Grassland covers approximately one-third of the area of China and plays an important role in the global terrestrial carbon(C) cycle.However,little is known about biomass C stocks and dynamics in these grasslands.Durin...Grassland covers approximately one-third of the area of China and plays an important role in the global terrestrial carbon(C) cycle.However,little is known about biomass C stocks and dynamics in these grasslands.During 2001-2005,we conducted five consecutive field sampling campaigns to investigate above-and below-ground biomass for northern China's grasslands.Using measurements obtained from 341 sampling sites,together with a NDVI(normalized difference vegetation index) time series dataset over 1982-2006,we examined changes in biomass C stock during the past 25 years.Our results showed that biomass C stock in northern China's grasslands was estimated at 557.5 Tg C(1 Tg=1012 g),with a mean density of 39.5 g C m-2 for above-ground biomass and 244.6 g C m-2 for below-ground biomass.An increasing rate of 0.2 Tg C yr-1 has been observed over the past 25 years,but grassland biomass has not experienced a significant change since the late 1980s.Seasonal rainfall(January-July) was the dominant factor driving temporal dynamics in biomass C stock;however,the responses of grassland biomass to climate variables differed among various grassland types.Biomass in arid grasslands(i.e.,desert steppe and typical steppe) was significantly associated with precipitation,while biomass in humid grasslands(i.e.,alpine meadow) was positively correlated with mean January-July temperatures.These results suggest that different grassland ecosystems in China may show diverse responses to future climate changes.展开更多
The knowledge of carbon(C) stock and its dynamics is crucial for understanding the role of grassland ecosystems in China's terrestrial C cycle.To date,a comprehensive assessment on C balance in China's grassla...The knowledge of carbon(C) stock and its dynamics is crucial for understanding the role of grassland ecosystems in China's terrestrial C cycle.To date,a comprehensive assessment on C balance in China's grasslands is still lacking.By reviewing published literature,this study aims to evaluate ecosystem C stocks(both vegetation biomass and soil organic C) and their changes in China's grasslands.Our results are summarized as follows:(1) biomass C density(C stock per area) of China's grasslands differed greatly among previous studies,ranging from 215.8 to 348.1 g C m-2 with an average of 300.2 g C m-2.Likewise,soil C density also varied greatly between 8.5 and 15.1 kg C m-2.In total,ecosystem C stock in China's grasslands was estimated at 29.1 Pg C.(2) Both the magnitude and direction of ecosystem C changes in China's grasslands differed greatly among previous studies.According to recent reports,neither biomass nor soil C stock in China's grasslands showed a significant change during the past 20 years,indicating that grassland ecosystems are C neutral.(3) Spatial patterns and temporal dynamics of grassland biomass were closely correlated with precipitation,while changes in soil C stocks exhibited close associations with soil moisture and soil texture.Human activities,such as livestock grazing and fencing could also affect ecosystem C dynamics in China's grasslands.展开更多
Above- and belowground biomasses of grasslands are important parameters for characterizing re- gional and global carbon cycles in grassland ecosystems. Compared with the relatively detailed in- formation for abovegrou...Above- and belowground biomasses of grasslands are important parameters for characterizing re- gional and global carbon cycles in grassland ecosystems. Compared with the relatively detailed in- formation for aboveground biomass (AGB), belowground biomass (BGB) is poorly reported at the re- gional scales. The present study, based on a total of 113 sampling sites in temperate grassland of the Inner Mongolia, investigated regional distribution patterns of AGB, BGB, vertical distribution of roots, and their relationships with environmental factors. AGB and BGB increased from the southwest to the northeast of the study region. The largest biomass occurred in meadow steppe, with mean AGB and BGB of 196.7 and 1385.2 g/m2, respectively; while the lowest biomass occurred in desert steppe, with an AGB of 56.6 g/m2 and a BGB of 301.0 g/m2. In addition, about 47% of root biomass was distributed in the top 10 cm soil. Further statistical analysis indicated that precipitation was the primary determinant factor in shaping these distribution patterns. Vertical distribution of roots was significantly affected by precipitation, while the effects of soil texture and grassland types were weak.展开更多
Biodiversity is thought to be essential for ecosystem stability, function and long-term sustainability. Since nitrogen is the limiting nutrient for plant growth in many terrestrial ecosystems, reactive nitrogen has th...Biodiversity is thought to be essential for ecosystem stability, function and long-term sustainability. Since nitrogen is the limiting nutrient for plant growth in many terrestrial ecosystems, reactive nitrogen has the potential to reduce the diversity of terrestrial vegetation and associated biota through favouring species adapted to quickly exploiting available nutrients. Although the potential has long been recognised, only recently has enough evidence come together to show beyond reasonable doubt that these changes are already occurring. Linked together, experimental, regional/empirical, and time-series research provide a powerful argument that enhanced deposition of reactive nitrogen across Great Britain, and potentially the rest of Europe, has resulted in a significant and ongoing decline in grassland species richness and diversity.展开更多
