Mechanisms responsible for N20 emissions from intertidal soils of the Yangtze Estuary

摘要

Estuarine and coastal wetland ecosystems are important sources of atmospheric nitrous oxide (N_2O). However, the underlying driver of emitted N_2O from estuarine and coastal wetlands remains poorly understood. Here, natural-abundance isotope technique was applied to characterize the processes responsible for N_2O emission from the intertidal soils of the Yangtze Estuary. Measured N_2O emission rates ranged from 0.70 to 2.15 μmol m-2-h~-1 with relatively high values at the upper estuarine sites. The б~15N, б~18O and SP (intramolecular ~15N site preference) of emitted N20 varied from -4.5 to 6.7%„, 42.4 to 53.2%o, and 6.7 to 15.4%o, respectively. Gross N20 production and consumption rates were within the ranges of 3.16-14.34 umol m~-2 h~-1 and 2.22— 12.54 μmol m~-2 h~-1, respectively, showing a similar spatial pattern to N_2O emission. N_2O 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 N_2O simultaneously controlled the variations in N_2O emission. Bacterial deni-trification was the dominant production pathway (78.22-97.36%). while hydroxylamine (NH20H) oxidation contributed 2.64-21.78% to N_2O production. Soil pH, Fe~2+/Fe~3+, sulfide and substrate availability were probably the main factors governing the N_2O emission dynamics. Overall, these results highlight the substantial role of NH_2OH oxidation and N_2O consumption in N_2O release in redox-dynamic soils of estuarine intertidal wetlands.