SEASONAL-CHANGES OF ROOT HYDRAULIC CONDUCTANCE (K-RL) IN 4 FOREST TREES - AN ECOLOGICAL INTERPRETATION

This paper deals with the possibility of relating root hydraulic param eters to an ecological index describing the continentality/oceanicity of four forest trees. Root hydraulic conductance (K-R) of seedlings of Fagus sylvatica L., Quercus ilex L., Quercus suber L. and Quercus pub escens Willd. was measured in May, August and November 1996. K-R was c alculated in terms of the relation of the water flow through intact ro ot systems in situ measured with the pressure chamber, and the pressur e driving the flow. The sufficiency of the root system to supply the f oliage was estimated by dividing K-R by the seedlings leaf surface are a (A(L)) thus Obtaining K-RL. In the spring, K-RL was largest in F. sy lvatica and smallest in Q. pubescens with intermediate values recorded in Q. ilex and Q. suber. All the species studied showed a large decli ne in K-RL just prior to the winter rest except for Q. suber which man tained K-RL approximately constant through the period of study. In mos t cases, K-RL changed in accordance with analogous changes in the flow . When the total seedlings' leaf surface area (A(L)) was plotted versu s K-RL, it appeared that K-RL Of Q. pubescens increased with A(L), pro portionally, while K-RL Of F. sylvatica was inversely related to A(L). This, together with the largest K-RL recorded in the summer in Q. pub escens, was interpreted as advantageous to this species (which is adap ted to semi-arid environments) in that: (a) roots could supply water t o foliage efficiently even during the adverse season and (b) the folia ge growth could be sustained even in summer. No statistically signific ant relation of K-RL to the continentality index calculated for the fo ur species studied on the basis of their European distribution, was fo und to exist. Nonetheless, our data appear to be encouraging for futur e research aimed at better interpreting the typical distribution areas of plant species.