Photosynthate distribution by microplankton in permanently ice-covered Antarctic desert lakes

The distribution of 14C-labeled photosynthate by microplankton in Lakes Vanda and Fryxell, Antarctica, was measured during the 1984-1985 austral summer. Both lakes had conspicuous deep chlorophyll maxima near the bottom of the oxygenated zone. DCMU sensitivity experiments revealed that photosynthesis below the chlorophyll maximum in Lake Fryxell was partially due to photosynthetic bacteria. These bacteria had notably higher protein and lower lipid labeling than overlying oxic microalgae. Protein labeling in the oxic microalgae had lower I/sub k/ and higher α values than for other photosynthetic end products, indicating that protein is synthesized more efficiently at low photosynthetic photon flux density than the other metabolites. The I/sub k/ values for complete photosynthesis are among the lowest yet recorded for phytoplankton