Alteration of nitrogen sink and emission by vegetation distribution in a wetland with significant change in water level.

In wetlands, hydrological conditions drive plant community distribution, forming vegetation zones with plant species and material cycling. This mediates nitrogen migration and NO emissions within wetlands. Five vegetation zones in a large wetland were studied during flooding and drought periods. Zones including mud flat, nymphoides, phalaris, carex, and reeds, distributed sequentially with increasing water level change rate. Carbon and nitrogen densities were higher during drought period. When sediments alternated between source and sink roles annually, NO emissions varied significantly with zones and water levels. Emission flux decreased with higher C:N ratio in sediments, approximating a threshold at 0.23 μg m h when C:N ratio exceeded 25. Denitrifying nirS and nirK genes and anammox hzsB gene varied significantly with water level, most prominently in mud flat and nymphoides zones. Plant distribution under hydrological conditions alters soil stoichiometric ratio, influencing NO emissions and microbial communities across vegetation zones. Therefore, in freshwater wetlands, hydraulic regulation and reduction in prolonged flooding would be an effective strategy for mitigation of greenhouse gas emissions.