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1

Temperate Grasslands  

Microsoft Academic Search

\\u000a The temperate-grassland biome occupies a large portion of the planet. Temperate grasslands represent the potential natural\\u000a vegetation of an area of 49 × 106km2, which is equivalent to 36% of the earth’s surface (Shantz 1954). This estimate of the area occupied by grasslands excludes savannas, but it does include grass and shrub deserts. The area\\u000a covered exclusively by grasslands is

Osvaldo E. Sala

2

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

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

Environmental Controls and Management Effects on Ecosystem Carbon Exchange in Two Grazed Temperate Grasslands  

NASA Astrophysics Data System (ADS)

Temperate grasslands constitute over 30% of the Earth's naturally-occurring biomes and make an important contribution towards the partial mitigation of anthropogenic greenhouse gas emissions by terrestrial ecosystems. Accumulation of carbon (C) in grassland systems predominantly takes place in below-ground repositories, enhanced by the presence of a stable soil environment with low carbon turnover rates, active rhizodeposition and high levels of residue and organic inputs. However, this C sequestration is strongly influenced by soil characteristics and climatic variables. Furthermore, in managed pasture systems, carbon exchange across the soil-atmosphere boundary is additionally affected by management activities, such as biomass removal, grazing events and the deposition or application of organic amendments. These biotic and abiotic factors contribute greatly towards the large uncertainty associated with the carbon balance of grassland ecosystems and demand further analysis. In the present study, the controls and drivers of carbon dynamics in two rotationally-grazed grasslands in Ireland were examined. The sites experience similar temperate climatic regimes but differ in soil texture classification and stocking rate. Eddy covariance measurements of net ecosystem exchange of carbon were complemented by regular assessment of standing biomass, leaf cover, harvest exports and organic amendment inputs. Our study showed that mild weather conditions and an extended growing season sustained net C accumulation at both sites for at least ten months of the year. Despite differing soil drainage characteristics, winter fluxes of net carbon exchange and its component fluxes, gross photosynthesis and ecosystem respiration, were highly comparable between the two sites. Management practices during the active growing season exerted a strong influence on both the direction and the rate of C exchange in the grassland systems, with a strong dependence, however, on the timing and intensity of the management effect. Harvest-induced reductions in productivity and net C uptake were generally greater than grazing-induced shifts, however the effects were at times mediated by environmental conditions. Our research highlighted the complex nature of the investigated grasslands resulting from the heterogeneous footprint induced by rotational grazing, grass harvesting and intensive management practices. Further work will focus on the applicability of different gap-filling methodologies for capturing the temporal and spatial variability observed. The potential of vegetation indices as a means of tracking sward development will also be investigated, with the aim of improving our understanding of the impact of vegetation dynamics on measured ecosystem carbon fluxes.

Ni Choncubhair, O.; Humphreys, J.; Lanigan, G.

2013-12-01

6

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

PubMed Central

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.

2013-01-01

7

Observing 13C labelling kinetics in CO2 respired by a temperate grassland ecosystem.  

PubMed

* The kinetic characteristics of the main sources of ecosystem respiration are quite unknown, partly because of methodological constraints. Here, we present a new open-top chamber (OTC) apparatus for continuous 13C/12C labelling and measurement of ecosystem CO2 fluxes, and report the tracer kinetics of nighttime respiration of a temperate grassland. * The apparatus includes four dynamic flow-through OTCs, a unit mixing CO2-free air with 13C-depleted CO2, and a CO2 analyser and an online isotope ratio mass spectrometer. * The concentration (367 +/- 6.5 micromol mol(-1)) and carbon isotopic composition, delta13C, (-46.9 +/- 0.4 per thousand) of CO2 in the OTCs were stable during photosynthesis as a result of high air through flux and minimal incursion through the buffered vent. Soil CO2 efflux was not affected by pressure effects during respiration measurements. The labelling kinetics of respiratory CO2 measured in the field agreed with that of excised soil + vegetation blocks measured in a laboratory-based system. The kinetics fitted a two-source system (r(2) = 0.97), with a rapidly labelled source (half-life 2.6 d) supplying 48% of respiration, and the other source (52%) releasing no tracer during 14 d of labelling. * Of the two sources supplying ecosystem respiration, one was closely connected to current photosynthesis (approximately autotrophic respiration) and the other was provided by decomposition of structural plant biomass (approximately heterotrophic respiration). PMID:19656304

Gamnitzer, Ulrike; Schäufele, Rudi; Schnyder, Hans

2009-10-01

8

Impact of inter-annual climatic variability on ecosystem carbon exchange in two grazed temperate grasslands with contrasting drainage regimes  

NASA Astrophysics Data System (ADS)

Temperate grasslands constitute over 30% of the Earth's naturally-occurring biomes and make an important contribution towards the partial mitigation of anthropogenic greenhouse gas emissions by terrestrial ecosystems. Accumulation of carbon (C) in grassland systems predominantly takes place in below-ground repositories, enhanced by the presence of a stable soil environment with low carbon turnover rates, active rhizodeposition and high levels of residue and organic inputs. Predicted future warming is expected to increase productivity in temperate zones, thereby enhancing rates of terrestrial carbon sequestration. However, the susceptibility of many ecosystems, including grasslands, to extreme climatic events and inter-annual variability has been demonstrated previously. Temperature anomalies as well as modifications in the temporal pattern and quantity of precipitation alter the balance between carbon uptake and release processes and a mechanistic understanding of ecosystem response to such changes is still lacking. In the present study, the impact of extreme inter-annual variability in summer rainfall and temperature on carbon dynamics in two rotationally-grazed grasslands in Ireland was examined. The sites experience similar temperate climatic regimes but differ in soil drainage characteristics. Eddy covariance measurements of net ecosystem exchange of carbon were complemented by regular assessment of standing biomass, leaf cover, harvest exports and organic amendment inputs. The summers of 2012 and 2013 showed contrasting climatic conditions, with summer precipitation 93% higher and 25% lower respectively than long-term means. In addition, soil temperatures were 7% lower and 11% higher than expected. Cool, wet conditions in 2012 facilitated net carbon uptake for more than ten months of the year at the poorly-drained site, however the ecosystem switched to a net source of carbon in 2013 during months with significantly reduced rainfall. In contrast, net C accumulation continued at the well-drained site despite the summer drought conditions. Total cumulative annual ecosystem respiration was 20% higher at the poorly-drained site than at the well-drained site in 2013, while a more modest increase in cumulative gross production (9.6%) was observed at the poorly-drained site for the same period. This research highlights the susceptibility of poorly-drained soils to accelerated efflux of carbon during soil drying cycles and points towards potential negative impacts of future warming scenarios, with significant carbon balance implications for grassland ecosystems.

Choncubhair, Órlaith Ní; Humphreys, James; Lanigan, Gary

2014-05-01

9

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.

10

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.

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

2012-01-01

11

Relation of chlorophyll fluorescence sensitive reflectance ratios to carbon flux measurements of montanne grassland and norway spruce forest ecosystems in the temperate zone.  

PubMed

We explored ability of reflectance vegetation indexes (VIs) related to chlorophyll fluorescence emission (R???/R???, R???/R???) and de-epoxidation state of xanthophyll cycle pigments (PRI, calculated as (R???- R???)/(R???-R???) to track changes in the CO? 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 CO? assimilation (A(MAX)) 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 ?(R???/R???) of grassland plant leaves under dark-to-full sunlight transition in the scale of minutes were significantly related to A(MAX) (R˛ = 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 R???/R??? with NEE and GPP. PMID:22701368

A?, Alexander; Malenovský, Zbyn?k; Urban, Otmar; Hanuš, Jan; Zitová, Martina; Navrátil, Martin; Vráblová, Martina; Olejní?ková, Julie; Spunda, Vladimír; Marek, Michal

2012-01-01

12

Net ecosystem exchange of grassland in contrasting wet and dry years  

Microsoft Academic Search

Temperate grasslands represent about 32% of the earth's land area and cover approximately 56% of the area of Ireland; yet their role as sources\\/sinks of atmospheric CO2 is not well quantified. We used an eddy covariance (EC) system to measure the net ecosystem exchange (NEE) at a managed grassland site in southern Ireland for 2 years. Rainfall in 2002 and

Vesna Jaksic; Gerard Kiely; John Albertson; Ram Oren; Gabriel Katul; Paul Leahy; Kenneth A. Byrne

2006-01-01

13

Effect of elevated CO 2 on soil N dynamics in a temperate grassland soil  

Microsoft Academic Search

The response of terrestrial ecosystems to elevated atmospheric CO2 is related to the availability of other nutrients and in particular to nitrogen (N). Here we present results on soil N transformation dynamics from a N-limited temperate grassland that had been under Free Air CO2 Enrichment (FACE) for six years. A 15N labelling laboratory study (i.e. in absence of plant N

Christoph Müller; Tobias Rütting; M. Kaleem Abbasi; Ronald J. Laughlin; Claudia Kammann; Tim J. Clough; Robert R. Sherlock; Jens Kattge; Hans-Jürgen Jäger; Catherine J. Watson; R. James Stevens

2009-01-01

14

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

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

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.

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

2013-01-01

17

Increasing water and nitrogen availability enhanced net ecosystem CO 2 assimilation of a temperate semiarid steppe  

Microsoft Academic Search

Changes in precipitation patterns and N cycling across the globe are likely to affect ecosystem primary productivity and CO2 exchanges, especially in arid and semi-arid grasslands. To evaluate the effects of water and N availability on ecosystem\\u000a CO2 fluxes, we conducted a manipulative field experiment with water and N addition in a temperate semiarid steppe in 2006 and\\u000a 2007 with

Liming Yan; Shiping Chen; Jianhui Huang; Guanghui Lin

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.

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

2011-01-01

19

Increasing land-use intensity decreases floral colour diversity of plant communities in temperate grasslands.  

PubMed

To preserve biodiversity and ecosystem functions in a globally changing world it is crucial to understand the effect of land use on ecosystem processes such as pollination. Floral colouration is known to be central in plant-pollinator interactions. To date, it is still unknown whether land use affects the colouration of flowering plant communities. To assess the effect of land use on the diversity and composition of flower colours in temperate grasslands, we collected data on the number of flowering plant species, blossom cover and flower reflectance spectra from 69 plant communities in two German regions, Schwäbische Alb (SA) and Hainich-Dün (HD). We analysed reflectance data of flower colours as they are perceived by honeybees and studied floral colour diversity based upon spectral loci of each flowering plant species in the Maxwell triangle. Before the first mowing, flower colour diversity decreased with increasing land-use intensity in SA, accompanied by a shift of mean flower colours of communities towards an increasing proportion of white blossom cover in both regions. By changing colour characteristics of grasslands, we suggest that increasing land-use intensity can affect the flower visitor fauna in terms of visitor behaviour and diversity. These changes may in turn influence plant reproduction in grassland plant communities. Our results indicate that land use is likely to affect communication processes between plants and flower visitors by altering flower colour traits. PMID:23568710

Binkenstein, Julia; Renoult, Julien P; Schaefer, H Martin

2013-10-01

20

Patterns of plant biomass allocation in temperate grasslands across a 2500-km transect in northern China.  

PubMed

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; Lü, Xiaotao; Wang, Xue; Li, Mai-He; Bai, Edith; Han, Xingguo; Xu, Zhuwen

2013-01-01

21

Off-season carbon dioxide exchange of a temperate mountain grassland in a warmer future climate  

NASA Astrophysics Data System (ADS)

It is well established that warming leads to an earlier onset and delayed termination of seasonal plant activity in the Northern hemisphere. Whether this goes along with an increase or decrease in the carbon dioxide (CO2) sink strength of terrestrial ecosystems, however, is much more controversial. We used a simple model that considers temperature, absorbed photosynthetically active radiation and day length to simulate the off-season, i.e. between the end and the start of the carbon uptake period (CUP), CO2 exchange of a temperate mountain grassland in Austria. The model was calibrated with a 10 year record of eddy covariance CO2 flux measurements. Our major findings were: The end of the CUP of this managed grassland was determined by the timing of the final harvest because the temperature response of daytime net carbon uptake in autumn was too weak to compensate for nighttime carbon losses. A critical day length, reached by the end of March, exists below which net carbon gain was impossible on a daily basis. Using five climate scenarios and comparing the periods 1961-1990 and 2021-2050 we were able to show that earlier onsets of the CUP under future warmer conditions (+1.0 to +1.7°C) were by far offset by earlier snow melting dates and thus a lengthening of the period before the critical day length was reached. In total however, off season losses hardly differed between the two investigated periods, which was due to compensating effects of larger CO2 losses in autumn and spring and smaller losses during winter. Taken together our study suggests the off-season CO2 exchange of temperate mountain grasslands to be resilient against climate change scenarios predicted for the middle of the 21st century.

Wohlfahrt, G.; Gobiet, A.; Hammerle, A.; Hörtnagl, L.; Irschick, C.; Themessl, M. J.

2012-12-01

22

Estimating carbon dioxide fluxes from temperate mountain grasslands using broad-band vegetation indices  

PubMed Central

The broad-band normalised difference vegetation index (NDVI) and the simple ratio (SR) were calculated from measurements of reflectance of photosynthetically active and short-wave radiation at two temperate mountain grasslands in Austria and related to the net ecosystem CO2 exchange (NEE) measured concurrently by means of the eddy covariance method. There was no significant statistical difference between the relationships of midday mean NEE with narrow- and broad-band NDVI and SR, measured during and calculated for that same time window, respectively. The skill of broad-band NDVI and SR in predicting CO2 fluxes was higher for metrics dominated by gross photosynthesis and lowest for ecosystem respiration, with NEE in between. A method based on a simple light response model whose parameters were parameterised based on broad-band NDVI allowed to improve predictions of daily NEE and is suggested to hold promise for filling gaps in the NEE time series. Relationships of CO2 flux metrics with broad-band NDVI and SR however generally differed between the two studied grassland sites indicting an influence of additional factors not yet accounted for.

Wohlfahrt, G.; Pilloni, S.; Hortnagl, L.; Hammerle, A.

2013-01-01

23

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

24

Mean age of carbon in fine roots from temperate forests and grasslands with different management  

NASA Astrophysics Data System (ADS)

Fine roots are the most dynamic portion of a plant's root system and a major source of soil organic matter. By altering plant species diversity and composition, soil conditions and nutrient availability, and consequently belowground allocation and dynamics of root carbon (C) inputs, land-use and management changes may influence organic C storage in terrestrial ecosystems. In three German regions, we measured fine root radiocarbon (14C) content to estimate the mean time since C in root tissues was fixed from the atmosphere in 54 grassland and forest plots with different management and soil conditions. Although root biomass was on average greater in grasslands 5.1 ± 0.8 g (mean ± SE, n = 27) than in forests 3.1 ± 0.5 g (n = 27) (p < 0.05), the mean age of C in fine roots in forests averaged 11.3 ± 1.8 yr and was older and more variable compared to grasslands 1.7 ± 0.4 yr (p < 0.001). We further found that management affects the mean age of fine root C in temperate grasslands mediated by changes in plant species diversity and composition. Fine root mean C age is positively correlated with plant diversity (r = 0.65) and with the number of perennial species (r = 0.77). Fine root mean C age in grasslands was also affected by study region with averages of 0.7 ± 0.1 yr (n = 9) on mostly organic soils in northern Germany and of 1.8 ± 0.3 yr (n = 9) and 2.6 ± 0.3 (n = 9) in central and southern Germany (p < 0.05). This was probably due to differences in soil nutrient contents and soil moisture conditions between study regions, which affected plant species diversity and the presence of perennial species. Our results indicate more long-lived roots or internal redistribution of C in perennial species and suggest linkages between fine root C age and management in grasslands. These findings improve our ability to predict and model belowground C fluxes across broader spatial scales.

Solly, E.; Schöning, I.; Boch, S.; Müller, J.; Socher, S. A.; Trumbore, S. E.; Schrumpf, M.

2013-07-01

25

Acetaldehyde exchange above a managed temperate mountain grassland  

NASA Astrophysics Data System (ADS)

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 4 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 of up to 16.5 nmol m-2 s-1 on the day of harvesting or 1 day later. During undisturbed conditions both periods with net uptake and net emissions of acetaldehyde were observed. The bidirectional nature of acetaldehyde fluxes was also reflected by clear diurnal cycles during certain time periods, indicating strong deposition processes before the first 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 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.

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

2014-06-01

26

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.

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

2013-01-01

27

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

28

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.

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

2013-01-01

29

Estimating net primary productivity of grasslands from field biomass measurements in temperate northern China  

Microsoft Academic Search

Data on field biomass measurements in temperate grasslands of northern China (141 samples from 74 sites) were obtained from\\u000a 23 Chinese journals, reports and books. Net primary productivity (NPP) of grasslands was estimated using three algorithms\\u000a (peak live biomass, peak standing crop and maximum minus minimum live biomass), respectively, based on availability of biomass\\u000a data in sites. 135 samples which

Jian Ni

2004-01-01

30

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

31

Water relations in grassland and desert ecosystems exposed to elevated atmospheric CO2.  

PubMed

Atmospheric CO2 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 CO2 enrichment, with an emphasis on water relations. Increasing CO2 led to decreased leaf conductance for water vapor, improved plant water status, altered seasonal evapotranspiration dynamics, and in most cases, periodic increases in soil water content. The extent, timing and duration of these responses varied among ecosystems, species and years. Across the grasslands of the Kansas tallgrass prairie, Colorado shortgrass steppe and Swiss calcareous grassland, increases in aboveground biomass from CO2 enrichment were relatively greater in dry years. In contrast, CO2-induced aboveground biomass increases in the Texas C3/C4 grassland and the New Zealand pasture seemed little or only marginally influenced by yearly variation in soil water, while plant growth in the Mojave Desert was stimulated by CO2 in a relatively wet year. Mediterranean grasslands sometimes failed to respond to CO2-related increased late-season water, whereas semiarid Negev grassland assemblages profited. Vegetative and reproductive responses to CO2 were highly varied among species and ecosystems, and did not generally follow any predictable pattern in regard to functional groups. Results suggest that the indirect effects of CO2 on plant and soil water relations may contribute substantially to experimentally induced CO2-effects, and also reflect local humidity conditions. For landscape scale predictions, this analysis calls for a clear distinction between biomass responses due to direct CO2 effects on photosynthesis and those indirect CO2 effects via soil moisture as documented here. PMID:15156395

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

2004-06-01

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

Water, temperature, and vegetation controls on halomethane fluxes from semiarid temperate grasslands  

Microsoft Academic Search

Methyl bromide (CH3Br) and methyl chloride (CH3Cl) are the dominant carriers of organic bromine and chlorine to the upper atmosphere, where they catalyze stratospheric ozone loss. Prior experiments indicate that temperate grasslands may be a significant sink for these gases, although large uncertainties exist regarding the range and magnitude of fluxes. Here we report the results of a combined field

Y. Teh; R. Rhew; T. Abel

2006-01-01

34

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

Microsoft Academic Search

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

Steven W. Kembel; James F. Cahill

2011-01-01

35

Identifying priority areas for ecosystem service management in South African grasslands  

Microsoft Academic Search

Grasslands provide many ecosystem services required to support human well-being and are home to a diverse fauna and flora. Degradation of grasslands due to agriculture and other forms of land use threaten biodiversity and ecosystem services. Various efforts are underway around the world to stem these declines. The Grassland Programme in South Africa is one such initiative and is aimed

Benis N. Egoh; Belinda Reyers; Mathieu Rouget; David M. Richardson

2011-01-01

36

Response of grassland ecosystems to prolonged soil moisture deficit  

NASA Astrophysics Data System (ADS)

Soil moisture is commonly used for predictions of plant response and productivity. Climate change is predicted to cause an increase in the frequency and duration of droughts over the next century, which will result in prolonged periods of below-normal soil moisture. This, in turn, is expected to impact regional plant production, erosion and air quality. In fact, the number of consecutive months of soil moisture content below the drought-period mean has recently been linked to regional tree and shrub mortality in the southwest United States. This study investigated the effects of extended periods of below average soil moisture on the response of grassland ANPP to precipitation. Grassland ecosystems were selected for this study because of their ecological sensitivity to precipitation patterns. It has been postulated that the quick ecological response of grasslands to droughts can provide insight to large scale functional responses of regions to predicted climate change. The study sites included 21 grassland biomes throughout arid-to-humid climates in the United States with continuous surface soil moisture records for 2-13 years during the drought period from 2000-2013. Annual net primary production (ANPP) was estimated from the 13-year record of NASA MODIS Enhanced Vegetation Index extracted for each site. Prolonged soil moisture deficit was defined as a period of at least 10 consecutive months during which soil moisture was below the drought-period mean. ANPP was monitored before, during and after prolonged soil moisture deficit to quantify shifts in the functional response of grasslands to precipitation, and in some cases, new species assemblages that included invasive species. Preliminary results indicated that when altered climatic conditions on grasslands led to an increase in the duration of soil water deficit, then the precipitation-to-ANPP relation became non-linear. Non-linearity was associated with extreme grassland dieback and changes in the historic species assemblage. The magnitude of change was related to the precipitation regime, where grasslands in hyper-arid and humid regimes were least likely to be affected by prolonged soil moisture deficit, and semiarid and mesic grasslands were most likely to be impacted, depending on the duration of the deficit. These results were applied to a large grassland region in Australia with soil moisture estimates from the European Space Agency (ESA) Soil Moisture Ocean Salinity (SMOS) sensor to demonstrate the continental-scale potential of this application with satellite measurements. These results are even more relevant for application with the higher-resolution NASA Soil Moisture Active Passive (SMAP) products to be available in 2015.

Ross, Morgan A.; Ponce-Campos, Guillermo E.; Barnes, Mallory L.; Hottenstein, John D.; Moran, M. Susan

2014-05-01

37

Ecosystem carbon and nitrogen accumulation after grazing exclusion in semiarid grassland.  

PubMed

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

Plant functional group composition modifies the effects of precipitation change on grassland ecosystem function.  

PubMed

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

39

Recurrent winter warming pulses enhance nitrogen cycling and soil biotic activity in temperate heathland and grassland mesocosms  

NASA Astrophysics Data System (ADS)

Winter air temperatures are projected to increase in the temperate zone, whereas snow cover is projected to decrease, leading to more extreme soil temperature variability, and potentially to changes in nutrient cycling. Therefore, we applied six winter warming pulses by infra-red heating lamps and surface heating wires in a field experiment over one winter in temperate heathland and grassland mesocosms. The experiment was replicated at two sites, a colder mountainous upland site with high snow accumulation and a warmer and dryer lowland site. Winter warming pulses enhanced soil biotic activity for both sites during winter, as indicated by 35% higher nitrogen (N) availability in the soil solution, 40% higher belowground decomposition and a 25% increase in the activity of the enzyme cellobiohydrolase. The mobilization of N differed between sites, and the incorporation of 15N into leaves was reduced by 31% in response to winter warming pulses, but only at the cold site, with significant reductions occurring for three of four tested plant species at this site. Furthermore, there was a trend of increased N leaching in response to the recurrent winter warming pulses. Overall, projected winter climate change in the temperate zone, with less snow and more variable soil temperatures, appears important for shifts in ecosystem functioning (i.e. nutrient cycling). While the effects of warming pulses on plant N mobilization did not differ among sites, reduced plant 15N incorporation at the colder temperate site suggests that frost damage may reduce plant performance in a warmer world, with important implications for nitrogen cycling and nitrogen losses from ecosystems.

Schuerings, J.; Jentsch, A.; Hammerl, V.; Lenz, K.; Henry, H. A. L.; Malyshev, A. V.; Kreyling, J.

2014-06-01

40

Extensive Management Promotes Plant and Microbial Nitrogen Retention in Temperate Grassland  

PubMed Central

Leaching losses of nitrogen (N) from soil and atmospheric N deposition have led to widespread changes in plant community and microbial community composition, but our knowledge of the factors that determine ecosystem N retention is limited. A common feature of extensively managed, species-rich grasslands is that they have fungal-dominated microbial communities, which might reduce soil N losses and increase ecosystem N retention, which is pivotal for pollution mitigation and sustainable food production. However, the mechanisms that underpin improved N retention in extensively managed, species-rich grasslands are unclear. We combined a landscape-scale field study and glasshouse experiment to test how grassland management affects plant and soil N retention. Specifically, we hypothesised that extensively managed, species-rich grasslands of high conservation value would have lower N loss and greater N retention than intensively managed, species-poor grasslands, and that this would be due to a greater immobilisation of N by a more fungal-dominated microbial community. In the field study, we found that extensively managed, species-rich grasslands had lower N leaching losses. Soil inorganic N availability decreased with increasing abundance of fungi relative to bacteria, although the best predictor of soil N leaching was the C/N ratio of aboveground plant biomass. In the associated glasshouse experiment we found that retention of added 15N was greater in extensively than in intensively managed grasslands, which was attributed to a combination of greater root uptake and microbial immobilisation of 15N in the former, and that microbial immobilisation increased with increasing biomass and abundance of fungi. These findings show that grassland management affects mechanisms of N retention in soil through changes in root and microbial uptake of N. Moreover, they support the notion that microbial communities might be the key to improved N retention through tightening linkages between plants and microbes and reducing N availability.

de Vries, Franciska T.; Bloem, Jaap; Quirk, Helen; Stevens, Carly J.; Bol, Roland; Bardgett, Richard D.

2012-01-01

41

Ecosystem change along a woody invasion chronosequence in a California grassland  

Microsoft Academic Search

Woody species have increased in abundance in many grassland ecosystems during the last century. To investigate the consequences of Baccharis pilularis encroachment into coastal California grasslands, we established a chronosequence of sites naturally invaded by Baccharis zero to 25 years ago. Increasing above- and below-ground biomass increase along the chronosequence drove increases in ecosystem N sequestration of ?700% and in

E. S. Zavaleta; L. S. Kettley

2006-01-01

42

Controls on soil organic carbon and nitrogen in Inner Mongolia, China: a cross-continental comparison of temperate grasslands  

NASA Astrophysics Data System (ADS)

Most global ecosystem models assume that controls over soil organic matter are alike in climatically similar regions. In this study, we tested the generality of controls over soil organic carbon (SOC) and soil organic nitrogen (SON) in temperate grasslands. We measured organic matter pools in Inner Mongolia, China along the Northeast China Transect, and analyzed the relationship of SOC and SON to climate, soil texture, and land use variables. We then compared our data to values simulated by a regression model developed in the U.S. Great Plains and tested in Argentina, and to Century model simulations. We found that, as in the US Great Plains, climate and soil texture variables could explain a large proportion of variation in observed SOC and SON, but a regression model developed in the Great Plains overestimated SOC and underestimated SON in Inner Mongolia. Using Century, we found that simulated SOC and SON values were sensitive to both inclusion of altered land use periods and changes in nitrogen deposition, and that the model that best fit our data included higher-intensity grazing and nitrogen deposition values higher than that in the US Great Plains. This model also produced aboveground net primary production (ANPP) values comparable with values observed in the literature for Inner Mongolia grasslands, but these values were higher than ANPP predicted by previously-published regression models. These results suggest that different controls over carbon cycling in Inner Mongolia may affect our ability to predict carbon pool sizes based on relationships in other regional models.

Evans, S. E.; Burke, I. C.; Lauenroth, W.

2010-12-01

43

Controls on soil organic carbon and nitrogen in Inner Mongolia, China: A cross-continental comparison of temperate grasslands  

NASA Astrophysics Data System (ADS)

Most global ecosystem models assume that controls over soil organic matter are alike in climatically similar regions. In this study, we tested the generality of controls over soil organic carbon (SOC) and soil organic nitrogen (SON) in temperate grasslands. We measured organic matter pools in Inner Mongolia, China, along the Northeast China Transect, and analyzed the relationship of SOC and SON to climate, soil texture, and land use variables. We then compared our data to values simulated by a regression model developed in the U.S. Great Plains and also to Century model simulations. We found that, as in the U.S. Great Plains, climate and soil texture variables could explain a large proportion of variation in observed SOC and SON, but a regression model developed in the Great Plains overestimated SOC and underestimated SON in Inner Mongolia. Using Century, we found that simulated SOC and SON values were sensitive to both inclusion of altered land use and changes in N deposition and that the model that best fit our data included higher-intensity grazing and N deposition values higher than that in the Great Plains. This model also produced aboveground net primary production (ANPP) values comparable with values observed in the literature for Inner Mongolian grasslands, but these values were higher than ANPP predicted by previously published regression models. These results suggest that different controls over SOC and SON cycling in Inner Mongolia may affect our ability to predict SOC and SON pool sizes using relationships in other regional models.

Evans, Sarah E.; Burke, Ingrid C.; Lauenroth, William K.

2011-09-01

44

Effects of vegetation control on ecosystem water use efficiency within and among four grassland ecosystems in China  

Microsoft Academic Search

Through 2-3-year (2003-2005) continuous eddy covariance measurements of carbon dioxide and water vapor fluxes, we examined the seasonal, inter-annual, and inter- ecosystem variations in the ecosystem-level water use efficiency (WUE, defined as the ratio of gross primary production, GPP, to evapotranspiration, ET) at four Chinese grassland ecosystems in the Qinghai-Tibet Plateau and North China. Representing the most prevalent grassland types

ZHONGMIN H U; UI Y U; Y INGNIAN L Iz; PEILI S HI; Z HENG

45

Seasonal variability of CH4 and N2O fluxes over a managed temperate mountain grassland  

NASA Astrophysics Data System (ADS)

The quantification of greenhouse gas (GHG) budgets on a global scale is an important step in assessing the effect of anthropogenic and biogenic controls on a future climate. In the past, measurements of CO2 fluxes were conducted over a wide array of ecosystems, leading to a better understanding of its exchange patterns on different time scales and more sophisticated models. However, only few studies quantified the fluxes of the other two major GHG, methane (CH4) and nitrous oxide (N2O), mainly due to expensive sensors and their time-consuming maintenance. In addition, early CH4 and N2O measurements mainly focused on ecosystems with presumably high emissions of CH4 (e.g. wetlands) or N2O (e.g. heavily fertilized crops). In recent years, devices for CH4 and N2O measurements became widely available and more studies are conducted over sites that exert small and often close-to-zero fluxes. Despite recent advances in sensor sensitivity and stability, the quantification of CH4 and N2O exchange rates remains challenging. Here we present measurements of CH4 and N2O exchange rates of a temperate mountain grassland managed as a hay meadow near the village Neustift in the Stubai Valley, Austria, that started in April 2010 by means of the eddy covariance method. The three wind components and the speed of sound were acquired at a time resolution of 20 Hz, while CH4 and N2O mixing ratios were recorded at 2 Hz by a quantum cascade laser absorption spectrometer (QCL-AS). Fluxes of both compounds were calculated using the virtual disjunct eddy covariance method (vDEC). For better comparability fluxes of N2O and CH4 were also converted to g CO2-equivalents and compared to the CO2 exchange at the same site. In addition to exchange rates, challenges regarding the calculation of GHG fluxes at the investigated grassland site will also be discussed. In 2011, deposition of CH4 was recorded on 9 days with average uptake rates of -0.6 nmol m-2 s-1. Peak emissions of up to 12.9 nmol m-2 s-1 were found in October, about 10 days after the 3rd cutting of the meadow. First results showed cumulative fluxes amounting to a net emission of CH4, corresponding to 58.6 g CO2-equivalents m-2 in 2011. N2O showed net deposition fluxes on 38 days and maximum uptake rates of -0.3 nmol m-2 s-1 during 7 consecutive days with nitrogen uptake in April 2011. Peak emissions of more than 1.2 nmol m-2 s-1 were observed at the end of November, about one month after fertilization. In total, the meadow was a source of N2O (118.9 g CO2-equivalents m-2). In comparison, cumulative fluxes of CO2 in 2011 resulted in a net uptake of -70.4 g CO2 m-2. Distinct diurnal cycles could be observed for N2O, e.g. in April with peak uptake rates of more than -0.7 nmol m-2 s-1 around noon, or in August with peak midday emissions of around 0.8 nmol m-2 s-1. Diurnal cycles of CH4 were less pronounced and more error-prone due to spikes in methane mixing ratios and fluxes, but nevertheless showed a tendency of methane release during the day, around noon up to 10.1 nmol m-2 s-1 in September.

Hoertnagl, Lukas; Wohlfahrt, Georg

2013-04-01

46

Acetone and Acetaldehyde Exchange Above a Managed Temperate Mountain Grassland  

NASA Astrophysics Data System (ADS)

The exchange of acetone and acetaldehyde was measured above an intensively managed hay meadow in the Stubai Valley (Tyrol, Austria) during the growing seasons in 2008 and 2009. Half-hourly fluxes of both compounds were calculated by means of the virtual disjunct eddy covariance (vDEC) method by combining the 3-dimensional wind data from a sonic anemometer with the compound specific volume mixing ratios quantified with a proton-transfer-reaction mass spectrometer (PTR-MS). The cutting of the meadow resulted in the largest perturbation of the VOC exchange rates. Peak emissions for both VOC species were observed during and right after the cutting of the meadow, with rates of up to 12.1 and 10.1 nmol m-2 s-1 for acetaldehyde and acetone, respectively, reflecting the drying of the wounded plant material. During certain time periods, undisturbed by management events, both compounds exhibited a clear diurnal cycle. Emission rates of up to 3.7 nmol m-2 s-1 for acetaldehyde and 3.2 nmol m-2 s-1 for acetone were measured in October 2008, while a uptake of both compounds with rates of up to 1.8 and 2.1 nmol m-2 s-1, respectively, could be observed in May 2009, when also clear compensation points of 0.3 ppb for acetaldehyde and 1.0 ppb for acetone were observed. In an effort to explore the controls on observed exchange patterns, a simple and multiple linear regression analysis was conducted. A clear interconnection between VOC concentrations and VOC exchange could be seen only in May 2009, when concentration values alone explained 30.6% and 11.7% of the acetaldehyde and acetone flux variance, respectively. However, when trying to predict the observed exchange patterns of both VOC species in a multiple linear regression based on supporting environmental measurements - including air and soil temperature, soil water content and PAR among others - the analysis yielded unsatisfactory results, accounting for 10% and 4% of the observed acetaldehyde and acetone flux variance over both measurement campaigns and during undisturbed conditions. The shortcomings in predicting VOC fluxes might be a consequence of missing parameters that were not captured by our meteorological data. The identification and quantification of biochemical cycles associated with soil and plant root processes and the possible influence of insect life cycles on VOC exchange might provide important information during the development and parameterization of VOC models. The total amount of carbon associated with the VOC flux of the two compounds was low: the grassland was a net source of acetaldehyde in both years with emissions of 21.8 mg C m-2 and 10.2 mg C m-2 in 2008 and 2009, respectively, while the meadow was a source of acetone in 2008 with 14.6 mg C m-2 and a sink in 2009 with a cumulative uptake of 5.0 mg C m-2.

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

2011-12-01

47

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

48

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

49

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.

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

2012-01-01

50

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

51

Separating drought effects from roof artefacts on ecosystem processes in a grassland drought experiment  

NASA Astrophysics Data System (ADS)

Given the predictions of increasing risk of long drought periods under various climate change scenarios, there have been numerous experimental field studies simulating drought using transparent roofs in different ecosystems and regions. Such roofs may, however, have unknown side effects, here called artefacts, on the response variables potentially confounding experimental results and misleading conclusions. Knowing the ecosystem response to such roof artefacts is therefore indispensible to correctly predict the effects of drought on the composition and functioning of ecosystems. We therefore aimed at filling this gap by studying the relevance of roof artefacts in a temperate grassland ecosystem. We compared pure drought effects to roof artefacts by measuring the response of three ecosystem properties (aboveground biomass, litter decomposition and plant metabolite profiles). We realized three treatments: a drought treatment simulated by means of transparent roofs, an unroofed control treatment receiving natural rainfall and a roofed control, with rain water applied according to ambient conditions. The roof constructions in our experiment caused a slight change in air (+0.14 °C during night) and soil (-0.45°C on warm days, +0.25 °C on cold nights) temperatures while photosynthetically active radiation was decreased (-16%) on bright days. Aboveground plant community biomass was reduced in the drought treatment (-41%), but there was no significant difference between the roofed and unroofed control, thus there was no measurable response of aboveground biomass to roof artefacts, but a considerable response to drought. Compared to the unroofed control, litter decomposition was decreased both in the drought treatment (-26%) and in the roofed control treatment (-18%), suggesting a response of litter decomposition to roof artefacts in addition to drought. Similarly, aboveground metabolite profiles in the model plant species Medicago x varia were significantly different from the unroofed control both in the drought and in the roofed control treatments. Our results stress the need for roofed control treatments when using transparent roofs for studying drought effects because of significant roof artefacts.

Vogel, Anja; Fester, Thomas; Eisenhauer, Nico; Scherer-Lorenzen, Michael; Schmid, Bernhard; Weisser, Wolfgang W.; Weigelt, Alexandra

2013-04-01

52

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

53

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

54

Identifying priority areas for ecosystem service management in South African grasslands.  

