Observed and predicted measurements of photosynthesis in a phytoplankton culture exposed to natural irradiance

Abstract

Photosynthesis-irradiance (P-I) curves were produced (using artificial illumination) from samples taken at 1 or more times per day from a continuous culture illuminated with sunlight. The continuous culture housed an O2 electrode used to measure photosynthesis semi-continuously. Rates of photosynthesis predicted from P-I curves agreed with photosynthesis observed in the culture only for days of low irradiance. For sunny days or for days of variable irradiance, P-I curves predicted neither the morning photosynthesis maximum nor the afternoon depression. Daily integrals of predicted and observed photosynthesis were probably within the possible errors of measurement.