Abstract: The Qinghai-Xizang Plateau is sensitive to global change. Grassland degradation in this region severely affects soil microorganisms and soil organic carbon (SOC). As stable microbial metabolites, soil microbial necromass C (MNC) and glomalin-related soil proteins (GRSP) play a key role in the formation and stabilization of SOC. We investigated the content of MNC and GRSP in alpine grasslands with different degradation degrees (non-degradation, light degradation, moderate degradation, and heavy degradation) on the Qinghai-Xizang Plateau. We further analyzed their contributions to SOC and influencing factors. The results showed that: 1) The contents of MNC (6.04-14.27 mg·g^-1) and GRSP (2.55-7.64 mg·g^-1) significantly decreased with increasing degradation degrees. T heir contributions to SOC remained stable. 2) The contribution of MNC to SOC (7.5%-68.3%) was 2.8 times as high as that of GRSP (3.3%-26.5%). With the decreases of SOC owing to degradation, the MNC was accordingly reduced at 1.7 times as GRSP. 3) Soil physicochemical properties and microbial biomass were key factors affecting the accumulation of MNC and GRSP. In summary, microbial metabolites (e.g., MNC and GRSP) were key for SOC maintenance, and consequently played a crucial role in alleviating the impacts of alpine grassland degradation.

Key words: alpine grassland, grassland degradation, soil organic carbon, glomalin-related soil protein, microbial necromass carbon