PubMed

Grasslands provide many ecosystem services required to support human well-being and are home to a diverse fauna and flora. Degradation of grasslands due to agriculture and other forms of land use threaten biodiversity and ecosystem services. Various efforts are underway around the world to stem these declines. The Grassland Programme in South Africa is one such initiative and is aimed at safeguarding both biodiversity and ecosystem services. As part of this developing programme, we identified spatial priority areas for ecosystem services, tested the effect of different target levels of ecosystem services used to identify priority areas, and evaluated whether biodiversity priority areas can be aligned with those for ecosystem services. We mapped five ecosystem services (below ground carbon storage, surface water supply, water flow regulation, soil accumulation and soil retention) and identified priority areas for individual ecosystem services and for all five services at the scale of quaternary catchments. Planning for individual ecosystem services showed that, depending on the ecosystem service of interest, between 4% and 13% of the grassland biome was required to conserve at least 40% of the soil and water services. Thirty-four percent of the biome was needed to conserve 40% of the carbon service in the grassland. Priority areas identified for five ecosystem services under three target levels (20%, 40%, 60% of the total amount) showed that between 17% and 56% of the grassland biome was needed to conserve these ecosystem services. There was moderate to high overlap between priority areas selected for ecosystem services and already-identified terrestrial and freshwater biodiversity priority areas. This level of overlap coupled with low irreplaceability values obtained when planning for individual ecosystem services makes it possible to combine biodiversity and ecosystem services in one plan using systematic conservation planning. PMID:21334134

Egoh, Benis N; Reyers, Belinda; Rouget, Mathieu; Richardson, David M

2011-06-01

55

Convergence of potential net ecosystem production among contrasting C3 grasslands  

PubMed Central

Metabolic theory and body size dependent constraints on biomass production and decomposition suggest that differences in the intrinsic potential net ecosystem production (NEPPOT) should be small among contrasting C3 grasslands and therefore unable to explain the wide range in the annual apparent net ecosystem production (NEPAPP) reported by previous studies. We estimated NEPPOT for nine C3 grasslands under contrasting climate and management regimes using multi-year eddy covariance data. NEPPOT converged within a narrow range suggesting little difference in the net carbon dioxide uptake capacity across C3 grasslands. Our results indicate a unique feature of C3 grasslands compared to other terrestrial ecosystems and suggest a state of stability in NEPPOT due to tightly coupled production and respiration processes. Consequently, the annual NEPAPP of C3 grasslands is primarily a function of seasonal and short-term environmental and management constraints, and therefore especially susceptible to changes in future climate patterns and associated adaptation of management practices.

Peichl, Matthias; Sonnentag, Oliver; Wohlfahrt, Georg; Flanagan, Lawrence B.; Baldocchi, Dennis D.; Kiely, Gerard; Galvagno, Marta; Gianelle, Damiano; Marcolla, Barbara; Pio, Casimiro; Migliavacca, Mirco; Jones, Michael B.; Saunders, Matthew

2013-01-01

56

Ecosystem Scale Fluxes of Water and Carbon in Semiarid Grassland and Shrubland  

Microsoft Academic Search

To understand how woody encroachment into grassland influences water and carbon cycling in semiarid environments, we measure ecosystem-scale water and carbon fluxes and identify factors that control variability of the fluxes. Flux measurements are made using both the Bowen ratio and eddy covariance methods, accompanied by measurements of soil moisture and radiation. We present data from both a grassland site

S. A. Kurc; E. E. Small

2003-01-01

57

Untangling the roles of fire, grazing and rainfall on small mammal communities in grassland ecosystems  

Microsoft Academic Search

In grassland systems across the globe, ecologists have been attempting to understand the complex role of fire, grazing and\\u000a rainfall in creating habitat heterogeneity and the consequences of anthropogenic control of these factors on ecosystem integrity\\u000a and functioning. Using a South African grassland ecosystem as a model, we investigated the impact of fire and grazing pressure\\u000a on small mammal communities

R. W. Yarnell; D. M. Scott; C. T. Chimimba; D. J. Metcalfe

2007-01-01

58

Agricultural impacts on ecosystem functioning in temperate areas of North and South America  

NASA Astrophysics Data System (ADS)

Land use has a large impact on ecosystem functioning, though evidences of these impacts at the regional scale are scarce. The objective of this paper was to analyze the impacts of agricultural land use on ecosystem functioning (radiation interception and carbon uptake) in temperate areas of North and South America. From land cover maps generated using high-resolution satellite images we selected sites dominated by row crops (RC), small grain crops (SG), pastures (PA), and rangelands (RA) in the Central Plains of USA and the Pampas of Argentina. These two regions share climatic characteristics and the agricultural conditions (crop types) are also very similar. Both areas were originally dominated by temperate grasslands. In these sites we extracted the temporal series of the normalized difference vegetation index (NDVI) from the NOAA satellites for the period 1989-1998 and calculated the mean seasonal NDVI curve for each site. Additionally, we calculated the mean annual NDVI, the maximum NDVI, the date of the year when the max NDVI was recorded and the interannual variability of these three attributes. We compared the mean values of each NDVI-derived attribute between land cover types and between continents. The NDVI seasonal patterns for each land cover type were roughly similar between the Central Plains and the Pampas during the growing season. The largest differences were observed during the winter and spring, when the NDVI of all land cover types in the Central Plains remained at lower values than in the Pampas. This was probably caused by the high annual thermal amplitude in the Central Plains that results in a much more restricted growing season. As a result of these differences in the shape of the NDVI curve, the mean annual NDVI in the Central Plains was lower than in the Pampas for all land cover types but the maximum NDVI did not differ importantly. In both regions, row crops delayed the date of the NDVI peak, small grain crops advanced it and pastures did not change it importantly, compared with rangelands. The interannual variability of the NDVI attributes was higher for small grains than for row crops in both regions. However, small grains crops were consistently more variable between years in the Central Plains than in the Pampas. The opposite occurred with pastures and rangelands, which were more variable in the Pampas than in the Central Plains. This paper confirms and generalizes previous findings that showed important imprints of land use on ecosystem functioning in temperate ecosystems. Our results support the idea that the changes in land cover that have occurred in the Central Plains and the Pampas leaded to similar changes in the way that ecosystems absorb solar radiation and in the patterns of carbon uptake.

Guerschman, Juan Pablo; Paruelo, José María

2005-07-01

59

Consequences of More Variable and Extreme Precipitation Regimes for Grassland Ecosystems (Invited)  

NASA Astrophysics Data System (ADS)

Precipitation patterns and amounts are critical environmental drivers for most ecosystems and rainfall patterns are forecast to become more variable, with increased frequency of large rainfall events and extended inter-rainfall droughts as well as more extreme droughts. We have been assessing the ecosystem consequences of these climate changes, using field-scale rainfall manipulation experiments to alter the timing of growing season rainfall events and to impose severe drought in intact grassland plots. Results indicate that there can be significant reductions in aboveground net primary productivity (ANPP) with altered rainfall patterns that included fewer but larger rain events and extended periods between rain events in more mesic grasslands. But this response has been variable among years. Moreover, responses in belowground net primary productivity (BNPP) do not always mirror ANPP responses. In more arid grasslands, experimental manipulations of precipitation regime can lead to responses in ANPP and BNPP opposite those in mesic grassland with the size of individual rain events having a disproportionate effect on ANPP in these drier grasslands. The role of large events, even though they are few in number, is likely very significant in grasslands, potentially offsetting the negative effects of reductions in precipitation amount. This may be true in many ecosystems. Results from extreme drought experiments in semi-arid grasslands were consistent with the view that grassland responses to alterations in precipitation inputs may depend as much on variability and patterns as on amount.

Knapp, A.; Hoover, D.; Wilcox, K.; Smith, M.

2013-12-01

60

Changes in soil organic carbon and other physical soil properties along adjacent Mediterranean forest, grassland, and cropland ecosystems in Turkey  

Microsoft Academic Search

Cultivation, overgrazing, and overharvesting are seriously degrading forest and grassland ecosystems in the Taurus Mountains of the southern Mediterranean region of Turkey. This study investigated the effects of changes on soil organic carbon (SOC) content and other physical soil properties over a 12-year period in three adjacent ecosystems in a Mediterranean plateau. The ecosystems were cropland (converted from grasslands in

F. Evrendilek; I. Celik; S. Kilic

2004-01-01

61

Future scenarios of soil water availability at managed grassland ecosystems in the Austrian Alps  

NASA Astrophysics Data System (ADS)

Available soil water is a major constraint for numerous ecosystem functions and is likely to be considerably affected by projected shifts in temperature and precipitation. Quantifying likely future changes in soil water content is therefore essential for assessing impacts of climate change on ecosystem functions. We present a data fusion approach addressing changes in soil water content of temperate grasslands in the Austrian Alps under future climate scenarios. We use a simple soil bucket model, characterized by an efficient structure and minimal requirements regarding meteorological inputs (solar radiation, precipitation and air temperature). The model is therefore suitable for the analysis of a wide range of ecological datasets. Model parameter were constrained by up to three different datasets (soil water content, evapotranspiration and snow water equivalent) using a Bayesian inversion scheme. Given a repository of data collected at ten sites in the Eastern Alps as well as a set of downscaled and error corrected (quantile mapping) regional climate scenarios, developed for the years 1961 - 2050 with 5 different regional/global climate models (CNRMRM, AITCCLM, KNMIRACMO, DMIHIRHAM, ETHZCLM) we simulated soil water content conditions under these future climate scenarios. Despite the simple model structure calibrated model runs do show a very good performance at the majority of investigated sites. Results show that if any trend can be found, the investigated ecosystems tend to higher soil water contents on average, associated with a distinct decrease in snow cover duration under future climate conditions. Regardless of these average trends some climate models cause an increasing frequency and a longer duration of extreme dry soil water conditions under future climate scenarios.

Hammerle, Albin; Calanca, Pierluigi; Themessl, Matthias; Gobiet, Andreas; Wohlfahrt, Georg

2014-05-01

62

Combining Eddy Covariance, Leaf Level Measurements and Modelling to Investigate Ecosystem Fluxes in Tropical Grasslands  

NASA Astrophysics Data System (ADS)

Our project determined seasonal and spatial variations in ecosystem fluxes of tropical grassland ecosystems by investigating three prominent grassland types along a hydrological gradient in the Okavango Delta, Botswana.To identify the environmental factors that control CO2 and H2O exchange in tropical grassland ecosystems, we successfully combined eddy covariance measurements, leaf level measurements and remotely sensed data.Grassland ecosystems growing under the same climate showed profound differences in ecosystem fluxes as well as what regulated those fluxes on an ecosystem level. The analysis of the eddy covariance measurements revealed a pronounced seasonal and spatial variation with maximum net ecosystem exchange (NE) varying between -25? mol -2 s-1 and -1? mol -2 s-1 across sites and seasons. Without water limitation the main factor for the differences in NE between ecosystems was nutrient content per vegetation unit. This importance of nutrient content was also confirmed by our leaf level measurements. Seasonal differences in NE varied between sites and were driven by phenology or temperature and light limitation.Eddy covariance measurements for this project were predominantly campaign measurements. To determine annual course and sum of NE, we adapted the ecosystem model BETHY (Biosphere-Energy Transfer Hydrology Scheme) by parameter inversion in combination with remotely sensed fraction of absorbed photosynthetically active radiation for each site.

Wohland, P.; Mantlana, B.; Kattge, J.

2007-12-01

63

Interannual and seasonal variability of CH4 and N2O exchange over a temperate mountain grassland  

NASA Astrophysics Data System (ADS)

Methane (CH4) and nitrous oxide (N2O) are major greenhouse gases and therefore play an important role in the atmosphere due to their warming potential. The various processes and mechanisms associated with the release and uptake of both compounds need further investigation to reliably assess CH4 and N2O budgets in different ecosystems. The exchange of CO2, CH4 and N2O was measured over 2 years at a temperate mountain grassland managed as a hay meadow near the village Neustift in the Stubai Valley, Austria. The three wind components, the speed of sound and the CO2mole densities were acquired at a time resolution of 20 Hz and used to calculate true eddy covariance CO2fluxes. CH4and N2O concentration values were recorded at 2 Hz, resulting in a disjunct time series when compared to the 20 Hz wind data. Fluxes of both compounds were then calculated using the virtual disjunct eddy covariance method (vDEC). The net ecosystem exchange of CO2 is monitored since 2001, while the measurement of CH4 and N2O fluxes started in April 2010. During the vegetation period, typical concentration values for CH4 and N2O were around 2.0 and 0.3 ppm, respectively, with both compounds exhibiting distinct diurnal cycles. Preliminary flux calculations showed minor, close-to-zero fluxes for both CH4 and N2O associated with large uncertainties owing to a number of corrections that need to be applied during post-processing. In this presentation we present final fluxes over two vegetation periods and investigate drivers on observed CH4and N2O emission patterns. The role of management events like harvesting of the vegetation and the spreading of manure will be investigated in detail and set in relation to previously published studies.

Hörtnagl, L.; Wohlfahrt, G.

2012-04-01

64

Winter photosynthetic activity of twenty temperate semi-desert sand grassland species.  

PubMed

The winter photosynthetic activity (quantified by net CO(2) assimilation rates and chlorophyll (Chl) a fluorescence parameters) of 20 plant species (including two lichens and two mosses) of a Hungarian temperate semi-desert sand grassland was determined on one occasion per year in 1984, 1989 and 1994. Throughout winter, the overwintering green shoots, leaves or thalli were regularly exposed to below zero temperatures at night and daytime temperatures of 0-5 degrees C. In situ tissue temperature varied between -2.1 and +6.9 degrees C and the photosynthetic photon flux density (PPFD) between 137 and 351 micromol m(-2)s(-1). Under these conditions 18 of the grassland species exhibited photosynthetic CO(2) uptake (range: vascular plants ca. 0.2-3.8 micromol m(-2)s(-1), cryptogams 0.3-2.79 micromol kg(-1)s(-1)) and values of 0.9-5.1 of the Chl fluorescence decrease ratio R(Fd). In 1984, Festuca vaginata and Sedum sexangulare had net CO(2) assimilation at leaf temperatures of -0.85 to -1.2 degrees C. In 1989, all species except Cladonia furcata showed net CO(2) assimilation at tissue temperatures of 0 to +3.3 degrees C, with the highest rates observed in Poa bulbosa and F. vaginata. The latter showed a net CO(2) assimilation saturation at a PPFD of 600 micromol m(-2)s(-1) and a temperature optimum between +5 and +18 degrees C. At the 1994 measurements, the photosynthetic rates were higher at higher tissue water contents. The two mosses and lichens had a net photosynthesis (range: 1.1-2.79 micromol CO(2)kg(-1)s(-1)) at 2 degrees C tissue temperature and at 4-5 degrees C air temperature. Ca. 80% of the vascular grassland plant species maintained a positive C-balance during the coldest periods of winter, with photosynthetic rates of 1.5-3.8 micromol CO(2)m(-2)s(-1). In an extremely warm beginning March of the relatively warm winter of 2006/2007, the dicotyledonous plants had much higher CO(2) assimilation rates on a Chl (range 6-14.9 micromol g(-1)Chl s(-1)) and on a dry weight basis (9-48 micromol kg(-1)dw s(-1)) than in the cold winter of 1994. However, the assimilation rates of the three investigated cryptogams (Tortula and two Cladonia) and the two grasses Festuca and Poa were not affected by this increase. The results indicate that the photosynthetic activity of temperate semi-desert sand grassland species can help somewhat in slowing the general CO(2) rise in winter and function as a potential carbon sink of the investigated semi-desert Hungarian grassland species. PMID:18346813

Tuba, Zoltán; Csintalan, Zsolt; Szente, Kálmán; Nagy, Zoltán; Fekete, Gábor; Larcher, Walter; Lichtenthaler, Hartmut K

2008-09-29

65

How do sheep affect plant communities and arthropod populations in temperate grasslands?  

PubMed

Grasslands being used in sheep farming systems are managed under a variety of agricultural production, recreational and conservational objectives. Although sheep grazing is rarely considered the best method for delivering conservation objectives in seminatural temperate grasslands, the literature does not provide unequivocal evidence on the impact of sheep grazing on pasture biodiversity. Our aim was therefore to review evidence of the impacts of stocking rate, grazing period and soil fertility on plant communities and arthropod populations in both mesotrophic grasslands typical of agriculturally improved areas and in native plant communities. We therefore conducted a literature search of articles published up to the end of the year 2010 using 'sheep' and 'grazing' as keywords, together with variables describing grassland management, plant community structure or arthropod taxa. The filtering process led to the selection of 48 articles, with 42 included in the stocking rate dataset, 9 in the grazing period dataset and 10 in the soil fertility dataset. The meta-analysis did not reveal any significant trends for plant species richness or plant community evenness along a wide stocking rate gradient. However, we found frequent shifts in functional groups or plant species abundance that could be explained by the functional properties of the plants in the community. The meta-analysis confirmed that increasing soil fertility decreased plant species richness. Despite the very limited dataset, plant species richness was significantly greater in autumn-grazed pastures than in ungrazed areas, which suggests that choosing an appropriate grazing period would be a promising option for preserving biodiversity in sheep farming systems. Qualitative review indicated that low grazing intensity had positive effects on Orthoptera, Hemiptera (especially phytophagous Auchenorrhyncha) and, despite a diverse range of feeding strategies, for the species richness of Coleoptera. Lepidoptera, which were favoured by more abundant flowering plants, also benefited from low grazing intensities. Spider abundance and species richness were higher in ungrazed than in grazed pastures. In contrast, there are insufficient published studies to draw any firm conclusions on the benefits of late grazing or stopping fertilization on insect diversity, and no grounds for including any of this information in decision support tools at this stage. PMID:23031474

Scohier, A; Dumont, B

2012-07-01

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

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

NASA Astrophysics Data System (ADS)

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 we present our experiences in conducting the monitoring of grassland ecosystem degradation in north China. Using the EOS/MODIS data, we develop an applicable method for the monitoring on the basis of net primary productivity (NPP). We assume that there is always a turf without degradation in the area of the same hydrothermal condition and type of grassland. We then use the NPP of the turf to determine the level of degradation in this area. The grassland region in north China can be divided into a number of small sub-regions for the determination and the division of sub-regions can be done according to the types of grassland. As far as every sub-region is concerned, we take the max NPP as the base line to determine the degradation of other pixels in the sub-region. The degradation can be graded into five levels: serious degradation, high degradation, medium degradation, light degradation and non-degradation. Finally we apply the method to analyze the spatial characteristics of grassland degradation in north China in the year 2005. The results show that the situation of grassland degradation in north China is very serious. 95.57% of the grassland in north China has suffered from deterioration to various levels, among which serious degradation, high degradation, medium degradation and light degradation account for 41.06%, 33.52%, 11.72% and 9.28% of the total, respectively.

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

2006-09-01

68

Climate change effects on groundwater dependent temperate forest ecosystems  

NASA Astrophysics Data System (ADS)

Models developed to predict the influence of changing climate on ecosystems often concentrate on vegetation in connection with soil moisture, but usually omit groundwater. However in temperate climate zones, groundwater can have a profound effect on the reaction of vegetation to climate change, because it strongly influences the spatio-temporal distribution of soil moisture and therefore water and oxygen stress of vegetation. Here we focus on the qualitative and quantitative effects of climate change on the zonation of vegetation and groundwater dynamics along a hill slope. To study this we developed a fully coupled hydrological-vegetation model, for a groundwater influenced temperate forest ecosystem. The vegetation model is based on the carbon assimilation model of Farquhar et al. (1980) and the extension of Daly et al. (2004), which includes transpiration of vegetation and accounts for the response to low soil moisture content. We modified this model to account for vegetation response to high soil moisture contents due to high groundwater levels, and we extended the model to include light competition, phenology and vegetation growth. To simulate the hydrological system the saturated-unsaturated flow model by van Beek (2002) is used. The coupled model was first compared to measured semi-hourly flux tower data of H2O and CO2, showing good results. Than simulation runs of 1000 years were performed to study the effect of climate change on soil water, groundwater and vegetation. We performed simulation runs with competition between wet and dry adapted species under current conditions and after climate change. Meteorological time series for the 2100 climate (SRESA2) were obtained from downscaling 6 different regional climate model runs from the ENSEMBLES project with a stochastic weather generator (Kilby et al., 2007). Results show that in the zones were the groundwater system is close to the surface, climate change causes large shifts in vegetation zonation of the dry and wet adapted species along the slope. On the other hand, effect on growth rate of vegetation in areas where groundwater is deeper is very small. This is caused by the buffering capacity of both the vegetation and the hydrological system, resulting in relatively small changes in vegetation dynamics. This study shows the importance of using a coupled groundwater vegetation model when studying temperate lowland areas. The coupled hydrological-vegetation model allows for detailed studies of qualitative and quantitative changes in spatial temporal patterns of vegetation under changing climate.

Bierkens, M. F.; Brolsma, R. J.; van Beek, R. L.; van Vliet, M. T.

2008-12-01

69

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

70

Seasonal and interannual variation in carbon dioxide, water vapor and energy fluxes in a northern temperate grassland  

Microsoft Academic Search

We made eddy covariance measurements of carbon dioxide, water vapor and energy flux in a native Canadian grassland ecosystem during 1998-2001. Our study period included a year with near average precipitation (1999), a year with higher than average precipitation (1998), and a year with below average precipitation (2000). Our objective was to analyze the effects of interannual climate variation on

L. B. Flanagan; L. A. Wever; P. J. Carlson

2001-01-01

71

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

72

Neogene paleoenvironmental and paleoclimatic change in southern temperate ecosystems — a southern perspective  

Microsoft Academic Search

Recently, a greatly increased number of macrofossil and pollen analytical records from Australasia and southern South America has permitted, for the first time, a comprehensive overview of past vegetation and climate change in southern temperate ecosystems. While the course of Neogene climatic change has been comparable to that of the temperate northern hemisphere, a distinctive southern hemisphere vegetation has evolved,

Vera Markgraf; Matt McGlone; Geoff Hope

1995-01-01

73

Ecosystem development in roadside grasslands: Biotic control, plant-soil interactions, and dispersal limitations  

USGS Publications Warehouse

Roadside grasslands undergoing secondary succession are abundant, and represent ecologically meaningful examples of novel, human-created ecosystems. Interactions between plant and soil communities (hereafter plant-soil interactions) are of major importance in understanding the role of biotic control in ecosystem functioning, but little is known about these links in the context of ecosystem restoration and succession. The assessment of the key biotic communities and interactions driving ecosystem development will help practitioners to better allocate the limited resources devoted to roadside grassland restoration. We surveyed roadside grasslands from three successional stages (0-2, 7-9, and > 20 years) in two Mediterranean regions of Spain. Structural equation modeling was used to evaluate how interactions between plants, biological soil crusts (BSCs), and soil microbial functional diversity (soil microorganisms) affect indicators of ecosystem development and restoration: plant similarity to the reference ecosystem, erosion control, and soil C storage and N accumulation. Changes in plant community composition along the successional gradient exerted the strongest influence on these indicators. High BSC cover was associated with high soil stability, and high soil microbial functional diversity from late-successional stages was associated with high soil fertility. Contrary to our expectations, the indirect effects of plants, mediated by either BSCs or soil microorganisms, were very weak in both regions, suggesting a minor role for plant-soil interactions upon ecosystem development indicators over long periods. Our results suggest that natural vegetation dynamics effectively improved ecosystem development within a time frame of 20 years in the grasslands evaluated. They also indicate that this time could be shortened if management actions focus on: (1) maintaining wellconserved natural areas close to roadsides to enhance plant compositional changes towards late-successional stages, (2) increasing BSC cover in areas under strong erosion risk, to avoid soil loss, and (3) enhancing soil microbial functional diversity in resource-limited areas, to enhance soil C and N accumulation. ?? 2011 by the Ecological Society of America.

Garcia-Palacios, P.; Bowker, M. A.; Maestre, F. T.; Soliveres, S.; Valladares, F.; Papadopoulos, J.; Escudero, A.

2011-01-01

74

Ecosystem development in roadside grasslands: biotic control, plant-soil interactions, and dispersal limitations.  

PubMed

Roadside grasslands undergoing secondary succession are abundant, and represent ecologically meaningful examples of novel, human-created ecosystems. Interactions between plant and soil communities (hereafter plant-soil interactions) are of major importance in understanding the role of biotic control in ecosystem functioning, but little is known about these links in the context of ecosystem restoration and succession. The assessment of the key biotic communities and interactions driving ecosystem development will help practitioners to better allocate the limited resources devoted to roadside grassland restoration. We surveyed roadside grasslands from three successional stages (0-2, 7-9, and >20 years) in two Mediterranean regions of Spain. Structural equation modeling was used to evaluate how interactions between plants, biological soil crusts (BSCs), and soil microbial functional diversity (soil microorganisms) affect indicators of ecosystem development and restoration: plant similarity to the reference ecosystem, erosion control, and soil C storage and N accumulation. Changes in plant community composition along the successional gradient exerted the strongest influence on these indicators. High BSC cover was associated with high soil stability, and high soil microbial functional diversity from late-successional stages was associated with high soil fertility. Contrary to our expectations, the indirect effects of plants, mediated by either BSCs or soil microorganisms, were very weak in both regions, suggesting a minor role for plant-soil interactions upon ecosystem development indicators over long periods. Our results suggest that natural vegetation dynamics effectively improved ecosystem development within a time frame of 20 years in the grasslands evaluated. They also indicate that this time could be shortened if management actions focus on: (1) maintaining well-conserved natural areas close to roadsides to enhance plant compositional changes towards late-successional stages, (2) increasing BSC cover in areas under strong erosion risk, to avoid soil loss, and (3) enhancing soil microbial functional diversity in resource-limited areas, to enhance soil C and N accumulation. PMID:22073661

García-Palacios, Pablo; Bowker, Matthew A; Maestre, Fernando T; Soliveres, Santiago; Valladares, Fernando; Papadopoulos, Jorge; Escudero, Adrián

2011-10-01

75

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

76

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

77

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

Microsoft Academic Search

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

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

2010-01-01

78

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

79

Mediterranean grassland soil fungi: Patterns of biodiversity, functional redundancy and soil carbon storage  

Microsoft Academic Search

Soil organic matter is a relevant carbon reservoir and CO2 sink in temperate grassland ecosystems and increased carbon uptake may mitigate climate change. Relatively little is known about the relationship between ecosystem function and soil fungal biodiversity in grasslands. However, this relationship is important because the saprotrophic microorganisms within the decomposer chain may, given their important role in the decomposition

A. M. Persiani; O. Maggi; J. Montalvo; M. A. Casado; F. D. Pineda

2008-01-01

80

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

81

A review of the most economically important poisonous plants to the livestock industry on temperate grasslands of China.  

PubMed

The majority of the literature on poisonous plant species in China is published in Chinese and not available to the majority of interested researchers and grassland managers in other countries. Therefore, a review of the Chinese literature was conducted to summarize the occurrence of poisonous plant species on temperate grasslands in China. We reviewed the literature to obtain general information on poisonous species but focus on locoweeds (Astragalus and Oxytropis spp.), drunken horse grass [Achnatherum inebrians (Hance) Keng ex Tzvelev] and langdu (Stellera chamaejasme L.) for information on their toxins, distribution and ecology, control methods and alternate uses. Of the almost 1300 poisonous species found on grasslands in China, these species are responsible for an estimated 80% of all livestock losses. This includes loss of performance as well as mortality. The locoweeds are a complex made up of Oxytropis and Astragalus species. The toxic principle in this complex, as well as in drunken horse grass, is the result of an endophyte fungus whereas in langdu it is produced by the plant. All these species are native to the grasslands, which suggest they have been a problem ever since herding began. Over that period of at least several millennia, herders would have learned and adapted to the presence of poisonous species. Strategies were developed and therapies employed to allow the animals to cope before and after poisoning. Nevertheless, grazing management could still be refined that would allow the use of the toxic legumes, while preventing poisonous symptoms, as has been tested elsewhere. PMID:23015535

Zhao, Mengli; Gao, Xinlei; Wang, Jing; He, Xiaolei; Han, Bing

2013-01-01

82

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.

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

2014-01-01

83

Does Plant Diversity Affect Carbon and Water-Use Efficiency in Grasslands? Evidence from a Biodiversity and Ecosystem Functioning Experiment  

NASA Astrophysics Data System (ADS)

In view of rapid species loss on a global scale it is imperative that we shed more light on how this loss of diversity will affect the functioning and functions of ecosystems. Previous research on biodiversity and ecosystem functioning has shown that plant biodiversity often has a positive relationship to net primary productivity (NPP), and/or net ecosystem productivity (NEP), particularly in temperate grassland systems (Hector et al 2002). One of the big ensuing questions is whether plant diversity also affects nutrient cycling and biogeochemical cycles in ecosystems. A more detailed look at the dynamics of carbon and water-use changes caused by plant diversity has only recently occurred (Caldeira et al 2001) but there is still much work to be done in this area. A large-scale grassland experiment entitled "The Jena Experiment" was started in spring 2002 in Germany in order to investigate the effect of plant diversity on ecosystem functioning, focussing mainly on element cycling and trophic interactions. Out of a total species pool of 60 species mixtures of 1 to 16 species and one to four functional groups were randomly selected and seeded as newly established communities on 82 plots of 20 x 20 m. The four functional groups consist of grasses, small and tall herbs, and legume species. With the use of natural abundance stable isotope ratios (?13C and ? 15N) in aboveground plant material, the relationship between plant diversity (both functional and species-driven) and productivity, water-use efficiency and nitrogen cycling was investigated. Results so far, show increased above-ground productivity with increasing species diversity as well as with increasing functional diversity of plants in a system. At community level, both carbon and nitrogen concentrations as well as ?13C in plants remained similar across the diversity gradient. In contrast we found a decrease in ? 15N values with increasing plant diversity. This suggests that bigger total carbon pools in more diverse systems can be attributed only to higher biomass, whereas some form of fractionation of ? 15N seems to be occurring during N uptake or in the soil in the most species-rich systems. Soil carbon also did not tend to respond to plant diversity levels. At the whole system scale there was no evidence for changes in water-use efficiency over the diversity gradient. Implications for the functioning of future grassland systems with reduced diversity will be discussed. References Caldeira, M. C., R. J. Ryel, et al. (2001) Mechanisms of positive biodiversity-production relationships: insights provided by delta C-13 analysis in experimental Mediterranean grassland plots. Ecology Letters 4(5): 439-443. Hector, A., E. Bazeley-White, et al. (2002). Overyielding in grassland communities: testing the sampling effect hypothesis with replicated biodiversity experiments. Ecology Letters 5(4): 502-511.

Temperton, V. M.; Buchmann, N.; Steinbeiß, S.; Gleixner, G.; Schulze, D.

2004-12-01

84

Interannual and seasonal variability of CH4 and N2O exchange over a temperate mountain grassland  

NASA Astrophysics Data System (ADS)

The quantification and understanding of the greenhouse gas (GHG) exchange between terrestrial ecosystems and the atmosphere is crucial when trying to assess the effect of anthropogenic and biogenic controls on a future climate. Using the eddy covariance method, fluxes of CO2 have been measured over a wide array of ecosystems, while measurements of the other two major GHG, methane (CH4) and nitrous oxide (N2O), were only conducted by few groups due to expensive scalar sensors and their time-consuming maintenance. These first measurments mainly focused on ecosystems that were believed to represent significant sources for CH4 (e.g. wetlands) or N2O (e.g. heavily fertilized crops). With CH4 and N2O measurement devices now being widely available, more measurements are made over sites that are characterized by relatively small and often close-to-zero fluxes, and despite recent advances in sensor sensitivity and stability, the quantification of these two GHG remains challenging. Here we report on the CO2, CH4 and N2O exchange measured over 2 years at a temperate mountain grassland managed as a hay meadow near the village Neustift in the Stubai Valley, Austria, by means of the eddy covariance method. The three wind components, the speed of sound and the CO2 mole densities were acquired at a time resolution of 20 Hz and used to calculate true eddy covariance CO2 fluxes. CH4 and N2O mixing ratios were recorded at 2 Hz by a quantum cascade laser absorption spectrometer (QCL-AS), resulting in a disjunct time series when compared to the 20 Hz wind data. Fluxes of both compounds were then calculated using the virtual disjunct eddy covariance method (vDEC). Mixing ratios of CH4 and N2O were then corrected for the cross-talk effect of water as described in earlier studies. The net ecosystem exchange of CO2 at the study site is monitored continously since 2001, while the measurement of CH4 and N2O fluxes started in April 2010. During the vegetation period, typical concentration values for CH4 and N2O were around 2.0 and 0.3 ppm, respectively, exhibiting distinct diurnal cycles. Emission and uptake could be observed for both compounds, and exchange rates showed a clear diurnal cycle during certain time periods. During the day, relatively large amounts of methane were emitted in September 2011, with peak emission rates of 24.9 nmol m-2 s-1 around noon, while relatively strong emissions of nitrous oxide could be observed in August 2011 (0.9 nmol m-2 s-1). However, during calm and stable nighttime conditions, mixing ratios of both compounds were often erratic with distinct spikes and high ambient concentration values, which propagated into the flux calculations and resulted in similarly erratic exchange rates, making further despiking necessary. The drivers of of CH4 and N2O exchange patterns during undisturbed conditions and the effect of management events like harvesting and the spreading of manure are investigated and set in relation to previously published studies on this matter.

Hörtnagl, L. J.; Wohlfahrt, G.

2012-12-01

85

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

86

Land use affects the net ecosystem CO2 exchange and its components in mountain grasslands  

PubMed Central

Changes in land use and management have been strongly affecting mountain grassland, however, their effects on the net ecosystem exchange of CO2 (NEE) and its components have not yet been well documented. We analysed chamber-based estimates of NEE, gross primary productivity (GPP), ecosystem respiration (R) and light use efficiency (LUE) of six mountain grasslands differing in land use and management, and thus site fertility, for the growing seasons of 2002 to 2008. The main findings of the study are that: (1) land use and management affected seasonal NEE, GPP and R, which all decreased from managed to unmanaged grasslands; (2) these changes were explained by differences in leaf area index (LAI), biomass and leaf-area-independent changes that were likely related to photosynthetic physiology; (3) diurnal variations of NEE were primarily controlled by photosynthetically active photon flux density and soil and air temperature; seasonal variations were associated with changes in LAI; (4) parameters of light response curves were generally closely related to each other, and the ratio of R at a reference temperature/ maximum GPP was nearly constant across the sites; (5) similarly to our study, maximum GPP and R for other grasslands on the globe decreased with decreasing land use intensity, while their ratio remained remarkably constant. We conclude that decreasing intensity of management and, in particular, abandonment of mountain grassland lead to a decrease in NEE and its component processes. While GPP and R are generally closely coupled during most of the growing season, GPP is more immediately and strongly affected by land management (mowing, grazing) and season. This suggests that management and growing season length, as well as their possible future changes, may play an important role for the annual C balance of mountain grassland.

Schmitt, M.; Bahn, M.; Wohlfahrt, G.; Tappeiner, U.; Cernusca, A.

2011-01-01

87

Productivity and sustainability influenced by biodiversity in grassland ecosystems  

Microsoft Academic Search

THE functioning and sustainability of ecosystems may depend on their biological diversity1-8. Elton's9 hypothesis that more diverse ecosystems are more stable has received much attention1,3,6,7,10-14, but Darwin's proposal6,15 that more diverse plant communities are more productive, and the related conjectures4,5,16,17 that they have lower nutrient losses and more sustainable soils, are less well studied4-6,8,17,18. Here we use a well-replicated field

David Tilman; David Wedin; Johannes Knops

1996-01-01

88

Seasonal changes in the soil microbial community in a grassland plant diversity gradient four years after establishment  

Microsoft Academic Search

Aboveground plant diversity is known to influence belowground diversity and ecosystem processes. However, the knowledge on soil microbial succession from an agricultural field to grassland varying in plant diversity is scarce. Therefore, we investigated the effects of vegetation cover, varying plant biodiversity and season on soil microbial parameters in a temperate grassland ecosystem. In May and October 2006 mixed soil

Maike Habekost; Nico Eisenhauer; Stefan Scheu; Sibylle Steinbeiss; Alexandra Weigelt; Gerd Gleixner

2008-01-01

89

The impacts of drainage, nutrient status and management practice on the full carbon balance of grasslands on organic soils in a maritime temperate zone  

NASA Astrophysics Data System (ADS)

Temperate grasslands on organic soils are diverse due to edaphic properties but also to regional management practices and this heterogeneity is reflected in the wide range of greenhouse gas flux values reported in the literature. In Ireland, most grasslands on organic soils were drained several decades ago and are managed as extensive pastures with little or no fertilisation. This study describes a two-year study of the net ecosystem carbon balance (NECB) of two such sites. We determined greenhouse gas (GHG) fluxes and waterborne carbon emissions in a nutrient rich grassland and compared it with values measured from two nutrient poor organic soils: a deep drained and a shallow drained site. GHG fluxes (CO2, CH4 and N2O) were determined using the chamber technique, and fluvial C fluxes were estimated by combining drainage water concentrations and flows. The nutrient rich site was an annual source of CO2 (NEE 233 g C m-2yr-1), CH4 neutral, and a small source of nitrous oxide (1.6 kg N2O-N ha-1yr-1). NEE at the shallow drained site was -89 and -99 g C m-2yr-1 in Years 1 and 2 respectively, and NEE at the deep drained site was +85 and -26 g C m-2yr-1 respectively. Low CH4 emissions (1.3 g C m-2yr-1) were recorded at the shallow drained nutrient poor site. Fluvial exports from the nutrient rich site totalled 69.8 g C m-2yr-1 with 54% as dissolved organic C (DOC). Waterborne C losses from the nutrient poor site reflected differences in annual runoff totalling 44 g C m-2yr-1 in Year 1 and 30.8 g C m-2yr-1 in Year 2. The NECB of the nutrient rich grassland was 663 g C m-2yr-1 with biomass exports being the major component accounting for 53%. The NECB of the nutrient poor deep drained site was less than half of the nutrient rich site (2 year mean 267 g C m-2yr-1). Although NEE at the nutrient poor shallow drained site was negative in both years, high biomass export meant it was a net C source (2 year mean NECB 103 g C m-2yr-1). While the impacts of the nutrient and drainage status on NEE, biomass exports and fluvial C losses were confirmed, inter-regional differences in management practice and climate are also significant factors which impact on the overall NECB of these ecosystems. Contrary to expectation, the NECB of nutrient poor drained organic soils under grasslands is not necessarily a large C source and this has implications for Ireland's choice of national GHG inventory reporting methodologies. This study can also aid the development of strategies to deliver reduced emissions tailored to local grassland types.

Renou-Wilson, F.; Barry, C.; Müller, C.; Wilson, D.

