Vegetation composition shapes denitrifier community structure and enhances nitrogen removal in estuarine wetlands:...

Estuarine wetlands are critical biogeochemical hotspots where vegetation and soil properties jointly regulate microbial processes such as denitrification. This study investigated soil physicochemical properties and denitrifying bacterial communities (harboring nirS and nirK genes) across different vegetation types (Reed, Zhongshanshan, and Reed-Willow Mix) and soil depths (0-20 cm, 20-40 cm, and 40-60 cm) in the mudflat of the Paihe River estuary, Chaohu Lake. Soil nutrient availability and pH varied significantly with vegetation, with mixed vegetation supporting higher organic matter, nitrate, and total phosphorus levels. Proteobacteria dominated both nirS and nirK-type communities, but nirS assemblages exhibited greater compositional richness and stronger depth-related shifts. Environmental drivers differed between groups, nirS communities correlated mainly with pH, total nitrogen, and C/N, whereas nirK communities were more responsive to pH, total phosphorus, and nitrate. Co-occurrence network analysis revealed vegetation and depth-dependent structural complexity, with mixed vegetation showing increased network complexity with depth. Denitrification rates declined with depth and ranked Reed-Willow Mix > Reed > Zhongshanshan. nirK taxa explained more rate variation than nirS, with Bradyrhizobium, Sinorhizobium, and Mesorhizobium most influential; regression implicated Brucella and Achromobacter positively and Bosea negatively. Mixed vegetation thus enhances denitrification by improving soil conditions and selecting nirK-dominated guilds in the active layer. The findings provide novel evidence that vegetation composition shapes both the structure and function of denitrifying microbial communities, with Reed-Willow Mix enhancing microbial diversity, interaction complexity, and denitrification efficiency. These results underscore the importance of vegetation management in sustaining nitrogen removal capacity and ecosystem functioning in estuarine wetlands.