Glomalin-related soil proteins in particulate and mineral-associated organic carbon pools in alpine grasslands with different degradation degrees

Glomalin-related soil proteins (GRSP) produced by arbuscular mycorrhizal fungi (AMF) can mitigate declining in soil organic carbon (SOC) in degraded alpine grasslands by regulating functional C pools, particulate organic C (POC) and mineral-associated organic C (MAOC). However, the mechanism by which GRSP regulates the formation of different functional C pools in alpine grasslands remains unclear. We investigated GRSP content in POC and MAOC in alpine grasslands with varying degradation gradients on the Qinghai-Xizang Plateau and analyzed how the AMF co-occurrence network modulates these variations. The GRSP content in POC and MAOC in heavy degradation grassland was reduced by 38.4 % and 37.5 % compared with non-degradation grassland. However, the relative contribution of GRSP in POC and MAOC increased by 9.9 % and 17.5 %, respectively. Grassland degradation decreased soil AMF diversity by 33.7 % but increased network stability by 53.2 % in alpine grasslands and network complexity by 5 times in alpine steppes. The random forest model highlighted that GRSP played a key role in soil functional C, especially in enhancing the contribution to MAOC. Further analyses revealed that the changes in the AMF community led to reduced POC and MAOC formation by decreasing GRSP content in POC and MAOC. GRSP is critical for POC and MAOC formation, and degradation-induced changes in AMF community structure increase the contribution of GRSP to the soil functional C pool. Therefore, protecting ecosystems with complex below-ground AMF communities contributes to stable SOC sequestration during grassland degradation, which is important for establishing and maintaining grassland SOC pools.