The mechanism of plant response to water availability is a crucial research area in ecosystem adaptation to dry environments.Global change in precipitation patterns exacerbates drought risks in many regions,necessitat...The mechanism of plant response to water availability is a crucial research area in ecosystem adaptation to dry environments.Global change in precipitation patterns exacerbates drought risks in many regions,necessitating investigations of tree responses to drought.However,compared with seasonal drought events,how water use characteristics respond to long-term rainfall reduction remains poorly characterized.Here,we assessed the effects of multi-year rainfall exclusion treatments(in the 4th and 5th years)on sap flow,canopy conductance(G_(C)),and the response pattern to varying transpiration driving force(vapor pressure deficit(VPD))and soil moisture conditions in a black locust(Robinia pseudoacacia)plantation in the China's Loess Plateau.The experimental platform includes paired plots of a 30%throughfall exclusion treatment and a control within the plantation.The reduction of soil water content(SWC),either as temporal variations or as a result of rainfall exclusion treatment,generally lowered sap flow,G_(C),and the sensitivity to VPD.The difference in each index between plots was substantially greater than that among temporal variations in SWC within a plot.The trees in the control plot showed strong responses of G_(C)to temporal SWC changes,exhibiting an isohydric behavior.However,those subjected to long-term rainfall exclusion treatment had lower variations in G_(C)and the sensitivity across different SWC,exhibiting an anisohydric behavior under limited water conditions.Additionally,rainfall exclusion treatment decreased basal area(BA)increment but increased water use efficiency(WUE).The transition to anisohydric behavior suggests an adventurous pattern of water use strategy that has risks of hydraulic damage and shoot mortality.These findings provide insights into the different adaptation strategies within a species to diverse intensity and duration of drought conditions,which is crucial for sustainable forest management under climate change conditions.展开更多
To understand the seasonal variations of water use efficiency(WUE)of coniferous plantation in the subtropical monsoon area,the experiment was conducted in 2003 and 2004 which presented two distinguished climatic condi...To understand the seasonal variations of water use efficiency(WUE)of coniferous plantation in the subtropical monsoon area,the experiment was conducted in 2003 and 2004 which presented two distinguished climatic conditions(severe summer drought in 2003 and normal climatic condition in 2004).The water stress influenced WUE greatly,which caused a special seasonal WUE pattern.WUE reached the minimum in summer drought and the maximum in winter,which was contrary to the variation of gross primary production(GPP)and canopy evaporation(Fw).In winter,GPP and Fw increased along with the increasing of air temperature and vapor pressure deficit(VPD),with the similar increasing rate.However,in drought summer,there was an adverse trend among GPP/Fw and air temperature and VPD,and the decreasing rate of GPP was far larger than that of Fw.In summer,the conservation of WUE was changed because of the environmental factors,resulting in the decreasing WUE.The photosynthesis and transpiration of vegetation were mainly controlled by the environmental factors in winter,and the impact of stomatal regulation was relatively weak.In summer,Fw was mainly controlled by the stomatal closure and GPP by both environmental factors and stomatal closure.展开更多
We constructed a coupled model for simulating plant photosynthesis and evapotranspiration (CPCEM). In the model, non-rectangular hyperbola is used to simulate leaf photosynthesis rate that is scaled up to estimate can...We constructed a coupled model for simulating plant photosynthesis and evapotranspiration (CPCEM). In the model, non-rectangular hyperbola is used to simulate leaf photosynthesis rate that is scaled up to estimate canopy gross photosynthesis rate by an integral method. Whole canopy in the model is separated into multi-layers, each of which is divided into sunlit leaves and shade leaves. Canopy net photosynthesis rate is expressed as a function of canopy conductance which is coupled with evapotranspiration. Included the coupled function,evapotranspiration is estimated with a two-layer submodel. The main features of CPCEM are: (1)easy suitability, (2) good physiological base, and (3) simple calculation procedure. Simulated results of CPCEM were compared with those by an eddy covariance system that was installed in a winter wheat farmland of the North China Plain. CPCEM gave a quite well diurnal and seasonal dynamics of net ecosystem exchange, compared with the measurements. The root mean square error between simulation and measurements was only about 2.94 μ mol m-2 s-1. Diurnal and seasonal patterns of latent heat flux with the CPCEM were similar to those of measurements.Whereas, simulated latent heat flux was evidently higher than the measured.展开更多
