Decoupling of functional traits from intraspecific patterns of growth and drought stress resistance

Intraspecific variation in functional traits may mediate tree species’
drought resistance, yet it remains unknown if trait variation is due to
genotype (G), environment (E), or GxE interactions. Understanding the
drivers of intraspecific trait variation and whether variation mediates
drought response can improve predictions of species’ response to future
drought. Using populations of quaking aspen spanning a climate gradient,
we investigated intraspecific variation in functional traits in the field
as well as the influence of G and E among propagules in a common garden.
We also tested for trait-mediated trade-offs in growth and drought stress
tolerance. We observed intraspecific trait variation among the
populations, yet this variation did not necessarily translate to higher
drought stress tolerance in hotter/drier populations. Additionally,
plasticity in the common garden was low, especially in propagules derived
from the hottest/driest population. We found no growth-drought stress
tolerance trade-offs and few traits exhibited significant relationships
with mortality in the natural populations, suggesting that intraspecific
trait variation among the traits measured did not strongly mediate
responses to drought stress. Our results highlight the limits of
trait-mediated responses to drought stress and the complex GxE
interactions that may underly drought stress tolerance variation in
forests in dry environments.