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

Methane (CH4) oxidation driven by soil aerobic methanotrophs demonstrates the capacity of grassland as a CH4sink. In this study, we compared the oxidation characteristics of atmospheric‐level and elevated concentration (10%) CH4in 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 CH4oxidation using DNA‐based stable‐isotope probing and Illumina Miseq sequencing. The results showed that the oxidation of atmospheric CH4only occurred in steppe and meadow soils where the USCγ group of methanotrophs was numerically dominant in the methanotroph community. Pasture soils, with their very low relative abundance of USCγ, did not show atmospheric CH4oxidation. However, a DNA‐stable isotope probing experiment with 10% CH4indicated that conventional CH4oxidizers (Methylocaldumand Methylocystis) rather than USCγ communities assimilated significant amounts of 13CH4for growth. The CH4oxidation mechanisms in the three experimental grassland soils varied significantly. The USCγ group may be obligate oligotrophic microorganisms or their growth requires specific unknown conditions. Grassland soils are methane (CH4) sinks, but their capacities vary between grassland types. In this study, atmospheric CH4consumption occurred in steppe and meadows but not in pasture. All three soils consumed elevated CH4. Methanotroph community differences between the three soils explain the variation in CH4consumption.