The leaf nitrogen(N)to phosphorus(P)ratio(N:P)is a critical indicator of nutrient dynamics and ecosystem function.Investigating temporal variations in leaf N:P can provide valuable insights into how plants adapt to en...The leaf nitrogen(N)to phosphorus(P)ratio(N:P)is a critical indicator of nutrient dynamics and ecosystem function.Investigating temporal variations in leaf N:P can provide valuable insights into how plants adapt to environmental changes and nutrient availability.However,limited research has been conducted on long-term temporal leaf N:P variation over a range of temperature zones.Using long-term monitoring data from the Chinese Ecosystem Research Network(CERN),we investigated temporal changes in leaf N and P stoichiometry for 50 dominant tree species from 10 typical forest sites across temperate and subtropical regions,and identified the underlying mechanisms driving these changes.For both regions combined,leaf P concentration of the 50 dominant tree species decreased(20.6%),whereas leaf N:P increased(52.0%)from 2005 to 2020.Leaf P decreased and leaf N:P increased in 67% and 69% of the tree species,respectively.The leaf N:P increase was primarily driven by the tree species in eastern subtropical forests,where global change factors and soil nutrients explained 68% of leaf N:P variation.The P limitation exhibited by tree species in eastern subtropical forest ecosystems intensified over time,and elevated temperature and CO_(2) levels,coupled with decreased soil available P concentrations,appear to be the main factors driving long-term leaf N:P increases in these forests.Investigating long-term variations in soil nutrients together with global change factors will improve our understanding of the nutrient status of forest ecosystems in the context of global change and will support effective forest ecosystem management.展开更多
Gross primary production(GPP) plays a crucial part in the carbon cycle of terrestrial ecosystems.A set of validated monthly GPP data from 1957 to 2010 in 0.5°× 0.5° grids of China was weighted from the ...Gross primary production(GPP) plays a crucial part in the carbon cycle of terrestrial ecosystems.A set of validated monthly GPP data from 1957 to 2010 in 0.5°× 0.5° grids of China was weighted from the Multi-scale Terrestrial Model Intercomparison Project using Bayesian model averaging(BMA).The spatial anomalies of detrended BMA GPP during the growing seasons of typical El Nino years indicated that GPP response to El Nino varies with Pacific Decadal Oscillation(PDO) phases: when the PDO was in the cool phase,it was likely that GPP was greater in northern China(32°–38°N,111°–122°E) and less in the Yangtze River valley(28°–32°N,111°–122°E);in contrast,when PDO was in the warm phase,the GPP anomalies were usually reversed in these two regions.The consistent spatiotemporal pattern and high partial correlation revealed that rainfall dominated this phenomenon.The previously published findings on how El Nino during different phases of PDO affecting rainfall in eastern China make the statistical relationship between GPP and El Nino in this study theoretically credible.This paper not only introduces an effective way to use BMA in grids that have mixed plant function types,but also makes it possible to evaluate the carbon cycle in eastern China based on the prediction of El Nino and PDO.展开更多
In 1958, a demonstrational cutting trial totaling 22.2 ha was established in a northern hardwood forest in Alberta, MI. Eight different treatments were installed, including four diameter-limit treatments (56 cm, 41 cm...In 1958, a demonstrational cutting trial totaling 22.2 ha was established in a northern hardwood forest in Alberta, MI. Eight different treatments were installed, including four diameter-limit treatments (56 cm, 41 cm, 30 cm, and 13 cm), three single-tree selection treatments with residual basal areas of 21 m2·ha–1, 16 m2·ha–1, and 11 m2·ha–1, and an uncut control. Within each treatment, a 0.4-ha permanent plot was established and subdivided into 0.04-ha square subplots. Harvests have been implemented every ten years with the most recent harvest occurring during the winter of 2008 - 2009. We quantified ground layer vegetation response before and after the most recent harvest. Nonmetric multidimensional scaling (NMS) ordination showed a very distinct separation between the most intensive management treatment (13-cm diameter-limit treatment) and the uncut control. Compositionally, the diameter-limit treatments moved with greater directionality and magnitude towards the 13-cm diameter-limit treatment following harvest, while compositional change in the residual basal area treatments was less pronounced and lacked strong directionality. Herbaceous species percent cover generally decreased with increasing residual overstory basal area across treatments. Weedy and early successional species were most abundant under lower residual basal area and diameter-limit treatments. Results based on 50 years of continuous management suggest that diameter-limit harvests likely have a greater impact on the herbaceous community than single-tree selection or no management.展开更多
It is of important referential values for the further understanding of the effects of fertilization on greenhouse gas emissions and the effects of winter green manure on soil carbon pool to study the effects of fertil...It is of important referential values for the further understanding of the effects of fertilization on greenhouse gas emissions and the effects of winter green manure on soil carbon pool to study the effects of fertilization on the greenhouse gas emissions and soil carbon pool during the growing season of winter Chinese milk vetch in the process of rice cultivation.This study investigated the effects of nitrogen application in late rice season on the yield of the succeeding Chinese milk vetch and greenhouse gas emissions as well as the soil carbon pool characteristics after the winter planting of Chinese milk vetch with the winter idling of no nitrogen application as the control.The results showed that the yield of Chinese milk vetch was the highest under the nitrogen application of 225 kg/hm^2 in the late rice season,reaching up to 18 388.97 kg/hm^2,which was significantly different from other treatments( P <0.05).Nitrogen application in late rice season increased the emissions of N_2 O,CH_4,CO_2 and global warming potential( GWP) in the growing season of Chinese milk vetch.Compared with the winter idling treatment,winter planting of Chinese milk vetch significantly increased the soil organic carbon and soil carbon pool management index.The yield of Chinese milk vetch was significantly positively correlated with N_2O and CH_4 emissions( P < 0.05),while it presented extremely significant positive correlations with CO_2 emissions,GWP,active organic carbon,and carbon pool management index( P < 0.01).Nitrogen application in the late rice season increased the emissions of N_2 O,CH_4,CO_2,and enhanced the greenhouse gas emission potential during the growing season of Chinese milk vetch.Therefore,without reducing the yield of rice,reducing the amount of nitrogen fertilizer in rice could reduce the greenhouse gas emissions in the growing season of succeeding Chinese milk vetch.展开更多
Adjustment of ecosystem root respiration to warmer climatic conditions can alter the autotrophic portion of soil respiration and influence the amount of carbon available for biomass production. We examined 44 publishe...Adjustment of ecosystem root respiration to warmer climatic conditions can alter the autotrophic portion of soil respiration and influence the amount of carbon available for biomass production. We examined 44 published values of annual forest root respiration and found an increase in ecosystem root respiration with increasing mean annual temperature （MAT）, but the rate of this cross-ecosystem increase （Q10 = 1.6） is less than published values for short-term responses of root respiration to temperature within ecosystems （Q10 = 2-3）. When specific root respiration rates and root biomass values were examined, there was a clear trend for decreasing root metabolic capacity （respiration rate at a standard temperature） with increasing MAT. There also were tradeoffs between root metabolic capacity and root system biomass, such that there were no instances of high growing season respiration rates and high root biomass occurring together. We also examined specific root respiration rates at three soil warming experiments at Harvard Forest, USA, and found decreases in metabolic capacity for roots from the heated plots. This decline could be due to either physiological acclimation or to the effects of co-occurring drier soils on the measurement date. Regardless of the cause, these findings clearly suggest that modeling efforts that allow root respiration to increase exponentially with temperature, with Q10 values of 2 or more, may over-predict root contributions to ecosystem CO2 efflux for future climates and underestimate the amount of C available for other uses, including net primary productivity.展开更多
Under global change and climate variations,determining the impacts of climate change and human activities on cropland net primary productivity(NPP)in Bangladesh,India and Myanmar(BIM)is of great significance for ident...Under global change and climate variations,determining the impacts of climate change and human activities on cropland net primary productivity(NPP)in Bangladesh,India and Myanmar(BIM)is of great significance for identifying yield-limiting factors,making adaptive agricultural management plans,and improving yields.Based on the GLOPEM-CEVSA model,through an integration of remote sensing data and LAI simulation,we investigated the impacts and spatiotemporal changes of water and human activities on BIM from 1982 to 2015.Three types of cropland NPPs were considered:actual NPP(NPPA),NPP affected by temperature and water(NPPWT),and NPP only affected by temperature(NPPT).Our analysis revealed that the water factor plays a predominant role in determining the NPP level in the BIM.Temperature variability was found to be conducive to NPPT,exhibiting an increasing trend of 10.66 g C m^(-2) yr^(-1).However,this trend was partially offset by precipitation variability,resulting in a net increase of 0.96 g C m^(-2) yr^(-1).In comparing temperature-driven NPP to temperature and water-driven NPP,water stress caused NPPT to decrease by 65.46% compared to NPPWT for the entire region.Cropland NPP in northwestern India and the central Deccan Plateau were significantly affected by water stress.Moreover,the influence of water on NPP in the BIM exhibited a substantial upward trend from 1982 to 2015,with Myanmar experiencing the most significant increase.The gap between NPPWT and NPPA in BIM demonstrated a notable decreasing trend during the same period,underscoring the positive impact of human activities on NPP.Inferences drawn from our findings suggest that with the implementation of rational and efficient crop management practices,there is a 36.80% potential improvement in NPPA compared to NPPWT in the BIM region,with India and Myanmar showing potential increases of 39.20% and 38.29%,respectively.These insights provide guidance for practical measures aimed at water resource management to enhance cropland productivity in the BIM,and they present a methodology for quantifying the effects of climatic changes and human activities at a regional scale.展开更多
The response of long-term vegetation changes and climate change has been a hot topic in recent research.Previously,a Landsat-based fusion model was developed and used to produce a dataset of normalized vegetation inde...The response of long-term vegetation changes and climate change has been a hot topic in recent research.Previously,a Landsat-based fusion model was developed and used to produce a dataset of normalized vegetation index(NDVI)for the Three-River Headwater region on the Qinghai-Tibet Plateau with a spatial resolution of 30 m and the time spanning the nearly 30 years from 1990 to 2018.In this study,the NDVI was applied to an analysis of the spatial and temporal changes in the alpine grassland and the impacts from climate change using the Theil-Sen Median method and linear regression.The results showed that:(1)The regional mean NDVI was 0.39and showed a spatial pattern of decreasing from the southeast to the northwest in the recent three decades.Among the three parks,the Lancang River Park had the highest NDVI(0.43),followed by the Yellow River Park(0.38)and Yangtze River Park(0.23).