本文选择天山北坡三工河流域作为研究区，基于碳稳定同位素技术，分析土壤有机碳（SOC ）δ13 C值随降雨量的变化，研究不同海拔梯度土壤剖面δ13 C值随采样深度的变化。结果显示，三工河流域降雨量在300 mm以下的采样点，SOC δ13 C 值随降雨量的增加呈递减趋势（R2＝0.97），而降雨量在300 mm～500 mm的采样点，δ13C值随降雨量变化不明显（R2＝0.04）；三工河流域纯C3植物采样点土壤剖面δ13 C值随采样深度呈现明显的富集效应，即土壤剖面下层δ13 C值大于上层，其平均差值为1.01‰，与其他相关区域研究结果一致；而沙质荒漠和土质荒漠采样点剖面下层与上层SOC δ13 C平均差值为4.33‰，其变化趋势与纯C3植物采样点相反，且其表层δ13 C值接近C4植物来源，底层接近C3植物来源，推断其地上历史植被可能经历了由C3到C4的演替过程。%Soil organic carbon (SOC) pool integrated the vegetation succession informa‐tion from several years to thousands of years scales .It is an ideal tool to understand carbon isotope composition change and terrestrial ecosystem pathways .In this study , the Sangong river watershed was taken as a case .We had estimated the change of vege‐tation and soil organic along a vertical gradient using the carbon isotopic method ,and analyzed the variations of mean SOC δ13 C values with the annual precipitation , and researched the variations in SOC and δ13 C values with profile depth in the study area . n The results showed that the SOC δ13C decreased significantly with the increasing annual precipitation (R2 =0.97) where the annual precipitation was less than 300 mm .When the annual precipitation was 300 mm ~ 500 mm , the SOC δ13 C was not significant changed with the increasing annual precipitation (R2 =0.04) .The enrichment effect of SOC δ13 C with depth was significant in the sample site of pure C3 vegetation , that means lower layer SOC δ13 C of profile was greater than the upper layer .The average difference of SOC δ13 C between lower layer and upper layer was 1.01‰ .The opposite trend of SOC δ13 C was presented in the Desert and Shrubland sites .And that ,the SOCδ13 C value of upper layer closed to C4 vegetation source ,and the lower layer closed to C3 vegetation source .Therefore ,we can infer that the vegetation may have experienced from C3 to C4 in the sandy desert and terrene desert sites .
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