POOR PHYSIOLOGICAL ADAPTATION TO ALKALINE CULTURE CONDITIONS IN CLOSTERIUM-ACUTUM VAR VARIABLE, A PLANKTONIC DESMID FROM EUTROPHIC WATERS

In contrast to other planktonic desmid taxa from eutrophic, alkaline habitats, cultures of Closterium acutum var. variabile experienced acute intoxication in Tris-buffered medium at pH 8.5. Also, in Hepes- and in bicarbonate-buffered medium at pH 8.5, cells showed chloroplast deformation and tended to die off. At pH 8.5 photosynthetic rates at low light intensities (up to c. 30 mumol m-2 s-1) were diminished by a factor of at least 2 compared with those at pH 7.0. Maximum phosphatase activity was found at pH 7.0. Reduced physiological activities at high pH as assessed in the culture experiments described here are discussed in relation to the distribution of Closterium acutum in the field.