Photosynthetic Response of Nereocystis Luetkeana (Phaeophyta) to High Light

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Photosynthetic response to high light was determined for Bull kelp, Nereocystis luetkeana (K. Mertens) Postels and Ruprecht in order to understand how this species is affected by short-term fluctuations in irradiance. Exposure of N. luetkeana blades to high intensity photosynthetically active radiation (1000 µmol photons m−2 s–1) caused increased non-photochemical quenching of fluorescence and higher de-epoxidation ratios for xanthophyll pigments indicating that energy-quenching xanthophylls were used to protect blades against photoinhibition. Despite initiation of these photoprotective mechanisms, maximum photochemical efficiency of photosystem II (Fv/Fm) decreased 40% in response to a 60 min exposure to 1000 µmol photons m−2 s–1 photosynthetically active radiation indicating that photoinhibition had occurred. Light-saturated rates of oxygen evolution were not changed significantly by the high light treatment. Recovery of maximum photochemical efficiency of photosystem II to within 8% of initial values occurred after a 300-min dim light period. Younger sections of the blades were slightly more susceptible to high light damage than older sections. Middle sections of the blades were more prone to light-induced damage at water temperatures of 7°C or 18°C, as compared to 13°C. Exposure to biologically effective ultraviolet-B radiation (UV-Bbe) (up to 4.5 kJ m–2 day–1) in photoinhibitory light conditions did not significantly affect light-induced damage to photosystem II.




Phycological Research