An understanding of the ecological and genetic mechanisms governing plant adaptation to environmental conditions is of fundamental interest in evolutionary biology, but also for meeting the challenges of global change in applied fields such as conservation biology and plant breeding. In this project, we integrate ecological and genomic approaches in field and lab experiments in a study of the functional and the genetic basis of plant adaptation. Our study systems are natural populations of the prime plant model organism, the selfing annual A. thaliana. Recombinant inbred lines, near-isogenic lines, and CRISPR/Cas-9 lines will be used in experiments designed to (a) identify traits and genomic regions subject to selection in contrasting climates in the field and under experimental conditions, (b) examine the functional and genetic basis of adaptive differences between populations and fitness tradeoffs, and (c) identify agents of selection in the native habitats. Recombinant inbred and near-isogenic lines were produced from a cross between two ecologically well characterized A. thaliana populations that exhibit striking adaptive differentiation. They therefore represent a uniquely suited genetic resource to study the functional and genetic basis of plant adaptation.