Biosynthesis and photosynthate allocation patterns of arctic ice algae

Abstract

Biochemical composition of the sea ice microbial community was measured in populations of different light histories in the Canadian Arctic (Resolute, N.W.T.). The average composition of the particulate organic matter [soluble and insoluble polysaccharide, particulate protein, intracellular free amino acids (IFAA), lipid, and chlorophyll a] was within the published range for microalgae, but lipid was a relatively large (31–59%) and protein a small (20–24%) part of the total. Protein and IFAA pools apparently comprised about 50% of the particulate organic nitrogen, of which 6–10% was in the IFAA pool. Over the entire spring growth season, the net synthesis of protein, IFAA, and Chl a (relative to total cell carbon) decreased with increasing light while relative synthesis of lipid and soluble polysaccharide increased, consistent with patterns of short‐term photosynthate allocation. In the early growth season patterns of synthesis were relatively insensitive to light, and rates of lipid synthesis were large for all light histories. Photosynthate allocation in 24‐h incubations greatly underestimated actual rates of net lipid synthesis and probably overestimated protein synthesis. Microalgae of cold, low‐light environments can display rates of lipid synthesis much larger than rates normally encountered in microalgae without displaying a corresponding pattern of shorter term photosynthate allocation.