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.
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