Interactive effect of nutrient concentration and ultraviolet radiation on three marine phytoplankton species

M A MARCOVAL; E W HELBLING

AIX-LES-BAINS, FRANCE

Congreso; 11th Congress of the European Society for Photobiology 2005.; 2005

Long term experiments (7 days) were conducted with three marine phytoplankton species - Thalassiosira fluviatilis, Heterocapsa triquetra and Prorocentrum micans -using both a temperature controlled (20¨¬ C) illuminated chamber (12:12 L:D cycle, 300 ¥ìmol photons m-2 s -1 for PAR, 15 Wm-2 for UV-A, and 0.7 Wm-2 for UV-B), and solar radiation during the austral summer. The cultures were grown in 4-liters UV-transparent Plexyglas containers and under at least 2 nutrient concentrations (natural seawater concentration and addition of 0.6 and 0.7 mM of NaPO4H2 and NaNO3, respectively) and under 3 radiation treatments (PAB, 280- 700 nm; PA, 320-700 nm; and P, 400-700 nm). Samples were taken every day at three times (8am, 1pm and 5pm) and photosynthetic parameters were measured with a Water PAM fluorometer (Walz). In addition, samples were taken for chl-a, and absorption characteristics determinations as well as for cell counts. T. fluviatilis was the most sensitive species to UVR, with cell concentration decreasing with time in samples exposed to UVR. The photosynthetic quantum yield (Y) decreased significantly during the day in all treatments, although recovery was observed during the night. H. triquetra and P. micans were more resistant to UVR, and even though Y decreased significantly at local noon, cells recovered during the day. In both species, local noon inhibition decreased with time thus indicating an acclimation to solar UVR. This acclimation seems to be attained through the synthesis of UV-absorbing compounds that significantly increased throughout the experiment. Samples exposed to UVR and with higher nutrient concentrations were those that had the higher amount of UV-absorbing compounds.