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New Mexico State University (2002)

Ultra-violet induced fluorescence for the investigation and discrimination of six arid desert-rangeland plants

Danielson Timothy L

Titre : Ultra-violet induced fluorescence for the investigation and discrimination of six arid desert-rangeland plants

Auteur : Timothy L Danielson

Université de soutenance : New Mexico State University

Grade : Doctor of Philosophy (PhD) 2002

In the past, the ability to determine the dietary botanical composition of free-ranging herbivores has relied on older, crude techniques. These techniques involved bite count data, sampling from the alimentary canal and/or sampling feces for microhistological analysis. These processes consume many man hours and have the ability to directly affect the target animal through human interaction and invasive procedures. We propose the spectroscopic technique of fluorescence as a rapid, accurate, non-invasive method for the determination of pre -digested plant material with future applications for post -digested plant material consumed by herbivores. It has previously been determined that plant material fluoresces in two regions of the visible spectrum. The dominant chlorophyll fluorescence is found in the 600-800 nm (red) region, while that, of yet unknown species, is observed in the 400-600 nm (blue-green) region. The present study consisted of characterizing the fluorescence signature of six pre-digested arid desert rangeland plants associated with foraging animals’ diet : Sporobolus flexuosus (mesa dropseed), Pleuraphis mutica (tobosa), Dithyrea wislizenii (spectacle pod), Sphaeralcea incana (pale globemallow), Flourensia cernua (tarbush), and Atriplex carnescens (four-wing saltbush). Each plant species was represented by nine individual plants. Three extraction solvents were examined for their capabilities of chromophore extraction : chloroform, hexane, and phosphate buffered saline (PBS). It was discovered that the PBS solvent dramatically reduced the extraction of chlorophyll (a strong fluorescence quencher) when compared to the organic solvents. Therefore, PBS was chosen as the primary solvent. The PBS was buffered to within the three pK a values associated with the phosphate ion to produce extraction solutions having pH values of 2.2, 7.5 and 12.5. Two different instrumental systems were developed for fluorescence measurements. One system, the "McPherson system," has the ability of high spectral resolution and high detector sensitivity. The second system, the "Chromex system," has advantages of short data acquisition times arid high signal-to-noise (SIN). Utilizing the 375-620 nm region of the fluorescence spectrum, the six plant species investigated were able to be distinguished. Discriminant function analysis (DFA) was the statistical tool applied to the acquired data. It provided classification rates for each plant species measured on two different instrumental systems and extracted at three different pH values. A 100% classification was achieved for the nine plants representing the six species that were measured on the Chromex system and extracted with the pH 2.2 PBS. Further chemical information was gained with the aid of curve fitting programs and deconvolution methods where the emission spectra can supply information on the identity and contribution of the fluorescing compounds within the plant. The results identified at least four major emission bands within the 375-620 nm region. Within these bands, each plant species has a characteristic contribution. Further investigations will be required in order to identify the chemical species responsible for the observed fluorescence in the blue-green region of the spectrum. With a better chemical understanding, the technique of fluorescence may become a rapid, accurate, inexpensive method for any investigation for plant identification and discrimination.

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Page publiée le 27 janvier 2012, mise à jour le 11 novembre 2018