内蒙古农牧交错带土地利用变化对作物生长季N_2O排放量的影响

在内蒙古农牧交错带,选择4个邻近、不同开垦年限(5、10和50 a)的农田,分别记为C5、C10和C50,以及天然草地作为研究样地;利用静态箱法,在2008—2010年作物生长季(4—10月)进行野外原位试验,研究了土地利用变化对N2O排放量的影响.结果表明:草地与C5、C10、C50农田土壤的N2O排放量在2008—2010年作物生长季均存在显著差异,F分别为53.8、17.3和153.0(P均小于0.001),草地N2O排放量分别为87.6、91.8和211.0 mg/m2.在2008—2010年作物生长季,C5和C10农田土壤N2O排放量比草地低10%~50%;随着开垦年限的增加,N2O累积排放量增加,C50在作物生长季的N2O排放量比草地高10%~30%.草地和不同开垦年限的农田土壤在作物生长季内N2O排放量的58.1%受土壤w(NH4+-N)和含水量的综合影响(R2=0.58,P0.01).

Effects of Land-Use Change from Grassland to Cropland on Seasonal N2O Emissions in Farming-Pastoral Ecotone of Inner Mongolia

Abstract: Four adjacent sites with different land-use histories were selected in the agro-grassland ecotone of Inner Mongolia over three growing seasons from 2008-2010. The sites included grassland and cropland cultivated for 5,0 and 50 years after their conversions. N₂O flux measurements were obtained using the closed-chamber method and performed continuously from April to October in 2008,9 and 2010, respectively. The results indicated significant differences of N₂O emissions between cropland and grassland in 2008 (F=53.8, P<0.001), 2009 (F=17.3, P<0.001) and 2010 (F=153.0, P<0.001). Seasonal cumulative N₂O emissions were 87.6,1.8, and 211.0 mg/m² during seven months for the growing seasons in 2008,9 and 2010. From 2008-2010, the cumulative seasonal N₂O emissions of the cropland soils that were 5 and 10 years old were 10%-50% less than those of the grasslands, and the seasonal N₂O emissions from 50 year-old cropland soil were 10%-30% greater than those of the grasslands. Thus, N₂O emissions increased with the growth of the cropland age from 5 to 50 years. The cumulative seasonal N₂O emissions of the grassland and cropland soils could be quantitatively predicted from the soil NH₄⁺-N and moisture concentrations (R²=0.58, P<0.01).