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Phosphorus availability modifies carbon production in Coccolithus pelagicus (Haptophyta)

Gerecht, A.C., Šupraha, L., Edvardsen, B., Langer, G., Henderiks, J.
Journal of experimental marine biology and ecology 2015 v.472 pp. 24-31
carbon dioxide, calcite, cell division, particulate organic carbon, Haptophyta, growth retardation, phosphates, photosynthesis, phosphorus
The coccolithophore Coccolithus pelagicus (Wallich) Schiller fixes CO2 into particulate organic carbon (POC) through photosynthesis and into particulate inorganic carbon (PIC) in the form of calcite. To examine the role of phosphorus (P) availability in the production of POC and PIC, C. pelagicus subsp. braarudii (Gaarder) Geisen et al. was grown in semi-continuous cultures at three initial phosphate concentrations (P-replete, 1, and 0.5μM [P]). Reduced P-availability (1 and 0.5μM [P]) decreased POC production, while PIC production only decreased when phosphate concentrations became growth limiting (0.5μM [P]). This decrease has not been observed previously in batch cultures, highlighting the inadequacy of the batch culture approach with regard to determining carbon production. The reduction in growth rate by 50% at 0.5μM [P] was accompanied by a doubling in cell volume (and POC). PIC production was halved, resulting in a lowered PIC to POC ratio. The average number of coccoliths per cell (and PIC content) remained the same among treatments, despite the significant change in cell size. Our data suggest that POC production in C. pelagicus is more sensitive towards a moderate reduction in phosphorus availability than PIC production. Once phosphorus availability limits cell division, however, phosphorus resources are invested into POC rather than PIC production. This reduces cell density and sinking rates, indicating that coccoliths do not act as ballast for reaching deeper nutrient-rich layers under nutrient limitation.