SEASONAL-CHANGES IN WATER POTENTIAL AND THE GROWTH OF YOUNG QUERCUS-RUBRA AND QUERCUS-PALUSTRIS PLANTS DURING SOIL DROUGHT

In order to compare the resistance of northern red oak (Quercus rubra L) and pin oak (Quercus palustris Moench) to soil drought, a green-house experiment has been carried out with seedlings grown in containers, where watering was stopped after the first or second growth flush. We measured leaf area, followed height and diameter growth, water potential (seasonal variation), and final biomass. With an optimal watering, both pin oak and northern red oak exhibited a similar height growth. During soil drought, both species exhibited a rather early stomatal regulation but pin oak presented a more severe reduction in height growth and leaf area. During drought, both species displayed a similar range of water potential of about -1.5 to -2.2 MPa. These results are in agreement with the published data for red oak. Both species behaved as mesophilous species and exhibited a strategy intermediate between genuine avoidance and tolerance during a drought. These results corroborate our intuitive knowledge of pin oak ecology and point out the limits of its use in forestry.