Chemical properties of foliar metabolomes represent a key axis of functional trait variation in forests of the tropical Andes

Plants interact with their environment through diverse specialized
metabolites that protect them from abiotic stressors like drought or
radiation and biotic stressors like herbivores or pathogens. However, few
studies have considered the chemical properties of metabolites as a
potential axis of functional trait variation along environmental
gradients.  Here, we examined how the chemical properties of
foliar metabolomes, such as mean aromaticity, hydrophobicity, and
polarity, as well as commonly used morphological traits, vary with climate
and elevation among 16 forest plots in the tropical Andes of Bolivia. We
found that chemical properties were weakly related to morphological traits
among tree species, yet both varied significantly with climate and
elevation. In particular, abundance-weighted mean hydrophobicity
decreased, and polar surface area increased with elevation and in colder
and drier climates. Additionally, co-occurring species showed increasing
chemical similarity with elevation for the most-aromatic and most-polar
metabolites. These results suggest that abiotic stress associated with
colder, drier climates and solar radiation acts as a filter for metabolome
chemical properties. This contrasts with chemical dissimilarity observed
at lower elevations, which is likely driven by pressure from
host-specialized enemies in warmer, wetter climates. Our results introduce
the possibility that chemical defenses may be constrained by abiotic
stressors. Morphological traits and foliar metabolome chemical properties
for each species-by-plot are reported in Dataset S1. Community-weighted
mean values are reported in Dataset S2. The structural similarities among
20,571 metabolites are reported as a Qemistree dendrogram in .tre
phylogeny format as Dataset S3. Masses, molecular formulae, predicted
structures, classifications, and chemical properties and sample-level
abundances for 20,571 unique metabolites are provided in Dataset S4.