Microbial community and enzyme activity respond differently to seasonal and edaphic factors in forest and grassland ecosystems

Although microbial community and function patterns have been extensively studied, little is known about whether the patterns are consistent in different ecosystems and how they are influenced by seasonality or other environmental factors. To test the driving factors of microbial communities and potential functions, we collected soil samples from five forests (mixed broadleaved-Korean pine forest, mixed pine and oak forest, deciduous broadleaved mixed forest, subtropical evergreen broad-leaved forest and tropical rainforest) and three grassland ecosystems (meadow steppe, semi-arid grassland and arid grassland) across China in three seasons (spring, summer and autumn). Microbial diversity based on the sequencing of 16S rRNA gene for bacteria and internal transcribed spacer (ITS) genes for fungi were measured, and potential functions represented by soil extracellular enzyme activities (EEAs) were analyzed. The results found that soil EEAs were significantly higher in summer than in spring and autumn, and both bacterial and fungal richness indices showed greater seasonal fluctuations than the diversity. Fungal richness indices were highest in summer in both forest and grassland ecosystems, while the lowest were observed in spring for forest and in autumn for grassland, respectively. In addition, fungal communities were closely related to ecosystem types, while bacterial communities were not significantly different across ecosystems and exhibited a broader habitat niche breadth, but the relative abundance of dominant bacterial phyla showed stronger correlations with environmental variables (including climate, soil properties and nutrients) in grassland than in forest ecosystems. The decoupling of microbial community and EEAs was observed in both forest and grassland ecosystems, indicating the function redundancy of soil microorganisms. The present study provided crucial information about the effects of ecosystem types, seasonality and edaphic factors on soil microbial communities and EEAs, and could advance the understanding of soil potential function responses to environmental changes.