Effect Of Grazing On Greenhouse Gases In A Sown Pasture In Temperate Semi-Arid Region

Ecosystem respiration (CO2), Methane (CH4) and Nitrous oxide (N2O) fluxes from a sown pasture in Inner Mongolia were monitored (from July 2012 to July 2015) by static opaque chamber/gas chromatography method at plots under continuous grazing, rotational grazing and ungrazing efforts, respectively. The results indicated that the sown pasture from Inner Mongolia region acted as a sink for CH4 (annual accumulation ranged from 1.3-1.5 kg C ha-1), and a source for N2O (annual accumulation ranged from ecosystem respiration 0.05-0.7 kg N ha-1), and the annual accumulation of ecosystem respiration ranged from 4.3-14.3t C ha-1. During the observation period, ecosystem respiration and CH4 showed a similar seasonal pattern, both with a low value of emission or absorption in freezing period, a high value in growing period and a moderate value in freezing-thaw period. However, N2O flux differed greatly between different observation year, and even negative fluxes were observed multiple times in the second and the third year.Correlation analysis of the fluxes and environmental factors from typical steppe suggested that soil temperature and soil moisture (WFPS%) were the main environmental factors that affecting the greenhouse gas emission. A significant negative hump-shaped nonlinear relationship was found between ecosystem respiration and soil moisture (P<0.01) while ecosystem respiration was positively correlated to soil temperature (P<0.01) in CG, RG and CK; Meanwhile, CH4 flux and soil moisture showed negative polynomial relation in CG (P<0.01), RG (P>0.05) and CK (P<0.01), and CH4 flux was significant negatively correlated to soil temperature in all sites; Though a significant positive relationship between N2O flux and soil moisture was found in all sites (P<0.01), we discovered a positive relationship between N2O flux and soil temperature only in CK (P<0.05).All the three Greenhouse gases were positively related to soil NH4+-N (P<0.05) in CK while only N2O in CG and ecosystem respiration in RG was positively related to soil NH4+-N. However, no relationship was found between the three Greenhouse gases with soil NO3- in any sites.Grazing effects significant affects ecosystem respiration and N2O flux in sown pasture, namely CG and RG differed significant with CK, but no statistical discrepancy was found between CG and RG (P>0.05). And grazing effects has no significant influence in CH4 flux in all three treatments.