Fluorosensing of water stress in plants: Diurnal changes of the mean lifetime and yield of chlorophyll fluorescence, measured simultaneously and at distance with a τ-LIDAR and a modified PAM-fluorimeter, in maize, sugar beet, and kalanchoë

We modified a PAM fluorimeter for remote detection from 0.5 m to 1 m distance by using a laser diode for excitation. It permitted us to compare directly and simultaneously measurements of relative fluorescence yield to the measurements of lifetime with the τ-LIDAR performed under natural conditions. The existence of a linear relationship, and therefore the equivalence between the lifetime and yield for chlorophyll fluorescence estimation in vivo was confirmed here for several plant types and under both optimal conditions and conditions of water stress. We have also shown that fluorescence lifetime measurements, with the τ-LIDAR, can be used to perform complex fluorescence quenching analysis in fluorosensing, like the one developed in the laboratory for near-contact measurements with PAM-fluorimetry. Water stress effects on fluorescence changes are especially pronounc ed in maize plants due to the C4 type of metabolism and the absence of photorespiration. This would permit the use of the steady state level of fluorescence (Fs, τs) for stress detection, provided that the irradiance is known or is estimated.