(2)An upward trending was found in the NDVI time series at a rate of 0.0031 yr^(-1)(R^(2)=0.62,P<0.01)over the whole period of 1990–2018.The increasing rate(0.00649 yr^(-1),R^(2)=0.71,P<0.01)in the latter period of 2005–2018 was nearly 2.3 times of that(0.00284 yr^(-1),R^(2)=0.31,P<0.01)in the previous period of1990–2005.In the latest periods,the three parks experienced rates that were 2.3 to 63 times the corresponding values in the early period.(3)The NDVI is correlated more positively with temperature than precipitation.The impacts of climate change decreased along with the coverage fraction from the higher,median and then lower levels.The climate change can explain 34%of the variability in the NDVI time series of the areas with a higher fraction of grassland coverage,while it was 31%for the median fraction and 20%for the lower fraction.This study is the first to use the 30 m NDVI dataset spanning nearly 30 years to analyze the spatial and temporal variability and climate impacts in the alpine grasslands of the Three-River Headwater region of the Qinghai-Tibet Plateau.The results provide a basis for assessments on the ecological management effects and ecological quality based on long-term baseline data with a higher spatial resolution.展开更多
The Bowen ratio(β) is used to quantify heat transfer from the land surface into the air, which is becoming a hot topic in research on the biogeophysical effects of land use and cover changes. The Three-River Headwate...The Bowen ratio(β) is used to quantify heat transfer from the land surface into the air, which is becoming a hot topic in research on the biogeophysical effects of land use and cover changes. The Three-River Headwaters(TRH), as a sensitive and fragile region, was selected as the study area. The β for 2001–2018 was estimated from the evapotranspiration product(ETMOD16) of MODIS and the net radiation of the land surface through the albedo from GLASS. The ETMOD16 data were evaluated against the observation data(ETOBS) at two alpine grassland flux towers obtained from ChinaFLUX. The interannual trend of the β was analyzed by multiple linear regression(MLR) and structure model(SEM) with the multiple factors of precipitation, temperature, humidity, albedo, and normalized difference vegetation index(NDVI, MOD09 Q1). The results show that the ETMOD16 values were significantly correlated with ETOBS, with a correlation coefficient above 0.70(P < 0.01) for the two sites. In 2001–2018, the regional mean β was 2.52 ± 0.77 for the whole grassland, and its spatial distribution gradually increased from the eastern to western region. The interannual β showed a downward trend with a slope of-0.025 and a multiple regression coefficient(R^(2)) of 0.21(P = 0.056). Most of the variability(51%) in the interannual β can be explained by the linear regression of the above multiple factors, and the temperature plays a dominant role for the whole region. The SEM analysis further shows that an increasing NDVI results in a decreasing albedo with a path coefficient of-0.57, because the albedo was negatively correlated with NDVI(R^(2) = 0.52, P < 0.01), which indicates a negative and indirect effect on β from vegetation restoration. An obvious warming climate was found to prompt more evapotranspiration, and restoring vegetation makes the land surface receive more radiation, which both resulted in a decreasing trend in the annual β. This study revealed the biogeophysical mechanisms of vegetation restoration under a changing climate, and demonstrated the Bowen ratio can be applied as an indicator of climate-regulating functions in ecosystem assessments.展开更多
Karst areas in southwest China have experienced significant land cover and land use change(LUCC)due to utilization for human activity and a comprehensive rocky desertification control project(RDCP)since 2008.It is imp...Karst areas in southwest China have experienced significant land cover and land use change(LUCC)due to utilization for human activity and a comprehensive rocky desertification control project(RDCP)since 2008.It is important to quantify the effect of LUCC on ecosystem productivity in this region for assessing the overall benefit of this ecological restoration project.In this study,we used using MODIS land cover and NPP products to investigate the relative contribution of LUCC to the change in net primary productivity(NPP)during 2008–2013 in Huanjiang County,one of first one hundred pilot counties to implement RDCP.Our results show that NPP increased in 95.53%of the county,and the average growth of NPP in non-rocky desertification area was higher than in rocky desertification or potential rocky desertification areas.LUCC has an important contribution(25.23%)to the NPP increase in the county,especially in the LUCC area(70.97%),which increased the average NPP by 3.9%and 10.5%,respectively.Across the six RDCP regions in the county,the average increase in NPP for the vegetation restoration measure of governed karst area is significantly greater than in the ungoverned karst area,and the positive change in NPP increased with the increasing implementation area of the vegetation restoration measure.展开更多
Shifting sands are one of the main contributors to desertification in China. This paper briefly reviews the measures and techniques which are used to protect traffic lines by stabilizing and fixing sands in the desert...Shifting sands are one of the main contributors to desertification in China. This paper briefly reviews the measures and techniques which are used to protect traffic lines by stabilizing and fixing sands in the desert and desertification-affected arid and semi-arid areas in north China. We introduce the types and features of these measures and techniques, including mechanical, chemical, and biological measures, and outline how they have been applied in different areas and in different traffic lines over the past six decades, from 1950 s to 2010 s, taking the Baotou-Lanzhou railway, the Qinghai-Tibet railway, and the Tarim Desert highway as examples Mechanical measures such as erecting sand-retaining wind walls and placing straw checkerboards have proved to be very efficient for stabilizing shifting sands and protecting traffic lines that pass through the desert areas. Chemical measures are not widely used in the current sand fixing systems because of their high cost and potential pollution risks. Biological measures are preferred because they exhibit much better sand fixation performance and longer duration than the former two types of measures despite their relatively high cost. A combination of different measures is usually adopted in some areas to attain better sand-fixing effects. Stabilizing sand dune surfaces with mechanical measures or irrigation from underground water or river if available helps early recruitment of some drought-tolerant plants(xerophytes). We also point out the restrictions for existing sand-fixing measures and techniques and future research orientation. This review has implications for addressing eco-environmental issues associated with infrastructure construction that is part of the Belt and Road Initiative in desert and desertification-affected arid and semi-arid areas in the Mongolian Plateau.展开更多
