Spring drying and intensified summer rainfall affected soil microbial community composition but not enzyme activity in a subtropical forest

The predicted changes in the seasonal precipitation pattern could influence the soil microbial communities composition and function. However, the responses of soil microbes to seasonal changes in precipitation are poorly understood, especially in subtropical forests with distinct dry-wet seasons. A manipulation experiment lasted for two years to determine the effects of reduced rainfall in spring and increased rainfall in summer (the wet season) on the composition and function of soil microbial community in a subtropical forest. We excluded 67% of throughfall during spring and then added the equivalent amount of water back to the exclusion plots in intense rainfall events during summer. Throughfall exclusion reduced the soil water content (SWC) by 4.8-6.5%, and water addition increased the SWC by 12.5% but without statistical significance. However, wet-season water addition significantly decreased the ratio of fungal to bacterial phospholipid fatty acids by 12.7% in a relatively dry year (2014). Amplicon sequencing indicated that water addition increased the rare bacterial phylum Gemmatimonadetes, which accounted for 0.59-0.73% of the total OTUs in the soil. Water addition also increased Basidiomycota and decreased Ascomycota; these two phyla accounted for 71-86% of the total fungal OTUs in the soil. Soil enzyme activities were unaffected by reduced rainfall in spring and increased rainfall in summer, expect that beta-1,4-glucosidase activity which was positively related to SWC. Our results suggest that bacteria are more responsive than fungi to reduced rainfall in the spring, while fungi are more responsive than bacteria to increased rainfall in the summer. To clarify how microbial functions change in response to changes in precipitation, future research should assess the expression of functional genes.