Effects Of Landuse Types On Greenhouse Gas Emissions And Ecosystem Carbon Balance In The Typical Steppe Of Inner Mongolia

There is no room for doubt on global warming now.Reducing the emissions of greenhouse gases?GHG?such as carbon dioxide?CO2?,methane?CH4?and nitrous oxide?N₂O?caused by human activities is the main measure to mitigate climate warming.Understanding the patterns and mechanisms of GHG emissions and their changes under human activities is the basis for developing a low-emissions management systems,and is the hotspot of current research.Grassland accounts for20%covering of the land cover.Grazing and mowing are the most important types of grass land-use.The impact of land use on the GHG emissions from grassland ecosystems is related to the grazing intensity,seasons of patterns,and with the frequency and intensity of mowing,as well as with the livestock composition and fertilizer management.Current research is relatively concentrated on the relationship between grazing intensity and GHG emissions,and few studies are on the effects of grazing methods?different seasonal patterns?,and mowing practice.In present study,we used an experimental platform of grassland use to determine the effects of Grazing,Mowing?M?and Fencing?F?on GHG emissions and ecosystem carbon balance in a typical steppe in Inner Mongolia,and to explore the underlying impact mechanisms.The grazing treatments included All-season Grazing?AG?,grazing 5 times in plant growing season?once a month from May to September?,and Spring&Summer Grazing?SG?,grazing twice in June and August.Grazing intensity in both treatments is same and moderate?grazing days×number of livestock in two treatments is same?.The results show that:?1?During plant growing season,the fluxes of ER,CH₄ and N₂O in the four treatments ranges respectively from?66.46±10.96?mg·m^-2·h^-1 to?93.68±13.32?mg·m^-2·h^-1,from?-61.94±2.63?ug·m^-2·h^-1 to?-68.29±3.25?ug·m^-2·h^-1,and from?2.18±0.23?ug·m^-2·h^-1 to?1.35±0.29?ug·m^-2·h^-1.ER contributes 97%and 99%of Global Warming Potential?GWP?and Global Temperature Change Potential?GTP?,respectively.?2?Compared with fencing,grazing under appropriate grazing pressure may reduce the GHG flux by 20%to 30%over the growing season,while mowing may lead to an increase in GHG fluxes.?3?Under the same moderate grazing intensity,GHG flux in AG with the higher grazing frequency,is 12%lower than that in SD with low grazing frequency.The results also show that soil moisture is closely related to the GHG flux,and the carbon cycle of steppe ecosystems.Different types of land use mainly affect GHG emissions by affecting soil moisture and other properties.The higher activity of methane oxidizing bacteria under the moderate grazing also support the measured results that grazing promote the CH₄ oxidation.High grazing frequency may enhance grassland CH₄uptake,compared with low grazing frequency.Our results provide basic scientific data for the development of a low-emission grassland management system.