Constrained Forest Methane Sink by Thermal Adaptation of Soil Methanotrophs

Climate warming can stimulate soil methanotroph-mediated CH₄ oxidation, thereby mitigating the increase in atmospheric CH₄ concentrations in response to anthropogenic activities. However, the positive response of microbial activity to warming often weakens over time owing to thermal adaptation. Whether soil methanotrophs also show such adaptation in response to warming remains unknown, adding considerable uncertainty to predictions of soil CH₄ sink in a warming world. Here, we collected soils from 67 forest sites spanning a broad thermal gradient to investigate the response of microbial CH₄ oxidation to long-term temperature change. We find that microbial CH₄ oxidation rates decrease with rising mean annual temperature, indicating that soil methanotrophs thermally adapt to long-term temperature change. Our results further show that the thermal adaptation of microbial CH₄ oxidation decreases following long-term exposure to experimentally elevated CH₄ concentrations. Our findings suggest that the enhancement of soil microbial CH₄ oxidation rates resulting from warming may be smaller than previously predicted and that considering thermal adaptation of microbial CH₄ oxidation under diverse CH₄ concentrations is crucial for accurate predictions of future soil CH₄ sinks.