Increasing biodiversity loss profoundly affects community structure and ecosystem functioning. However, the differences in community assembly and potential drivers of the co-occurrence network structure of soil fungi and bacteria in association with tree species richness gradients are poorly documented. Here, we examined soil fungal and bacterial communities in a Chinese subtropical tree species richness experiment (from 1 to 16 species) using amplicon sequencing targeting the internal transcribed spacer 2 and V4 hypervariable region of the rRNA genes, respectively. Tree species richness had no significant effect on the diversity of either fungi or bacteria. In addition to soil and spatial distance, tree species richness and composition had a significant effect on fungal community composition but not on bacterial community composition. In fungal rather than bacterial co-occurrence networks, the average degree, degree centralization, and clustering coefficient significantly decreased, but the modularity significantly increased with increasing tree species richness. Fungal co-occurrence network structure was influenced by tree species richness and community composition as well as the soil carbon: nitrogen ratio, but the bacterial co-occurrence network structure was affected by soil pH and spatial distance. This study demonstrates that the community assembly and potential drivers of the co-occurrence network structure of soil fungi and bacteria differ in the subtropical forest. IMPORTANCE Increasing biodiversity loss profoundly affects community structure and ecosystem functioning. Therefore, revealing the mechanisms associated with community assembly and co-occurrence network structure of microbes along plant species diversity gradients is very important for understanding biodiversity maintenance and community stability in response to plant diversity loss. Here, we compared the differences in community assembly and potential drivers of the co-occurrence network structure of soil fungi and bacteria in a subtropical tree diversity experiment. In addition to soil and spatial distance, plants are more strongly predictive of the community and co-occurrence network structure of fungi than those of bacteria. The study highlighted that plants play more important roles in shaping community assembly and interactions of fungi than of bacteria in the subtropical tree diversity experiment.
Keywords: bacteria; co-occurrence network; community assembly; fungi; plant species diversity; subtropical forest.