Understanding the stability of terrestrial carbon sinks(S-TCS)contributes to more accurate prediction of the terrestrial carbon sink(TCS)in the context of future global change and helps inform climate change mitigatio...Understanding the stability of terrestrial carbon sinks(S-TCS)contributes to more accurate prediction of the terrestrial carbon sink(TCS)in the context of future global change and helps inform climate change mitigation policies.Here,focusing on China,we analyzed the spatial distribution and driving mechanisms for the S-TCS,quantified by the interannual variability of the TCS,using three independent approaches(atmospheric inversions,ecosystem carbon cycle models,and machine learning models based on flux tower observations).We found that the interannual variability of the TCS in China is relatively small compared with the conterminous United States and geographic Europe,indicating a generally stable TCS in China.Spatially,the S-TCS is lower in the North China Plain,Northeast China Plain,and western Yunnan-Guizhou Plateau than in other regions,with varying underlying mechanisms.Large interannual variations in precipitation and high TCS sensitivities to precipitation fluctuations explain the low S-TCS in the North China Plain and Northeast China Plain,while high TCS sensitivities to temperature variations drive the low S-TCS in the western Yunnan-Guizhou Plateau.Our findings highlight the importance of considering local contexts for stabilizing and enhancing China’s TCS in a changing environment.展开更多
Background:An accurate assessment of the carbon budget is a crucial part of projecting future climate change and its impact on ecosystems.Grasslands foster multiple ecological functions including support for wild anim...Background:An accurate assessment of the carbon budget is a crucial part of projecting future climate change and its impact on ecosystems.Grasslands foster multiple ecological functions including support for wild animals and livestocks.Herbivores intake forage biomass carbon,then digest and metabolize,and finally retain some carbon.The carbon processes have not been well quantified,resulting in uncertainties in the estimation of regional carbon budgets for grassland ecosystems.Methods:An animal metabolic carbon flux model was developed for herbivores in the Three-Rivers Headwaters region of China.The forage intake and metabolic carbon rates were estimated through metabolic body weight and daily digested measures for the main herbivore species.Results:The carbon intake was 5.52 Tg C year−1(45%)from partial aboveground biomass(12.2 Tg C year−1),in which 39.31%was released into the atmosphere by respiration CO_(2),43.77%was returned to the ecosystem as feces and urine,and 16.96%was retained in herbivores for population regeneration or for human well-being.Conclusions:This study,as the first research on this topic,quantified the carbon flux of herbivores and found livestock accounts for a major part of consumed carbon on grasslands,which is important for understanding regional carbon budgets to mitigate and adapt to climate change over grasslands worldwide.展开更多
Introduction:Climate change is expected to impose significant tension on the geographic distribution of tree species.Yet,tree species range shifts may be delayed by their long life spans,capacity to withstand long per...Introduction:Climate change is expected to impose significant tension on the geographic distribution of tree species.Yet,tree species range shifts may be delayed by their long life spans,capacity to withstand long periods of physiological stress,and dispersal limitations.Wildfire could theoretically break this biological inertia by killing forest canopies and facilitating species redistribution under changing climate.We investigated the capacity of wildfire to modulate climate-induced tree redistribution across a montane landscape in the central Rocky Mountains under three climate scenarios(contemporary and two warmer future climates)and three wildfire scenarios(representing historical,suppressed,and future fire regimes).Methods:Distributions of four common tree species were projected over 90 years by pairing a climate niche model with a forest landscape simulation model that simulates species dispersal,establishment,and mortality under alternative disturbance regimes and climate scenarios.Results:Three species(Douglas-fir,lodgepole pine,subalpine fir)declined in abundance over time,due to climate-driven contraction in area suitable for establishment,while one species(ponderosa pine)was unable to exploit climate-driven expansion of area suitable for establishment.Increased fire frequency accelerated declines in area occupied by Douglas-fir,lodgepole pine,and subalpine fir,and it maintained local abundance but not range expansion of ponderosa pine.Conclusions:Wildfire may play a larger role in eliminating these conifer species along trailing edges of their distributions than facilitating establishment along leading edges,in part due to dispersal limitations and interspecific competition,and future populations may increasingly depend on persistence in locations unfavorable for their establishment.展开更多
基金supported by the National Natural Science Foundation of China(No.42030509)the Special Project on National Science and Technology Basic Resources Investigation of China(No.2021FY100705).
