The stems and leaves of submerged macrophytes usually grow below the water surface and could provide a good biological carrier for the colonization and growth of planktonic bacteria in water. Therefore, attached bacteria on the stem and leaf surfaces of submerged macrophytes are important components and play a crucial role in aquatic ecosystems. To further understand the structure characteristics and functional differences of the bacterial community attached to the stems and leaves of submerged macrophytes, the submerged macrophytes Potamogeton crispus and the overlying water and sediment were sampled and analyzed in this study. The results showed that a total of 10 320 OTUs were detected in the P. crispus samples, the overlying water samples, and the sediment samples. These OTUs included 64 phyla, 189 classes, 448 orders, 721 families, and 1 366 genera. The richness and diversity of bacterial communities in sediments were the highest, followed by the stem and leaves of P. crispus, and the alpha diversity index of planktonic bacteria in water was the lowest. Significant differences （P<0.05） were observed among the four alpha diversity indices of the three source samples. Bacterial communities with greater similarity were obtained from the same source samples, but there was more distinct community composition dissimilarity in bacteria collected from the submerged macrophytes and the overlying water and sediment samples （P<0.05）. At the level of phylum, order, and genus classification, the relative abundance of most dominant bacterial species, non-dominant species, and occasional species showed significant differences among the three source samples （P<0.05）. Proteobacteria, Actinobacteria, and Bacteroidetes were common dominant bacterial phyla for the three source samples, while Firmicutes were unique dominant phyla for attachment bacteria on the plant stem and leaves of P. crispus. There were differences in carbohydrate metabolism, energy metabolism, amino acid metabolism, cofactors, and vitamin metabolism among the three source samples （P<0.05）. The relative abundance of chemical heterotrophic and oxidative heterotrophic functional types in the stem and leaf samples of P. crispus was higher than that in the overlying water and sediment samples. In addition, higher nitrate reduction, nitrogen respiration, and nitric acid respiration functions were observed in sediment samples. To summarize, the stems and leaves have the potential to encourage bacterial colonization and create a unique bacterial community on the surface of submerged macrophytes. Submerged P. crispus macrophytes and their surroundings （water and sediment） play different roles in the biogeochemical cycling of nutrients in the freshwater ecosystem.
Keywords: bacteria; diversity; fresh water; function; submerged macrophytes.