Nitrous oxide surface fluxes in a low Arctic heath:Effects of experimental warming along a natural snowmelt gradient

• Published in: Soil Biology and Biochemistry
• Main Authors: Kolstad, Elisabeth, Michelsen, Anders, Ambus, Per Lennart
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2021
• Subjects: Climate change; Greenland; NO; Snowbed; Soil nitrogen cycling; Tundra; Arctic
• Online Access: https://pure.au.dk/portal/en/publications/aaaa4c44-aaf9-4c5c-9603-86db6e6a0f7a; https://doi.org/10.1016/j.soilbio.2021.108346; http://www.scopus.com/inward/record.url?scp=85108422289&partnerID=8YFLogxK

Climate change is profound in the Arctic where increased snowfall during winter and warmer growing season temperatures may accelerate soil nitrogen (N) turnover and increase inorganic N availability. Nitrous oxide (N 2 O) is a potent greenhouse gas formed by soil microbes and in the Arctic, the production is seen as limited mainly by low inorganic N availability. Hence, it can be hypothesized that climate change in the Arctic may increase total N 2 O emissions, yet this topic remains understudied. We investigated the combined effects of variable snow depths and experimental warming on soil N cycling in a factorial field study established along a natural snowmelt gradient in a low Arctic heath ecosystem. The study assessed N 2 O surface fluxes, gross N mineralization and nitrification rates, potential denitrification activity, and the pools of soil microbial, soil organic and soil inorganic N, carbon (C) and phosphorus (P) during two growing seasons. The net fluxes of N 2 O averaged 1.7 μg N 2 O–N m −2 h −1 (range −3.6 to 10.5 μg N 2 O–N m −2 h −1 ), and generally increased from ambient (1 m) to moderate (2–3 m) snow depths. At the greatest snow depth (4 m) where snowmelt was profoundly later, N 2 O fluxes decreased, likely caused by combined negative effects of low summer temperatures and high soil moisture. Positive correlations between N 2 O and nitrate (NO 3 − ) and dissolved organic N (DON) suggested that the availability of N was the main controlling variable along the snowmelt gradient. The maximum N 2 O fluxes were observed in the second half of August associated with high NO 3 − concentrations. The effect of growing season experimental warming on N 2 O surface flux varied along the snowmelt gradient and with time. Generally, the experimental warming stimulated N 2 O fluxes under conditions with increased concentrations of inorganic N. In contrast, warming reduced N 2 O fluxes when inorganic N was low. Experimental warming had no clear effects on soil inorganic N. The study suggests that if increased ...