Aims The response pattern of terrestrial soil respiration to warming during non-growing seasons is a poorly understood phenomenon,though many believe that these warming effects are potentially significant.This study w...Aims The response pattern of terrestrial soil respiration to warming during non-growing seasons is a poorly understood phenomenon,though many believe that these warming effects are potentially significant.This study was conducted in a semiarid temperate steppe to examine the effects of warming during the non-growing seasons on soil respiration and the underlying mechanisms associated therewith.Methods This experiment was conducted in a semiarid temperate grassland and included 10 paired control and experimental plots.Experimental warming was achieved with open top chambers(OTCs)in October 2014.Soil respiration,soil temperature and soil moisture were measured several times monthly from November 2014 to April 2015 and from November 2015 to April 2016.Microbial biomass carbon(MBC),microbial biomass nitrogen(MBN)and available nitrogen content of soil were measured from 0 to 20 cm soil depth.Repeated measurement ANOVAs and paired-sample t tests were conducted to document the effect of warming,and the interactions between warming and time on the above variables.Simple regressions were employed to detect the underlying causality for the observed effects.Important Findings Soil respiration rate was 0.24μmol m^(−2) s^(−1) in the control plots during the non-growing seasons,which was roughly 14.4%of total soil carbon flux observed during growing seasons.Across the two non-growing seasons,warming treatment significantly increased soil temperature and soil respiration by 1.48℃(P<0.001)and 42.1%(P<0.01),respectively,when compared with control plots.Warming slightly,but did not significantly decrease soil moisture by 0.66%in the non-growing seasons from 2015 to 2016.In the non-growing seasons 2015–16,experimental warming significantly elevated MBC and MBN by 19.72%and 20.99%(both P<0.05),respectively.In addition,soil respiration responses to warming were regulated by changes in soil temperate,MBC and MBN.These findings indicate that changes in non-growing season soil respiration impact other components in the carbon c展开更多
Soil microbial biomass is critical for biogeochemical cycling and serves as precursor for carbon(C)sequestration.The anthropogenic nitrogen(N)input has profoundly changed the pool of soil microbial biomass.However,tra...Soil microbial biomass is critical for biogeochemical cycling and serves as precursor for carbon(C)sequestration.The anthropogenic nitrogen(N)input has profoundly changed the pool of soil microbial biomass.However,traditional N deposition simulation experiments have been exclusively conducted through infrequent N addition,which may have caused biased effects on soil microbial biomass compared with those under the natural and continuous N deposition.Convincing data are still scarce about how the different N addition frequencies affect soil microbial biomass.By independently manipulating the frequencies(2 times vs.12 times N addition yr^(–1))and the rates(0–50 g N m^(−2) yr^(−1))of N addition,our study aimed to examine the response of soil microbial biomass C(MBC)to different N addition frequencies with increasing N addition rates.Soil MBC gradually decreased with increasing N addition rates under both N addition frequencies,while the soil MBC decreased more at low frequency of N addition,suggesting that traditional studies have possibly overestimated the effects of N deposition on soil microbial biomass.The greater soil microbial biomass loss with low N frequency resulted from the intensifed soil acidifcation,higher soil inorganic N,stronger soil C and N imbalance,less net primary production allocated to belowground and lower fungi to bacteria ratio.To reliably predict the effects of atmospheric N deposition on soil microbial functioning and C cycling of grassland ecosystems in future studies,it is necessary to employ both the dosage and the frequency of N addition.展开更多
We report extent and rate of land use/land cover change in a forest-grassland mosaic of Rio Grande do Sul,Brazil,during a recent period of increasing conflicts between native habitat protection and conversion.The area...We report extent and rate of land use/land cover change in a forest-grassland mosaic of Rio Grande do Sul,Brazil,during a recent period of increasing conflicts between native habitat protection and conversion.The area is part of the Atlantic rain forest biome,a Global Biodiversity Hotspot.Analyzing Landsat and Google Earth imagery,and calculating an effective conservation risk index(ECRI)as ratio of converted to remnant area,we specifically compared the effectiveness of designated fully protected areas(FP-PAs)and Sustainable Use areas(SU-PAs)in preventing conversion of native forest and grassland hab-itats for agri-and silviculture,relative to areas outside.Grassland area decreased by 17%,corresponding to a net loss of 59,671 ha,in the entire area.Forest gains exceeded losses,and ECRI was zero inside Full Protection PAs.Non-native tree plantation area increased by 94%over the entire study area;cropland increased by 7%.Conversion for silviculture predominated outside the designated PAs and conversion for agriculture predominated inside the designated PAs.ECRI was generally higher for grassland than forest,and in SU-PAs,grassland ECRI was several times higher than in areas without any protection status.These developments are in stark contrast to the high standards of the Brazilian protected area system and corre-sponding International Union for Conservation of Nature and Natural Resources categories.They are due to protracted regularization of land conversion and establishment of designated protection areas.Further-more,they reveal the dilemma of previously managed grasslands in strictly protected areas being eventually succeeded by forest,and the hazards of broad interpretation of the term“sustainable development”.展开更多
