Between light and dark, source and sink: N2O dynamics in a subarctic, nutrient-poor permafrost peatland

Global warming and associated permafrost thaw in the Arctic raise concerns about increased greenhouse gas emissions. Nitrous oxide (N₂O) is a potent greenhouse gas produced in soils, but the magnitude of N₂O fluxes from permafrost regions remains highly uncertain. While high N₂O emissions for nutrient-rich, bare Arctic soils have been reported, for nutrient-poor soils that dominate the region the magnitude and drivers of N₂O fluxes have rarely been investigated. We present an unprecedented dataset of 1487 chamber flux observations covering three snow-free seasons in a nutrient-poor thawing permafrost peatland in northern Sweden. Our results show that this ecosystem can act as a continuous and non-negligible, albeit small, sink of N₂O during the snow-free season, which has not been reported from in-situ studies before. We also discovered a continuous N₂O hotspot that indicates potential for substantial N₂O production and net emissions in specific areas of the peatland. Our study identifies complex controls of N₂O fluxes, highlighting interactions between photosynthetically active radiation (PAR), carbon dioxide (CO₂) fluxes, and other environmental factors. We show that PAR is an important but not exclusive driver, with differences in the set of drivers and shape of dependencies between light and dark conditions.

Our results underscore the non-negligible N₂O fluxes in nutrient-poor Arctic soils and the presence of hot spots which may be important for the total landscape scale N₂O budget. The crucial role of soil-plant-atmosphere interactions in N₂O dynamics and the role of light as a driver of N₂O flux may have implications for global greenhouse gas budgets and climate mitigation and should be further investigated in future studies.