EFFECT OF HYDROGEN-ION CONCENTRATION ON CHLORELLA PHOTOSYNTHESIS

Aquatic green plants can assimilate carbon dioxide in solutions of widely varying hydrogen-ion concentration. Our purpose in investigating the rate of photosynthesis as a function of this factor was to clarify the interpretation of experiments in carbonate mixtures, where the concentrations of carbonate and bicarbonate ions and of free carbon dioxide all vary with the hydrogen-ion concentration. The relationships are shown in figure. 1, where the percentage of total carbon dioxide in each of these three forms is plotted against the pH. The range covered by the carbonate mixtures is to the right of pH 8. From here the proportion of bicarbonate, which is at first maximal, declines with increasing pH, and the carbonate, extremely low at first, rises gradually to its maximum somewhere beyond pH 12. At the same time the proportion of free carbon dioxide declines