Physiological plasticity in water relations and leaf structure of understory versus open-grown Cerciscanadensis in northeastern Kansas

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Abstract
Field and laboratory studies were used to evaluate physiological plasticity in water relations and leaf structural characteristics of Cercis canadensis L. (redbud) saplings growing in a gallery forest understory and an adjacent prairie in eastern Kansas. Two study periods were defined based on high (greater than -0.2 MPa in May) and low (-1.5 MPa in July) predawn soil water potential (.phi.soil). Leaf conductance to water vapor diffusion (gwv) was greater for prairie than understory redbud saplings during both sampling periods (maximum gwv = 7.5-8.7 mm s-1). Moreover, gwv for prairie redbud remained high at both high and low .phi.soil, but was significantly lower for understory redbud during midday at low .phi.soil. Transpiration flux was also higher in the prairie than in the understory site and reached a maximum for prairie redbud (318 mg m-2s-1) in July, in conjunction with high leaf to air vapor pressure deficits (maximum, 5.3 kPa). Leaf water potential declined significantly at both sites with decreased .phi.soil and the minimum values (-3.0 MPa) were recorded in understory redbud. Leaves of prairie redbud were significantly smaller, thicker, and had higher specific leaf mass and stomatal density than leaves of understory redbud, which are consistent with differences between xeric and mesic species, respectively. These differences in water relations and leaf morphology between understory and prairie redbud suggest a high degree of physiological plasticity for this species in eastern Kansas.