Water relations of oak species on and adjacent to a Maryland serpentine soil

<p>The predominant oaks of the Maryland Piedmont (<em>Quercus alba</em> and <em>Q. velutina</em>) do not occur on serpentine soils. On serpentine sites they are replaced by <em>Q. stellata</em> and <em>Q. marilandica</em>. Soil and plant water relations were measured to evaluate water as a limiting factor to distribution of oaks on serpentine soil. May through August soil water potentials of serpentine soils were not lower than adjacent nonserpentine soils. Dawn xylem water potentials of oaks on serpentine soils were similar to nonserpentine oaks during early and midsummer. By late summer, water potentials of the oaks on serpentine sites were higher. Dawn xylem water potentials and soil water potentials were significantly correlated for all species. A significant correlation between xylem water potential and stomatal conductance was found for the oaks on the serpentine soils. No such correlation was found for oaks on nonserpentine soil, but a xylem water potential threshold for stomatal closure was observed. Despite differences in their responses to moisture availability, water does not appear to be the environmental factor responsible for the distributional pattern of these species.</p>