Genus-wide variation in foliar polyphenolics in eucalypts. (December 2017) - Marsh, Karen J.
Abstract: Many studies quantify total phenolics or total tannins, but understanding the ecological role of polyphenolic secondary metabolites requires at least an understanding of the diversity of phenolic groups present. We used UPLC-MS/MS to measure concentrations of different polyphenol groups - including the four most common tannin groups, the three most common flavonoid groups, and quinic acid derivatives - in foliage from 628 eucalypts from the genera Eucalyptus, Angophora and Corymbia . We also tested for phylogenetic signal in each of the phenolic groups. Many eucalypts contained high concentrations of polyphenols, particularly ellagitannins, which have been relatively poorly studied, but may possess strong oxidative activity. Because the biosynthetic pathways of many phenolic compounds share either precursors or enzymes, we found negative correlations between the concentrations of several of the constituents that we measured, including proanthocyanidins (PAs) and hydrolysable tannins (HTs), HTs and flavonol derivatives, and HTs and quinic acid derivatives. We observed moderate phylogenetic signal in all polyphenol constituents, apart from the concentration of the prodelphinidin subunit of PAs and the mean degree of polymerisation of PAs. These two traits, which have previously been shown to be important in determining plants' protein precipitation capacity, may have evolved under selection, perhaps in response to climate or herbivore pressure. Hence, the signature of evolutionary history appears to have been erased for these traits. This study is an important step in moving away from analysing "totals" to a better understanding of how phylogenetic effects influence phenolic composition, and how this in turn influences ecological processes. Graphical abstract: We analysed the polyphenol composition of more than 500 species of eucalypts from ten phylogenetic clades and found them to be rich in hydrolysable tannins. Highlights: We used UPLC-MS/MS to quantify polyphenols in foliage from 628 eucalypts. Many eucalypt species contained high concentrations of ellagitannins. The concentrations of some polyphenol groups were negatively correlated. Many phenolic traits appear to be phylogenetically conserved. Natural selection may be operating on two traits that affect protein-binding.