Foliar metabolomes of woody plant communities across an elevational gradient on Mount Washington (New Hampshire, USA)

Abstract Background and Aims Plants produce myriad specialized metabolites that constitute the metabolome and mediate responses to abiotic and biotic factors. Elevational gradients, where environmental conditions change predictably over short distances, are natural laboratories for examining plant chemical variation. Using a temperate montane system, we examine how woody plant metabolomes vary with elevation, between leaf forms, and among phylogenetic lineages. Methods We collected leaves from 23 woody plant species at 18 sites from 320 to 1,700 meters on Mount Washington, New Hampshire, United States, representing distinct vegetative zones and both deciduous and evergreen habits. Untargeted metabolomics identified 6065 unique chemical features, which were assigned to functional classes and corresponding pathways using NPClassifier. We analyzed metabolomic composition, diversity, and phylogenetic structure to test for elevational patterns in plant chemistry by leaf functional groups and vegetative zones. Key Results Metabolomes were structured based on leaf functional group and elevation, with distinct chemical clustering corresponding to vegetative zones: broad-leaved deciduous forest, needle-leaved evergreen forest, and alpine tundra. Weak phylogenetic signal in most instances suggests that local environment imposes strong selection on chemical traits, such as through the resource availability hypothesis, which we find support for. Community investment in individual chemical classes shifted towards abiotic defenses – such as flavonoids, fatty acids, and cryoprotectants – with increasing elevation, while biotically-defensive phenolic acids decreased due to species turnover along the gradient. Overall chemical composition of metabolomes and classes biosynthetically and functionally contrasted in their patterns. Conclusions While plant metabolomes clustered by leaf functional groups in multidimensional trait space, elevational patterns in chemical class investment were clearer when viewed from the community lens, rather than by leaf functional group. These patterns suggest there are stratified phytochemical landscapes along elevation within which higher trophic levels exist, and that abiotic factors strongly structure the community metabolomes of Mount Washington.