The eddy covariance technique has emerged as an important tool to directly measure carbon dioxide,water vapor and heat fluxes between the terrestrial ecosystem and the atmosphere after a long history of fundamental re...The eddy covariance technique has emerged as an important tool to directly measure carbon dioxide,water vapor and heat fluxes between the terrestrial ecosystem and the atmosphere after a long history of fundamental research and technological developments.With the realization of regional networks of flux measurements in North American,European,Asia,Brazil,Australia and Africa,a global-scale network of micrometeorological flux measurement(FLUXNET)was established in 1998.FLUXNET has made great progresses in investigating the environmental mechanisms controlling carbon and water cycles,quantifying spatial-temporal patterns of carbon budget and seeking the"missing carbon sink"in global terrestrial ecosystems in the past ten years.The global-scale flux measurement also built a platform for international communication in the fields of resource,ecology and environment sciences.With the continuous development of flux research,FLUXNET will introduce and explore new techniques to extend the application fields of flux measurement and to answer questions in the fields of bio-geography,eco-hydrology,meteorology,climate change,remote sensing and modeling with eddy covariance flux data.As an important part of FLUXNET,ChinaFLUX has made significant progresses in the past three years on the methodology and technique of eddy covariance flux measurement,on the responses of CO_(2)and H_(2)O exchange between the terrestrial ecosystem and the atmosphere to environmental change,and on flux modeling development.Results showed that the major forests on the North-South Transect of Eastern China(NSTEC)were all carbon sinks during 2003 to 2005,and the alpine meadows on the Tibet Plateau were also small carbon sinks.However,the reserved natural grassland,Leymus chinensis steppe in Inner Mongolia,was a carbon source.On a regional scale,temperature and precipitation are the primary climatic factors that determined the carbon balance in major terrestrial ecosystems in China.Finally,the current research emphasis and future directions of ChinaFLUX were presented.By combining flux network and terrestrial transect,ChinaFLUX will develop integrated research with multi-scale,multi-process,multi-subject observations,placing emphasis on the mechanism and coupling relationships between water,carbon and nitrogen cycles in terrestrial ecosystems.展开更多
Network of eddy covariance observation is measuring long-term carbon and water fluxes in contrasting ecosystems and climates.As one important reference of independently evaluating scalar flux estimates from eddy covar...Network of eddy covariance observation is measuring long-term carbon and water fluxes in contrasting ecosystems and climates.As one important reference of independently evaluating scalar flux estimates from eddy covariance,energy balance closure is used widely in study of carbon and water fluxes.Energy balance closure in ChinaFLUX was evaluated by statistical regression of turbulent energy fluxes(sensible and latent heat)against available energy(net radiation,soil heat flux,canopy heat storage)and the energy balance ratio(EBR)and the frequency distribution of relative errors of energy balance(S).The trends of diurnal and seasonal variation of energy balance in ChinaFLUX were analyzed.The results indicated that the imbalance was prevalent in all observation sites,but there were little differences among sites because of the properties variation of sites.The imbalance was greater during nocturnal periods than daytime and closure was improved with friction velocity intensifying.Generally the results suggested that estimates of the scalar turbulent fluxes of sensible and latent heat were underestimated and/or that available energy was overestimated.Finally,we discussed certain factors that are contributed to the imbalance of energy,such as systematic errors associated with the sampling mismatch,systematic instrument bias,neglected energy sinks,low and high frequency loss of turbulent fluxes and advection of heat and water vapor.展开更多
