Dr. Contreras-Quintana, Sergio

Plant leaf waxes are used as vegetation biomarkers in several archives (i.e. soils, lake and marine sediments), study of these compounds in modern plants is needed to makes their application and interpretation more robust. However, in the South American Temperate Forest (STF), few species have been studied. The main goal of this research was to characterize twelve dominant modern species of the STF using three classes of leaf wax compounds, n-alkanoic acids, n-alkanes and n-alkanols. In addition, we evaluate the potential of leaf waxes as a vegetation and chemotaxonomic biomarker in the region, considering species that were found in different sampling sites and therefore environmental conditions. Clear differences among leaf wax abundance (μg/g) and ACL (average chain length) within and among the twelve species were found. Only the ACL of n-alkanoic acids and n-alkanols allows differentiation between leaf habit species (i.e. evergreen vs. deciduous), with high values associated with evergreen and low values with deciduous plants. This study differentiates the five species found in more than one site (i.e. different environmental condition) using different combinations of leaf waxes and in addition using only n-alkanes. It was not possible to differentiate among all sites with any combination of leaf waxes. The differences in the distribution of leaf waxes among species is an expected pattern in the study area, and it seems reliable to use the ACL as a vegetation biomarker differentiating between evergreen and deciduous species. The clear chemotaxonomic differences among the five species exposed to different and natural environmental conditions and the high preservation potential of the study area allow us to suggest that leaf waxes are likely a reliable tool to be incorporated in quantitative models to track vegetation and may be useful as a chemotaxonomic biomarker at the species level.

A. araucana is an endemic species of the temperate forests from Chile and Argentina; protected in both countries and categorized as in danger of extinction. Individuals of this species have begun to show foliar damage (i.e., discoloration) in branches and upper parts. The discoloration begins from the base to the top and from the trunk to the branches with necrotic rings appearing; in some cases causing death; and is currently attributed to an as yet unknown disease. This study focuses on the first protective layer of plants against environmental stress and pathogens; known as leaf waxes. The abundance and distribution of three classes of leaf waxes (long chain fatty acids; alkanes and alcohols) were measured in healthy individuals of A. araucana from different sites and individuals that present foliar damage (sick individuals). In the case of sick individuals; their leaf waxes were measured considering the level of leaf damage; that is; leaves without; medium and full foliar damage. The most abundant class of leaf wax in both sick and healthy individuals was fatty acids; followed by alkanes and then alcohols; with common dominant chains; C28 fatty acid; C29 alkane and C24 alcohol. Sick individuals have higher abundances of alkanes and alcohols than healthy individuals. The leaves of sick individuals have lower values of distribution indices (the carbon preference index of fatty acids and average chain length of alkanes) as foliar damage increases that are interpreted as a reduction of in vivo biosynthesis of waxes. This is the first evidence of A. araucana response to a still unknown disease that is killing individuals of this endemic species.