Activity of anaerobic methane oxidation driven by different electron acceptors and the relative microbiome in paddy fields across various rice growth periods and soil layers

Currently, little is understood about the role of different anaerobic oxidation of methane (AOM) pathways and their relative contributions in reducing CH₄ emissions from rice fields. The potential rates of AOM caused by nitrate-, iron-, and sulfate-reduction, as well as the anaerobic methanotrophic (ANME-2d) archaeal absolute abundance and community composition were investigated across varying rice growth periods (tillering, jointing, flowering, and maturing) and soil layers (0–10, 10–20, 20–30, and 30–40 cm). The average potential rate of nitrate-AOM (2.73 nmol ¹³CO₂ g^-1 d^-1) was significantly higher than those of iron- (1.15 nmol ¹³CO₂ g^-1 d^-1) and sulfate-AOM (0.42 nmol ¹³CO₂ g^-1 d^-1) across growth periods and soil layers. The AOM rates in surface soils (0–20 cm) and earlier periods (tillering and jointing) were significantly higher than those in deep soils (20–40 cm) and later periods (flowering and maturing), respectively. Differently, ANME-2d archaeal absolute abundance and community compositions were only significantly affected by soil layers, with the highest absolute abundance in the 10–20 cm layer. The organic carbon content and availability of electron acceptor were the primary factors governing the rates of different AOM pathways and community of ANME-2d archaea. Overall, this study provided the variation in AOM rates driven via multiple electron acceptors and ANME-2d archaeal community across rice growth periods and soil layers, and provided an important scientific basis for precise quantification of AOM as a potential CH₄ sink in rice fields.