the photosynthesis: Respiration ratio of some unicellular marine algae

Cultures of eleven unicellular algae were grown at various values of pH between 6 and 10, obtained by varying the supply of CO 2. In this pH range, the value of the ratio photosynthesis: respiration showed a maximum. It is suggested that the algae may be placed in three groups according to the values of the ratio at these maxima. In the first there was only Amphidinium, which gave a mean ratio of only 2.7; in the second, Chaetoceros 3.3, Chroomonas 5.3, Gymnodinium 4.0, Nitzschia sp., 5.7, and Phaeodactylum 4.0; and in the third, Biddulphia 7.3, Cylindrotheca 7.0, Dunaliella 9.1, Monochrysis 8.3, and Nitzschia closterium 9.0. The highest rates of photosynthesis were found between pH 7.1 and 7.5, except for Nitzschia closterium pH 6.3, Amphidinium pH 8.2 and Phaeodactylum pH 10.0. Most algae gave an assimilation number of ≈ 400 mol O 2 · mol −1, chlorophyll a · h −1.