Effect Of Grazing On Methane Flux And Related Microbes In Inner Mongolia Grassland Soils

Methane （CH₄） is one of the most important greenhouse gases, a long-term global warming potential 21 times greater than that of CO2. There are many sources of CH₄, including non-biological sources such as biomass burning, volcanic activity and biological sources mediated by microbes. The major sink of CH₄ includse photochemical oxidation by the hydroxyl radical in the atmosphere and biological oxidation by methanotrophs in soil. Grassland soil is an important sink of CH₄. The Inner Mongolian grassland is a major terrestrial ecosystem and has an important role to play in regulating greenhouse gas fluxes.The experimental site of this study was located at the Baiyinxile pasture in Xilinhot, where long-term research has been carried out to determine the impact of enclosure from grazing, mowing, and different intensities of grazing on grassland productivity and soil properties. In addition, we also studied the impact of sheep dung and urine on CH₄ emissions and related microbial communities on an experimental site in Chaokewula County. We used static chamber methods, PCR-DGGE, Real-time PCR, cloning and sequencing, and DNA-SIP to investigate the impact of grazing on methane flux and related microbes in the soil from these experimental sites.The results showed that in the soils on the Baiyinxile pasture where different management treatments were applied （Enclosure, Mowing or Grazing）, the Type I methanotrophs were main CH₄ oxidizers. Enclosure, Moderate grazing and mowing all increased the abundance and the community structure diversity of the methanotrophs, and these changes were mainly related to differences in soil moisture. However, no significant differences were found on the abundance of methanogens under different the different management treatments, even though enclosure had a different the community structure from the other treatments.Methane flux showed seasonal variations, and the addition of sheep excreta （dung and urine）, with different concentrations of nitrogen （N） inhibited soil methane uptake （oxidation）. As the amount of synthetic urine increased, the ammonium （NH₄+） concentration increased and so did the methane flux. The addition of dung was controlled by the soil-atmosphere gas exchange. Dung applied at the intermediate rate （3 kg/m2） had the biggest inhibitory effect on soil CHU uptake.Different intensities of grazing did not have a significant impact on the abundance of methanotrophs. The methanotroph abundance in the light grazing treatment （SRI.5） was initially low, but showed the strongest methane oxidation activity after the soil was exposed to high concentrations of CH₄. Type II methanotrophs in in this SRI.5 treatment showed even stronger methane oxidation activity than the dominant Type I methanotrophs usually found in the grassland soils. Light grazing （SRI.5） was the suitable grazing intensity for soil methane uptake of Inner Mongolia grassland.