Nitrogen Fixation by Some Algae in Arizona Soils

Abstract

Abstract Algal and lichen crusts and subsurface soil samples were collected from virgin and cultivated areas and analyzed for nitrogen and carbon. These crusts were incubated in the laboratory to determine if nitrogen could be fixed with time under the conditions stated. Algae isolated from the crusts also were tested for nitrogen‐fixing ability and quantitative information was obtained for some species in pure and mixed culture experiments. Species of algae belonging to the genera Nostoc Vauch., Scytonema Ag., and Anabaena were shown to fix atmospheric nitrogen. Certain coccoid forms may fix nitrogen. In the absence of Azotobacter , soil algae were shown to grow autotrophically and to contribute appreciably to the combined carbon and nitrogen status of Arizona soils.