Elevated and atmospheric-level methane consumption by soil methanotrophs of three grasslands in China

Background:Methane(CH4)oxidation driven by soil aerobic methanotrophs demonstrates the capacity of grassland as a CH4 sink.Methods:In this study,we compared the oxidation characteristics of atmospheric-level and elevated concentration(10%)CH4 in a typical grassland(steppe)on the Loess Plateau,an alpine meadow(meadow)on the Qinghai-Tibet Plateau,and an inland arid-area artificial grassland(pasture)in northwest China and investigated the communities of active methanotrophs and their contribution to CH4 oxidation using DNA-based stable-isotope probing and Illumina Miseq sequencing.Results:The results showed that the oxidation of atmospheric CH4 only occurred in steppe and meadow soils where the USCγgroup of methanotrophs was numerically dominant in the methanotroph community.Pasture soils,with their very low relative abundance of USCγ,did not show atmospheric CH4 oxidation.However,a DNA-stable isotope probing experiment with 10%CH4 indicated that conventional CH4 oxidizers(Methylocaldum and Methylocystis)rather than USCγcommunities assimilated significant amounts of 13CH4 for growth.Conclusions:The CH4 oxidation mechanisms in the three experimental grassland soils varied significantly.The USCγgroup may be obligate oligotrophic microorganisms or their growth requires specific unknown conditions.