to simulate forage yield, herbage consumption, animal products (e.g. milk), animal respiration and animal CH4 emissions. These new variables combined with organic C fertilizer applied on the field could provide a more complete view of grasslands C fluxes for applications of the model on a grid. The 11 site simulations of this study show that European grasslands generally are C sinks (positive NBP). At grazed grasslands, both C export in the form of milk production and CH4 emissions by animals only consist a minor part of net primary production (NPP), and this means that NBP mainly depends on NPP. On the contrary, the cut sites accumulate less C in soils because a large part of NPP has been exported as forage production. Furthermore, theoretically potential of productivity and livestock density in European grassland can be predicted by ORCHIDEE-GM, based on the strategy modeling of the optimal livestock density and management change.

Chang, Jinfeng; Viovy, Nicolas; Vuichard, Nicolas; Ciais, Philippe; Wang, Tao; Cozic, Anne; Lardy, Romain; Graux, Anne-Isabelle; Klumpp, Katja; Martin, Raphael; Soussana, Jean-François

2013-04-01

363

The nest predator community of grassland birds responds to agroecosystem habitat at multiple scales  

E-print Network

. The tallgrass prairie biome of the North American Great Plains is a critically endangered ecosystem, with B2% of the native ecosystem remaining (Noss et al. 1995, Hoekstra et al. 2005). Remaining grassland fragments latrans, and garter snakes Thamnophis spp., which add to predation pressure from predators, such as ground

McCarty, John P.

364

An Assessment of Grazing Effects on Soil Carbon Stocks in Grasslands Gervasio Pin~eiro,1  

E-print Network

An Assessment of Grazing Effects on Soil Carbon Stocks in Grasslands Gervasio Pin~eiro,1 Jose´ M. Abstract Grazing; modifies the structure and function of ecosystems, affecting soil organic carbon (SOC) storage. Although grazing effects on some ecosystem

Nacional de San Luis, Universidad

365

Impact of spring drought on ecosystem carbon and water dynamics in Switzerland  

NASA Astrophysics Data System (ADS)

Europe has experienced a number of exceptional weather events such as severe droughts and heat spells (2003 & 2010), disastrous flood events (2002 & 2005), and severe storms with wind throw (1999 & 2005) during the past decade that heavily disturbed the carbon and water balance of terrestrial ecosystems. For the future, regional climate models have predicted more intense and frequent extreme events. Up to date, our knowledge about the changes in ecosystem carbon and water dynamics in response to such extreme events is still limited. In Switzerland, the recent spring 2011 was the warmest and driest since start of meteorological measurements in 1864, following an exceptionally dry winter. This combination resulted in a pronounced spring drought - particularly during the months March and April - with severe effects on ecosystems phenology, agricultural production and water supply. We synthesize data from the regional eddy covariance network Swiss FluxNet to assess the impact of this extreme weather event on ecosystem carbon dioxide and water vapour fluxes. Swiss FluxNet integrates the major plant functional types of deciduous and coniferous forest, grassland and cropland across elevation gradients in Switzerland. The objectives of our synthesis study are to assess (1) the range and magnitude of ecosystem fluxes, (2) daily and monthly carbon and water budgets, (3) the phenological development of vegetation compared to average years, and (4) potential carry-over effects (hysteresis) during and following the spring drought 2011 in Switzerland. The results will present the first synthesis study of the regional network Swiss FluxNet and provide an improved understanding of the ecosystem response to spring drought in temperate and alpine climates. We will finally discuss the implications of our results for ecosystem management and for further regional synthesis studies.

Wolf, S.; Merbold, L.; Eugster, W.; Lehner, I.; Ammann, C.; Buchmann, N.

