Responses of functional genes to submerged plants restoration and their impacts on the sediment phosphorus source-sink shifts

Submerged plants play a vital role in ecological restoration and eutrophic water purification, influencing microbial communities within ecosystems by altering environmental factors, yet the specific pathways through which their associated functional genes regulate phosphorus (P) transformation remain unclear. This study aims to construct a submerged plants-algae-water-sediment composite system to investigate the response characteristics of microbial P cycling functional genes during submerged plants restoration and their influence on P transformation processes within the system. Results indicated that submerged plant cultivation suppresses algal growth and reduces dissolved total phosphorus (DTP) and soluble reactive phosphorus (SRP) in the overlying water by 29.6%-46.8% and 17.6%- 39.7%, respectively. Sediments showed a trend toward shifting from a source state to a sink state. Due to the inhibitory effect of plant root exudates on certain bacterial growth, the abundance of the phylum Proteobacteria decreased, while community diversity increased. Analysis of functional genes revealed that P cycling genes changed significantly before and after submerged plant cultivation, with the phoA gene showing a marked increase (from 277.65 to 323.68 Transcripts Per Million (TPM), total), indicating enhanced P mineralization. The ppx-gppA gene showed the greatest abundance (257.00-357.06 TPM). Functional genes showed significant correlations (p < 0.05) with physicochemical properties, sediment P, and source-sink transformation parameters, indicating that submerged plants can have an impact on functional genes and the transformation of sediment phosphorus source pools, primarily via indirect effects. This study provides theoretical support for deepening the understanding of P transformation mechanisms in submerged plants remediation.