Laser-Induced Fluorescence (LIF) from Plant Foliage

The fluorescence spectra and fluorescence induction kinetics of plants excited with a pulsed nitrogen laser beam emitting at 337 nm were found to be correlated with plant type, as well as with changes in the physiology of the plant as the result of various kinds of environmental stress. The plant types that were studied included herbaceous dicots, monocots, hardwoods, conifers, and algae. These plant types could be identified on the basis of differences in either the number of fluorescent bands, or the relative intensity of the bands. The dicots and monocots had fluorescent maxima at 440, 685, and 740 nm. The monocots could be distinguished from the dicots by virtue of having a much higher 440/685 nm ratio. Hardwoods and conifers had an additional fluorescence band at 525 nm, but healthy conifers did not have a band at 685 nm. The algae had fluorescence bands at only 685 and 740 nm. Differences in the fluorescent spectra that could be related to vigor status were observed in conifers growing in an area where atmospheric deposition, i.e., acid rain and heavy metals, is known to be significant. Changes in the fluorescence spectra and fluorescence induction kinetics were also seen in plants grown under conditions of nutrient and drought stress.