bacterioplankton community in the reservoir

The widespread salinization of freshwater ecosystems poses a significant threat to their biodiversity, functioning, and services that they provide. The coastal reservoirs are at high risk of water salinization, greatly threatening the functionality of reservoirs due to their various and complex salt transport processes. However, the ecological characteristics of the bacterioplankton communities, key participants in maintaining ecosystem stability and function in coastal reservoirs, are not well understood. This study examined the vertical distribution, co-occurrence patterns, and assembly processes of total, abundant, and rare bacterioplankton communities in the upper, middle, and bottom water layers at nine sites around Beidagang Reservoir using high-throughput sequencing and multivariate statistical analyses. Our results indicated that salinization occurred, with total dissolved solids and chemical ion concentrations increasing with depth. Significant differences were observed in bacterioplankton richness and community structure (total, abundant, rare) between the upper and middle layers and between the upper and bottom layers. Most identified keystone species belonged to rare taxa in the middle and bottom layers, where subnetwork stability was higher than in the upper layer. Rare taxa displayed greater stability and more complex interspecies relationships than abundant taxa. Null models revealed that abundant taxa were mainly influenced by stochastic processes, while rare taxa and the total bacterioplankton community were more influenced by deterministic processes (especially homogeneous selection). Both salinity and nutrient variables explained more variation in abundant taxa than in the rare taxa using distance-based redundancy analysis and variance partitioning analysis. Abundant taxa exhibited wider niche breadth, stronger spatial turnover, and greater dispersal capacity than rare taxa, indicating that geographic factors may play a significant role in the assemblage of abundant taxa. These results enriched our understanding of interactions and ecological assembly mechanisms of rare and abundant bacterioplankton communities, environmental monitoring, and management in coastal reservoirs.