Metabolome-Wide, Phylogenetically Controlled Comparison Indicates Higher Phenolic Diversity in Tropical Tree Species.

Guille Peguero,Karel Klem,Jordi Sardans,Otmar Urban,Joan Maspons,Josep Peñuelas,Albert Gargallo-Garriga

doi:10.3390/plants10030554

Abstract

Tropical plants are expected to have a higher variety of defensive traits, such as a more diverse array of secondary metabolic compounds in response to greater pressures of antagonistic interactions, than their temperate counterparts. We test this hypothesis using advanced metabolomics linked to a novel stoichiometric compound classification to analyze the complete foliar metabolomes of four tropical and four temperate tree species, which were selected so that each subset contained the same amount of phylogenetic diversity and evenness. We then built Bayesian phylogenetic multilevel models to test for tropical–temperate differences in metabolite diversity for the entire metabolome and for four major families of secondary compounds. We found strong evidence supporting that the leaves of tropical tree species have a higher phenolic diversity. The functionally closer group of polyphenolics also showed moderate evidence of higher diversity in tropical species, but there were no differences either for the entire metabolome or for the other major families of compounds analyzed. This supports the interpretation that this tropical–temperate contrast must be related to the functional role of phenolics and polyphenolics.

Highlights

Attempting to explain the latitudinal gradient of plant diversity has been a major focus of interest since the age of the pioneer naturalists [1]
To exclude any evolutionary effect on the metabolomic differences between tropical and temperate species, we selected four tropical and four temperate tree species so that each subset encompassed the same amount of phylogenetic diversity and evenness, i.e., the total branch length and mean distances between the species in each phylogenetic subtree were equivalent (Table 1 and Figure S1)
The metabolomic profiles of the species indicated that tropical trees tended to have more metabolites than did temperate trees (2280 ± 148 vs. 2111 ± 147, respectively; hereafter mean ± standard deviation of the posterior distribution estimate)

Summary

Introduction

Attempting to explain the latitudinal gradient of plant diversity has been a major focus of interest since the age of the pioneer naturalists [1] Building upon these early observations, the modern synthesizers laid out the hypothesis that the strength of biotic interactions, antagonistic relationships with competitors, herbivores and pathogens, increase toward the tropics [2]. The advances in mass spectrometry and nuclear magnetic resonance allow for unprecedented characterizations of complete metabolomes, which are renewing interest in the links between taxonomic and phytochemical diversity [21,24,25,26] In addition to these breakthroughs in analytical chemistry, the development of Bayesian comparative methods facilitates the modeling of the phylogenetic structure of the data and the inclusion of intraspecific variability in trait analyses, thereby seamlessly incorporating the evolutionary relationships among species within the inferential process [27]. We analyzed the similarity of the complete foliar metabolomes and of their phenolic profiles to check for differences according to region of origin and to assess variations within and between species in chemical composition

Species Selection and Sample Processing

Data Analysis

Results

Discussion