Sediment microbiomes associated with the rhizosphere of emergent macrophytes in a shallow, subtropical lake

Rhizosphere microbiota has received much attention due to their associations with plant growth and their fundamental importance in terrestrial ecosystems. However, relatively few studies have focused on rhizosphere microbial communities associated with aquatic macrophytes in freshwater lakes. We hypothesized that the rhizosphere microbiome would reflect the presence of macrophyte roots and the concomitant microhabitat conditions the roots create. Here, high-throughput sequencing and network analysis were employed to compare the composition and structure of bacterial communities in the rhizosphere of two common emergent macrophytes, Zizania latifolia and Phragmites australis, with the surrounding sediments in Lake Taihu (China). Results indicated that bacterial diversity, community composition, and co-occurrence networks differed between the communities of bulk sediments and the communities of rhizosphere and surface sediments. Richness and phylogenetic diversity were higher and more taxa were enriched in the rhizosphere and surface sediment communities compared with bulk sediment communities. No differences were detected between bacterial communities in rhizosphere and surface sediments, nor between rhizospheres sediment communities of the two macrophyte species. Anaerobic taxa were more abundant in bulk sediment communities. Among the co-occurrence networks, more nodes (operational taxonomic units) and edges (connections) with higher average degree as well as more topologically important nodes were found in rhizosphere and surface sediment communities relative to bulk communities. These findings suggest that rhizosphere microbiome communities are influenced by the presence of macrophyte roots, with oxygenated rhizosphere and surface sediment communities being more diverse, and organized into more interconnected co-occurrence networks.