干旱区生态环境知识资源中心

The Ordos sand land is a typical sandy desertification area in northern China. Changes of soil organic matter and the combined humus in soil aggregate could be the index of soil desertification. The objectives of this study were: (i) to analyze the changes in soil organic carbon during the desertification process; (ii) to assess the distribution of soil combined humus and its changes in different aggregates. In this study, we selected the typical communities that represented a series of plant succession stages in the desertification process. Soil samples were collected from the plots under three successional plant communities and analyzed for total organic matter (SOM) under different degenerated gradients. We classified the aggregates into different groups and determined the combined humus in different size aggregates using the mechanical analysis method. The results showed that SOM decreased remarkably in surface soil (0-5 cm) from the steppe grass Stipa Bungeana to desert grass Cynanchum komorovii, during the desertification process. The fractions of soil combined humus were 36.63%, 28.84%, and 39.53% for loose combined humus, stable combined humus and tight combined humus with respectively average content. All fractions of soil combined humus carbon content decreased as the aggregate size decreased. In the desertification process at the Ordos sand land, the stable combined humus and tight combined humus decreased strongly in >50 mu m aggregate. The decreasing of humus carbon is mainly due to the losing of stable combined humus, especially in large size aggregates. With the development of the desertification, the soil organic carbon decreased with remarkable difference among different stages and the combined humus decreased with remarkable difference in different size aggregates among different stages.