Grassland degradation changes vegetation productivity as well as the accumulation and decomposition rates of soil organic matter. It therefore influences the carbon cycle and soil carbon storage of grassland ecosystems. Reports on the state of the environment in China issued in 2011 showed that 90% natural grassland has experienced at least some degree of degradation and 50% has experienced moderate to severe degradation. The grassland degradation can be divided into two related processes: vegetation degradation and soil degradation, both affecting grassland carbon budgets. So we measured variations of the vegetation-soil system carbon storage include aboveground plant parts monthly during the growing season (from May to September) and soil and roots at depth of 0-50cm in a typical steppe in Xilinhot, Inner Mongolia, in areas with light, moderate, and severe degradation in 2011-2012.
The results showed the soil had the highest organic carbon storage, followed by roots and aboveground plant parts. The rate of vegetation degradation is not necessarily consistent with the rate of soil degradation because of a time lag between them. The dominant vegetation species is Stipa. grandis, however, in severely degraded areas, the dominant species changes to Stipa krylovii. During the period of two years of observation, there was a big difference between annual rainfall. In dry year, the vegetation-soil carbon storage was highest at light degraded sites, and so did the soil carbon storage and aboveground carbon storage, root carbon storage and soil carbon storage showed a decreasing trend with the increased degradation. In wet year, aboveground carbon storage and root carbon storage were highest at light degraded sites, and the precipitation level had a significant effect on carbon storage. However, besides precipitation, there are more factors influencing the carbon storage. So we still need further study in a long term to discuss the carbon storage in the process of grassland degradation by combining various factors.