OLISTHODISCUS LUTEUS (CHRYSOPHYCEAE). IV. EFFECTS OF LIGHT INTENSITY AND TEMPERATURE ON PHOTOSYNTHESIS, AND CELLULAR COMPOSITION1

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Abstract
The effect of light intensity and temperature on photosynthesis, chlorophyll a, and cellular concentrations of nitrogen and carbon in an axenic clone of Olisthodiscus luteus Carter following incubation in both indoor and outdoor growth chambers was determined. Populations were grown outdoors and photosynthesis determined in a graded series of light intensities yielding 4–524 total ly (per 6 h) and temperatures from 5 to 23 C and indoors at 0.3–40 total ly and 5–30 C. In both series, photosynthesis was saturated at low light (∼10 total ly or 0.028 ly · min −1) and showed only slight inhibition at the higher light intensities. Chlorophyll a·cell−1 had a maximum at 15 C with declining values at extremes of temperature. Carbon and nitrogen were more variable between indoor and outdoor experiments. Populations incubated indoors increased their carbon (130–225 pg·cell−1) and nitrogen (23–35 pg·cell−1) content as a function of light and temperature from 5 to 20 C. The outdoor series had increases in cellular N and C as a function of light and temperature below 14 C but maximum C·cell−1 (175 pg) and N·cell−1 (>27 pg) as well as wide variations in assimilation number occurred between 14–21 C. Assimilation numbers (O. luteus in natural waters.