Carbon fluxes in temperate grassland ecosystems are characterized by large inter-annual variations due to fluctuations in precipitation and land water availability. Since an eddy flux tower has been in operation in th...Carbon fluxes in temperate grassland ecosystems are characterized by large inter-annual variations due to fluctuations in precipitation and land water availability. Since an eddy flux tower has been in operation in the Xilin Gol grassland, which belongs to typical temperate grassland in North China, in this study, observed eddy covariance flux data were used to critically evaluate the biophysical performance of different remote sensing vegetation indices in relation to carbon fluxes. Furthermore, vegetation photosynthesis model (VPM) was introduced to estimate gross primary production (GPP) of the grassland ecosystem for assessing its dependability. As defined by the input variables of VPM, Moderate Resolution Imaging Spectroradimeter (MODIS) and standard data product MOD09A1 were downloaded for calculating enhanced vegetation index (EVI) and land surface water index (LSWI). Measured air temperature (Ta) and photosynthetically active radiation (PAR) data were also included for model simulating. Field CO2 flux data, during the period from May, 2003 to September, 2005, were used to estimate the “observed” GPP (GPP obs) for validation. The seasonal dynamics of GPP predicted from VPM (GPP VPM) was compared quite well (R 2=0.903, N=111, p<0.0001) with the observed GPP. The aggregate GPP VPM for the study period was 641.5 g C·m?2, representing a ～6% over-estimation, compared with GPP obs. Additionally, GPP predicted from other two typical production efficiency model (PEM) represents either higher overestimation or lower underestimation to GPP obs. Results of this study demonstrate that VPM has potential for estimating site-level or regional grassland GPP, and might be an effective tool for scaling-up carbon fluxes.展开更多
As an important component of FLUXNET,Asia is increasingly becoming the hotspot in global carbon research for its vast territory,complex climate type and vegetation diversity.The present three regional flux observation...As an important component of FLUXNET,Asia is increasingly becoming the hotspot in global carbon research for its vast territory,complex climate type and vegetation diversity.The present three regional flux observation networks in Asia(i.e.AsiaFlux,KoFlux and ChinaFLUX)have 54 flux observation sites altogether,covering tropic rainforest,evergreen broad-leaved forest,broad-leaved and coniferous mixed forest,shrubland,grassland,alpine meadow and cropland ecosystems with a latitudinal distribution from 2°N to 63°N.Long-term and continuous fluxes of carbon dioxide,water vapor and energy between the biosphere and atmosphere are mainly measured with eddy covariance technique to(1)quantify and compare the carbon,water and energy budgets across diverse ecosystems;(2)quantify the environmental and biotic controlling mechanism on ecosystem carbon,water and energy fluxes;(3)validate the soil-vegetation-atmosphere model;and(4)serve the integrated study of terrestrial ecosystem carbon and water cycle.Over the last decades,great advancements have been made in the theory and technology of flux measurement,ecosystem flux patterns,simulation and scale conversion by Asian flux community.The establishment of ChinaFLUX has greatly filled the gap of flux observation and research in Eurasia.To further promote the flux measurement and research,accelerate data sharing and improve the data quality,it is necessary to present a methodological system of flux estimation and evaluation over complex terrain and to develop the integrated research that combines the flux measurement,stable isotope measurement,remote sensing observation and GIS technique.It also requires the establishment of the Joint Committee of Asian Flux Network in the Asia-Pacific region in order to promote the cooperation and communication of ideas and data by supporting project scientists,workshops and visiting scientists.展开更多
Many studies on global climate have forecast major changes in the amounts and spatial patterns of precipitation that may significantly affect temperate grasslands in arid and semi-arid regions.As a part of ChinaFLUX,e...Many studies on global climate have forecast major changes in the amounts and spatial patterns of precipitation that may significantly affect temperate grasslands in arid and semi-arid regions.As a part of ChinaFLUX,eddy covariance flux measurements were made at a semi-arid Leymus chinensis steppe in Inner Mongolia,China during 2003-2004 to quantify the response of carbon exchange to environmental changes.Results showed that gross ecosystem production(FGEP)and ecosystem respiration(Reco)of the steppe were significantly depressed by water stress due to lack of precipitation during the growing season.Temperature was the dominant factor affecting FGEP and Reco in 2003,whereas soil moisture imposed a significant influence on both Reco and FGEP in 2004.Under wet conditions,Reco showed an exponentially increasing trend with temperature(Q10=2.0),but an apparent reduction in the value of Reco and its temperature sensitivity were observed during the periods of water stress(Q10=1.6).Both heat and water stress can cause decrease in FGEP.The sea-sonality of ecosystem carbon exchange was strongly correlated with the variation of precipitation.With less precipitation in 2003,the steppe sequestrated carbon in June and July,and went into a senescence in early August due to water stress.As compared to 2003,the severe drought during the spring of 2004 delayed the growth of the steppe until late June,and the steppe became a CO_(2)sink from early July until mid-September,with ample precipitation in August.The semi-arid steppe released a total of 9.7 g C·m-2 from May 16 to the end of September 2003,whereas the net carbon budget during the same period in 2004 was close to zero.Long-term measurements over various grasslands are needed to quantify carbon balance in temperate grasslands.展开更多
