Driving factors for soil fungal and bacterial community assembly in topical forest of China

Abstract

Understanding the assembly of soil microbial communities of tropical forest is of great significance for the protection of biodiversity in tropical areas. Many studies have been carried out on biodiversity and its maintenance mechanism in tropical regions. However, the effects of land use and seasonal variation on the assembly of soil fungal and bacterial communities in tropical forests remains unknown. To fill this research gap, 16S rRNA and ITS sequences were used to evaluate the assembly mechanisms of soil bacterial and fungal communities using 260 soil samples collected from tropical rainforest and rubber plantation sites across Hainan Island, South China. A majority (~60%) of observed OTUs conformed with neutral model expectations, indicating that neutral processes were important for the assembly of soil microbial communities. For bacterial communities, the NST (normalized stochasticity ratio) was higher in the tropical rainforest (0.746 in the dry season, 0.684 in the rainy season) versus rubber plantation sites (0.647, 0.584), regardless of season. This indicated rainforest were more stochastic than rubber plantation for soil bacterial community assembly. For fungal communities, rubber plantation communities showed greater stochasticity (NST = 0.578) than rainforest communities (NST = 0.388) in the dry season, but the reverse was true in the rainy season (NST = 0.852 for rubber plantations; NST = 0.978 for rainforest). Both the NST results and structural equation modeling showed that bacterial communities were more stochastic in the dry season, while fungal communities were more stochastic in the rainy season; the effects of seasonal changes on assembly therefore differed between bacterial and fungal communities. More importantly, forest types did not have a direct impact on the assembly of bacterial or fungal communities, but exerted indirect effects via soil pH and soil available potassium.