Inorganic carbon transport in microalgae. II: Uptake of HCO 3− ions during photosynthesis of five microalgal species

Abstract

Ankistrodesmus braunii, Chlamydomonas reinhardii, Chlorella fusca, Chlorella vulgaris and Scenedesmus obliquus were tested for uptake of HCO 3 − ions during photosynthesis. NaH 14CO 3 was injected into illuminated algal suspensions (pH 5.7; 500 μM unlabelled HCO 3 −; 15°C). 14C-fixation rate was estimated during the time course of isotope equilibration between HCO 3 − and CO 2, which occurred at a rate constant of approx. 0.07 s −1 under the conditions employed. All algal species were able to take up HCO 3 − ions provided they had been adapted to low CO 2 level prior to the experiment. In this case the percentage of HCO 3 − uptake in total carbon uptake was similar to the percentage of HCO 3 − ions in total inorganic carbon concentration at the pH of the medium (15% at pH 5.7). In contrast, when adapted to high CO 2 level (2%), most species used only free CO 2 in photosynthesis.