TEMPERATURE-ACCLIMATION OF RESPIRATION AND PHOTOSYNTHESIS IN THE BROWN ALGA LAMINARIA-SACCHARINA

Sporophytes of the brown alga Laminaria saccharina (L.) Lamour grown at 15-degrees-C contained significantly more chlorophyll a (chl a) than did similar plants grown at 5-degrees-C. The increase in chl a in 15-degrees-C plants was due to increased numbers of photosystem II reaction centes, and possibly to increased photosynthetic unit size, compared with 5-degrees-C plants. These changes were associated with increased alpha-values (photosynthetic efficiencies) in 15-degrees-C-grown L. saccharina relative to 5-degrees-C-grown plants. The changes in alpha together with reduced respiration rates allowed 15-degrees-C-grown L. saccharina to achieve net photosynthesis and light-saturated photosynthesis at a lower photon fluence rate (PFR) than 5-degrees-C plants when both groups were assayed at the same temperature (15-degrees-C). The photon fluence rates necessary to reach the compensation point and achieve light-saturated photosynthesis (I(c) and I(k), respectively) increased with increasing incubation temperature in L. saccharina grown at both 5 and 15-degrees-C. However, acclimation responses to growth temperature compensated for the short-term effect of temperature on I(c) and I(k). Consequently, plants grown at 5 and 15-degrees-C were able to achieve similar rates of light-limited photosynthesis, and similar I(c) and I(k) values at their respective growth temperatures. These responses are undoubtedly important for perennial seaweeds such as L. saccharina, which frequently grow in light-limited habitats and experience pronounced seasonal changes in water temperature.