Dr. Contreras-Quintana, Sergio

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.

In the hyperarid Atacama Desert, water availability plays a crucial role in allowing plant survival. Along with scant rainfall, marine advective fog frequently occurs along the coastal escarpment fueling isolated mono-specifc patches of Tillandsia vegetation. In this study, we investigate the lipid biomarker composition of the bromeliad Tillandsia landbeckii (CAM plant) to assess structural adaptations at the molecular level as a response to extremely arid conditions. We analyzed long-chain n-alkanes and fatty acids in living specimens (n=59) collected from the main Tillandsia dune ecosystems across a 350 km coastal transect. We found that the leaf wax composition was dominated by n-alkanes with concentrations (total average 160.8±91.4 µg/g) up to three times higher than fatty acids (66.7±40.7 µg/g), likely as an adaptation to the hyperarid environment. Signifcant diferences were found in leaf wax distribution (Average Chain Length [ACL] and Carbon Preference Index [CPI]) in the northern zone relative to the central and southern zones. We found strong negative correlations between fatty acid CPI and n-alkane ACL with precipitation and surface evaporation pointing at fne-scale adaptations to low moisture availability along the coastal transect. Moreover, our data indicate that the predominance of n-alkanes is refecting the function of the wax in preventing water loss from the leaves. The hyperarid conditions and good preservation potential of both n-alkanes and fatty acids make them ideal tracers to study late Holocene climate change in the Atacama Desert.