Nitrogen Fixation in Arctic Coastal Tundra in Relation to Vegetation and Micro-Relief

A study to estimate nitrogen fixation input in arctic coastal tundra was carried out using the acetylene reduction assay. Areal estimation was attempted by high intensity sampling over a limited area of tundra containing both high-centred and low-centred polygons with their corresponding variations in micro-vegetation. The highest average rates of acetylene reduction were obtained from cores in damp interpolygonal troughs (10.50 µmoles ethylene/m²-hr) where mats of the blue-green alga Nostoc were abundant. Wet moss-algal associations in hydric meadows showed high nitrogenase activity (average 6.86 µmoles ethylene/m²-hr) and dry high-centred polygons were comparatively inactive (2.80 µmoles ethylene/m²-hr). The lichens Peltigera sp. and Stereocaulon sp. were the most active nitrogen fixers in the drier tundra. Nitrogen fixation increased with rising temperature with a measured Q10 for Nostoc commune of 3.7.