中文摘要：

对地下有机碳库变化的认识是全球碳循环研究的重要内容，传统的研究方法存在着一定的局限性。限制了我们对地下碳库的深入了解。由于在土壤有机碳分解过程中伴随有碳同位素变化，因此．我们可以借助对土壤碳同位素变化的研究来揭示土壤有机碳周转。本文通过对贡嘎山东坡土壤剖面中的碳同位素测量，发现：1）土壤有机质分解过程中存在的碳同位素分馏能够解释90％的土壤有机碳同位素随深度的变化；2）土壤有机质分解过程中的碳同位素分馏系数α在低海拔和高海拔地点均有较大的值，指示着土壤有机碳在高海拔地区可能也存在较快的分解速度；3）在贡嘎山东坡．温度对土壤有机碳分解没有明显影响，而土壤水分和底物（凋落物）的品质特性显著地影响土壤有机质分解速度。土壤水分增加能够促进有机质分解；具有高品质特性（即有高纤维素含量、低木质素含量和低C／N比值）的底物（凋落物）具有较快的周转速度。

英文摘要：

Understanding of the change of below-ground organic carbon pool is an important issue of global carbon cycles. The drawbacks existing in some traditional studies on soil carbon turnover have limited the further understanding of the dynamic change of soil organic carbon. Since carbon isotope fractionation occurs in decomposition of organic matter, we are able to explore soil carbon turnover through studying the variation in carbon isotope of soil organic matter （δ^13CSOM）. In this study, we measured δ^13CSOM in soil profiles on the eastern slope of Mount Gongga and found that the carbon isotope fractionation during decomposition of organic matter can explain 90% vertical variation in δ^13CSOM with soil depth, and that carbon isotope fractionation factor （α） during decomposition of organic matter was great at both lower and higher altitudes, suggesting that soil carbon turnover was also quick in the areas with high elevation. In addition, we also found that temperature did not play a role in soil carbon turnover, while soil water and substrate （litter） quality both had a significant effect. Increase in soil water availability improved decomposition of organic matter ; those substrates with high quality （ i. e. high cellulose, low lignin and low C/N value） had a great rate of decomposition.