Study On The Effect Of Different Land-use Types On Soil Methanotroph Abundance And Methane Uptake Rate In A Typical Steppe Of Inner Mongolia,China

Microbial oxidation is the only biological sink of atmospheric methane?CH₄?.It is essential to understand the variation of CH₄ fluxes of the grassland ecosystems in response to grassland use types for developing low-emission management system.Here we measured the CH₄ flux and the soil methanotroph abundance of a typical steppe ecosystem under grazing,mowing and enclosure management in central Inner Mongolia,with the aims to determine the effects of these grassland use types on CH₄ flux in the typical steppe ecosystem,and test the hypothesis that pmoA functional gene abundance regulates CH₄ fluxes.The measurements were conducted on the experimental grassland that had experienced 4 divergent grassland use treatments over 5 years.The treatments were whole plant-growing season grazing from May to September?WG?,spring&summer grazing?twice in May and July??SG?,autumn mowing?M?and enclosure?E?.We determined CH₄ flux using static chamber method,and quantified the abundance of pmoA functional genes using molecular techniques,in addition to investigate plant biomass and soil physiochemical properties.The results showed that moderate grazing significantly enhanced CH₄ uptake rate and the abundance of methanotroph abundance?i.e.,the pmoA gene copy number per gram of dry soil?.The pmoA gene copy number ranged from 6.9×10⁴ to 3.9×10⁵ per gram of dry soil in plant growing season.The CH₄ uptake rate was?83.75±2.79??g·m^-2·h^-1 under WG,which was significantly higher than that under SG,M or E by13.80%,28.43%and 22.85%respectively.Moderate grazing significantly enhanced soil sand content,total carbon?TC?,total nitrogen?TN?,but reduced soil NH₄⁺-N concentration,NO₃^--N concentration,and plant production.Mowing significantly enhanced soil temperature,TC,but reduced soil moisture.The CH₄ uptake rate was significantly and positively correlated with abundance of CH₄ oxidizing bacteria,as well as soil temperature,total organic carbon?TOC?,TC,and TN?P<0.05?;but negatively correlated with soil moisture,NH₄⁺-N content and plant biomass?P<0.05?.The abundance of CH₄ oxidizing bacteria was significantly and positively correlated with soil sand content,TC,TN?P<0.05?,but negatively correlated with soil moisture,NH₄⁺-N content,NO₃^--N content,and plants biomass?P<0.05?.We conclude that the steppe ecosystem is a CH₄ sink under all land-use types in central Inner Mongolia,and moderate grazing enhances methanotroph abundance and CH₄ uptake by improving soil sand content,and reducing plant production.Mowing has no significant effect on grassland methanotroph abundance and CH₄ uptake.The factors that significantly affect the abundance of methane oxidizing bacteria are soil texture,soil moisture,TC,TN,NH₄⁺-N content,NO₃^--N content and plant biomass;And that affect the CH₄ uptakes are the abundance of methane oxidizing bacteria,in addition to soil temperature,soil moisture,TOC,TC,TN,NH₄⁺-N content and plant biomass.These results provide new evidence for the effects of different land use types on the CH₄ fluxes in grassland ecosystems,and are of significance for the development of low-emission grassland management system.