Using C 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 (NO) 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 NO 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 CO production confimed DAMO did occur in both the paddy-peatland and the undisturbed peatland, the rates of which increased with NO additions, but decreased logarithmically with time. When NO was added, there were no significant differences between the CH oxidation in the paddy-peatland and peatland samples after 36 hours of incubation (97.08 vs. 143.69 nmol g dry peat) and the potential DAMO rate after incubation for 1 hour (92.53 vs. 69.99 nmol gh). These results indicate that the occurrence of DAMO in peatlands might be controlled by the amount of NO applied and the depth to which it penetrates into the anoxic layer.