Tree-ring carbon isotopic constraints on carbon-water exchanges between atmosphere and biosphere in drought regions in northwestern China

The comparison between the carbon isotope and the index of ring width of a pine disc from the Tuomuer Peak region in Xinjiang shows that the effects o f climate changes on the tree-ring growth and carbon isotopic fractionation varies with time. The reason is probably relative to the characters of cli mate changes and adaptability of the tree-ring growth to climate changes. T he relationships between the atmospheric CO2 level and the revised delta(13 )C(air) by the tree-ring carbon isotope indicate that the carbon cycle is n ot in a steady state, but under a stage-change condition in this area. It a lso can be concluded that the ratio of CO2 from the terrestrial eco-system has increased, and the flux of CO2 exchange between the atmosphere and the biosphere was gradually increasing over the past century. In addition, the results also confirm the validity and superiority of the carbon isotope to the research of the water-use efficiency.