Abstract
SUMMARY: Counts using the most probable number method show that there are aerobic and anaerobic nitrogen‐fixing bacteria associated with mats of blue‐green algae in kikuyu lawns. Both types of bacteria are more numerous in the surface layers of soil adjacent to the mats of algae. Acetylene reduction by bacteria was only detected when glucose was added to either the soils or the algal mats.Mats of algae composed entirely of non‐heterocystous blue‐green algae were unable to reduce acetylene in situ or in any of the experimental conditions employed in the laboratory.