文摘The leaf nitrogen(N)to phosphorus(P)ratio(N:P)is a critical indicator of nutrient dynamics and ecosystem function.Investigating temporal variations in leaf N:P can provide valuable insights into how plants adapt to environmental changes and nutrient availability.However,limited research has been conducted on long-term temporal leaf N:P variation over a range of temperature zones.Using long-term monitoring data from the Chinese Ecosystem Research Network(CERN),we investigated temporal changes in leaf N and P stoichiometry for 50 dominant tree species from 10 typical forest sites across temperate and subtropical regions,and identified the underlying mechanisms driving these changes.For both regions combined,leaf P concentration of the 50 dominant tree species decreased(20.6%),whereas leaf N:P increased(52.0%)from 2005 to 2020.Leaf P decreased and leaf N:P increased in 67% and 69% of the tree species,respectively.The leaf N:P increase was primarily driven by the tree species in eastern subtropical forests,where global change factors and soil nutrients explained 68% of leaf N:P variation.The P limitation exhibited by tree species in eastern subtropical forest ecosystems intensified over time,and elevated temperature and CO_(2) levels,coupled with decreased soil available P concentrations,appear to be the main factors driving long-term leaf N:P increases in these forests.Investigating long-term variations in soil nutrients together with global change factors will improve our understanding of the nutrient status of forest ecosystems in the context of global change and will support effective forest ecosystem management.
基金supported by the National Key Research and Development Program of China (Grant Nos.2016YFA0602501 and 2018YFA0606004)the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant Nos.XDA20040301 and XDA20020201)。
文摘Gross primary production(GPP) plays a crucial part in the carbon cycle of terrestrial ecosystems.A set of validated monthly GPP data from 1957 to 2010 in 0.5°× 0.5° grids of China was weighted from the Multi-scale Terrestrial Model Intercomparison Project using Bayesian model averaging(BMA).The spatial anomalies of detrended BMA GPP during the growing seasons of typical El Nino years indicated that GPP response to El Nino varies with Pacific Decadal Oscillation(PDO) phases: when the PDO was in the cool phase,it was likely that GPP was greater in northern China(32°–38°N,111°–122°E) and less in the Yangtze River valley(28°–32°N,111°–122°E);in contrast,when PDO was in the warm phase,the GPP anomalies were usually reversed in these two regions.The consistent spatiotemporal pattern and high partial correlation revealed that rainfall dominated this phenomenon.The previously published findings on how El Nino during different phases of PDO affecting rainfall in eastern China make the statistical relationship between GPP and El Nino in this study theoretically credible.This paper not only introduces an effective way to use BMA in grids that have mixed plant function types,but also makes it possible to evaluate the carbon cycle in eastern China based on the prediction of El Nino and PDO.
文摘In 1958, a demonstrational cutting trial totaling 22.2 ha was established in a northern hardwood forest in Alberta, MI. Eight different treatments were installed, including four diameter-limit treatments (56 cm, 41 cm, 30 cm, and 13 cm), three single-tree selection treatments with residual basal areas of 21 m2·ha–1, 16 m2·ha–1, and 11 m2·ha–1, and an uncut control. Within each treatment, a 0.4-ha permanent plot was established and subdivided into 0.04-ha square subplots. Harvests have been implemented every ten years with the most recent harvest occurring during the winter of 2008 - 2009. We quantified ground layer vegetation response before and after the most recent harvest. Nonmetric multidimensional scaling (NMS) ordination showed a very distinct separation between the most intensive management treatment (13-cm diameter-limit treatment) and the uncut control. Compositionally, the diameter-limit treatments moved with greater directionality and magnitude towards the 13-cm diameter-limit treatment following harvest, while compositional change in the residual basal area treatments was less pronounced and lacked strong directionality. Herbaceous species percent cover generally decreased with increasing residual overstory basal area across treatments. Weedy and early successional species were most abundant under lower residual basal area and diameter-limit treatments. Results based on 50 years of continuous management suggest that diameter-limit harvests likely have a greater impact on the herbaceous community than single-tree selection or no management.
基金Supported by the National Key Research and Development Program(No.2016YFD0300208)the National Natural Science Foundation of China(No.41661070)
文摘It is of important referential values for the further understanding of the effects of fertilization on greenhouse gas emissions and the effects of winter green manure on soil carbon pool to study the effects of fertilization on the greenhouse gas emissions and soil carbon pool during the growing season of winter Chinese milk vetch in the process of rice cultivation.This study investigated the effects of nitrogen application in late rice season on the yield of the succeeding Chinese milk vetch and greenhouse gas emissions as well as the soil carbon pool characteristics after the winter planting of Chinese milk vetch with the winter idling of no nitrogen application as the control.The results showed that the yield of Chinese milk vetch was the highest under the nitrogen application of 225 kg/hm^2 in the late rice season,reaching up to 18 388.97 kg/hm^2,which was significantly different from other treatments( P <0.05).Nitrogen application in late rice season increased the emissions of N_2 O,CH_4,CO_2 and global warming potential( GWP) in the growing season of Chinese milk vetch.Compared with the winter idling treatment,winter planting of Chinese milk vetch significantly increased the soil organic carbon and soil carbon pool management index.The yield of Chinese milk vetch was significantly positively correlated with N_2O and CH_4 emissions( P < 0.05),while it presented extremely significant positive correlations with CO_2 emissions,GWP,active organic carbon,and carbon pool management index( P < 0.01).Nitrogen application in the late rice season increased the emissions of N_2 O,CH_4,CO_2,and enhanced the greenhouse gas emission potential during the growing season of Chinese milk vetch.Therefore,without reducing the yield of rice,reducing the amount of nitrogen fertilizer in rice could reduce the greenhouse gas emissions in the growing season of succeeding Chinese milk vetch.
