Sporophytes of the brown alga
Laminaria saccharina (L.) Lamour grown at 15°C contained significantly more chlorophyll
a (chl
a) than did similar plants grown at 5°C. The increase in chl
a in 15°C plants was due to increased numbers of photosystem II reaction centes, and possibly to increased photosynthetic unit size, compared with 5°C plants. These changes were associated with increased
values (photosynthetic efficiencies) in 15°C-grown
L. saccharina relative to 5°C-grown plants. The changes in
together with reduced respiration rates allowed 15°C-grown
L. saccharina to achieve net photosynthesis and light-saturated photosynthesis at a lower photon fluence rate (PFR) than 5°C plants when both groups were assayed at the same temperature (15°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°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°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.Please address all correspondence and requests for reprints to I.R. Davison
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