Role of methanogenesis and methanotrophy in CH fluxes from rice paddies under elevated CO concentration and elevated temperature.

The differential responses of methanogenesis and methanotrophy to elevated carbon dioxide concentrations ([CO]) (e[CO]) and elevated temperature ([T]) (e[T]) may lead to dramatic changes in the response of CH emissions from rice paddies to global warming. In this study, we systematically investigated the responses and mechanisms of CH flux from rice paddies to e[CO] and e[T] based on the production and oxidation of CH. The CH flux, soil properties, and soil methanogenesis and methanotrophy were observed under CK (ambient [CO] + ambient [T]), EC (e[CO] by 200 μmol mol + ambient [T]), ET (ambient [CO] + e[T] by 2 °C), and ECT (e[CO] by 200 μmol mol + e[T] by 2 °C) treatments. The results revealed that EC, ET, and ECT significantly increased the cumulative amount of CH (CAC) in the rice paddies by 10.63, 15.20, and 11.77 kg ha, respectively, compared with CK. ECT increased the CAC in the rice paddies by 1.14 kg ha compared with EC. Moreover, EC, ET, and ECT significantly enhanced the methane production potential (MPP) and methane oxidation potential (MOP) and tended to increase the mcrA gene abundance of the methanogens. EC tended to prompt the pmoA gene abundance of the methanotrophs, but the effect of ET on the pmoA gene abundance was less consistent across the growth stages. ECT significantly decreased the relative abundances of Methanosarcina and Methylocystis (Type II) by 4.9 % and 14.2 %, respectively, while it increased the relative abundance of Methylosarcina (Type I) by 24.0 % compared with CK. Overall, the increased MPP/MOP, mcrA/pmoA, and microbial biomass carbon under climate change increased the CH flux from the rice paddies. The contribution of e[CO] to the CH flux was significantly enhanced by e[T], which could further exacerbate the risk of global climate change induced by e[CO].