ABSTRACT
Algae are a large diverse assemblage of ubiquitous oxygen-evolving phototrophic organisms. They are represented by cyanobacteria (bluegreen algae) and eukaryotic organisms belonging to Chlorophyta, Rhodophyta, Phaeophyta, Chrysophyta, Cryptophyta, Dinophyta, Euglenophyta, and Haptophyta. Cyanobacteria are the oldest group of oxygen-evolving photosynthetic prokaryotic organisms and are very important in both aquatic and terrestrial ecosystems because of their ability to fix carbon and dinitrogen (Dohler, 1986). Microalgae form an important component of soil microflora and are ubiquitous, probably accounting for up to 27% of the total microbial biomass in the soil (McCann and Cullimore, 1979). These organisms are involved in maintaining soil fertility besides oxygen production (Bold and Wynne, 1978). The important functional attributes of soil algae are addition of organic matter via carbon fixation, N2-fixation, and surface consolidation of soil besides being primary colonizers of barren areas (Metting, 1981). Also, cyanobacteria are more widespread than the other free-living micro-organisms capable of dinitrogen fixation (Bums and Hardy, 1975) and are thus very important for the nitrogen economy of soils. In addition, free-living and symbiotic cyanobacteria are commonly the principal agents for input of N as components of biological crusts in semi-arid lands and deserts (Metting, 1981).