2011-12-01

366

The Impact of Climate Variability on the Wildfire Behaviour of Distinct Land Ecosystems  

NASA Astrophysics Data System (ADS)

The objective of our research is to investigate the impact of climate variability on geographic, ecological, seasonal and inter-annual distributions and magnitudes of biomass burning and on the correspondent quantity and quality of pyrogenic emissions, across a variety of ecosystems. With this purpose, we used 10 years of monthly, 1°x1° gridded burnt fraction and pyrogenic emissions data, from the Global Fire Emissions Database version 2 (GFEDv2), together with land-cover data, from the Goddard Institute of Space Studies (GISS), and with climate data from ECMWF reanalyses, the Global Precipitation Climatology Project (GPCP) and the Global Hydrology Resource Centre (GHRC). Knowledge about the ecosystems -- climatology, topography, orography, vegetation species and structure -- did not influence the statistical analyses themselves, which relied only on data for 1°x1° resolution pixels, but it was used before and after, first to choose eco-regions (ecosystems within geographical regions) with a reasonable ecological, geographic and climatic homogeneity, and then to draw conclusions and explanations. Overall, the climate parameters that showed significant statistical relationships with burnt area (absolute rank-correlations above 70%), in more eco-regions, were air and soil temperature, humidity, rainfall, wind and lightning density, and also precipitation and snow cover up to 6 months preceeding the fire season. The most extreme cases of inter-annual variability occurred in equatorial rainforests. These ecosystems rarely burn, since they are sparsely populated and lightning strikes are almost always simultaneous with rain, but, when fires do occur, like during ENSO related droughts, a great quantity of carbon is released to the atmosphere, because of the rainforests rich content in fuel loads. Monsoon moist-deciduous forests also became very prone to fires, in years when the onset of the rainy season was delayed. Earlier snow melt and/or diminished winter precipitation appeared associated with larger burnt areas during the fire season in northern temperate forests. The world ecosystems with more wildfires were grasslands and tropical/ subtropical drought-deciduous woodlands and shrublands. In subtropical shrublands and grasslands, fires tended to repeat the same behaviour year after year, with shrubs and grass growing quickly during the wet summer season, particularly with positive anomalies of relative humidity and rainfall, and then burning easily during the dry winter season, specially with positive temperature anomalies and fast winds. The strongest positive rank-correlations between wildfires and air or soil temperature (above +0.8) were found in African grasslands with 10-40% wood cover. The strongest negative rank-correlations with air humidity and rainfall (below -0.7) were also found mostly in African ecosystems: grasslands, tropical rainforests, tropical/ subtropical evergreen broad-leaved forests, evergreen sclerophyllous woodlands, tropical/ subtropical drought-deciduous forests and woodlands and xeromorphic shrublands. In African tropical regions, burnt area was negatively rank-correlated (below -0.75) with lightning, because thunderstorms are usually followed by convective rain; in subtropical regions, where many lightning strikes occur during dry weather, rank-correlations became positive, albeit weakly (below +0.4). It was also in Africa that burnt area was more strongly positively linked with fast winds: in tropical/ subtropical drought-deciduous woodlands (above +0.8) and in grasslands and shrublands (above +0.6). Relative humidity was generally found to be the most useful predictor of wildfire activity, but good statistical models with humidity as the predictor (correlations above 80% between real and predicted burnt area and residuals normally distributed) were found almost exclusively in grasslands and shrublands, especially in Africa, where fire behaviour was more regular. In forests and woodlands, where wildfires had more irregular patterns, and fire return periods were larger, there were not enou

Viegas, L.; Stevenson, D.; Merchant, C.

2009-04-01

367

Plants reverse warming effect on ecosystem water balance  

E-print Network

that global warming may increase aridity in water- limited ecosystems by accelerating evapotranspiration. WePlants reverse warming effect on ecosystem water balance Erika S. Zavaleta* , Brian D. Thomas show that interactions between warming and the dominant biota in a grassland ecosystem produced

Zavaleta, Erika

368

Eddy covariance based carbon fluxes from differently grazed grassland in Inner Mongolia, China  

NASA Astrophysics Data System (ADS)

