Growth Response of Thalassiosira pseudonana Hasle and Heimdal Clone 3H to Illumination, Temperature and Nitrogen Source

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Abstract
Exponential phase division rate ofThalassiosira pseudonana Hasle and Heimdal clone 3H was studied in response to illumination intensity, day length, temperature, and nitrogen sources and concentrations. An apparatus is described for performing factorial experiments at three temperatures using day/night cyclic light of varied intensity. Population density was measured without subsampling using nephelometry calibrated with direct cell counts in parallel cultures. Cell division rates were computed by regression analysis of population densities during exponential growth. Exponential phase cell division rate was proportional to day length while division rate saturation intensity was the same with 12 or 24 hours of light per day. However, exponential phase was abbreviated under the more natural discontinuous illumination and ultimate cell yield was achieved by growth occuring during the phase of decreasing relative growth rate. We observed an optimal temperature range which always included 21 C but which varied in size with illumination intensity and with nitorgen source and concentration. Growth rate was affected by interactions among illumination intensity, temperature and nitrogen sources and concentrations. Under continuous illumination and nitrogen limination, the diatom did not respond additively to combinations of nitrogen sources in the growth medium.

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