Effects of organic carbon sources on growth, photosynthesis, and respiration of Phaeodactylum tricornutum

Abstract

The growth, photosynthesis, and respiration of the marine diatom Phaeodactylum tricornutum were examined under photoautotrophic and mixotrophic conditions. 100 mM glycerol, acetate, and glucose significantly increased specific growth rate, and mixotrophic growth achieved higher biomass concentrations. Under mixotrophic conditions, respiration rate (Rd) and light compensation irradiance (Ic) were significantly higher, but net maximum photosynthetic O2 evolution rate (Pm) and saturation irradiance (Ik) were depressed. Organic carbon sources decreased the cell photosynthetic pigment content and chlorophyll a to c ratio, but with a higher carotenoid to chlorophyll a ratio. Ratios of variable to maximum chlorophyll fluorescence (Fv/Fm) and 77 K fluorescence spectra of mixotrophic cells indicated a reduced photochemical efficiency of photosystem II. The results were accompanied by lower electron transport rate. Therefore, organic carbon sources reduced the photosynthesis efficiency, and the enhancement of biomass of P. tricornutum implied that organic carbon sources had more pronounced effects on respiration than on photosynthesis.