Aims Changing climate and land use patterns make it increasingly important that the hydrology of catchments and ecosystems can be reliably characterized.The aim of this paper is to identify the biophysical factors tha...Aims Changing climate and land use patterns make it increasingly important that the hydrology of catchments and ecosystems can be reliably characterized.The aim of this paper is to identify the biophysical factors that determine the rates of water vapor loss from different types of vegetation,and to seek,from an array of currently available satelliteborne sensors,those that might be used to initialize and drive landscape-level hydrologic models.Important Findings Spatial variation in the mean heights,crowd widths,and leaf area indices(LAI)of plant communities are important structural variables that affect the hydrology of landscapes.Canopy stomatal conductance(G)imposes physiological limitation on transpiration by vegetation.The maximum value of G(Gmax)is closely linked to canopy photosynthetic capacity,which can be estimated via remote sensing of foliar chlorophyll or nitrogen contents.Gcan be modeled as a nonlinear multipliable function of:(i)leaf–air vapor pressure deficit,(ii)water potential gradient between soil and leaves,(iii)photosynthetically active radiation absorbed by the canopy,(iv)plant nutrition,(v)temperature and(vi)the CO_(2) concentration of the air.Periodic surveys with Light Detection and Ranging(LiDAR)and interferometric RADAR,along with high-resolution spectral coverage in the visible,near-infrared,and thermal infrared bands,provide,along with meteorological data gathered from weather satellites,the kind of information required to model seasonal and interannual variation in transpiration and evaporation from landscapes with diverse and dynamic vegetation.展开更多
基金supported by the National Key R&D Program of China(No.2017YFC0504601)an open fund of the State Key Laboratory of Soil and Water Conservation and Desertification Control(No.F2010121002-202424).
文摘The mechanism of plant response to water availability is a crucial research area in ecosystem adaptation to dry environments.Global change in precipitation patterns exacerbates drought risks in many regions,necessitating investigations of tree responses to drought.However,compared with seasonal drought events,how water use characteristics respond to long-term rainfall reduction remains poorly characterized.Here,we assessed the effects of multi-year rainfall exclusion treatments(in the 4th and 5th years)on sap flow,canopy conductance(G_(C)),and the response pattern to varying transpiration driving force(vapor pressure deficit(VPD))and soil moisture conditions in a black locust(Robinia pseudoacacia)plantation in the China's Loess Plateau.The experimental platform includes paired plots of a 30%throughfall exclusion treatment and a control within the plantation.The reduction of soil water content(SWC),either as temporal variations or as a result of rainfall exclusion treatment,generally lowered sap flow,G_(C),and the sensitivity to VPD.The difference in each index between plots was substantially greater than that among temporal variations in SWC within a plot.The trees in the control plot showed strong responses of G_(C)to temporal SWC changes,exhibiting an isohydric behavior.However,those subjected to long-term rainfall exclusion treatment had lower variations in G_(C)and the sensitivity across different SWC,exhibiting an anisohydric behavior under limited water conditions.Additionally,rainfall exclusion treatment decreased basal area(BA)increment but increased water use efficiency(WUE).The transition to anisohydric behavior suggests an adventurous pattern of water use strategy that has risks of hydraulic damage and shoot mortality.These findings provide insights into the different adaptation strategies within a species to diverse intensity and duration of drought conditions,which is crucial for sustainable forest management under climate change conditions.
