Prokaryotic and Eukaryotic Communities Characteristic in the Water Column and Sediment along the Xiangjiang River, China

Microbial communities are central components of river ecosystems. They are involved in the transportation and transformation of certain pollutants, including nutrients discharged into surface water. Knowledge of microbial community structures is vital for understanding biochemical circulation in aquatic ecosystems. However, most of the research that is currently being conducted focuses more on bacterial diversity and less on eukaryotes, which also play key roles in the nutrient cycle. In this study, 10 sampling sites along the Xiangjiang River were selected, covering the entire reaches of Changsha City, China. Both prokaryotic and eukaryotic diversity and composition in the water and sediment samples were investigated. The results showed that conductivity, TN, and NH4+-N were the main environmental parameters influencing the distribution of microbial communities in the river water column. Proteobacteria, Acidobacteria, and Actinobacteria were the dominant bacteria in sediments. The most abundant taxa in the water samples were Proteobacteria, Actinobacteria, and Firmicutes, with Chloroplastida being the dominant eukaryote. Eukaryotes in sediments are much spatially stochastic. Function analysis showed that bacteria in the water column had more phototrophic genes than those in the sediment samples, while the latter had more nitrogen-transformation-involved genes. This suggested that river sediment is more active in the global nitrogen cycle, while the overlying water plays an important role in oxygenic photosynthesis.