The Relation of Acetylene Reduction to Heterocyst Frequency in Blue-Green Algae

The variation of acetylene reduction activity and heterocyst frequency with culture age, was studied in five species of blue-green algae. The heterocyst frequency varied between 2.5 to 12.3 per cent of total cells; and the acetylene reduction activity varied 2.0-fold (average). It is suggested that an estimate of the nitrogen fixation rates in blue-green algae may be made by in situ heterocyst counts and acetylene reduction measurements.