Seabird-affected taluses are denitrification hotspots and potential N₂O emitters in the High Arctic

In High Arctic tundra ecosystems, seabird colonies create nitrogen cycling hotspots because of bird-derived labile organic matter. However, knowledge about the nitrogen cycle in such ornithocoprophilous tundra is limited. Here, we determined denitrification potentials and in-situ nitrous oxide (N₂O) emissions of surface soils on plant-covered taluses under piscivorous seabird cliffs at two sites (BL and ST) near Ny-Ålesund, Svalbard, in the European High Arctic. Talus soils at both locations had very high denitrification potentials at 10 °C (2.62-4.88 mg N kg^-1 dry soil h^-1), near the mean daily maximum air temperature in July in Ny-Ålesund, with positive temperature responses at 20 °C (Q10 values, 1.6-2.3). The talus soils contained abundant denitrification genes, suggesting that they are denitrification hotspots. However, high in-situ N₂O emissions, indicating the presence of both active aerobic nitrification and anaerobic denitrification, were observed only at BL (max. 16.6 µg N m^-2 h^-1). Rapid nitrogen turnover at BL was supported by lower carbon-to-nitrogen ratios, higher nitrate content, and higher δ¹⁵N values in the soils at BL compared with those at ST. These are attributed to the 30-fold larger seabird density at BL than at ST, providing the larger organic matter input.