2014-04-01

90

Soil heavy metal concentrations, microbial biomass and enzyme activities in a contaminated grassland ecosystem  

Microsoft Academic Search

Soil enzyme activities and microbial biomass were measured in a grassland ecosystem with a wide range of heavy metal concentrations ranging from 7.2 to 48.1 mmol kg?1 (As, Cd, Cr, Cu, Ni, Pb and Zn) in portions of the U.S. Army's Aberdeen Proving Ground, Maryland, U.S.A. Total and fluorescein diacetate active (FDA) fungal biomass, FDA-active bacterial biomass, substrate-induced respiration (SIR),

Roman G. Kuperman; Margaret M. Carreiro

1997-01-01

91

Tropical freshwater ecosystems have lower bacterial growth efficiency than temperate ones  

PubMed Central

Current models and observations indicate that bacterial respiration should increase and growth efficiency (BGE) should decrease with increasing temperatures. However, these models and observations are mostly derived from data collected in temperate regions, and the tropics are under-represented. The aim of this work was to compare bacterial metabolism, namely bacterial production (BP) and respiration (BR), bacterial growth efficiency (BGE) and bacterial carbon demand (BCD) between tropical and temperate ecosystems via a literature review and using unpublished data. We hypothesized that (1) tropical ecosystems have higher metabolism than temperate ones and, (2) that BGE is lower in tropical relative to temperate ecosystems. We collected a total of 498 coupled BP and BR observations (Ntotal = 498; Ntemperate = 301; Ntropical = 197), calculated BGE (BP/(BP+BR)) and BCD (BP+BR) for each case and examined patterns using a model II regression analysis and compared each parameter between the two regions using non-parametric Mann–Whitney U test. We observed a significant positive linear regression between BR and BP for the whole dataset, and also for tropical and temperate data separately. We found that BP, BR and BCD were higher in the tropics, but BGE was lower compared to temperate regions. Also, BR rates per BP unit were at least two fold higher in the tropics than in temperate ecosystems. We argue that higher temperature, nutrient limitation, and light exposure all contribute to lower BGE in the tropics, mediated through effects on thermodynamics, substrate stoichiometry, nutrient availability and interactions with photochemically produced compounds. More efforts are needed in this study area in the tropics, but our work indicates that bottom-up (nutrient availability and resource stoichiometry) and top-down (grazer pressure) processes, coupled with thermodynamic constraints, might contribute to the lower BGE in the tropics relative to temperate regions.

Amado, Andre M.; Meirelles-Pereira, Frederico; Vidal, Luciana O.; Sarmento, Hugo; Suhett, Albert L.; Farjalla, Vinicius F.; Cotner, James B.; Roland, Fabio

2013-01-01

92

Seasonal and interannual variation in carbon dioxide, water vapor and energy fluxes in a northern temperate grassland  

NASA Astrophysics Data System (ADS)

We made eddy covariance measurements of carbon dioxide, water vapor and energy flux in a native Canadian grassland ecosystem during 1998-2001. Our study period included a year with near average precipitation (1999), a year with higher than average precipitation (1998), and a year with below average precipitation (2000). Our objective was to analyze the effects of interannual climate variation on ecosystem metabolism. Change in soil moisture was the most important ecological factor controlling carbon gain in this grassland ecosystem. Maximum gross photosynthesis and apparent quantum yield differed among years at the time of peak photosynthetic activity. The ecosystem accumulated a total of 112 g C per square meter from the time the eddy covariance measurements were initiated in June 1998 until the end of December 2000, with most of the C gained during 1998. Calculations of bulk parameters such as omega and the Priestley-Taylor coefficient indicated that evapotranspiration was strongly controlled by surface conductance in this grassland. A non-linear model that included functions for vapor pressure deficit, photon flux density, and available soil moisture explained a large proportion of the variation in the surface conductance data. In order to accurately model surface conductance, separate model coefficients need to be used for a wet year compared to average and drought years, which had very similar model coefficients. Our data indicated that carbon and water flux varies asymmetrically in response to interannual variation in precipitation, with increases in productivity and water-use in a wet year being much more pronounced than reductions in a drought year.

Flanagan, L. B.; Wever, L. A.; Carlson, P. J.

2001-12-01

93

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

94

Partitioning of evapotranspiration and its controls in four grassland ecosystems: Application of a two-source model  

Microsoft Academic Search

Quantifying the partitioning of evapotranspiration (ET) and its controls are particularly important for accurate prediction of the climatic response of ecosystem carbon, water, and energy budgets. In this study, we employed the Shuttleworth–Wallace model to partition ET into soil water evaporation (E) and vegetation transpiration (T) at four grassland ecosystems in China. Two to three years (2003–2005) of continuous measurements

Zhongmin Hu; Guirui Yu; Yanlian Zhou; Xiaomin Sun; Yingnian Li; Peili Shi; Yanfen Wang; Xia Song; Zemei Zheng; Li Zhang; Shenggong Li

2009-01-01

95

Current Distribution of Ecosystem Functional Types in Temperate South America  

Microsoft Academic Search

We described, classified, and mapped the functional heterogeneity of temperate South America using the seasonal dynamics of\\u000a the Normalized Difference Vegetation Index (NDVI) from NOAA\\/AVHRR satellites for a 10-year period. From the seasonal curves\\u000a of NDVI, we calculated (a) the annual integral (NDVI-1), used as an estimate of the fraction of photosynthetic active radiation\\u000a absorbed by the canopy and hence

José M. Paruelo; Esteban G. Jobbágy; Osvaldo E. Sala

2001-01-01

96

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

97

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 10Ĺ 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; Pińeiro, Gustavo; Gutiérrez, Ofelia; Panario, Daniel

2012-11-01

98

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.

Xia, Jianyang; Wan, Shiqiang

2012-01-01

99

Simulating the impacts of land use in northwest Europe on Net Ecosystem Exchange (NEE): the role of arable ecosystems, grasslands and forest plantations in climate change mitigation.  

PubMed

In this study, we compared measured and simulated Net Ecosystem Exchange (NEE) values from three wide spread ecosystems in the southeast of Ireland (forest, arable and grassland), and investigated the suitability of the DNDC (the DeNitrification-DeComposition) model to estimate present and future NEE. Although, the field-DNDC version overestimated NEE at temperatures >5 °C, forest-DNDC under-estimated NEE at temperatures >5 °C. The results suggest that the field/forest DNDC models can successfully estimate changes in seasonal and annual NEE from these ecosystems. Differences in NEE were found to be primarily land cover specific. The annual NEE was similar for the grassland and arable sites, but due to the contribution of exported carbon, the soil carbon increased at the grassland site and decreased at the arable site. The NEE of the forest site was an order of magnitude larger than that of the grassland or arable ecosystems, with large amounts of carbon stored in woody biomass and the soil. The average annual NEE, GPP and Reco values over the measurement period were -904, 2379 and 1475 g C m(-2) (forest plantations), -189, 906 and 715 g C m(-2) (arable systems) and -212, 1653 and 1444 g C m(-2) (grasslands), respectively. The average RMSE values were 3.8 g C m(-2) (forest plantations), 0.12 g C m(-2) (arable systems) and 0.21 g C m(-2) (grasslands). When these models were run with climate change scenarios to 2060, predictions show that all three ecosystems will continue to operate as carbon sinks. Further, climate change may decrease the carbon sink strength in the forest plantations by up to 50%. This study supports the use of the DNDC model as a valid tool to predict the consequences of climate change on NEE from different ecosystems. PMID:23384575

Abdalla, Mohamed; Saunders, Matthew; Hastings, Astley; Williams, Mike; Smith, Pete; Osborne, Bruce; Lanigan, Gary; Jones, Mike B

2013-11-01

100

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

101

Testing the Link between Functional Diversity and Ecosystem Functioning in a Minnesota Grassland Experiment  

PubMed Central

The functional diversity of a community can influence ecosystem functioning and reflects assembly processes. The large number of disparate metrics used to quantify functional diversity reflects the range of attributes underlying this concept, generally summarized as functional richness, functional evenness, and functional divergence. However, in practice, we know very little about which attributes drive which ecosystem functions, due to a lack of field-based tests. Here we test the association between eight leading functional diversity metrics (Rao’s Q, FD, FDis, FEve, FDiv, convex hull volume, and species and functional group richness) that emphasize different attributes of functional diversity, plus 11 extensions of these existing metrics that incorporate heterogeneous species abundances and trait variation. We assess the relationships among these metrics and compare their performances for predicting three key ecosystem functions (above- and belowground biomass and light capture) within a long-term grassland biodiversity experiment. Many metrics were highly correlated, although unique information was captured in FEve, FDiv, and dendrogram-based measures (FD) that were adjusted by abundance. FD adjusted by abundance outperformed all other metrics in predicting both above- and belowground biomass, although several others also performed well (e.g. Rao’s Q, FDis, FDiv). More generally, trait-based richness metrics and hybrid metrics incorporating multiple diversity attributes outperformed evenness metrics and single-attribute metrics, results that were not changed when combinations of metrics were explored. For light capture, species richness alone was the best predictor, suggesting that traits for canopy architecture would be necessary to improve predictions. Our study provides a comprehensive test linking different attributes of functional diversity with ecosystem function for a grassland system.

Butterfield, Bradley J.; Reich, Peter B.

2012-01-01

102

Testing the link between functional diversity and ecosystem functioning in a Minnesota grassland experiment.  

PubMed

The functional diversity of a community can influence ecosystem functioning and reflects assembly processes. The large number of disparate metrics used to quantify functional diversity reflects the range of attributes underlying this concept, generally summarized as functional richness, functional evenness, and functional divergence. However, in practice, we know very little about which attributes drive which ecosystem functions, due to a lack of field-based tests. Here we test the association between eight leading functional diversity metrics (Rao's Q, FD, FDis, FEve, FDiv, convex hull volume, and species and functional group richness) that emphasize different attributes of functional diversity, plus 11 extensions of these existing metrics that incorporate heterogeneous species abundances and trait variation. We assess the relationships among these metrics and compare their performances for predicting three key ecosystem functions (above- and belowground biomass and light capture) within a long-term grassland biodiversity experiment. Many metrics were highly correlated, although unique information was captured in FEve, FDiv, and dendrogram-based measures (FD) that were adjusted by abundance. FD adjusted by abundance outperformed all other metrics in predicting both above- and belowground biomass, although several others also performed well (e.g. Rao's Q, FDis, FDiv). More generally, trait-based richness metrics and hybrid metrics incorporating multiple diversity attributes outperformed evenness metrics and single-attribute metrics, results that were not changed when combinations of metrics were explored. For light capture, species richness alone was the best predictor, suggesting that traits for canopy architecture would be necessary to improve predictions. Our study provides a comprehensive test linking different attributes of functional diversity with ecosystem function for a grassland system. PMID:23300787

Clark, Christopher M; Flynn, Dan F B; Butterfield, Bradley J; Reich, Peter B

2012-01-01

103

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

104

Changes in soil microbial biomass and residual indices as ecological indicators of land use change in temperate permanent grassland.  

PubMed

The relationship between microbial biomass, residues and their contribution to microbial turnover is important to understand ecosystem C storage. The effects of permanent grassland (100 % ryegrass--PG), conversion to modified grassland (mixture of grass and clover--MG) or maize monoculture (MM) on the dynamics of soil organic C (SOC), microbial biomass, fungal ergosterol and microbial residues (bacterial muramic acid and fungal glucosamine) were investigated. Cattle slurry was applied to quantify the effects of fertilisation on microbial residues and functional diversity of microbial community across land use types. Slurry application significantly increased the stocks of microbial biomass C and S and especially led to a shift in microbial residues towards bacterial tissue. The MM treatment decreased the stocks of SOC, microbial biomass C, N and S and microbial residues compared with the PG and MG treatments at 0-40 cm depth. The MM treatment led to a greater accumulation of saprotrophic fungi, as indicated by the higher ergosterol-to-microbial biomass C ratio and lower microbial biomass C/S ratio compared with the grassland treatments. The absence of a white clover population in the PG treatment caused a greater accumulation of fungal residues (presumably arbuscular mycorrhizal fungi (AMF), which do not contain ergosterol but glucosamine), as indicated by the significantly higher fungal C-to-bacterial C ratio and lower ergosterol-to-microbial biomass C ratio compared with the MG treatment. In addition to these microbial biomass and residual indices, the community level physiological profiles (CLPP) demonstrated distinct differences between the PG and MG treatments, suggesting the potential of these measurements to act as an integrative indicator of soil functioning. PMID:24549746

Murugan, Rajasekaran; Loges, Ralf; Taube, Friedhelm; Sradnick, André; Joergensen, Rainer Georg

2014-05-01

105

Responses of desert, semi-arid grassland and scrub-oak ecosystems to elevated CO2  

NASA Astrophysics Data System (ADS)

We compared observations from free air CO2 enrichment (FACE) experiments at dry (desert, semi-arid grassland and scrub-oak) sites, to predictions from a suite of ecosystem models with differing complexity, ranging from a parsimonious forest growth model (GDAY) to a comprehensive land surface model (OCN). Dry ecosystems have often been predicted to increase in net primary productivity (NPP) and net C uptake over time in response to elevated CO2 (eCO2) because of increased N fixation, and alleviation of drought-stress due to reduced stomatal conductance. However, experiments at the Nevada Desert FACE (NDFF), the semi-arid prairie grassland FACE (PHACE), and the scrub-oak Kennedy Space Center open-top chamber experiment (KSCO), have revealed that dry ecosystems display a more complex biogeochemical response to eCO2. Insights into the processes determining the responses of dry ecosystems to eCO2 were gained by evaluating model estimates against site data, and by dissecting model responses to eCO2. Site level findings at PHACE indicated that eCO2 enabled more rapid C turnover, resulting in a net ecosystem C loss. Conversely, at PHACE, models such as OCN simulated a decrease in N leaching and an increase in NPP because of eCO2, leading to increased C storage. Leaf cover and NPP at KSCO initially increased with eCO2 before declining due to reduced N fixation and increased N leaching. At NDFF, eCO2 only increased plant growth during one abnormally wet year; in subsequent years, soil crust cyanobacteria decreased in abundance, and gains in biomass were not sustained. In OCN simulations at NDFF, eCO2 increased water-use efficiency and NPP in years with average to above-average precipitation. Through examination of the reasons for discrepancies between observed and modeled ecosystem responses to eCO2, processes determining the biogeochemical responses of dry ecosystems to eCO2 were elucidated.

Luus, Kristina; Walker, Anthony; de Kauwe, Martin; Hungate, Bruce; Megonigal, J. Patrick; Lu, Meng; Fenstermaker, Lynn; Nowak, Robert; Morgan, Jack; Medlyn, Belinda; Norby, Richard; Zaehle, Sönke

2014-05-01

106

Synchronous dynamics of zooplankton competitors prevail in temperate lake ecosystems.  

PubMed

Although competing species are expected to exhibit compensatory dynamics (negative temporal covariation), empirical work has demonstrated that competitive communities often exhibit synchronous dynamics (positive temporal covariation). This has led to the suggestion that environmental forcing dominates species dynamics; however, synchronous and compensatory dynamics may appear at different length scales and/or at different times, making it challenging to identify their relative importance. We compiled 58 long-term datasets of zooplankton abundance in north-temperate and sub-tropical lakes and used wavelet analysis to quantify general patterns in the times and scales at which synchronous/compensatory dynamics dominated zooplankton communities in different regions and across the entire dataset. Synchronous dynamics were far more prevalent at all scales and times and were ubiquitous at the annual scale. Although we found compensatory dynamics in approximately 14% of all combinations of time period/scale/lake, there were no consistent scales or time periods during which compensatory dynamics were apparent across different regions. Our results suggest that the processes driving compensatory dynamics may be local in their extent, while those generating synchronous dynamics operate at much larger scales. This highlights an important gap in our understanding of the interaction between environmental and biotic forces that structure communities. PMID:24966312

Vasseur, David A; Fox, Jeremy W; Gonzalez, Andrew; Adrian, Rita; Beisner, Beatrix E; Helmus, Matthew R; Johnson, Catherine; Kratina, Pavel; Kremer, Colin; de Mazancourt, Claire; Miller, Elizabeth; Nelson, William A; Paterson, Michael; Rusak, James A; Shurin, Jonathan B; Steiner, Christopher F

2014-08-01

107

Potential climate change impacts on temperate forest ecosystem processes  

USGS Publications Warehouse

Large changes in atmospheric CO2, temperature and precipitation are predicted by 2100, yet the long-term consequences for carbon, water, and nitrogen cycling in forests are poorly understood. We applied the PnET-CN ecosystem model to compare the long-term effects of changing climate and atmospheric CO2 on productivity, evapotranspiration, runoff, and net nitrogen mineralization in current Great Lakes forest types. We used two statistically downscaled climate projections, PCM B1 (warmer and wetter) and GFDL A1FI (hotter and drier), to represent two potential future climate and atmospheric CO2 scenarios. To separate the effects of climate and CO2, we ran PnET-CN including and excluding the CO2 routine. Our results suggest that, with rising CO2 and without changes in forest type, average regional productivity could increase from 67% to 142%, changes in evapotranspiration could range from –3% to +6%, runoff could increase from 2% to 22%, and net N mineralization could increase 10% to 12%. Ecosystem responses varied geographically and by forest type. Increased productivity was almost entirely driven by CO2 fertilization effects, rather than by temperature or precipitation (model runs holding CO2 constant showed stable or declining productivity). The relative importance of edaphic and climatic spatial drivers of productivity varied over time, suggesting that productivity in Great Lakes forests may switch from being temperature to water limited by the end of the century.

Peters, Emily B.; Wythers, Kirk R.; Zhang, Shuxia; Bradford, John B.; Reich, Peter B.

2013-01-01

108

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

Microsoft Academic Search

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,

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

2011-01-01

109

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

Microsoft Academic Search

Understanding how food web interactions alter the processing of limiting nutrient elements is an important goal of ecosystem\\u000a 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\\u000a in Inner Mongolia (China). With increased grasshopper feeding, plant biomass declined fourfold, litter

Guangming Zhang; Xingguo Han; James J. Elser

2011-01-01

110

Impact of climate variations on surface albedo of a temperate grassland  

Microsoft Academic Search

Albedo controls surface energy balance and affects the microclimate conditions of ecosystems. Changes in albedo could induce significant changes in climate. Anthropogenic and natural factors, such as land cover and land use change, could result in the albedo change of land surfaces. In this study, we used Moderate Imaging Spectroradiometer (MODIS) data and climate station observations to investigate the albedo

Shusen Wang; Andrew Davidson

2007-01-01

111

Simulated water fluxes during the growing season in semiarid grassland ecosystems under severe drought conditions  

NASA Astrophysics Data System (ADS)

To help improve understanding of how changes in climate and land cover affect water fluxes, water budgets, and the structure and function of regional grassland ecosystems, the Grassland Landscape Productivity Model (GLPM) was used to simulate spatiotemporal variation in primary water fluxes. The study area was a semiarid region in Inner Mongolia, China, in 2002, when severe drought was experienced. For Stipa grandis steppe, Leymus chinensis steppe, shrubland, and croplands, the modeled total, daily and monthly averaged, and maximum evapotranspiration during the growing season and the modeled water deficits were similar to those measured in Inner Mongolia under similar precipitation conditions. The modeled temporal variations in daily evaporation rate, transpiration rate, and evapotranspiration rate for the typical steppes also agreed reasonably well with measured trends. The results demonstrate that water fluxes varied in response to spatiotemporal variations in environmental factors and associated changes in the phenological and physiological characteristics of plants. It was also found that transpiration and evapotranspiration (rather than precipitation) were the primary factors controlling differences in water deficit among land cover types. The results also demonstrate that specific phenomena occur under severe drought conditions; these phenomena are considerably different to those occurring under normal or well-watered conditions. The findings of the present study will be useful for evaluating day-scale water fluxes and their relationships with climate change, hydrology, land cover, and vegetation dynamics.

Zhang, Na; Liu, Chengyu

2014-05-01

112

Plant community composition promotes multiple ecosystem functions in grassland at low and high soil fertility  

NASA Astrophysics Data System (ADS)

It is well known that plant species richness can enhance primary productivity through complementarity in resource use by component plant species. Fewer studies have explored the role of plant species diversity and composition for the delivery of other ecosystem services than primary production and its dependency on resource availability. In this study we investigated how carbon (C) and nitrogen (N) stocks in vegetation, soil and soil microbes, the loss of C and N from soil through leaching and ecosystem exchange rates of CO2 are affected by the composition and richness of grassland plant communities and soil fertility. We used two soils of contrasting fertility in which we planted plant communities using a pool of six plant species from one of three functional groups (legumes, forbs and C3 grasses). The levels of plant species richness were one, two, three or six species and were composed of one, two or three functional groups. Soil fertility stimulated pools of C and N in shoots and roots, and the soil microbial biomass, but also increased significantly with increased plant functional group and plant species richness. Moreover, plant diversity suppressed N and water loss via soil leaching. We also found changes in the C and N content in soil, but these were not related to the richness of plant species or functional groups. The changes in soil were rather specifically due to the abundance of the legumes. The leaching of water and N was related negative to plant species richness but also specifically to the abundance of the forb species. Our findings show that the relation between plant community composition and storage of C and N in vegetation is not directly reflected in the changes in C and N storage in soil. These soil based storage functions, and the leaching of N from soil, appeared to be most strongly related to different key plant species. Together these results indicate that the maintenance of plant diversity is important to sustain the multiple functions grasslands provide.

de Deyn, Gerlinde; Ostle, Nick; Bardgett, Richard

2010-05-01

113

Water- and Plant-Mediated Responses of Ecosystem Carbon Fluxes to Warming and Nitrogen Addition on the Songnen Grassland in Northeast China  

PubMed Central

Background Understanding how grasslands are affected by a long-term increase in temperature is crucial to predict the future impact of global climate change on terrestrial ecosystems. Additionally, it is not clear how the effects of global warming on grassland productivity are going to be altered by increased N deposition and N addition. Methodology/Principal Findings In-situ canopy CO2 exchange rates were measured in a meadow steppe subjected to 4-year warming and nitrogen addition treatments. Warming treatment reduced net ecosystem CO2 exchange (NEE) and increased ecosystem respiration (ER); but had no significant impacts on gross ecosystem productivity (GEP). N addition increased NEE, ER and GEP. However, there were no significant interactions between N addition and warming. The variation of NEE during the four experimental years was correlated with soil water content, particularly during early spring, suggesting that water availability is a primary driver of carbon fluxes in the studied semi-arid grassland. Conclusion/Significance Ecosystem carbon fluxes in grassland ecosystems are sensitive to warming and N addition. In the studied water-limited grassland, both warming and N addition influence ecosystem carbon fluxes by affecting water availability, which is the primary driver in many arid and semiarid ecosystems. It remains unknown to what extent the long-term N addition would affect the turn-over of soil organic matter and the C sink size of this grassland.

Jiang, Li; Guo, Rui; Zhu, Tingcheng; Niu, Xuedun; Guo, Jixun; Sun, Wei

2012-01-01

114

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.

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

2010-01-01

115

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

116

The ecosystem carbon accumulation after conversion of grasslands to pine plantations in subtropical red soil of South China  

NASA Astrophysics Data System (ADS)

Since 1980s, afforestation in China has led to the establishment of over 0.53 × 108 ha of new plantation forests. While this leads to rapid accumulation of carbon (C) in vegetation, the effects of afforestation on soil C are poorly understood. In this study, a new version of the Atmosphere-Vegetation Interaction Model (AVIM2) was used to examine how changes in plant C inputs following afforestation might lead to changes in soil C at one of the Chinaflux sites and to estimate the effect of afforestation on ex-grassland. The potential total C accumulation of tree plantation was also predicted. The model was calibrated by net ecosystem exchange (NEE), ecosystem respiration (RE) and gross primary production (GPP) based on eddy-covariance measurements. The simulated vegetation C and soil C stocks were compared with the filed observations. The simulates indicate that after 22 yr of conversion of grassland to needle leaf forests (Pinus massoniana and Pinus elliottii), the net carbon accumulation in tree ecosystem was 1.96 times more than that in grassland. The soil C in the initial 7 yr of planting decreased at a rate of 0.1871 kg C m-2 yr-1, and after that it increased at a rate of 0.090 kg C m-2 yr-1. The C accumulation in the studied plantation ecosystem is estimated to be 76-81% of that value in equilibrium state (the net ecosystem productivity approaches to zero). Sensitivity analyses show that conversion from grassland to plantation caused an initial (7 or 8 yr) periods of decrease in soil C stocks in wider red soil area of southern China. The soil C stocks were reduced between 19.2 and 20.4% in the initial decreasing period. After 7 or 8 yr C loss, the increased in soil C stocks was predicted to be between 0.073 and 0.074 kg C m-2 yr-1.

Huang, Mei; Ji, Jinjun; Li, Kerang; Liu, Yunfeng; Yang, Fengting; Tao, Bo

2007-07-01

117

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

118

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

119

Partitioning of evapotranspiration through oxygen isotopic measurements of water pools and fluxes in a temperate grassland  

NASA Astrophysics Data System (ADS)

isotopic measurements of water provide a promising tool for partitioning of ecosystem evapotranspiration (ET). This approach, however, is still facing some challenges due to the uncertainties in estimating the isotopic compositions of ET and its components. In this study, a tunable diode laser analyzer was deployed for in situ measurements of the oxygen isotopic compositions of water vapor. Using these measurements together with samples of water in plant and soil pools, we partitioned ET via estimating the oxygen isotopic compositions of ET (?ET) and that of its two components, i.e., plant transpiration (?T) and soil water evaporation (?E). A new ?T model was developed in this study, which illustrated consistent estimations with the traditional model. Most of the variables and parameters in the new model can be measured directly with high accuracy, making its potential to be used at other sites high. Our results indicate that the ratio of plant transpiration to evapotranspiration (T/ET) illustrates a "U" shape diurnal pattern. Mean T/ET at 0630-1830 during the sampling days was 83%. Soil depth of 15 cm is a reasonable depth for soil water sampling for estimating ?E at this site. We also investigated the uncertainties in estimating these three terms and their effects on partitioning. Overall, in terms of partitioning, the uncertainties are relatively small from ?T and ?E but quite large from ?ET. Quantifying and improving the precision of ?ET should be a priority in future endeavors of ET partitioning via the stable isotopic approach.

Hu, Zhongmin; Wen, Xuefa; Sun, Xiaomin; Li, Linghao; Yu, Guirui; Lee, Xuhui; Li, Shenggong

2014-03-01

120

Impacts of grazing intensity on denitrification and N 2 O production in a semi-arid grassland ecosystem  

Microsoft Academic Search

N2O production from denitrification in soils contributes to the enhanced greenhouse effect and the destruction of the stratospheric\\u000a ozone. Ungulate grazing affects denitrification and the production of N2O. The short-term effect of grazing on denitrification and N2O production has been examined in several grassland ecosystems. However, the effects of long-term grazing have rarely been\\u000a studied. We measured denitrification and N2O

Yuqing Xu; Shiqiang Wan; Weixin Cheng; Linghao Li

2008-01-01

121

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

122

The origin of the indigenous grasslands of southeastern South Island in relation to pre-human woody ecosystems  

Microsoft Academic Search

Immediately before human settlement, dense tall podocarp-angiosperm forest dominated the moist Southland and southern coastal Otago districts. Open, discontinuous podocarp-angiosperm forest bordered the central Otago dry interior, extending along the north Otago coast. Grassland was mostly patchy within these woody ecosystems, occurring on limited areas of droughty or low-nutrient soils and wetlands, or temporarily after infrequent fire or other disturbance.

M. S. McGlone

2001-01-01

123

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

124

Influence of early snowmelt on phenology and ecosystem productivity of an unmanaged mountain grassland of northwestern Italian Alps  

NASA Astrophysics Data System (ADS)

Mountain regions are expected to be particularly influenced by future climate change with increasing temperature, change in precipitation patterns and duration of snow cover. In particular climate change is foreseen to impact alpine ecosystems by increasing of weather extremes (e.g. heat waves, droughts, exceptional anticipated snowmelt). Although different studies attested the effect of climate change on vegetation phenological shifts, uncertainties exist on the impacts of such shifts on ecosystem processes and hence on the ecosystem-climate feedbacks. High-altitude grasslands are snow-covered for most of the year and act as a net carbon source throughout all the snow period. Little is still known on the effects of spring warming and early snowmelt on annual carbon budget of these alpine ecosystems. Being part of the PhenoAlp project (www.phenoalp.eu) this study evaluated the effect of an exceptional early snowmelt observed in 2011 on the relationship between plant phenology and the ecosystem functioning of an unmanaged grassland of northwestern Italian Alps located at 2160 m asl. The following main questions were addressed: does an early snowmelt date increase the length of the growing season? If so, what is the effect on the productivity of the ecosystem? For this purpose continuous measurements of CO2 exchange across the biosphere/atmosphere interface assessed by means of eddy covariance since summer 2008 were evaluated. In order to analyse the relationship between phenology and ecosystem productivity, we extracted phenological indicators from CO2 flux time-series. Results showed shifts in the phenological indicators considered and a clear effect on the dynamics of the NEE (Net Ecosystem CO2 Exchange) and GPP (Gross Primary Production) time-courses as a consequence of earlier snowmelt. The grassland turned from a source to a sink more than one month in advance compared to previous years. The earlier onset of biological activity was also supported by evaluations of canopy greening, LAI and vegetation indices. Beside this highly anticipated beginning of the growing season, we found a slower general dynamics of carbon flux components and lower summer peaks of NEE and GPP in 2011 compared to previous years, with different implications on the growing season productivity and the annual carbon balance of the grassland.

Galvagno, M.; Cremonese, E.; Migliavacca, M.; Morra di Cella, U.; Rossini, M.; Colombo, R.

2012-04-01

125

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

126

Satellite-based analysis of evapotranspiration and water balance in the grassland ecosystems of Dryland East Asia.  

PubMed

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

127

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.

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

128

Separating Drought Effects from Roof Artifacts on Ecosystem Processes in a Grassland Drought Experiment  

PubMed Central

1 Given the predictions of increased drought probabilities under various climate change scenarios, there have been numerous experimental field studies simulating drought using transparent roofs in different ecosystems and regions. Such roofs may, however, have unknown side effects, called artifacts, on the measured variables potentially confounding the experimental results. A roofed control allows the quantification of potential artifacts, which is lacking in most experiments. 2 We conducted a drought experiment in experimental grasslands to study artifacts of transparent roofs and the resulting effects of artifacts on ecosystems relative to drought on three response variables (aboveground biomass, litter decomposition and plant metabolite profiles). We established three drought treatments, using (1) transparent roofs to exclude rainfall, (2) an unroofed control treatment receiving natural rainfall and (3) a roofed control, nested in the drought treatment but with rain water reapplied according to ambient conditions. 3 Roofs had a slight impact on air (+0.14°C during night) and soil temperatures (?0.45°C on warm days, +0.25°C on cold nights), while photosynthetically active radiation was decreased significantly (?16%). Aboveground plant community biomass was reduced in the drought treatment (?41%), but there was no significant difference between the roofed and unroofed control, i.e., there were no measurable roof artifact effects. 4 Compared to the unroofed control, litter decomposition was decreased significantly both in the drought treatment (?26%) and in the roofed control treatment (?18%), suggesting artifact effects of the transparent roofs. Moreover, aboveground metabolite profiles in the model plant species Medicago x varia were different from the unroofed control in both the drought and roofed control treatments, and roof artifact effects were of comparable magnitude as drought effects. 5 Our results stress the need for roofed control treatments when using transparent roofs for studying drought effects, because roofs can cause significant side effects.

Vogel, Anja; Fester, Thomas; Eisenhauer, Nico; Scherer-Lorenzen, Michael; Schmid, Bernhard; Weisser, Wolfgang W.; Weigelt, Alexandra

2013-01-01

129

Investigation of Water Stress Effects on Soil and Ecosystem Respiration in Boreal and Temperate Forests  

NASA Astrophysics Data System (ADS)

The Biometeorology and Soil Physics Group of the University of British Columbia has been making long-term measurements (1994-2006) of carbon dioxide exchange between several Canadian forests and the atmosphere as part of the Boreal Ecosystem Research and Monitoring Sites program (BERMS) and the Fluxnet Canada Research Network (FCRN). Here, we summarize our efforts to better understand the biophysical processes driving the spatial and temporal variability of carbon dioxide fluxes in boreal (aspen and black spruce) and west-coast temperate (Douglas-fir) forests using eddy covariance, automated chamber and soil carbon dioxide concentration measurement techniques. More specifically, we focus on the issue of water stress effects on the production and transport of carbon dioxide through soil and ecosystem respiration. Using long-term estimates of ecosystem respiration derived from tower-based eddy covariance measurements of the net carbon dioxide exchange, we contrast the response of boreal aspen and black spruce forests to a severe drought that affected much of the western plains of North America from 2001 to 2003. These measurements are used together with automated chamber measurements of soil carbon dioxide efflux to investigate the role of soil water availability in soil respiration processes at hourly, daily, yearly and interannual time scales. Using solid-state infrared sensors in a temperate Douglas-fir forest and in controlled laboratory experiments, we discuss the effects of soil water availability and precipitation on the dynamics of carbon dioxide concentrations and diffusivity in soils. Finally, using root-exclusion techniques in black spruce and Douglas-fir forests, we attempt to partition soil respiration between its rhizospheric and heterotrophic components and investigate the control of soil water availability on each component.

Gaumont-Guay, D.; Black, T.; Jassal, R. S.; Barr, A. G.; Nesic, Z.

2006-12-01

130

Measured and Simulated Nitrous Oxide Emissions from Ryegrass- and Ryegrass/White Clover-Based Grasslands in a Moist Temperate Climate  

PubMed Central

There is uncertainty about the potential reduction of soil nitrous oxide (N2O) emission when fertilizer nitrogen (FN) is partially or completely replaced by biological N fixation (BNF) in temperate grassland. The objectives of this study were to 1) investigate the changes in N2O emissions when BNF is used to replace FN in permanent grassland, and 2) evaluate the applicability of the process-based model DNDC to simulate N2O emissions from Irish grasslands. Three grazing treatments were: (i) ryegrass (Lolium perenne) grasslands receiving 226 kg FN ha?1 yr?1 (GG+FN), (ii) ryegrass/white clover (Trifolium repens) grasslands receiving 58 kg FN ha?1 yr?1 (GWC+FN) applied in spring, and (iii) ryegrass/white clover grasslands receiving no FN (GWC-FN). Two background treatments, un-grazed swards with ryegrass only (G–B) or ryegrass/white clover (WC–B), did not receive slurry or FN and the herbage was harvested by mowing. There was no significant difference in annual N2O emissions between G–B (2.38±0.12 kg N ha?1 yr?1 (mean±SE)) and WC-B (2.45±0.85 kg N ha?1 yr?1), indicating that N2O emission due to BNF itself and clover residual decomposition from permanent ryegrass/clover grassland was negligible. N2O emissions were 7.82±1.67, 6.35±1.14 and 6.54±1.70 kg N ha?1 yr?1, respectively, from GG+FN, GWC+FN and GWC-FN. N2O fluxes simulated by DNDC agreed well with the measured values with significant correlation between simulated and measured daily fluxes for the three grazing treatments, but the simulation did not agree very well for the background treatments. DNDC overestimated annual emission by 61% for GG+FN, and underestimated by 45% for GWC-FN, but simulated very well for GWC+FN. Both the measured and simulated results supported that there was a clear reduction of N2O emissions when FN was replaced by BNF.

Li, Dejun; Lanigan, Gary; Humphreys, James

2011-01-01

131

Effects of grassland restoration programs on ecosystems in arid and semiarid China.  

PubMed

We explored the ecological effects of grassland restoration programs using satellite imagery and field plots sampling data and analyzing the patterns and mechanisms of land cover change and vegetation activities in arid and semiarid China during the period from 1982 to 2008. The grassland cover in the 1980s, 2000 and 2005 was compared before and after the restoration programs. The variability of net primary production (NPP) and rain use efficiency (RUE) were analyzed as indicators of vegetation productivity. Our study showed that changes in grassland cover were closely related to the relative area of farmland, with increases in grassland being caused by returning farmland to grassland and decreases being caused by reclamation for agriculture. The results of NPP and RUE measurements over the past 30 years showed systematic increases in the area of grassland in most regions, especially from 2000 to 2008. This fact was reflected by intensified vegetation activity and cannot be completely explained by the warmer and wetter climate, which suggested a contribution from restored, ungrazed grasslands. Our analysis indicates that both vegetation activity and grassland cover increased in regions in which grassland and rangeland restoration programs were implemented. PMID:23391757

Huang, Lin; Xiao, Tong; Zhao, Zhiping; Sun, Chaoyang; Liu, Jiyuan; Shao, Quanqin; Fan, Jiangwen; Wang, Junbang

2013-03-15

132

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...

133

Ecosystem impacts of compost and manure applications to California grazed grassland soils  

NASA Astrophysics Data System (ADS)

Organic matter amendments, such as compost and manure, are often applied to grasslands to improve soil conditions and enhance net primary productivity. It has been proposed that this land management strategy can sequester carbon (C) in soils and may therefore contribute to climate change mitigation. However, the net mitigation potential of organic amendments depends in part on the ecosystem response following land-application, which is likely to vary with the amendment chemical quality (C, N, C:N). To investigate the differences in ecosystem response to soil amendments of various qualities, we established research plots on three grazed annual grasslands in northern California. The study sites were sampled for soil chemical and physical properties (bulk density, temperature, and moisture), plant community composition, and peak season net primary productivity prior to and following treatment applications. In October 2011, before the rainy season, we applied a thin layer of organic amendments to the study plots. At each site, three replicate plots were treated with fresh manure (1.2 % N, 15.8 % C, C:N = 13.5), three plots were treated with a commercial plant-waste compost (2.4 % N, 26.6 % C, C:N = 11.1), and three plots were left untreated as controls. At one site, 3 additional plots received a thin layer of compost with a lower N concentration and a higher C:N ratio (1.9 % N, 27.4 % C, C:N = 14.5). All plots were sampled for greenhouse gas emissions (N2O, CH4, and CO2, n=3 per plot) using vented chambers shortly after the organic matter was applied, and then intensively following three rain events throughout the rainy season. Results showed that dry amendments were associated with negligible trace gas fluxes, but that these fluxes increased after rain events. Nitrous oxide emissions increased slightly after the first rain event and reached peak levels (approximately 20 ng N cm-1 h-1 for the manure and high N compost only) after three days, following second rain event. The emissions from the high N compost declined more quickly than the manure emissions during the dry-up period. The low N compost exhibited the lowest peak emissions (< 5 ng N cm-1 h-1). Nitrous oxide emissions for all amendments quickly declined and were negligible on both wet and dry days sampled during mid-rainy season. These results suggest that trace gas emissions may not strongly offset the mitigation potential for organic matter amendments. However, differences in the amendment type and quality can influence the offset magnitude. These findings will be presented within the context of other key ecosystem characteristics, such as plant community composition, net primary productivity, and soil conditions.

