Elevated temperature promotes methane-dependent arsenate reduction in paddy soils

Elevated temperature significantly impacts arsenic (As) bioavailability and speciation in soils. Methane (CH₄)-dependent arsenate reduction (M-AsR), a process in which As(V) reduction coupled with aerobic or anaerobic methane oxidation, has been extensively demonstrated in paddy soils. However, the intricacies of M-AsR under future global warming scenarios remain unclear. In this study, we aimed to investigate the effect of elevated temperature on M-AsR by conducting incubations with soil inocula and microcosm. Our findings indicated that M-AsR was highly sensitive to elevated temperature. Specifically, the generation rates of ¹³CO₂ and As(III) increased by 72.6 % and 36.1 %, respectively, when the temperature rose from 28 °C (the average daytime temperature in the rice-growing regions) to 33 °C (the future temperature condition). Quantitative polymerase chain reaction (qPCR) analysis revealed a positive correlation between temperature and the abundance of the arrA gene, the pmoA2 gene and the ANME-mcrA gene. Additionally, microbial community composition at 33 °C differed markedly from 28 °C. It was characterized by a greater relative abundance of type II methanotrophs (e.g., Beijerinckiaceae) and anaerobic methanotrophic archaea (e.g., Methanosarcinaceae), and by a decrease in type I methanotrophs (e.g., Methylomonaceae). Overall, our results highlight the importance of temperature in regulating M-AsR in paddy soils. Elevated temperature has the potential to significantly enhance the M-AsR pathway by changing the abundance of functional microorganisms and reshaping the microbial community.