Moderate Grazing Intensity by Tibetan Sheep Enhances Soil Microbial Biomass in Alpine Grasslands via Dung–Soil Interactions

Alpine grasslands are critical ecosystems for ecological security and livestock production on the Qinghai‐Tibet Plateau and are highly sensitive to grazing disturbance. Grazing influences soil nutrient cycling and microbial processes through livestock excretion inputs, yet the mechanisms by which grazing intensity regulates microbial biomass carbon (MBC) and nitrogen (MBN) through dung–soil interactions remain unclear. Based on a long‐term controlled grazing experiment, this study examined the relationships among dung nutrients, soil physicochemical properties, and microbial biomass under different Tibetan sheep grazing intensities (no grazing, light grazing, moderate grazing, and heavy grazing). The results showed that moderate grazing significantly increased soil MBC and MBN, while also resulting in the highest levels of dung dissolved organic carbon and nitrogen. Structural equation modeling indicated that dung nutrients did not directly affect microbial biomass but indirectly drove microbial responses by altering soil physicochemical indicators such as dissolved organic carbon, dissolved organic nitrogen, and available nitrogen. The dominant factors influencing MBC and MBN differed: MBC was regulated by the synergistic effects of carbon, nitrogen, and phosphorus resources, while MBN was more dependent on nitrogen availability. This study reveals an indirect pathway of “moderate grazing‐optimized dung nutrients‐improved soil properties‐enhanced microbial biomass,” supports the applicability of the Intermediate Disturbance Hypothesis in alpine grasslands, and emphasizes the crucial role of grazing intensity regulation in maintaining microbe‐mediated ecosystem functions. These findings provide a mechanistic basis for the sustainable management of alpine grasslands.