Proportion of mycorrhiza-associated trees mediates community assemblages of soil fungi but not of bacteria

Recent studies have shown that mycorrhizal trees can greatly influence soil microbial communities, which in turn play important roles in the function offorest ecosystems. However, there is lack of understanding how the composition of trees with different mycorrhizal types affects soil microbial communities. Here, we collected 1606 soil samples from a 25-ha subtropical forest plot to investigate how the proportion of arbuscular mycorrhizal (AM) versus ectomycorrhizal (EcM) trees mediated soil microbial assemblages. Results showed the alpha diversities of both soil fungal and bacterial communities were significantly positively correlated with the ratio of AM/EcM trees. The AM/EcM tree ratio was important to the fungal community assembly, whereas soil pH was key to the bacterial communities. The increase in the AM/EcM tree ratio decreased the importance of stochastic forces in assembling fungal communities, while it had no significant effect on the bacterial communities. The differential importance of the AM/EcM tree ratio to fungal and bacterial communities highlights the role of mycorrhiza-associated tree composition in regulating soil microbial communities. This finding suggests that forests with different AM/EcM tree ratios would have different soil microbial communities, potentially leading to differences in soil nutrient cycling and in return different tree diversity and forest productivity.