Patterns of carbon assimilation in a microalgal community from annual sea ice, east Antarctica

Abstract

Patterns of carbon assimilation into photosynthetic end products were measured in annual sea ice near the Antarctic stations of Davis and Mawson, during December 1982, following the peak of the spring ice algal bloom. Rates of14C assimilation in the ice communities, measured with an in situ sampler-incubation chamber ranged from 1.58–32.92 mg Cm-2h-1 $$(\bar x = 11.5)$$ during this period. The partitioning of14C bicarbonate into four subcellular fractions (chloroform-soluble, methanol/water (MeOH/H2O)-soluble, trichloroacetic acid (TCA)-soluble, and TCA-residue) and the efficacy of extraction was determined. During in situ incubations (3–4 h), it was found that a major proportion of the label $$(\bar x = 53\% )$$ was incorporated into a (1→3)-glucan which was distributed between the neutral MeOH/H2O-and TCA-soluble fractions. The remainder of the label was found in the chloroform-(lipid; $$\bar x = 18\% $$ ), charged MeOH/H2O-soluble (amino/organic acids; $$\bar x = 17\% $$ ) and TCA-residue (protein; $$\bar x = 12\% $$ ). The glucan accounted for 93% of the cellular carbohydrate of ice algae and had a linkage composition similar to the reserve (1→3)-β-D-glucan found in cultured diatoms. High14C-incorporation into MeOH/H2O- and TCA-soluble fractions also occurred over a 24 h in vitro incubation, although incorporation into protein, at the expense of the other fractions, continued during the night. While primary productivity in the ice communities was still appreciable during December, the prominent synthesis of reserve glucan and the decreasing cellular ratios of protein/carbohydrate suggests that the ice algae may be nutrient limited during this period.