Using ¹³C isotopes to explore denitrification-dependent anaerobic methane oxidation in a paddy-peatland

Peatlands are organic-matter-rich but nitrogen-limited natural systems, the carbon/nitrogen (C/N) status of which are subject to increasing exposure from long-term nitrate (NO₃^-) fertilizer inputs and atmospheric nitrogen (N) deposits. To manage and protect these unique environments, an improved understanding of denitrification-dependent anaerobic oxidation of methane (DAMO) in peatlands is needed. In this study, we used stable isotope measurements and incubation with NO₃^- additions to facilitate an investigation and comparison of the potential DAMO rates in a paddy-peatland that has been influenced by N fertilizer over 40 years and an undisturbed peatland in northeast China. Monitoring of ¹³CO₂ production confimed DAMO did occur in both the paddy-peatland and the undisturbed peatland, the rates of which increased with NO₃^- additions, but decreased logarithmically with time. When NO₃^- was added, there were no significant differences between the CH₄ oxidation in the paddy-peatland and peatland samples after 36 hours of incubation (97.08 vs. 143.69 nmol g^-1 dry peat) and the potential DAMO rate after incubation for 1 hour (92.53 vs. 69.99 nmol g^-1h^-1). These results indicate that the occurrence of DAMO in peatlands might be controlled by the amount of NO₃^- applied and the depth to which it penetrates into the anoxic layer.