Abstract: Submerged macrophytes play a vital role in regulating phosphorus (P) cycling in freshwater ecosystems, yet how plant identity and phenology influence microbial interactions and P mobilization across the sediment-water interface remains poorly understood. In this study, we employed high-throughput sequencing, network-based ecological analysis, and high-resolution measurements of phosphorus diffusion to investigate how five submerged macrophytes, across three growth stages, influence microbial community dynamics, co-occurrence networks, and sediment P release. High-throughput 16S rRNA gene sequencing revealed that plant species and growth stage jointly shaped microbial diversity. Water microbial communities showed greater compositional responsiveness to plant identity and growth stage, yet were assembled predominantly by stochastic processes, while sediment microbial communities were jointly structured by deterministic and stochastic processes. Co-occurrence network analysis showed that water networks were more densely connected but less stable than those in sediment. Sediment microbial diversity and negative cohesion in water microbial networks were positively associated with phosphorus diffusion fluxes, whereas positive cohesion in water microbial networks showed the opposite pattern. Cross-habitat microbial networks further revealed that sediment-derived key bridge taxa, mainly affiliated with Firmicutes, Proteobacteria, Actinobacteriota, and Cyanobacteria, were significantly associated with microbial biomass, enzyme activity, and P flux, suggesting a potential role in linking water-sediment microbial organization with P cycling. These findings underscore the importance of plant identity and microbial connectivity in shaping internal P cycling and provide a cross-habitat microbial perspective for optimizing macrophyte-based restoration strategies.

Key words: Submerged macrophytes, Growth stages, Microbial communities, Cross-habitat microbial networks, Phosphorus dynamics