Abstract:Wetlands play an important role in nitrogen storage, especially at high latitudes. Natural wetlands are characterized by anaerobic conditions and low turnover rates of organic matter, and are thus important terrestrial sinks for nitrogen. Nitrous oxide (N2O) is an important atmospheric trace gas and a component of the biological nitrogen cycle. It is agreed that the observed increase in atmospheric concentrations of greenhouse gases like N2O has led to a warming of the earth's surface. Nitrous oxide also contributes to the depletion of stratospheric ozone. Nitrogen losses in the form of N2O, during the decomposition of wetland soils have recently attracted considerable attention because of their contribution to global climate change. Despite intensive international research, even the newest global N2O balance still casts considerable uncertainties when evaluating the specific sources of enhanced N2O. The wetlands of the Xiaoxing'an Mountains are important natural forested wetlands in China. Fluxes of N2O have been measured in various ecosystems but few studies have investigated the emissions of N2O from the freshwater marsh ecosystems in the Xiaoxing'an Mountains. In this paper, N2O fluxes were measured in the Carex schmidtii marsh and Betula ovalifolia-Carex schmidtii shrub swamp ecosystems of the Xiaoxing'an Mountains in the growing seasons of 2007 and 2008. Static chamber and gas chromatography was used to study the seasonal and inter-annual variations of N2O flux and its relationship with environmental factors. Annual N2O emissions from the marsh and shrub swamp were 0.14 and 0.29 kg/hm2 in 2007 and 0.68 kg/hm2 and -0.10 kg/hm2 in 2008. There were obvious seasonal changes in N2O emissions during the measurement period except in the shrub swamp in 2008. The largest emissions were either in summer or summer and fall for both years (0.0037 mg · N2O m-2 · h-1 and 0.0082 mg · N2O m-2 · h-1 for the marsh and shrub swamp in 2007 and 0.016 mg · N2O m-2 · h-1 and -0.0025 mg · N2O m-2 · h-1 for marsh and shrub swamp in 2008). There was no significant difference in N2O emissions between the different ecosystems, but annual differences in N2O emission were observed in the shrub swamp and not in the marsh ecosystem. N2O fluxes from the marsh were significantly negatively correlated with water table (r=-0.52,P <0.05,n=15)in 2007 and the water table influenced the variation of N2O emissions throughout the growing season. The N2O fluxes in the marsh and shrub swamp ecosystems of the Xiaoxing'an Mountains were not significantly correlated with temperature (air temperature, temperature inside chamber and soil temperature at 0, 5, 10, 15, 20, 30, 40 cm). The gaseous losses of soil N from the study area to the atmosphere were small therefore the Carex schmidtii marsh and Betula ovalifolia-Carex schmidtii shrub swamp ecosystems of the Xiaoxing'an Mountains were sinks or low sources of N2O during the growing season. The emissions of N2O were strongly affected by the water table and exhibited seasonal changes.