What drives biological nitrogen fixation in high arctic tundra: Moisture or temperature?

• Published in: Ecosphere
• Main Authors: Rousk, Kathrin, Sorensen, Pernille Laerkedal, Michelsen, Anders
• Other Authors: Det Frie Forskningsråd, Carlsbergfondet, Danmarks Grundforskningsfond
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2018
• Subjects: Ecology; Ecology, Evolution, Behavior and Systematics; Climate change; Greenland; Subarctic; Tundra
• Online Access: http://dx.doi.org/10.1002/ecs2.2117; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2Fecs2.2117; https://esajournals.onlinelibrary.wiley.com/doi/pdf/10.1002/ecs2.2117

Abstract Biological nitrogen (N 2 ) fixation is one of the main sources of available N for pristine ecosystems such as subarctic and arctic tundra. Although this has been acknowledged more than a decade ago, few attempts have been undertaken to identify the foremost driver of N 2 fixation in the high Arctic. Here, we report results from in situ measurements of N 2 fixation throughout the main growing period (June–August) in high arctic tundra, Greenland, in climate change treatments, shading and warming, and control. Nitrogen fixation was also measured in cores that received additional water prior to the measurements. The climate change field treatments did not lead to significant changes in any measured parameters; however, N 2 fixation was promoted by adding water, and moisture was the most important factor influencing N 2 fixation in all climate change field treatments. Maximum N 2 fixation rates were measured below 14°C soil temperature, which is much lower than the theoretical and previously reported temperature optimum for the nitrogenase enzyme. Diazotroph (N 2 fixing bacteria) communities are adapted to low temperatures in high arctic settings, and increased temperature in a future climate may lead to decreased N 2 fixation rates, or to a shift in diazotroph communities.