小兴安岭典型苔草和灌木沼泽N_2O排放及影响因子

N_2O Emission and its driving factors from typical marsh and shrub swamp in Xiaoxing′an Mountains,Northeast China

为了研究小兴安岭林区典型苔草和灌木沼泽N2O排放通量的季节动态、年际动态及其与环境因子的关系,并估算排放总量,2007和2008年在植物生长季采用静态箱-气相色谱法,对小兴安岭林区典型修氏苔草(Carex schmidtii)沼泽和油桦-修氏苔草(Betula ovalifolia-Carex schmidtii)灌木沼泽N2O排放进行了监测。结果表明,苔草和灌木沼泽2007年生长季N2O排放总量分别为0.14 kg/hm2和0.29 kg/hm2;2008年分别为0.68 kg/hm2和-0.10 kg/hm2。苔草和灌木沼泽N2O排放通量除灌木沼泽2008年变化规律性不明显外,均具有比较显著的季节变化,最大排放出现在夏季或夏、秋季节,其中2007年N2O排放平均通量为0.0037 mg.m-.2h-1和0.0082 mg.m-.2h-1;2008年为0.016 mg.m-.2h-1和-0.0025 mg.m-.2h-1。分析表明,苔草沼泽N2O排放年际差异不显著,灌木沼泽N2O排放年际差异显著;不同类型沼泽间N2O排放差异不显著;仅苔草沼泽2007年N2O排放通量与水位具有显著的负相关性(r=-0.52,P<0.05,n=15)。

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.