CHEMICAL CHARACTERIZATION OF PHYTOLITHS WITH RAMAN SPECTROSCOPY: WHAT IS INSIDE
Jessica Sanchez1, Eric Potma2.
1California State University, Fullerton, Fullerton, CA, 2University of California, Irvine, Irvine, CA.
Phytoliths are silica bodies formed by biomineralization in plants where soluble monosilicic acid is assimilated by the plant and precipitated within the cells and intracellular spaces as amorphous silica. During mineral precipitation, organic matter (OM) can be trapped in the inorganic matrix and, when the plant dies, phytoliths remain in the soil. These can be collected and used for paleoreconstructions based on morphology and isotope content of the trapped OM. The source of the OM in phytoliths has not been well constrained. This study uses Raman spectroscopy to determine the nature of OM in phytoliths obtained from a previous isotope study. These phytoliths were isolated from modern plants, Sorghum bicolor, growing in 6 different experimental conditions. Our purpose is to determine if phytolith carbon changes with different growing conditions. Ideally, differences in OM type and distribution between these treatments could give information about the OM source. Samples of bilobate phytoliths were analyzed in the C-H stretching region (2,700 - 3,200 cm-1) and the fingerprint region (1,300 - 1,800 cm-1) of the vibrational spectrum. Results show that the average spectra for each treatment exhibits consistent, common vibrational bands; however, there are slight differences between the spectra of phytoliths from each treatment. The data suggest the presence of carbohydrates, lignin, and possibly lipids. Moreover, the OM is heterogeneously distributed throughout the phytoliths. Further research will focus on spectral imaging and Raman surveys of silica structures. Information on the nature of OM in phytoliths may aid in determining a mechanism of entrapment.