U. Rinderle

Application of chlorophyll fluorescence in ecophysiology

SummaryIn vivo chlorophyll fluorescence measurements have become a valuable tool in ecophysiology. Fluorescence emission spectra are influenced by the reabsorption of the tissue and indicate the composition of the antenna system and are influenced by the chlorophyll content per leaf area. The fluorescence induction kinetics (“Kautsky effect”) can be used to study photosynthetic activity. These rapid, non-destructive methods can be applied for ecophysiological field research to check the vitality of plants and to document stress effects on the photosynthetic apparatus. The Rfd-values (Rfd=fd/fs), the ratio of the fluorescence decrease (fd) to the steady state fluorescence (fs), can be taken as a rapid vitality index of the leaves and trees. We here describe fundamental chlorophyll fluorescence results of leaves which are needed for the interpretation of in vivo fluorescence signatures in stress physiology and in the forest dieback research.

Decrease of the chlorophyll fluorescence ratio F690/F730 during greening and development of leaves

SummaryUsing the two-wavelength chlorophyll fluorometer the fluorescence induction kinetics (Kautsky effect) were measured simultaneously in the 690 nm and 730 nm region for ten common tree species during the greening period (April to July). The chlorophyll-fluorescence ratio F690/F730 (i.e. ratio of fluorescence intensity at the two maxima near 690 and 730 nm) was calculated from the laser-induced induction kinetics (He/Ne-laser 632.8 nm) at the fluorescence maximum and the steady state. The ratio F690/F730 decreases with increasing chlorophyll content of developing leaves. Its dependence on the chlorophyll content can be fairly well expressed by a power function which has a general validity for leaves, pigment extracts and chloroplast suspensions. The ratio F690/F730 is somewhat higher at maximum (fm) than at steady-state fluorescence (fs), but there is a very good correlation between both values. The ratio F690/F730 is a good indicator of the chlorophyll content and can be used as a non-destructive measure of the chlorophyll content of leaves. It also appears to be a suitable fluorescence parameter in the future remote sensing of the physiological state of the vegetation by laser-equipped airborne systems.

The chlorophyll fluorescence ratio F690/F730 in leaves of different chlorophyll content

The red laser-induced chlorophyll-fluorescence induction kinetics of predarkened leaf samples were registered simultaneously in the 690 and 730 nm regions i.e., in the region of the two chlorophyll fluorescence emission maxima. From the induction kinetics the chlorophyll fluorescence ratio F690/F730 was calculated. The ratio F690/F730 shows to be dependent on the chlorophyll content of leaves. It is significantly higher in needles of damaged spruces (values of 0.45–0.9) than in normal green needles of healthy trees (values of 0.35–0.5). During development and greening of maple leaves the ratio F690/F730 decreases with increasing chlorophyll content. Determination of the ratio F690/F730 can be a suitable method of monitoring changes in chlorophyll content in a non-destructive way in the same leaves during development or the yellowish-green discolouration of needles of damaged spruces in the Black Forest with the typical tree decline symptoms.

THE CHLOROPHYLL FLUORESCENCE RATIO F690/F735 AS A POSSIBLE STRESS INDICATOR

The chlorophyll fluorescence emission spectra, as excited by blue and red light including laser light, were determined depending on the chlorophyll content and the photosynthetic activity of leaves and needles. The fluorescence-emission spectra exhibit two maxima or a shoulder in the 690 nm and the 735 nm region. The corresponding fluorescence ratio F690/F735 for green leaves is higher (values of 0.8 to 1.1) when excited with blue light (range 400 to 500 nm) than excited with light in the yellow to red wavelength region (525 to 633 nm), which only yields values for F690/F735 of 0.5 to 0.7. The values for the ratio F690/F735 are drastically increased with decreasing chlorophyll content of leaves and to a lower degree also by a decline of photosynthetic activity (e.g. herbicide treatment, needles of damaged forest trees) no matter whether the fluorescence is excited by red or blue light. Since stress induces a lower chlorophyll content as well as lower rates of photosynthesis, the ratio F690/F735 can be taken as indicator of stress to plants. The application of the ratio F690/F735 in detecting stress to terrestrial vegetation via remote sensing of the chlorophyll fluorescence is discussed.

Detection of stress in coniferous forest trees with the VIRAF spectrometer

The Visible Infrared Reflectance Absorbance Fluorescence (VIRAF) spectrometer was applied in outdoor measurements to compare the needles of two spruce trees differently affected by the forest decline in the Northern Black Forest in Germany. Changes of the reflectance signatures due to loss of chlorophyll or other damage effects are interpreted with the help of other techniques currently used for the evaluation of physiological activity. The VIRAF spectrometer was used to examine the spectra of reflectance, absorption, and chlorophyll fluorescence. The measurements were carried out with the same sample without changing its position. By means of the two-wavelength chlorophyll fluorometer and pulse amplitude modulation fluorometer the fluorescence induction kinetics and several fluorescence parameters were determined as an indicator of vitality. In addition, the rate of photosynthetic CO/sub 2/ fixation and the stomatal closure were studied using a CO/sub 2/H/sub 2/O porometer. >

Chlorophyll Fluorescence Signatures as Vitality Indicator in Forest Decline Research

The chlorophyll-fluorescence signatures of the needles of healthy (damage class 0/1, Althof, 450 m above sea level) and damaged spruce trees (damage class 3/4, Mauzenberg 700 m altitude) in the northern Black Forest were determined by using a self-constructed portable field fluorometer as well as the PAM-fluorometer. These new instruments allow measurement of the red-laser-induced chlorophyll fluorescence induction kinetics (Kautsky effect) at 690 and 730 nm, the determination of the Rfd-values (Rfd 690 and Rfd 730) as vitality index, and the stress-adaptation index Ap as well as the photochemical Q-quenching and the non-photochemical E-quenching of the spruce needles. The differences in the fluorescence signatures and photosyn-thetic activity between the needles of healthy and damaged trees are presented. In the needles of the damaged trees the Rfd-values, the capacity for photosynthesis and the reoxidation of QA are strongly reduced, whereas the non-photochemical E-quenching is increased.