Responses Of Vegetation Carbon And Water Use Efficiencies To Climate And Land Use Changes In China’s Karst Areas

Wide distribution of karst areas in China,accounting for over one-third of the country’s land area.It is crucial to reveal the influencing factors of vegetation carbon use efficiency（CUE）and water use efficiency（WUE）in ecosystems.However,the relationship between climate and land use change and karst CUE and WUE in China is still unclear.Therefore,based on China’s high-precision climate data,land use data,total primary productivity（GPP）,net primary productivity（NPP）and evapotranspiration（ET）data from 2000 to 2020,this paper discusses the response of CUE and WUE to climate and land use change in karst areas by using Theil-Sen trend analysis,Mann-Kendall test,partial derivative and other methods.The spatial and temporal distribution and change of CUE and WUE in karst areas are revealed;On this basis,the impacts of climate and land use change on CUE and WUE are analyzed;The contribution value and contribution rate of climate and land use change to CUE and WUE are quantified.The following conclusions are obtained:（1）The solar radiation shows a significant downward trend.From2000 to 2020,the average values of precipitation,temperature,solar radiation,and evapotranspiration were 707.88 mm,7.733℃,and5395.59 MJ m^-2,respectively.Precipitation and temperature show an increasing trend,with trend values of 1.94 mm yr^-1and 0.017℃yr^-1,respectively.The solar radiation shows a decreasing trend,with a trend value of-9.4 MJ m^-2yr^-1.（2）In wasteland,the CUE value is highest and the WUE value is lowest.The average value of CUE is 0.541,showing an increasing trend during the study period(1.6×10^-3yr^-1),the average WUE is 1.251g C kg^-1H₂O,showing an overall downward trend(-2.7×10^-3g C kg^-1H₂O yr^-1).Among all land use types,wasteland has the highest CUE value（0.624）,forest land has the highest WUE value(1.747 g C kg^-1H₂O),and wasteland has the lowest WUE value(0.276 g C kg^-1H₂O).（3）The contribution of solar radiation to CUE and WUE and the area of the main control area are the largest.The contribution values of precipitation and solar radiation to CUE are 0.262 and 0.638,respectively,and the contribution values to WUE are 0.218 and 0.794,respectively.The areas controlled by precipitation and solar radiation on CUE account for 31.2%and 48.19%of the total area,respectively,while the areas controlled by WUE account for 34.58%and 45.44%of the total area,respectively.The contribution rates of solar radiation to CUE and WUE are 33.86%and 32.65%,respectively,mainly distributed in the karst areas of the Qinghai Tibet Plateau and the northern karst areas.Overall,CUE shows an upward trend while WUE shows a downward trend.The contribution value,main control area,and contribution rate of solar radiation to CUE and WUE are the largest among the four factors.Deeply studying the impact of climate and land use change on CUE and WUE is of great significance for clarifying the carbon water cycle of ecosystems,the response mechanism to climate change,and promoting the healthy development of the ecological environment.