To assess carbon budget for shrub ecosystems on the Qinghai-Tibet Plateau,CO_(2)flux was measured with an open-path eddy covariance system for an alpine shrub ecosystem during growing and non-growing seasons.CO_(2)flu...To assess carbon budget for shrub ecosystems on the Qinghai-Tibet Plateau,CO_(2)flux was measured with an open-path eddy covariance system for an alpine shrub ecosystem during growing and non-growing seasons.CO_(2)flux dynamics was distinct between the two seasons.During the growing season from May to September,the ecosystem exhibited net CO_(2)uptake from 08:00 to 19:00(Beijing Standard Time),but net CO_(2)emission from 19:00 to 08:00.Maximum CO_(2)uptake appeared around 12:00 with values of 0.71,1.19,1.46 and 0.67 g CO_(2)m-2 h-1 for June,July,August and September,respectively.Diurnal fluctuation of CO_(2)flux showed higher correlation with photosynthetic photon flux density than temperature.The maximum net CO_(2)influx occurred in August with a value of 247 g CO_(2)m-2.The total CO_(2)uptake by the ecosystem was up to 583 g CO_(2)m-2 for the growing season.During the non-growing season from January to April and from October to December,CO_(2)flux showed small fluctuation with the largest net CO_(2)efflux of 0.30 g CO_(2)m-2 h-1 in April.The diurnal CO_(2)flux was close to zero during most time of the day,but showed a small net CO_(2)efflux from 11:00 to 18:00.Diurnal CO_(2)flux,is significantly correlated to diurnal temperature in the non-growing season.The maximum monthly net CO_(2)efflux appeared in April,with a value of 105 g CO_(2)m-2.The total net CO_(2)efflux for the whole non-growing season was 356 g CO_(2)m-2.展开更多
文摘The eddy covariance technique has emerged as an important tool to directly measure carbon dioxide,water vapor and heat fluxes between the terrestrial ecosystem and the atmosphere after a long history of fundamental research and technological developments.With the realization of regional networks of flux measurements in North American,European,Asia,Brazil,Australia and Africa,a global-scale network of micrometeorological flux measurement(FLUXNET)was established in 1998.FLUXNET has made great progresses in investigating the environmental mechanisms controlling carbon and water cycles,quantifying spatial-temporal patterns of carbon budget and seeking the"missing carbon sink"in global terrestrial ecosystems in the past ten years.The global-scale flux measurement also built a platform for international communication in the fields of resource,ecology and environment sciences.With the continuous development of flux research,FLUXNET will introduce and explore new techniques to extend the application fields of flux measurement and to answer questions in the fields of bio-geography,eco-hydrology,meteorology,climate change,remote sensing and modeling with eddy covariance flux data.As an important part of FLUXNET,ChinaFLUX has made significant progresses in the past three years on the methodology and technique of eddy covariance flux measurement,on the responses of CO_(2)and H_(2)O exchange between the terrestrial ecosystem and the atmosphere to environmental change,and on flux modeling development.Results showed that the major forests on the North-South Transect of Eastern China(NSTEC)were all carbon sinks during 2003 to 2005,and the alpine meadows on the Tibet Plateau were also small carbon sinks.However,the reserved natural grassland,Leymus chinensis steppe in Inner Mongolia,was a carbon source.On a regional scale,temperature and precipitation are the primary climatic factors that determined the carbon balance in major terrestrial ecosystems in China.Finally,the current research emphasis and future directions of ChinaFLUX were presented.By combining flux network and terrestrial transect,ChinaFLUX will develop integrated research with multi-scale,multi-process,multi-subject observations,placing emphasis on the mechanism and coupling relationships between water,carbon and nitrogen cycles in terrestrial ecosystems.
基金was supported by the Chinese Academy of Sciences(Grant No.KZCX1-SW-01)the Ministry of Science and Technology of China(Grant No.2002CB412500).
