Differentiating Among Plant Spectra by Combining pH Dependent Photoluminescence Spectroscopy with Multi-Way Principal Component Analysis (MPCA)

Photoluminescence spectroscopic probes offer the potential for differentiation among plant species in real-time. 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 effi- ciency of other plant compounds pH seemed appropriate as an additional dimension within our multi-way principal com- ponent 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.