Fv/Fm, RLC and JIP: the value of chlorophyll-fluorescence in ecophysiological research

Abstract

Chlorophyll-fluorescence measurements can be performed at any time, independent of weather conditions. 1. Data (Fv/Fm) from light- and dark-adapted leaves were collected in the morning, at noon and in the afternoon. Comparison with those measured pre-dawn and/ or after 1 hour of ´recovery`, allows interpretation of: the photochemical quench (qP); the energy quench (qE1) fast relaxing (<10min, de-protonation, conformal changes); the qE2 slow relaxing (>1 hour, re-conversion of Zeaxanthin to Violaxanthin), and the photoinhibitory quench, qI (> 6 hours, repair of PS II, triggered D1). With rising light intensities during the morning, qP was accompanied by a strong qE1, whereas with decreasing light intensities in the afternoon, qE1 nearly vanishes, followed by a reduction in qE2 and even in qI. 2. Rapid light curves (RLC) allow the calculation of electron-transport rates (ETR) and can give a good estimate of the absolute quantum yield and gross photosynthesis when combined with data for the light absorption of chlorophyll in leaves. Thus, photosynthetic gas exchange rates, when measured under saturating CO2, will compare to both light response of gross photosynthesis as calculated from ETR and light curves from C4 plants. 3. The JIP-Test (R. Strasser) analyses the induction curve in detail, and yields a complex pattern of information. Under drought stress, a differential analyse of pre-dawn data and controls resulted in characteristic patterns of absorption, energy conversion and electron transport. In all cases additional information (on, for example, ontogenesis, water relations, and especially local climatic conditions) is needed to interpret data causally.