Developing tree improvement strategies for challenging environmental stresses under global climate change: a review from traditional tree breeding to genomics of adaptive traits for the quaking aspen

Quaking or trembling aspen in North America and Euro-Asia (Populus tremuloides and P. tremula, respectively) are both widely distributed species with a long history of scientific research and tree improvement work in areas such as carbon sequestration, biomass, bioenergy, wood, and fiber, as well as studies evaluating the social, economic, and ecological benefits of the species. This chapter reviews the ecological genetics and genomics of quaking aspens adaptive traits with a broad perspective of the relationship between phenotypic variation and genetic (G) and environmental (E) effects as well as their interactions (GxE). Based on recent studies, several adaptive traits are discussed, including spring and fall phenology and stress tolerance to environmental factors such as frost, salinity, drought, heat, UV radiation, etc. We also conducted a meta-analysis of empirical studies on adaptive traits of P. tremuloides and its sister species, as research using P. tremuloides as a true "model species" is currently limited. However, molecular tools and experimental designs in the form of different common gardens constitute an integrated pathway for the development of traits and varieties/populations to promote reforestation under changing climatic conditions.