Abstract: In order to obtain the equilibrium mode of grassland carbon sequestration and grazing management to provide a scientific basis for carbon sequestration management of grassland ecosystem, this paper studied the vegetation and soil carbon and nitrogen density under a short-term grazing gradient in an alpine forb meadow ecosystem on the northeastern QinghaiTibetan Plateau, China. Under the grazing gradient, the existing total vegetation carbon storage decreased with increasing grazing intensity, i.e., no grazing (SCK) > light grazing (SL) > moderate grazing (SM) > heavy grazing (SH). The annual net primary carbon production was in the order of SM >SL >SH > SCK, indicating that moderate grazing could promote vegetation carbon storage, while overgrazing or no grazing was in reverse. In the soil layers of 0-40 cm, the total organic carbon density and total nitrogen density had the same variation pattern, i.e., SCK > SH> SM > SL. However, in topsoil (0-10 cm), the organic carbon density was in the order of SH > SM > SL > SCK, while the total nitrogen density was of SH > SCK > SM > SL. In 10-20 cm, 20-30 cm, and 30-40 cm soil layers, both the organic carbon density and the total nitrogen density declined in the order of SCK > SH > SL > SM. A slight difference was observed in the soil carbon and nitrogen density between 0-10 cm and 10-40 cm layers, indicating that shortterm grazing had different effects on the soil carbon and nitrogen between surface layer and deeper layers. Under the grazing gradient, soil C/N in different layers of 0-40 cm had somewhat difference. Overall, the soil C/N under the grazing gradient except CK was suitable for microbial mineralization. Regression analysis showed that under the grazing gradient, soil carbon density in all layers was positively correlated with soil nitrogen density (P<0.01).

Key words: height-diameter model, stand variables, Chinese fir plantation., nonlinear mixed-effect model