Efficiency of carbon assimilation and photoacclimation in a small unicellular Chaetoceros species from the Weddell Sea (Antarctica): influence of temperature and irradiance

Abstract

It is well established that Antarctic phytoplankton and sea-ice algae are able to thrive at low temperatures and it has been proposed that a reduction in respiration may be important in enabling them to do this. This possibility was studied in an Antarctic clone of a small unicellular Chaetoceros species isolated from the Weddell Sea (Antarctica), using comparative measurements of C assimilation during long- and short-term incubation series over a range of temperatures (−1.5 to 4°C) at two irradiances (5 and 55 μmol m 2s −1). Even though doubling times varied considerably, the total amount of C assimilated per cell per generation time was similar at each of the temperature and light conditions. However, over one cell cycle, significant respiratory C losses were determined by divergences in C assimilation patterns between cumulative and long-term incubations at both light intensities at 0 and 4 °C. At −1.5 °C, insignificant C losses were recorded. No significant extracellular release of dissolved organic material (DOC) was observed. It is hypothesised that an increase in C assimilation and growth rates at higher temperatures in this diatom is achieved at the expense of a decrease in efficiency of C metabolism. This study provides further evidence that respiration rates during light periods are of importance in C mass balance determinations of algae. The photoacclimation potential of this species was also investigated over the same temperature range. Differences in photosynthetic parameters and Chl a concentrations between “low”- and “high”-light-acclimated cells revealed a high photoacclimation capacity irrespective of incubation temperature.