EFFECTS OF CULTURE IN HIGH CO2 ON THE PHOTOSYNTHETIC PHYSIOLOGY OF FUCUS-SERRATUS

The lower intertidal macroalga Fucus serratus was cultured in high CO2 (5 kPa CO2) and air (33 Pa CO2) for three weeks to investigate possible adjustments to its photosynthetic physiology. When cultured in high CO2, the CO2 compensation point increased and affinity for CO2 decreased when measured with the thallus exposed to air. For the submersed alga, the pH compensation point and photon yield decreased. There was little change in the level of chlorophyll a and the rate of dark 14C fixation following culture at high CO2. The shift from a C4-type to Cj-type gas exchange physiology is comparable with the response of microphytes to high C02 acclimation. At the end of the three week period, the high CO2algae still possessed the ability to utilize bicarbonate ions as a source of inorganic carbon, but with a reduced capacity. As there was no change in the rates of dark fixation between low and high CO2cultured algae, it is concluded that this process is not directly involved in the inorganic carbon concentrating mechanism. © 1990 Taylor & Francis Group, LLC.