Nitrogen-fixing cyanobacteria in the mountain-tundra ecosystems of the northern regions of the Urals (diversity, functional characteristics)

In biological soil crusts (BSC) of mountain tundras of three northern regions of the Urals, 131 species of cyanobacteria from 46 genera were identified. Nitrogen fixers make up about 40% of the total diversity. The complex of dominants is formed by representatives of the genera Nostoc, Stigonema, Scytonema. Based on the study of the nitrogen-fixing activity of biological crusts dominated by cyanobacteria, two groups were distinguished: those with high and low rates of nitrogen fixation. High rates of nitrogen fixation, on average 3.17 mg C2H4 m-2h-1, are typical for BSC dominated by Nostoc commune Vaucher ex Bornet & Flahault or Stigonema ocellatum Thuret ex Bornet & Flahault, low rates, on average 1.01 mg C2H4 m-2h-1, for BC dominated by Stigonema minutum Hassall ex Bornet et Flahault. It has been shown that the nitrogen fixation of the studied BSCs depends to a greater extent on the composition of the dominant cyanobacteria species in soil crusts than on the geographic zone in which the samples were collected.