Investigating on relationship between effective quantum efficiency and irradiance

Models describing the relationship between effective quantum efficiency of PS II (ΦPSII) and irradiance (I) are routinely used to determine how irradiance influences effective quantum efficiency and photosynthetic electron transport rate (ETR). However, with no single model one can accurately describe the relationship between ΦPSII and I, and explain the interdependence between ΦPSII and biophysical properties of photosynthetic pigments, especially in plants growing under low level irradiances. Basing on the mechanistic model of photosynthetic electron transport rate we have developed the model of the relationship between ΦPSII and I. The new model reveals that ΦPSII increases with photochemistry (kP) and heat dissipation (kD). Furthermore, the values of key parameters calculated using the new model were compared with the values calculated with two other empirical models. The new model was perfectly fitted to the light-response curves of ΦPSII. The key calculated photosynthetic parameters: maximum ΦPSII, maximum ETR and their corresponding saturation irradiance were close to the measured values. In addition, our model associates ΦPSII with intrinsic features of photosynthetic pigments. We concluded that ΦPSII decreased with increasing I due to the decrease in the effective absorption cross-section of photosynthetic pigments molecules.HighlightA model of the relationship between effective quantum efficiency of PS II (ΦPSII) and irradiance (I) has been developed. Using this new model it was found that ΦPSII decreased with increasing I due to the decrease in the effective absorption cross-section of photosynthetic pigments molecules.AbbreviationsETRElectron transport rateETRmaxMaximum electron transport rateFSteady-state fluorescenceFm′Maximum fluorescence in the lightFvVariable fluorescence yield of the dark-adapted leafgiDegeneration of energy level of photosynthetic pigment molecules in the ground state igkDegeneration of energy level of photosynthetic pigment molecules in the excited state kIIrradianceNPQNon-photochemical quenchingN0Total light-harvesting pigment moleculesPARsatSaturation irradiance corresponding to ETRmaxkPRate of photochemical reactionkDRate of non-radiative heat dissipationPS IIPhotosystem IIaeInitial slope of light-response curve of electron transport rateα′Fraction of light absorbed by PS IIβ′Leaf absorptanceξ1Probability of photochemistryξ2Probability of non-radiative heat dissipationξ3Probability of fluorescenceσikEigen-absorption cross-section of photosynthetic pigment from ground state i to excited state k due to light illuminationEffective optical absorption cross-section of photosynthetic pigment molecule from ground state i to excited state k due to light illuminationφExciton-use efficiency in PS IIτAverage lifetime of the photosynthetic pigment molecules in the lowest excited stateΣPSIIEffective quantum efficiency of PS II