Rhizosphere Soil Microbial Community Under Ice in a High-Latitude Wetland: Different Community Assembly Processes Shape Patterns of Rare and Abundant Microbes.

The rhizosphere soil microbial community under ice exhibits higher diversity and community turnover in the ice-covered stage. The mechanisms by which community assembly processes shape those patterns are poorly understood in high-latitude wetlands. Based on the 16S rRNA gene and ITS sequencing data, we determined the diversity patterns for the rhizosphere microbial community of two plant species in a seasonally ice-covered wetland, during the ice-covered and ice-free stages. The ecological processes of the community assembly were inferred using the null model at the phylogenetic bins (taxonomic groups divided according to phylogenetic relationships) level. Different effects of ecological processes on rare and abundant microbial sub-communities (defined by the relative abundance of bins) and bins were further analyzed. We found that bacterial and fungal communities had higher alpha and gamma diversity under the ice. During the ice-free stage, the dissimilarity of fungal communities decreased sharply, and the spatial variation disappeared. For the bacterial community, homogeneous selection, dispersal limitation, and ecological processes (undominated processes) were the main processes, and they remained relatively stable across all stages. For the fungal community, during the ice-covered stage, dispersal limitation was the dominant process. In contrast, during the ice-free stage, ecological drift processes were more important in the rhizosphere, and ecological drift and homogeneous selection processes were more important in the rhizosphere. Regarding the different effects of community assembly processes on abundant and rare microbes, abundant microbes were controlled more by homogeneous selection. In contrast, rare microbes were controlled more by ecological drift, dispersal limitation, and heterogeneous selection, especially bacteria. This is potentially caused by the low growth rates or the intermediate niche breadths of rare microbes under the ice. Our findings suggest the high diversity of microbial communities under the ice, which deepens our understanding of various ecological processes of community assembly across stages and reveals the distinct effects of community assembly processes on abundant and rare microbes at the bin level.