Grasslands are one of the dominating vegetation types in the world. In China grasslands capture 400 Mha. This huge area has great influence on water and carbon stocks and fluxes. Water and carbon exchange influence the local concentration of greenhouse gases. In the steppe of Inner Mongolia (China) problems exist of overgrazing, erosion and ongoing desertification. Through these processes the seasonal patterns of the carbon cycles are changed. Within the project MAGIM (Matter fluxes in grasslands of Inner Mongolia as influenced by stocking rate), which is a multidisciplinary project bringing together German and Chinese expertise, fluxes of CO2 and H2O were measured by the eddy covariance (EC) method. The study site is in the Xilin River catchment in the Northeast of Inner Mongolia Autonomous Region, China. The region is a continental temperate semiarid zone with cold dry winters and warm humid summers. The annual mean temperature is about 2 °C and the annual precipitation is 350 mm. The EC measurements at Leymus chinensis steppe include various grazing intensities (heavily grazed, continuously grazed, winter grazed, ungrazed since 1979) by one permanent and one roving tower. From 2004 to 2006, there were continuous measurements at the ungrazed site (Leymus chinensis). The roving tower was used in the vegetation period at the grazed sites. In general, carbon fluxes are small in Inner Mongolia: At the ungrazed site an average negative net ecosystem exchange NEE was observed of -0.13 g C m-2 d-1 (C sink) over all observations from 2004 to 2006. During roving periods only, ungrazed was C neutral, but the heavily grazed site showed a positive NEE of 0.48 g C m-2 s-1 (C source). The intermediately grazed sites switched from CO2 sink to source. Lack of precipitation reduced the CO2 sink or increased the CO2 source. So, precipitation and its seasonal pattern are the major drivers controlling the atmospheric fluxes. Temperature and soil moisture, as drivers of respiration, had additional influence. We assume that the steppe in Inner Mongolia will be a CO2 source in a changed climate characterized by increased temperatures and higher precipitation.

Vetter, Sylvia; Ketzer, Bettina; Bernhofer, Christian

2010-05-01

369

The amplifying effects of humans on fire regimes in temperate rainforests in western Patagonia  

Microsoft Academic Search

During European colonization and settlement of southern hemisphere temperate ecosystems, historical fire regimes were often dramatically altered by either burning vast areas to create farmland, or reducing fire frequencies by suppressing fires or by eliminating aboriginal populations that formerly set fires. To determine the historical range of variability of wildfire and the potential human influences on wildfire activity in temperate

Andrés Holz; Thomas T. Veblen

2011-01-01

370

Earth on Edge : Ecosystems  

NSDL National Science Digital Library

This site provides information about the six ecosystems on which life on Earth most heavily depends: agricultural, forest, freshwater, grassland, coastal, and urban. It is part of a Public Broadcasting System (PBS) project, which includes a discussion guide. Ecosystems are described as communities of interacting organisms and the physical environment in which they live. The goods and services that ecosystems provide are said to form the foundation of human economies. Ecosystems purify air and water, help to control climate, and produce valuable soil-services. Site users may access a discussion guide to accompany the broadcast of the video/television program, which can be used in colleges, secondary schools, and in community groups. Case studies are taken from the companion book, World Resources 2000-2001: Ecosystems and People: The Fraying Web of Life, and from Pilot Analysis of Global Ecosystems: Agroecosystems (World Resources Institute). This online text includes profiles, case studies, and ecosystem assessments with references to ecosystems around the world. A list of additional resources includes links to environmental organizations, books, and periodicals.

Mock, Gregory; Vanasselt, Wendy

2000-01-01

371

Impacts of tree rows on grassland birds and potential nest predators: a removal experiment.  

