Dose-response patterns of anaerobic oxidation of methane to nitrogen addition in Chinese paddy fields

Anaerobic oxidation of methane (AOM) has been identified as a previously overlooked methane sink in paddy fields, and it is known to be stimulated by nitrogen inputs. However, important knowledge gaps remain regarding the response patterns of AOM potential to different levels of nitrogen addition, as well as the optimal nitrogen levels that maximize AOM. Here, we investigated AOM potential across six Chinese paddy fields under NaNO₃ additions of 0-200 mg N kg^-1 (with increments of 40 mg N kg^-1). The AOM potential quantified by ¹³CH₄ isotopic experiments was observed to increase linearly with nitrogen input, peaking at 120-160 mg N kg^-1, after which the stimulatory effect plateaued or declined. AOM potential responses differed among sampling sites, and sites characterized by lower background available nitrogen levels or higher conductivity were more responsive to nitrogen addition. Furthermore, high-throughput sequencing and principal coordinates analysis revealed that the community composition of ANME-2d archaea played a more prominent role than that of NC10 bacteria in modulating AOM responses to nitrogen addition. Overall, this study revealed the dose-dependent stimulation of AOM potential by nitrogen addition in different Chinese paddy soils, highlighting the critical roles of soil inorganic nitrogen availability, conductivity, and the ANME-2d archaeal community in shaping AOM responses.