Anaerobic methane oxidation coupled to arsenate reduction in paddy soils: Insights from laboratory and field studies

Anaerobic methane oxidation (AOM) coupled to nitrate, sulfate and iron has been most extensively studied. Recently, AOM coupled with arsenate reduction (AOM-AsR) was demonstrated in laboratory microcosm incubation, however whether AOM-AsR is active in the field conditions remains elusive. Here, we used ¹³C-labeled methane (¹³CH₄) to investigate the AOM-AsR process in both anaerobic microcosms and field conditions with identical soils. Our results revealed the occurrence of AOM-AsR in the field, but AOM-AsR in the field was not as active as that which occurred in the laboratory (AOM-AsR contributed approximately 33.87% and 80.76% of total As release in the field and laboratory studies, respectively). This occurred because the laboratory setting provided a more suitable condition for the AOM-AsR process. Moreover, the results suggested that the relative abundance of mcrA from the ANME-2d was the most abundant. Our results clearly demonstrate that the AOM-AsR is active in both the laboratory and field conditions. Moreover, the results highlight the potential risk the AOM-AsR for pose for As contamination in rice paddies.