Emergent Macrophytes Specifically Regulate Ammonia-Oxidizing Microbial Communities and Functions: Comammox Dominance and N2O Emission Effects

AIMS: Emergent macrophytes regulate nitrogen-cycling microbial processes in lake riparian zones, though the mechanisms underlying these species-specific effects remain to be fully elucidated. This study investigated the structure, functional activity, and environmental drivers of three ammonia-oxidizing microbial communities in sediments with different emergent macrophytes (Phragmites australis, Typha orientalis, and Thalia dealbata) in Meixi Lake, Changsha. METHODS AND RESULTS: Metagenomic sequencing, quantitative PCR (qPCR), potential nitrification rate, and N2O yield were integrated to reveal the influence of riparian vegetation on the structural dynamics and ecological effects of ammonia-oxidizing microorganisms. The results indicated that the emergent macrophytes altered the sediment physicochemical properties, thereby exerting certain selective effects on specific ammonia-oxidizing microbial communities. The microbial community structure was similar in the P. australis and T. orientalis sediments, whereas significantly different in the T. dealbata sediment. Comammox Nitrospira dominated across all sediments, with a maximum absolute abundance of 2.10 × 109 copies g-1. Notably, the T. orientalis sediment exhibited the highest comammox-driven potential nitrification rate (1.196 mg N kg⁻¹ d⁻¹), while the T. dealbata sediment showed the highest N2O production rate (3.042 ng N g-1 h-1). Environmental factor analysis revealed that organic matter and plant biomass facilitated N2O emissions driven by comammox and ammonia-oxidizing archaea (AOA), respectively. Furthermore, AOA abundance was positively regulated by pH whereas negatively regulated by ammonium nitrogen (NH₄⁺-N). CONCLUSIONS: This study demonstrates that different emergent macrophytes influence the nitrogen transformation processes by modulating the abundance and activity of key microbial communities, providing a scientific basis for optimizing plant configuration in ecological restoration to mitigate greenhouse gas emissions.