Effects of grazing intensity on biomass and soil physical and chemical characteristics in alpine meadow in the source of three rivers

Human activity has adversely affected global carbon(C) and nitrogen(N), and contributed to an alteration of climate that will generate discernible feedbacks to all organisms and ecosystems on earth. The purpose of this study was to provide the basis of degrading mechanisms in alpine meadow research and understanding global C reserves and quantifying the pools and changing of soil carbon under grazing intensity. The combined methods of field survey and experiment analysis were applied to detect the influence of biomass and soil carbon characteristics under different grazing intensity: enclosure (EN), light grazing (LG), moderate grazing (MG), heavy grazing(HG) and control (CK)on an alpine meadow. The experiment plots were located in the Yushu Longbao alpine meadow. The results showed that aboveground biomass and underground biomass of grassland were maximum in EN treatment. With the grazing intensity increasing, the aboveground biomass and underground biomass decreased. The soil moisture in EN and LG treatments were significantly higher(P＜0.05) than the other treatments which influenced by grazing disturbance. In the soil profile, the soil moisture decreased with soil depth increase in all treatments. Trampling of grazed not only influenced soil moisture but also impacted soil bulk density, the soil bulk density increased with the grazing intensity increasing. The soil organic carbon(SOC) and total nitrogen were also influenced by grazing, the total nitrogen decreased in the following order: LG＞EN＞MG＞CK＞HG whereas the SOC decreased in the following order LG＞EN＞MG＞HG＞CK. Optium trampling of grazing increased soil bulk density, however, but the effects on meadow vegetation and soil structure of high grazing intensity were not benefical for sustainable development of grassland ecosystem.