DeLonge, M. S.; Silver, W. L.

2012-12-01

134

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

135

Role of vegetation in modulating rainfall interception and soil water flux in ecosystems under transition from grassland to woodland  

NASA Astrophysics Data System (ADS)

Vegetation exerts strong control on the hydrological budget by shielding the soil from rainfall through interception and modulating water transmission in the soil by altering soil properties and rooting zone water extraction. Therefore, a change in vegetation alters the water cycle by a combination of a passive, rainfall redistribution mechanism controlled by the physical dimensions of vegetation and active, water extracting processes resulting from physiological attributes of different plants. As a result, the role of vegetation on the water cycle is likely to change where vegetation is under transition such as in the southern Great Plains of USA due to woody plant encroachment. However, it remains largely unknown how this physiognomic transformation from herbaceous cover to woody canopy alters rainfall influx, soil water transmission and efflux from the soil profile and consequently alters historic patterns of runoff and groundwater recharge. This knowledge is critical for both water resource and ecosystem management. We conducted a comprehensive, 5-year study involving direct quantification of throughfall and stemflow for grassland and encroached juniper woodland (Juniperus virginiana), water efflux through transpiration using an improved Granier thermal dissipation method (trees) and ET chamber (grassland), soil moisture storage and dynamics (capacitance probe) and streamflow (small catchment). We calibrated a prevailing hydrological model (SWAT) based on observed data to simulate potential change in runoff and recharge for the Cimarron River basin (study site located within this basin) under various phases of grassland to woodland transition. Our results show that juniper encroachment reduces throughfall reaching the soil surface compared with grassland under moderate grazing. The evergreen junipers transpired water year-round including fall and winter when the warm season grasses were senescent. As a result, soil water content and soil water storage on the encroached catchment were generally lower than on the grassland catchment, especially proceeding the seasons of peak rainfall in spring and fall. Frequency and magnitude of streamflow events was observed to be substantially reduced in the encroached catchment. Model simulation suggests that conversion of all existing grassland to juniper in the Cimarron River basin will increase overall water efflux through evapotranspiration sufficient to substantially reduce water yield for streamflow. Rapid transformation of mesic grasslands to a woodland state with juniper encroachment, if not confined, has the potential to reduce soil water, streamflow and flow duration of ephemeral streams. Slowing the expansion of woody encroachment into grasslands might be considered as a land-based strategy to sustain or even augment streamflow and groundwater recharge to meet the increase in water demand under increasing climate variability and population growth in the southern Great Plains of USA

Zou, Chris; Will, Rodney; Stebler, Elaine; Qiao, Lei

2014-05-01

136

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

137

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

138

Microbial Enzymatic Response to Reduced Precipitation and Added Nitrogen in a Southern California Grassland Ecosystem  

NASA Astrophysics Data System (ADS)

Microbial enzymes play a fundamental role in ecosystem processes and nutrient mineralization. Although there have been many studies concluding that global climate change affects plant communities, the effects on microbial communities in leaf litter have been much less studied. We measured extracellular enzyme activities in litter decomposing in plots with either reduced precipitation or increased nitrogen in a grassland ecosystem in Loma Ridge National Landmark in Southern California. We used a reciprocal transplant design to examine the effects of plot treatment, litter origin, and microbial community origin on litter decomposition and extracellular enzyme activity. Our hypothesis was that increased nitrogen would increase activity because nitrogen often limits microbial growth, while decreased precipitation would decrease activity due to lower litter moisture levels. Samples were collected in March 2011 and analyzed for the activities of cellobiohydrolase (CBH), ?-glucosidase (BG), ?-glucosidase (AG), N-acetyl-?-D-glucosaminidase (NAG), ?-xylosidase (BX), acid phosphatase (AP), and leucine aminopeptidase (LAP). None of the factors in the nitrogen manipulation had a significant effect on any of the enzymes, although BG, CBH, and NAG increased marginally significantly in plots with nitrogen addition (p = 0.103, p = 0.082, and p = 0.114, respectively). For the precipitation manipulation, AG, BG, BX, CBH, and NAG significantly increased in plots with reduced precipitation (p = 0.015, p <0.001, p<0.001, and p<0.001, respectively) while LAP significantly decreased (p = 0.002). LAP catalyzes the hydrolysis of polypeptides, so reduced LAP activity could result in lower rates of enzyme turnover in the reduced precipitation treatment. We also observed that AP significantly increased (p = 0.014) in litter originating from reduced precipitation plots, while AG, BX, and LAP significantly decreased (p = 0.011, p = 0.031, and 0.005, respectively). There were no significant correlations found between fungal or bacterial mass and enzymatic activity with either of the treatment types. Our results suggest that increased enzymatic activity due to drought could mitigate negative effects of moisture limitation on decomposition. However, this mitigating effect may be offset by declines in enzyme activity due to changes in plant community composition and associated litter chemistry in response to drought.

Alster, C. J.; German, D.; Allison, S. D.

2011-12-01

139

The effect of climate change on groundwater dependent temperate forest ecosystems  

NASA Astrophysics Data System (ADS)

Models developed to predict the influence of changing climate on ecosystems often concentrate on vegetation in connection with soil moisture, but usually omit groundwater. However in temperate climate zones, groundwater can have a profound effect on the reaction of vegetation to climate change, because it strongly influences the spatio-temporal distribution of soil moisture and therefore water and oxygen stress of vegetation. Here we focus on the qualitative and quantitative effects of climate change on the zonation of vegetation and groundwater dynamics along a hill slope. To study this we developed a fully coupled hydrological-vegetation model, for a groundwater influenced temperate forest ecosystem. The vegetation model is based on the carbon assimilation model of Farquhar et al. (1980) and the extension of Daly et al. (2004), which includes transpiration of vegetation and accounts for the response to low soil moisture content. We modified this model to account for vegetation response to high soil moisture contents due to high groundwater levels, and we extended the model to include light competition, phenology and vegetation growth. To simulate the hydrological system the saturated-unsaturated flow model by van Beek (2002) is used. The coupled model was first compared to measured semi-hourly flux tower data of H2O and CO2, showing good results. Than simulation runs of 1000 years were performed to study the effect of climate change on soil water, groundwater and vegetation. We performed simulation runs with competition between wet and dry adapted species under current conditions and after climate change. Meteorological time series for the 2100 climate (SRESA2) were obtained from downscaling 6 different regional climate model runs from the ENSEMBLES project with a stochastic weather generator (Kilby et al., 2007). Results show that in the zones were the groundwater system is close to the surface, climate change causes shifts in vegetation zonation of the dry and wet adapted species along the slope. The increase in number of dry days during summer also causes an overall decline of biomass for both species, an effect that is partially mitigated by increased ambient CO2 concentration. This study shows the importance of using a coupled groundwater vegetation model when studying temperate lowland areas. The coupled hydrological-vegetation model allows for detailed studies of qualitative and quantitative changes in spatial temporal patterns of vegetation under changing climate.

Brolsma, R. J.; Bierkens, M. F. P.

2009-04-01

140

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

141

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

142

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 multispectral sensor for monitoring mean midday gross ecosystem production (GEPm) in a dynamic subalpine grassland ecosystem of the Italian Alps equipped with an eddy covariance flux tower. Reflectance observations were collected for five consecutive years by means of a multispectral radiometer system. Spectral vegetation indices were calculated from reflectance measurements at particular wavelengths. Different models based on linear regression and on multiple regression were developed to estimate GEPm. Chlorophyll-related indices including red-edge part of the spectrum in their formulation were the best predictors of GEPm, explaining most of its variability during the five consecutive years of observations characterized by different climatic conditions. Integrating mean midday photosynthetically active radiation into the model resulted in a general decrease in the accuracy of estimates. Also, the use of the reflectance approach instead of the VIs approach did not lead to considerably improved results in estimating GEPm.

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

2014-03-01

143

Invasive C4 Perennial Grass Alters Net Ecosystem Exchange in Mixed C3/C4 Savanna Grassland  

NASA Astrophysics Data System (ADS)

The invasion of ecosystems by non-native plants that differ from native plants in physiological characteristics and phenology has the potential to alter ecosystem function. In Texas and other regions of the southern central plains of the United States, the introduced C4 perennial grass, Bothriochloa ischaemum, invades C3/C4 mixed grasslands and savannas, resulting in decreased plant community diversity (Gabbard 2003; Harmoney et al 2004). The objective of this study was to quantify how the conversion of these mixed grass communities to C4 dominated, B. ischaemum monocultures impacts carbon cycling and sequestration. Seasonal measurements of Net Ecosystem Exchange (NEE) of CO2, leaf level gas exchange and soil respiration were compared between savanna grassland plots composed of either naturally occurring B. ischaemum monocultures or native mixed grasses (n=16). NEE was measured using a closed system chamber that attached to permanently installed stainless steel bases. Temperature, soil moisture, aerial percent species cover and leaf area index were also monitored in plots to explain variability in measured responses. Results showed that NEE differed seasonally between invaded and native plots due to 1) greater leaf surface area per unit ground area in invaded plots, 2) differences in phenological patterns of plant activity and 3) differences in responses to water limitation between invaded and native plots. Cold season and summer drought NEE were driven primarily by belowground respiration in both plot types, however spring uptake activity commenced two months later in invaded plots. This later start in invaded plots was compensated for by greater uptake throughout the growing season and in particular during the drier summer months. Differences in NEE between plot types were not due to differences in soil respiration nor were they due to greater leaf level photosynthetic capabilities of B. ischaemum relative to the dominant native grasses. NEE, soil respiration and biomass accumulation were limited by temperature and soil moisture in both native and invaded plots; however, invaded areas were less sensitive to both higher temperatures and lower soil moisture. Preliminary modeling results suggest that from January-August 2006, invaded grasslands stored approximately one third more carbon than native grasslands, making them 20% less of a carbon source than native plots during this year of record high temperatures and drought. Gabbard, BL. 2003. The Population Dynamics and Distribution of the Exotic Grass,Bothriochloa ischaemum, PhD Dissertation, University of Texas, Austin, TX Harmoney et al. 2004. Herbicide Effects on Established Yellow Old World Bluestem (Bothriochloa ischaemum). Weed Technology 18:545 550

Basham, T. S.; Litvak, M.

2006-12-01

144

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

145

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

146

The impact of extreme summer drought on the short-term carbon coupling of photosynthesis to soil CO2 efflux in a temperate grassland  

NASA Astrophysics Data System (ADS)

Along with predicted climate change, increased risks for summer drought are projected for Central Europe. However, large knowledge gaps exist in terms of how drought events influence the short-term ecosystem carbon cycle. Here, we present results from 13CO2 pulse labeling experiments at an intensively managed lowland grassland in Switzerland. We investigated the effect of extreme summer drought on the short-term coupling of freshly assimilated photosynthates in shoots to roots as well as to soil CO2 efflux. Summer drought was simulated using rainout shelters during two field seasons (2010 and 2011). Soil CO2 efflux and its isotopic composition were measured with custom-built chambers coupled to a quantum cascade laser spectrometer (QCLAS-ISO, Aerodyne Research Inc., MA, USA). During the 90 min pulse labeling experiments, we added 99.9 atom % 13CO2 to the grass sward. In addition to the isotopic analysis of soil CO2 efflux, this label was traced over 31 days into bulk shoots, roots and soil. Drought reduced the incorporation of recently fixed carbon into shoots and increased carbon allocation below-ground relative to total tracer uptake. Contrary to our hypothesis, we did not find a change in allocation speed in response to drought, although drought clearly reduced soil CO2 efflux rates. 19 days after pulse labeling, only about 60% of total tracer uptake was lost via soil CO2 efflux under drought compared to about 75% under control conditions. Predisposition of grassland by spring drought lead to different responses to summer drought in 2011 compared to 2010, suggesting increased sensitivity of grassland to consecutive drought events as predicted under future climate change.

Burri, S.; Sturm, P.; Prechsl, U. E.; Knohl, A.; Buchmann, N.

2013-07-01

147

Understanding coupled climatic and ecosystem responses to global climate change in the Central Grasslands  

SciTech Connect

A long-term National Park Service research program to assess the potential effect of global climate change on the Central Grasslands Biogeographic Area is underway. The program consists of two integrated projects: Projecting climate and vegetation change at regional to landscape scales; and Predicting the effect of global change on vegetation in park landscapes at the plot to landscape scales. Together, these integrated field and modeling studies establish a means to validate mesoscale and landscape vegetation models, a central goal of the NPS Global Change Research Program. Vegetation life form modeling suggests that under climate change scenarios the distribution of grassland vegetation zones will undergo major shifts. Results indicate that climate change impacts that reduce water availability will more severely depress productivity of C[sub 3] grass communities relative to C[sub 4] grass communities.

Falkner, M.B.; Detling, J.; Ojima, D.; Pielke, R.A.; Stohlgren, T.J. (Colorado State Univ., Ft. Collins (United States)); Kittel, T.G.F. (Colorado State Univ., Ft. Collins (United States) UCAR, Boulder, CO (United States)); Lenihan, J.; Neilson, R. (Oregon State Univ., Corvallis (United States)); Reiners, W. (Univ. of Wyoming, Laramie (United States))

1993-06-01

148

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

149

Differential effects of elevated ultraviolet-B radiation on plant species of a dune grassland ecosystem  

Microsoft Academic Search

In a greenhouse study, plants of three monocotyledonous and five dicotyledonous species, which occur in a Dutch dune grassland, were exposed to four levels of ultraviolet-B (UV-B) radiation. UV-B levels simulated up to 30% reduction of the stratospheric ozone column during summertime in The Netherlands. Six of the plant species studied in the greenhouse were also exposed to enhanced UV-B

Marcel Tosserams; Erwin Magendans; Jelte Rozema

1997-01-01

150

Nitric oxide emission from arid grassland and shrubland ecosystems in southern New Mexico  

SciTech Connect

Soil nitrogen losses are characteristic of the transition from semi-arid grassland to arid shrubland in the southwestern United States. Nitrogen gas emission from soil microbial activity contributes to the long-term reduction of soil fertility associated with desertification. We investigated nitric Oxide (NO) emission from arid soils in the Jornada Experimental Range, near Las Cruces, New Mexico. During the dry season, mean NO fluxes from coarse-textured soils in a Boutelcua grassland and a Larrea shrubland were similar (0.12 and 0.15 ng NO-N cm[sup [minus]2] hr[sup [minus]1], respectively), and higher than flexes from fine-textured soils in a Flourensia shrubland (0.02 ng NO-N cm[sup [minus]2] hr[sup [minus]1]). In a wetting experiment, mean NO fluxes were higher under shrub canopies of Larrea and Flourensia, reflecting the accumulation of soil organic matter under shrubs in islands of fertility. In the Larrea shrubland, mean NO fluxes were ten times higher under shrubs than between shrubs (12.9 vs. 1.29 ng NO-N cm[sup [minus]2] hr[sup [minus]1]).

Hartley, A.E.; Schlesinger, W.H. (Duke Univ., Durham, NC (United States))

1993-06-01

151

Spatial pattern of nitrogen isotopes as an indicator of ecosystem responses to rainfall in semi-arid and arid grasslands  

NASA Astrophysics Data System (ADS)

Nitrogen (N) is an essential element for plant growth, however, whether it is a limiting factor of plant growth in water-limited areas is still not clear. Here we examined spatial variations of plant and soil stable N isotopes along a 3200 km precipitation gradient and proposed a conceptual model to explain ecosystem responses to increasing precipitation in arid and semi-arid grasslands in China. Soil ?15N increased with increasing MAP in areas with MAP < 200 mm, but decreased in areas with 200 mm < MAP < 500 mm. Variations of foliar ?15N, soil total N, and soil C: N provided further evidence of a threshold at MAP = 200 mm for precipitation effects. Results indicated that soil microbes can be activated by precipitation even when MAP < 200 mm while plant N uptake can only be activated when MAP > 200 mm. In areas with MAP < 200 mm, productivity was limited by water, but not nitrogen, although soil N is low. This study provides fundamental inputs for future process-based modeling of nutrient cycling in arid and semi-arid areas. If future climate change leads to drier climate in dryland, the uncoupled plant and microbial response may cause more N losses and higher ecosystem vulnerability. 3 Soil organic carbon (Soil C, a), total nitrogen (Soil N, b), C/N (c) and ?15N (d) of study sites along a MAP gradient. Relationship between MAP and foliar ?15N (a) and root ?15N (b).

WANG, C.; Bai, E.; Liu, D.; Fang, T. Y.; Jiang, P.; Han, G. X.

2013-12-01

152

Sediment deposition and soil nutrient heterogeneity in two desert grassland ecosystems, southern New Mexico  

Microsoft Academic Search

The role of wind in changing the spatial heterogeneity of soil resources in erosion-dominated semiarid ecosystems is well\\u000a known. Yet the effect of windblown sediment deposition on soil nutrient distribution and ecosystem dynamics at local and landscape scales\\u000a has received little attention. We examined the effects of enhanced sediment deposition on the spatial distribution of soil\\u000a nutrients at the Jornada

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

2009-01-01

153

Effects of short term and long term soil warming on ecosystem phenology of a sub-arctic grassland: an NDVI-based approach  

NASA Astrophysics Data System (ADS)

Phenology has been defined as the study of the timing of recurring biological events and the causes of their timing with regard to abiotic and biotic factors. Ecosystem phenology, including the onset of the growing season and its senescence in autumn, plays an important role in the carbon, water and energy exchange between biosphere and atmosphere at higher latitudes. Factors that influence ecosystem phenology can therefore induce important climate-controlling feedback mechanisms. Global surface temperatures have been predicted to increase in the coming decades. Hence, a better understanding of the effect of temperature on ecosystem phenology is essential. Natural geothermal soil temperature gradients in Iceland offer a unique opportunity to study the soil temperature (Ts) dependence of ecosystem phenology and distinguish short-term (transient) warming effects (in recently established Ts gradients) from long-term (permanent) effects (in centuries-old Ts gradients). This research was performed in the framework of an international research project (ForHot; www.forhot.is). ForHot includes two natural grassland areas with gradients in Ts, dominated by Festuca sp., Agrostis sp.. The first warmed area was created in 2008, when an earthquake in S-Iceland caused geothermal systems to be shifted to previously cold soils. The second area is located about 3 km away from this newly warmed grassland. For this area, there are proofs that the natural soil warming has been continuous for at least 300 year. In the present study we focus on Ts elevation gradients of +0 to +10°C. The experiment consists of five transects with five temperature levels (+0,+1,+3,+5 and +10°C) in the two aforementioned grassland ecosystems (n=25 in each grassland). From April until November 2013, weekly measurements of the normalized difference vegetation index (NDVI) were taken. In the short-term warmed grassland, the greening of the vegetation was 36 days advanced at +10°C Ts and the date of 50% greening was advanced by 23 days at +5°C and by 32 days at +10°C Ts. However, no difference in the date of maximum greening or in the onset of senescence occurred. In contrast, in the long-term warmed grassland, the start of the growing season was not affected by Ts and the 50% greening point occurred only 10 days earlier at +5°C and 15 days earlier at +10°C Ts. However, the timing of maximum greening was advanced by 19 days at +5°C and even by 32 days at +10°C Ts. Again, the onset of senescence did not change with Ts. Significant Ts effects on ecosystem phenology of subarctic grasslands only occurred at warming of 5°C or higher. This study also demonstrates that short-term Ts effects on ecosystem phenology are not necessarily good predictors for long-term changes in sub-arctic grasslands. In the short-term (5 years warming), soil warming induced an early onset of the growing season, which was later compensated by faster greening on colder soils, so that maximum greenness was reached simultaneously irrespective of Ts. In contrast, the long-term Ts warming did not induce earlier onset of the growing season, but it led to faster greening on warm soils, which again led to an advance in timing of maximum greenness. This difference between short- and long-term responses in phenology might be caused by either phenotypic plasticity (acclimation) or by a genetic selection (evolution) of the grass populations where the warming has been ongoing for centuries. Such processes are at present not included in modelling predictions of climate change responses of natural ecosystems, but may offer important negative feedback mechanisms to warming which will reduce its effects.

Leblans, Niki; Sigurdsson, Bjarni D.; Janssens, Ivan A.

2014-05-01

154

Response of plant community composition and productivity to warming and nitrogen deposition in a temperate meadow ecosystem  

NASA Astrophysics Data System (ADS)

Climate change has profound influences on plant community composition and ecosystem functions. However, its effects on plant community composition and net primary productivity are not well understood. A field experiment was conducted to examine the effects of warming, nitrogen (N) addition, and their interactions on plant community composition and productivity in a temperate meadow ecosystem in northeast China. Experimental warming significantly increased species richness, evenness and diversity, by contrast, N addition highly reduced species richness, evenness and diversity. Warming reduced the importance value of gramineous species but increased in forbs, N addition had the opposite effect. Warming had a significant positive effect on belowground productivity, but had a negative effect on aboveground biomass. The influences of warming on aboveground productivity were dependent on precipitation. Experimental warming had little effect on aboveground productivity in the years with higher precipitation, but significantly suppressed the growth of aboveground in dry years. Our results suggest that warming had indirect effects on plant productivity via altering water availability. Nitrogen addition significantly increased above- and belowground productivity, suggesting that N is one of the most important limiting factors which determine plant productivity in the studied meadow steppe. Significant interactive effects of warming plus N addition on belowground productivity were also detected. Our observations revealed that climate changes (warming and N deposition) plays significant roles in regulating plant community composition and productivity in temperate meadow steppe.

Zhang, T.; Guo, R.; Gao, S.; Guo, J. X.; Sun, W.

2014-05-01

155

Sierra Nevada Grasslands: Interactions Between Livestock Grazing and Ecosystem Structure and Function 1  

Microsoft Academic Search

Livestock grazing plays an integral role in the grass-dominated ecosystems of the Sierra Nevada. Grazing has been asserted to influence such key ecological characteristics as water quality, net primary productivity, nutrient cycling, plant and animal diversity, wildlife habitat availability, and oak regeneration (Belsky and others 1999, Kauffmann and Krueger 1984). Although there are many reports of these effects, an important

Barbara H. Allen-Diaz

156

Speed of Carbon Cycling in Grassland Ecosystems by Destructive and Non-destructive Techniques  

Microsoft Academic Search

The allocation of recently assimilated C to below- vs. aboveground plant components and the time this C remains inside the ecosystem are the key uncertainties in global terrestrial C models. Recent studies reported the time lag between the photosynthetic C uptake and its following respiration through the rooting systems in the magnitude from minutes to days. Studies in situ are

O. Gavrichkova; I. Inglima; C. Lubritto; F. Cotrufo; D. Papale; R. Valentini

2009-01-01

157

Oldest Evidence of Toolmaking Hominins in a Grassland-Dominated Ecosystem  

Microsoft Academic Search

Background: Major biological and cultural innovations in late Pliocene hominin evolution are frequently linked to the spread or fluctuating presence of C4 grass in African ecosystems. Whereas the deep sea record of global climatic change provides indirect evidence for an increase in C4 vegetation with a shift towards a cooler, drier and more variable global climatic regime beginning approximately 3

Thomas W. Plummer; Peter W. Ditchfield; Laura C. Bishop; John D. Kingston; Joseph V. Ferraro; David R. Braun; Fritz Hertel; Richard Potts

2009-01-01

158

Report on the IAI Workshop On The Comparative Studies Of Temperate terrestrial Ecosystems  

NSF Publications Database

The workshop was convened by the Inter-American Institute for Global Change Research (IAI), created in May of 1992 to address the need for advanced study of regionally significant global change issues. Productive Systems (1) What are the potential biophysical impacts and adaptations of climate change on major agricultural systems, (e.g., highly produc- tive agriculture, sustainable agriculture, grasslands). Major Concerns 1. What are the global change forcing functions important to the region...

159

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 Central

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.

Zinta, Gaurav; Van den Ende, Wim; Janssens, Ivan A.; Asard, Han

2014-01-01

160

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

161

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.

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

2011-01-01

162

Comparison of Ecosystem Water-use Efficiency Among Douglas fir Forest, Aspen Forest and Grassland Using Eddy Covariance and Carbon Isotope Techniques  

NASA Astrophysics Data System (ADS)

Comparisons were made among Douglas fir forest, aspen (broad leaf deciduous) forest and wheatgrass (C3) grassland for ecosystem-level water-use efficiency. Water-use efficiency (WUE) was defined as the ratio of photosynthetic CO2 assimilation rate and evapo-transpiration (ET) rate. The ET data measured by eddy covariance were screened so that they overwhelmingly represented transpiration. The three sites used in this comparison spanned a range of vegetation (plant functional) types and environmental conditions within western Canada. When compared in the relative order Douglas fir (located on Vancouver Island, B.C), aspen (northern Saskatchewan), grassland (southern Alberta), the sites demonstrated a progressive decline in precipitation and a general increase in maximum air temperature and atmospheric saturation deficit (D) during the mid-summer. The average WUE at the grassland site was 2.6 mmol mol-1, which was much lower than the average values observed for the two other sites (aspen: 5.4, Douglas fir: 8.1). The differences in WUE among sites were primarily due to variation in ET. The highest maximum ET rates were approximately 5, 3.2 and 2.7 mm day-1 for the grassland, aspen and Douglas fir sites, respectively. There was a strong negative correlation between WUE and D for all sites. We also made seasonal measurements of the carbon isotope ratio of ecosystem respired CO2 (?R) in order to test for the expected correlation between shifts in environmental conditions and changes to the ecosystem-integrated ratio of leaf intercellular to ambient CO2 concentration (ci/ca). There was a consistent increase in ?R values in the grassland, aspen forest and Douglas fir forest associated with a seasonal reduction in soil moisture. Comparisons were made between WUE measured using eddy covariance with that calculated based on atmospheric saturation deficit and ?R measurements. There was excellent agreement between WUE values calculated using the two techniques. Our ?R measurements indicated that ci/ca values were quite similar among the Douglas fir, aspen and grassland sites, despite large variation in environmental conditions among sites. This implied that the shorter-lived grass species had relatively high ci/ca values for the D of their habitat. By contrast, the longer-lived Douglas fir trees were more conservative in water-use with lower ci/ca values relative to their habitat D. This illustrates the interaction between biological and environmental characteristics influencing ecosystem-level water-use efficiency.

Flanagan, L. B.; Ponton, S.; Alstad, K. P.; Johnson, B. G.; Morgenstern, K.; Kljun, N.; Black, T. A.; Barr, A. G.

2005-12-01

163

Timing of climate variability and grassland productivity  

PubMed Central

Future climates are forecast to include greater precipitation variability and more frequent heat waves, but the degree to which the timing of climate variability impacts ecosystems is uncertain. In a temperate, humid grassland, we examined the seasonal impacts of climate variability on 27 y of grass productivity. Drought and high-intensity precipitation reduced grass productivity only during a 110-d period, whereas high temperatures reduced productivity only during 25 d in July. The effects of drought and heat waves declined over the season and had no detectable impact on grass productivity in August. If these patterns are general across ecosystems, predictions of ecosystem response to climate change will have to account not only for the magnitude of climate variability but also for its timing.

Craine, Joseph M.; Nippert, Jesse B.; Elmore, Andrew J.; Skibbe, Adam M.; Hutchinson, Stacy L.; Brunsell, Nathaniel A.

2012-01-01

164

Seasonal patterns of ammonium and nitrate uptake in nine temperate forest ecosystems  

Microsoft Academic Search

Summary Seasonal patterns of net N mineralization and nitrification in the 0–10 cm mineral soil of 9 temperate forest sites were analyzed using approximately monthlyin situ soil incubations. Measured nitrification rates in incubated soils were found to be good estimates of nitrification in surrounding forest soils. Monthly net N mineralization rates and pools of ammonium-N in soil fluctuated during the

Knute J. Nadelhoffer; John D. Aber; Jerry M. Melillo

1984-01-01

165

Complementarities between Biomass and FluxNet data to optimize ORCHIDEE ecosystem model at European forest and grassland sites  

NASA Astrophysics Data System (ADS)

Assimilation of data from several measurements provides knowledge of the model's performance and uncertainties. In this work we investigate the complementary of Biomass data to net CO2 flux (NEE) and latent heat flux (LE) in optimising parameters of the biogeochemical model ORCHIDEE. Our optimisation method is a gradient based iterative method. We optimized the model at the French forest sites, European beech forest of Hesse (48 .67°N, 7.06°E) and maritime pine forest of Le Bray (44.72°N, 0.77°W). First we adapted the model to represent the past clearcut on these two sites in order to obtain a realistic age of the forest. The model-data improvement in terms of aboveground biomass will be discussed. We then used FluxNet and Biomass data, separately and altogether, in the optimization process to assess the potential and the complementarities of these two data stream. For biomass data optimization we added parameters linked to allocation to the optimization scheme. The results show a decrease in the uncertainty of the parameters after optimization and reveal some structural deficiencies in the model. In a second step, data from ecosystem manipulation experiment site Brandbjerg (55.88°N, 11.97°E), a Danish grassland site, were used for model optimisation. The different ecosystem experiments at this site include rain exclusion, warming, and increased CO2 concentration, and only biomass data were available and used in the optimization for the different treatments. We investigate the ability of the model to represent the biomass differences between manipulative experiments with a given set of parameters and highlight model deficiencies.

Thum, T.; Peylin, P.; Granier, A.; Ibrom, A.; Linden, L.; Loustau, D.; Bacour, C.; Ciais, P.

2010-12-01

166

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.

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

2006-01-01

167

The role of grasslands in food security and climate change  

PubMed Central

Background Grasslands are a major part of the global ecosystem, covering 37 % of the earth's terrestrial area. For a variety of reasons, mostly related to overgrazing and the resulting problems of soil erosion and weed encroachment, many of the world's natural grasslands are in poor condition and showing signs of degradation. This review examines their contribution to global food supply and to combating climate change. Scope Grasslands make a significant contribution to food security through providing part of the feed requirements of ruminants used for meat and milk production. Globally, this is more important in food energy terms than pig meat and poultry meat. Grasslands are considered to have the potential to play a key role in greenhouse gas mitigation, particularly in terms of global carbon storage and further carbon sequestration. It is estimated that grazing land management and pasture improvement (e.g. through managing grazing intensity, improved productivity, etc) have a global technical mitigation potential of almost 1·5 Gt CO2 equivalent in 2030, with additional mitigation possible from restoration of degraded lands. Milk and meat production from grassland systems in temperate regions has similar emissions of carbon dioxide per kilogram of product as mixed farming systems in temperate regions, and, if carbon sinks in grasslands are taken into account, grassland-based production systems can be as efficient as high-input systems from a greenhouse gas perspective. Conclusions Grasslands are important for global food supply, contributing to ruminant milk and meat production. Extra food will need to come from the world's existing agricultural land base (including grasslands) as the total area of agricultural land has remained static since 1991. Ruminants are efficient converters of grass into humanly edible energy and protein and grassland-based food production can produce food with a comparable carbon footprint as mixed systems. Grasslands are a very important store of carbon, and they are continuing to sequester carbon with considerable potential to increase this further. Grassland adaptation to climate change will be variable, with possible increases or decreases in productivity and increases or decreases in soil carbon stores.

O'Mara, F. P.

2012-01-01

168

The Ecological Significance of the Herbaceous Layer in Temperate Forest Ecosystems  

Microsoft Academic Search

Despite a growing awareness that the herbaceous layer serves a special role in maintaining the structure and function of forests, this stratum remains an underappreciated aspect of forest ecosystems. In this article I review and synthesize information concerning the herb layer's structure, composition, and dynamics to emphasize its role as an integral component of forest ecosystems. Because species diversity is

FRANK S. GILLIAM

2007-01-01

169

Evaluation of Ecohydrologic Model Parsimony at Local and Regional Scales in a Semiarid Grassland Ecosystem  

NASA Astrophysics Data System (ADS)

In this paper we aim to develop an ecohydrology model with low number of parameters that can capture regional ecohydrological dynamics, including soil moisture, seasonality of live and dead biomass, and root-zone water balance. Such a simplified and efficient ecohydrology model would be most useful for landscape evolution modeling studies, model experiments to examine the emergent properties of vegetation on the landscape, and to develop data assimilation strategies for soil moisture and vegetation states. For this purpose, we couple a zero-dimensional land surface model based on a vertically-averaged representation of soil moisture in the root-zone, with vegetation dynamics providing the evolution of live and dead vegetation biomass through time. Five variants of the model, each with certain combinations of different model time steps (daily versus interstorm), representations of potential evapotranspiration, and a factor for water use efficiency (WUE) are defined and compared against observations in a grassland site located in the Sand Hills region of Nebraska, USA. Observations include field measurements of soil moisture, and live and dead biomass, as well as MODIS-derived LAI. Results show that the simplest model configuration using a constant WUE term, representing potential evapotranspiration from a cosine function, and operating on inter-storm model time step can capture the vegetation dynamics nearly as good as daily model simulations with variable WUE. Application of the model at the regional reveals the model sensitivity to a senescence parameter that control the decay of live aboveground vegetation, and the dependence of this parameter to regional variations in annual precipitation.

Istanbulluoglu, E.; Wang, T.; Wedin, D.

2010-12-01

170

Photosynthetic recovery of foliage after wind disturbance activates ecosystem CO2 uptake in cool temperate forests of northern Japan  

NASA Astrophysics Data System (ADS)

The effects of wind disturbance on forest dynamics and ecosystem CO2 exchange were examined in cool temperate forests of northern Japan during 2004-2008 using eddy covariance (EC) measurements. One site was a young, even-aged, monoculture, deciduous forest; the other was an uneven-aged mixed forest of evergreen and deciduous overstory tree species, including some over 200 years old. On 8 September 2004, a strong typhoon struck the forests, after which leaf and branch amounts decreased in young growth forest, but foliage showed little change in old growth forest. By 2006, foliage at the young-growth forest had recovered to the 2004 pretyphoon state. Average daily accumulated gross primary production (GPPd), terrestrial ecosystem respiration (TERd), and net ecosystem exchange (NEEd) were assessed for six growth stages annually. After the typhoon, large increases in GPPd were found during the growing stage of overstory tree species with high photosynthetic rates compared to that before the typhoon. Pronounced increases in GPPd and corresponding large reductions in NEEd were detected at the young-growth forest, indicating that NEEd was largely regulated by GPPd throughout the growing stages. Although EC measurements contain uncertainty, our continuous EC measurements revealed that interannual variability in meteorological variables and structural changes in foliage have only small impacts on GPP and NEE, while photosynthetic recovery of foliage from typhoon damage has high potential to increase GPP and enhance NEE as compared with those under nondamage conditions.

Toda, Motomu; Kolari, Pasi; Nakai, Taro; Kodama, Yuji; Shibata, Hideaki; Yoshida, Toshiya; Uemura, Shigeru; Sumida, Akihiro; Kato, Kyoko; Ono, Kiyomi; Hara, Toshihiko

2011-06-01

171

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

172

Representing the effects of alpine grassland vegetation cover on the simulation of soil thermal dynamics by ecosystem models applied to the Qinghai-Tibetan Plateau  

NASA Astrophysics Data System (ADS)

surface temperature is a critical boundary condition for the simulation of soil temperature by environmental models. It is influenced by atmospheric and soil conditions and by vegetation cover. In sophisticated land surface models, it is simulated iteratively by solving surface energy budget equations. In ecosystem, permafrost, and hydrology models, the consideration of soil surface temperature is generally simple. In this study, we developed a methodology for representing the effects of vegetation cover and atmospheric factors on the estimation of soil surface temperature for alpine grassland ecosystems on the Qinghai-Tibetan Plateau. Our approach integrated measurements from meteorological stations with simulations from a sophisticated land surface model to develop an equation set for estimating soil surface temperature. After implementing this equation set into an ecosystem model and evaluating the performance of the ecosystem model in simulating soil temperature at different depths in the soil profile, we applied the model to simulate interactions among vegetation cover, freeze-thaw cycles, and soil erosion to demonstrate potential applications made possible through the implementation of the methodology developed in this study. Results showed that (1) to properly estimate daily soil surface temperature, algorithms should use air temperature, downward solar radiation, and vegetation cover as independent variables; (2) the equation set developed in this study performed better than soil surface temperature algorithms used in other models; and (3) the ecosystem model performed well in simulating soil temperature throughout the soil profile using the equation set developed in this study. Our application of the model indicates that the representation in ecosystem models of the effects of vegetation cover on the simulation of soil thermal dynamics has the potential to substantially improve our understanding of the vulnerability of alpine grassland ecosystems to changes in climate and grazing regimes.

Yi, S.; Li, N.; Xiang, B.; Wang, X.; Ye, B.; McGuire, A. D.

2013-07-01

173

Predicting the response of a temperate forest ecosystem to atmospheric CO[sub 2] increase  

SciTech Connect

This report summarizes the second year of research progress. Included are progress reports for the following studies: the responses of temperate forest tree to 3 years of exposure to elevated carbon dioxide, and high and low nutrient and light levels; pot-size limitations in carbon dioxide studies, interactive effects of carbon dioxide and soil moisture availability on tree seedling's tissue water relations, growth, and niche characteristics; individual versus population responses to elevated carbon dioxide levels in two species of annual weeds; and the development of gypsy moth larvae raised on gray and yellow birth foliage grown in ambient and elevated carbon dioxide environments.

