Geo-climatic gradient shapes functional trait variations in Salix eriocephala Michx

Intraspecific variations in seasonal phenology and growth physiology reflect adaptation to local climate. To explore the patterns of local adaptation along latitudinal and longitudinal clines, we used thirty-four populations of Salix eriocephala sourced from its natural ranges across Canada. The genotypes were examined for 6 phenology and 19 ecophysiology traits over two growing seasons under common garden condition. Photosynthetic assimilation rate (A) increased with increase in latitude when measured during free growth. In spite, the negative correlation between stomatal density and stomatal conductance (g s), higher A is facilitated via larger pore length among genotypes from short growing seasons. In addition, higher A, was positively associated with total leaf nitrogen and leaf mass per unit area. No population level differences were observed for water use-efficiency (Δ 13 C), however nitrogen isotope discrimination (δ 15 N) displayed latitudinal clines. Growing season phenological traits considered in this study accounted high heritability (H 2 = 0.65-0.94). Melampsora rust infestation also displayed a strong latitudinal cline with high-latitude genotypes being more susceptible. Overall, the results support the hypothesis that functional trait variations are largely explained by climate of origin and facilitate selection of parents with superior adaptive traits in the Canadian willow improvement program for bioenergy and environmental applications.