Aims Individual growth constitutes a major component of individual fitness.However,measuring growth rates of herbaceous plants non-destructively at the individual level is notoriously difficult.This study,based on an ...Aims Individual growth constitutes a major component of individual fitness.However,measuring growth rates of herbaceous plants non-destructively at the individual level is notoriously difficult.This study,based on an accurate non-destructive method of aboveground biomass estimation,aims to assess individual relative growth rates(RGRs)of some species,identify its environmental drivers and test its consequences on community patterning.We specifically address three questions:(i)to what extent environmental conditions explain differences in individual plant growth between sites,(ii)what is the magnitude of intraspecific variability of plant individual growth within and between sites and(iii)do species-averaged(dis-)advantage of individual growth compared with the whole vegetation within a site correlate with species ranking at the community level?Methods We monitored the growth of individuals of four common perennial species in 18 permanent grasslands chosen along a large pedoclimatic gradient located in the Massif Central,France.We measured soil properties,levels of resources and meteorological parameters to characterize environmental conditions at the site level.This design enables us to assess the influence of environmental conditions on individual growth and the relative extent of inter-individual variability of growth explained within and between sites.We determined the ranking of each of the four species in each site with botanical surveys to assess the relationship between species-averaged growth(dis-)advantage relative to the whole community and species rank in the community.Important Findings We found that environmental conditions explain a significant proportion of individual growth variability,and that this proportion is strongly variable between species.Light availability was the main driver of plant growth,followed by rainfall amount and potential evapotranspiration,while soil properties had only a slight effect.We further highlighted a moderate to high within-site inter-individual variability of growth.展开更多
基金supported by the National Natural Science Foundation of China (Grant Nos. 90711002 and 90211016)
文摘Grassland covers approximately one-third of the area of China and plays an important role in the global terrestrial carbon(C) cycle.However,little is known about biomass C stocks and dynamics in these grasslands.During 2001-2005,we conducted five consecutive field sampling campaigns to investigate above-and below-ground biomass for northern China's grasslands.Using measurements obtained from 341 sampling sites,together with a NDVI(normalized difference vegetation index) time series dataset over 1982-2006,we examined changes in biomass C stock during the past 25 years.Our results showed that biomass C stock in northern China's grasslands was estimated at 557.5 Tg C(1 Tg=1012 g),with a mean density of 39.5 g C m-2 for above-ground biomass and 244.6 g C m-2 for below-ground biomass.An increasing rate of 0.2 Tg C yr-1 has been observed over the past 25 years,but grassland biomass has not experienced a significant change since the late 1980s.Seasonal rainfall(January-July) was the dominant factor driving temporal dynamics in biomass C stock;however,the responses of grassland biomass to climate variables differed among various grassland types.Biomass in arid grasslands(i.e.,desert steppe and typical steppe) was significantly associated with precipitation,while biomass in humid grasslands(i.e.,alpine meadow) was positively correlated with mean January-July temperatures.These results suggest that different grassland ecosystems in China may show diverse responses to future climate changes.
文摘The knowledge of carbon(C) stock and its dynamics is crucial for understanding the role of grassland ecosystems in China's terrestrial C cycle.To date,a comprehensive assessment on C balance in China's grasslands is still lacking.By reviewing published literature,this study aims to evaluate ecosystem C stocks(both vegetation biomass and soil organic C) and their changes in China's grasslands.Our results are summarized as follows:(1) biomass C density(C stock per area) of China's grasslands differed greatly among previous studies,ranging from 215.8 to 348.1 g C m-2 with an average of 300.2 g C m-2.Likewise,soil C density also varied greatly between 8.5 and 15.1 kg C m-2.In total,ecosystem C stock in China's grasslands was estimated at 29.1 Pg C.(2) Both the magnitude and direction of ecosystem C changes in China's grasslands differed greatly among previous studies.According to recent reports,neither biomass nor soil C stock in China's grasslands showed a significant change during the past 20 years,indicating that grassland ecosystems are C neutral.(3) Spatial patterns and temporal dynamics of grassland biomass were closely correlated with precipitation,while changes in soil C stocks exhibited close associations with soil moisture and soil texture.Human activities,such as livestock grazing and fencing could also affect ecosystem C dynamics in China's grasslands.