Bazzaz, F.A.

1993-01-01

174

Modelling grassland phenology and growth using near-surface remote sensing derived time series  

NASA Astrophysics Data System (ADS)

Both the size and the duration of rain events have a significant influence on the phenology and growth of grasslands. This pulse-response nature of grasslands makes quantifying intra and inter-annual variability in grassland growth challenging and large uncertainties remain on which precipitation characteristics have the greatest influence on grassland phenology, growth and ecosystem productivity. Here we present modeled results of soil water content and grassland growth on a daily timestep from 16 grassland sites (40 site years) across arid, temperate and tropical biomes. We build upon a simple threshold-delay concept with provisions for influences of soil temperature and photoperiod on plant growth. Modelled soil water content and grassland growth are based upon limited set of widely available climatic drivers such as daily precipitation, minimum and maximum temperature, to facilitate scaling, and validated against near-surface remote sensing (PhenoCam) data of vegetation greenness. This simple model framework allows us to explore future effects of changes in the size and duration of precipitation events as well as temperature on grassland phenology and growth across different biome types.

Hufkens, Koen; Chen, Min; Richardson, Andrew D.

2014-05-01

175

Biodiversity effects on yield and unsown species invasion in a temperate forage ecosystem  

PubMed Central

Background and Aims Current agricultural practices are based on growing monocultures or binary mixtures over large areas, with a resultant impoverishing effect on biodiversity at several trophic levels. The effects of increasing the biodiversity of a sward mixture on dry matter yield and unsown species invasion were studied. Methods A field experiment involving four grassland species [two grasses – perennial ryegrass (Lolium perenne) and cocksfoot (Dactylis glomerata) – and two legumes – red clover (Trifolium pratense) and white clover (Trifolium repens)], grown in monocultures and mixtures in accordance with a simplex design, was carried out. The legumes were included either as single varieties or as one of two broad genetic-base composites. The experiment was harvested three times a year over three years; dry matter yield and yield of unsown species were determined at each harvest. Yields of individual species and interactions between all species present were estimated through a statistical modelling approach. Key Results Species diversity produced a strong positive yield effect that resulted in transgressive over-yielding in the second and third years. Using broad genetic-base composites of the legumes had a small impact on yield and species interactions. Invasion by unsown species was strongly reduced by species diversity, but species identity was also important. Cocksfoot and white clover (with the exception of one broad genetic-base composite) reduced invasion, while red clover was the most invaded species. Conclusions The results show that it is possible to increase, and stabilize, the yield of a grassland crop and reduce invasion by unsown species by increasing its species diversity.

Frankow-Lindberg, B. E.; Brophy, C.; Collins, R. P.; Connolly, J.

2009-01-01

176

Soil environmental conditions and microbial build-up mediate the effect of plant diversity on soil nitrifying and denitrifying enzyme activities in temperate grasslands.  

PubMed

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

177

Nitrogen controls plant canopy light-use efficiency in temperate and boreal ecosystems  

NASA Astrophysics Data System (ADS)

Optimum daily light-use efficiency (LUE) and normalized canopy photosynthesis (GEE*) rate, a proxy for LUE, have been derived from eddy covariance CO2 flux measurements obtained at a range of sites located in the mid to high latitudes. These two variables were analyzed with respect to environmental conditions, plant functional types (PFT) and leaf nitrogen concentration, in an attempt to characterize their variability and their potential drivers. LUE averaged 0.0182 mol/mol with a coefficient of variation of 37% (42% for GEE*). Foliar nitrogen N of the dominant plant species was found to explain 71% of LUE (n = 26) and 62% of GEE* (n = 44) variance, across all PFTs and sites. Mean Annual Temperature, MAT, explained 27% of LUE variance, and the two factors (MAT and N) combined in a simple linear model explain 80% of LUE and 76% GEE* variance. These results showed that plant canopies in the temperate, boreal and arctic zones fit into a general scheme closely related to the one, which had been established for plant leaves worldwide. The N-MAT-LUE relationships offer perspectives for LUE-based models of terrestrial photosynthesis based on remote sensing. On a continental scale, the decrease of LUE from the temperate to the arctic zone found in the data derived from flux measurements is not in line with LUE resulting from inversion of atmospheric CO2.

Kergoat, Laurent; Lafont, SéBastien; Arneth, Almut; Le Dantec, ValéRie; Saugier, Bernard

2008-12-01

178

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

SciTech Connect

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 W. [Department of Ecology, Evolution, and Behavior, University of MN, St. Paul, MN 55108, USA

2013-08-14

179

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, 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, Jesus; 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

180

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

181

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.

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

182

Cattle Grazing and Tracked Vehicle Training on Central and Southwest U.S. Army Lands: Potential Consequences for Grassland Ecosystems.  

National Technical Information Service (NTIS)

Sustainability of training lands continues to be a primary concern for natural resource managers on Army installations. Tracked vehicle training, the main disturbance of grasslands, does not occur in isolation from other land uses including cattle grazing...

J. A. Guretzky J. S. Fehmi A. B. Anderson

2005-01-01

183

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

184

An Assessment of Aquatic Ecosystem Health in a Temperate Watershed Using the Index of Biological Integrity  

Microsoft Academic Search

The health effect of an aquatic ecosystem on habitat modifications were evaluated in the Keum river watershed, Korea during 1977–1996 using the Index of Biological Integrity (IBI) based on fish assemblages. Values of IBI, based on overall sites, averaged 35 (range: 26–45, n = 38) before dam construction, indicating a “fair health condition” based on the modified criteria of Karr and Chu

Kwang-Guk An; Shin-Sok Choi

2003-01-01

185

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

186

The Ecological Significance of the Herbaceous Layer in Temperate Forest Ecosystems  

NSDL National Science Digital Library

This peer-reviewed article from the November 2007 issue of BioScience examines the importance of the herbaceous layer of the forest ecosystem. Despite a growing awareness that the herbaceous layer serves a special role in maintaining the structure and function of forests, this stratum remains an underappreciated aspect of forest ecosystems. In this article I review and synthesize information concerning the herb layer's structure, composition, and dynamics to emphasize its role as an integral component of forest ecosystems. Because species diversity is highest in the herb layer among all forest strata, forest biodiversity is largely a function of the herb-layer community. Competitive interactions within the herb layer can determine the initial success of plants occupying higher strata, including the regeneration of dominant overstory tree species. Furthermore, the herb layer and the overstory can become linked through parallel responses to similar environmental gradients. These relationships between strata vary both spatially and temporally. Because the herb layer responds sensitively to disturbance across broad spatial and temporal scales, its dynamics can provide important information regarding the site characteristics of forests, including patterns of past land-use practices. Thus, the herb layer has a significance that belies its diminutive stature.

Frank Gilliam (;)

2007-11-01

187

Effects of nutrient supply on intrinsic water-use efficiency of temperate semi-natural grassland under rising atmospheric CO2  

NASA Astrophysics Data System (ADS)

C3 plants generally increase photosynthesis (A) and decrease stomatal conductance (gs) under elevated CO2 [1]. However, nitrogen limitation has been shown to constrain the response of A [2] and could thus limit the increase in intrinsic water-use efficiency Wi. Stable carbon isotope studies on trees have shown that Wi increased in forests during the last century. Recently we showed that Wi has also increased in nutrient limited grassland ecosystems [3, 4]. We have now examined a 50 year-long record of Wi from community-level carbon isotope discrimination (13?) derived from archived hay and herbage samples (Park Grass Continuous Hay Experiment, Rothamsted, England [5]). We tested the hypothesis that plant responses to increasing atmospheric CO2 have resulted in a greater increase in Wi where plants received adequate nutrient inputs, because of the expected stronger increase in A with higher nutrient supply. We examined whether the response to rising CO2 was uniform across fertilizer treatments. Archived samples from five plots on Park Grass with different annual fertilizer applications (1. No N or PK; 2. 48 kg N ha-1, No PK; 3. No N +PK; 4. 48 kg N ha-1 +PK; 5. 96 kg N ha-1 +PK), covering the 1960 - 2009 period, were used. During the study period, atmospheric CO2 concentration increased by 22%. 13? was calculated from carbon isotope composition ?13C (= [(Rsample/Rstandard) - 1], with R the 13C/12C ratio in the sample or standard). 13? is a proxy of the leaf-level coupling of CO2 and transpiration fluxes, and a measure of Wi, with Wi = A/gs = ca (1 - ci / ca) / 1.6 and ci / ca = (13? - a) / (b - a), (a=4.4‰, b=27‰). Linear regression showed significant 13? increases: 0.1‰ per 10 ppm CO2 increase on the control (P<0.05), the PK treatment (P<0.001) and the low N, PK treatment (P<0.05). On the low N treatment, the increase was only significant at the 10% level. On the high N, PK treatment 13? increased by 0.04‰ per 10 ppm, but this was not significant (P = 0.18). Slopes did not differ significantly. Kernel regression showed increasing Wi on all treatments. As Wi was derived from 13?, it was apparent that there were no significant differences in plant responses to rising CO2 on plots with different fertilizer inputs. This indicates that the regulation of A and gs under the recent increase in atmospheric CO2 did not differ between the treatments. No increases in yields were observed on the studied plots. Thus, if an increase in A occurred, it did not result in an increase in above ground biomass, even on the well fertilized plot. We suggest that the increase in Wi was achieved mainly by a decrease in gs. This could lead to decreased transpiration of water and increased surface run-off or drainage from this grassland. [1] Ainsworth, E.A. & Rogers, A. (2007) Plant Cell Environ 30, 258-270 [2] Stitt & Krapp (1999) Plant Cell Environ 22, 583-621 [3] Barbosa et al. (2010) Glob Change Biol 16, 1171-1180 [4] Köhler et al. (2010) Glob Change Biol 16, 1531-1541 [5] Silvertown et al. (2006) J Ecol 94, 801-814

Koehler, I. H.; MacDonald, A.; Poulton, P.; Auerswald, K.; Schnyder, H.

2010-12-01

188

Remote sensing of canopy chemistry and nitrogen cycling in temperate forest ecosystems  

NASA Technical Reports Server (NTRS)

The use of images acquired by the Airborne Imaging Spectrometer, an experimental high-spectral resolution imaging sensor developed by NASA, to estimate the lignin concentration of whole forest canopies in Wisconsin is reported. The observed strong relationship between canopy lignin concentration and nitrogen availability in seven undisturbed forest ecosystems on Blackhawk Island, Wisconsin, suggests that canopy lignin may serve as an index for site nitrogen status. This predictive relationship presents the opportunity to estimate nitrogen-cycling rates across forested landscapes through remote sensing.

Wessman, Carol A.; Aber, John D.; Peterson, David L.; Melillo, Jerry M.

1988-01-01

189

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

190

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

191

The relation between productivity and species diversity in temperate-Arctic marine ecosystems.  

PubMed

Energy variables, such as evapotranspiration, temperature, and productivity explain significant variation in the diversity of many groups of terrestrial plants and animals at local to global scales. Although the ocean represents the largest continuous habitat on earth with a vast spectrum of primary productivity and species richness, little is known about how productivity influences species diversity in marine systems. To search for general relationships between productivity and species richness in the ocean, we analyzed data from three different benthic marine ecosystems (epifaunal communities on subtidal rock walls, on navigation buoys in the Gulf of St. Lawrence, and Canadian Arctic macrobenthos) across local to continental spatial scales (<20 to >1000 km) using a standardized proxy for productivity, satellite-derived chlorophyll a. Theoretically, the form of the function between productivity and species richness is either monotonically increasing or decreasing, or curvilinear (hump- or U-shaped). We found three negative linear and three hump-shaped relationships between chlorophyll a and species richness out of 10 independent comparisons. Scale dependence was suggested by more prevalent diversity-productivity relationships at smaller (local, landscape) than larger (regional, continental) spatial scales. Differences in the form of the functions were more closely allied with community type than with scale, as negative linear functions were restricted to sessile epifauna while hump-shaped functions occurred in Arctic macrobenthos (mixed epifauna, infauna). In two of the data sets, (St. Lawrence epifauna and Arctic macrobenthos) significant effects of chlorophyll a co-varied with the effects of salinity, suggesting that environmental stress as well as productivity influences diversity in these marine systems. The co-varying effect of salinity may commonly arise in broad-scale studies of productivity and diversity in marine ecosystems when attempting to sample the largest range of productivity, often encompassing a coastal-oceanic gradient. PMID:19097485

Witman, Jon D; Cusson, Mathieu; Archambault, Philippe; Pershing, Andrew J; Mieszkowska, Nova

2008-11-01

192

Inferring terrestrial photosynthetic light use efficiency of temperate ecosystems from space  

NASA Astrophysics Data System (ADS)

Terrestrial ecosystems absorb about 2.8 Gt C yr-1, which is estimated to be about a quarter of the carbon emitted from fossil fuel combustion. However, the uncertainties of this sink are large, on the order of ±40%, with spatial and temporal variations largely unknown. One of the largest factors contributing to the uncertainty is photosynthesis, the process by which plants absorb carbon from the atmosphere. Currently, photosynthesis, or gross ecosystem productivity (GEP), can only be inferred from flux towers by measuring the exchange of CO2 in the surrounding air column. Consequently, carbon models suffer from a lack of spatial coverage of accurate GEP observations. Here, we show that photosynthetic light use efficiency (?), hence photosynthesis, can be directly inferred from spaceborne measurements of reflectance. We demonstrate that the differential between reflectance measurements in bands associated with the vegetation xanthophyll cycle and estimates of canopy shading obtained from multiangular satellite observations (using the CHRIS/PROBA sensor) permits us to infer plant photosynthetic efficiency, independently of vegetation type and structure (r2 = 0.68, compared to flux measurements). This is a significant advance over previous approaches seeking to model global-scale photosynthesis indirectly from a combination of growth limiting factors, most notably pressure deficit and temperature. When combined with modeled global-scale photosynthesis, satellite-inferred ? can improve model estimates through data assimilation. We anticipate that our findings will guide the development of new spaceborne approaches to observe vegetation carbon uptake and improve current predictions of global CO2 budgets and future climate scenarios by providing regularly timed calibration points for modeling plant photosynthesis consistently at a global scale.

Hilker, Thomas; Coops, Nicholas C.; Hall, Forrest G.; Nichol, Caroline J.; Lyapustin, Alexei; Black, T. Andrew; Wulder, Michael A.; Leuning, Ray; Barr, Alan; Hollinger, David Y.; Munger, Bill; Tucker, Compton J.

2011-09-01

193

Response of carbon dioxide emissions to sheep grazing and N application in an alpine grassland - Part 2: Effect of N application  

NASA Astrophysics Data System (ADS)

Widespread nitrogen (N) enrichment resulting from anthropogenic activities has led to great changes in carbon exchange between the terrestrial biosphere and the atmosphere. Grassland is one of the most sensitive ecosystems to N deposition. However, the effect of N deposition on ecosystem respiration (Re) in grasslands has been conducted mainly in temperate grasslands, which are limited largely by water availability, with few studies focused on alpine grasslands that are primarily constrained by low temperatures. Failure to assess the magnitude of the response in Re outside the growing season (NGS) in previous studies also limits our understanding of carbon exchange under N deposition conditions. To address these knowledge gaps we used a combination of static closed chambers and gas chromatography in an alpine grassland from 2010 to 2011 to test the effects of N application on ecosystem respiration (Re) both inside and outside the growing season. There was no significant change in CO2 emissions under N application. Re outside the growing season was at least equivalent to 9.4% of the CO2 fluxes during the growing season (GS). Annual Re was calculated to be 279.0-403.9 g CO2 m-2 yr-1 in Bayinbuluk alpine grasslands. In addition, our results indicate that soil temperature was the dominant abiotic factor regulating variation in Re in the cold and arid environment. Our results suggest that short-term N additions exert no significant effect on CO2 emissions in alpine grassland.

Gong, Y. M.; Mohammat, A.; Liu, X. J.; Li, K. H.; Christie, P.; Fang, F.; Song, W.; Chang, Y. H.; Han, W. X.; Lü, X. T.; Liu, Y. Y.; Hu, Y. K.

2014-04-01

194

Ecosystem impacts of folivory and frugivory by Japanese macaques in two temperate forests in Yakushima.  

PubMed

Comparing animal consumption to plant primary production provides a means of assessing an animal's impact on the ecosystem and an evaluation of resource limitation. Here, we compared annual fruit and leaf consumption by Japanese macaques (Macaca fuscata) relative to the annual production of these foods in the lowlands and highlands of Yakushima Island, Japan. We estimated consumption by macaques by the direct observation of macaque groups for 1 year in each habitat. We estimated leaf production as the sum of leaf litter fall (corrected for the effect of translocated organic and inorganic matter) and folivory by insects (assumed to be 10%) and by macaques. We estimated fruit production as the sum of fruit litter fall and consumption by birds (estimated by the seed fall) and macaques. The impact of macaque folivory at the community level was negligible relative to production (?0.04%) compared with folivory by insects (assumed to be 10%); however, for some species, macaque folivory reached up to 10.1% of production. Tree species on which macaques fed did not decline in abundance over 13 years, suggesting that their folivory did not influence tree species dynamics. For the three major fleshy-fruited species in the highland site, macaques consumed a considerable portion of total fruit production (6-40%), rivaling the consumption by birds (32-75%). We conclude that at the community level, macaque folivory was negligible compared with the leaf production, but frugivory was not. Am. J. Primatol. 76:596-607, 2014. © 2013 Wiley Periodicals, Inc. PMID:24375432

Hanya, Goro; Fuse, Mieko; Aiba, Shin-Ichiro; Takafumi, Hino; Tsujino, Riyou; Agetsuma, Naoki; Chapman, Colin A

2014-06-01

195

Decomposition of organic carbon in fine soil particles is likely more sensitive to warming than in coarse particles: an incubation study with temperate grassland and forest soils in northern china.  

PubMed

It is widely recognized that global warming promotes soil organic carbon (SOC) decomposition, and soils thus emit more CO2 into the atmosphere because of the warming; however, the response of SOC decomposition to this warming in different soil textures is unclear. This lack of knowledge limits our projection of SOC turnover and CO2 emission from soils after future warming. To investigate the CO2 emission from soils with different textures, we conducted a 107-day incubation experiment. The soils were sampled from temperate forest and grassland in northern China. The incubation was conducted over three short-term cycles of changing temperature from 5°C to 30°C, with an interval of 5°C. Our results indicated that CO2 emissions from sand (>50 µm), silt (2-50 µm), and clay (<2 µm) particles increased exponentially with increasing temperature. The sand fractions emitted more CO2 (CO2-C per unit fraction-C) than the silt and clay fractions in both forest and grassland soils. The temperature sensitivity of the CO2 emission from soil particles, which is expressed as Q10, decreased in the order clay>silt>sand. Our study also found that nitrogen availability in the soil facilitated the temperature dependence of SOC decomposition. A further analysis of the incubation data indicated a power-law decrease of Q10 with increasing temperature. Our results suggested that the decomposition of organic carbon in fine-textured soils that are rich in clay or silt could be more sensitive to warming than those in coarse sandy soils and that SOC might be more vulnerable in boreal and temperate regions than in subtropical and tropical regions under future warming. PMID:24736659

Ding, Fan; Huang, Yao; Sun, Wenjuan; Jiang, Guangfu; Chen, Yue

2014-01-01

196

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  

NASA Astrophysics Data System (ADS)

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 to a cool-temperate deciduous broad-leaved forest in Takayama (36N, 137E, 1420m ASL) and a cool-temperate evergreen coniferous forest in Fujiyoshida (35N, 138E, 1030m ASL), central Japan. Models of nitrogen cycle were introduced into a revised terrestrial ecosystem model Sim-CYCLE, which is a simple box-type carbon cycle model simulating net ecosystem CO2 exchange on the basis of ecophysiological relationships. Using the model, photosynthetic and respiratory CO2 fluxes were simulated during the periods from 1948 to 2004 at daily step using time-series climate data. On average during the last 10 years, the model estimated that the temperate forest absorbed net CO2 and CH4 at rates of 804.53 g CO2 m-2 yr-1 and 0.34 g CH4 m-2 yr-1, and net released N2O at a rate of 0.02 g N2O m-2 yr-1, respectively. Based on the 100-year GWP of greenhouse gases in IPCC (2001), the forest was estimated to have a negative (i.e. ameliorating) effect of GWP by 807.74 g CO2 (equivalent) m-2 yr-1. Because the results seem reasonable, we are working on scaling-up of the model to regional scale, in our forthcoming studies.

Ito, A.; Inatomi, M.

2007-12-01

197

Model analysis of grazing effect on above-ground biomass and above-ground net primary production of a Mongolian grassland ecosystem  

NASA Astrophysics Data System (ADS)

In this study, we have analyzed the productivity of a grassland ecosystem in Kherlenbayan-Ulaan (KBU), Mongolia under non-grazing and grazing conditions using a new simulation model, Sim-CYCLE grazing. The model was obtained by integrating the Sim-CYCLE [Ito, A., Oikawa, T., 2002. A simulation model of carbon cycle in land ecosystems (Sim-CYCLE): a description based on dry-matter production theory and plot-scale validation. Ecological Modeling, 151, pp. 143-176] and a defoliation formulation [Seligman, N.G., Cavagnaro, J.B., Horno, M.E., 1992. Simulation of defoliation effects on primary production of warm-season, semiarid perennial- species grassland. Ecological Modelling, 60, pp. 45-61]. The results from the model have been validated against a set of field data obtained at KBU showing that both above-ground biomass (AB) and above-ground net primary production ( Np,a) decrease with increasing grazing intensity. The simulated maximum AB for a year maintains a nearly constant value of 1.15 Mg DM ha -1 under non-grazing conditions. The AB decreases and then reaches equilibrium under a stocking rate ( Sr) of 0.4 sheep ha -1 and 0.7 sheep ha -1. The AB decreases all the time if Sr is greater than 0.7 sheep ha -1. These results suggest that the maximum sustainable Sr is 0.7 sheep ha -1. A similar trend is also observed for the simulated Np,a. The annual Np,a is about 1.25 Mg DM ha -1 year -1 and this value is also constant under non-grazing conditions. The annual Np,a decreases and then reaches equilibrium under an Sr of 0.4 sheep ha -1 and 0.7 sheep ha -1, but the Np,a decreases all the time when Sr is greater than 0.7 sheep ha -1. It also indicates that the maximum sustainable Sr is 0.7 sheep ha -1. Transpiration ( ET) and evaporation ( EE) rates were determined by the Penman-Monteith method. Simulated results show that ET decreases with increasing Sr, while EE increases with increasing Sr. At equilibrium, the annual mean evapotranspiration ( E) is 189.11 mm year -1 under non-grazing conditions and 187.46 mm year -1 under an Sr of 0.7 sheep ha -1. This indicates that the water budget of the KBU grassland ecosystem is not significantly affected by grazing.

Chen, Yuxiang; Lee, Gilzae; Lee, Pilzae; Oikawa, Takehisa

2007-01-01

198

Seasonal Belowground Ecosystem and Eco-enzymatic Responses to Soil pH and Phosphorus Availability in Temperate Hardwood Forests  

NASA Astrophysics Data System (ADS)

Atmospheric acid deposition can increase phosphorus (P) limitation in temperate hardwood forests by increasing N availability, and therefore P demand, and/or by decreasing pH and occluding inorganic P. However, only recently have studies demonstrated that P limitation can occur in temperate forests and very little is known about the temporal aspects of P dynamics in acidic forest soils and how seasonal shifts in nutrient availability and demand influence microbial investment in extracellular enzymes. The objectives of this study were to investigate how P availability and soil pH influence seasonal patterns of nutrient cycling and soil microbial activity in hardwood forests that experience chronic acid deposition. We experimentally manipulated soil pH, P, or both for three years and examined soil treatment responses in fall, winter, spring, early summer, and late summer. We found that site (glaciated versus unglaciated) and treatment had the most significant influence on nutrient pools and cycling. In general, nutrient pools were higher in glaciated soils than unglaciated for measured nutrients, including total C and N (2-3 times higher), extractable inorganic nitrogen, and readily available P. Treatment had no impact on total C and N pools in either region, but did affect other measured nutrients such as ammonium, which was greatest in the elevated pH treatment for both sites. As expected, readily available P pools were highest in the elevated P treatments (3 fold increase in both sites), but raising pH decreased available P pools in the glaciated site. Raising soil pH increased both net N mineralization rates and net P mineralization rates, regardless of site. Nitrification responses were complex, but we observed an overall significant nitrification increase under elevated pH, particularly in the growing season. Extracellular enzyme activity showed more seasonal patterns than site and treatment effects, exhibiting significant growing season activity reductions for all enzymes measured. Phosphatase enzymes did not respond to our treatments and were generally greatest in the unglaciated soils, particularly in winter and spring. Enzyme stoichiometric relationships revealed that soil microbial populations in the glaciated site were consistently less P and N-limited than unglaciated sites but this difference was less pronounced during the growing season. The trajectory of nutrient limitation in response to soil pH and P availability was highly variable, but we observed that enzyme ratios in the early summer were particularly shifted relative to other seasons suggesting that both sites were increasingly P and N-limited during this period. Overall, our results suggest that ecosystem and microbial responses to soil pH and P availability vary with both season and site history and that more spatially and temporally explicit observations are needed to improve our understanding of ecosystem acidification, nutrient limitation, and the cost-benefit relationships of microbial investments in extracellular enzymes.

Smemo, K. A.; Deforest, J. L.; Petersen, S. L.; Burke, D.; Hewins, C.; Kluber, L. A.; Kyker, S. R.

2013-12-01

199

Effect of land management on ecosystem carbon fluxes at a subalpine grassland site in the Swiss Alps  

Microsoft Academic Search

Summary The influence of agricultural management on the CO2 budget of a typical subalpine grassland was investigated at the Swiss CARBOMONT site at Rigi-Seebodenalp (1025?m a.s.l.) in Central Switzerland. Eddy covariance flux measurements obtained during the first growing season from the mid of spring until the first snow fall (17 Mai to 25 September 2002) are reported. With respect to

N. Rogiers; W. Eugster; M. Furger; R. Siegwolf

2005-01-01

200

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

201

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.

Schatz, Heinrich; Maraun, Mark

2010-01-01

202

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

203

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

204

Effects of winter temperature and summer drought on net ecosystem exchange of CO2 in a temperate peatland  

NASA Astrophysics Data System (ADS)

Northern peatlands are one of the most important global sinks of atmospheric carbon dioxide (CO2); their ability to sequester C is a natural feedback mechanism controlled by climatic variables such as precipitation, temperature, length of growing season and period of snow cover. In the UK it has been predicted that peatlands could become a net source of carbon in response to climate change with climate models predicting a rise in global temperature of ca. 3oC between 1961-1990 and 2100. Land-atmosphere exchange of CO2in peatlands exhibits marked seasonal and inter-annual variations, which have significant short- and long-term effects on carbon sink strength. Net ecosystem exchange (NEE) of CO2 has been measured continuously by eddy-covariance (EC) at Auchencorth Moss (55° 47'32 N, 3° 14'35 W, 267 m a.s.l.), a temperate peatland in central Scotland, since 2002. Auchencorth Moss is a low-lying, ombrotrophic peatland situated ca. 20 km south-west of Edinburgh. Peat depth ranges from 5 m and the site has a mean annual precipitation of 1155 mm. The vegetation present within the flux measurement footprint comprises mixed grass species, heather and substantial areas of moss species (Sphagnum spp. and Polytrichum spp.). The EC system consists of a LiCOR 7000 closed-path infrared gas analyser for the simultaneous measurement of CO2 and water vapour and of a Gill Windmaster Pro ultrasonic anemometer. Over the 10 year period, the site was a consistent yet variable sink of CO2 ranging from -34.1 to -135.9 g CO2-C m-2 yr-1 (mean of -69.1 ± 33.6 g CO2-C m-2 yr-1). Inter-annual variability in NEE was positively correlated to the length of the growing seasons and mean winter air temperature explained 93% of the variability in summertime sink strength, indicating a phenological memory-effect. Plant development and productivity were stunted by colder winters causing a net reduction in the annual carbon sink strength of this peatland where autotrophic processes are thought to be dominant. The site is wet throughout most of the year (water table depth < 5 cm below the peat surface), but there are indications that drought enhanced heterotrophic respiration and depressed gross primary productivity (GPP); a sustained drought during the summer of 2010 (maximum water table depth 36 cm below surface) was accompanied by a two-fold increase in total respiration and a 30% decrease in GPP. The cold preceding winter could also have contributed to lowering GPP, and disentangling the confounding adverse effects of drought and winter climate on GPP is thus not straightforward. Whilst 2010 had the smallest NEE in the 2002-2012 period, the largest values were found for years with warm winters and relatively wet growing seasons. A simple parameterisation of the effects of PAR on GPP of and air temperature on ecosystem respiration, suggest that a rise in air temperature of 1° C between 2012 and 2065 could lead to a 73% increase in the carbon sink strength of the peatland, provided hydrological conditions remain unchanged. This demonstrates that climate change is not likely to change this peatland into a carbon source by 2100.

Helfter, Carole; Campbell, Claire; Dinsmore, Kerry; Drewer, Julia; Coyle, Mhairi; Anderson, Margaret; Skiba, Ute; Nemitz, Eiko; Billett, Michael; Sutton, Mark

2014-05-01

205

Dew water isotopic ratios and their relationships to ecosystem water pools and fluxes in a cropland and a grassland in China.  

PubMed

Dew formation has the potential to modulate the spatial and temporal variations of isotopic contents of atmospheric water vapor, oxygen and carbon dioxide. The goal of this paper is to improve our understanding of the isotopic interactions between dew water and ecosystem water pools and fluxes through two field experiments in a wheat/maize cropland and in a short steppe grassland in China. Measurements were made during 94 dew events of the D and (18)O compositions of dew, atmospheric vapor, leaf, xylem and soil water, and the whole ecosystem water flux. Our results demonstrate that the equilibrium fractionation played a dominant role over the kinetic fractionation in controlling the dew water isotopic compositions. A significant correlation between the isotopic compositions of leaf water and dew water suggests a large role of top-down exchange with atmospheric vapor controlling the leaf water turnover at night. According to the isotopic labeling, dew water consisted of a downward flux of water vapor from above the canopy (98%) and upward fluxes originated from soil evaporation and transpiration of the leaves in the lower canopy (2%). PMID:21822725

Wen, Xue-Fa; Lee, Xuhui; Sun, Xiao-Min; Wang, Jian-Lin; Hu, Zhong-Min; Li, Sheng-Gong; Yu, Gui-Rui

2012-02-01

206

Controls on the fate, structure and function of dissolved organic carbon and nitrogen in a California grassland, oak woodland and conifer ecosystem  

NASA Astrophysics Data System (ADS)

In California, oak woodlands and grasslands, have been expanding their geographic range over the past 100 years, and are projected to extend upward along the western slopes of the Sierra Nevada foothills in response to climate change. Since vegetation type plays a large role in soil formation and carbon (C) and nitrogen (N) cycling, shifts in vegetation distribution could impact C and N storage and processing. This study was designed to determine if dissolved organic carbon (DOC) and nitrogen (DON) production, composition, biodegradation and sorption in the mineral soil of a grassland, oak woodland and conifer ecosystem is related to the type of plant material from which it is derived and how these processes are correlated with temperature. A field experiment where leachates from transplanted soil columns were collected over two rainy seasons at a grassland, oak woodland and conifer field location was combined with laboratory batch adsorption and biodegradation using litter and soil from the same sites. Specific ultra-violet absorbance at 254 nm (SUVA 254), 13C nuclear magnetic resonance (13C NMR) and fractionation of dissolved organic matter (DOM) into hydrophilic and hydrophobic factions was used to determine the structural composition of the DOC solutions. In the laboratory, surface litter from the grass, oak and a conifer site were incubated with de-ionized water for 5, 15 or 96 hours at 4, 20 or 30oC. Incubation time had little effect on DOC structure while vegetation type and temperature had significant effects on DOC functional groups. Increased incubation time and temperature significantly increased DOC and DON concentration. Percent biodegradable DOC was positively correlated to increasing heteroaliphatic functional groups. Since grass, oak and pine DOM solutions had the highest levels of biodegradation using soil inoculums from the sites where the surface litter originated, biodegradation appears to be related to site microbial activity. In batch adsorption studies, an increase in incubation temperature is related to an increase in sorption and biodegradation. There were no significant correlations between adsorption and DOC functional groups. Soil iron and aluminum content were found to play a larger role in DOC adsorption than DOC functional group concentration. Therefore, sorption appears to be primarily controlled by ecosystem soil characteristics and a thermodynamic relationship with temperature rather than surface litter type. In the field experiment, neither DOC, DON nor SUVA 254 values of column leachates differed significantly with surface litter or soil type. However, the 15 month incubation of the soil columns containing all three soil types at all three field locations resulted in several significant changes in soil C and N parameters. Percent C, water extractable DOC and soil C:N all increased in the soil from the pine location that was incubated at the oak and grass location. These changes indicate that the soils at mixed conifer sites in the Sierra Nevada foothills could store increased levels of soil C if grassland and oak woodland vegetation shift into the areas currently dominated by mixed conifers.

Pittiglio, S. L.; Zasoski, R.

2010-12-01

207

The impacts of land-use change from grassland to bioenergy Short Rotation Coppice (SRC) Willow on the crop and ecosystem greenhouse gas balance  

NASA Astrophysics Data System (ADS)

The aim of this research is to better understand the greenhouse gas balance of land-use transition to bioenergy cropping systems in a UK context. Given limited land availability, addressing the food-energy-water nexus remains a challenge, and it is imperative that bioenergy crops are sited appropriately and that competition with food crops is minimized. Here we present the results of a years' worth of soil and GHG data for a conversion from ex-set aside grassland to short rotation coppice (SRC) willow for bioenergy on a commercial scale. Initial results indicate that willow was a net sink for CO2 in comparison to grassland which was a net source of CO2. This provides evidence that the GHG balance of transitions to SRC bioenergy crops will potentially result in increased soil carbon. The empirical findings from this study have been combined with modelled estimates for the site to both test and validate the ECOSSE model. Initial comparisons show that the model is able to accurately predict the respiration occurring at the field site, suggesting that it is a valuable approach for up-scaling from point sites such as this to wider geographical areas and for considering future climate scenarios. The modelling output will also provide a user-friendly tool for land owners which will determine the GHG and soil carbon effects of changing land to bioenergy for UK. This work is based on the Ecosystem Land Use Modelling & Soil Carbon GHG Flux Trial (ELUM) project, which was commissioned and funded by the Energy Technologies Institute (ETI). This work was also jointly funded by the Carbo Biocrop Project.

Harris, Zoe M.; Alberti, Giorgio; Dondini, Marta; Smith, Pete; Taylor, Gail

2014-05-01

208

Precipitation patterns alter growth of temperate vegetation  

Microsoft Academic Search

In this paper, we use growing season Normalized Difference Vegetation Index (NDVI) as an indicator of plant growth to quantify the relationships between vegetation production and intra-annual precipitation patterns for three major temperate biomes in China: grassland, deciduous broadleaf forest, and deciduous coniferous forest. With increased precipitation, NDVI of grassland and deciduous broadleaf forest increased, but that of deciduous coniferous

Jingyun Fang; Shilong Piao; Liming Zhou; Jinsheng He; Fengying Wei; Ranga B. Myneni; Compton J. Tucker; Kun Tan

2005-01-01

209

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.

DANGOL, Dharma Raj; MAHARJAN, Keshav Lall

2013-01-01

210

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

211

Predicting the response of a temperate forest ecosystem to atmospheric CO{sub 2} increase. Annual report, 1992--1993  

SciTech Connect

This report summarizes the second year of research progress. Included are progress reports for the following studies: the responses of temperate forest tree to 3 years of exposure to elevated carbon dioxide, and high and low nutrient and light levels; pot-size limitations in carbon dioxide studies, interactive effects of carbon dioxide and soil moisture availability on tree seedling`s tissue water relations, growth, and niche characteristics; individual versus population responses to elevated carbon dioxide levels in two species of annual weeds; and the development of gypsy moth larvae raised on gray and yellow birth foliage grown in ambient and elevated carbon dioxide environments.

Bazzaz, F.A.

1993-03-01

212

Evaluation of Grassland Dynamics in the Northern-Tibet Plateau of China Using Remote Sensing and Climate Data  

PubMed Central

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 ET0 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 ET0 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.

Zhang, Jiahua; Yao, Fengmei; Zheng, Lingyun; Yang, Limin

2007-01-01

213

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

214

Soil microbial biomass response to woody plant invasion of grassland  

Microsoft Academic Search

Woody plant proliferation in grasslands and savannas has been documented worldwide in recent history. To better understand the consequences of this vegetation change for the C-cycle, we measured soil microbial biomass carbon (Cmic) in remnant grasslands (time 0) and woody plant stands ranging in age from 10 to 130 years in a subtropical ecosystem undergoing succession from grassland to woodlands

J. D. Liao; T. W. Boutton

2008-01-01

215

SPATIAL DISTRIBUTION OF GRASSLAND BIOMASS IN CHINA  

Microsoft Academic Search

Estimating carbon storage in terrestrial ecosystems has been a central focus of research over the past two decades because of its importance to terrestrial carbon cycles and ecosystem processes. As one of the most widespread ecosystem types , China' s grasslands play an important role in global change research. The grass2 lands in China , which are distributed primarily throughout

216

75 FR 73911 - Grassland Reserve Program  

Federal Register 2010, 2011, 2012, 2013

...herbaceous plant other than those in the grass family. Functions and values of grasslands and shrublands means ecosystem services provided, including domestic animal productivity, biological productivity, plant and animal richness and...

