Healthy aquatic ecosystems are essential for human beings. However, anthropogenic activities severely worsen water quality. In this study, using assembling mesocosms, we developed an efficient and easy-to-handle method to monitor the water quality by measuring the electrical conductivity (EC) of water. Our data demonstrate that the growth of two submersed macrophytes, Vallisneria natans and Vallisneria spinulosa, improves water quality by decreasing EC. Furthermore, using high-throughput DNA sequencing, we analyzed the microbial community abundance and structure in sediment and water columns with or without plant growth. We generated 33,775 amplicon sequence variants from 69 samples of four sediment groups (BkM, CtM, VnR, and VsR) and three water column sample groups (CtW, VnW, and VsW). The results show that the relative abundance of bacteria was higher in the sediment than in the water column. Moreover, the diversity and composition of microbiomes were altered by Vallisneria spp. growth, and the α-diversity of the microbial communities decreased due to submersed macrophytes in both the sediment and water columns. The β-diversity of the microbial communities also varied significantly with or without Vallisneria spp. growth for both the sediment and water columns.

Medicago polymorpha serves as an important green manure, forage, and edible wild vegetable. Symbiotic nitrogen fixation represents its primary nitrogen source; nevertheless, rhizobial strains that establish symbiotic interactions with this plant have rarely been isolated, particularly from distinctive wetland habitats. In this work, sinorhizobial strain 98002 was isolated from root nodules of wild M. polymorpha collected at Poyang Lake wetland. Scanning electron microscopy (SEM) was applied to observe its cellular morphological features, and molecular identification combining 16S rRNA sequencing and six concatenated housekeeping gene multilocus sequence analysis (MLSA) confirmed the isolate as Sinorhizobium medicae. Antibiotic susceptibility tests demonstrated that strain 98002 was fully sensitive to seven common antibiotics. Host inoculation assays further verified that this indigenous strain could develop pink nodules on M. polymorpha roots and remarkably improve host biomass accumulation under nitrogen-deficient conditions. This indigenous rhizobial resource serves as promising germplasm for sustainable M. polymorpha cultivation in the Poyang Lake basin.