THE ACCLIMATED RESPONSE OF GROWTH, PHOTOSYNTHESIS, COMPOSITION, AND CARBON BALANCE TO TEMPERATURE IN THE PSYCHROPHILIC ICE DIATOM NITZSCHIA-SERIATA

Nitzschia seriata Cleve, a common member of marine bottom ice communities in the Arctic, was grown in unialgal batch cultures to test for compensatory mechanisms for the low temperatures (- 1.8-degrees-C) typical of its natural habitat. The upper lethal limit for growth was between 12-degrees and 15-degrees-C, and the optimum was between 6-degrees and 12-degrees-C. The Arrhenius function adequately (R2 = 73%) fitted the relationship between growth rate and temperature from - 1.6-degrees up to 10-degrees-C, with an average Q10 of 1.9 over the entire range. Light-saturated and light-limited rates of photosynthesis (normalized to chlorophyll a or cell carbon) showed complete compensation from 12-degrees to 4-degrees-C. Photosynthetic rates, especially at light saturation, declined rapidly at temperatures below 4-degrees-C. Susceptibility to photoinhibition was greatest al the lowest growth temperatures. Cellular composition (chlorophyll a, protein, polysaccharide, and lipid contents) was not systematically related to temperature in any simple way, although cell size (carbon per cell) was maximal at the lowest growth temperature. Dark respiration was unmeasurably low (< 0.015 day-1) at all growth temperatures. The strategy of adaptation in N. seriata may be characterized as optimizing efficiency and compensation, rather than maximization, of growth rate.