2010-11-29

217

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

218

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

219

A biophysical NPZ model with iron for the Gulf of Alaska: Reproducing the differences between an oceanic HNLC ecosystem and a classical northern temperate shelf ecosystem  

NASA Astrophysics Data System (ADS)

Modeling the coastal Gulf of Alaska (CGOA) is complicated by the highly diverse physical and biological features influencing productivity and energy flow through the region. The GOA consists of the offshore oceanic environment, characterized by iron limitation, high-nutrients and low-chlorophyll. The coastal environment is consistently downwelling, with high iron levels from glacial melt water and runoff, but lower concentrations of macronutrients, and with a spring bloom, nutrient depletion cycle (low-nutrient, high-chlorophyll). Cross-shelf movement of water masses mixes coastal and oceanic ecosystem elements. Simulations and field data indicate that the minimum model complexity necessary to characterize lower trophic-level production and biomass in the offshore and coastal regions includes 10 boxes: iron, nitrate, ammonium, small phytoplankton, large phytoplankton, small microzooplankton, large microzooplankton, small copepods, large oceanic copepods and detritus, with copepod mortality as a model closure term. We present the model structure, equations required (and initial parameters used) to simulate onshore and offshore lower trophic-level production in the Gulf of Alaska, along with the information from field data and simulations used to construct the model. We show the results of simulations with and without iron, and with and without two size classes of phytoplankton. These simulations indicate that our method of inclusion of iron works well to distinguish the coastal and the oceanic ecosystems, and that the inclusion of two size categories of phytoplankton is also necessary to generate the differences between these two ecosystems.

Hinckley, S.; Coyle, K. O.; Gibson, G.; Hermann, A. J.; Dobbins, E. L.

2009-12-01

220

Algal biomass and primary production within a temperate zone sandstone  

SciTech Connect

The use of dimethyl sulfoxide (DMSO) to extract chlorophyll a and {sup 14}C-labelled photosynthate from endolithic algae of sparsely vegetated, cold temperate grasslands on the Colorado Plateau in Arizona has yielded the first estimates of biomass and photosynthesis for this unusual community. These subsurface microorganisms are found widespread in exposed Coconino Sandstone, a predominant formation in this cold temperate region. The endolithic community in Coconino Sandstone, composed primarily of coccoid blue-green and coccoid/sarcinoid green algae, yielded a biomass value (as chlorophyll a content) of 87 mg m{sup {minus}2} rock surface area and a photosynthetic rate of 0.37 mg CO{sub 2} dm{sup {minus}2} hr{sup {minus}1} or 0.48 mg CO{sub 2} mg{sup {minus}1} chl a hr{sup {minus}1}. The endolithic algal community contributes moderate biomass (5-10%) and substantial photosynthesis (20-80%) to the sparse grassland ecosystem.

Bell, R.A.; Sommerfeld, M.R. (Arizona State Univ., Tempe (USA))

1987-02-01

221

Above and belowground ecosystem biomass and carbon pools in an age-sequence of temperate pine plantation forests  

Microsoft Academic Search

We assessed the successional development of above- and belowground ecosystem biomass and carbon (C) pools in an age-sequence of four White pine (Pinus strobus L.) plantation stands (2-, 15-, 30-, and 65-years-old) in Southern Ontario, Canada. Biomass and C stocks of above- and belowground live and dead tree biomass, understorey and forest ground vegetation, forest floor C (LFH-layer), and woody

Matthias Peichl; M. Altaf Arain

2006-01-01

222

Nematode community structure as indicator of soil functioning in European grassland soils  

Microsoft Academic Search

This investigation analyses whether soil nematode diversity is correlated with soil functional parameters to serve as bioindicator of soil functioning. The analysis focuses on the interrelations of nematofauna, microflora, and soil nitrogen pools. The sites studied represent six major European grassland types: Northern tundra, atlantic heath, wet grassland, seminatural temperate grassland, East European steppe, and mediterranean garigue. Continental and local

Klemens Ekschmitt; Gabor Bakonyi; Marina Bongers; Tom Bongers; Sven Boström; Hülya Dogan; Andrew Harrison; Péter Nagy; Efimia M. Papatheodorou; Björn Sohlenius; George P. Stamou; Volkmar Wolters

2001-01-01

223

Effects of an increase in summer precipitation on leaf, soil, and ecosystem fluxes of CO2 and H2O in a sotol grassland in Big Bend National Park, Texas.  

PubMed

Global climate models predict that in the next century precipitation in desert regions of the USA will increase, which is anticipated to affect biosphere/atmosphere exchanges of both CO(2) and H(2)O. In a sotol grassland ecosystem in the Chihuahuan Desert at Big Bend National Park, we measured the response of leaf-level fluxes of CO(2) and H(2)O 1 day before and up to 7 days after three supplemental precipitation pulses in the summer (June, July, and August 2004). In addition, the responses of leaf, soil, and ecosystem fluxes of CO(2) and H(2)O to these precipitation pulses were also evaluated in September, 1 month after the final seasonal supplemental watering event. We found that plant carbon fixation responded positively to supplemental precipitation throughout the summer. Both shrubs and grasses in watered plots had increased rates of photosynthesis following pulses in June and July. In September, only grasses in watered plots had higher rates of photosynthesis than plants in the control plots. Soil respiration decreased in supplementally watered plots at the end of the summer. Due to these increased rates of photosynthesis in grasses and decreased rates of daytime soil respiration, watered ecosystems were a sink for carbon in September, assimilating on average 31 mmol CO(2) m(-2) s(-1) ground area day(-1). As a result of a 25% increase in summer precipitation, watered plots fixed eightfold more CO(2) during a 24-h period than control plots. In June and July, there were greater rates of transpiration for both grasses and shrubs in the watered plots. In September, similar rates of transpiration and soil water evaporation led to no observed treatment differences in ecosystem evapotranspiration, even though grasses transpired significantly more than shrubs. In summary, greater amounts of summer precipitation may lead to short-term increased carbon uptake by this sotol grassland ecosystem. PMID:17180661

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

2007-04-01

224

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

225

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

226

Changes in biomass carbon stocks in China's grasslands between 1982 and 1999  

Microsoft Academic Search

Terrestrial ecosystems in the northern latitudes are significant carbon sinks for atmospheric CO2; however, few studies come from grassland ecosystems. Using national grassland resource inventory data, NDVI (normalized difference vegetation index) time series data set, and a satellite-based statistical model, this study identifies changes in the size and distribution of aboveground biomass carbon (C) stocks for China's grasslands between 1982

Shilong Piao; Jingyun Fang; Liming Zhou; Kun Tan; Shu Tao

2007-01-01

227

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.

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

2011-01-01

228

Effects of elevated CO?, warming and drought episodes on plant carbon uptake in a temperate heath ecosystem are controlled by soil water status.  

PubMed

The impact of elevated CO?, periodic drought and warming on photosynthesis and leaf characteristics of the evergreen dwarf shrub Calluna vulgaris in a temperate heath ecosystem was investigated. Photosynthesis was reduced by drought in midsummer and increased by elevated CO? throughout the growing season, whereas warming only stimulated photosynthesis early in the year. At the beginning and end of the growing season, a T × CO? interaction synergistically stimulated plant carbon uptake in the combination of warming and elevated CO?. At peak drought, the D × CO? interaction antagonistically down-regulated photosynthesis, suggesting a limited ability of elevated CO? to counteract the negative effect of drought. The response of photosynthesis in the full factorial combination (TDCO?) could be explained by the main effect of experimental treatments (T, D, CO?) and the two-factor interactions (D × CO?, T × CO?). The interactive responses in the experimental treatments including elevated CO? seemed to be linked to the realized range of treatment variability, for example with negative effects following experimental drought or positive effects following the relatively higher impact of night-time warming during cold periods early and late in the year. Longer-term experiments are needed to evaluate whether photosynthetic down-regulation will dampen the stimulation of photosynthesis under prolonged exposure to elevated CO?. PMID:21410715

Albert, K R; Ro-Poulsen, H; Mikkelsen, T N; Michelsen, A; Van Der Linden, L; Beier, C

2011-07-01

229

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.

230

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

231

Phytoplankton Diversity and Community Composition along the Estuarine Gradient of a Temperate Macrotidal Ecosystem: Combined Morphological and Molecular Approaches  

PubMed Central

Microscopical and molecular analyses were used to investigate the diversity and spatial community structure of spring phytoplankton all along the estuarine gradient in a macrotidal ecosystem, the Baie des Veys (eastern English Channel). Taxa distribution at high tide in the water column appeared to be mainly driven by the tidal force which superimposed on the natural salinity gradient, resulting in a two-layer flow within the channel. Lowest taxa richness and abundance were found in the bay where Teleaulax-like cryptophytes dominated. A shift in species composition occurred towards the mouth of the river, with the diatom Asterionellopsis glacialis dramatically accumulating in the bottom waters of the upstream brackish reach. Small thalassiosiroid diatoms dominated the upper layer river community, where taxa richness was higher. Through the construction of partial 18S rDNA clone libraries, the microeukaryotic diversity was further explored for three samples selected along the surface salinity gradient (freshwater - brackish - marine). Clone libraries revealed a high diversity among heterotrophic and/or small-sized protists which were undetected by microscopy. Among them, a rich variety of Chrysophyceae and other lineages (e.g. novel marine stramenopiles) are reported here for the first time in this transition area. However, conventional microscopy remains more efficient in revealing the high diversity of phototrophic taxa, low in abundances but morphologically distinct, that is overlooked by the molecular approach. The differences between microscopical and molecular analyses and their limitations are discussed here, pointing out the complementarities of both approaches, for a thorough phytoplankton community description.

Bazin, Pauline; Jouenne, Fabien; Friedl, Thomas; Deton-Cabanillas, Anne-Flore; Le Roy, Bertrand; Veron, Benoit

2014-01-01

232

Phytoplankton Diversity and Community Composition along the Estuarine Gradient of a Temperate Macrotidal Ecosystem: Combined Morphological and Molecular Approaches.  

PubMed

Microscopical and molecular analyses were used to investigate the diversity and spatial community structure of spring phytoplankton all along the estuarine gradient in a macrotidal ecosystem, the Baie des Veys (eastern English Channel). Taxa distribution at high tide in the water column appeared to be mainly driven by the tidal force which superimposed on the natural salinity gradient, resulting in a two-layer flow within the channel. Lowest taxa richness and abundance were found in the bay where Teleaulax-like cryptophytes dominated. A shift in species composition occurred towards the mouth of the river, with the diatom Asterionellopsis glacialis dramatically accumulating in the bottom waters of the upstream brackish reach. Small thalassiosiroid diatoms dominated the upper layer river community, where taxa richness was higher. Through the construction of partial 18S rDNA clone libraries, the microeukaryotic diversity was further explored for three samples selected along the surface salinity gradient (freshwater - brackish - marine). Clone libraries revealed a high diversity among heterotrophic and/or small-sized protists which were undetected by microscopy. Among them, a rich variety of Chrysophyceae and other lineages (e.g. novel marine stramenopiles) are reported here for the first time in this transition area. However, conventional microscopy remains more efficient in revealing the high diversity of phototrophic taxa, low in abundances but morphologically distinct, that is overlooked by the molecular approach. The differences between microscopical and molecular analyses and their limitations are discussed here, pointing out the complementarities of both approaches, for a thorough phytoplankton community description. PMID:24718653

Bazin, Pauline; Jouenne, Fabien; Friedl, Thomas; Deton-Cabanillas, Anne-Flore; Le Roy, Bertrand; Véron, Benoît

2014-01-01

233

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

234

Recurrent soil freeze-thaw cycles enhance grassland productivity.  

PubMed

Ongoing global warming will increase the frequency of soil freeze-thaw cycles (FTCs) in cool-temperate and other high-latitude regions. The spatial relevance of seasonally frozen ground amounts to c. 55% of the total land area of the northern hemisphere. Evidence suggests that FTCs contribute to nutrient dynamics. Knowledge of their effects on plant communities is scarce, although plants may be the decisive factor in controlling ecosystem functions such as nutrient retention. Here, the effects are analysed of five additional FTCs in winter for the above- and below-ground productivity of experimental grassland communities and soil enzymatic activity over the following growing season. Freeze-thaw cycles increased the above-ground productivity but reduced root length over the whole subsequent growing season. In summer, no changes in soil enzymatic activities representing the carbon, nitrogen and phosphorus cycles were observed in the FTC-manipulated plots, except for an increased cellobiohydrolase activity. Changes in productivity resulting in an increased shoot-to-root ratio and shifts in timing are capable of altering ecosystem stability and ecosystem services, such as productivity and nutrient retention. PMID:18069954

Kreyling, Juergen; Beierkuhnlein, Carl; Pritsch, Karin; Schloter, Michael; Jentsch, Anke

2008-01-01

235

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

236

[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

237

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

Microsoft Academic Search

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 habitat for grassland songbirds, though little is known about the quality of this habitat. A short-term study on songbirds at three NPS properties complemented current monitoring, providing an among park comparison addressing grassland bird productivity

Sarah E Rehme

2010-01-01

238

The greenhouse gas balance of European grasslands  

Microsoft Academic Search

The long-term carbon balance (NBP) of grasslands is estimated by combining scarce multi-year eddy-covariance observations at ecosystem observation sites where information on carbon inputs and harvesting removals is available. Following accounting for carbon leached to rivers, we estimated grasslands to be net carbon sinks of 74±10 g C m-2 yr-1. Uncertainties arise from the small number of sites and the

P. Ciais; J. F. Soussana; N. Vuichard; S. Luyssaert; A. Don; I. A. Janssens; S. L. Piao; R. Dechow; J. Lathičre; F. Maignan; M. Wattenbach; P. Smith; C. Ammann; A. Freibauer; E. D. Schulze

2010-01-01

239

Application of the ORCHIDEE global vegetation model to evaluate biomass and soil carbon stocks of Qinghai-Tibetan grasslands  

Microsoft Academic Search

The cold grasslands of the Qinghai-Tibetan Plateau form a globally significant biome, which represents 6% of the world's grasslands and 44% of China's grasslands. Yet little is known about carbon cycling in this biome. In this study, we calibrated and applied a process-based ecosystem model called Organizing Carbon and Hydrology in Dynamic Ecosystems (ORCHIDEE) to estimate the C fluxes and

Kun Tan; Philippe Ciais; Shilong Piao; Xiaopu Wu; Yanhong Tang; Nicolas Vuichard; Shuang Liang; Jingyun Fang

2010-01-01

240

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.

Herzog, R.

241

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

242

Biodiversity and stability in grasslands  

Microsoft Academic Search

ONE of the ecological tenets justifying conservation of biodiversity is that diversity begets stability. Impacts of biodiversity on population dynamics and ecosystem functioning have long been debated1-7, however, with many theoretical explorations2-6,8-11 but few field studies12-15. Here we describe a long-term study of grasslands16,17 which shows that primary productivity in more diverse plant communities is more resistant to, and recovers

David Tilman; John A. Downing

1994-01-01

243

Grassland birds: An overview of threats and recommended management strategies  

USGS Publications Warehouse

Grassland ecosystems are dependent on periodic disturbance for habitat maintenance. Historically, grazing by native herbivores and prairie fires were the agents principally responsible for maintaining grassland areas. However, elimination of native herbivores, wide-spread fire suppression, and conversion for agriculture have greatly altered grasslands in the United States and Canada. Because of these landscape changes, many grassland birds are increasingly dependent on land managers for habitat creation, maintenance, and health. Grazing, prescribed burning, and mowing/haying are the most frequently used, and versatile, grassland management techniques. Grassland birds prefer a wide range of grass heights and densities, with some species preferring short sparse vegetation, and others preferring taller, more dense vegetation. Due to differences in species habitat preferences and regional differences in soils and floristics, the responses of individual grassland species to specific grassland management practices can be variable and often are regionally dependent. As a result, management of grassland areas is best directed toward the creation of a mosaic of grassland habitat types. This habitat mosaic is probably best maintained through some type of rotational management system in which sections of large grassland areas receive management on a regular schedule. Such a rotational system would provide a variety of habitat types in every year, would ensure the availability of suitable habitat for birds at either end of the grassland management spectrum, and also would provide habitat for birds whose preferences lie between these extremes.

Vickery, P.D.; Herkert, J.R.; Knopf, F.L.; Ruth, J.; Keller, C.E.

2000-01-01

244

Soil Carbon Recovery of Degraded Steppe Ecosystems of the Mongolian Plateau  

NASA Astrophysics Data System (ADS)

Mongolian steppe grassland systems are critical source of ecosystem services to societal groups in temperate East Asia. These systems are characterized by their arid and semiarid environments where rainfall tends to be too variable or evaporative losses reduce water availability to reliably support cropping systems or substantial forest cover. These steppe ecosystems have supported land use practices to accommodate the variable rainfall patterns, and seasonal and spatial patterns of forage production displayed by the nomadic pastoral systems practiced across Asia. These pastoral systems are dependent on grassland ecosystem services, including forage production, wool, skins, meat and dairy products, and in many systems provide critical biodiversity and land and water protection services which serve to maintain pastoral livelihoods. Precipitation variability and associated drought conditions experienced frequently in these grassland systems are key drivers of these systems. However, during the past several decades climate change and grazing and land use conversion have resulted in degradation of ecosystem services and loss of soil organic matter. Recent efforts in China and Mongolia are investigating different grazing management practices to restore soil organic matter in these degraded systems. Simulation modeling is being applied to evaluate the long-term benefits of different grazing management regimes under various climate scenarios.

Ojima, D. S.; Togtohyn, C.; Qi, J.

2013-12-01

245

Variation in the carbon and oxygen isotope composition of plant biomass and its relationship to water-use efficiency at the leaf- and ecosystem-scales in a northern Great Plains grassland.  

PubMed

Measurements of the carbon (?(13) Cm ) and oxygen (?(18) Om ) isotope composition of C3 plant tissue provide important insights into controls on water-use efficiency. We investigated the causes of seasonal and inter-annual variability in water-use efficiency in a grassland near Lethbridge, Canada using stable isotope (leaf-scale) and eddy covariance measurements (ecosystem-scale). The positive relationship between ?(13) Cm and ?(18) Om values for samples collected during 1998-2001 indicated that variation in stomatal conductance and water stress-induced changes in the degree of stomatal limitation of net photosynthesis were the major controls on variation in ?(13) Cm and biomass production during this time. By comparison, the lack of a significant relationship between ?(13) Cm and ?(18) Om values during 2002, 2003 and 2006 demonstrated that water stress was not a significant limitation on photosynthesis and biomass production in these years. Water-use efficiency was higher in 2000 than 1999, consistent with expectations because of greater stomatal limitation of photosynthesis and lower leaf ci /ca during the drier conditions of 2000. Calculated values of leaf-scale water-use efficiency were 2-3 times higher than ecosystem-scale water-use efficiency, a difference that was likely due to carbon lost in root respiration and water lost during soil evaporation that was not accounted for by the stable isotope measurements. PMID:23862667

Flanagan, Lawrence B; Farquhar, Graham D

2014-02-01

246

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

247

Effects of the nematofauna on microbial energy and matter transformation rates in European grassland soils  

Microsoft Academic Search

The effect of the nematofauna on the microbiology and soil nitrogen status was studied in 6 major European grassland types\\u000a (Northern tundra (Abisko, Sweden), Atlantic heath (Otterburn, UK), wet grassland (Wageningen, Netherlands), semi-natural temperate\\u000a grassland (Linden, Germany), East European steppe (Pusztaszer, Hungary) and Mediterranean garigue (Mt. Vermion, Greece). To\\u000a extend the range of temperature and humidity experienced locally during the

Klemens Ekschmitt; Gabor Bakonyi; Marina Bongers; Tom Bongers; Sven Boström; Hülya Dogan; Andrew Harrison; Athanassios Kallimanis; Péter Nagy; Anthony G. O'Donnell; Björn Sohlenius; George P. Stamou; Volkmar Wolters

1999-01-01

248

Invasion by Aegilops triuncialis (Barb Goatgrass) Slows Carbon and Nutrient Cycling in a Serpentine Grassland  

Microsoft Academic Search

Invasive plant species alter plant community composition and ecosystem function. In the United States, California native grasslands\\u000a have been displaced almost completely by invasive annual grasses, with serpentine grasslands being one of the few remaining\\u000a refugia for California grasslands. This study examined how the invasive annual grass, Aegilops triuncialis, has altered decomposition processes in a serpentine annual grassland. Our objectives

Rebecca E. Drenovsky; Katharine M. Batten

2007-01-01

249

Spatial distribution of soil organic carbon and its influencing factors in desert grasslands of the hexi corridor, northwest china.  

PubMed

Knowledge of the distribution patterns of soil organic carbon (SOC) and factors that influence these patterns is crucial for understanding the carbon cycle. The objectives of this study were to determine the spatial distribution pattern of soil organic carbon density (SOCD) and the controlling factors in arid desert grasslands of northwest China. The above- and belowground biomass and SOCD in 260 soil profiles from 52 sites over 2.7×104 km2 were investigated. Combined with a satellite-based dataset of an enhanced vegetation index during 2011-2012 and climatic factors at different sites, the relationships between SOCD and biotic and abiotic factors were identified. The results indicated that the mean SOCD was 1.20 (SD:+/- 0.85), 1.73 (SD:+/- 1.20), and 2.69 (SD:+/- 1.91) kg m-2 at soil depths of 0-30 cm, 0-50 cm, and 0-100 cm, respectively, which was smaller than other estimates in temperate grassland, steppe, and desert-grassland ecosystems. The spatial distribution of SOCD gradually decreased from the southeast to the northwest, corresponding to the precipitation gradient. SOCD increased significantly with vegetation biomass, annual precipitation, soil moisture, clay and silt content, and decreased with mean annual temperature and sand content. The correlation between BGB and SOCD was closer than the correlation between AGB and SOCD. Variables could together explain about 69.8%, 74.4%, and 78.9% of total variation in SOCD at 0-30 cm, 0-50 cm, and 0-100 cm, respectively. In addition, we found that mean annual temperature is more important than other abiotic factors in determining SOCD in arid desert grasslands in our study area. The information obtained in this study provides a basis for accurately estimating SOC stocks and assessing carbon (C) sequestration potential in the desert grasslands of northwest China. PMID:24732375

Wang, Min; Su, Yongzhong; Yang, Xiao

2014-01-01

250

Spatial Distribution of Soil Organic Carbon and Its Influencing Factors in Desert Grasslands of the Hexi Corridor, Northwest China  

PubMed Central

Knowledge of the distribution patterns of soil organic carbon (SOC) and factors that influence these patterns is crucial for understanding the carbon cycle. The objectives of this study were to determine the spatial distribution pattern of soil organic carbon density (SOCD) and the controlling factors in arid desert grasslands of northwest China. The above- and belowground biomass and SOCD in 260 soil profiles from 52 sites over 2.7×104 km2 were investigated. Combined with a satellite-based dataset of an enhanced vegetation index during 2011–2012 and climatic factors at different sites, the relationships between SOCD and biotic and abiotic factors were identified. The results indicated that the mean SOCD was 1.20 (SD:+/? 0.85), 1.73 (SD:+/? 1.20), and 2.69 (SD:+/? 1.91) kg m?2 at soil depths of 0–30 cm, 0–50 cm, and 0–100 cm, respectively, which was smaller than other estimates in temperate grassland, steppe, and desert-grassland ecosystems. The spatial distribution of SOCD gradually decreased from the southeast to the northwest, corresponding to the precipitation gradient. SOCD increased significantly with vegetation biomass, annual precipitation, soil moisture, clay and silt content, and decreased with mean annual temperature and sand content. The correlation between BGB and SOCD was closer than the correlation between AGB and SOCD. Variables could together explain about 69.8%, 74.4%, and 78.9% of total variation in SOCD at 0–30 cm, 0–50 cm, and 0–100 cm, respectively. In addition, we found that mean annual temperature is more important than other abiotic factors in determining SOCD in arid desert grasslands in our study area. The information obtained in this study provides a basis for accurately estimating SOC stocks and assessing carbon (C) sequestration potential in the desert grasslands of northwest China.

Wang, Min; Su, Yongzhong; Yang, Xiao

2014-01-01

251

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

252

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

SciTech Connect

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.

Peterson, M.A.

1982-06-01

253

Carbon Sequestration Rates and the Energy Balance of Turf in the Denver Urban Ecosystem and in an Adjacent Native Grassland Under Contrasting Management Practices  

NASA Astrophysics Data System (ADS)

Although urban areas occupy just a few percent of US land area, they are expanding rapidly and are expected to maintain this trend for the foreseeable future. Within these domains is the largest irrigated crop in the US - lawns. Utilizing eddy covariance instruments, surface chambers, and destructive leaf sampling, well watered, fertilized lawns in metropolitan Denver were found to sequester substantially more carbon (1.3 T C ha-1 yr-1) than adjacent native grassland (0.6 T C ha-1 yr-1) over a growing season. Due to the semi-arid environment, contrasts in lawn management (irrigation and fertilization) led to wide variation in carbon sequestration rates, evapotranspiration, and the sensible and latent heat partitioning of the energy balance. Measured leaf area was correlated with remotely sensed vegetation indices obtained from aircraft and satellite hyperspectral instruments to quantify spatial variability in leaf area over contrasting land surfaces and lawn management practices. These relations applied to continuing acquisition of remotely sensed data provide us with a means to assess potential variability in carbon sequestration in space and time domains.

Anderson, D. E.; Powell, K.; Szanko, G.; Mladinich, C.; Curry, S.; Griebel, A.

2010-12-01

254

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.

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

2002-01-01

255

Stimulation of Symbiotic N2 Fixation in Trifolium repens L. under Elevated Atmospheric pCO2 in a Grassland Ecosystem.  

PubMed Central

Symbiotic N2 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 CO2 partial pressure (pCO2). The effect of elevated pCO2 (60 Pa) on symbiotic N2 fixation (15N-isotope dilution method) was investigated using Free-Air-CO2-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 N2 fixation increased significantly in T. repens under elevated pCO2. All additionally assimilated N was derived from symbiotic N2 fixation, not from the soil. In the mixtures exposed to elevated pCO2, an increased amount of symbiotically fixed N (+7.8, 8.2, and 6.2 g m-2 a-1 in 1993, 1994, and 1995, respectively) was introduced into the system. Increased N2 fixation is a competitive advantage for T. repens in mixed swards with pasture grasses and may be a crucial factor in maintaining the C:N ratio in the ecosystem as a whole.

Zanetti, S.; Hartwig, U. A.; Luscher, A.; Hebeisen, T.; Frehner, M.; Fischer, B. U.; Hendrey, G. R.; Blum, H.; Nosberger, J.

1996-01-01

256

Stimulation of Symbiotic N2 Fixation in Trifolium repens L. under Elevated Atmospheric pCO2 in a Grassland Ecosystem.  

PubMed

Symbiotic N2 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 CO2 partial pressure (pCO2). The effect of elevated pCO2 (60 Pa) on symbiotic N2 fixation (15N-isotope dilution method) was investigated using Free-Air-CO2-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 N2 fixation increased significantly in T. repens under elevated pCO2. All additionally assimilated N was derived from symbiotic N2 fixation, not from the soil. In the mixtures exposed to elevated pCO2, an increased amount of symbiotically fixed N (+7.8, 8.2, and 6.2 g m-2 a-1 in 1993, 1994, and 1995, respectively) was introduced into the system. Increased N2 fixation is a competitive advantage for T. repens in mixed swards with pasture grasses and may be a crucial factor in maintaining the C:N ratio in the ecosystem as a whole. PMID:12226411

Zanetti, S.; Hartwig, U. A.; Luscher, A.; Hebeisen, T.; Frehner, M.; Fischer, B. U.; Hendrey, G. R.; Blum, H.; Nosberger, J.

1996-10-01

257

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.

Fiala, Karel; Tuma, Ivan; Holub, Petr

2012-01-01

258

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

259

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

260

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

261

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.

Grime, J. Philip; Fridley, Jason D.; Askew, Andrew P.; Thompson, Ken; Hodgson, John G.; Bennett, Chris R.

2008-01-01

262

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?˛ yr?ą 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?˛ s?ą 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

263

Biotransference and biomagnification of selenium copper, cadmium, zinc, arsenic and lead in a temperate seagrass ecosystem from Lake Macquarie Estuary, NSW, Australia  

Microsoft Academic Search

In this study the biotransference of selenium copper, cadmium, zinc, arsenic and lead was measured in a contaminated seagrass ecosystem in Lake Macquarie, NSW, Australia, to determine if biomagnification of these trace metals is occurring and if they reach concentrations that pose a threat to the resident organisms or human consumers. Selenium was found to biomagnify, exceeding maximum permitted concentrations

M Barwick; W Maher

2003-01-01

264

Effect of the conversion of grassland to spring wheat field on the CO 2 emission characteristics in Inner Mongolia, China  

Microsoft Academic Search

Chinese grasslands have undergone great changes in land use in recent decades. Approximately 18.2% of the present arable land in China originated from the cultivation of grassland, but its impact on the carbon cycle has not been fully understood. This study was conducted in situ for 3 years to assess the comprehensive effects of cultivation of temperate steppe on soil

Yu-Chun Qi; Yun-She Dong; Ji-Yuan Liu; Manfred Domroes; Yuan-Bo Geng; Li-Xin Liu; Xing-Ren Liu; Xiao-hong Yang

2007-01-01

265

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.

He, Nianpeng; Yu, Qiang; Wang, Ruomeng; Zhang, Yunhai; Gao, Yang; Yu, Guirui

2013-01-01

266

Earthworm-Mycorrhiza Interactions Can Affect the Diversity, Structure and Functioning of Establishing Model Grassland Communities  

PubMed Central

Both earthworms and arbuscular mycorrhizal fungi (AMF) are important ecosystem engineers co-occurring in temperate grasslands. However, their combined impacts during grassland establishment are poorly understood and have never been studied. We used large mesocosms to study the effects of different functional groups of earthworms (i.e., vertically burrowing anecics vs. horizontally burrowing endogeics) and a mix of four AMF taxa on the establishment, diversity and productivity of plant communities after a simulated seed rain of 18 grassland species comprising grasses, non-leguminous forbs and legumes. Moreover, effects of earthworms and/or AMF on water infiltration and leaching of ammonium, nitrate and phosphate were determined after a simulated extreme rainfall event (40 l m?2). AMF colonisation of all three plant functional groups was altered by earthworms. Seedling emergence and diversity was reduced by anecic earthworms, however only when AMF were present. Plant density was decreased in AMF-free mesocosms when both anecic and endogeic earthworms were active; with AMF also anecics reduced plant density. Plant shoot and root biomass was only affected by earthworms in AMF-free mesocosms: shoot biomass increased due to the activity of either anecics or endogeics; root biomass increased only when anecics were active. Water infiltration increased when earthworms were present in the mesocosms but remained unaffected by AMF. Ammonium leaching was increased only when anecics or a mixed earthworm community was active but was unaffected by AMF; nitrate and phosphate leaching was neither affected by earthworms nor AMF. Ammonium leaching decreased with increasing plant density, nitrate leaching decreased with increasing plant diversity and density. In order to understand the underlying processes of these interactions further investigations possibly under field conditions using more diverse belowground communities are required. Nevertheless, this study demonstrates that belowground-aboveground linkages involving earthworms and AMF are important mediators of the diversity, structure and functioning of plant communities.

Zaller, Johann G.; Heigl, Florian; Grabmaier, Andrea; Lichtenegger, Claudia; Piller, Katja; Allabashi, Roza; Frank, Thomas; Drapela, Thomas

2011-01-01

267

Climate change alters growing season flux dynamics in mesic grasslands  

Microsoft Academic Search

Changing climate could affect the functioning of grassland ecosystems through variation in climate forcings and by altering\\u000a the interactions of forcings with ecological processes. Both the short and long-term effects of changing forcings and ecosystem\\u000a interactions are a critical part of future impacts to ecosystem ecology and hydrology. To explore these interactions and identify\\u000a possible characteristics of climate change impacts

Matt D. Petrie; Nathaniel A. Brunsell; Jesse B. Nippert

268

Convergent responses of nitrogen and phosphorus resorption to nitrogen inputs in a semiarid grassland  

USGS Publications Warehouse

Human activities have significantly altered nitrogen (N) availability in most terrestrial ecosystems, with consequences for community composition and ecosystem functioning. Although studies of how changes in N availability affect biodiversity and community composition are relatively common, much less remains known about the effects of N inputs on the coupled biogeochemical cycling of N and phosphorus (P), and still fewer data exist regarding how increased N inputs affect the internal cycling of these two elements in plants. Nutrient resorption is an important driver of plant nutrient economies and of the quality of litter plants produce. Accordingly, resorption patterns have marked ecological implications for plant population and community fitness, as well as for ecosystem nutrient cycling. In a semiarid grassland in northern China, we studied the effects of a wide range of N inputs on foliar nutrient resorption of two dominant grasses, Leymus chinensis and Stipa grandis. After 4 years of treatments, N and P availability in soil and N and P concentrations in green and senesced grass leaves increased with increasing rates of N addition. Foliar N and P resorption significantly decreased along the N addition gradient, implying a resorption-mediated, positive plant–soil feedback induced by N inputs. Furthermore, N : P resorption ratios were negatively correlated with the rates of N addition, indicating the sensitivity of plant N and P stoichiometry to N inputs. Taken together, the results demonstrate that N additions accelerate ecosystem uptake and turnover of both N and P in the temperate steppe and that N and P cycles are coupled in dynamic ways. The convergence of N and P resorption in response to N inputs emphasizes the importance of nutrient resorption as a pathway by which plants and ecosystems adjust in the face of increasing N availability.

Lü, Xiao-Tao; Reed, Sasha; Yu, Qiang; He, Nian-Peng; Wang, Zheng-Wen; Han, Xing-Guo

2013-01-01

269

Is the lack of leguminous savanna trees in grasslands of South Africa related to nutritional constraints?  

Microsoft Academic Search

As with many grasslands globally, the Highveld grasslands of South Africa are tree-less, despite having a climate that can\\u000a support tree growth. Models predict that fire maintains these grasslands. The question arises as to why fire-tolerant savanna\\u000a trees do not survive in these ecosystems? Savanna tree survival in mesic areas is restricted by demographic bottlenecks, specifically\\u000a limitations to sapling-escape from

Julia L. Wakeling; Michael D. Cramer; William J. Bond

2010-01-01

270

Evaluating Eddy Covariance Flux Filtering Methods For Producing Ecosystem-Representative Carbon Exchange Estimates For A Fetch-Limited Temperate Forest  

NASA Astrophysics Data System (ADS)

Producing time-integrated (daily to annual) estimates of ecosystem-atmosphere carbon exchanges from eddy covariance (EC) measurements requires the careful exclusion of non-representative fluxes prior to gap-filling model application. Half-hourly fluxes are typically excluded when atmospheric turbulence is below an acceptable level (friction velocity threshold, u*Th), or when the relative contribution from non-target surfaces is greater than a tolerable amount (footprint threshold, fpTh). In this study, we compare and evaluate a variety of commonly-used footprint- and friction velocity-filtering methods applied to six years (2006-2011) of carbon flux estimates for a fetch-limited, 74-year old planted Eastern white pine (Pinus Strobus L.) forest in southern Ontario, Canada. A data-driven approach was used, where factorial combinations of footprint models, fpTh values and u*Th determination methods were applied prior to gap-filling. Filtering applications were compared in terms of the quantity and distribution of data removed, while ANOVA and multiple comparison tests were used to quantify the influence of these applications on annual estimates of Net Ecosystem Productivity (NEP), Ecosystem Respiration (RE) and Gross Ecosystem Productivity (GEP). Finally, preferred filtering applications were selected using an objective evaluation of gap-filling model performance metrics to provide information on the internal consistency of the filtered data. Results showed that the choice of footprint model and fpTh exerted a greater influence on NEP, RE and GEP estimates than the u*Th estimation method used. Variation in u*Th estimates were partly explained by footprint filtering specifications, indicating significant u*Th differences between the target forest and the surrounding forested and agricultural land. Applying the footprint model of Kljun (2004. Bound. Layer Met. 112[3]) at fpTh = 0.8 resulted in greatest improvement in model performance; increasing fpTh above this value diminished performance markedly, as insufficient input data quantity and temporal coverage caused poor parameterization. Thus, footprint filter application at this site (and likely other sites), must balance competing needs: accepting only the most representative flux data, while retaining a sufficient amount for successful gap-filling model operation. Compared to the no-footprint (control) case, applying these optimal filtering methods increased annual NEP estimates between 75 and 250 g C m-2 y-1, implying that this forest sequesters substantially more carbon annually than the surrounding landscape. NEP changes were solely attributed to decreased annual RE estimates, as GEP varied only minimally between different footprint and friction velocity applications. This result, caused by a significant day/night flux footprint discrepancy, suggests the need for half-hourly footprint filter application and analyses at all EC flux tower sites that experience measurement fetch limitations.

Brodeur, J. J.; Peichl, M.; Arain, M.

2013-12-01

271

Aboveground net primary production dynamics in a northern Chihuahuan Desert ecosystem.  

