Response of growth and biochemical composition to variations in daylength, temperature, and irradiance in the marine diatom Thalassiosira pseudonana (Bacillariophyceae)

The relationships between the growth rate of the marine diatom Thalassiosira pseudonana (Hustedt) and irradiance, daylength, and temperature were determined in nutrient-sufficient semicontinuous cultures. The initial slopes of the growth versus total daily irradiance curves were not affected by temperature or daylength, Growth versus irradiance was best modeled as a hyperbolic function at short daylengths and better modeled as an exponential function at longer daylengths, The maximum or light-saturated growth rates at each daylength were modeled as a hyperbolic function of daylength, This model was extended in a novel manner to include temperature dependence providing a framework that can be used to interpret other experimental data on growth rate versus daylength, The resulting model should be useful in global models of phytoplankton growth. Carbon, nitrogen, and chi a quotas were influenced by daylength, irradiance, and temperature. Both C and N quotas were positive exponential functions of irradiance, whereas N and chi a quotas were significantly greater for cells grown at the lower temperature. The ratio chi a:C quota (chl a:Q(c)) was a strong negative exponential function of total daily irradiance, Cells grown at 10 degrees C had significantly greater chi a:Q(c) ratios than those grown at 18 degrees C, and daylength also had a significant positive influence on chi a:Q(c). The apparent effect of daylength on chi a:Q(c) was removed by standardizing chi a:Q(c) to growth rate (mu), resulting in a temperature-dependent relationship between chi a:Q(c).mu(-1) and irradiance that accounted for 95% of the variation in the data.