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Effects of varying copper concentrations on photosynthesis of Gracilaria Salicornia Agardh (Gracilariaceae) and Padina Santae-Crusis Borgesen (Dictyotaceae)


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Biology Department, College of Arts and Sciences - University of San Carlos


The relative effects of copper (Cu²?) exposure on the photosynthesis-irradiance parameters (Ik, Pmax, ?, R) and the mean daily growth rate of the red alga Gracilaria salicornia and brown alga Padina santae-crusis were investigated through series of comparative experiments. The photosynthesis effeciency (?) showed a decreasing pattern with increasing Cu²? concentration. Light saturation (Ik) for both algae increased at lower concentration and showed transient shift at 12.5 µg Cu²? 1¯1. The shifting of Ik could be due to the adjustment of the ratio of functional PSII RCs to light harvesting complex II (LHCII) or an alteration of photosynthesis unit.The maximum photosynthesis (Pmax) of P. santae-crusis was found to be higher in algae exposed to 12.5-25 µg Cu²? 1¯1 compared to those exposed to Cu²? free medium, this could be possibly due to the Cu²? limitation in the control. Unlike P. santae-crusis, G. salicornia exposed to Cu²? free medium as well as those at 12.5-25 µg Cu²? 1¯1 were comparable, maybe because of their differences in Cu requirement or maybe due to the higher thallus surface area of P. santae-crusis compared to G. salicornia. But, both algae showed decreasing Pmax values starting from 50 to 500 µg Cu²? 1¯1 suggesting the detrimental effects of Cu²? at the higher concentration. The respiration data showed a non-linear pattern due to some delay of the effect of copper on the respiratory system. Of the various physiological endpoints measured, growth proved to be the most sensitive to Cu²? with the reductions of mean daily growth rate starting at 12.5 µg Cu²? 1¯1 for G. salicornia and negative growth rate at 500 µg Cu²? 1¯1 for P. santae-crusis. Chlorosis symptoms such as the degradation of the thin outer layer and bleaching were evident at the intermediate to the highest Cu²? concentraton (50 to 500 µg Cu²? 1¯1). The results of the study is strongly suggested severe impact of Cu²? at the high concentration on P-I parameters and growth rate of G. salicornia and P. santae-crusis.


The main objectives of this study is to determine the effects of varying copper concentrations (control, 12.5, 25, 50, 250, 500 µg Cu²? 1?1) on the rate of photosynthesis of Gracilaria salicornia and Padina santae-crusis at different light irradiances (0, 200, 400, 600, 800, 1000 µmol m¯² s¯1). Specifically, the study aims to: (1) determine the different P-I parameters: initial slope (?), saturating irradiance level (Ik), maximum photosynthesis (Pmax), and respiration (R) of both species of algae, (2) evaluate the influence of elevated Cu²? concentrations on P-I curve parameters, and (3) compare the parameters (?, Ik Pmax, R) of both algae. As an ancillary objective, the effect of Cu²? on the mean daily growth of G. salicornia and P. santae-crusis was determined.


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