Atmospheric methane oxidation is affected by grassland type and grazing and negatively correlated to total soil respiration in arid and semiarid grasslands in Inner Mongolia

Abstract

Methane (CH₄) is an important trace greenhouse gas and atmospheric CH₄ uptake by high-affinity methanotrophs in grassland soil accounts for an important proportion of the terrestrial CH₄ sink. However, our understanding of the comprehensive effects of grassland type and grazing treatment on active soil methanotrophs and atmospheric CH₄ uptake is still under debate. This study investigates the impact of grazing on CH₄ oxidation rate and active atmospheric CH₄ oxidizing methanotroph communities in two arid and semiarid grassland ecosystems (meadow and desert) by detecting transcripts of methane monooxygenase (pmoA) genes. Atmospheric CH₄ oxidation rates differed according to grassland type and grazing treatment. The highest activity was found in desert grasslands with moderate grazing and the lowest activity in meadow grasslands with exclosures. The differences in activities were linked with changes in abundance, composition and co-occurrence network patterns of active methanotrophs and CO₂ production rate. Redundancy, correlation and random forest analyses indicated that pmoA transcripts, available phosphorus (AP), NO₃‾−N, and CO₂ production rate were the most important factors predicting active methanotroph community composition and atmospheric CH₄ oxidation activity in these grassland ecosystems. A glucose amendment incubation experiment showed that addition of glucose increased heterotrophic microbial respiration and inhibited atmospheric CH₄ oxidation. This study provides evidence that CO₂ production rate is an important factor associated with atmospheric CH₄ oxidation activity in arid and semiarid grassland ecosystems and suggests that interactions between methanotrophs and other heterotrophs influence methanotroph activity in grassland ecosystems.