Abstract
The use of relative variable fluorescence (RVF) of chlorophyll, as measured in the presence of Diuron, an inhibitor of electron transfer, for the estimation of the photosynthetic activity of plankton microalgae was analyzed under a wide range of light intensities in the PAR region. Oxygen evolution rates (estimated by the method of light and dark bottles and the amperometric method), RVF, and chlorophyll a concentration were measured in parallel in natural algal cenoses and microecosystems. When the previously used regression equation, in the form A = b(ΔF/Fd)CchlI, where A is O2 evolution rate (g/(m3 h), ΔF/Fd is RVF (relative units), Cchl is chlorophyll a concentration (mg/m3), and I is light intensity (W/m2), was verified in the PAR region, we observed a nonlinear dependence of the correction coefficient b on I, which can be described by the formula b = 6.227 × 103√I. This result agrees with the hypothesis that chlorophyll a fluorescence quenching comprises photochemical (qQ) and energy (qE) components. On the basis of the energy model, we determined the upper limit bmax = 0.003 for light intensity range I< 4.4 W/m2 and the lower limit bmin = 0.0003 for I = 400 W/m2.
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