| Popis: |
Among approximately two thousand species of blue-green algae, about five hundred possess heterocysts and have the ability to fix atmospheric nitrogen. Certain non-heterocystous, filamentous algae also fix nitrogen, but only under microaerobic or anaerobic conditions. Because blue-green algae are photoautotrophic and develop in the upper soil layer, where conditions are usually aerobic, nitrogen fixation by non-heterocystous algae is much slower than by heterocystous blue-green algae. In the soils of the USSR, 133 species of heterocystous blue- green algae, among them about 30 nitrogen-fixing species are widely spread. |
