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

Abstract

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 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 CH₄ oxidation. However, a DNA-stable isotope probing experiment with 10% CH₄ indicated that conventional CH₄ oxidizers (Methylocaldum and Methylocystis) rather than USCγ communities assimilated significant amounts of ¹³CH₄ for growth.

Conclusions

The CH₄ oxidation mechanisms in the three experimental grassland soils varied significantly. The USCγ group may be obligate oligotrophic microorganisms or their growth requires specific unknown conditions.