Acetylene Reduction by Blue‐green Algae in Sub‐tropical Grassland

SUMMARY In situ measurements using the acetylene reduction technique showed that mats of blue‐green algae found amongst kikuyu grass fixed nitrogen throughout the day and night. Daylight fixation increased throughout the morning, fell during the hottest part of the day, and reached a peak (19.2 mg C2H4 m−2 h−1) during the afternoon. Nitrogen fixation was higher on overcast days than on hot sunny days. Nocturnal fixation was also due to blue‐green algae and was sensitive to temperature changes.