Maximum quantum yield and action spectrum of photosynthesis and fluorescence in chlorella

The maximum yield of oxygen production in Chlorella was found, in new, systematic experiments, not to exceed 0.12, under a great variety of conditions. Measurements were made on autospores and other synchronous cultures, at different CO₂ concentrations, at very low light intensities, and in the presence of ‘catalytic’ amounts of blue light. The action spectra (quantum yield as a function of wavelength) of photosynthesis, and of chlorophyll a fluorescence in vivo, were measured on the same Chlorella cell suspensions. In both cases, a decline in the yield was observed in the red beginning at about 675–680 nm. The yield declines to 50% of the maximum, on both curves, at 690–695 nm. A strong dip was observed in the action spectra of both fluorescence and photosynthesis at 660–665 nm.