Comprehensive effects of a sedge plant on CH₄ and N₂O emissions in an estuarine marsh

Although there have been numerous studies focusing on plants’ roles in methane (CH₄) emissions, the influencing mechanism of wetland plants on nitrous oxide (N₂O) emissions has rarely been studied. Here, we test whether wetland plants also play an important role in N₂O emissions. Gas fluxes were determined using the in situ static flux chamber technique. We also carried out pore-water extractions, sedge removal experiments and tests of N₂O transportation. The brackish marsh acted as a net source of both CH₄ and N₂O. However, sedge plants played the opposite role in CH₄ and N₂O emissions. The removal of the sedges led to reduced CH₄ emissions and increased accumulation of CH₄ inside the sediment. Apart from being a conduit for CH₄ transport, the sedges made a greater contribution to CH₄ oxidation than CH₄ production. The sedges exerted inhibitory effects on the release of N₂O. The N₂O was barely detectable inside the sediment in both vegetated and vegetation-removed plots. The denitrification measurements and nitrogen addition (the addition rates were equal to 0.028, 0.056 and 0.112 g m⁻²) experiments suggest that denitrification associated with N₂O production occurred mainly in the surface sediment layer. The vascular sedge could transport atmospheric N₂O downward into the rhizosphere. The rhizospheric sediment, together with the vascular sedge, became an effective sink of atmospheric N₂O.