Plant and Soil, 2010, Vol.331(1), pp.341-359
In order to identify the effects of land-use/cover types, soil types and soil properties on the soil-atmosphere exchange of greenhouse gases (GHG) in semiarid grasslands as well as provide a reliable estimate of the midsummer GHG budget, nitrous oxide (N 2 O), methane (CH 4 ) and carbon dioxide (CO 2 ) fluxes of soil cores from 30 representative sites were determined in the upper Xilin River catchment in Inner Mongolia. The soil N 2 O emissions across all of the investigated sites ranged from 0.18 to 21.8 μg N m -2 h -1 , with a mean of 3.4 μg N m -2 h -1 and a coefficient of variation (CV, which is given as a percentage ratio of one standard deviation to the mean) as large as 130%. CH 4 fluxes ranged from -88.6 to 2,782.8 μg C m -2 h -1 (with a CV of 849%). Net CH 4 emissions were only observed from cores taken from a marshland site, whereas all of the other 29 investigated sites showed net CH 4 uptake (mean: -33.3 μg C m -2 h -1 ). CO 2 emissions from all sites ranged from 3.6 to 109.3 mg C m -2 h -1 , with a mean value of 37.4 mg C m -2 h -1 and a CV of 66%. Soil moisture primarily and positively regulated the spatial variability in N 2 O and CO 2 emissions (R 2 = 0.15–0.28, P 〈 0.05). The spatial variation of N 2 O emissions was also influenced by soil inorganic N contents ( P 〈 0.05). By simply up-scaling the site measurements by the various land-use/cover types to the entire catchment area (3,900 km 2 ), the fluxes of N 2 O, CH 4 and CO 2 at the time of sampling (mid-summer 2007) were estimated at 29 t CO 2 -C-eq d -1 , -26 t CO 2 -C-eq d -1 and 3,223 t C d -1 , respectively. This suggests that, in terms of assessing the spatial variability of total GHG fluxes from the soils at a semiarid catchment/region, intensive studies may focus on CO 2 exchange, which is dominating the global warming potential of midsummer soil-atmosphere GHG fluxes. In addition, average GHG fluxes in midsummer, weighted by the areal extent of these land-use/cover types in the region, were approximately -30.0 μg C m -2 h -1 for CH 4 , 2.4 μg N m -2 h -1 for N 2 O and 34.5 mg C m -2 h -1 for CO 2 .
GHG fluxes ; Land-use/cover ; Semi-arid grassland ; Xilin River catchment
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