Revista Chilena de Historia Natural 82 (1): 43-61, 2009
RESEARCH ARTICLE
Photosynthetic responses to UV-radiation of intertidal macroalgae from the Strait of Magellan
(Chile)
For the first time, the photosynthetic performance of field-grown macroalgae from the
Magellan Strait was evaluated with respect to their photoadaptation in the field and acclimation potential to ultraviolet radiation. Five
macroalgal species were collected in the eulittoral and the upper sublittoral: Ulva intestinalis,
Porphyra columbina, Adenocystis utricularis, Desmarestia confervoides and
D. ligulata. Photosynthesis vs. irradiance (P-I) curves of macroalgae cultivated in the laboratory
under low white light intensities more than a week were used to assess the acclimation potential to irradiance conditions in the field.
Both, photosynthetic parameters referred to as maximum electron transport rate (ETRmax) and light saturation points of
photosynthesis (I<sub>k</sub>) were species-specific and did not correlate with the position on the shore. Ik ranging
between 80 and 215 µmol photons m<sup>-2</sup> s<sup>-1</sup> was indicative of moderate sun-adaptation in
all studied species. The acclimation potential to UV-radiation was determined as the extent and the rates (minh) of PSII inhibition
(resulting from decreased maximum PSII-quantum yield (Fv/Fm)) after four hours of UV-exposure and as the subsequent rates of
recovery (mrec) in dim PAR. The results suggest that photosynthesis of each species during UV-exposure was transiently down
regulated rather than damaged. Furthermore, no reductions in ETRmax were detected after 4 h exposure to UV-A and UV-B-radiation,
and consequently the Calvin cycle could not be affected. Thus, Fv/Fm was a more sensitive parameter than ETRmax explaining the
photosynthetic UV acclimation. Both, the rates of inhibition and the rates of recovery were not correlated with the morpho-functional
groups of macroalgae nor to their vertical distribution. Thus, although the capacity to acclimate to UV-radiation varied among the
different species, data suggest that such responses are based on metabolic adjustments or possibly photoprotective strategies. In
conclusion and taking into account the light adaptation characteristics, all species collected in the midlittoral and the upper sublittoral at
the Strait of Magellan seem to be well acclimated to UV-B doses occurring at their habitat, which might be a pre-requisite to withstand
enhanced solar UV-B during ozone depletion or summertime irradiance conditions.
Key words:
UV-radiation,
macroalgae, photosynthesis, photoacclimation, Strait of Magellan
