Genome‐wide signatures of environmental adaptation in European aspen (Populus tremula) under current and future climate conditions

Future climate change has been predicted to disrupt local adaptation in many perennial plants, such as forest trees, but the magnitude and location of these effects are thus far poorly understood. Here, we assess local adaptation to current climate in European aspen (Populus tremula) by using environmental association analyses to identify genetic variants associated with two representative climate variables describing current day variation in temperature and precipitation. We also analysed patterns of genetic differentiation between southern and northern populations and observe that regions of high genetic differentiation are enriched for SNPs that are significantly associated with climate. Using variants associated with climate, we examined patterns of isolation by distance and environment and used spatial modelling to predict the geographic distribution of genomic variation in response to two scenarios of future climate change. We show that climate conditions at a northern reference site will correspond to climate conditions experienced by current day populations located 4–8 latitude degrees further south. By assessing the relationship between phenotypic traits and vegetative fitness, we also demonstrate that southern populations harbour genetic variation that likely would be adaptive further north under both climate change scenarios. Current day populations at the lagging edge of the distribution in Sweden can therefore serve as sources for introducing adaptive alleles onto northern populations, but the likelihood of this largely depends on naturally occurring levels of gene flow.