Laser-induced fluorescence of green plants. 3: LIF spectral signatures of five major plant types

A technique amenable to remote sensing use which utilizes laser-induced fluorescence (LIF) properties of plants has been successfully used in the laboratory to identify five major plant types. These included herbaceous dicots, herbaceous monocots, conifers, hardwoods, and algae. Each of these plant types exhibited a characteristic LIF spectra when excited by a pulsed N2 laser emitting at 337 nm. Although monocots and dicots possess common fluorescence maxima at 440, 685, and 740 nm, they could be differentiated from one another by using the ratio of the square of the fluorescence intensity at 440 nm to the nonsquared intensity at 685 nm, i.e., (440)2/685. In all cases, monocots yielded a significantly higher ratio. Conifers have fluorescence maxima at 440, 525, and 740 nm but none at 685 nm. Hardwoods exhibited fluorescence at 440, 525, 685, and 740 nm. Algae had very low fluorescence at 440 nm, no fluorescence at 525 nm, and fluorescence maxima at 685 and 740 nm. For algae, the ratio of the fluorescence intensity at 685 nm to that at 740 nm was much greater than that for monocots, dicots, and hardwoods. The potential use of the LIF technique for individual species identification is suggested.     

Analysis of selected trace organics in advanced wastewater treatment systems

Effluents through four different pilot tertiary wastewater treatment systems were monitored for selected trace organic compounds. The effects of using ozone, free and combined chlorine residuals in these systems were also studied. Advanced treatment of secondary effluent using various combinations of flocculation (alum and polymer), dual media filtration, and carbon adsorption were evaluated for production/removal of volatile halogenated organics, polynuclear aromatics, chlorinated pesticides, and polychlorinated biphenyls. Gas chromatographic methods were used for the analysis of these different classes of compounds: specific techniques and analytical parameters are described. Salient results included: drastic increases in trihalomethane production using free chlorine residuals: disinfection with combined chlorine species does not produce significant levels of trihalomethanes: approximately 90% reduction in trihalomethane levels by carbon adsorption: absence of detectable quantities of polynuclear aromatics: significant decreases in pesticide and PCB levels by carbon adsorption and chlorination. Statistical dependence of trihalomethane production on soluble COD, suspended solids and chloramine levels was evident from multiple linear regression calculations.     

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.     

Fluorescence sensing systems: In vivo detection of biophysical variations in field corn due to nitrogen supply

Leaf and canopy fluorescence properties of field corn (Zea mays L.) grown under varying levels of nitrogen (N) fertilization were characterized to provide an improved N sensing capability which may assist growers in site-specific N management decisions. In vivo fluorescence emissions can occur in the wavelength region from 300 to 800 nm and are dependent on the wavelength of illumination. These light emissions have been grouped into five primary bands with maxima most frequently received from corn at 320 nm (UV), 450 nm (blue), 530 nm (green), 685 nm (red), and 740 nm (far-red). Two active fluorescence sensing systems have been custom developed; a leaf level Fluorescence Imaging System (FIS), and a canopy level Laser Induced Fluorescence Imaging System (LIFIS). FIS sequentially acquires high-resolution images of fluorescence emission bands under darkened laboratory conditions, while LIFIS simultaneously acquires four band images of plant canopies ≥1 m² under ambient sunlit conditions. Fluorescence emissions induced by these systems along with additional biophysical measures of crop condition; namely, chlorophyll content, N/C ratio, leaf area index (LAI), and grain yield, exhibited similar curvilinear responses to levels of supplied N. A number of significant linear correlations were found among band emissions and several band ratios versus measures of crop condition. Significant differences were obtained for several fluorescence band ratios with respect to the level of supplied N. Leaf adaxial versus abaxial surface emissions exhibited opposing trends with respect to the level of supplied N. Evidence supports that this confounding effect could be removed in part by the green/blue and green/red ratio images. The FIS and LIFIS active fluorescence sensor systems yielded results which support the underlying hypothesis that leaf and canopy fluorescence emissions are associated with other biophysical attributes of crop growth and this information could potentially assist in the site-specific management of variable-rate N fertilization programs.