Diurnal Variations in Chlorophyll a Content of Some Fresh-Water Algae

Abstract

Diurnal variations in the rate of photosynthesis of phytoplankton of natural waters have been recently described. Doty and Oguri (1957) observed variations up to eight-fold in the ability of oceanic phytoplankton to photosynthetically fix carbon. The high values occurred during evening hours. The authors suggest the possibility of variations in chlorophyll content as an explanation of the fluctuation in productivity. A similar periodicity in photosynthetic activity, but of smaller magnitude (only two-fold), was observed by Yentsch and Ryther (1957). They found a daily periodic variation in chlorophyll content and rate of chlorophyll synthesis. Shimada (1958) likewise found diurnal variation in -photosynthesis rate correlated with a similar variation in chlorophyll a concentration of phytoplankton. These observations were done on natural oceanic phytoplankton populations. To further study the concept of ,a daily variation in chlorophyll concentration, we attempted to measure the chlorophyll content of several unicellular algae grown under laboratory conditions during a 24 hr period.