Morphological and physiological responses of oak seedlings (Quercus petraea and Q-robur) to moderate drought

Abstract

To study their responses to a moderate drought, seedlings of sessile (Quercus petraea [Matt.] Liebl.) and pedunculate oak (Q. robur L.) were grown in outdoor lysimeters that allowed unrestricted root growth. They were subjected to a moderate drought from mid-June to the end of August. The stomatal conductance remained almost unaffected by drought. In the drought-stressed seedlings, the relative foliar water deficits were significantly higher, and the predawn leaf water potentials were significantly lower than in the control plants. The decrease in osmotic pressures at maximum turgor and at the point of turgor loss in the drought-stressed plants indicated osmotic adjustment. The ratio of leaf to fine-root biomass was significantly diminished in the drought-stressed seedlings. In combination with previous observations, the results indicate that, in the Central-European oak species, a shift in biomass compartmentation is the predominant process in acclimation to drought since it also occurs under severe drought stress in contrast to osmotic adjustment, which was only found under conditions of a moderate drought.