[Variation of below-ground carbon sequestration under long term cultivation and grazing in the typical steppe of Nei Monggol in North China].

Human activities have changed the earth surface mostly, which caused many environment issues now. We aimed to detect the process that human activities exert on ecosystem by investigating and analyzing the changes of plant community, especially underground soil and root carbon sequestration under long-term cultivation and grazing in typical steppe area of Nei Monggol, North China. The carbon sequestration on the root and soil in three plots of typical steppe area: 26-year exclosure grassland (E26), continuous grazing grassland (LG) and 35-year cultivated tillage (LC) were measured. The carbon storage in the layer of 0-40 cm showed a trend that E26 (7 307.59 g x m(-2) and 950.32 g x m(-2)) approximately LG (7834.01 g x m(-2) and 843.43 g x m(-2)) > LC (4537.04 g x m(-2) and 277.35 g x m(-2)), occupied 88.49%, 90.28% and 94.24% of total soil-root carbon respectively. The original composition structure of plant-soil system was completely destroyed by human cultivation, and it also led to sever soil erosion as well. The sand content in soil of LC at layers 0-10 cm, 10-20 cm were increasing by 81% and 39% compared to E26. On the other hand, the root biomass of LG at 0-40 cm decreased by 71%. Cultivation resulted in significant decrease of the carbon storages in soil and root. Therefore, the present cultivation should be ceased and the optimum measurements should be taken to make the tillage restore to natural grassland condition. Continuous grazing led to the significantly changes of the above-ground vegetation characteristics such as community height, coverage and biomass. While the changes of soil organic content and root biomass was not remarkable under grazing. However, the bulk density of surface soil (0-10 cm) exhibited significant increase in LG compared to E26, which indicated that the present grazing pressure have been reaching the threshold of grassland capacity. Therefore, the present grazing pressure should be decreased properly in order to avoid more serious degradation.