Genetic variation in leaf traits and gas exchange response to vapor pressure deficit in two contrasting conifer species

1. Mechanistically predicting the evolutionary response of tree species to climate change requires an understanding of genetic variation in relevant traits. Here we compared the phenotypic and genetic variation in the Leaf Economics Spectrum (LES) traits and the response of gas exchange to vapor pressure deficit (VPD) in lodgepole pine (Pico) and white spruce (Pigl), an early and a late successional species dominating the boreal forests of western Canada. 2. We measured gas exchange, foliar nitrogen, and lamina mass to area ratio in 697 app. 30-year-old trees in two field progeny trials. We analyzed the response of gas exchange rates to VPD using a novel quantitative genetic model, the function-valued trait approach. 3. Pico showed greater phenotypic variation in the LES traits and greater genetic variation in photosynthetic rate than Pigl, but the species showed no significant difference in their phenotypic correlations between the LES traits. Pico showed a less sensitive stomatal resp...