Effect Of Grazing Intensity On The Emissions Of N₂, N₂O, NO, CO₂, CH₄ In Temperate Semiarid Grasslands

Emissions of carbon dioxide(CO2), nitrous oxide(N2O), methane(CH4) to the atmosphere is the primary cause of global warming in the global climate change, and the importance of terrestrial ecosystems as either source or sink of greenhouse gases. Grasslands play a crucial role of the terrestrial ecosystem, cover about 20% of the temperate land surface of the Earth and are widely used as pasture. Most of the grassland suffers from degradation due to overgrazing. Carbon and nitrogen cycle of the soil in the grassland may be changed by grazing.The soils were taken from the Leymus Chinensis grassland of Inner Mongolia with ungrazed(UG), light grazed(LG) and heavy grazed(HG) since 2004. Using a gas-flow-soil-core technique to measure the emissions of N2, N2 O, NO(nitric oxide), CO2 and CH4 for each soil sample simultaneously. The soil samples collected from three plots with different grazing intensities were incubated at two levels of O2 concentrations(sufficient: 20% O2, and less sufficient: 10% O2) and two incubation temperatures(the lowest and average temperature during the growing season: 5°C and 20°C). Adding amount of simulated rainwater to make the soil moisture was set to 65% WFPS. To understand the effect of grazing intensity on the greenhouse gases emissions, and estimate the annual N2 emissions in grassland soil. The major conclusions of this study are as follows:1. The emission rates of N2 from the three different grazing intensity were in the range of 3.05 ~ 22.77 μg N h-1 kg-1 ds, 7.05 ~ 58.32 μg N h-1 kg-1 ds and 0.87 ~ 8.43 μg N h-1 kg-1 ds, respectively. N2 O were in the range of- 0.02 ~ 8.91 μg N h-1 kg-1 ds,- 0.01 ~ 15.43 μg N h-1 kg-1 ds and- 0.002 ~ 4.18 μg N h-1 kg-1 ds, respectively. The emission rates of NO were very low and all less than 0.36 μg N h-1 kg-1 ds. CO2 were in the range of 0.001 ~ 1.15 mg C h-1 kg-1 ds,- 0.005 ~ 2.39 mg C h-1 kg-1 ds and 0.01 ~ 2.41 mg C h-1 kg-1 ds. The flux of CH4 performed for absorption, and emission rates in the rage of- 0.09 ~ 0.01 μg C h-1 kg-1 ds,- 0.15 ~ 0.15 μg C h-1 kg-1 ds, and- 0.05 ~ 0.01 μg C h-1 kg-1 ds, respectively. The dynamic of gases emission rates were significantly affected by temperature, and not sensitive to oxygen.2. The effect of grazing intensity on the cumulative emissions of N2, N2 O and CO2 was not obvious. With the increased of grazing intensity, the cumulative emission of N2 O and the CH4 uptake were both reduced.3. Using the N2:N2O molar ratios of different culture conditions, and the insitu observation of N2 O emissions from the grow season. Estimated the N2 emissions were 0.08(UG), 0.11(LG) and 0.16(HG) kg N ha-1, respectively.4. Carbon and nitrogen content of the soil varied during the incubated. The soil ammonium contents decreased and the soil nitrate contents increased after the incubated. The cumulative nitrogenous gases emissions accounted for 1.4%- 3.6% of the changes of soil ammonium and nitrate contents.