Soil microbial distribution and assembly are related to vegetation biomass in the alpine permafrost regions of the Qinghai-Tibet Plateau

It is generally believed that there is a vegetation succession sequence from alpine marsh meadow to desert in the alpine ecosystem of the Qinghai-Tibet Plateau. However, we still have a limited understanding about distribution patterns and community assemblies of microorganisms' response to such vegetation changes. Hence, across a gradient represented by three types of alpine vegetation from swamp meadow to meadow to steppe, the soil bacterial, fungal and archaeal diversity was evaluated and then associated with their assembly processes, and glacier foreland vegetation was also surveyed as a case out of this gradient. Vegetation biomass was found to decrease significantly along the vegetation gradient. In contrast to irregular shifts in alpha diversity, bacterial and fungal beta diversities that were dominated by species replacement components (71.07-79.08%) significantly increased with the decreasing gradient in vegetation biomass (P < 0.05). These trends of increase were also found in the extent of stochastic bacterial and fungal assembly. Moreover, an increase in microbial beta diversity but a decrease in beta nearest taxon index were observed along with increased discrepancy in vegetation biomass (P < 0.001). Stepwise regression analyses and structural equation models suggested that vegetation biomass was the major variable that was related to microbial distribution and community assembly, and there might be associations between the dominance of species replacements and stochastic assembly. These findings enhanced our recognition of the relationship between vegetation and soil microorganisms and would facilitate the development of vegetation-microbe feedback models in alpine ecosystems.