Investigations Of Tree-ring Growths And Stable Isotopes In Fuzhou

Understanding the responses of tree growth and intrinsic water-use efficiency(iWUE)to anthropogenic CO2 increase and climate warming provides important benchmarks for evaluating future forest dynamics under different scenarios of warming and CO2 changes.Relative to short instrumental data of the past few decades,long-term tree-ring width and stable carbon isotopic(?13C)data are invaluable to fully comprehend their interactions during the entire industrial era since?1850.Here,we present a tree-ring width chronology(1856-2015)and ?13C series(1876-2015)of Pinus massoniana for Yongtai county of Fujian province,humid subtropical China,a "green island" relative to other dry subtropical area of the world.Tree growth was limited by precipitation of a hydrological year from previous November to current October(r = 0.568,p<0.001)and the stable carbon isotope discrimination(?13C)was strongly correlated with relative humidity in September-October(r =-0.677,p<0.001)of current growing season.We found that the iWUE increased by 40.9%since 1876 and the atmospheric CO2 concentration(ca)explained 93.9%of the iWUE variance during the study period.Specifically,we found that the ci/ca decreased during the study period whereas intercellular CO2 concentration(ci)increased.The negative relationship between tree-ring width and iWUE indicated that increasing iWUE may not lead to long-term enhancement of tree growth.Our results indicated that drought-induced limitation of tree growth response to rising CO2,and trees may mitigate the negative effects of a decrease in water availability through a reduction in stomatal conductance.