Estimation of the Photosynthetic Electron Flow in Intact Leaves: Effect of Modulated Light Intensity on the Fluorescence Parameters Fv/Fm and ΔF/Fm’

Abstract

Previous studies have confirmed the validity of the measurement of quantum yield in PS II for estimating the rate of linear electron transport in leaves (Je) by simultaneous measurements of chlorophyll fluorescence and gas exchange [1], because the product of the quantum yield of PS II (Φpsii) and the photon incidence absorbed by PS II (Ipsii) permits the calculation of Je from the equation Je=(Φpsii)(Ipsii). Genty et al.[2] showed that a linear relationship is obtained between the quantum yield of PS II (ΔF/Fm’) and the apparent quantum yield of CO2 assimilation in non-photorespiratory conditions. However, the actual values of Φpsii and Ipsii are difficult to determine in intact leaves. At present, two different methods for estimating Je have been proposed. Edward and Baker [3] calculated Je from the equation, Je=1/2(ΔF/Fm’)•(PFDabs), under the assumption that the photon flux density absorbed by a leaf (PFDabs) is equally distributed between PS I and PS II. Another method is based on the linear relationship between the relative measurement of quantum yield of PS II (ΔF/Fin’) and the apparent quantum yield of gross CO2 assimilation under non-photorespiratory conditions [2, 4, 5, 6]. They used the relationship for estimating the electron flow under photorespiratory conditions (Je) in leaves.