Changes in ecological characteristic and soil carbon sequestration along the retrogressive succession of grassland ecosystem on western Songnen Plain

Grassland degradation is one of the major ecological problems in western Jilin province. Grassland degradation changes the carbon balance of grassland ecosystem. During the degradation, different plant communities of grassland ecosystem formed along the retrogressive succession in western Songnen Plain, such as Leymus chinensis→Chloris virgata→Puccinellia tenuiflora→Suaeda glauca, then saline-alkali land. The experimental sites were located in Jiang-jia-dian meadow, which is one of the largest three natural Leymus chinensis steppe in China. The chronosequence approach (space-for-time substitution) is a viable tool for obtaining integrated information on successional studies, the primary objective of this study was to certain the impact of retrogressive succession on the soil carbon sequestration of grassland ecosystem. Six sampling strips (50cm×50cm) and four profiles were selected in each experimental sites for measuring plant species, cover, aboveground biomass, soil bulk density, total N and soil organic carbon. The results showed that the plant community composition changed, and the number of plant species and the cover decreased. Moreover, SOC were positively related to soil moisture and soil total nitrogen (P<0.05), retrogressive succession caused by grassland degradation affected not only in the surface layer, but also notably in the deeper layers. It is not a simple carbon source, moderate grassland degradation had a positive effect on carbon reserve while excessive degradation would accelerate the loss of grassland carbon reserve.