基金Supported by the National Natural Science Fundation of China (Grant Nos. 90211016, 40021101 and 30700090)
文摘Above- and belowground biomasses of grasslands are important parameters for characterizing re- gional and global carbon cycles in grassland ecosystems. Compared with the relatively detailed in- formation for aboveground biomass (AGB), belowground biomass (BGB) is poorly reported at the re- gional scales. The present study, based on a total of 113 sampling sites in temperate grassland of the Inner Mongolia, investigated regional distribution patterns of AGB, BGB, vertical distribution of roots, and their relationships with environmental factors. AGB and BGB increased from the southwest to the northeast of the study region. The largest biomass occurred in meadow steppe, with mean AGB and BGB of 196.7 and 1385.2 g/m2, respectively; while the lowest biomass occurred in desert steppe, with an AGB of 56.6 g/m2 and a BGB of 301.0 g/m2. In addition, about 47% of root biomass was distributed in the top 10 cm soil. Further statistical analysis indicated that precipitation was the primary determinant factor in shaping these distribution patterns. Vertical distribution of roots was significantly affected by precipitation, while the effects of soil texture and grassland types were weak.
文摘Biodiversity is thought to be essential for ecosystem stability, function and long-term sustainability. Since nitrogen is the limiting nutrient for plant growth in many terrestrial ecosystems, reactive nitrogen has the potential to reduce the diversity of terrestrial vegetation and associated biota through favouring species adapted to quickly exploiting available nutrients. Although the potential has long been recognised, only recently has enough evidence come together to show beyond reasonable doubt that these changes are already occurring. Linked together, experimental, regional/empirical, and time-series research provide a powerful argument that enhanced deposition of reactive nitrogen across Great Britain, and potentially the rest of Europe, has resulted in a significant and ongoing decline in grassland species richness and diversity.
基金supported by the National Natural Science Foundation of China(32192462,32192460)the Chinese Universities Scientific Fund(2020RC009)the 2115 Talent Development Program of China Agricultural University(1201-00109017).
基金supported by the National Natural Science Foundation of China(31670477,31800399)China Postdoctoral Science Foundation(2018M642738,2018M642739)Henan Province Foundation and Advanced Technology Project(192102110085).
文摘Aims The response pattern of terrestrial soil respiration to warming during non-growing seasons is a poorly understood phenomenon,though many believe that these warming effects are potentially significant.This study was conducted in a semiarid temperate steppe to examine the effects of warming during the non-growing seasons on soil respiration and the underlying mechanisms associated therewith.Methods This experiment was conducted in a semiarid temperate grassland and included 10 paired control and experimental plots.Experimental warming was achieved with open top chambers(OTCs)in October 2014.Soil respiration,soil temperature and soil moisture were measured several times monthly from November 2014 to April 2015 and from November 2015 to April 2016.Microbial biomass carbon(MBC),microbial biomass nitrogen(MBN)and available nitrogen content of soil were measured from 0 to 20 cm soil depth.Repeated measurement ANOVAs and paired-sample t tests were conducted to document the effect of warming,and the interactions between warming and time on the above variables.Simple regressions were employed to detect the underlying causality for the observed effects.Important Findings Soil respiration rate was 0.24μmol m^(−2) s^(−1) in the control plots during the non-growing seasons,which was roughly 14.4%of total soil carbon flux observed during growing seasons.Across the two non-growing seasons,warming treatment significantly increased soil temperature and soil respiration by 1.48℃(P<0.001)and 42.1%(P<0.01),respectively,when compared with control plots.Warming slightly,but did not significantly decrease soil moisture by 0.66%in the non-growing seasons from 2015 to 2016.In the non-growing seasons 2015–16,experimental warming significantly elevated MBC and MBN by 19.72%and 20.99%(both P<0.05),respectively.In addition,soil respiration responses to warming were regulated by changes in soil temperate,MBC and MBN.These findings indicate that changes in non-growing season soil respiration impact other components in the carbon c
基金supported by the National Natural Science Foundation of China(42130515 and31770506)the Open Foundation of the State Key Laboratory of Urban and Regional Ecology of Chinathe Open Foundation of the State Key Laboratory of Grassland Agro-ecosystems of China。
