In April-May 1986, sea-ice microalgae (southeastern Hudson Bay, Canadian Arctic) were acclimated to temperatures ranging from -1.5 ° to 10 °C for short periods (3 h), after which photosynthesis and carboxylating enzyme activities were measured, b Pmax increased after acclimation to 10 °C while photosynthetic parameters a, 13 and I k as well as activities of PePC and PePCk did not show any significant change after temperature acclimab tion. Contrary to Pmax, the activity of RuBPC was lower for algae acclimated to 3 °-10 °C, the observed response increasing with temperature. There was also a seasonal trend in the response of RuBPC, the ability to compensate for rapid temperature changes being higher in May. These results show that ice algae were photosynthetically adaptable in the range of temperatures tested. For RuBPC, adaptability developed seasonally when the environmental temperature started to fluctuate in May. Photosynthetic acclimatization to temperature may be of high ecological significance in extending the growth season of ice-algae.
* Contribution to the programs of GIROQ (Groupe interuniversitaire de recherches oc6anographiques du Qu6bec) and of the Maurice-Lamontagne Institute (Department of Fisheries and Oceans)