Photosynthetic adaptation to temperature in the red algae Lomentaria baileyana and Lomentaria orcadensis

Photosynthetic responses to temperature were examined in tetrasporophytes of Lomentaria baileyana and Lomentaria orcadensis (Rhodophyta). These species have different temperature ranges for growth that reflect seasonal temperature extremes in their natural distributions. L. baileyana is a temperate-subtropical species which grows between 15 and 33°C, whereas L. orcadensis is a boreal-temperate species which grows between 10 and 20°C. Interspecific differences in the photosynthetic responses to temperature were similar to those for growth, suggesting that photosynthesis may determine the temperature range over which Lomentaria tetrasporophytes can grow. Light-saturated rates of photosynthesis were higher in L. orcadensis below 15°C, whereas L. baileyana could photosynthesize at temperatures above 30°C, which inhibited photosynthesis in L. orcadensis. These differences were attributable to genetic adaptations of photosynthetic metabolism because both species were grown under identical conditions for several months prior to the experiments. Phycoerythrin fluorescence studies and photosynthesis-irradiance responses determined in red and green light indicated that the high-temperature-induced breakdown of energy transfer from phycoerythrin to the photosynthetic reaction centres occurred at a lower temperature in L. orcadensis than in L. baileyana. Low-temperature-enhanced photoinhibition may account for the decreased photosynthetic performance of L. baileyana at temperatures below 15°C.