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

Abstract Although there have been numerous studies focusing on plants' roles in methane (CH 4 ) emissions, the influencing mechanism of wetland plants on nitrous oxide (N 2 O) emissions has rarely been studied. Here, we test whether wetland plants also play an important role in N 2 O 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 N 2 O transportation. The brackish marsh acted as a net source of both CH 4 and N 2 O. However, sedge plants played the opposite role in CH 4 and N 2 O emissions. The removal of the sedges led to reduced CH 4 emissions and increased accumulation of CH 4 inside the sediment. Apart from being a conduit for CH 4 transport, the sedges made a greater contribution to CH 4 oxidation than CH 4 production. The sedges exerted inhibitory effects on the release of N 2 O. The N 2 O 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 N 2 O production occurred mainly in the surface sediment layer. The vascular sedge could transport atmospheric N 2 O downward into the rhizosphere. The rhizospheric sediment, together with the vascular sedge, became an effective sink of atmospheric N 2 O.