Stability of provenance differences during development of hard maple seedlings irrigated at two frequencies

Traits associated with drought resistance vary with provenance of hard mapl es (Acer sp.), but the stability of differences ex situ and over time is un known. We compared growth, dry-matter partitioning, leaf anatomy, and water relations of seedlings from central Iowa, eastern Iowa, and the northeaste rn United States over 2 years. Some seedlings from each of the three proven ances were used as well-irrigated controls. The remaining seedlings were dr ought-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 ratio s 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 w eight, and their abaxial surfaces had more stomates and trichomes, than did leaves from the Northeast. Drought stress reduced conductance only in plan ts from central Iowa. Across provenances, drought stress reduced stomatal f requency, surface area of laminae, and dry weights of laminae and roots, an d increased root : shoot dry-weight ratio. Leaf water potential of plants s ubjected to drought was lower at predawn and higher at midday than that of control plants. Drought did not cause osmotic adjustment in leaves. We conc lude that the stability of foliar differences among provenances of hard map les validates using these traits as criteria for selecting ecotypes for use in managed landscapes prone to drought.