文摘Soil microbial biomass is critical for biogeochemical cycling and serves as precursor for carbon(C)sequestration.The anthropogenic nitrogen(N)input has profoundly changed the pool of soil microbial biomass.However,traditional N deposition simulation experiments have been exclusively conducted through infrequent N addition,which may have caused biased effects on soil microbial biomass compared with those under the natural and continuous N deposition.Convincing data are still scarce about how the different N addition frequencies affect soil microbial biomass.By independently manipulating the frequencies(2 times vs.12 times N addition yr^(–1))and the rates(0–50 g N m^(−2) yr^(−1))of N addition,our study aimed to examine the response of soil microbial biomass C(MBC)to different N addition frequencies with increasing N addition rates.Soil MBC gradually decreased with increasing N addition rates under both N addition frequencies,while the soil MBC decreased more at low frequency of N addition,suggesting that traditional studies have possibly overestimated the effects of N deposition on soil microbial biomass.The greater soil microbial biomass loss with low N frequency resulted from the intensifed soil acidifcation,higher soil inorganic N,stronger soil C and N imbalance,less net primary production allocated to belowground and lower fungi to bacteria ratio.To reliably predict the effects of atmospheric N deposition on soil microbial functioning and C cycling of grassland ecosystems in future studies,it is necessary to employ both the dosage and the frequency of N addition.
基金Marion Lang and Julia-Maria Hermann acknowledge funding by Deutsche Forschungsgemeinschaft(DFG:KO1741/2-2,KO1741/3-1).
文摘We report extent and rate of land use/land cover change in a forest-grassland mosaic of Rio Grande do Sul,Brazil,during a recent period of increasing conflicts between native habitat protection and conversion.The area is part of the Atlantic rain forest biome,a Global Biodiversity Hotspot.Analyzing Landsat and Google Earth imagery,and calculating an effective conservation risk index(ECRI)as ratio of converted to remnant area,we specifically compared the effectiveness of designated fully protected areas(FP-PAs)and Sustainable Use areas(SU-PAs)in preventing conversion of native forest and grassland hab-itats for agri-and silviculture,relative to areas outside.Grassland area decreased by 17%,corresponding to a net loss of 59,671 ha,in the entire area.Forest gains exceeded losses,and ECRI was zero inside Full Protection PAs.Non-native tree plantation area increased by 94%over the entire study area;cropland increased by 7%.Conversion for silviculture predominated outside the designated PAs and conversion for agriculture predominated inside the designated PAs.ECRI was generally higher for grassland than forest,and in SU-PAs,grassland ECRI was several times higher than in areas without any protection status.These developments are in stark contrast to the high standards of the Brazilian protected area system and corre-sponding International Union for Conservation of Nature and Natural Resources categories.They are due to protracted regularization of land conversion and establishment of designated protection areas.Further-more,they reveal the dilemma of previously managed grasslands in strictly protected areas being eventually succeeded by forest,and the hazards of broad interpretation of the term“sustainable development”.
基金supported by the Region Auvergne-Rhône-Alpes and the European Regional Development Fund(FEDER)(grant no.AV0008781).
文摘Aims Individual growth constitutes a major component of individual fitness.However,measuring growth rates of herbaceous plants non-destructively at the individual level is notoriously difficult.This study,based on an accurate non-destructive method of aboveground biomass estimation,aims to assess individual relative growth rates(RGRs)of some species,identify its environmental drivers and test its consequences on community patterning.We specifically address three questions:(i)to what extent environmental conditions explain differences in individual plant growth between sites,(ii)what is the magnitude of intraspecific variability of plant individual growth within and between sites and(iii)do species-averaged(dis-)advantage of individual growth compared with the whole vegetation within a site correlate with species ranking at the community level?Methods We monitored the growth of individuals of four common perennial species in 18 permanent grasslands chosen along a large pedoclimatic gradient located in the Massif Central,France.We measured soil properties,levels of resources and meteorological parameters to characterize environmental conditions at the site level.This design enables us to assess the influence of environmental conditions on individual growth and the relative extent of inter-individual variability of growth explained within and between sites.We determined the ranking of each of the four species in each site with botanical surveys to assess the relationship between species-averaged growth(dis-)advantage relative to the whole community and species rank in the community.Important Findings We found that environmental conditions explain a significant proportion of individual growth variability,and that this proportion is strongly variable between species.Light availability was the main driver of plant growth,followed by rainfall amount and potential evapotranspiration,while soil properties had only a slight effect.We further highlighted a moderate to high within-site inter-individual variability of growth.