基金Supported by the US Department of Energy’s Office of Science (BER)through the Northeastern and Midwestern Regional Centers of the National Institute for Climatic Change Research at The Pennsylvania State Universityand Michigan Technological Universitya National Science Foundation CAREER Award to Serita Frey.
文摘Adjustment of ecosystem root respiration to warmer climatic conditions can alter the autotrophic portion of soil respiration and influence the amount of carbon available for biomass production. We examined 44 published values of annual forest root respiration and found an increase in ecosystem root respiration with increasing mean annual temperature （MAT）, but the rate of this cross-ecosystem increase （Q10 = 1.6） is less than published values for short-term responses of root respiration to temperature within ecosystems （Q10 = 2-3）. When specific root respiration rates and root biomass values were examined, there was a clear trend for decreasing root metabolic capacity （respiration rate at a standard temperature） with increasing MAT. There also were tradeoffs between root metabolic capacity and root system biomass, such that there were no instances of high growing season respiration rates and high root biomass occurring together. We also examined specific root respiration rates at three soil warming experiments at Harvard Forest, USA, and found decreases in metabolic capacity for roots from the heated plots. This decline could be due to either physiological acclimation or to the effects of co-occurring drier soils on the measurement date. Regardless of the cause, these findings clearly suggest that modeling efforts that allow root respiration to increase exponentially with temperature, with Q10 values of 2 or more, may over-predict root contributions to ecosystem CO2 efflux for future climates and underestimate the amount of C available for other uses, including net primary productivity.
基金The National Natural Science Foundation of China(31861143015)The Natural Science Foundation of Shandong Province,China(ZR2023QC254).
文摘Under global change and climate variations,determining the impacts of climate change and human activities on cropland net primary productivity(NPP)in Bangladesh,India and Myanmar(BIM)is of great significance for identifying yield-limiting factors,making adaptive agricultural management plans,and improving yields.Based on the GLOPEM-CEVSA model,through an integration of remote sensing data and LAI simulation,we investigated the impacts and spatiotemporal changes of water and human activities on BIM from 1982 to 2015.Three types of cropland NPPs were considered:actual NPP(NPPA),NPP affected by temperature and water(NPPWT),and NPP only affected by temperature(NPPT).Our analysis revealed that the water factor plays a predominant role in determining the NPP level in the BIM.Temperature variability was found to be conducive to NPPT,exhibiting an increasing trend of 10.66 g C m^(-2) yr^(-1).However,this trend was partially offset by precipitation variability,resulting in a net increase of 0.96 g C m^(-2) yr^(-1).In comparing temperature-driven NPP to temperature and water-driven NPP,water stress caused NPPT to decrease by 65.46% compared to NPPWT for the entire region.Cropland NPP in northwestern India and the central Deccan Plateau were significantly affected by water stress.Moreover,the influence of water on NPP in the BIM exhibited a substantial upward trend from 1982 to 2015,with Myanmar experiencing the most significant increase.The gap between NPPWT and NPPA in BIM demonstrated a notable decreasing trend during the same period,underscoring the positive impact of human activities on NPP.Inferences drawn from our findings suggest that with the implementation of rational and efficient crop management practices,there is a 36.80% potential improvement in NPPA compared to NPPWT in the BIM region,with India and Myanmar showing potential increases of 39.20% and 38.29%,respectively.These insights provide guidance for practical measures aimed at water resource management to enhance cropland productivity in the BIM,and they present a methodology for quantifying the effects of climatic changes and human activities at a regional scale.
