Soil bacterial and fungal diversity and compositions respond differently to forest development

Forest development gradually changes the above-ground plant community, but the potential effects on the below-ground microbial community remain unclear, particularly at the various succession stages. Here, we investigated six vegetation types that covered two succession stages (early and late stages) during forest development. The early stage showed changes from two pioneer communities (Benda plaryphylla and Populus davidicma) to two mixed communities (Populus davidiana with Pinus tabuliformis), while the late stage showed changes from the two mixed communities to two climax communities (Quercus wutaishanica and Pinus tabuliformis). Illumina sequencing of the 16S rRNA gene and ITS gene were carried out to analyze soil microbial (bacterial and fungal) diversity and composition. Soil properties (i.e., moisture, bulk density, texture, ammonium nitrogen, nitrate nitrogen, organic carbon, total nitrogen, and total phosphorus) were also determined. The results showed that forest development had positive effects on microbial diversity. Particularly, bacterial diversity successions proceed faster than that of fungi at the early stage. Proteobacteria and Bacteroidetes significantly increased, but Actinobacteria and Acidobacteria significantly decreased during forest development. In contrast, the effect sizes of Proteobacteria, Actinobacteria, and Acidobacteria at the early stage were larger than those at the late stage. The dominant fungi phyla (i.e., Ascomycota, Basidiomycota, and Zygomycota) across all soil samples responded insignificantly to forest development Such differential responses of the microbial diversity and dominant phyla were significantly correlated with soil texture, soil organic carbon, and total nitrogen. In contrast, the effect size of soil properties on bacterial phyla was larger than that on fungal phyla. Collectively, these results emphasize that the responses of the microbial community to forest development depend on the succession stage, and also suggest that bacteria and fungi may not follow the same successional trajectories due to the differed responses of bacteria and fungi to changing soil texture and carbon/nitrogen contents during forest development.