Environmental filtering drives bacterial community structure and function in a subalpine area of northern China.

Microbial community assembly is affected by the trade-off between deterministic and stochastic processes, but the mechanisms underpinning their relative influences remain elusive. This knowledge gap strongly limits our ability to predict the effect of environmental filtering on microbial community structure and function. To improve the understanding of mechanisms underlying community assembly processes, we investigated bacterial community structure and function on a subalpine shady slope and a sunny slope in the Pangquangou National Nature Reserve in North China. By integrating the results of a null model and the RC metric, we inferred that a deterministic process, that is, environmental filtering, drove bacterial community biogeographical patterns. Edaphic factors caused the largest contribution to microbial community structure, followed by vegetation and spatial variables. Among edaphic factors, total carbon (TC) and total nitrogen (TN) were the most important factors as determined by redundancy analysis (RDA). Moreover, network analysis suggested that the status of bacterial community co-occurrence was significantly greater than that of exclusive relationships. Under environmental stress, there was no significant difference in the overall bacterial community structure on the different slopes, while significant differences were observed in relation to community functions. Given this, we inferred that the degrees of response of bacterial community structure and function to varying environments were not consistent. In conclusion, our results contribute to the understanding of deterministic versus stochastic balance in bacterial community assembly and the response mechanisms of community structure and function to environmental heterogeneity.