The anaerobic oxidation of methane (AOM) mediated by microorganisms is a key process in the reduction of methane emissions, and AOM-coupled electron acceptors have been shown to regulate methane emissions into the atmosphere in marine systems. Paddy fields are a significant source of methane and account for 20% of global methane emissions, but the effect of electron acceptors on the methane emission process in flooded paddy fields has been poorly characterized.
LUO dan and Prof. YAO huaiying from the institute of urban environment selected paddy soil samples were taken from the surface layer in a rice-wheat rotation field near Ningbo city for an anaerobic incubation experiment. It was published in Science of the Total Environment on May 15. Here, they added 13C-labeled CH4 (13CH4) into anaerobic microcosms to evaluate the role of electron acceptors by measuring the methane oxidation rate and the enrichment of 13C-labeled CO2 (13CO2). And then combined DNA-stable isotope probing (DNA-SIP) with amplicon sequencing to study the active microorganisms.
They found that the addition of biochar had no significant effect on AOM rate, while the addition of NO3- and Fe3+ significantly increased AOM rates. Moreover, the addition of NO3- and Fe3+ increased the rate of conversion of 13CH4 to 13CO2 compared to the control. In addition, to further demonstrate the occurrence of nitrate-dependent and iron-dependent AOM they performed a stoichiometry experiment. These results are in agreement with the theoretical values based on the thermodynamically equations.
They proposed ferric iron and nitrate act as terminal electron acceptors that can promote the oxidation of CH4 to CO2 and thus effectively mitigate the greenhouse gas emission in paddy soil. Furthermore, this work provides DNA-SIP based evidence that ferric iron-dependent AOM and nitrate-dependent AOM are mainly driven by iron-reducing bacteria and nitrate-reducing bacteria, respectively. This study may be helpful to understanding the global geochemical cycle and the regulation of methane emissions.
