Effect of pH on growth of acid stream algae

Five species of algae (Chlamydomonas applanata var. acidophila, Euglena mutabilis, Gloeochrysis turfosa, Hormidium rivulare, Stichococcus bacillaris) were isolated from a stream at pH 2·6–3·1, and their laboratory growth studied. Growth of all species could occur at pH values lower than those from which they were isolated, the lowermost limits being quite similar to those recorded for the particular species growing anywhere in England. Morphological differences were apparent with all five species at the lowermost pH values. These took place with Stichococcus bacillaris at pH values at which there was little reduction in growth rate, but with the other species obvious differences in morphology were correlated with a marked reduction in growth rate below the optimum rate. At the uppermost pH value tested, however, no obvious morphological differences were apparent. The effect of including 10% stream water in the medium was rather similar for all five species. No influence on growth rate was detectable at the lower pH values, but higher pH values led to a decrease in growth rate as compared with that found in medium lacking stream water.