Action Spectra of the Photosynthetic Emerson Enhancement: Using Three-Light Beams on a Bare Platinum Electrode in Algae of the Chlorophytes, Rhodophytes, Dinoflagellates, Cryptomonads, and Cyanobacteria Divisions

High-resolution action spectra of photosynthetic Emerson enhancement were determined using a unique, custom-built three-beam oxygen electrode system in the Joliot configuration, featuring a bare platinum cathode. This specialized apparatus utilized three independent light beams—including one modulated at 10 Hz to precisely quantify real-time changes in the quantum yield of Photosystem II resulting from the simultaneous excitation of Photosystem I. This methodology provides a direct and physiologically relevant analysis of radiant energy distribution between the two photosystems in intact algal cells, achieving a level of precision that remains a benchmark in the field. Comprehensive spectra were obtained for key representatives of five major algal divisions: Rhodophyta, Chlorophyta, Dinophyta, Cryptophyta, and Cyanobacteria. The results demonstrate that enhancement spectra vary systematically according to the excitation balance between the photosystems. Furthermore, photoadaptation studies in Glenodinium sp. and Rhodomonas D3 revealed taxon-specific responses in energy distribution under high irradiance. By integrating these high-resolution measurements with contemporary photosynthetic theory, this work clarifies fundamental biophysical mechanisms of spectral photoadaptation and provides critical insights into the ecological zonation of algal species in coastal aquatic environments.