Genetic divergence along a climate gradient shapes chemical plasticity of a foundation tree species to both changing climate and herbivore damage

Abstract

Climate change is threatening the persistence of many tree species via independent and interactive effects on abiotic and biotic conditions. In addition, changes in temperature, precipitation, and insect attacks can alter the traits of these trees, disrupting communities and ecosystems. For foundation species such as Populus, phytochemical traits are key mechanisms linking trees with their environment and are likely jointly determined by interactive effects of genetic divergence and variable environments throughout their geographic range. Using reciprocal Fremont cottonwood (Populus fremontii) common gardens along a steep climatic gradient, we explored how environment (garden climate and simulated herbivore damage) and genetics (tree provenance and genotype) affect both foliar chemical traits and the plasticity of these traits. We found that (1) Constitutive and plastic chemical responses to changes in garden climate and damage varied among defense compounds, structural compounds, and leaf nitrogen. (2) For both defense and structural compounds, plastic responses to different garden climates depended on the climate in which a population or genotype originated. Specifically, trees originating from cool provenances showed higher defense plasticity in response to climate changes than trees from warmer provenances. (3) Trees from cool provenances growing in cool garden conditions expressed the lowest constitutive defense levels but the strongest induced (plastic) defenses in response to damage. (4) The combination of hot garden conditions and simulated herbivory switched the strategy used by these genotypes, increasing constitutive defenses but erasing the capacity for induction after damage. Because Fremont cottonwood chemistry plays a major role in shaping riparian communities and ecosystems, the effects of changes in phytochemical traits can be wide reaching. As the southwestern US is confronted with warming temperatures and insect outbreaks, these results improve our capacity to predict ecosystem consequences of climate change and inform selection of tree genotypes for conservation and restoration purposes.

Abiotic stress rather than biotic interactions drives contrasting trends in chemical richness and variation in alpine willows

“…High‐elevation plants are typically expected to be filtered by abiotic conditions, resulting in increased similarity in their chemistry and other functional traits (Asplund et al, 2022; Bakhtiari et al, 2021). However, climatic spatial heterogeneity typically increases with elevation (Rasmann et al, 2014) which can support specific microhabitat preferences in high‐altitude plants and variation or plasticity in their chemistry (Eisenring et al, 2022; Massatti & Knowles, 2016). Several of the high‐elevation willow species studied here inhabit different microhabitats.…”

Evidence of climate‐driven selection on tree traits and trait plasticity across the climatic range of a riparian foundation species

“…Both the population collection sites and garden locations span an elevation gradient of almost 2000 m, consistent with the species' range and including a difference of 12°C mean annual temperature and >500 mm in mean annual precipitation across source locations and ~350 mm across gardens. These gardens have demonstrated genetic and environmental differences in phenology (Cooper et al, 2019), leaf litter traits (Jeplawy et al, 2021), and phytochemical defense compounds (Eisenring et al, 2022). The benefit of these experimental gardens is enhanced by the inclusion of genomic data based on the identification of >9000 single nucleotide polymorphisms (SNPs) for all genotypes planted across the three gardens.…”

Genetic underpinnings of arthropod community distributions in Populus trichocarpa

“…Numerous community genetics studies have demonstrated significant heritability of herbivore distributions among genotypes of various plant species (Genung et al ., 2012; Tovar‐Sánchez et al ., 2015; Gosney et al ., 2021). Our understanding of these arthropod community and plant genetic interactions has further expanded through research focused on the interplay between environment and plant chemical characteristics, especially in keystone forest trees species belonging to Eucalyptus (Barbour et al ., 2009a,b; Andrew et al ., 2010; Külheim et al ., 2011; Gosney et al ., 2017, 2021) and Populus (Eisenring et al ., 2021, 2022). Many of these same studies have often been limited in their ability to identify specific genes underlying individual arthropod distributions, let alone entire community interactions (Barker et al ., 2019; Wimp et al ., 2019).…”