Free-living cyanobacteria and their nitrogen fixation activity in a high arctic environment. Environmental factors influencing the nitrogen fixation activity

anabaena arctic region arctic tundra azote bacteria gram negativa biologie du sol coasts costa ecological succession environmental factors facteur du milieu factores ambientales fertilidad del suelo fixation de l'azote nitrification nitrogen nitrogen fixation nostoc primary productivity productividad primaria seasonal variation soil biology soil fertility spitzbeg svalbard toundra arctique tundra artica