In recent years,the development of experimental and analytical methods has greatly increased the number of publications related to tree-ring stable carbon(C)isotopes.Based on the bibliometric method,we summarized related studies and categorized them into three major themes:'climatology','physiology',and'ecology'.The results showed that:studies on tree-ring stable C isotopes were clustered in the mid-latitude Northern Hemisphere,with fewer sites in low and high latitudes and the Southern Hemisphere.The published works were mainly focused on climatology and physiology while there was fewer research in the field of ecology.The analysis of climate sensitivity of indicated that tree-ring stable C isotopes correlate positively to temperatures in 88.46％of the total sampling sites and that C isotopes from about 81.25％sites respond negatively to humidity.The responses were more consistent in high-latitude regions which were mainly related to summer,while climate responses are more variable in middle and low latitudes.A detailed synthesis of relevant publications in the most recent decade showed that there is an increasing implication in the field of physiology.Tree-ring stable C isotopes can reflect the intrinsic water-use efficiency of trees and have been used to study the physiological response of trees to climatic and non-climatic disturbances,such as drought,fire,and atmospheric pollution.Stable C isotope data of tree rings have also been used to assess forest productivity and to enhance the accuracy of dynamic vegetation and physiological models.Future studies are needed to better understand the fractionation mechanism of stable C isotopes after photosynthesis,explore the potential of tree-ring stable C isotopes for reconstructing paleoclimate and environment,and reveal the significance of intra-annual variations of tree-ring stable C isotope ratios(δ13C).Moreover,tree-ring stable C isotopes can be combined with physiological process models or dynamic vegetation models to predict future climate and environment changes.
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