PubMed

Globally, grasslands and the wildlife that inhabit them are widely imperiled. Encroachment by shrubs and trees has widely impacted grasslands in the past 150 years. In North America, most grassland birds avoid nesting near woody vegetation. Because woody vegetation fragments grasslands and potential nest predator diversity and abundance is often greater along wooded edge and grassland transitions, we measured the impacts of removing rows of trees and shrubs that intersected grasslands on potential nest predators and the three most abundant grassland bird species (Henslow's sparrow [Ammodramus henslowii], Eastern meadowlark [Sturnella magna], and bobolink [Dolichonyx oryzivorus]) at sites in Wisconsin, U.S.A. We monitored 3 control and 3 treatment sites, for 1 yr prior to and 3 yr after tree row removal at the treatment sites. Grassland bird densities increased (2-4 times for bobolink and Henslow's sparrow) and nesting densities increased (all 3 species) in the removal areas compared to control areas. After removals, Henslow's sparrows nested within ?50 m of the treatment area, where they did not occur when tree rows were present. Most dramatically, activity by woodland-associated predators nearly ceased (nine-fold decrease for raccoon [Procyon lotor]) at the removals and grassland predators increased (up to 27 times activity for thirteen-lined ground squirrel [Ictidomys tridecemlineatus]). Nest success did not increase, likely reflecting the increase in grassland predators. However, more nests were attempted by all 3 species (175 versus 116) and the number of successful nests for bobolinks and Henslow's sparrows increased. Because of gains in habitat, increased use by birds, greater production of young, and the effective removal of woodland-associated predators, tree row removal, where appropriate based on the predator community, can be a beneficial management action for conserving grassland birds and improving fragmented and degraded grassland ecosystems. PMID:23565144

Ellison, Kevin S; Ribic, Christine A; Sample, David W; Fawcett, Megan J; Dadisman, John D

2013-01-01

372

Habitat and landscape associations of breeding birds in native and restored grasslands  

USGS Publications Warehouse

In the midwestern United States, less than 1% of the original tallgrass prairie ecosystem remains. State and federal agencies have responded to this habitat loss with programs and land acquisition that have increased the amount of grassland on the landscape by restoring grassland from other land-use practices. We assessed the effects of habitat restoration and the relative contribution of local habitat and landscape factors on breeding grassland birds in northern Iowa. During the 1999 and 2000 breeding seasons, we surveyed grassland birds in 10 tallgrass prairies and 10 restored grasslands that contained a wide diversity of habitat and landscape conditions. Densities of common bird species were similar between habitat types, except for grasshopper sparrows (Ammodramus savannarum) and savannah sparrows (Passerculus sandwichensis), which were 4 and 9 times more dense in restored grasslands, respectively. Species richness of breeding birds was similar between habitat types. Habitat structure was different in prairies and restored grasslands; restored grasslands had 7% less total vegetation cover and 3% more bare ground. A nested, multiscale analysis indicated that habitat structure explained some variation in species richness and bird density of all common species, yet addition of landscape structure improved models for species richness and for density of 4 of 8 species considered, explaining an additional 10-29% of the variation. Edge-density metrics were the most common variables entering into landscape models; most species had lower densities in landscapes with high edge density. Our results indicate that restored grassland habitats contain bird communities generally similar to those in native prairie habitats in northern Iowa, suggesting that restored grasslands may provide similar habitat suitability for most grassland birds. In addition, both local habitat and landscape factors can be important for managing breeding grassland birds.

Fletcher, Jr. , R. J.; Koford, R. R.

2002-01-01

373

Impacts of Tree Rows on Grassland Birds and Potential Nest Predators: A Removal Experiment  

PubMed Central

Globally, grasslands and the wildlife that inhabit them are widely imperiled. Encroachment by shrubs and trees has widely impacted grasslands in the past 150 years. In North America, most grassland birds avoid nesting near woody vegetation. Because woody vegetation fragments grasslands and potential nest predator diversity and abundance is often greater along wooded edge and grassland transitions, we measured the impacts of removing rows of trees and shrubs that intersected grasslands on potential nest predators and the three most abundant grassland bird species (Henslow’s sparrow [Ammodramus henslowii], Eastern meadowlark [Sturnella magna], and bobolink [Dolichonyx oryzivorus]) at sites in Wisconsin, U.S.A. We monitored 3 control and 3 treatment sites, for 1 yr prior to and 3 yr after tree row removal at the treatment sites. Grassland bird densities increased (2–4 times for bobolink and Henslow’s sparrow) and nesting densities increased (all 3 species) in the removal areas compared to control areas. After removals, Henslow’s sparrows nested within ?50 m of the treatment area, where they did not occur when tree rows were present. Most dramatically, activity by woodland-associated predators nearly ceased (nine-fold decrease for raccoon [Procyon lotor]) at the removals and grassland predators increased (up to 27 times activity for thirteen-lined ground squirrel [Ictidomys tridecemlineatus]). Nest success did not increase, likely reflecting the increase in grassland predators. However, more nests were attempted by all 3 species (175 versus 116) and the number of successful nests for bobolinks and Henslow’s sparrows increased. Because of gains in habitat, increased use by birds, greater production of young, and the effective removal of woodland-associated predators, tree row removal, where appropriate based on the predator community, can be a beneficial management action for conserving grassland birds and improving fragmented and degraded grassland ecosystems. PMID:23565144

