Grazing Intensity Affects Soil Organic Carbon Stock and Its Chemical Compositions in Potentilla fruticosa Shrublands on the Tibetan Plateau

Potentilla fruticosa shrubland is a large component of the alpine ecosystem and provides significant resources for grazing on the Tibetan Plateau. However, how the grazing intensity affects soil organic carbon (SOC) in alpine shrublands is still unclear. Using data from 44 sites, we explored SOC, soil chemical compositions, and controlling factors for SOC stock in four grazing disturbances of heavy grazing (HG), moderate grazing (MG), light grazing (LG), and no grazing (NG) in the Tibetan Plateau P. fruticosa shrubland. Our results showed that the ecological indicators of the basal diameter of shrublands, belowground biomass, height, ground cover, aboveground biomass of shrublands and herbs, litter of branches, and litter of foliage were all significantly different in different grazing disturbances. The diversity of bacteria and fungi did not show a significantly different among the four grazing types. The SOC stocks in NG (11.49 ± 1.36 kg m −2 ) and LG (10.99 ± 1.49 kg m −2 ) were significantly larger than that in HG (9.24 ± 1.11 kg m −2 ), which supported that SOC was different in different grazing types. The SOC stock difference was insignificant between LG and MG (9.84 ± 1.54 kg m −2 ). A significantly larger indicator of alkyl C/O-alkyl C (A/OA, a ratio of persistent C accumulation relative to more labile C) was existing in LG than in HG, and the difference of A/OA among NG, LG, and MG was not significant. Decreasing SOC in different grazing types mainly resulted from changes in plant characteristics, which controlled the litter, finally affecting SOC stock. Besides, soil characteristics, e.g., soil pH, temperature, and moisture, significantly also played an important role in controlling SOC in different grazing types. Considering the persistence of SOC and SOC stock, LG and MG may be the proper choice for the alpine shrubland of P. fruticosa across the Tibetan Plateau, and HG should be avoided for sustainable development.