Study On Greenhouse Gases Fluxes And Carbon Balance In Grassland With Disturbance Of Anthropogenic Activity

Land reclamation and intensive grazing are the major anthropogenic activities in Inner Mongolia grassland at present time. Thus land use pattern in this area has been changed dramatically over the past few decades, and will continue to change at a higher rate. It has been suggested that anthropogenic activities be making more contribution to the global soil-vegetation sink of atmospheric carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). This study was designed to address the effects of cultivation and grazing on the fluxes of greenhouse gases (CH4, N2O and CO2) with the enclosed chamber and GC technique, and the effects of grazing on the balance of carbon in Xilin River Basin, Inner Mongolia.Two sets of sites were established to investigate the fluxes of CH4, NaO and CO2 between soil-vegetation and atmosphere interface in situ. One set of sites are composed of field experiments in a native Stipa baicalensis community with soil of chernozem and an adjacent spring wheat cropland from May to September of 1998. The second set of sites include field experiments in an fence-enclosed plot of Artemisia frigida-short bunchgrasses steppe as a control and three other plots with different grazing intensities (i.e. 1.33, 4, 6.67 sheep/hm2, respectively) from July of 1998 to February of 2000. In the second set of sites, beside greenhouse gases, soil organic carbon (SOC), and net primary productivity (NPP) were also determined to close the carbon budget.The results indicated that the native meadow steppe was a sink for atmospheric CH4 and grassland reclamation did not change this effect significantly. Rates of CKU consumption in cropland were 24.57 ugC.m-2.h-1 but only 23.38 ugC.m-2.h-1 in undisturbed grassland. However, the effect of cultivation on observed CH4 consumption rates was less than of seasonal changes in that both consumption rates had similar obvious seasonal dynamics during the investigating period.The native meadow steppe was a source for atmospheric N2O and large diurnal and seasonal variation were observed in N2O flux with a range from -0.484 to 7.425 ugN.m-2.h-1. There appeared two peaks for N2O flux in the growing season which occurred in middle May and late July through middle August. Cultivation increased the emission of N2O by 52%, but decreased the effects of seasonal change. Average seasonal N2O flux was 2.914 ugN.m-2.h-1. Besides, Artemisia frigida-short bunchgrass steppe was a sink for atmospheric CH4 and a source for N2O but the fluxes were lower than in -meadow steppe. Season and grazing influenced CO2 and N2O fluxes significantly but not for of grazing on CH4 consumption rate. The CO2flux under different grazing intensities ranked in the order of the Middle Grazing Intensity (MG) > the Heavy Grazing Intensity (HG) > the Light Grazing Intensity (LG) > Fencing (NG), while HG > MG > NG > LG for N2O flux.Data from the experiment suggest that Artemisia frigida-short bunchgrass steppe may shift from carbon sink to carbon source due to the dual influences of climate change and anthropogenic activities.