Deepened Snow in Combination with Summer Warming Increases Growing Season Nitrous Oxide Emissions in Dry Tundra, But Not in Wet Tundra

Abstract

Climate changes in the Arctic (increased winter snowfall and higher summer air temperatures) may affect soil biogeochemical processes and hence surface N2O fluxes. However, arctic studies addressing these impacts on N2O fluxes are scarce. This study assessed surface N2O fluxes during three growing seasons in a dry heath and wet fen in West Greenland, subjected to field manipulations with deepened winter snow and summer warming. The soil capacity for potential denitrification activity (PDA) and potential net N2O production (N2Onet) was further measured to evaluate denitrification and N2O consumption potential. The surface N2O fluxes averaged 0.49 ± 0.42 and 2.6 ± 0.84 µg N2O-N m−2 h−1 , and total emissions were 212 ± 151 and 114 ± 63 g N2O-N (scaled to the entire study area of 0.15 km2 ), at the dry and wet tundra, respectively. The experimental summer warming, and in combination with deepened snow, significantly increased N2O emissions at the dry tundra, but not at the wet tundra. The deepened snow increased winter soil temperatures and growing season soil N availability (DON, NH4 + - N or NO3 - -N), but no main effect of deepened snow on N2O fluxes was found at either tundra ecosystem. The mean PDA was 5- and 121-fold higher than the N2Onet at the dry and wet tundra, respectively, which suggests that most produced N2O might be rapidly reduced to dinitrogen (N2). This study revealed modest but evident surface N2O fluxes from tundra ecosystems in Western Greenland. For the particular study area, N2O emission was a main positive driver for non-CO2 global warming potential with a growing season contribution of 97 kg CO2-eq. The study further suggests that projected increases in winter precipitation and summer air temperature may increase N2O emissions, particularly at the dry tundra dominating in this region.

Keywords: Arctic, Greenland, dry heath, Fen, global warming potentialN2O budget