One result of the ozone depletion in the Antarctic is an increase in the transmission of ultraviolet radiation to the earth's surface. This project addresses the effect of ultraviolet radiation on phytoplankton physiology. Methods will be developed to generate environmentally-relevant action spectra (wavelength-dependent biological weighing functions) for photoinhibition of photosynthesis in phytoplankton. Action spectra will be measured using an experimental incubator that exposes phytoplankton to combinations of ultraviolet and visible radiation. Photoinhibition will also be examined with new indicator assays. Three types of assay will be tested: 1) fluorescence-based measurements designed to distinguish the primary damage to photosynthesis from ultraviolet vs visible radiation; 2) a spectrophotometric measurement of photosystem II reaction center activity that also might distinguish the effects of ultraviolet radiation from those of excess visible light; 3) a technique to measure repair function that is very sensitive to ultraviolet radiation and to excess visible light. The action spectra will be used to model photoinhibition. The indicator assays will quantify photoinhibition without relying on incubation- based measurements of photosynthesis. Models and methods will be tested by comparison with direct measurements of the harmful effects of ultraviolet and excess visible radiation on photosynthesis by natural phytoplankton in the Antarctic.
