Measurement of photosynthesis and photosynthetic efficiency in two diatoms

Growth, photosynthesis and photosynthetic efficiency have been measured in two diatoms: the commonly studied Phaeodactylum tricornutum and the sand diatom Amphora coffeaeformis . Both diatoms were grown under very high light and under low light (40 µmol.m ⁻².s ⁻¹). Photosynthesis was measured as oxygen yield and as electron transport rate. The ratios of photons absorbed by photosystem II to O ₂ evolved (quantum number), based on chlorophyll a (Θ*) and on surface area (Θ) for P. tricornutum and A. coffeaeformis under low light were between 5 and 6 and 9 and 11, respectively, and under high light were between 16 and 18 and 14 and 17, respectively. P vs E and ETR vs E curves were measured and from the oxygen yield results only a small amount of photoinhibition was observed. In A. coffeaeformis strong non-photochemical quenching was observed. The results show that diatoms exhibit flexible photosynthetic systems and under optimal conditions are very efficient.