Measurement of differences in red chlorophyll fluorescence and photosynthetic activity between sun and shade leaves by fluorescence imaging

With a flash-lamp chlorophyll (Chl) fluorescence imaging system (FL-FIS) th e photosynthetic activity of several thousand image points of intact shade and sun leaves of beech were screened in a non-destructive way within a few seconds. The photosynthetic activity was determined via imaging the Chi fl uorescence at maximum F-p and steady state fluorescence F-s of the inductio n kinetics (Kautsky effect) and by a subsequent determination of the images of the fluorescence decrease ratio R-Fd and the ratio F-p/F-s. Both fluore scence ratios are linearly correlated to the photosynthetic CO2 fixation ra tes. This imaging method permitted to detect the gradients in photosyntheti c capacity and the patchiness of photosynthetic quantum conversion across t he leaf. Sun leaves of beech showed a higher photosynthetic capacity and di fferential pigment ratios (Chl a/b and Chls/carotenoids) than shade leaves. Profile analysis and histogram of the Chl fluorescence yield and the Chl f luorescence ratios allow to quantify the differences in photosynthetic acti vity between different leaf parts and between sun and shade leaves with a h igh statistical significance.