Drought response strategies are coupled with leaf habit in 35 evergreen and deciduous oak (Quercus) species across a climatic gradient in the Americas

Abstract

• Survival strategies under contrasting environments often result from trade-offs in plant function. Adaptations to stress involve investment in resistance mechanisms that enhance survivorship but limit growth. We test the hypothesis that among the oaks (Quercus spp.) of the Americas some species will have greater drought resistance at the cost of reduced growth capacity. • We investigate trait variation in relation to native environments in species representing the major lineages within the oak phylogeny and test their response to three experimental water treatments. • Trade-offs between drought resistance strategies, such as osmolyte accumulation in leaves, and growth appear in all lineages, indicating both adaptation and evolutionary constraints in physiological traits. Species from mesic environments did not show evidence of faster growth or more resource-acquisitive traits. Xeric species had higher gas exchange rates despite lower stomatal pore area but did not have the capacity to increase growth in well-watered treatments. • Leaf habit plays an important role in drought resistance strategy. Evergreen species show drought tolerance or drought avoidance but require investment of resources like leaf solutes that limit growth under well-watered conditions. In contrast, deciduous species appear to follow a drought tolerance strategy, growing under all water treatments in spite of the risk. • The data included here was used to develop allometric equations to model growth for the study.