Short-term effect of temperature on the photokinetics of microalgae from the surface layers of Antarctic pack ice

Microalgae growing within brine channels (85 psu salinity) of the surface ice layers of Antarctic pack ice showed considerable photosynthetic tolerance to the extreme environmental condition. Brine microalgae exposed to temperatures above -5 degrees C and at irradiances up to 350 mu mol photons.m(-2).s(-1) showed no photosynthetic damage or limitations. Photosynthesis was limited (but not photoinhibited) when brine microalgae were exposed to -10 degrees C, provided the irradiance remained under 50 mu mol photons.m(-2).s(-1). The highest level of photosynthetic activity (maximum relative electron transport rate [rETR(max)]) in brine microalgae growing within the surface layer of sea ice was at approximately 18 mu mol electrons.m(-2).s(-1), which occurred at -1.8 degrees C. Effective quantum yield of PSII and rETR(max) of the halotolerant brine microalgae exhibited a temperature-dependent pattern, where both parameters were higher at -1.8 degrees C and lower at -10 degrees C. Relative ETRmax at temperatures above -5 degrees C were stable across a wide range of irradiance.