Thermal Dissipation Related to Chlorophyll Fluorescence and Photosynthesis*

Energy taken up by light absorption of the leaf pigments is transformed in the process of the photosynthetic quantum conversion into photosynthesis, chlorophyll fluorescence and thermal dissipation. The mostly inverse correlation between chlorophyll fluorescence and photosynthetic activity has been extensively studied in the past, whereas only few studies dealt with the thermal dissipation. In many publications the intensity of thermal dissipation is a matter of speculation deduced from a lower chlorophyll fluorescence and expressed as non-photochemical quenching or rate constant for thermal decay. This review shows that by means of the photoacoustic technique one is able to really measure thermal dissipation. The principle of this method is outlined and examples are given for measurements of thermal photoacoustic signals of leaves related to chlorophyll fluorescence and photosynthesis. The various studies show that thermal dissipation is neither neglectibly low, nor constant or always parallel to chlorophyll fluorescence. Thus it is clearly demonstrated that thermal dissipation should always be measured in order to fully understand the energy balance in the photosynthetic quantum conversion.