Interactive effects of ultraviolet radiation and nutrient addition on growth and photosynthesis performance of four species of marine phytoplankton.

ALEJANDRA MARCOVAL, M; VIRGINIA ESTELA VILLAFAÑE; WALTER HELBLING, E

JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY B-BIOLOGY

Año: 2007 vol. 89 p. 78 - 87

1011-1344

Experiments (6–8 days) were carried out during the austral summer of 2005 in Chubut, Argentina (43 S, 65 W) to determine theinteractive effects of solar UVR (280–400 nm) and nutrient addition on growth and chlorophyll fluorescence of four species of marinephytoplankton – the diatoms Thalassiosira fluviatilis Hustedt and Chaetoceros gracilis Schu¨ tt, and the dinoflagellates Heterocapsa triquetra(Ehrenberg) Stein and Prorocentrum micans (Ehrenberg). Samples were incubated under three radiation treatments (two sets of eachradiation treatment): (a) samples exposed to full solar radiation (PAR + UVR, PAB treatment, 280–700 nm); (b) samples exposed toPAR and UV-A (PA treatment, 320–700 nm) and (c) samples exposed only to PAR (P treatment, 400–700 nm). At the beginning ofthe experiments, nutrients (i.e., NaPO4H2 and NaNO3) were added to one set of samples from each radiation treatment (‘‘N’’ cultures)whereas in the other, the nutrients concentration was that of the culture medium. At all times, the lowest growth rates (l) were determinedin the PAB treatments, where enriched cultures had significantly higher l (P < 0.05) than non-enriched cultures. Daily cycles ofphotochemical quantum yield (Y) displayed a pattern of relatively high values early in the morning with a sharp decrease at noon; recoverywas observed late in the afternoon. In general, higher Y values were determined in enriched cultures than in non-enriched cultures. Asthe experiments progressed, acclimation (estimated as the difference between Y at noon and that at time zero) was observed in all speciesalthough in variable degree. All species displayed some degree of UVR-induced decrease in the photochemical quantum yield, although itwas variable among treatments and species. However, this effect decreased with time, and this pattern was more evident in the dinoflagellates,as the concentration of UV-absorbing compounds increased. Thus, under conditions of nutrient enrichment as may occur byriver input or by re-suspension by mixing, dinoflagellates outcompete with diatoms because they may have a higher fitness underUVR stress.