文摘Network of eddy covariance observation is measuring long-term carbon and water fluxes in contrasting ecosystems and climates.As one important reference of independently evaluating scalar flux estimates from eddy covariance,energy balance closure is used widely in study of carbon and water fluxes.Energy balance closure in ChinaFLUX was evaluated by statistical regression of turbulent energy fluxes(sensible and latent heat)against available energy(net radiation,soil heat flux,canopy heat storage)and the energy balance ratio(EBR)and the frequency distribution of relative errors of energy balance(S).The trends of diurnal and seasonal variation of energy balance in ChinaFLUX were analyzed.The results indicated that the imbalance was prevalent in all observation sites,but there were little differences among sites because of the properties variation of sites.The imbalance was greater during nocturnal periods than daytime and closure was improved with friction velocity intensifying.Generally the results suggested that estimates of the scalar turbulent fluxes of sensible and latent heat were underestimated and/or that available energy was overestimated.Finally,we discussed certain factors that are contributed to the imbalance of energy,such as systematic errors associated with the sampling mismatch,systematic instrument bias,neglected energy sinks,low and high frequency loss of turbulent fluxes and advection of heat and water vapor.
基金the International Partnership Project of Chinese Academy of Sciences (Grant No. CXTD-Z2005-1)National Basic Research Program of China (Grant No. 2002CB412501)NASA Land Cover and Land Use Change (LCLUC) Program (Grant Nos. NAG5-11160, NNG05GH80G)
文摘Carbon fluxes in temperate grassland ecosystems are characterized by large inter-annual variations due to fluctuations in precipitation and land water availability. Since an eddy flux tower has been in operation in the Xilin Gol grassland, which belongs to typical temperate grassland in North China, in this study, observed eddy covariance flux data were used to critically evaluate the biophysical performance of different remote sensing vegetation indices in relation to carbon fluxes. Furthermore, vegetation photosynthesis model (VPM) was introduced to estimate gross primary production (GPP) of the grassland ecosystem for assessing its dependability. As defined by the input variables of VPM, Moderate Resolution Imaging Spectroradimeter (MODIS) and standard data product MOD09A1 were downloaded for calculating enhanced vegetation index (EVI) and land surface water index (LSWI). Measured air temperature (Ta) and photosynthetically active radiation (PAR) data were also included for model simulating. Field CO2 flux data, during the period from May, 2003 to September, 2005, were used to estimate the “observed” GPP (GPP obs) for validation. The seasonal dynamics of GPP predicted from VPM (GPP VPM) was compared quite well (R 2=0.903, N=111, p<0.0001) with the observed GPP. The aggregate GPP VPM for the study period was 641.5 g C·m?2, representing a ～6% over-estimation, compared with GPP obs. Additionally, GPP predicted from other two typical production efficiency model (PEM) represents either higher overestimation or lower underestimation to GPP obs. Results of this study demonstrate that VPM has potential for estimating site-level or regional grassland GPP, and might be an effective tool for scaling-up carbon fluxes.
基金supported by the Knowledge Innovation Project of the Chinese Academy of Sciences(Grant No.KZCX1-SW-01-01A)the National Key Research and Development Program(Grant No.2002CB412501).
文摘As an important component of FLUXNET,Asia is increasingly becoming the hotspot in global carbon research for its vast territory,complex climate type and vegetation diversity.The present three regional flux observation networks in Asia(i.e.AsiaFlux,KoFlux and ChinaFLUX)have 54 flux observation sites altogether,covering tropic rainforest,evergreen broad-leaved forest,broad-leaved and coniferous mixed forest,shrubland,grassland,alpine meadow and cropland ecosystems with a latitudinal distribution from 2°N to 63°N.Long-term and continuous fluxes of carbon dioxide,water vapor and energy between the biosphere and atmosphere are mainly measured with eddy covariance technique to(1)quantify and compare the carbon,water and energy budgets across diverse ecosystems;(2)quantify the environmental and biotic controlling mechanism on ecosystem carbon,water and energy fluxes;(3)validate the soil-vegetation-atmosphere model;and(4)serve the integrated study of terrestrial ecosystem carbon and water cycle.Over the last decades,great advancements have been made in the theory and technology of flux measurement,ecosystem flux patterns,simulation and scale conversion by Asian flux community.The establishment of ChinaFLUX has greatly filled the gap of flux observation and research in Eurasia.To further promote the flux measurement and research,accelerate data sharing and improve the data quality,it is necessary to present a methodological system of flux estimation and evaluation over complex terrain and to develop the integrated research that combines the flux measurement,stable isotope measurement,remote sensing observation and GIS technique.It also requires the establishment of the Joint Committee of Asian Flux Network in the Asia-Pacific region in order to promote the cooperation and communication of ideas and data by supporting project scientists,workshops and visiting scientists.