基金The Second Tibetan Plateau Scientific Expedition and Research(STEP)Program(2019QZKK0302)The Joint Research Project of the People’s Government of Qinghai Province and Chinese Academy of Sciences(LHZX-2020-07)The National Natural Science Foundation of China(31971507)。
文摘The response of long-term vegetation changes and climate change has been a hot topic in recent research.Previously,a Landsat-based fusion model was developed and used to produce a dataset of normalized vegetation index(NDVI)for the Three-River Headwater region on the Qinghai-Tibet Plateau with a spatial resolution of 30 m and the time spanning the nearly 30 years from 1990 to 2018.In this study,the NDVI was applied to an analysis of the spatial and temporal changes in the alpine grassland and the impacts from climate change using the Theil-Sen Median method and linear regression.The results showed that:(1)The regional mean NDVI was 0.39and showed a spatial pattern of decreasing from the southeast to the northwest in the recent three decades.Among the three parks,the Lancang River Park had the highest NDVI(0.43),followed by the Yellow River Park(0.38)and Yangtze River Park(0.23).(2)An upward trending was found in the NDVI time series at a rate of 0.0031 yr^(-1)(R^(2)=0.62,P<0.01)over the whole period of 1990–2018.The increasing rate(0.00649 yr^(-1),R^(2)=0.71,P<0.01)in the latter period of 2005–2018 was nearly 2.3 times of that(0.00284 yr^(-1),R^(2)=0.31,P<0.01)in the previous period of1990–2005.In the latest periods,the three parks experienced rates that were 2.3 to 63 times the corresponding values in the early period.(3)The NDVI is correlated more positively with temperature than precipitation.The impacts of climate change decreased along with the coverage fraction from the higher,median and then lower levels.The climate change can explain 34%of the variability in the NDVI time series of the areas with a higher fraction of grassland coverage,while it was 31%for the median fraction and 20%for the lower fraction.This study is the first to use the 30 m NDVI dataset spanning nearly 30 years to analyze the spatial and temporal variability and climate impacts in the alpine grasslands of the Three-River Headwater region of the Qinghai-Tibet Plateau.The results provide a basis for assessments on the ecological management effects and ecological quality based on long-term baseline data with a higher spatial resolution.
基金The National Key Basic Research and Development Program (2017YFC0503803)The National Natural Science Foundation of China (31971507)+1 种基金Qinghai Province Science and Technology Program (2018-ZJ-T09)CAS-Qinghai Province Joint Program on Three-River Headwaters National Park (YHZX-2020-07)。
文摘The Bowen ratio(β) is used to quantify heat transfer from the land surface into the air, which is becoming a hot topic in research on the biogeophysical effects of land use and cover changes. The Three-River Headwaters(TRH), as a sensitive and fragile region, was selected as the study area. The β for 2001–2018 was estimated from the evapotranspiration product(ETMOD16) of MODIS and the net radiation of the land surface through the albedo from GLASS. The ETMOD16 data were evaluated against the observation data(ETOBS) at two alpine grassland flux towers obtained from ChinaFLUX. The interannual trend of the β was analyzed by multiple linear regression(MLR) and structure model(SEM) with the multiple factors of precipitation, temperature, humidity, albedo, and normalized difference vegetation index(NDVI, MOD09 Q1). The results show that the ETMOD16 values were significantly correlated with ETOBS, with a correlation coefficient above 0.70(P < 0.01) for the two sites. In 2001–2018, the regional mean β was 2.52 ± 0.77 for the whole grassland, and its spatial distribution gradually increased from the eastern to western region. The interannual β showed a downward trend with a slope of-0.025 and a multiple regression coefficient(R^(2)) of 0.21(P = 0.056). Most of the variability(51%) in the interannual β can be explained by the linear regression of the above multiple factors, and the temperature plays a dominant role for the whole region. The SEM analysis further shows that an increasing NDVI results in a decreasing albedo with a path coefficient of-0.57, because the albedo was negatively correlated with NDVI(R^(2) = 0.52, P < 0.01), which indicates a negative and indirect effect on β from vegetation restoration. An obvious warming climate was found to prompt more evapotranspiration, and restoring vegetation makes the land surface receive more radiation, which both resulted in a decreasing trend in the annual β. This study revealed the biogeophysical mechanisms of vegetation restoration under a changing climate, and demonstrated the Bowen ratio can be applied as an indicator of climate-regulating functions in ecosystem assessments.
基金The National Key Research&Development Program of China(2016YFC0500204)The National Natural Science Foundation of China(41571130043,31420103917,31971512)。
文摘Karst areas in southwest China have experienced significant land cover and land use change(LUCC)due to utilization for human activity and a comprehensive rocky desertification control project(RDCP)since 2008.It is important to quantify the effect of LUCC on ecosystem productivity in this region for assessing the overall benefit of this ecological restoration project.In this study,we used using MODIS land cover and NPP products to investigate the relative contribution of LUCC to the change in net primary productivity(NPP)during 2008–2013 in Huanjiang County,one of first one hundred pilot counties to implement RDCP.Our results show that NPP increased in 95.53%of the county,and the average growth of NPP in non-rocky desertification area was higher than in rocky desertification or potential rocky desertification areas.LUCC has an important contribution(25.23%)to the NPP increase in the county,especially in the LUCC area(70.97%),which increased the average NPP by 3.9%and 10.5%,respectively.Across the six RDCP regions in the county,the average increase in NPP for the vegetation restoration measure of governed karst area is significantly greater than in the ungoverned karst area,and the positive change in NPP increased with the increasing implementation area of the vegetation restoration measure.
