Climatic factors and fertilization rates co-regulate anaerobic methane oxidation driven by multiple electron acceptors in Chinese paddy fields

Paddy fields constitute a substantial anthropogenic reservoir of methane, with their inundation management fostering an ideal habitat for anaerobic methane oxidation. Within this context, a novel clade of anaerobic methanotrophic (ANME) archaea, known as ANME-2d, has been identified as capable of catalyzing anaerobic methane oxidation in conjunction with nitrate and metal oxide reduction processes within paddy fields. Nevertheless, our comprehension of the mechanisms governing anaerobic methane oxidation and its pivotal role in regulating methane emissions within rice paddies remains limited. This study quantified the rates of nitrate- and iron (III)-driven anaerobic methane oxidation through 13C-labeled stable isotope tracing experiments in Chinese paddy fields spanning diverse climate zones. Additionally, it investigated the ANME-2d archaeal community using quantitative polymerase chain reaction and high-throughput sequencing techniques. The nitrate-driven anaerobic methane oxidation contributed 10.9% to methane emission reduction. This contribution is equal to the previously identified contribution of nitrite-driven anaerobic methane oxidation (11.2%) mediated via NC10 bacteria, but played more important roles than iron-driven one (4.1%). The rates of nitrate- and nitrite-driven anaerobic methane oxidation differed significantly among climate zones and showed positive correlation with the mean annual temperature. Furthermore, their rates were more sensitive to temperature increases at higher and lower latitudes, respectively, under both representative concentration pathways 2.6 and 8.5. The rate of anaerobic methane oxidation driven by nitrate exhibited a positive correlation with nitrogen fertilization rate but displayed a negative correlation with phosphorus fertilization rate. Conversely, the rate of anaerobic methane oxidation driven by iron showed no significant correlation with either nitrogen or phosphorus fertilization rates. This study underscores the great potential of anaerobic methane oxidation in mitigating global warming, particularly under the conditions of future climate change and elevated nitrogen loading. These findings underline the necessity of incorporating anaerobic methane oxidation as a crucial parameter in methane emission prediction models.