ARS | Publication request: Differentiating among plant spectra by combining pH dependent photoluminescence spectroscopy with multi-way principal component analysis (MPCA)

Submitted to: Open Agriculture Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 5, 2010
Publication Date: March 1, 2011
Citation: Anderson, D.M., Danielson, T.L., Obeidat, S.M., Rayson, G.D., Estell, R.E., Bai, B., Fredrickson, E.L. 2011. Differentiating among plant spectra by combining pH dependent photoluminescence spectroscopy with multi-way principal component analysis (MPCA). The Open Agriculture Journal. 5:1-9.

Interpretive Summary: As new approaches are employed to determine the botanical composition from pre- and post-digested plant materials composing free-ranging animal diets it becomes necessary to concurrently employ the most robust statistical techniques that will optimize discrimination among the plants that make up these mixtures. The use of fluorometry, where the extraction solvent can vary in pH, is one example of how complex multidimensional data set can arise. This paper describes the use of multi-way principal component analysis (MPCA) as a technique to improved discrimination within a plant life form where species differences are not readily apparent from the observation of plotted spectral data alone. Where several pH's of a buffered saline extraction solvent were used to extract fluorophores it was possible to discriminate between two grasses using MPCA while this was not possible using only principal component analysis (PCA). These preliminary data suggest MPCA may be preferred over PCA when attempting to discriminate differences among plant species using fluorometry.

Technical Abstract: Knowing the botanical composition of the standing crop is essential for managing ecosystem health and herbivory. Photoluminescence spectroscopic probes offer the potential for real-time measurements of animal diet composition. Spectral emission signatures (excitation at 365 nm) from three different pH (2.2, 7.5 and 12.5) phosphate buffered saline (PBS) extracts from two grasses, Sporobolus flexuosus (Thurb. ex Vasey) Rydb., [mesa dropseed], and Pleuraphis mutica Buckley [tobosa], two forbs, Dimorphocarpa wislizenii (Engelm.) Rollins [spectacle pod], and Sphaeralcea incana Torrey [pale globemallow], and leaves and twigs from two shrubs Flourensia cernua DC. [tarbush], and Atriplex canescens (Pursh) Nutt., [fourwing saltbush] were examined. Since pH has been shown to be pivotal in affecting extraction efficiency of other plant compounds pH seemed appropriate as an additional dimension within our multi-way principal component analysis (MPCA) to differentiate among six different plant species. In particular, MPCA allowed differentiation between Sporobolus and Pleuraphis that was not possible using only principal component analysis (PCA). This research suggests MPCA may be a more appropriate tool than PCA when attempting to discriminate among plant species.