A Study of Photosynthetic Light Reactions, and A New Interpretation of Sun and Shade Phytoplankton

Abstract

The relationship of photosynthesis to light intensity is examined, using phytoplankton cultured in different environments. The graphical means used in presenting the data are shown, and the desirability of normalizing the curves is discussed. In a less than optimal environment, the principal stage of photosynthesis affected is the rate of dark reactions. This causes the h to shift toward lower light intensities so that the maximum rate of photosynthesis is achieved at lower intensities. In phytoplanktonic ecology it has been the practice to utilize the position of the h as an index for classifying populations as sun or shade types. The experimental data presented make it doubtful that the h can be used in this manner. It is believed that the variation in the shape of the photosynthetic light curve for natural populations is more of a response to physiological stress than to classical adaptation.