为了探讨土壤有机质在降解过程中的迁移、赋存规律 ,利用C3植物与C4 植物明显的δ13C值差异 ,选取贵州茂兰保护区内农林生态系统发生转换生长的地域 ,分析土壤的不同粒径组分和比重组分中土壤有机质的δ13C值 .结果表明 ,粗砂中的土壤有机质年代最新 ,细粉中的土壤有机质年代最老 ,有机质在降解过程中 ,在土壤各粒径组分中的迁移次序是 :粗砂 <细砂 <粗粉 <粘土 <细粉 ;土壤重组分中的有机质年代较老 ,以降解充分、稳定的有机无机复合体为主 ,相对而言 ,轻组分中的有机质含有更多的降解尚不充分、活性较大的有机质 In order to investigate the migration and occurrence regularity of soil organic matter during degradation, the differences of δ13C values ​​of C3 plants and C4 plants were analyzed. The areas of conversion of agroforestry in the Maolan Nature Reserve of Guizhou Province were selected to analyze the different particle size groups Δ13C values ​​of soil organic matter in the soil fractions and fractions were analyzed.The results showed that the soil organic matter in the grit was the newest in age and the soil organic matter was the oldest in the fines and the migration of organic matter in various soil particle fractions during the degradation The order is: coarse sand