Abstract

To model global processes which happen under the climate change, we should know the input of cyanobacterial communities to nitrogen balance in high latitude regions. It is widely known that the Arctic and mountain ecosystems are highly sensitive to changes of the climate. The forecasted increase in temperature in high latitudes, undoubtedly, will cause shifts in scale and rate of biogeochemical N-cycles and result in transformations of plant communities. The reliable forecasting of changes in the functional organization of ecosystems is only possible if vast and broad experimental data is taken into account in the models. Both seasonal and daily values of N2-fixation process has to be evaluated in various plant communities from different zones under variety of conditions. For balanced estimations, the various types of arctic ecosystems have to be included in the studies. The N2-fixation activity is barely studied on large territories of plain and mountain tundra of the NortheastEuropean Arctic. The article sums up results of a research on nitrogenase activity ratesin the soil crusts dominated byStigonema species.The species of the genus arewidespreadinthestudied regions, they have capability to fix nitrogen and they are important contributors to the N-inputin cryogenic disturbed soils. The nitrogen-fixing activity of investigated crusts was studied and the measured rates were 0.59-0.80 mg С₂Н₄ m^-2 h^-1under 15°С (frequent midday temperature in July)and 0.97-1.64 mgC₂H₄m^-2 h^-1 under 21°С(optimal temperature for N2-fixation in the Arctic). Crusts with the dominance of Stigonema genus from different regions of the European North-East have close rates of N2-fixing activity in latitudinal and altitudinal gradients under similar environmental conditions.The obtained values might be used to calculate the input of crustswith Stigonemato the N-balancein mountain and plain tundras for calculating global balance for high latitudes.

Keywords: Cyanobacteria/cyanoprokaryota; Black Stigonema crusts; N2 fixation; European arctic