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

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 nitrogen. 2) For both defense and structural compounds, plastic
responses to garden climate depended on the climate in which a population
or genotype evolved. Specifically, trees originating from cool provenances
showed higher defense plasticity in response to climate changes than trees
from hotter provenances. 3) Trees from cool provenances growing in cool
conditions expressed the lowest constitutive defense levels but the
strongest induced (plastic) defenses. 4) The combination of hot growing
conditions and simulated herbivory switched the strategy used by these
genotypes, increasing constitutive defenses but erasing the capacity for
induction. Because Fremont cottonwood chemistry plays a major role in
shaping riparian communities and ecosystems in the southwestern US, 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.