MOLECULAR VARIATION IN LEAF WAX N-ALKANES AND CHEMOTAXONOMIC IMPLICATIONS FOR THE PETM

Because long-chain n-alkanes (n-C₂₁ to n-C₃₇) are found in the epicuticular leaf waxes of all vascular plants and are stable, long-lived molecules, the study of their molecular composition stands to serve as a potentially powerful tool in the fields of chemotaxonomy and paleoecology. This study attempts to evaluate the usefulness of n-alkane distributions as identifiers of terrestrial plant species and groups using data from a wide range of plant species. The species sampled were grown at the Chicago Botanic Garden and Lincoln Conservatory and represented angiosperms, gymnosperms, and ferns; deciduous and evergreen species; and needle and broadleaf species. n-Alkane composition is shown to be highly conservative within individual plants across a growing season and from different locations within a tree's canopy; composition is also largely conservative within a species but less so within higher groupings. Within species, there is a correlation between the weighted mean of n-alkanes and the dispersion about that mean, possibly due to functional constraints on the biosynthesis of n-alkanes. This study also investigates the application of modern n-alkane data to the reconstruction of ancient plant community dynamics during the Paleocene-Eocene Thermal Maximum (PETM), ~55.8 Ma. The local flora of the Bighorn Basin, Wyoming, is known to have shifted from a deciduous mixed angiosperm/gymnosperm forest to an entirely different suite of evergreen angiosperm species at the onset of the PETM, concurrent with a rapid, intense global warming event. This study concludes that the shift in paleosol n-alkane composition at the onset of the PETM is not related to the change in the local plant community. Rather, n-alkane distribution may be related more directly to temperature and climate change.