Seasonal and Spatial Variations in Riverine Functional Genes Related to Phosphorus Cycling and Their Responses to Environmental Factors in the Chishui River Basin

In our research we analyzed a series of water quality parameters and conducted a metagenomic analysis of the microbial community in the Chishui River (in southwestern China), aiming to explore the microbial driving mechanisms of the phosphorus cycle in the river ecosystem. The research results indicated that the concentrations of total phosphorus (TP) and soluble reactive phosphorus (SRP) were higher in summer, suggesting seasonal differences in exogenous input and water body biogeochemical processes. The concentration of manganese (Mn) is higher in autumn, and it shows a significant positive correlation with Soluble reactive phosphorus (SRP). This may indicate the contribution of endogenous release from sediments to phosphorus in the water body. There were significant differences in the abundance of phosphorus cycling functional genes between summer and autumn. For example, in summer, the abundances of high-affinity phosphate transporter (pstB), inorganic phosphate dissolution (pqqC), and polyphosphate decomposition (ppx) were significantly higher. This might be to adapt to high productivity and the potential lack of phosphorus, or it could be that the microorganisms carrying these genes have a greater advantage during the summer. In contrast, the relative abundance of phosphonate (phn) and glycerophosphate (ugpQ) was significantly higher in autumn, indicating that the metabolic focus of the microorganisms has shifted towards the utilization of organic phosphorus, or that the microorganisms that are adept at utilizing organic phosphorus have taken the dominant ecological position in this situation. Moreover, the analysis of the microbial community showed that the Proteobacteria phylum (Pseudomonad phylum) was the main phylum, and the relative abundance of key functional bacterial genera (such as Limnohabitans, Acinetobacter) reflected seasonal changes, which was consistent with the above functional gene patterns. Spearman correlation analysis indicated that environmental physical and chemical parameters (such as iron, dissolved oxygen, dissolved organic carbon, pH value) jointly regulated the composition and distribution of phosphorus cycling functional genes. Our research results demonstrated that the microbial community plays a crucial regulatory role in the biogeochemical cycle of the river ecosystem through the transformation of functional genes and the changes in community structure. The research results emphasize that attention must be paid to the phosphorus cycling process regulated by microorganisms and its impact, in order to control water body eutrophication and maintain the stability of the ecosystem.