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Rolston St. Hilaire and William R. Graves

Selection of sugar maples (Acer saccharum Marsh.) and black maples (Acer saccharum Marsh. ssp. nigrum Desm. or Acer nigrum Michx. f.) that will be more resilient than existing cultivars in managed landscapes could be facilitated by defining relationships between geographic origin and foliar traits critical to leaf function. We examined variation in leaf morphology and anatomy of both taxa, known collectively as hard maples, near 43 °N latitude and tested for relationships between foliar traits and the longitude of origin from 70 ° to 94 °W longitude. Leaves exposed to direct solar radiation were sampled from up to 20 trees indigenous at each of 42 sites during 1995 and 1996. All leaves from east of 75.84 °W and from 92.73 °W and further west expressed morphological characters associated with sugar maple and black maple, respectively; leaves with intermediate traits were found between these two longitudes. Leaves from 90 ° to 94 °W had the highest surface area due to increases in the areas of middle and proximal portions of laminae. Up to 1162 trichomes/cm2 were present on the abaxial surface of laminae from west of 85 °W, while laminae from further east were glabrous or had ≤300 trichomes/cm2. Laminae from western habitats also had relatively high stomatal frequency, and stomatal apertures of laminae west of 91 °W were particularly narrow. Longitude did not affect specific weight and thickness of laminae, which averaged 5.5 mg·cm-2 and 90 μm, respectively. Principal component analysis of laminar traits showed existence of two clusters. A large group dominated by data from trees in New England also contained data from trees as far west as ≈93 °W longitude; data for trees further west were clustered separately. Although phenotypic continua were defined, laminae west of 93 °W were distinct, which suggests trees selected there may function differently in managed landscapes than trees selected from native populations further east.

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Rolston St. Hilaire and William R. Graves

Traits associated with drought resistance vary with provenance of hard maples (Acer sp.), but the stability of differences ex situ and over time is unknown. We compared growth, dry-matter partitioning, leaf anatomy, and water relations of seedlings from central Iowa, eastern Iowa, and the northeastern United States over 2 years. Some seedlings from each of the three provenances were used as well-irrigated controls. The remaining seedlings were drought-stressed and irrigated based on evapotranspiration. Across irrigation treatments, plants from Iowa had shorter stems and higher specific weight of lamina, root: shoot dry-weight ratios, and root: lamina dry-weight ratios than did plants from the northeastern United States when treatments began. Biomass partitioning did not differ based on provenance after irrigation treatment for 2 years, but leaves from central Iowa had a higher specific weight, and their abaxial surfaces had more stomates and trichomes, than did leaves from the Northeast. Drought stress reduced conductance only in plants from central Iowa. Across provenances, drought stress reduced stomatal frequency, surface area of laminae, and dry weights of laminae and roots, and increased root: shoot dry-weight ratio. Leaf water potential of plants subjected to drought was lower at predawn and higher at midday than that of control plants. Drought did not cause osmotic adjustment in leaves. We conclude that the stability of foliar differences among provenances of hard maples validates using these traits as criteria for selecting ecotypes for use in managed landscapes prone to drought.