INTERACTIONS BETWEEN LIGHT, NH4+, AND CO2 IN BUOYANCY REGULATION OF ANABAENA FLOS‐AQUAE (CYANOPHYCEAE)1

Abstract

ABSTRACTBuoyancy of the gas‐vacuolate alga Anabaena flosaquae Brébisson was measured under various levels of light, NH4+, and CO2. At high irradiance (50 μE · m−2·−1) the alga was non‐buoyant regardless of the availability of CO2 and NH4+. At low irradiance (≤10 μE · m −2· s−1) buoyancy was controlled by the availability of NH4+ and CO2. When NH4+ was abundant, algal buoyancy was high over a wide range of CO2 concentrations. In the absence of NH4+, algal buoyancy was reduced at high CO2 concentrations, however as the CO2 concentration declined below about 5 μmol · L−1, algal buoyancy increased. These results help explain why gas vacuolate, nitrogen‐fixing blue‐green algae often form surface blooms in eutrophic lakes.