Extreme drought alters methane uptake but not methane sink in semi-arid steppes of Inner Mongolia

Global climate change, particularly drought, is expected to alter grassland methane (CH₄) oxidation, a key natural process against atmospheric greenhouse gas accumulation, yet the extent of this effect and its interaction with future atmospheric CH₄ concentrations increases remains uncertain. To address this research gap, we measured CH₄ flux during an imposed three-month rain-free period corresponding to a 100-year recurrence drought in soil mesocosms collected from 16 different Eurasian steppe sites. We also investigated the abundance and composition of methanotrophs. Additionally, we conducted a laboratory experiment to explore the impact of elevated CH₄ concentration on the CH₄ uptake capacity of grassland soil under drought conditions. We found that regardless of the type of grassland, CH₄ flux was still being absorbed at its peak, meaning that all grasslands functioned as persistent CH₄ sinks even when the soil water content (SWC) was <5 %. A bell-shaped relationship between SWC and CH₄ uptake was observed in the soils. The average maximum CH₄ oxidation rate in the meadow steppe was higher than that in the typical and desert steppe soils during extreme drought. The experimental elevation of atmospheric CH₄ concentration counteracted the anticipated reduction in CH₄ uptake related to physiological water stress on methanotrophic soil microbes under the drought stress. On the contrary, we found that across the regional scale, nitrogen, phosphorous, and total soil organic content played a crucial role in moderating the duration and magnitude of CH₄ uptake with respect to SWC. USC-γ (Upland Soil Cluster γ) and JR-3 (Jasper Ridge Cluster) were the dominant group of soil methanotrophic bacteria in three types of grassland. However, the methanotrophic abundance, rather than the methanotrophic community composition, was the dominant microbiological factor governing CH₄ uptake during the drought.