Diversified chemical profiles of cuticular wax on alpine meadow plants of the Qinghai-Tibet Plateau

Main conclusion: The alpine meadow plants showed great intra- and inter-genera variations of chemical profiles of cuticular waxes. Abstract: Developing an understanding of wax structure-function relationships that will help us tackle global climate change requires a detailed understanding of plant wax chemistry. The goal in this study was to provide a catalog of wax structures, abundances, and compositions on alpine meadow plants. Here, leaf waxes from 33 plant species belonging to 11 families were sampled from alpine meadows of the east side of the Qinghai-Tibet Plateau. Across these species, total wax coverage varied from 2.30 μg cm⁻² to 40.70 μg cm⁻², showing variation both within as well as between genera and suggesting that wax variation is subject to both environmental and genetic effects. Across all wax samples, more than 140 wax compounds belonging to 13 wax compound classes were identified, including both ubiquitous wax compounds and lineage-specific compounds. Among the ubiquitous compounds (primary alcohols, alkyl esters, aldehydes, alkanes, and fatty acids), chain length profiles across a wide range of species point to key differences in the chain length specificity of alcohol and alkane formation machinery. The lineage-specific wax compound classes (diols, secondary alcohols, lactones, iso-alkanes, alkyl resorcinols, phenylethyl esters, cinnamate esters, alkyl benzoates, and triterpenoids) nearly all consisted of isomers with varying chain lengths or functional group positions, making the diversity of specialized wax compounds immense. The comparison of species relationships between chemical data and genetic data highlighted the importance of inferring phylogenetic relationships from data sets that contain a large number of variables that do not respond to environmental stimuli.