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Abstract: Epidermal and stomatal cell traits were examined on late leaves of 40 black cottonwood (Populus trichocarpa Torr. & Gray) clones originating from the mesic Nisqually, and xeric Yakima river valleys of Washington. Four leaves per clone were collected from 1-year-old trees in two replicated common gardens located in Puyallup (western Washington) and Wenatchee (eastern Washington). In Puyallup-grown material, Yakima clones had abaxially 14% smaller epidermal cell diameters (CDIAM) and 27% greater cell densities (CDEN; No. per mm2), and 25% smaller leaves than Nisqually clones (p < 0.03). Abaxial stomatal densities (STDEN; No. per mm2) were highest (206) in the lower elevation, xeric-origin Yakima clones, as compared with an average of 120 in Nisqually clones. A higher proportion of Yakima leaves had shorter stomates than those from the Nisqually at both sites (p < 0.002). Besides shorter stomates (p < 0.030), the lower elevation Yakima clones generally had higher STDEN and ratios of STDEN to CDEN than those clones from the upper group (p < 0.098). Acclimation of Wenatchee-grown clones to the hotter, drier summer climate was also evident, as they generally had smaller CDIAM, and higher CDEN and STDEN than those grown at Puyallup. Genetic variances (among rivers, groups within river, and clones within group within river) ranged from 42 to 84% with clone being dominant for epidermal traits while the other two components were dominant for stomatal traits. In the Yakima leaves, much of the genetic variance (group and clone within group) resided in the group component. Broad-sense heritabilities averaged 72%, indicating moderately strong genetic control in most traits. This study provides further evidence of genetic variation in P. trichocarpa at the regional and local scales across the Washington Cascades.
Key words: Populus trichocarpa, black cottonwood, stomata, adaptation, acclimation, genetic variation.
Resume : Les auteurs ont examine les caracteristiques des cellules epidermiques et stomatales chez les feuilles tardives de 40 clones du Populus trichocarpa Torr. & Gray provenant de vallees mesique (Nisqually) et xerique (Yakima) de rivieres de l'etat de Washington. Ils ont recoM quatre feuilles de chaque clone sur des arbres ages d'un an, en deux jardins communs repliques, localises a Puyallup (Washington ouest ) et Wenatchee (Washington est ). Chez le materiel cultive A Puyallup, les clones de Yakima montrent...