THE IMPACT OF WATER AND NUTRIENT DEFICIENCIES ON THE GROWTH, GAS-EXCHANGE AND WATER RELATIONS OF RED OAK AND CHESTNUT OAK

Red oak (Quercus rubra), a mesic species, and chestnut oak (Quercus prinus), a xeric species, were grown in a greenhouse with and without fertilizer (F+ and F-, respectively) and subjected to a 10-week drydown (W-) or kept well watered (W+). In both species, fertilized seedlings exhibited greater reductions in mean net photosynthesis (A), leaf conductance (g(wv)), leaf water potential (PSI(leaf)) and water use efficiency (WUE) during the drydown than unfertilized seedlings. In the W- treatments, red oak showed greater reductions in A, g(wv) and PSI(leaf) than chestnut oak. Differential fertilization of the seedlings of both species had a greater effect on tissue water relations than differential watering. During the latter weeks of the drydown, there was no osmotic adjustment in red oak, but chestnut oak in the F+/W- treatment had significantly lower osmotic potentials at full and zero turgor than seedlings in any of the other treatments. The results indicate that high nutrient availability does not improve the drought tolerance of these two oak species.