Lower Compositional Variation and Higher Network Complexity of Rhizosphere Bacterial Community in Constructed Wetland Compared to Natural Wetland

Macrophyte rhizosphere microbes, as crucial components of the wetland ecosystem, play an important role in maintaining the function and stability of natural and constructed wetlands. Distinct environmental conditions and management practices between natural and constructed wetlands would affect macrophytes rhizosphere microbial communities and their associated functions. Nevertheless, the understanding of the diversity, composition, and co-occurrence patterns of the rhizosphere bacterial communities in natural and constructed wetlands remains unclear. Here, we used 16S rRNA gene high-throughput sequencing to characterize the bacterial community of the rhizosphere and bulk sediments of macrophyte Phragmites australis in representative natural and constructed wetlands. We observed higher alpha diversity of the bacterial community in the constructed wetland than that of the natural wetland. Additionally, the similarity of bacterial community composition between rhizosphere and bulk sediments in the constructed wetland was increased compared to that of the natural wetland. We also found that plants recruit specific taxa with adaptive functions in the rhizosphere of different wetland types. Rhizosphere samples of the natural wetland significantly enriched the functional bacterial groups that mainly related to nutrient cycling and plant-growth-promoting, while those of the constructed wetland-enriched bacterial taxa with potentials for biodegradation. Co-occurrence network analysis showed that the interactions among rhizosphere bacterial taxa in the constructed wetland were more complex than those of the natural wetland. This study broadens our understanding of the distinct selection processes of the macrophytes rhizosphere-associated microbes and the co-occurrence network patterns in different wetland types. Furthermore, our findings emphasize the importance of plant-microbe interactions in wetlands and further suggest P. australis rhizosphere enriched diverse functional bacteria that might enhance the wetland performance through biodegradation, nutrient cycling, and supporting plant growth.