Effects of solar UV stress on chlorophyll fluorescence kinetics of intertidal macroalgae from southern Spain: a case study in Gelidium species

Photoinhibition and recovery kinetics after short exposure to solar radiati on following three different irradiance treatments of irradiances (PAR, PAR +UVA and PAR+UVA+UVB) was assessed in two intertidal species of the genus G elidium, Gelidium sesquipedale and G. latifolium, collected from Tarifa (so uthern Spain) using in vivo chlorophyll fluorescence (PAM fluorometry). Aft er 3 h UV radiation exposure, optimal quantum efficiency (F-v/F-m) in G. se squipedale decreased between 25 and 35% relative to the control, Under PAR alone, values decreased to 60%. In G. latifolium, photoinhibition did not e xceed 40%. Similar results were found for the effective quantum yield (Delt a F/F-m'), however, no marked differences in relation to light treatments w ere seen. When plants were shaded for recovery from stress, only in G. lati folium a significant increase in photosynthesis was observed (between 80 an d 100% of control). In contrast, photosynthesis of G. sesquipedale suffered a chronic photoinhibition or photodamage under the three light irradiances . Full solar radiation (PAR+UVA+UVB) affected also the electron transport r ate in both species. Here, initial slopes of electron transport vs, irradia nce curves decreased up to 60% of controls. Although the recovery kinetic u nder PAR+UVA+UVB conditions was delayed in G. latifolium, after 24 h recove ry this species reached significantly higher than G. sesquipedale. PAR impa ired electron trasport only in G. sesquipedale. Overall, both species are c haracterized by different capacity to tolerate enhanced solar radiation. G. latifolium is a sun adapted plant, well suited to intertidal light conditi ons, whereas G. sesquipedale, growing at shaded sites in the intertidal zon e, is more vulnerable to enhanced UV radiation.