PULSE FLUOROMETER FOR REMOTE MEASURING OF CHLOROPHYLL FLUORESCENCE FROM LABORATORY PLANT STANDS

A pulse fluorometer was developed for remote measuring of chlorophyll fluorescence from small (10 x 20 cm) stands of plants grown under labo ratory conditions. During measurement, the stand is illuminated with a weak probing flash (10 mu s), and fluorescence pulses are measured re motely by a photodiode. The fluorometer registers the following charac teristics: original (dark) fluorescence level (F-0); maximum fluoresce nce yield (F-m), measured 50 mu s after illumination of the stand with a powerful saturating Bash, and the kinetics of changes in chlorophyl l fluorescence yield (induction curve of chlorophyll fluorescence, F(t )) after additional illumination of the stand with continuous light. A n advantage of the remote measurements is obtaining averaged data for ail plants of the stand. This avoids data scattering resulting from in dividual plant variability. The high frequency of the measurements (ca . I Hz) provides for high precision and reproducibility in measuring f luorescence. Testing the fluorometer on stands of different plant spec ies grown in a mock-up of the Svet space-greenhouse showed that F-0 is well correlated with the dry weight of plant stands. This allows meas urement of plant growth rate as the difference in plant biomasses esti mated in any two successive measurements, with time resolution of abou t one hour. Recording the amplitude and kinetics of chlorophyll variab le fluorescence makes it possible to investigate age-dependent changes in the physiological state of plants and plant responses to environme ntal factors.