Daily variations on photosynthesis, pigmentation and photoprotection of Plocamium cartilagineum (Plocamiaceae, Rhodophyta)

Abstract

ABSTRACT Field studies are a useful tool to understanding how seaweeds develop protective mechanisms against environmental variation and acclimate to them. These mechanisms can include morphological changes, inhibition of electron transportation rate, pigments and UV-absorbing compounds production. The present paper evaluates the daily cycle of photosynthesis and biochemistry of Plocamium cartilagineum from Spain under varying radiation and temperature conditions. For this purpose, four sites were chosen at La Herradura beach, Spain. Photosynthetically active radiation (PAR) and ultraviolet radiation (UVR) were measured in situ at the sites, and ETR in situ (electron transport rate) as an estimator of photosynthetic capacity was determined. Algal thalli from each site were sampled throughout the day at 09:30, 11:00, 13:00, 15:30, 17:00, 19:30 h, to quantify photosynthetic pigments, UV-photoprotective compounds (i.e. mycosporine-like amino acids, MAAs), and antioxidant capacity. Higher irradiance and temperature at two sites directly influenced ETR in situ . Algae from the site with highest PAR and UV radiation had dynamic photoinhibition when compared to algae from a more shaded site during certain periods of the day. Lower pigment concentrations were observed in algae that received higher irradiances, suggesting photoacclimation. Samples found at the site exposed to the highest ultraviolet-A radiation had the highest concentrations of mycosporine-like amino acids between 15:30 h and 19:30 h. MAAs proportion varied among the sites and during the day. We conclude that environmental conditions in the short-term influenced photosynthetic parameters and the accumulation of pigments and MAAs in P. cartilagineum showing its high physiological plasticity.