基金This study was supported by the Chi-nese Academy of Sciences and the Ministry of Science and Technology through grants KZCX1-SW-01 and 2002CB412500.
文摘Many studies on global climate have forecast major changes in the amounts and spatial patterns of precipitation that may significantly affect temperate grasslands in arid and semi-arid regions.As a part of ChinaFLUX,eddy covariance flux measurements were made at a semi-arid Leymus chinensis steppe in Inner Mongolia,China during 2003-2004 to quantify the response of carbon exchange to environmental changes.Results showed that gross ecosystem production(FGEP)and ecosystem respiration(Reco)of the steppe were significantly depressed by water stress due to lack of precipitation during the growing season.Temperature was the dominant factor affecting FGEP and Reco in 2003,whereas soil moisture imposed a significant influence on both Reco and FGEP in 2004.Under wet conditions,Reco showed an exponentially increasing trend with temperature(Q10=2.0),but an apparent reduction in the value of Reco and its temperature sensitivity were observed during the periods of water stress(Q10=1.6).Both heat and water stress can cause decrease in FGEP.The sea-sonality of ecosystem carbon exchange was strongly correlated with the variation of precipitation.With less precipitation in 2003,the steppe sequestrated carbon in June and July,and went into a senescence in early August due to water stress.As compared to 2003,the severe drought during the spring of 2004 delayed the growth of the steppe until late June,and the steppe became a CO_(2)sink from early July until mid-September,with ample precipitation in August.The semi-arid steppe released a total of 9.7 g C·m-2 from May 16 to the end of September 2003,whereas the net carbon budget during the same period in 2004 was close to zero.Long-term measurements over various grasslands are needed to quantify carbon balance in temperate grasslands.
基金supported by the Knowledge Innovation Project of the Chinese Academy of Sci-ences(Grant Nos.KZCX1-SW-01-01A5and KZCX1-09-01)the State Key Basic Research Plan of China(GrantNo.2002CB412501)+2 种基金and partly by the joint research projects between National Institute for En-vironmental Studies,Japan and Northwest Plateau Institute of BiologyChinese Academy of Sciences(Grant Nos.13575035 and B13)as well as partly by the project of Asia-PacificEnvironmental Innovation Strategy(APEIS).
文摘To assess carbon budget for shrub ecosystems on the Qinghai-Tibet Plateau,CO_(2)flux was measured with an open-path eddy covariance system for an alpine shrub ecosystem during growing and non-growing seasons.CO_(2)flux dynamics was distinct between the two seasons.During the growing season from May to September,the ecosystem exhibited net CO_(2)uptake from 08:00 to 19:00(Beijing Standard Time),but net CO_(2)emission from 19:00 to 08:00.Maximum CO_(2)uptake appeared around 12:00 with values of 0.71,1.19,1.46 and 0.67 g CO_(2)m-2 h-1 for June,July,August and September,respectively.Diurnal fluctuation of CO_(2)flux showed higher correlation with photosynthetic photon flux density than temperature.The maximum net CO_(2)influx occurred in August with a value of 247 g CO_(2)m-2.The total CO_(2)uptake by the ecosystem was up to 583 g CO_(2)m-2 for the growing season.During the non-growing season from January to April and from October to December,CO_(2)flux showed small fluctuation with the largest net CO_(2)efflux of 0.30 g CO_(2)m-2 h-1 in April.The diurnal CO_(2)flux was close to zero during most time of the day,but showed a small net CO_(2)efflux from 11:00 to 18:00.Diurnal CO_(2)flux,is significantly correlated to diurnal temperature in the non-growing season.The maximum monthly net CO_(2)efflux appeared in April,with a value of 105 g CO_(2)m-2.The total net CO_(2)efflux for the whole non-growing season was 356 g CO_(2)m-2.
