Application of the Karlsruhe CCD-OMA LIDAR-Fluorosensor in Stress Detection of Plants

Abstract

Summary The Karlsruhe CCD-OMA LIDAR-Fluorosensor (excitation: cw HeNe laser, 632.8 nm; detection:complete chlorophyll fluorescence spectra between 650-800 nm within 10 ms) was developed in a joint project by the Technical University of Budapest and the University of Karlsruhe for a non-destructive stress detection of plants. The computer-aided fluorosensor permits to measure the full fluorescence spectra at 8 different time intervals during the chlorophyll fluorescence induction kinetics, from which the the variable chlorophyll fluorescence ratio Rfd as plant vitality index can be calculated. The position of the chlorophyll fluorescence emission maxima of green leaves are found in the red region near 690 nm and the far-red region near 735 nm. The wavelength position of the two maxima remained unchanged during the light-induced fluorescence induction kinetics (Kautsky effect). The absolute fluorescence intensity and the ratio of the two chlorophyll fluorescence bands (F690/F735) depended on the chlorophyll content and the photosynthetic activity of a leaf as has been demonstrated here with the CCD-OMA LIDAR fluorosensor. With increasing chlorophyll content of the leaf the fluorescence intensity of the red band near 690 nmdecreased, whereas that of the far-red band near 735 nm remained constant or slightly increased. Consequendy, the fluorescence ratio F690/F735 increased with decreasing chlorophyll concentration of leaves (curvi-linear relationship: y = a·x-b). Changes in the fluorescence ratio F690/F735 can be taken as an indicator of long-term stress affecting the chlorophyll content of leaves. The inverse relationship between the intensity of the chlorophyll fluorescence and the rate of photosynthesis (Kautsky effect) can be used for detecting, via Rfd-values, a short-term damage to plants, which affects photosynthetic activity, but does not yet decrease the chlorophyll content of the leaf. Damage or stress is indicated by low Rfd-values (ratio fluorescence decrease) or low Ap-values (stress adaptation index). Examples are shown for different types of damage and/or stresses (water stress, forest decline phenomena, application of a herbicide inhibiting photosynthesis, and biological stress, e.g. damage by mites). The Karlsruhe CCD-OMA LIDAR-Fluorosensor proved to be a valuable tool for fast detection of stress to plants in the laboratory, but can also be applied for ground-truth control measurements during remote sensing of the state of health of terrestrial vegetation.