Ecophysiology and genetic diversity of hard maples indigenous to eastern North America

Hilaire, Rolston
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I examined foliar traits of sugar maple (Acer saccharum Marsh.) and black maple (Acer saccharum Marsh. ssp. nigrum Desm. or Acer nigrum Michx. f.) indigenous near 43°N latitude from 70° to 94°W longitude. Laminae from 90° to 94°W had the highest surface area and a slightly higher percentage of their area in the proximal portion of the blade than leaves from further east. Up to 800 trichomes/cm2 were on the abaxial surface of laminae from west of 85°W longitude, whereas laminae from further east had fewer than 200 trichomes/cm2. Westerly laminae had relatively high stomatal frequency, and stomatal apertures of laminae west of 91°W longitude were particularly narrow. Principal component analysis showed that trees west of 93.1°W longitude in Iowa formed a distinct cluster, while trees from the remaining locations clustered into a second group. In another experiment, I compared water relations, growth, and foliar traits of frequently irrigated and drought-stressed hard maples from central Iowa, eastern Iowa, and the eastern United States. Seedlings irrigated frequently had higher xylem diameter, lamina area, lamina dry mass, root dry mass, shoot:root dry mass ratio, and lamina area:xylem diameter ratio than plants subjected to drought. Although drought reduced predawn leaf water potential, midday water potentials were higher for seedlings subjected to drought (-1.44 MPa) than for frequently irrigated plants (-1.92 MPa). Specific lamina mass and trichome frequency were highest for leaves from central Iowa, for which means were 5.97 mg·cm-2 and 531 trichomes/cm2, respectively. Averaged over regions, drought-stressed plants had 483 abaxial stomates/mm2, while plants irrigated more frequently had 596 stomates/mm2. Interactions of seedling origin and irrigation treatment affected stem length, shoot and total dry masses, and stomatal conductance, which was reduced during drought only among plants from central Iowa. Restriction site patterns in chloroplast DNA for plants from central Iowa, eastern Iowa, and the eastern United States were determined. Analysis of the ndhA intron revealed that TaqI gave a polymorphic site that showed chloroplast types were not geographically localized. My results could impact the selection and evaluation of hard maples for use in managed landscapes prone to drought.