On the Action Spectra of Photosynthesis and Spectral Dependence of the Quantum Efficiency

Analysis of the results obtained during the investigation of the photosynthetic oxygen evolution upon irradiation with short saturating flashes and of the widely accepted Kok’s model for the reactions leading to the oxygen production showed that the photosynthetic irradiance should be non-linear (quadratic or higher degree of dependence) under low irradiance. This non-linearity of the irradiance curves leads to several consequences on the action spectra of photosynthesis and particularly on the decrease of the quantum efficiency in the spectrum regions where pigment absorption is lower, as we demonstrated in our earlier investigations (Zeinalov, 1982; Maslenkova et al., 1994). An attempt for estimating the action spectra and spectral dependence of the quantum efficiency of photosynthesis in Scenedesmus acutus is presented using a polarographic oxygen rate electrode and irradiation with two light beams, one of them being continuous and the other one modulated. The obtained results show that after compensation of the initial non-linear part of the irradiance curves in the estimating of the action spectra and quantum efficiency of photosynthesis the values for the investigated parameters in the spectral regions with low absorbances increase significantly.