Ellison, Kevin S.; Ribic, Christine A.; Sample, David W.; Fawcett, Megan J.; Dadisman, John D.

2013-01-01

374

Model-data fusion across ecosystems: from multi-site optimizations to global simulations  

NASA Astrophysics Data System (ADS)

This study uses a variational data assimilation framework to simultaneously constrain a global ecosystem model with eddy covariance measurements of daily net carbon (NEE) and latent heat (LE) fluxes from a large number of sites grouped in seven plant functional types (PFTs). It is an attempt to bridge the gap between the numerous site-specific parameter optimization works found in the literature and the generic parameterization used by most land surface models within each PFT. The present multi-site approach allows deriving PFT-generic sets of optimized parameters enhancing the agreement between measured and simulated fluxes at most of the sites considered, with performances often comparable to those of the corresponding site-specific optimizations. Besides reducing the PFT-averaged model-data root-mean-square difference (RMSD) and the associated daily output uncertainty, the optimization improves the simulated CO2 balance at tropical and temperate forests sites. The major site-level NEE adjustments at the seasonal scale are: reduced amplitude in C3 grasslands and boreal forests, increased seasonality in temperate evergreen forests, and better model-data phasing in temperate deciduous broadleaf forests. Conversely, the poorer performances in tropical evergreen broadleaf forests points to deficiencies regarding the modeling of phenology and soil water stress for this PFT. An evaluation with data-oriented estimates of photosynthesis (GPP) and ecosystem respiration (Reco) rates indicates distinctively improved simulations of both gross fluxes. The multi-site parameter sets are then tested against CO2 concentrations measured at 53 locations around the globe, showing significant adjustments of the modeled seasonality of atmospheric CO2 concentration, whose relevance seems PFT-dependent, along with an improved interannual variability. Lastly, a global scale evaluation with remote sensing NDVI measurements indicates an improvement of the simulated seasonal variations of the foliar cover for all considered PFTs.

Kuppel, S.; Peylin, P.; Maignan, F.; Chevallier, F.; Kiely, G.; Montagnani, L.; Cescatti, A.

2014-05-01

375

Carbon sink activity and GHG budget of managed European grasslands  

NASA Astrophysics Data System (ADS)

In agriculture, a large proportion (89%) of greenhouse gas (GHG) emission saving potential may be achieved by means of soil C sequestration. Recent demonstrations of carbon sink activities of European ecosystemes, however, often questioned the existence of C storing grasslands, as though a net sink of C was observed, uncertainty surrounding this estimate was larger than the sink itself (Janssens et al., 2003, Schulze et al., 2009. Then again, some of these estimates were based on a small number of measurements, and on models. Not surprising, there is still, a paucity of studies demonstrating the existence of grassland systems, where C sequestration would exceed (in CO2 equivalents) methane emissions from the enteric fermentation of ruminants and nitrous oxide emissions from managed soils. Grasslands are heavily relied upon for food and forage production. A key component of the carbon sink activity in grasslands is thus the impact of changes in management practices or effects of past and recent management, such as intensification as well as climate (and -variation). We analysed data (i.e. flux, ecological, management and soil organic carbon) from a network of European grassland flux observation sites (36). These sites covered different types and intensities of management, and offered the opportunity to understand grassland carbon cycling and trade-offs between C sinks and CH