基金This work was supported by the Na-tional Outstanding Young Scientists Foundation of China(Grant No.30225012)the Knowledge Innovation Program of the Chinese Academy of Sciences(Grant No.KZCX1-SW01-01A)+1 种基金the National Basic Research Program of China(Grant No 2002CB412501)the Asia-Pacific Environ-mental Innovation Strategy Project(APEIS).
文摘To understand the seasonal variations of water use efficiency(WUE)of coniferous plantation in the subtropical monsoon area,the experiment was conducted in 2003 and 2004 which presented two distinguished climatic conditions(severe summer drought in 2003 and normal climatic condition in 2004).The water stress influenced WUE greatly,which caused a special seasonal WUE pattern.WUE reached the minimum in summer drought and the maximum in winter,which was contrary to the variation of gross primary production(GPP)and canopy evaporation(Fw).In winter,GPP and Fw increased along with the increasing of air temperature and vapor pressure deficit(VPD),with the similar increasing rate.However,in drought summer,there was an adverse trend among GPP/Fw and air temperature and VPD,and the decreasing rate of GPP was far larger than that of Fw.In summer,the conservation of WUE was changed because of the environmental factors,resulting in the decreasing WUE.The photosynthesis and transpiration of vegetation were mainly controlled by the environmental factors in winter,and the impact of stomatal regulation was relatively weak.In summer,Fw was mainly controlled by the stomatal closure and GPP by both environmental factors and stomatal closure.
文摘We constructed a coupled model for simulating plant photosynthesis and evapotranspiration (CPCEM). In the model, non-rectangular hyperbola is used to simulate leaf photosynthesis rate that is scaled up to estimate canopy gross photosynthesis rate by an integral method. Whole canopy in the model is separated into multi-layers, each of which is divided into sunlit leaves and shade leaves. Canopy net photosynthesis rate is expressed as a function of canopy conductance which is coupled with evapotranspiration. Included the coupled function,evapotranspiration is estimated with a two-layer submodel. The main features of CPCEM are: (1)easy suitability, (2) good physiological base, and (3) simple calculation procedure. Simulated results of CPCEM were compared with those by an eddy covariance system that was installed in a winter wheat farmland of the North China Plain. CPCEM gave a quite well diurnal and seasonal dynamics of net ecosystem exchange, compared with the measurements. The root mean square error between simulation and measurements was only about 2.94 μ mol m-2 s-1. Diurnal and seasonal patterns of latent heat flux with the CPCEM were similar to those of measurements.Whereas, simulated latent heat flux was evidently higher than the measured.
文摘Aims Changing climate and land use patterns make it increasingly important that the hydrology of catchments and ecosystems can be reliably characterized.The aim of this paper is to identify the biophysical factors that determine the rates of water vapor loss from different types of vegetation,and to seek,from an array of currently available satelliteborne sensors,those that might be used to initialize and drive landscape-level hydrologic models.Important Findings Spatial variation in the mean heights,crowd widths,and leaf area indices(LAI)of plant communities are important structural variables that affect the hydrology of landscapes.Canopy stomatal conductance(G)imposes physiological limitation on transpiration by vegetation.The maximum value of G(Gmax)is closely linked to canopy photosynthetic capacity,which can be estimated via remote sensing of foliar chlorophyll or nitrogen contents.Gcan be modeled as a nonlinear multipliable function of:(i)leaf–air vapor pressure deficit,(ii)water potential gradient between soil and leaves,(iii)photosynthetically active radiation absorbed by the canopy,(iv)plant nutrition,(v)temperature and(vi)the CO_(2) concentration of the air.Periodic surveys with Light Detection and Ranging(LiDAR)and interferometric RADAR,along with high-resolution spectral coverage in the visible,near-infrared,and thermal infrared bands,provide,along with meteorological data gathered from weather satellites,the kind of information required to model seasonal and interannual variation in transpiration and evaporation from landscapes with diverse and dynamic vegetation.
