FLUOROSENSING OF WATER-STRESS IN PLANTS - DIURNAL CHANGES OF THE MEANLIFETIME AND YIELD OF CHLOROPHYLL FLUORESCENCE, MEASURED SIMULTANEOUSLY AND AT DISTANCE WITH A TAU-LIDAR AND A MODIFIED PAM-FLUOROMETER, INMAIZE, SUGAR-BEET, AND KALANCHOE

We modified a PAM fluorimeter for remote detection from 0.5 m to 1 m d istance by using a laser diode for excitation. It permitted us to comp are directly and simultaneously measurements of relative fluorescence yield to the measurements of lifetime with the tau-LIDAR performed und er natural conditions. The existence of a linear relationship, and the refore the equivalence between the lifetime and yield for chlorophyll fluorescence estimation in vivo was confirmed here for several plant t ypes and under both optimal conditions and conditions of water stress. We have also shown that fluorescence lifetime measurements, with the tau-LIDAR, can be used to perform complex fluorescence quenching analy sis in fluorosensing, like the one developed in the laboratory for nea r-contact measurements with PAM-fluorimetry, Water stress effects on f luorescence changes are especially pronounced in maize plants due to t he C4 type of metabolism and the absence of photorespiration. This wou ld permit the use of the steady state level of fluorescence (F-s, tau( s)) for stress detection, provided that the irradiance is known or is estimated. (C) Elsevier Science Inc., 1996.