Assessing the potential of ammonia oxidizing bacteria to produce nitrous oxide in soils of a high arctic lowland ecosystem on Devon Island, Canada

Abstract

The contribution of nitrifiers (ammonia-oxidizing bacteria (AOB)) and denitrifiers to nitrous oxide (N 2O) emission from arctic soils remains inconclusive. Based on preliminary experiments, we hypothesized that AOB are the primary producers of N 2O in a high arctic lowland ecosystem on Devon Island, Nunavut, Canada. In part 1 of the study, flux chambers were installed in a catena to determine in situ fluxes of gases (N 2O and carbon dioxide (CO 2)) from 16 June to 13 July 2004. Although fluxes were low, N 2O production occurred in the wettest area of the landscape when ammonium levels were high. As ammonium, but not nitrate, levels declined in the wet sedge meadow, N 2O emissions correspondingly decreased. In part 2, the contribution of nitrification and denitrification to N 2O production was assessed by Acetylene Inhibition Assay and 15N isotopically enriched incubations. Ammonium fertilization stimulated N 2O emissions to a greater extent than nitrate, and acetylene had a greater impact on N 2O emissions in ammonium-fertilized soils than in nitrate-amended soils. Stable isotope analysis indicated that at 50–55% water filled pore space, nitrification was the dominant (>80%) N 2O emitting process. In part 3, molecular analyses of the two N 2O producing groups indicated the both nitrifiers and denitrifiers did not differ between landforms. Our results suggest nitrifier denitrification is the dominant process occurring in these arctic soils and that the role of denitrifiers in N 2O release from arctic soils needs to be re-evaluated.