Decoupled responses of soil microbial diversity and ecosystem functions to successive degeneration processes in alpine pioneer community.

Many alpine ecosystems are undergoing vegetation degradation because of global changes, which are affecting ecosystem functioning and biodiversity. The ecological consequences of alpine pioneer community degradation have been less studied than glacial retreat or meadow degradation in alpine ecosystems. We document the comprehensive responses of microbial community characteristics to degradation processes using field-based sampling, conduct soil microcosm experiments to simulate the effects of global change on microorganisms, and explore their relationships to ecosystem functioning across stages of alpine pioneer community degradation. Our work provides the first evidence that alpine pioneer community degradation led to declines of 27% in fungal richness, 8% in bacterial richness, and about 50% in endemic microorganisms. As vegetation degraded, key ecosystem functions such as nutrient availability, soil enzymatic activity, microbial biomass, and ecosystem multifunctionality progressively increased. However, soil respiration rate and carbon storage exhibited unbalanced dynamics. Respiration rate increased by 190% during the middle stage of degradation compared with the primary stage, and it decreased by 38% in the later stage. This indicates that soil carbon loss or emission increases during the mid-successional stage, whereas in later successional stages, alpine meadows become significant carbon sinks. Compared with microbial community characteristics (such as richness of total and functional taxa, and network complexity), community resistance contributes more significantly to ecosystem functions. Especially, the bacterial community resistance is crucial for ecosystem functioning, yet it is greatly impaired by nitrogen addition. Based on microbial network, community assembly, and community resistance analyses, we conclude that fungi are more vulnerable to environmental changes and show smaller contributions to ecosystem functions than bacteria in degrading alpine ecosystems. Our findings enhance the knowledge of the distinct and synergistic functional contributions of microbial communities in degrading alpine ecosystems and offer guidance for developing restoration strategies that optimize ecosystem functioning of degraded alpine plant communities.