THE BLUE-GREEN ALGAE AS THE NITROGEN FIXATORS

Abstract

This chapter discusses the role of blue–green algae as the nitrogen fixators. The common algae that belong to red, brown, and green algae and others have no ability to fix atmospheric nitrogen. The algal nitrogen fixators are limited to the blue–green algae. Among these, about 30 are known to be nitrogen fixators. Most species are concentrated in the order Nostocales, in which only the species belonging to the family Oscillatoriaceae have no nitrogen fixing capacity. As this family has no heterocysts, Oscillatoriaceae not being a fixator is in accord with the finding that all fixators have, without exception, heterocysts in their trichomes. The capacity of these organisms for nitrogen fixation is lower than in bacteria such as Azotobacter, Clostridium, and others. The amounts of total nitrogen fixed by blue-green algae Tolypothrix tenuis, Calothrix brevissima and Anabaenopsis circularis per 100 ml of nitrogen-free media in 2 months have been found to be 9.6 mg, 5.2 mg and 3.4 mg.