Seasonal and site-specific variations in nitrogen fixation in a high arctic area, Ny-Ålesund, Spitsbergen

Abstract

Nitrogen fixation was measured in different habitats in the area of Ny-Ålesund, Spitsbergen, using the acetylene reduction method on intact soil cores and Nostoc commune growing in macroscopic sheet communities. The samples were incubated both under constant conditions (19 °C and 200 μE∙m−2∙s−1) and under in situ conditions. Cyanobacteria were considered to be the major nitrogen-fixing organisms. The nitrogen fixation rates showed a seasonal variation during the growing season of 1994, with low activities just after the snow melt, increasing until the middle of August and showing a rapid decline after the snow fell on August 29. The soil temperature at the time of sampling showed a positive, linear correlation with the nitrogen fixation activities measured on intact soil cores, whereas the nitrogen fixation activities measured in situ of N. commune showed a positive, linear dependence on the moisture content in the sheets and the incubation temperatures inside the incubation vessels during the experiments. The optimal temperature of the nitrogen fixation activity was about 20 °C, both for N. commune and a Puccinellia salt marsh. The highest nitrogen fixation rate measured in situ was at a patterned ground, which had the highest pH, the highest concentrations of extractable calcium and magnesium, and the highest C:N ratio measured.Key words: nitrogen fixation, cyanobacteria, Nostoc commune, high arctic.