Microbial community assembly and its influencing factors of secondary forests in Qinling Mountains

Forest soil microbial community is easily modified by changes in plant composition. Therefore, differences in the assembly of soil microbial community within different forest types should be evaluated to gain a deeper understanding of microbial biodiversity and forest system functioning. In the present study, pine, oak, and pine-oak mixed forests at different developmental stages (young, immature, and mature forests) were evaluated to explore the assembly, co-occurrence network, and influencing factors of bacterial and fungal community. The assembly of bacterial community was dominated by deterministic processes (homogeneous selection), whereas the assembly of fungal community was dominated by stochastic processes (dispersion limited). At the young forest stage, the proportion of deterministic processes in bacterial community assembly among the three forest types differed less. In contrast, the proportion of deterministic processes at the immature and mature forest stages in the bacterial community assembly in the pine-oak mixed forest was larger than that in the pure forests. The proportion of stochastic processes in the assembly of fungal community in the pine-oak mixed forest was greater than that in the pure forests and was observed at all forest stages. Network analysis showed that the links and average degree of bacteria in the pine-oak mixed forest were lower than that of the pure forests, whereas the network topological features of fungi in the pine-oak mixed forest were higher than that of the pure forests. The stochastic processes increased microbial co-occurrence. The results of the random forest indicated that Pielou's evenness index (E) of plant was the most important predictor of fungal community assembly, and Shannon's diversity index (H) of plant also was the critical factor influencing bacterial community assembly. Our study demonstrated the importance of plant diversity in the assembly of forest soil microbial community.