INTRACELLULAR PHOTOSYNTHATE ALLOCATION AND THE CONTROL OF ARCTIC MARINE ICE ALGAL PRODUCTION¹

Abstract

ABSTRACT Ice algae are a case study in photo‐autotrophic growth and metabolism under chronically low temperature and irradiance. We measured the allocation of 14 C‐labelled photosynthate among major classes of intracellular carbon (low molecular weight compounds, or LMW; lipid; protein; and polysaccharide) and found light‐dependent changes in allocation broadly similar to photo‐adaptive responses known in phytoplankton at higher temperatures; average relative allocation to protein varied inversely (10–37%) and allocation to lipids and polysaccharides directly (10–23%, and 16–21%, respectively) with the sub‐inhibiting irradiance levels we employed (3.5–33.0 μE·M −2 ·s −1 ). Unlike many observations at higher temperatures, ours indicated (on average) a large and light‐insensitive allocation to LMW (ca. 40%) and a greater light‐sensitivity in lipid than in polysaccharide allocation. At the higher incubation irradiances, resembling in situ levels typical of areas with little (0–5 cm) snow cover, allocation to protein was often low (10–13%) compared to many observations of nutrient‐sufficient or light‐limited phytoplankton. Allocation to protein increased substantially (to ca. 40%) during a period of intensified tidal mixing, and assimilation numbers also attained a maximum at about the same time. Suck dynamics show that the ice algae are not constrained to their often protein‐poor allocation by the constantly low ambient temperature. Rather, they display marked shifts in metabolism consistent with major changes in light and inorganic nutrient supply, driven in part by the physical process of tidal mixing.