PubMed

Aboveground net primary production (ANPP) dynamics are a key element in the understanding of ecosystem processes. For semiarid environments, the pulse-reserve framework links ANPP to variable and unpredictable precipitation events contingent on surficial hydrology, soil moisture dynamics, biodiversity structure, trophic dynamics, and landscape context. Consequently, ANPP may be decoupled periodically from processes such as decomposition and may be subjected to complex feedbacks and thresholds at broader scales. As currently formulated, the pulse-reserve framework may not encompass the breadth of ANPP response to seasonal patterns of precipitation and heat inputs. Accordingly, we examined a 6-year (1999-2004), seasonal record of ANPP with respect to precipitation, soil moisture dynamics, and functional groups in a black grama (Bouteloua eriopoda) grassland and a creosotebush (Larrea tridentata) shrubland in the northern Chihuahuan Desert. Annual ANPP was similar in the grassland (51.1 g/m(2)) and shrubland (59.2 g/m(2)) and positively correlated with annual precipitation. ANPP differed among communities with respect to life forms and functional groups and responses to abiotic drivers. In keeping with the pulse-reserve model, ANPP in black grama grassland was dominated by warm-season C(4) grasses and subshrubs that responded to large, transient summer storms and associated soil moisture in the upper 30 cm. In contrast, ANPP in creosotebush shrubland occasionally responded to summer moisture, but the predominant pattern was slower, non-pulsed growth of cool-season C(3) shrubs during spring, in response to winter soil moisture accumulation and the breaking of cold dormancy. Overall, production in this Chihuahuan Desert ecosystem reflected a mix of warm-temperate arid land pulse dynamics during the summer monsoon and non-pulsed dynamics in spring driven by winter soil moisture accumulation similar to that of cool-temperate regions. PMID:17968592

Muldavin, Esteban H; Moore, Douglas I; Collins, Scott L; Wetherill, Karen R; Lightfoot, David C

2008-02-01

272

Food webs in Mongolian grasslands: The analysis of C and N natural abundances  

Microsoft Academic Search

Overgrazing often lowers species richness and productivity of grassland communities. For Mongolian grassland ecosystems, a lack of detailed information about food-web structures makes it difficult to predict the effects of overgrazing on species diversity and community composition. We analysed the ?C and ?N signatures of herbaceous plants, arthropods (grouped by feeding habit), wild and domestic mammals, and humans in central

Ayato Kohzu; T. Iwata; M. Kato; J. Nishikawa; Eitaro Wada; N. Amartuvshin; B. Namkhaidorj; N. Fujita

2009-01-01

273

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

274

Diversity and abundance of photosynthetic sponges in temperate Western Australia  

Microsoft Academic Search

BACKGROUND: Photosynthetic sponges are important components of reef ecosystems around the world, but are poorly understood. It is often assumed that temperate regions have low diversity and abundance of photosynthetic sponges, but to date no studies have investigated this question. The aim of this study was to compare the percentages of photosynthetic sponges in temperate Western Australia (WA) with previously

Marie-Louise Lemloh; Jane Fromont; Franz Brümmer; Kayley M Usher

2009-01-01

275

Different response of bulk and n-alkane ?13C signatures to seasonal shifts in environmental conditions in a temperate coastal ecosystem  

NASA Astrophysics Data System (ADS)

The carbon isotope signal recorded in land plants represents an important reservoir of information for reconstructing climatically driven shifts in plant ecophysiology and biochemistry. Analytical advances have led to widespread usage of compound-specific (CS) carbon isotope analysis of leaf wax biomarkers, such as n-alkanes, in addition to traditional bulk isotope methods, to identify shifts in the relative percentage of C3 and C4 vegetation contributing to the sedimentary record. Recent studies, however, have extended the application of leaf wax biomarkers, using bulk and n-alkane ?13C values interchangeably to derive information about plant-environment relations, both in modern ecosystems and throughout the geological past. Even though previous work on C3 plants has shown a clear link between climatically influenced plant physiology and bulk ?13C values, further research is needed to establish whether the same link can be seen in leaf wax biomarkers. To address this question, we collected bulk and n-alkane ?13C data from plants growing at Stiffkey marsh on the north Norfolk coast, UK over a period of 15 months. Maximum interspecies variation in weighted average (WA) n-alkane ?13C among C3 species was typically 2-3o greater than in bulk. We observed a close correlation in the bulk and WA n-alkane ?13C seasonal trends from C3 grasses and reeds (R2=0.9, P

Eley, Yvette; Pedentchouk, Nikolai; Dawson, Lorna

2014-05-01

276

Atmospheric particulate deposition in temperate deciduous forest ecosystems: interactions with the canopy and nutrient inputs in two beech stands of Northeastern France.  

PubMed

As wood harvests are expected to increase to satisfy the need for bio-energy in Europe, quantifying atmospheric nutrient inputs in forest ecosystems is essential for forest management. Current atmospheric measurements only take into account the <0.45 ?m fraction and dry deposition is generally modeled. The aims of this study were to quantify atmospheric particulate deposition (APD), the >0.45 ?m fraction of atmospheric deposition, below the canopy, to study the influence of the canopy on APD, and to determine the influence of APD below canopy to nutrient input-output budgets with a focus on base cations calcium, magnesium and potassium, and phosphorus. APD was sampled every four weeks by passive collectors. We divided APD into an organic and a mineral fraction, respectively POM and MDD. MDD was divided into a soluble and a hardly soluble fraction in hydrogen peroxide, referred to as S-MDD and H-MDD, respectively. In order to better understand the influence of the canopy on APD, we studied APD in three pathways below the canopy (litterfall, stemflow and throughfall), and in open field. Our results indicated that APD in throughfall (123 ± 64 kg ha(-1)year(-1)) was significantly higher and synchronic with that in open field (33 ±9 kg ha(-1)year(-1)) in the two study sites. This concerned both POM and MDD, suggesting a large interception of APD by foliar surfaces, which is rapidly washed off by rain within four weeks. Throughfall H-MDD was the main pathway with an average of 16 ± 2 kg ha(-1)year(-1). Stemflow and litterfall were neglected. In one study site, canopy intercepted about 8 kg ha(-1)year(-1) of S-MDD. Although base cations and phosphorus inputs by APD are lower than those of <0.45 ?m deposition, they contributed from 5 to 32% to atmospheric deposition and improved the nutrient budget in one of the study sites. PMID:24784745

Lequy, Emeline; Calvaruso, Christophe; Conil, Sébastien; Turpault, Marie-Pierre

2014-07-15

277

[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

278

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

279

WOODY PLANTS IN GRASSLANDS: POST-ENCROACHMENT STAND DYNAMICS  

Microsoft Academic Search

Woody plant abundance is widely recognized to have increased in savannas and grasslands worldwide. The lack of information on the rates, dynamics, and extent of increases in shrub abundance is a major source of uncertainty in assessing how this vegetation change has influenced biogeochemical cycles. Projecting future consequences of woody cover change on ecosystem function will require knowledge of where

Dawn M. Browning; Steven R. Archer; Gregory P. Asner; Mitchel P. McClaran; Carol A. Wessman

2008-01-01

280

Rhizodeposition stimulated by elevated CO 2 in a semiarid grassland  

Microsoft Academic Search

Summary • Rhizodeposition, or the addition of C from roots to soil C pools, is expected to increase if net primary production is stimulated and some excess C is allocated below-ground. We investigated the effects of 5 yrs of elevated CO 2 on below- ground C dynamics in a native, C 3 -C 4 grassland ecosystem in Colorado, USA. •

Elise Pendall; Arvin R. Mosier; Jack A. Morgan

281

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

282

PITS CONSERVE SPECIES DIVERSITY IN AN OVERGRAZED GRASSLAND  

Microsoft Academic Search

Decrease in species diversity by overgrazing is one of the crucial indicators for ecosystem deterioration. Sika deer ( Cervus nippon Tamminck) has grazed various plants on Nakajima Island, Hokkaido, Japan, for a few decades, due to low food availability. We examined if diverse microtopography supported high species diversity by conserving specific plants on the grassland of the island where overgrazing

S. TSUYUZAKI; H. TAKAHASHI

283

Elevated CO 2 increases belowground respiration in California grasslands  

Microsoft Academic Search

This study was designed to identify potential effects of elevated CO2 on belowground respiration (the sum of root and heterotrophic respiration) in field and microcosm ecosystems and on the annual carbon budget. We made three sets of respiration measurements in two CO2 treatments, i.e., (1) monthly in the sandstone grassland and in microcosms from November 1993 to June 1994; (2)

Yiqi Luo; Robert B. Jackson; Christopher B. Field; Harold A. Mooney

1996-01-01

284

Seasonal variation in ecosystem parameters derived from FLUXNET data  

NASA Astrophysics Data System (ADS)

The carbon dioxide sink is in a complex way related to weather and climate. In order to better understand the relationship and feedbacks, we present a methodology to simulate observed carbon dioxide flux data with a simple vegetation model (5PM) with weekly varying model parameters. The model parameters explain the interaction between vegetation and seasonal climate more general than the flux data. Two parameters (Rref and E0) are related to ecosystem respiration and three parameters (Jm, ? and ?) to photosynthesis and transpiration. We quantified the weekly variability of ecosystem parameters as a function of vegetation type and climate region. After statistical quality checks 121 FLUXNET sites were available for analysis of the weekly varying model parameters. The simulations of these sites have high correlation coefficients (r2=0.6 to 0.8) between the observed and simulated carbon and water fluxes. With weekly parameters we determined average seasonal cycles for the different combinations of vegetation type and climate regions (PFTs). The variation between PFTs is large, which provides an excellent dataset to study the differences in ecosystem characteristics. In general we observed that needleleaf forests and grasslands in warmer climates have relatively constant parameter values during the year. Broadleaf forests in all climate regions have large seasonal variation for each of the five parameters. In boreal regions parameter values are always lower than in temperate regions. A large seasonality of the model parameters indicates a strong relation between vegetation and climate. This suggests that climate change will have the largest impact on the terrestrial carbon fluxes in boreal regions and for deciduous forests, and less for grasslands and evergreen forests.

Groenendijk, M.; van der Molen, M. K.; Dolman, A. J.

2009-03-01

285

Serial tempering without exchange.  

PubMed

Serial tempering is a computational method that turns the temperature T (or more generally any independent ? parameter) into a dynamical variable. It is shown that, under conditions for which this variable is fast, serial tempering is equivalent to the umbrella sampling method with a single effective potential. This equivalence is demonstrated using both a small one-dimensional system and a small solvated peptide. The suggestion is then made to replace the serial tempering protocol with the equivalent umbrella sampling calculation. This approach, serial tempering without exchange (STeWiE), has the same performance as serial tempering in the limit that exchanges are frequent, is simpler to implement, and has fewer adjustable parameters than conventional serial tempering. The equivalence of serial tempering and STeWiE also provides a convenient route for estimating and optimizing the performance of serial tempering simulations and other generalized-ensemble methods. PMID:20866132

Nymeyer, Hugh

2010-09-21

286

Serial tempering without exchange  

NASA Astrophysics Data System (ADS)

Serial tempering is a computational method that turns the temperature T (or more generally any independent ? parameter) into a dynamical variable. It is shown that, under conditions for which this variable is fast, serial tempering is equivalent to the umbrella sampling method with a single effective potential. This equivalence is demonstrated using both a small one-dimensional system and a small solvated peptide. The suggestion is then made to replace the serial tempering protocol with the equivalent umbrella sampling calculation. This approach, serial tempering without exchange (STeWiE), has the same performance as serial tempering in the limit that exchanges are frequent, is simpler to implement, and has fewer adjustable parameters than conventional serial tempering. The equivalence of serial tempering and STeWiE also provides a convenient route for estimating and optimizing the performance of serial tempering simulations and other generalized-ensemble methods.

Nymeyer, Hugh

2010-09-01

287

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

288

Depression of net ecosystem CO 2 exchange in semi-arid Leymus chinensis steppe and alpine shrub  

Microsoft Academic Search

Uptake and release of carbon in grassland ecosystems is very critical to the global carbon balance and carbon storage. In this study, the dynamics of net ecosystem CO2 exchange (FNEE) of two grassland ecosystems were observed continuously using the eddy covariance technique during the growing season of 2003. One is the alpine shrub on the Tibet Plateau, and the other

Yu-Ling Fu; Gui-Rui Yu; Xiao-Min Sun; Ying-Nian Li; Xue-Fa Wen; Lei-Ming Zhang; Zheng-Quan Li; Liang Zhao; Yan-Bin Hao

2006-01-01

289

Managing grassland for production, the environment and the landscape. Challenges at the farm and the landscape level  

Microsoft Academic Search

Grasslands are increasingly considered not only for their contribution to livestock production but also in their various functions with respect to the environment and the landscape. There is an accumulation of scientific evidence about the environmental functions of grasslands, such as their role in the conservation of biodiversity, in the regulation of physical and chemical fluxes in ecosystems, and the

Annick Gibon

2005-01-01

290

Response of net ecosystem gas exchange to a simulated precipitation pulse in a semi-arid grassland: the role of native versus non-native grasses and soil texture  

Microsoft Academic Search

Physiological activity and structural dynamics in arid and semi-arid ecosystems are driven by discrete inputs or “pulses” of growing season precipitation. Here we describe the short-term dynamics of ecosystem physiology in experimental stands of native ( Heteropogon contortus) and invasive ( Eragrostis lehmanniana) grasses to an irrigation pulse across two geomorphic surfaces with distinctly different soils: a Pleistocene-aged surface with

Travis E. Huxman; Jessica M. Cable; Danielle D. Ignace; J. Alex Eilts; Nathan B. English; Jake Weltzin; David G. Williams

2004-01-01

291

Seasonal greening in grasslands  

NASA Astrophysics Data System (ADS)

Grasslands cover about one quarter of the Earth's land and are currently considered to act as carbon sinks, taking up an estimated 0.5 Gt C per year. Thus, robust understanding of the grassland biome (e.g. representation of seasonal cycle of plant growth and the amount of green mass, often referred to as phenology, in global carbon models) plays a key role in understanding and predicting the global carbon cycle. The focus of this research is on improvement of a grassland biome representation in a biosphere model, which sometimes fails to correctly represent the phenology of vegetation. For this purpose, as a part of Simple Biosphere model (SiB3), a phenology model is tested and improved to provide more realistic representation of plant growth dependence on available moisture, which along with temperature and light controls plant growth. The new methodology employs integrated soil moisture in plant growth simulation. This new representation addresses the nature of the plants to use their root system to access the water supply. At same time it represents the plant's moisture recourses more accurately than the currently used vapor pressure method, which in grasslands is often non-correlated with soil conditions. The new technique has been developed and tested on data from the Skukuza flux tower site in South Africa and evaluated at 6 different flux tower sites around the world covering a variety of climate conditions. The technique is relatively easy and inexpensive to implement into the existing model providing excellent results capturing both the onset of green season and greening cycle at all locations. Although the method is developed for grasslands biome its representation of natural plant processes provides a good potential for its global use.

Orescanin, Biljana

292

Carbon dioxide exchange in a semidesert grassland through drought-induced vegetation change  

Microsoft Academic Search

Global warming may intensify the hydrological cycle and lead to increased drought severity and duration, which could alter plant community structure and subsequent ecosystem water and carbon dioxide cycling. We report on the net ecosystem exchange of carbon dioxide (NEE) of a semidesert grassland through a severe drought which drove succession from native bunchgrasses to forbs and to eventual dominance

Russell L. Scott; Erik P. Hamerlynck; G. Darrel Jenerette; M. Susan Moran; Greg A. Barron-Gafford

2010-01-01

293

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...

294

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

295

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

296

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.

Ellison, Kevin S.; Ribic, Christine A.; Sample, David W.; Fawcett, Megan J.; Dadisman, John D.

2013-01-01

297

Small mammal herbivory: Feedbacks that help maintain desertified ecosystems  

Microsoft Academic Search

We tested the hypothesis that herbivores contribute to feedbacks maintaining arid ecosystems in a degraded state. We studied small mammal herbivory on a subshrub, broom snakeweed (Gutierrezia sarothrae), and perennial grasses at three sites: (1) ungrazed black grama (Bouteloua eriopoda) grassland; (2) grassland degraded by intense short-duration grazing; and (3) mesquite (Prosopis glandulosa) coppice dunes. Snakeweed was browsed by herbivores

G. A. Roth; W. G. Whitford; Y. Steinberger

2009-01-01

298

36 CFR 222.52 - National Grasslands.  

Code of Federal Regulations, 2013 CFR

...2013-07-01 2013-07-01 false National Grasslands. 222.52 Section 222.52 Parks...MANAGEMENT Grazing Fees § 222.52 National Grasslands. Grazing fees for National Grasslands will be established under concepts and...

2013-07-01

299

Tempered For Safety  

NSDL National Science Digital Library

This document provides a learning module on tempered safety glass. In this activity, instructors demonstrate the fracture toughness of tempered glass, thereby illustrating how the glass is toughened and introducing the concept of the fractography of glass. It can be used in classrooms from elementary to college levels.

Reidmeyer, Mary R.

2011-09-20

300

Interactive effects of grazing, drought, and fire on grassland plant communities in North America and South Africa.  

PubMed

Grazing, fire, and climate shape mesic grassland communities. With global change altering all three factors, understanding how grasslands respond to changes in these combined drivers may aid in projecting future changes in grassland ecosystems. We manipulated rainfall and simulated grazing (clipping) in two long-term fire experiments in mesic grasslands in North America (NA) and South Africa (SA). Despite their common drivers, grasslands in NA and SA differ in evolutionary history. Therefore, we expected community structure and production in NA and SA to respond differently to fire, grazing, and drought. Specifically, we hypothesized that NA plant community composition and production would be more responsive than the SA plant communities to changes in the drivers and their interactions, and that despite this expected stability of SA grasslands, drought would be the dominant factor controlling production, but grazing would play the primary role in determining community composition at both sites. Contrary to our hypothesis, NA and SA grasslands generally responded similarly to grazing, drought, and fire. Grazing increased diversity, decreased grass cover and production, and decreased belowground biomass at both sites. Drought alone minimally impacted plant community structure, and we saw similar treatment interactions at the two sites. Drought was not the primary driver of grassland productivity, but instead drought effects were similar to or less than grazing and fire. Even though these grasslands differed in evolutionary history, they responded similarly to our fire, grazing, and climate manipulations. Overall, we found community and ecosystem convergence in NA and SA grasslands. Grazing and fire are as important as climate in controlling mesic grassland ecosystems on both continents. PMID:24649650

Koerner, Sally E; Collins, Scott L

2014-01-01

301

Temporal and spatial variability and controls of soil respiration in a temperate steppe in northern China  

NASA Astrophysics Data System (ADS)

In this study, soil respiration and environmental variables were examined to explore the temporal and spatial variability and controls of soil respiration in eight plant communities along an east-west transect in a temperate steppe of Inner Mongolia, China. Our results show that there was substantial temporal (coefficient of variation (CV) = 58.6 ± 1.54%, n = 14) and spatial variability (CV = 32.6 ± 2.65%, n = 8) in soil respiration. Soil temperature and moisture were more important than plant growth in controlling the seasonal patterns of within-site soil respiration in all the eight steppe communities. Spatial differences in soil respiration rate could be mainly attributed to the differences in soil moisture and net primary productivity (NPP) among the study sites, whereas soil temperature played a minor role in regulating the spatial pattern of soil respiration. Significantly, positive site-to-site correlations were found between soil respiration and site soil traits such as soil C, N, and clay contents. In contrast, soil respiration was negatively correlated with soil bulk density and sand content. These findings indicate that the relative importance of abiotic and biotic factors in regulating soil respiration differs temporally from spatially. The conclusions drawn from the present study provide valuable information for developing future models of soil respiration driven by site climatic and soil variables, applicable for large-scale estimates of soil respiration in grassland ecosystems.

Chen, Quansheng; Wang, Qibing; Han, Xingguo; Wan, Shiqiang; Li, Linghao

2010-06-01

302

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

303

Floristic diversity and the richness of locally endangered plant species of semi-natural grasslands under different management practices, southern Kyushu, Japan  

Microsoft Academic Search

Background: The rapid decline of semi-natural grasslands in Japan threatens many relic and endemic plant species. There is insufficient knowledge on how the impacts of land-use changes and management of grasslands have been affecting grassland ecosystems and what conservation measures may be taken to conserve as much of the existing plant diversity as possible.Aim: We assessed the existing management regimes

Nobuki Kawano; Kozo Kawano; Masahiko Ohsawa

2009-01-01

304

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

305

On intergranular tempered martensite embrittlement  

Microsoft Academic Search

Tempering of martensitic alloy steels is generally required to impart adequately high toughness instead of brittleness in the as-quenched state. When hardened steels are tempered in the range of 250--400 C, however, a loss in toughness can occur in spite of the decrease in strength with increasing tempering temperature. This phenomenon is referred to as tempered martensite embrittlement (TME). In

K. B. Lee; S. H. Yoon; S. I. Hong; H. Kwon

1995-01-01

306

Seasonal variation in ecosystem parameters derived from FLUXNET data  

NASA Astrophysics Data System (ADS)

The carbon dioxide sink is related in a complex way to weather and climate. In order to better understand the relationship and feedbacks, we present a methodology to simulate observed carbon dioxide flux data with a simple vegetation model (5PM) with weekly varying model parameters. The model parameters explain the interaction between vegetation and seasonal climate more general than the flux data. Two parameters (Rref and E0) are related to ecosystem respiration and three parameters (Jm, λ and ?) to photosynthesis and transpiration. We quantified the weekly variability of ecosystem parameters as a function of vegetation type and climate region. The objective of this paper is to quantify the short term variability of ecosystem parameters of different vegetation types and climate regions. Specific questions we want to address: (1) are the model parameters clearly different between PFTs and (2) do the model parameters vary in an understandable way and (3) does the variation in model parameters have implications for our understanding of the feedback between vegetation and climate? After statistical quality checks, 122 FLUXNET sites were available for analysis of the weekly varying model parameters. The simulations of these sites have high correlation coefficients (r2 = 0.6 to 0.8) between the observed and simulated carbon and water fluxes. With weekly parameters we determined average seasonal cycles for the different combinations of vegetation type and climate regions (PFTs). The variation between PFTs is large, which provides an excellent dataset to study the differences in ecosystem characteristics. In general we observed that needleleaf forests and grasslands in warmer climates have relatively constant parameter values during the year. Broadleaf forests in all climate regions have large seasonal variation for each of the five parameters. In boreal regions parameter values are always lower than in temperate regions. A large seasonality of the model parameters indicates a strong relation between vegetation and climate. This suggests that climate change will have the largest impact on the terrestrial carbon fluxes in boreal regions and for deciduous forests, and less for grasslands and evergreen forests.

Groenendijk, M.; van der Molen, M. K.; Dolman, A. J.

2009-04-01

307

Extreme precipitation patterns and reductions of terrestrial ecosystem production across biomes  

NASA Astrophysics Data System (ADS)

Precipitation regimes are predicted to shift to more extreme patterns that are characterized by more heavy rainfall events and longer dry intervals, yet their ecological impacts on vegetation production remain uncertain across biomes in natural climatic conditions. This in situ study investigated the effects of these climatic conditions on aboveground net primary production (ANPP) by combining a greenness index from satellite measurements and climatic records during 2000-2009 from 11 long-term experimental sites in multiple biomes and climates. Results showed that extreme precipitation patterns decreased the sensitivity of ANPP to total annual precipitation (PT) at the regional and decadal scales, leading to decreased rain use efficiency (RUE; by 20% on average) across biomes. Relative decreases in ANPP were greatest for arid grassland (16%) and Mediterranean forest (20%) and less for mesic grassland and temperate forest (3%). The cooccurrence of heavy rainfall events and longer dry intervals caused greater water stress conditions that resulted in reduced vegetation production. A new generalized model was developed using a function of both PT and an index of precipitation extremes and improved predictions of the sensitivity of ANPP to changes in precipitation patterns. Our results suggest that extreme precipitation patterns have substantially negative effects on vegetation production across biomes and are as important as PT. With predictions of more extreme weather events, forecasts of ecosystem production should consider these nonlinear responses to altered extreme precipitation patterns associated with climate change.

Zhang, Yongguang; Susan Moran, M.; Nearing, Mark A.; Ponce Campos, Guillermo E.; Huete, Alfredo R.; Buda, Anthony R.; Bosch, David D.; Gunter, Stacey A.; Kitchen, Stanley G.; Henry McNab, W.; Morgan, Jack A.; McClaran, Mitchel P.; Montoya, Diane S.; Peters, Debra P. C.; Starks, Patrick J.

2013-03-01

308

Introduction to Grassland Management. Instructor Guide, Student Reference [and] Crop and Grassland Plant Identification Manual.  

ERIC Educational Resources Information Center

This packet contains an Instructor guide and student reference for a course in introduction to grassland management, as well as a crop and grassland plant identification manual. The three-unit curriculum contains the following 11 lessons: (unit I, grasslands and grassland plants): (1) an introduction to grasslands; (2) plant classification; (3)…

Suits, Susie

309

Consequences of artichoke thistle invasion and removal on carbon and water cycling in a Mediterranean grassland  

NASA Astrophysics Data System (ADS)

Changes in vegetation structure and composition may interact with management activities to influence biosphere-atmosphere exchanges of mass and energy in unforeseen ways. Increases in the distribution and density of artichoke thistle (Cynara cardunculus), a perennial, non-native forb in Californian coastal grasslands, may alter seasonal dynamics of ecosystem C-assimilation and evapotranspiration (ET). During spring and summer 2006, we compared midday net ecosystem CO2 exchange (NEE) and ET among adjacent grassland plots where thistle was present and where it was absent. Estimates of NEE supported the prediction that deeply-rooted thistles increase ecosystem C-assimilation. Measurements of midday ecosystem respiration demonstrated that increases in ecosystem C-assimilation were associated with increased ecosystem photosynthesis rather than declines in respiration. Furthermore, the presence of C. cardunculus increased midday ET but did not influence shallow soil moisture or ecosystem water use efficiency. Following the initial sampling in late April, we removed C. cardunculus from half the thistle- containing plots with spot applications of herbicide. Three weeks later, fluxes in thistle-removal plots were indistinguishable from those in plots where thistles were never present, suggesting additive rather than interactive effects of thistles on grassland CO2 exchange and ET. Similar to woody-encroachment in some semi-arid ecosystems, C. cardunculus invasion in Californian grasslands increases ecosystem CO2 assimilation. Moreover, our results suggest that herbicide removal of C. cardunculus may be accompanied by few legacy effects. Future research should focus on the effects of C. cardunculus on early-growing season fluxes and belowground C-storage, and the interaction between the spread of non-native species and climate variability on biosphere-atmosphere exchanges of carbon and water.

Potts, D. L.; Harpole, W. S.; Suding, K. N.; Goulden, M. L.

2006-12-01

310

[Spatiotemporal differentiation of land cover change and grassland degradation pattern in Yangtze River headwaters area].  

PubMed

Based on field survey data, remote sensing images and statistical data, this paper analyzed the spatiotemporal differentiation of land use and grassland degradation patterns in Yangtze River headwaters area in 1987-2007, and discussed the main natural factors (elevation, position and slope) leading to the changes of this area's grassland ecological environment. In 1987-2007, the fragmentation of this area' s landscape patterns had an increasing trend, and natural environment and climate change were the main driving forces of land use pattern change. There existed significant differences in the areas of grassland degradation at different altitudes. Grassland degradation mainly occurred at altitudes 4800-5100 m. The grassland degradation area tended to increase with increasing elevation, and the proportions of the degradation area varied greatly over different slopes and aspects. The climate in the study area became warm and dry, and the spatial structure of regional land cover changed obviously. The distribution patterns of grassland degradation at different elevation, position and slope coincided with alpine environment and human disturbances, suggesting that alpine environment and climatic change were the decisive factors to the grassland ecosystem pattern in Yangtze River headwaters area. PMID:22919830

Guo, Luo; Du, Shi-Hong; Xue, Da-Yuan; Cai, Liang

2012-05-01

311

Contrasting response of grassland versus forest carbon and water fluxes to spring drought in Switzerland  

NASA Astrophysics Data System (ADS)

Since the European summer heat wave of 2003, considerable attention has been paid to the impacts of exceptional weather events on terrestrial ecosystems. While our understanding of the effects of summer drought on ecosystem carbon and water vapour fluxes has recently advanced, the effects of spring drought remain unclear. In Switzerland, spring 2011 (March-May) was the warmest and among the driest since the beginning of meteorological measurements. This study synthesizes Swiss FluxNet data from three grassland and two forest ecosystems to investigate the effects of this spring drought. Across all sites, spring phenological development was 11 days earlier in 2011 compared to the mean of 2000-2011. Soil moisture related reductions of gross primary productivity (GPP) were found at the lowland grassland sites, where productivity did not recover following grass cuts. In contrast, spring GPP was enhanced at the montane grassland and both forests (mixed deciduous and evergreen). Evapotranspiration (ET) was reduced in forests, which also substantially increased their water-use efficiency (WUE) during spring drought, but not in grasslands. These contrasting responses to spring drought of grasslands compared to forests reflect different adaptive strategies between vegetation types, highly relevant to biosphere-atmosphere feedbacks in the climate system.

Wolf, Sebastian; Eugster, Werner; Ammann, Christof; Häni, Matthias; Zielis, Sebastian; Hiller, Rebecca; Stieger, Jacqueline; Imer, Dennis; Merbold, Lutz; Buchmann, Nina

2013-09-01

312

Eutrophication weakens stabilizing effects of diversity in natural grasslands.  

PubMed

Studies of experimental grassland communities have demonstrated that plant diversity can stabilize productivity through species asynchrony, in which decreases in the biomass of some species are compensated for by increases in others. However, it remains unknown whether these findings are relevant to natural ecosystems, especially those for which species diversity is threatened by anthropogenic global change. Here we analyse diversity-stability relationships from 41 grasslands on five continents and examine how these relationships are affected by chronic fertilization, one of the strongest drivers of species loss globally. Unmanipulated communities with more species had greater species asynchrony, resulting in more stable biomass production, generalizing a result from biodiversity experiments to real-world grasslands. However, fertilization weakened the positive effect of diversity on stability. Contrary to expectations, this was not due to species loss after eutrophication but rather to an increase in the temporal variation of productivity in combination with a decrease in species asynchrony in diverse communities. Our results demonstrate separate and synergistic effects of diversity and eutrophication on stability, emphasizing the need to understand how drivers of global change interactively affect the reliable provisioning of ecosystem services in real-world systems. PMID:24531763

Hautier, Yann; Seabloom, Eric W; Borer, Elizabeth T; Adler, Peter B; Harpole, W Stanley; Hillebrand, Helmut; Lind, Eric M; MacDougall, Andrew S; Stevens, Carly J; Bakker, Jonathan D; Buckley, Yvonne M; Chu, Chengjin; Collins, Scott L; Daleo, Pedro; Damschen, Ellen I; Davies, Kendi F; Fay, Philip A; Firn, Jennifer; Gruner, Daniel S; Jin, Virginia L; Klein, Julia A; Knops, Johannes M H; La Pierre, Kimberly J; Li, Wei; McCulley, Rebecca L; Melbourne, Brett A; Moore, Joslin L; O'Halloran, Lydia R; Prober, Suzanne M; Risch, Anita C; Sankaran, Mahesh; Schuetz, Martin; Hector, Andy

2014-04-24

313

Effects of assimilate supply on root and microbial components of soil respiration in a mountain grassland.  

NASA Astrophysics Data System (ADS)

Soil respiration is the main source of carbon emitted from terrestrial ecosystems. Soil CO2 originates from multiple processes, comprising respiration by plant roots, mycorrhizae and microbes in the rhizosphere, as well as respiration due to soil organic matter (SOM) decomposition. Thus, components of soil respiration have different controls and show varying responses to changing environmental conditions and to the supply of fresh assimilates from photosynthesis. For grasslands there is still little information available as to what extent root and microbial respiration respond to reduced or enhanced assimilate supply. The aim of this study was to assess effects of assimilate supply on root and microbial components of soil respiration in a temperate mountain grassland. Root and microbial components were separated and quantified by applying the Substrate Induced Respiration method (SIR) in situ using a ?13C labelled sucrose solution, and analysing ?13C of the subsequently respired CO2. Assimilate supply was modified by clipping and shading treatments, which strongly reduced photosynthetic C supply, and by applying a sucrose solution 8 days after clipping and shading. We tested the hypotheses that (1) due to a reduction of assimilate supply, soil respiration would be lower in the clipped and shaded than in the control treatment, that (2) the microbial contribution to soil respiration would be lower in the assimilate-limited than in the control treatments, and that (3) priming effects following the addition of sucrose would be stronger in shaded and mowed treatments than in control plots. Our results showed that clipping and shading reduced soil respiration significantly. Whilst the microbial contribution to soil respiration was 61% in control plots, it amounted to only 50-48% in clipped and shaded plots, respectively. Sucrose application did not affect root respiration in any of the plots, but generally stimulated microbial respiration. The measured priming effect in our experiment was markedly higher in the control than in the substrate limited treatments. It was likely related to an increase in microbial biomass turnover and not to SOM degradation, which suggests an apparent priming effect. Our results indicate that substrate limitation through lower or no photosynthesis generated by clipping and shading lead to a reduction of soil respiration, which was reversed by application of a labile C source. We conclude that short-term variations in fresh organic carbon availability may have more pronounced effects on microbial, than on root respiration. This needs to be accounted for when modelling soil C fluxes in highly dynamic environments.

Schmitt, M.; Siegwolf, R.; Ekblad, A.; Pfahringer, N.; Bahn, M.

2012-04-01

314

Grazing effects on seasonal dynamics and interannual variabilities of spectral reflectance in semi-arid grassland in Inner Mongolia  

Microsoft Academic Search

Detecting the influences of land management on seasonal dynamics and interannual variabilities of grassland surface reflectance\\u000a is of scientific and practical importance as it can help to monitor grazing effects on the grassland ecosystem. We conducted\\u000a spectral reflectance measurements at five differently grazed sites in Inner Mongolia, China, during the growing seasons of\\u000a 2005 and 2006 using a portable, highly

Liya Fan; Bettina Ketzer; Huizhi Liu; Christian Bernhofer

2011-01-01

315

Importance of boreal grasslands in Sweden for butterfly diversity and effects of local and landscape habitat factors  

Microsoft Academic Search

A widespread decline in biodiversity in agro-ecosystems has been reported for several groups of organisms in Western Europe.\\u000a The butterfly fauna was studied in 60 selected semi-natural grasslands in a coniferous-dominated boreal landscape in south-eastern\\u000a Sweden. The aim was to investigate how butterfly assemblages were affected by the amount of semi-natural grasslands in the\\u000a surrounding landscape. Furthermore, we wanted to

Karl-Olof Bergman; Lena Ask; John Askling; Hĺkan Ignell; Henrik Wahlman; Per Milberg

2008-01-01

316

Arthropods of a semi-natural grassland in an urban environment: the John F. Kennedy International Airport, New York  

Microsoft Academic Search

Semi-natural grassland habitat fragments, such as those found on airports, might be important for arthropod conservation and\\u000a biodiversity in urban ecosystems. The objectives of this study were to: (1) describe the arthropod communities present within\\u000a the grasslands on the John F. Kennedy International Airport and (2) assess spatial and temporal variation in those arthropod\\u000a communities. We collected arthropods using a

Lisa Kutschbach-Brohl; Brian E. Washburn; Glen E. Bernhardt; Richard B. Chipman; Laura C. Francoeur

2010-01-01

317

Distribution and Nodulation of Spontaneous Legume Species in Grasslands and Shrublands in Mediterranean Lebanon  

Microsoft Academic Search

In Lebanon, a country known for its biodiversity and plant richness, many threats including quarries endanger its natural habitats and ecosystems. With the objective of finding the most suitable legume-rhizobia associations for revegetation trials, we surveyed grasslands and shrublands in an altitudinal transect up to 1302 m in Mediterranean subhumid and humid regions. For comparison, two abandoned quarries on hard limestone

Thérčse Atallah; Hélčne Rizk; Abdallah Cherfane; Firas Bou Daher; Rouba El-Alia; Phillipe De Lajuide; Samih Hajj

2008-01-01

318

Effect of land use on carbon dioxide, water vapour and energy exchange over terrestrial ecosystems in Southwestern France during the CERES campaign  

Microsoft Academic Search

Eddy fluxes were measured over different ecosystems, winter and summer crops, a maritime pine forest at different stages of development and grassland, from 17 May to 26 June 2005 in the southwestern region of France. During the experiment, summer crops started growing whereas winter crops and grassland achieved their senescence. Comparatively, the other ecosystems had a much slower growth emphasized

N. Jarosz; P. Béziat; J. M. Bonnefond; Y. Brunet; J. C. Calvet; E. Ceschia; J. A. Elbers; R. W. A. Hutjes; O. Traullé

2009-01-01

319

Remaining large grasslands may not be sufficient to prevent grassland bird declines  

Microsoft Academic Search

Grassland birds are in steep decline throughout many regions of the world. In North America, even some common species have declined by >50% over the last few decades. Declines in grassland bird populations have generally been attributed to widespread agricultural conversion of grasslands; more than 80% of North American grasslands have been converted to agriculture and other land uses, for

Anthony W. King; William E. Jensen

2008-01-01

320

Field evidence for differences in post-fire aeolian transport related to vegetation type in semi-arid grasslands  

NASA Astrophysics Data System (ADS)

Disturbances such as wildfires, which cause a temporary reduction in vegetation cover, can greatly accelerate soil erosion by wind and promote dust emissions. Enhanced erosion leads to a reduction in soil fertility and the post-fire mobilisation of soil and associated emissions of dust represent a significant concern for ecosystem management and risk assessment. Here we investigate the temporal change of aeolian activity following a wildfire within both a managed grassland and an adjacent shrub encroached grassland at the Cimarron National Grassland, KS, USA. Our results indicate that, even though the grassland and shrub encroached grassland sites exhibit comparable aeolian activity soon after the fire, the duration of the post-disturbance period of aeolian activity (or "window of disturbance") is shorter in the case of grassland than in the case of shrub encroached grassland. The degree of post-fire aeolian transport and its attenuation with time is strongly affected by the antecedent vegetation type. These findings have implications for management of semi-arid grasslands under both changing vegetation types (shrub encroachment) and disturbance (fire) regimes.

Ravi, Sujith; Baddock, Matthew C.; Zobeck, Ted M.; Hartman, Joe

2012-12-01

321

On intergranular tempered martensite embrittlement  

SciTech Connect

Tempering of martensitic alloy steels is generally required to impart adequately high toughness instead of brittleness in the as-quenched state. When hardened steels are tempered in the range of 250--400 C, however, a loss in toughness can occur in spite of the decrease in strength with increasing tempering temperature. This phenomenon is referred to as tempered martensite embrittlement (TME). In this study, the intergranular type of TME has been analyzed in terms of impact toughness and fracture behavior on isothermal and isochronal tempering. The alloy systems chosen are the commercial 4140 and 4340 steels. The 4340 steel contains the alloying element Ni which enhances the intrinsic toughness.

