Effects of temperature, irradiance, and daylength on the marine diatom leptocylindrus danicus cleve. I. Photosynthesis and cellular composition

Rates of 14C uptake and cellular composition of C, N, and Chl a in the marine diatom Leptocylindrus danicus Cleve were measured in axenic batch culture under 49 combinations of temperature (5, 10, 15, 20 °C), daylength (15: 9, 12: 12, 9: 15 LD), and irradiance (at least four irradiances per daylength). 14C uptake exhibited a temperature-dependent daylength effect. Similar P-I curves characterized cells grown under 15: 9 and 12: 12 LD; P max values were 17.2, 11.2, 4.3, and 1.8 pg C. pg Chl a −1. h −1 at 20, 15, 10, and 5°C, respectively. Under 9:15 LD at 20 and 15°C, the lightsaturated photosynthetic rate was ≈50% that in cells grown under longer daylengths. 14C uptake was independent of daylength at 10 and 5°C. The initial slope, a, of cells grown under long daylengths increased by five-fold between 5 and 20 °C. α values of cells grown under 9: 15 LD at 15 and 20 °C were depressed relative to longer daylengths. Chl a was inversely related to irradiance, and increased with temperature from 10 to 20 °C, whereas cell carbon and nitrogen showed a similar temperature dependence but was not influenced by irradiance or daylength. The C : N ratio and cell volume were independent of temperature, irradiance, and daylength. Both the C : Chl a and N : Chl a ratios increased with irradiance by greater amounts at lower temperatures.