Effects of UV radiation and temperature on photosynthesis as measured by PAM fluorescence in the red alga Gelidium pulchellum (Turner) Kutzing

Potosynthetic performance in response to UV radiation was measured in the r ed alga Gelidium pulchellum Turner (Kutzing) from northern Portugal in the laboratory. The experiments basically consisted of exposures to three diffe rent UV radiation conditions (PAR+UV-A+UV-B; PAR+UV-A and PAR alone) using artificial lamps and cut off foils followed by incubations at low irradianc e of white light to determine the recovery capacity. The effects of two dif ferent PAR backgrounds (105 and 480 mu mol photon m(-2) s(-1)) and two grow th temperatures (15 and 25 degreesC) as additional factors were also assess ed. The optimal quantum yield of fluorescence (F-v/F-m) decreased after 12 h exposure to PAR+UV (equivalent to a weighted UV dose closed to 150 kJ m(- 2); from photoinhibition of PSII electron transport action spectrum). The e lectron transport was also impaired by UV radiation. The PAR background was a key factor determining the UV responses in this species: thalli exposed to high PAR background (480 mu mol m(-2) s(-1)) exhibited a greater degree of photoinhibition and a slower recovery than plants irradiated by 105 mu m ol m(-2) s(-1). On the other hand, an incubation temperature of 15 degreesC exacerbated the effect of UV radiation on photosynthesis (increased photoi nhibition) followed by a slowing down in the recovery kinetic compared to s amples incubated at 25 degreesC. These results suggest that repair processe s may be stimulated with increasing growth temperature.