Vegetation composition modulates the interaction of climate warming and elevated nitrogen deposition on nitrous oxide flux in a boreal peatland.

Northern peatlands with large organic nitrogen (N) storage have the potential to be N2 O hotspots under climate warming, elevated N deposition, and vegetation composition change caused by climate change. However, the interactions of these three factors and the primary controls on N2 O fluxes in peatlands are not well-known. Here, the three factors were manipulated in a boreal bog in western Newfoundland, Canada for 5 years. We found that warming mitigated the positive N effect on N2 O fluxes in the mid-growing season under intact vegetation owing to the increase of available N uptake by vegetation and less N for N2 O production. In contrast, warming strengthened the N effect on N2 O fluxes in the early growing season under the absence of graminoids or shrubs, which could be attributed to the increase of available carbon and nitrogen for N2 O production. It should be noted that these effects were not observed under the condition of low carbon availability. In addition, gross primary production was found as a critical control on N2 O fluxes under N addition. Our findings emphasize that the interaction of abiotic (warming and elevated nitrogen deposition) and biotic factors (vegetation composition change) on N2 O fluxes should be taken into account in order to project N2 O fluxes in peatland ecosystems accurately.