Physiological Responses of Phytoflagellates to Dissolved Organic Substrate Additions. 2. Dominant Role of Autotrophic Nutrition inPyrenomonas salina(Cryptophyceae)

摘要

The enhancement of algal growth by organic substrate assimilation is a common laboratory observation, yet few studies have addressed the interaction of dissolved organic compounds and environmental factors for controlling the relative contribution of heterotrophy and autotrophy to the nutrition of these algae. The effects of light intensity and glycerol addition on the growth, cell volume, pigmentation, and carbon uptake of the facultative heterotroph,Pyrenomonas salinaSantore, were examined. Glycerol addition to cultures growing at a limiting light intensity increased the growth rate, increased the average cell volume and cellular starch content, decreased the cellular phycoerythrin to chlorophyllαratio, and had no effect on the CO2fixation rate cell−1. Glycerol addition to cultures growing at a moderate light intensity that was saturating for photo-autotrophic growth increased the average cell volume and cellular starch content but had no effect on the CO2fixation rate cell−1. The results indicate that autotrophy was the major process for carbon acquisition during the growth ofP. salina, but that carbon acquisition from glycerol catabolism also was used to partially support growth of the alga at the limiting light intensity. In addition, glycerol presumably was used to fulfill the energy and/or reductant requirements of the alga, and to increase the reserve carbohydrate (sta