Effects of temperature on photosynthetic parameters and TEP production in eight species of marine microalgae

The effects of temperature on photosynthesis and transparent exopolymeric particle (TEP) production for 8 planktonic species belonging to 3 microalgal phyla (Heteronkontophyta, Dinophyta and Haptophyta) were investigated. Nutrient-replete semi-continuous cultures were grown at 13 temperatures between 5 and 25°C or 35°C (depending on the lethal temperature). A non-linear parametric model was applied to data on growth rate, photosynthetic parameters (electron transport rate, ETR), light utilization efficiency, a) and TEP production. The maximal photosynthetic activity at optimal temperature of production varied from 2.70 (Pavlova lutheri) to 4.64 (Thalassiosira pseudonana) mmol e- (mg chl a)-1 h-1. The variation in the photoacclimation state confirmed the similarity of acclimation trends at low temperature to those at high irradiance. However, different responses were observed between species, highlighting the fact that photoacclimation mechanisms vary interspecifically for both light harvesting and downstream photosynthetic metabolism. TEP production was lowest in Isochrysis galbana and greatest in Lepidodinium chlorophorum (6 vs. 380 mg xanthan equiv [mg chl a]-1 d-1). The proportion of carbon fixed by photosynthesis and excreted as TEP was 70.8% for L. chlorophorum, while other species excreted 6.7 to 30 %. A linear relationship was found between the ETR(T) and TEP(T) models for the 3 diatoms, indicating a coupling between photosynthetic activity and TEP production. This provides a new outlook on carbon excretion, which has classically been described as a consequence of nutrient stress.