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Response of CO_2 Concentration Parameters and Water-Use Efficiency Derived from Tree Ring δ~(13)C Series to Atmospheric CO_2 Increase

CHEN Tuo 1 , QIN Da he 1 , LI Jiang feng 2 , REN Jia wen 1 , SUN Wei zhen 1 (1.Laboratory of Ice Core and Cold Regions Environment, CAREERI, CAS, Lanzhou Gansu 730000, China; 2.Xinjiang Institute of Meteorology, rümuqi X  
The well documented increase in CO 2 content of atmosphere since the beginning of industrialization has been variously attributed to the anthropogenic activities, such as agricultural explosion, global deforestation and enhanced fossil fuel combustion and so on. It was estimated that about one third of anthropogenic CO 2 released to atmosphere was taken up by terrestrial plants. To evaluate how the land carbon reservoir has been acting as a sink to the anthropogenic CO 2 input to atmosphere, it is important to study how plants in forests physiologically adjust to the changing atmospheric conditions. This has been studied intensively using controlled experiments, but it has been difficult to scale short term observations to long term ecosystem level response. However, models of carbon discrimination during carbon fixation show that C 3 plants are not passive recorders: carbon isotopic variations are subjected to strong physiological control through leaf gas exchange regulation. Therefore, records of carbon discrimination in tree ring cellulose could be used to study past variations of the ecophysiology of trees in reaction to environmental variations, in addition to the reconstruction of past environments. In this paper, based on the tree ring series from Zhaosu County of Xinjiang, the changes of the ratio of CO 2 concentration in the intercellular space of leaves to that on the atmosphere (C i /C a ), CO 2 concentration in the intercellular space of leaves (C i ) and plant water use efficiency ( A/g ) derived from carbon isotope chronology were analyzed for the past 240 a. The results show a relatively constant C i /C a value of 0 52 during the whole period, suggesting a strategy of response of plants to increased atmospheric CO 2 concentration. Significant increasing trends of C i and A/g are also found, implying more carbon being fixed; Further analysis shows that their changes are related to atmospheric CO 2 concentration, thus it is demonstrated that trees maybe take up the portion of anthropogenic CO 2 from another aspect.
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