Mechanisms responsible for N2O emissions from intertidal soils of the Yangtze Estuary

Abstract Estuarine and coastal wetland ecosystems are important sources of atmospheric nitrous oxide (N2O). However, the underlying driver of emitted N2O from estuarine and coastal wetlands remains poorly understood. Here, natural-abundance isotope technique was applied to characterize the processes responsible for N2O emission from the intertidal soils of the Yangtze Estuary. Measured N2O emission rates ranged from 0.70 to 2.15 μmol m−2 h−1, with relatively high values at the upper estuarine sites. The δ15N, δ18O and SP (intramolecular 15N site preference) of emitted N2O varied from −4.5 to 6.7‰, 42.4 to 53.2‰, and 6.7 to 15.4‰, respectively. Gross N2O production and consumption rates were within the ranges of 3.16–14.34 μmol m−2 h−1 and 2.22–12.54 μmol m−2 h−1, respectively, showing a similar spatial pattern to N2O emission. N2O consumption proportion varied from 69.56 to 90.31%, which was generally lower at the upper estuarine sites. The gross production rates and consumption degree of N2O simultaneously controlled the variations in N2O emission. Bacterial denitrification was the dominant production pathway (78.22–97.36%), while hydroxylamine (NH2OH) oxidation contributed 2.64–21.78% to N2O production. Soil pH, Fe2+/Fe3+, sulfide and substrate availability were probably the main factors governing the N2O emission dynamics. Overall, these results highlight the substantial role of NH2OH oxidation and N2O consumption in N2O release in redox-dynamic soils of estuarine intertidal wetlands.