Light-mediated recovery of N2-fixation in the blue-green algae Anabaena spp. in O2 supersaturated waters.

It is well known that N2-fixation in blue-green algae is O2 sensitive. However, at least two species of the filamentous, N2-fixing blue-green alga Anabaena possess an indigenous mechanism allowing recovery of nitrogenase activity during O2 supersaturation. The process is light-mediated and appears to employ photoreduction as a means of overcoming N2 inhibition. Such recovery should optimize radiant energy utilization and N2 fixation in freshwater blooms, which are often O2 supersaturated during peak daylight hours.