Warming decouples associations between microbial network complexity and ecosystem multifunctionality in alpine grasslands

Climate change and grassland degradation have become great challenges for ecosystem multifunctionality, which is mediated by microbial communities and their interactions. However, influences of warming and grassland degradation on soil microbial interactions and their relationship with ecosystem multifunctionality still remain vague, and it is unclear whether warming could exacerbate or mitigate degradation from these prospects. In this study, we conducted a field study in alpine grasslands on the Qinghai-Tibet Plateau to investigate the effects of warming and grassland degradation (i.e., non-degraded, ND; moderately degraded, MD; and severely degraded, SD) on soil microbial network properties and their association with ecosystem multifunctionality comprising nutrient provision, biomass production, and ecosystem processes indices. Results showed that microbial network complexity, characterized by edge number, node degree, graph diameter, and graph density, was 109.5 238.8 % higher in MD than in ND or SD, likely explained by the intermediate disturbance hypothesis. Warming stimulated the network complexity by 78.7 92.8% in MD due to the prevalence of prokaryote and the escalation of their negative interactions, likely implying the fiercer resource competition that may restrain the grassland restoration; while warming weakened it by 35.4 59.9 % and 35.0 47.4 % in ND and SD, respectively, due to declines in all interaction types, indicating undermined structure of microbial interactions that may prevent the restoration of degradation grassland. Consistently, the ecosystem multifunctionality was not stimulated by warming significantly in various degradation stages. Interestingly, the microbial network complexity, rather than diversity, was positively correlated with the ecosystem's multifunctionality under control, which was eliminated by warming. Overall, warming changed the microbial network complexity by making the strong stronger in MD while the weak weaker in ND and SD. These divergent changes by warming decouple associations of microbial network complexity with ecosystem multifunctionality. Altered microbial network complexity under future warming scenarios may tend to hamper the multifunctionality restoration of alpine grasslands, though with different mechanisms in various degradation stages.