基金The Strategic Priority Research Program of Chinese Academy of Sciences (Pan-TPE, XDA2003020202)The National Natural Science Foundation of China (31961143022)。
文摘Shifting sands are one of the main contributors to desertification in China. This paper briefly reviews the measures and techniques which are used to protect traffic lines by stabilizing and fixing sands in the desert and desertification-affected arid and semi-arid areas in north China. We introduce the types and features of these measures and techniques, including mechanical, chemical, and biological measures, and outline how they have been applied in different areas and in different traffic lines over the past six decades, from 1950 s to 2010 s, taking the Baotou-Lanzhou railway, the Qinghai-Tibet railway, and the Tarim Desert highway as examples Mechanical measures such as erecting sand-retaining wind walls and placing straw checkerboards have proved to be very efficient for stabilizing shifting sands and protecting traffic lines that pass through the desert areas. Chemical measures are not widely used in the current sand fixing systems because of their high cost and potential pollution risks. Biological measures are preferred because they exhibit much better sand fixation performance and longer duration than the former two types of measures despite their relatively high cost. A combination of different measures is usually adopted in some areas to attain better sand-fixing effects. Stabilizing sand dune surfaces with mechanical measures or irrigation from underground water or river if available helps early recruitment of some drought-tolerant plants(xerophytes). We also point out the restrictions for existing sand-fixing measures and techniques and future research orientation. This review has implications for addressing eco-environmental issues associated with infrastructure construction that is part of the Belt and Road Initiative in desert and desertification-affected arid and semi-arid areas in the Mongolian Plateau.
基金supported by the National Key R&D Program of China(Grant No.2019YFA0607304)。
文摘Understanding the stability of terrestrial carbon sinks(S-TCS)contributes to more accurate prediction of the terrestrial carbon sink(TCS)in the context of future global change and helps inform climate change mitigation policies.Here,focusing on China,we analyzed the spatial distribution and driving mechanisms for the S-TCS,quantified by the interannual variability of the TCS,using three independent approaches(atmospheric inversions,ecosystem carbon cycle models,and machine learning models based on flux tower observations).We found that the interannual variability of the TCS in China is relatively small compared with the conterminous United States and geographic Europe,indicating a generally stable TCS in China.Spatially,the S-TCS is lower in the North China Plain,Northeast China Plain,and western Yunnan-Guizhou Plateau than in other regions,with varying underlying mechanisms.Large interannual variations in precipitation and high TCS sensitivities to precipitation fluctuations explain the low S-TCS in the North China Plain and Northeast China Plain,while high TCS sensitivities to temperature variations drive the low S-TCS in the western Yunnan-Guizhou Plateau.Our findings highlight the importance of considering local contexts for stabilizing and enhancing China’s TCS in a changing environment.
基金Second Tibetan Plateau Scientific Expedition and Research(STEP)program(Grant No.2019QZKK0302)CAS-Qinghai Province Joint program on Three-River Headwaters National Park(Grant No.LHZX-2020-07)Qinghai Natural Science Fund Innovation Team Project(Grant No.2021-ZJ-902).
文摘Background:An accurate assessment of the carbon budget is a crucial part of projecting future climate change and its impact on ecosystems.Grasslands foster multiple ecological functions including support for wild animals and livestocks.Herbivores intake forage biomass carbon,then digest and metabolize,and finally retain some carbon.The carbon processes have not been well quantified,resulting in uncertainties in the estimation of regional carbon budgets for grassland ecosystems.Methods:An animal metabolic carbon flux model was developed for herbivores in the Three-Rivers Headwaters region of China.The forage intake and metabolic carbon rates were estimated through metabolic body weight and daily digested measures for the main herbivore species.Results:The carbon intake was 5.52 Tg C year−1(45%)from partial aboveground biomass(12.2 Tg C year−1),in which 39.31%was released into the atmosphere by respiration CO_(2),43.77%was returned to the ecosystem as feces and urine,and 16.96%was retained in herbivores for population regeneration or for human well-being.Conclusions:This study,as the first research on this topic,quantified the carbon flux of herbivores and found livestock accounts for a major part of consumed carbon on grasslands,which is important for understanding regional carbon budgets to mitigate and adapt to climate change over grasslands worldwide.
文摘Introduction:Climate change is expected to impose significant tension on the geographic distribution of tree species.Yet,tree species range shifts may be delayed by their long life spans,capacity to withstand long periods of physiological stress,and dispersal limitations.Wildfire could theoretically break this biological inertia by killing forest canopies and facilitating species redistribution under changing climate.We investigated the capacity of wildfire to modulate climate-induced tree redistribution across a montane landscape in the central Rocky Mountains under three climate scenarios(contemporary and two warmer future climates)and three wildfire scenarios(representing historical,suppressed,and future fire regimes).Methods:Distributions of four common tree species were projected over 90 years by pairing a climate niche model with a forest landscape simulation model that simulates species dispersal,establishment,and mortality under alternative disturbance regimes and climate scenarios.Results:Three species(Douglas-fir,lodgepole pine,subalpine fir)declined in abundance over time,due to climate-driven contraction in area suitable for establishment,while one species(ponderosa pine)was unable to exploit climate-driven expansion of area suitable for establishment.Increased fire frequency accelerated declines in area occupied by Douglas-fir,lodgepole pine,and subalpine fir,and it maintained local abundance but not range expansion of ponderosa pine.Conclusions:Wildfire may play a larger role in eliminating these conifer species along trailing edges of their distributions than facilitating establishment along leading edges,in part due to dispersal limitations and interspecific competition,and future populations may increasingly depend on persistence in locations unfavorable for their establishment.
