Drought Avoidance Strategy Research Articles

Drought resistance of Quercus pubescens as a function of root hydraulic conductance, xylem embolism and hydraulic architecture.

Water relations, xylem embolism, root and shoot hydraulic conductance of both young plants in the field and potted seedlings of Quercus pubescens have been studied with the aim of investigating whether these variables may account for the well known adaptation of this oak species to arid habitats. Our data revealed that Q. pubescens is able to maintain high leaf relative water contents under water stress conditions. In fact, relative water contents measured in summer (July) did not differ from those recorded in April. This was apparently achieved by compensating water loss by an equal amount of water uptake. Such a drought avoidance strategy was made possible by the recorded high hydraulic efficiency of stems and roots under water stress. In fact, root hydraulic conductance of field-grown plants was maintained high in summer when the percentage loss of hydraulic conductance of stems was lowest. The hydraulic architecture of young plants of Q. pubescens measured in terms of partitioning of hydraulic resistances along the water pathway revealed that the highest hydraulic resistance was located in stems of the current year's growth. This hydraulic architecture is interpreted as consistent with the adaptation of Q. pubescens to arid habitats as a consequence of the recorded seasonal changes in water relation parameters as well as in root and stem hydraulics.

Root hydraulic conductance of six forest trees: possible adaptive significance of seasonal changes

ABSTRACT Root hydraulic conductance (KR was measured in terms of the ratio of volume flow through roots (F) and to the pressure (P) driving the flow in six forest trees growing in habitats characterized by different water availabilities Le. Acer campestre L., Castanea sativa Miller, Fraxinus ornus L., Fraxinus oxycarpa Bieb., Ceratonia siliqua L. and Olea oleaster Hoffmg. et Link. Measurements were made in May, August and November 1996. KR as normalized for unit leaf surface area (KRL), was higher in species growing in humid environments (A. campestre and C. sativa) than in others (C. siliqua and O. oleaster) typical of aria zones. A. campestre and C. sativa showed declining KRL values from spring to autumn while the latter had highest KRL values in summer. This is in agreement with the typical drought avoidance strategy of C. siliqua which is based on large water losses balanced by equal water uptake from the soil. Plots of F and of A (leaf surface area) to KRL as well as annual percent changes in F, AL and KRL suggest that changes in KRL are mainly due to analogous changes in F, except for O. oleaster where opposite balanced changes in F and AL contributed in maintaining the KRL constant from August to November.

Drought Avoidance Strategy in Ceratonia siliqua L., a Mesomorphic-leaved Tree in the Xeric Mediterranean Area

Drought Avoidance Strategy in Ceratonia siliqua L., a Mesomorphic-leaved Tree in the Xeric Mediterranean Area