Abstract
In recent decades, the rising severity of summer heatwaves has increased
the co-occurrence of heat and drought stress leading to forest mortality
and to reductions in crop yield. Plant responses to this combined stress
can be unique from the response to either independent stress, yet few
studies have investigated these responses in tree species. Our work
examines adjustment of several primary metabolites and polyamine (stress
indicating secondary metabolites) in paper birch and white spruce
subjected to two seasons of repeated heatwaves, drought, and elevated
CO2. Our objectives were to determine if the metabolic
adjustments in response to heatwave+drought stress are: 1) unique or
shared with either individual stress; 2) greater in birch compared to
spruce; and 3) carried over into the following season. Our data show
that white spruce displayed many metabolic responses that were unique to
the combined stress, especially in the first year, while paper birch
displayed few. Further, the unique responses in spruce seen in the first
season stress exposure did not carry into the following season
indicating possible stress memory. Our data highlights the importance of
considering species-specific responses to multiple stressors when making
predictions about forest response to future climate scenarios.