摘要
1 Background THE C<sub>i</sub>/C<sub>a</sub>, the ratio of intercellular and ambient C0<sub>2</sub> partial pressure, is internally controlled by thestomatal conductance and assimilation rate, and is externally affected by the atmospheric CO<sub>2</sub> concentration and climate changes. C<sub>i</sub>/C<sub>a</sub> can be only estimated by the isotopic fractionation equation of Farquchar. However, this method is limited by the very little observation of atmospheric δ<sup>13</sup> C before1980. Leavitt had to interpolate the atmospheric δ<sup>13</sup> C by means of the polynomial. A geochemicalmethod to model C<sub>i</sub>/C<sub>a</sub> by tree-ring δ<sup>13</sup>C has been developed to reduce the dependence. By the estimated tree-ring C<sub>i</sub>/ C<sub>a</sub>, the authors here discuss C0<sub>2</sub> and water exchanges between the atmosphere and biosphere that greatly influence the climate
