Nitrous oxide fluxes of a boreal abandoned pasture do not significantly differ from an adjacent natural bog despite distinct environmental conditions.

Land-use conversion of pristine boreal peatlands for agricultural purposes is an ongoing process and projected to become more intensive with rising population growth and increased demands for food production. However, agricultural use of peatlands affects the production and emission of nitrous oxide (NO), a very potent greenhouse gas currently gaining more attention in the global assessment of greenhouse gases. While the intensity of NO emissions depends on a range of environmental factors, including hydrological parameters, temperature and the availability of nitrogen in soils, key driving processes remain poorly understood. In order to understand the effects of land-use change on the peatland ecosystem, we quantified NO fluxes under different land-use in a comparative study between a natural bog and an adjacent abandoned pasture in Newfoundland, Canada. We conducted in situ gas flux measurements using the static chamber method over five growing seasons. In addition, we measured photosynthetic rates and environmental parameters, namely soil temperature and moisture, water table and concentrations of total nitrogen and dissolved organic carbon in pore waters. According to previous studies, we hypothesized higher NO emissions from the abandoned pasture due to drainage compared to the natural bog. However, despite significant differences of environmental parameters and photosynthetic rates, we found no significant difference of NO fluxes between the two sites. We argue that NO production at the abandoned pasture was inhibited due to exhaustion of plant-available nitrogen as a result of increased gross primary production compared to the natural bog. We conclude that the effect of drainage and fertilization on NO fluxes during the growing season was superposed by vegetation composition change effects at the abandoned pasture, leading to similar NO fluxes at both sites.