Effects of four environmental variables on photosynthesis-irradiance relationships in Antarctic sea-ice microalgae

Abstract

The effects of temperature, salinity, growth irradiance and diel periodicity of incident irradiance on photosynthesis-irradiance (P-I) relationships were examined in natural populations of sea-ice microalgae from McMurdo Sound in the austral spring of late 1984. Both Pmb (photosynthetic rate at optimum irradiance) and αb (initial slope or P-I curve) were temperature-dependent reaching optimal rates at approximately +6° and +2°C, respectively. P-I relationships showed little difference at 20 and 33‰ S; however, no measurable photosynthesis by sea-ice microalgae was detected in a 60‰ S solution of brine collected from the upper layers of congelation ice. Although diel periodicity characteristic of the under-ice light field appeared to have little effect on P-I relationships, changes in growth irradiance had a profound effect. An increase in growth irradiance from 7 μE m-2 s-1 (ambient) to 35 or 160 μE m-2 s-1 resulted in a transient three-fold increase in Pmb and Ik (index of photoadaptation) during the first four days, followed by a sharp decline. The effects of these environmental factors on ice algal photosynthesis may influence the distribution of microalgae in sea-ice environments.