© 1998 Heron Publishing—Victoria, Canada
Drought tolerance, xylem sap abscisic acid and stomatal conductance during soil drying: a comparison of canopy trees of three
temperate deciduous angiosperms
Nancy J. Loewenstein (1) and Stephen G. Pallardy (1)
1. School of Natural Resources, 1-31 Agriculture Building, University of Missouri, Columbia, MO 65211, USA / Received September 10, 1997
Summary
Patterns of water relations, xylem sap abscisic acid concentration ([ABA]) and stomatal aperture were characterized and compared
in drought-sensitive black walnut (Juglans nigra L.), less drought-sensitive sugar maple (Acer saccharum Marsh.) and drought-tolerant white oak (Quercus alba L.) trees co-occurring in a second-growth forest in Missouri, USA. There were strong correlations among reduction in predawn
leaf water potential, increased xylem sap [ABA] and stomatal closure in all species. Stomatal conductance was more closely
correlated with xylem sap ABA concentration than with ABA flux or xylem sap pH and cation concentrations. In isohydric black
walnut, increased concentrations of ABA in the xylem sap appeared to be primarily of root origin, causing stomatal closure
in response to soil drying. In anisohydric sugar maple and white oak, however, there were reductions in midday leaf water
potential associated with stomatal closure, making it uncertain whether drought-induced xylem sap ABA was of leaf or root
origin. The role of root-originated xylem sap ABA in these species as a signal to the shoot of the water status of the roots
is, therefore, less certain.
Keywords:
Acer saccharum, desiccation avoidance, drought adaptation, Juglans nigra, Quercus alba, root–shoot communication, trees, woody plants.
