Inorganic carbon accumulation by the marine diatomPhaeodactylum tricornutum

Abstract

The ability of the diatom Phaeodactylum tricornutum to accumulate inorganic carbon was investigated using the silicone oil centrifugation technique. At internal inorganic carbon concentrations less than 0.2 mol m^-3 the internal inorganic carbon concentration was always greater than expected assuming CO₂ assimilation based on diffusion. When tested at 2.0 mol m^-3, the normal inorganic carbon concentration of seawater, the internal inorganic carbon concentration was less than the external concentration. Apparently this alga has the ability to accumulate inorganic carbon. When grown in poorly aerated media P. tricornutum is able to reduce the inorganic carbon concentration of the media to a greater extent than during growth in well-aerated media. Cells that have experienced inorganic carbon depletion are able to accumulate inorganic carbon to a greater extent than cells from well-aerated cultures when tested at low external inorganic carbon concentrations. Inorganic carbon photosynthesis dose-response curves showed that carbon-depleted cells have a higher affinity for inorganic carbon than cells from well-aerated cultures. δ¹³C values of carbon-depleted cultures were less negative than those of well-aerated cultures. These results are discussed in relation to previously reported inorganic carbon-photosynthesis dose-response curves. This alga is able to alter the mechanism of inorganic carbon acquisition in response to changes in the external inorganic carbon concentration.