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

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 under-standing 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.

Automated summary

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. The results show that the atmospheric CH4 oxidation rates differ according to grassland type and grazing treatment, with the highest activity found in desert grasslands and the lowest activity in meadow grasslands. The study also suggests that CO2 production rate is an important factor associated with atmospheric CH4 oxidation activity in these grassland ecosystems.