Effects Of Different Grazing Intensities On Greenhouse Gases Flux In Typical Steppe Of Inner Mongolia

Recently,the greenhouse gas emission from human activity had a profound impact on carbon and nitrogen cycling in the terrestrial ecosystems,which affected the structure and function of entire ecosystem.The typical grassland in Inner Mongolia is an important ecological security shelter in China.As main land use form,grazing affected ecosystem process and regulated greenhouse gas emission,which had important feedback to climate change.This study investigated the effects of the grazing on greenhouse gas emissions and soil environmental factors of typical grassland in Inner Mongolia,and analyzed the relationships between greenhouse gas emissions and soil environmental factors,to reveal the mechanism in the impact of grazing intensity on greenhouse gas emissions.This study will provide a scientific basis for management of typical steppe ecosystems on adapting climate change and theoretic support for establishing policies on the reduction of greenhouse gases emissions in typical steppes.In this study,we carried out an experiment with four grazing levels in typical grassland of Inner Mongolia in 2017 and 2018.We measured flux of carbon dioxide?CO₂?,methane?CH₄?and nitrous oxide?N₂O?by static chamber method for.We also measured the changes of soil environmental factors under grazing intensities.Moreover,we analyzed the relationships between greenhouse gas emissions and soil environmental factors.The main conclusions are:?1?The emission of CO₂ increased with the intensity of grazing.Significantly positive correlations were found between CO₂ emission flux and soil microbial carbon content,10 cm depth soil temperature and moisture in typical grasslands.Grazing significantly affected soil microbial carbon content,and soil microbial biomass carbon content was significantly higher in M and H than CK.However,soil moisture decreased significantly in M and H treatments.Therefore,the response of soil microbial biomass carbon content dominanted the impact of grazing on CO₂ emissions on typical grassland.?2?The uptake of CH₄ decreased with the intensity of grazing.CH₄flux was positively correlated with soil nitrate nitrogen content and soil temperature,and negatively correlated with soil bulk density.However,a unimodal relationship was found between CH₄ flux and soil moisture.The CH₄ flux increased first and then decreased with the increase of soil moisture.Soil nitrate nitrogen content was significantly higher in H than CK.Soil bulk density increased significantly with grazing intensity,while soil moisture decreased significantly in M and H treatments.Therefore,the impact of grazing on CH4 uptake was dominated by the response of soil bulk density on typical grassland.?3?The emission of N₂O increased with the intensity of grazing.Significantly positive correlations were found between N₂O emission flux and soil ammonium nitrogen content,nitrate nitrogen content,pH,soil temperature and soil moisture.The soil pH,ammonium nitrogen and nitrate nitrogen content were significantly higher in grazing treatments than CK,while soil moisture was significantly lower in M and H treatments.Therefore,the effect of grazing on N₂O emissions was dominated by the response of soil pH and available nitrogen content on typical grassland.The N₂O emission flux of typical grassland was positively correlated with them.?4?Grazing promoted the emission of CO₂ and CH₄,and depressed the uptake of N₂O.The flux of each greenhouse gas had significant seasonality.The flux was significantly higher in growing season than that in the winter and freeze-thawing season.As converted into carbon dioxide equivalents,the emission of greenhouse gas grew with the intensity of grazing,and CO2 contributed most to the total annual greenhouse gas emissions.In summary,this study further confirmed the significant effects of different grazing intensity on the carbon and nitrogen cycle of typical grassland ecosystems from the perspective of three greenhouse gas?CO₂,CH₄ and N₂O?fluxes.Grazing affects the physical and chemical properties of typical grassland soils,resulting in changes in soil greenhouse gas flux.These conclusions are of great significance for predicting the future greenhouse gas emission patterns of typical grasslands and establishing a reasonable and efficient grazing system within the study area.