Lee, K.B.; Yoon, S.H.; Hong, S.I.; Kwon, H. [Kookmin Univ., Seoul (Korea, Republic of)] [Kookmin Univ., Seoul (Korea, Republic of)

1995-04-15

322

Biogeochemical cycling in an annual grassland matrix: Responses and feedbacks to climate change  

NASA Astrophysics Data System (ADS)

I used empirical methods and model simulations to examine the effects of altered rainfall, climate warming, and grazing management on biogeochemical cycling in a Northern California annual grassland landscape. Greenhouse gas fluxes from ecosystems in the annual grassland matrix create feedbacks to climate change and my primary research aim was to measure the magnitude of fluxes and their major environmental controls along multiple spatial and temporal scales. A multi-year field experiment in the Sierra Foothills of Northern California tested the effects of 50% increased rainfall quantity and a longer wet season on annual grassland net primary production, soil respiration, nitrous oxide (N2O) fluxes, inorganic nitrogen cycling, litter decomposition, net ecosystem production, and other ecosystem functions. Changes in rainfall timing had a much stronger effect on soil respiration relative to altered wet-season rainfall totals, with implications that a longer or later wet season could result in significant losses of soil carbon (C). On a regional scale, I assessed the radiative warming potential of inland freshwater wetlands situated within the annual grassland matrix and contrasted this value with that of annual grasslands. Three years of monthly flux measurements revealed that spring-fed wetlands emitted more N2O and methane (CH4) than grasslands on a per-area basis, but that more radiative warming potential was attributable to grasslands when scaled up to the state. I conducted a laboratory incubation of grassland soils subjected to a range of temperature and wet-up levels. Temperature was a good linear predictor of cumulative CO 2 fluxes over the experiment but was a poorer predictor of N2O production, which was more strongly limited by moisture availability. Finally, I employed the DayCent soil organic matter model to explore longer-term effects of altered climate and grazing intensity on soil C storage, plant dynamics, and N2O emissions. According to the model, warming and wet-season extension increased both CO2 and N2O fluxes, whereas grazing removal caused divergent effects, enhancing N2O emissions and decreasing CO2 fluxes. In sum, these findings contribute toward a better understanding of how global change and ecosystem management affect biogeochemical fluxes and ecosystem stability.

Chou, Wendy Wen-Ting

323

Modeling carbon cycle dynamics and response to drought in semi-arid ecosystems  

NASA Astrophysics Data System (ADS)

The southwestern United States is presently experiencing a multi-year drought. Though the carbon uptake per unit area of the semi-arid biomes in this region is smaller than that of more temperate biomes, these biomes cover roughly 40 percent of the world's land surface, and thus make a significant contribution to the global terrestrial biological carbon cycle. Here we test the ability of two land surface model structures to diagnose the carbon cycle dynamics of semi-arid landscapes during the ongoing extreme drought. We use the New Mexico Elevation Gradient (NMEG) as a testbed for these modeling experiments. The NMEG comprises eight eddy covariance towers observing ecosystems ranging from desert grassland ( 1600 m elevation) to alpine mixed coniferous forest ( 3000 m elevation). During the drought the ecosystems observed by these towers saw their annual net carbon uptake decline between 33 and 100 percent (50 to 150 gC m^{-2} year^{-1}), with two of the eight sites becoming net sources of carbon to the atmosphere and one transitioning from a net carbon sink to carbon-neutral. We parametrize a simple light-use efficiency (LUE)-based model (Vegetation Photosynthesis and Respiration Model, VPRM) and a complex model which simulates many land surface processes (Community Land Model, CLM). We explore the capacity of both models to diagnose the terrestrial carbon cycle in semi-arid biomes where water availability is highly episodic.

Hilton, T. W.; Fox, A. M.; Krofcheck, D. J.; Litvak, M. E.

2012-12-01

324

How soil moisture, rain pulses, and growth alter the response of ecosystem respiration to temperature  

Microsoft Academic Search

In this paper, we analyzed 3 years of carbon flux data from continuous eddy covariance measurements to investigate how soil moisture, rain pulses, and growth alter the response of ecosystem respiration to temperature. The data were acquired over an annual grassland and from the grass understory of an oak\\/grass savanna ecosystem in California. We observed that ecosystem respiration was an

Liukang Xu; Dennis D. Baldocchi; Jianwu Tang

2004-01-01

325

How do land management practices affect net ecosystem CO2 exchange of an invasive plant infestation?  

Microsoft Academic Search

Ecosystem gas and energy exchanges of invasive plant infestations under different land management practices have been subject of few studies and thus little is known. Our goal is to characterize seasonal changes in net ecosystem CO2 exchange (NEE) through the processes of photosynthesis (GEP) and ecosystem respiration (Reco) of a grassland used as pasture yet infested by perennial pepperweed (Lepidium

O. Sonnentag; M. Detto; B. Runkle; M. Kelly; D. D. Baldocchi

2009-01-01

326

Foraging strategy of cattle in patchy grassland  

Microsoft Academic Search

We tested several strategies of foraging that grazing herbivores may adopt in a patchy habitat in relation to energy intake. The patch selection of cattle was investigated in an Agrostis\\/Festuca grassland and in a Lolium grassland in 13 observation periods over 2 years. Both grasslands were stocked with five yearling steers. Bite counts were made on patches of different vegetation

Michiel F. Wallis Vries; Cees Daleboudt

1994-01-01

327

Grasslands, people, and conservation: over-the-horizon learning exchanges between African and American pastoralists.  

PubMed

The world's grasslands and large migratory populations of wildlife have been disproportionately lost or disrupted by human activities, yet are poorly represented in protected areas. The major threats they face are land subdivision and the loss of large-scale dynamic processes such as wildlife migrations and fire. The large-scale dynamical processes and ubiquity of livestock economies and cultures across the grasslands calls for an integrated ecosystem approach to conservation to make up the shortfall in protected-area coverage. Ranchers and pastoralists will be more inclined to adopt an integrated landscape approach to conservation if they also see the threats to wildlife and grassland ecosystems as affecting their livelihoods and way of life. We arranged a series of learning exchanges between African and American pastoralists, ranchers, scientists, and conservationists aimed at building the collaboration and consensus needed to conserve grasslands at a landscape level. There was broad agreement on the threat of land fragmentation to livelihoods, wildlife, and grasslands. The exchanges also identified weaknesses in prevailing public, private, and community modes of ownership in halting fragmentation. New collaborative approaches were explored to attain the benefits of privatization while keeping the landscape open. The African-U.S. exchanges showed that learning exchanges can anticipate over-the-horizon problems and speed up the feedback loops that underlie adaptive management and build social and ecological resilience. PMID:18544088

Curtin, Charles; Western, David

2008-08-01

328

Net primary production of the grass and swamp ecosystems  

Microsoft Academic Search

Paper presents estimates of above-ground, below-ground, and total production in grasslands, meadows and steppe of the forest-steppe\\u000a and steppe regions, and production of moss peat ecosystems of the northern, middle, and southern taiga forests. Total production\\u000a varies in grasslands from 520 to 6670 g\\/(m2 year) and depends on hydrothermal conditions and the regime of the use of herbage, in moss

A. A. Titlyanova

2008-01-01

329

Modelling short-term CO 2 fluxes and long-term tree growth in temperate forests with ASPECTS  

Microsoft Academic Search

The net ecosystem exchange (NEE) of CO2 between temperate forests and the atmosphere governs both carbon removal from the atmosphere and forest growth. In recent years, many experiments have been conducted to determine temperate forest NEE. These data have been used by forest modellers to better understand the processes that govern CO2 fluxes, and estimate the evolution of these fluxes

Daniel P Rasse; Louis François; Marc Aubinet; Andrew S Kowalski; Inge Vande Walle; Eric Laitat; Jean-Claude Gérard

2001-01-01

330

Assessing Endangered Ecosystems in the Inland Skeena Region  

Microsoft Academic Search

The southeastern Skeena region of British Columbia supports a rich variety of ecosystems with distinctive transitional or ecotonal characteristics. A 2-year pilot study was carried out to inventory and assess rare and endangered terrestrial ecosystems in the low- elevation Sub-Boreal Spruce (SBS) and Interior Cedar-Hemlock (ICH) biogeoclimatic zones. Scrub-steppe or savanna-steppe, grassland, and herbaceous meadow ecosystems are highly threatened by

Sybille Haeussler; Anne Hetherington

331

Carbon and Water Exchanges in a Chronosequence of Temperate White Pine Forest  

Microsoft Academic Search

Quantification of carbon sink or source strengths of temperate forest ecosystems, growing in northern mid-latitudes, is essential to resolve uncertainties in carbon balance of the world's terrestrial ecosystems. Long-term flux measurements are needed to quantify seasonal and annual variability of carbon and water exchanges from these ecosystems and to relate the variability to environmental and physiological factors. Such long-term measurements

M. Arain; N. Restrepo; M. Pejam; M. Khomik

2003-01-01

332

Consequences of prescribed fire and grazing on grassland ant communities.  

PubMed

Prescribed fire and livestock grazing are used for the management and restoration of native grasslands the world over; however, the effects of these management techniques on ant communities are unclear. We examined the response of ants to these disturbances in grasslands in northern California. Twenty-four 30 by 30 m plots were established across two sites that received one of four treatments: grazing, fire, grazing and fire, or no treatment. Ants were censused using 240 pitfall traps with one preburn and two postburn samples (14 d and 1 yr after burning). We analyzed ant abundance using broadly defined groups based on feeding habit and/or habitat use and detected no grazing effect but a significant fire effect that differed by group. Immediate postfire sampling showed an increase in cryptic species (particularly Brachymyrmex depilis). One year after the fire, no response was detected for cryptic species, but burned plots had greater abundance of seed harvesters. Analysis of vegetation showed burned plots had significantly greater forb cover, which might have provided greater food resources, and also lower biomass, which might have facilitated foraging. Understanding the effects of these management tools on ant abundance complements our understanding of their effect on vegetation and assists conservation practitioners effectively manage grassland ecosystems both in California and beyond. PMID:19389280

Underwood, Emma C; Christian, Caroline E

2009-04-01

333

Temper tantrums in group care  

Microsoft Academic Search

Temper tantrums are common, troubling behaviors encountered by workers in group care settings. This paper initially reviews\\u000a the current state of theory and research into temper tantrums both within and outside the group care arena. The normal developmental\\u000a context of the temper tantrum is described and a number of theoretical perspectives are reviewed. Explanations for the persistence\\u000a of tantrum behaviors

Howard I. Bath

1994-01-01

334

New spectral vegetation indices based on the near-infrared shoulder wavelengths for remote detection of grassland phytomass  

PubMed Central

This article examines the possibility of exploiting ground reflectance in the near-infrared (NIR) for monitoring grassland phytomass on a temporal basis. Three new spectral vegetation indices (infrared slope index, ISI; normalized infrared difference index, NIDI; and normalized difference structural index, NDSI), which are based on the reflectance values in the H25 (863–881 nm) and the H18 (745–751 nm) Chris Proba (mode 5) bands, are proposed. Ground measurements of hyperspectral reflectance and phytomass were made at six grassland sites in the Italian and Austrian mountains using a hand-held spectroradiometer. At full canopy cover, strong saturation was observed for many traditional vegetation indices (normalized difference vegetation index (NDVI), modified simple ratio (MSR), enhanced vegetation index (EVI), enhanced vegetation index 2 (EVI 2), renormalized difference vegetation index (RDVI), wide dynamic range vegetation index (WDRVI)). Conversely, ISI and NDSI were linearly related to grassland phytomass with negligible inter-annual variability. The relationships between both ISI and NDSI and phytomass were however site specific. The WinSail model indicated that this was mostly due to grassland species composition and background reflectance. Further studies are needed to confirm the usefulness of these indices (e.g. using multispectral specific sensors) for monitoring vegetation structural biophysical variables in other ecosystem types and to test these relationships with aircraft and satellite sensors data. For grassland ecosystems, we conclude that ISI and NDSI hold great promise for non-destructively monitoring the temporal variability of grassland phytomass.

VESCOVO, LORIS; WOHLFAHRT, GEORG; BALZAROLO, MANUELA; PILLONI, SEBASTIAN; SOTTOCORNOLA, MATTEO; RODEGHIERO, MIRCO; GIANELLE, DAMIANO

2013-01-01

335

Emissions from Miombo Woodland and Dambo Grassland Savanna Fires  

NASA Technical Reports Server (NTRS)

Airborne measurements of trace gases and particles over and downwind of two prescribed savanna fires in Zambia are described. The measurements include profiles through the smoke plumes of condensation nucleus concentrations and normalized excess mixing ratios of particles and gases, emission factors for 42 trace gases and seven particulate species, and vertical profiles of ambient conditions. The fires were ignited in plots of miombo woodland savanna, the most prevalent savanna type in southern Africa, and dambo grassland savanna, an important enclave of miombo woodland ecosystems. Emission factors for the two fires are combined with measurements of fuel loading, combustion factors, and burned area (derived from satellite burn scar retrievals) to estimate the emissions of trace gases and particles from woodland and grassland savanna fires in Zambia and southern Africa during the dry season (May-October) of 2000. It is estimated that the emissions of CO2, CO, total hydrocarbons, nitrogen oxides (NOx as NO), sulfur dioxide (SO2), formaldehyde, methyl bromide, total particulate matter, and black carbon from woodland and grassland savanna fires during the dry season of 2000 in southern Africa contributed 12.3%, 12.6%, 5.9%, 10.3%, 7.5%, 24.2%, 2.8%, 17.5%, and 11.1%, respectively, of the average annual emissions from all types of savanna fires worldwide. In 2000 the average annual emissions of methane, ethane, ethene, acetylene, propene, formaldehyde, methanol, and acetic acid from the use of biofuels in Zambia were comparable to or exceeded dry season emissions of these species from woodland and grassland savanna fires in Zambia.

Sinha, Parikhit; Hobbs, Peter V.; Yokelson, Robert J.; Blake, Donald R.; Gao, Song; Kirchstetter, Thomas W.

2004-01-01

336

Emissions from miombo woodland and dambo grassland savanna fires  

NASA Astrophysics Data System (ADS)

Airborne measurements of trace gases and particles over and downwind of two prescribed savanna fires in Zambia are described. The measurements include profiles through the smoke plumes of condensation nucleus concentrations and normalized excess mixing ratios of particles and gases, emission factors for 42 trace gases and seven particulate species, and vertical profiles of ambient conditions. The fires were ignited in plots of miombo woodland savanna, the most prevalent savanna type in southern Africa, and dambo grassland savanna, an important enclave of miombo woodland ecosystems. Emission factors for the two fires are combined with measurements of fuel loading, combustion factors, and burned area (derived from satellite burn scar retrievals) to estimate the emissions of trace gases and particles from woodland and grassland savanna fires in Zambia and southern Africa during the dry season (May-October) of 2000. It is estimated that the emissions of CO2, CO, total hydrocarbons, nitrogen oxides (NOx as NO), sulfur dioxide (SO2), formaldehyde, methyl bromide, total particulate matter, and black carbon from woodland and grassland savanna fires during the dry season of 2000 in southern Africa contributed 12.3%, 12.6%, 5.9%, 10.3%, 7.5%, 24.2%, 2.8%, 17.5%, and 11.1%, respectively, of the average annual emissions from all types of savanna fires worldwide. In 2000 the average annual emissions of methane, ethane, ethene, acetylene, propene, formaldehyde, methanol, and acetic acid from the use of biofuels in Zambia were comparable to or exceeded dry season emissions of these species from woodland and grassland savanna fires in Zambia.

Sinha, Parikhit; Hobbs, Peter V.; Yokelson, Robert J.; Blake, Donald R.; Gao, Song; Kirchstetter, Thomas W.

2004-06-01

337

Impacts of Woody Plant Encroachment and Cultivation on Soil Carbon and Soil Water Flux Across a Precipitation Gradient in Grassland  

NASA Astrophysics Data System (ADS)

Land-use/cover changes affect flux and storages of water and carbon, which are becoming increasingly important in light of the projected climate change and water shortages around the world. Cultivation of food crops and woody-plant encroachment are two such changes that are prevalent in grassland ecosystems. We compared belowground water flux and carbon storage in adjacent stands of natural grasslands and woody- encroached or cultivated plots. Stands were located in 5 sites across a precipitation gradient in the Pampa grasslands of varying soil texture in Argentina. Soil cores were excavated to 9 meters or to groundwater level and analyzed for soil moisture and chloride to estimate groundwater recharge rates using the chloride mass balance and chloride displacement methods. Cores were also analyzed for soil organic and inorganic carbon. Comparison of soil chloride profiles under the land-use/cover change from the natural grasslands suggested reduced recharge and/or higher groundwater use under woody plants and enhanced recharge under cultivation compared to the grasslands. Chloride concentrations differed up to 3-fold between the grassland and the two land-use/cover changes. Soil organic carbon was similar or significantly higher under woody plants and lower under cultivation compared with grasslands. The changes in water yield are discussed in context of the estimated carbon sequestration measured at the sites. Valuation of such changes would help determine the optimum land-use/cover under global environmental changes.

Kim, J. H.; Jobbágy, E. G.; Jackson, R. B.

2008-12-01

338

North Temperate Lakes Long-Term Ecological Research (NTL-LTER)  

NSDL National Science Digital Library

The University of Wisconsin's world-renown Center for Limnology operates the North Temperate Lakes Long-Term Ecological Research program, emphasizing long-term ecological phenomena in urban, agricultural, and forested watersheds. This information-rich site offers general and detailed information on the North Temperate Lakes LTER's impressive array of projects. Research projects encompass several themes, including long-term trends in physical, chemical, and biological properties of lake ecosystems; the dynamics of internal and external processes affecting lake ecosystems; the temporal responses of lake ecosystems to disturbance and stress; the interaction between spatial heterogeneity and temporal variability of lake ecosystems; and lake-ecosystem properties in a broad regional context. Also of interest are descriptions of lake properties, a searchable bibliography, biodiversity and species lists, and more than a dozen online datasets ranging from Aquatic Macrophytes through Zooplankton. A query-able climate data section and Links to Other Sites of Interest round out the site.

1998-01-01

339

Assessing risks from drought and heat stress in productive grasslands under present and future climatic conditions  

NASA Astrophysics Data System (ADS)

Grasslands cover the majority of the world's agricultural area, provide the feedstock for animal production, contribute to the economy of farms, and deliver a variety of ecological and societal services. Assessing responses of grassland ecosystems to climate change, in particular climate-related risks, is therefore an important step toward identifying adaptation options necessary to secure grassland functioning and productivity. Of particular concern are risks in relation to drought and extreme temperatures, on the one hand because grasslands are very sensitive to water stress, on the other hand also because global warming is expected to increase the occurrence and intensity of these events in many agricultural areas of the world. In this contribution we review findings of ongoing experimental and modelling activities that aim at examining the implications of climate extremes and climate change for grassland vegetation dynamics and herbage productivity. Data collected at the Jura foot in western Switzerland indicate that water scarcity and associated anomalous temperatures slowed plant development in relation to both the summer drought of 2003 as well as the spring drought of 2011, with decline in annual yields of up to 40%. Further effects of drought found from the analysis of recent field trials explicitly designed to study the effects of different water management regimes are changes in the functional composition and nutritive value of grasslands. Similar responses are disclosed by simulations with a process based grassland ecosystem model that was originally developed for the simulation of mixed grass/clover swards. Simulations driven with historical weather records from the Swiss Plateau suggest that drought and extreme temperature could represent one of the main reasons for the observed yield variability in productive systems. Simulations with climate change scenarios further reveal important changes in ecosystem dynamics for the current century. The results show that herbage growth could basically benefit from increasing temperatures and CO2 concentrations, which promote in particular the development of clover. However, productivity is found to decline in the long term on the background of a projected decrease in summer precipitation. This has implications for future grassland production across Europe and in other agricultural area of the world, and calls for the adoption of adaptation measures.

Calanca, Pierluigi; Mosimann, Eric; Meisser, Marco; Deléglise, Claire

2014-05-01

340

Measuring dry plant residues in grasslands: A case study using AVIRIS  

NASA Technical Reports Server (NTRS)

Grasslands, savannah, and hardwood rangelands are critical ecosystems and sensitive to disturbance. Approximately 20 percent of the Earth's surface are grasslands and represent 3 million ha. in California alone. Developing a methodology for estimating disturbance and the effects of cumulative impacts on grasslands and rangelands is needed to effectively monitor these ecosystems. Estimating the dry biomass residue remaining on rangelands at the end of the growing season provides a basis for evaluating the effectiveness of land management practices. The residual biomass is indicative of the grazing pressure and provides a measure of the system capacity for nutrient cycling since it represents the maximum organic matter available for decomposition, and finally, provides a measure of the erosion potential for the ecosystem. Remote sensing presents a possible method for measuring dry residue. However, current satellites have had limited application due to the coarse spatial scales (relative to the patch dynamics) and insensitivity of the spectral coverage to resolve dry plant material. Several hypotheses for measuring the biochemical constituents of dry plant material, particularly cellulose and lignin, using high spectral resolution sensors were proposed. The use of Airborne Visible/Infrared Imaging Spectrometers (AVIRIS) to measure dry plant residues over an oak savannah on the eastern slopes of the Coast Range in central California was investigated and it was asked what spatial and spectral resolutions are needed to quantitatively measure dry plant biomass in this ecosystem.

Fitzgerald, Michael; Ustin, Susan L.

1992-01-01

341

Density of insect-pollinated grassland plants decreases with increasing surrounding land-use intensity.  

PubMed

Pollinator declines have raised concerns about the persistence of plant species that depend on insect pollination, in particular by bees, for their reproduction. The impact of pollinator declines remains unknown for species-rich plant communities found in temperate seminatural grasslands. We investigated effects of land-use intensity in the surrounding landscape on the distribution of plant traits related to insect pollination in 239 European seminatural grasslands. Increasing arable land use in the surrounding landscape consistently reduced the density of plants depending on bee and insect pollination. Similarly, the relative abundance of bee-pollination-dependent plants increased with higher proportions of non-arable agricultural land (e.g. permanent grassland). This was paralleled by an overall increase in bee abundance and diversity. By isolating the impact of the surrounding landscape from effects of local habitat quality, we show for the first time that grassland plants dependent on insect pollination are particularly susceptible to increasing land-use intensity in the landscape. PMID:25040328

Clough, Yann; Ekroos, Johan; Báldi, András; Batáry, Péter; Bommarco, Riccardo; Gross, Nicolas; Holzschuh, Andrea; Hopfenmüller, Sebastian; Knop, Eva; Kuussaari, Mikko; Lindborg, Regina; Marini, Lorenzo; Ockinger, Erik; Potts, Simon G; Pöyry, Juha; Roberts, Stuart Pm; Steffan-Dewenter, Ingolf; Smith, Henrik G

2014-09-01

342

Aboveground biomass in Tibetan grasslands  

Microsoft Academic Search

This study investigated spatial patterns and environmental controls of aboveground biomass (AGB) in alpine grasslands on the Tibetan Plateau by integrating AGB data collected from 135 sites during 2001–2004 and concurrent enhanced vegetation index derived from MODIS data sets. The AGB was estimated at 68.8gm?2, with a larger value (90.8gm?2) in alpine meadow than in alpine steppe (50.1gm?2). It increased

Y. H. Yang; J. Y. Fang; Y. D. Pan; C. J. Ji

2009-01-01

343

A Landscape Analysis of Grassland Birds in a Valley Grassland-Oak Woodland Mosaic1  

Microsoft Academic Search

While little research has been done on California grassland birds, their populations are thought to be declining due to habitat loss, fragmentation, and degradation. We investigated the association between California grassland birds and their landscape-scale habitat matrix. The habitat is a mosaic of valley grassland with blue oak and coast live oak woodlands. In this study, we used logistic regression

Devii Rao; Sasha Gennet; Michele Hammond; Peter Hopkinson; James Bartolome

344

Description, calibration and sensitivity analysis of the local ecosystem submodel of a global model of carbon and nitrogen cycling and the water balance in the terrestrial biosphere  

SciTech Connect

We have developed a geographically-distributed ecosystem model for the carbon, nitrogen, and water dynamics of the terrestrial biosphere TERRA. The local ecosystem model of TERRA consists of coupled, modified versions of TEM and DAYTRANS. The ecosystem model in each grid cell calculates water fluxes of evaporation, transpiration, and runoff; carbon fluxes of gross primary productivity, litterfall, and plant and soil respiration; and nitrogen fluxes of vegetation uptake, litterfall, mineralization, immobilization, and system loss. The state variables are soil water content; carbon in live vegetation; carbon in soil; nitrogen in live vegetation; organic nitrogen in soil and fitter; available inorganic nitrogen aggregating nitrites, nitrates, and ammonia; and a variable for allocation. Carbon and nitrogen dynamics are calibrated to specific sites in 17 vegetation types. Eight parameters are determined during calibration for each of the 17 vegetation types. At calibration, the annual average values of carbon in vegetation C, show site differences that derive from the vegetation-type specific parameters and intersite variation in climate and soils. From calibration, we recover the average C{sub v} of forests, woodlands, savannas, grasslands, shrublands, and tundra that were used to develop the model initially. The timing of the phases of the annual variation is driven by temperature and light in the high latitude and moist temperate zones. The dry temperate zones are driven by temperature, precipitation, and light. In the tropics, precipitation is the key variable in annual variation. The seasonal responses are even more clearly demonstrated in net primary production and show the same controlling factors.

Kercher, J.R. [Lawrence Livermore National Lab., CA (United States)] [Lawrence Livermore National Lab., CA (United States); Chambers, J.Q. [Lawrence Livermore National Lab., CA (United States)] [Lawrence Livermore National Lab., CA (United States); [California Univ., Santa Barbara, CA (United States). Dept. of Biological Sciences

1995-10-01

345

Methane production and consumption in grassland and boreal ecosystems  

NASA Technical Reports Server (NTRS)

The objectives of the this project were to develop a mechanistic understanding of methane production and oxidation suitable for incorporation into spatially explicit models for spatial extrapolation. Field studies were undertaken in Minnesota, Canada, and Colorado to explore the process controls over the two microbial mediated methane transformations in a range of environments. Field measurements were done in conjunction with ongoing studies in Canada (the Canadian Northern Wetlands Projects: NOWES) and in Colorado (The Shortgrass Steppe Long Term Ecological Research Project: LTER). One of the central hypotheses of the proposal was that methane production should be substrate limited, as well as being controlled by physical variables influencing microbial activity (temperature, oxidation status, and pH). Laboratory studies of peats from Canada and Minnesota (Northern and Southern Boreal) were conducted with amendments of a methanogenic substrate at multiple temperatures and at multiple pHs (the latter by titrating samples). The studies showed control by substrate, pH, and temperature in order in anaerobic samples. Field and laboratory manipulations of natural plant litter, rather than an acetogenic substrate, showed similarly large effects. The studies concluded that substrate is an important control over methanogenesis, that substrate availability in the field is closely coupled to the chemistry of the dominant vegetation influencing its decomposition rate, that most methane is produced from recent plant litter, and that landscape changes in pH are an important control, highly correlated with vegetation.

Schimel, David S.; Burke, Ingrid C.; Johnston, Carol; Pastor, John

1994-01-01

346

Soil biotic processes remain remarkably stable after 100-year extreme weather events in experimental grassland and heath  

Microsoft Academic Search

Climate change will increase the recurrence of extreme weather events such as drought and heavy rainfall. Evidence suggests\\u000a that extreme weather events pose threats to ecosystem functioning, particularly to nutrient cycling and biomass production.\\u000a These ecosystem functions depend strongly on below-ground biotic processes, including the activity and interactions among\\u000a plants, soil fauna, and micro-organisms. Here, experimental grassland and heath communities

Juergen Kreyling; Carl Beierkuhnlein; Michael Elmer; Karin Pritsch; Monica Radovski; Michael Schloter; Jens Wöllecke; Anke Jentsch

2008-01-01

347

Grassland degradation in the Western of Songnen plain  

Microsoft Academic Search

Based on RS and GIS techniques, three-period (1986, 1995, 2000) remote sensing images are interpreted in order to gain spatial information about grassland landscape in the Western of Songnen plain, then spatial-temporal dynamics of grassland and the natural, human factor of grassland degradation are analyzed. The results show that grassland area decreased 24.7%. Grassland degradation is serious. Grassland is mainly

Shufeng Zheng; Kai Meng; Yuan Sun

2011-01-01

348

Orbital-scale climate forcing of grassland burning in southern Africa  

PubMed Central

Although grassland and savanna occupy only a quarter of the world's vegetation, burning in these ecosystems accounts for roughly half the global carbon emissions from fire. However, the processes that govern changes in grassland burning are poorly understood, particularly on time scales beyond satellite records. We analyzed microcharcoal, sediments, and geochemistry in a high-resolution marine sediment core off Namibia to identify the processes that have controlled biomass burning in southern African grassland ecosystems under large, multimillennial-scale climate changes. Six fire cycles occurred during the past 170,000 y in southern Africa that correspond both in timing and magnitude to the precessional forcing of north–south shifts in the Intertropical Convergence Zone. Contrary to the conventional expectation that fire increases with higher temperatures and increased drought, we found that wetter and cooler climates cause increased burning in the study region, owing to a shift in rainfall amount and seasonality (and thus vegetation flammability). We also show that charcoal morphology (i.e., the particle's length-to-width ratio) can be used to reconstruct changes in fire activity as well as biome shifts over time. Our results provide essential context for understanding current and future grassland-fire dynamics and their associated carbon emissions.

Daniau, Anne-Laure; Sanchez Goni, Maria Fernanda; Martinez, Philippe; Urrego, Dunia H.; Bout-Roumazeilles, Viviane; Desprat, Stephanie; Marlon, Jennifer R.

2013-01-01

349

Effects of nitrogen deposition and cattle grazing on productivity, invasion impact, and soil microbial processes in a serpentine grassland  

Microsoft Academic Search

In recent decades, human activities have vastly increased the amount of biologically available nitrogen (N) in the biosphere. The resulting increase in N availability has broadly affected ecosystems through increased productivity, changes in species composition, altered nutrient cycles, and increases in invasion by exotic plant species, especially in systems that were historically low in N. California serpentine grasslands are N-limited

J. Pasari; D. Hernandez; P. C. Selmants; D. Keck

2010-01-01

350

Estimating aboveground biomass of grassland having a high canopy cover: an exploratory analysis of in situ hyperspectral data  

Microsoft Academic Search

To improve the estimation of aboveground biomass of grassland having a high canopy cover based on remotely sensed data, we measured in situ hyperspectral reflectance and the aboveground green biomass of 42 quadrats in an alpine meadow ecosystem on the Qinghai–Tibetan Plateau. We examined the relationship between aboveground green biomass and the spectral features of original reflectance, first-order derivative reflectance

Jin Chen; Song Gu; Miaogen Shen; Yanhong Tang; Bunkei Matsushita

2009-01-01

351

Seed-to-seed potential allelopathic effects between Ligularia virgaurea and native grass species of Tibetan alpine grasslands  

Microsoft Academic Search

Allelopathy is an important process in plant communities, but the role of seed allelopathy in natural ecosystems remains poorly\\u000a understood. In the present study, we examined the potential allelopathic effects of Ligularia virgaurea (a dominant species in degraded Tibetan grasslands) seeds on the germination of four native grass species (Festuca sinensis, Agrostis gigantean, Bromus inermis, and Elymus nutans). The results

Shiting Zhang; Junpeng Liu; Xiaohui Bao; Kechang Niu

2011-01-01

352

The Effects of Fishing on Marine Ecosystems  

Microsoft Academic Search

We review the effects of fishing on benthic fauna, habitat, diversity, community structure and trophic interactions in tropical, temperate and polar marine environments and consider whether it is possible to predict or manage fishing-induced changes in marine ecosystems. Such considerations are timely given the disillusionment with some fishery management strategies and that policy makers need a scientific basis for deciding

Simon Jennings; Michel J. Kaiser

1998-01-01

353

Mycorrhizal response to elevated CO[sub 2] in serpentine grassland communities  

SciTech Connect

I measured four aspects of mycorrhizal ecology (vesicular-arbuscular mycorrhizal [VAM] root length, percent root colonized, intraradical concentration of the mycorrhizal fungal membrane sterol ergosterol, and substrate spore density) in three experimental systems, each with treatments at ambient ( 350ppm) and twice ambient (700ppm) atmospheric CO[sub 2]. The systems differ in degree of manipulation, ranging from a single species grown in sand in controlled environment chambers, to intact grassland ecosystem plots enclosed in ventilated open-top chambers, and including single to six species serpentine substrate profile. While elevated CO[sub 2] increased all measures of mycorrhizal activity in the most controlled system, it appeared to have no effect on these properties in the intact serpentine grassland ecosystem. Ongoing examination of the intermediate microcosm systems may elucidate whether plant species or substrate properties (such as microbial communities) are responsible for these observed differences in mycorrhizal response.

Whitbeck, J.L. (Stanford Univ., CA (United States))

1993-06-01

354

Lack of eutrophication in a tallgrass prairie ecosystem over 27 years.  

PubMed

Many North American grasslands are receiving atmospheric nitrogen (N) deposition at rates above what are considered critical eutrophication thresholds. Yet, potential changes in grassland function due to anthropogenic N deposition are poorly resolved, especially considering that other dynamic factors such as land use and precipitation can also affect N availability. To better understand whether elevated N deposition has altered ecosystem structure or function in North American grasslands, we analyzed a 27-year record of ecophysiological, community, and ecosystem metrics for an annually burned Kansas tallgrass prairie. Over this time, despite increasing rates of N deposition that are within the range of critical loads for grasslands, there was no evidence of eutrophication. Plant N concentrations did not increase, soil moisture did not decline, forb diversity did not decline, and the relative abundance of dominant grasses did not shift toward more eutrophic species. Neither aboveground primary productivity nor N availability to plants increased. The fates of deposited N in grasslands are still uncertain, and could include management losses through burning and grazing. However, evidence from this grassland indicates that eutrophication of North American grassland ecosystems is not an inevitable consequence of current levels of N deposition. PMID:25000754

McLauchlan, Kendra K; Craine, Joseph M; Nippert, Jesse B; Ocheltree, Troy W

2014-05-01

355

Isotopic Evidence that Trees Enhance Nitrogen Inputs and Cycling in California Grassland Savanna  

Microsoft Academic Search

Woody vegetation is distributed patchily in many arid and semi-arid ecosystems, where it is often associated with elevated nitrogen (N) pools and availability in islands of fertility. We measured N availability and del15N in paired blue-oak versus annual grass dominated patches to characterize the causes and consequences of spatial variation in N dynamics of grassland-savanna in Sequoia - Kings Canyon

S. Perakis; C. Kellogg

2006-01-01

356

Effects of long term CO 2 enrichment on microbial community structure in calcareous grassland  

Microsoft Academic Search

Elevated CO2 generally increases plant productivity, and has been found to alter plant community composition in many ecosystems. Because\\u000a soil microbes depend on plant-derived C and are often associated with specific plant species, elevated CO2 has the potential to alter structure and functioning of soil microbial communities. We investigated soil microbial community\\u000a structure of a species-rich semi-natural calcareous grassland that

Diana Ebersberger; Nicola Wermbter; Pascal A. Niklaus; Ellen Kandeler

2004-01-01

357

Grazers and soil moisture determine the fate of added 15 NH 4 + in Yellowstone grasslands  

Microsoft Academic Search

The influence of ungulate grazers on nutrient cycling and ecosystem productivity in grasslands has been shown to differ with\\u000a moisture, nutrient availability, and feedbacks between above- and belowground activities. We examined the movement of nitrogen\\u000a (N), applied as (15NH4)2SO4, through both dry and mesic sites in the northern range of Yellowstone National Park to test the hypothesis that plants were

Holly A. Ewing; Peter M. Groffman; Douglas A. Frank

2010-01-01

358

Surface characteristics of grasslands in Inner Mongolia as detected by micrometeorological measurements  

Microsoft Academic Search

A roving tower concept was used to compare a semi-arid grassland site in Inner Mongolia (China), which was fenced in 1979\\u000a and ungrazed thereafter (UG79) with differently grazed semi-arid steppe ecosystems. The study was conducted during three consecutive\\u000a years characterised by contrasting precipitation. The different grazing intensities included continuously and moderately grazed\\u000a (CG), winter grazed (WG), and heavily grazed (HG).

Bettina Ketzer; Huizhi Liu; Christian Bernhofer

2008-01-01

359

Woody Plant Invasion of Grassland: Changes in Whole-Soil Carbon Storage and Dynamics  

Microsoft Academic Search

Woody plant encroachment into grass-dominated ecosystems has been a globally significant land cover change over the past century, but its biogeochemical consequences remain largely unquantified. In the Rio Grande Plains of Texas, grasslands and savannas dominated by C4 grasses (d13C = -14 o\\/oo) have undergone succession over the past 150 y to subtropical thorn woodlands dominated by C3 trees\\/shrubs (d13C

T. W. Boutton; J. D. Liao

2003-01-01

360

Does a warmer climate with frequent mild water shortages protect grassland communities against a prolonged drought?  

Microsoft Academic Search

Global warming accelerates land surface drying, increasing the incidence of extreme climatic events such as severe droughts\\u000a with detrimental effects on ecosystem functions and structure. We investigated the effects of an imposed severe drought (24 days)\\u000a on fully established synthesized grassland communities with three species richness (S) levels (one, three or nine species), grown for 3 years at either ambient air temperatures

C. Zavalloni; B. Gielen; C. M. H. M. Lemmens; H. J. De Boeck; S. Blasi; S. Van den Bergh; I. Nijs; R. Ceulemans

2008-01-01

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