Leaf hydraulic conductance (K-leaf) is known to lie an important determinant of plant gas exchange and photosynthesis. Little is known about the long-term impact of different environmental factors on the hydraulic construction of leaves and its eventual consequences on leaf gas exchange. In this study. we investigate the impact of soil water availability on K-leaf of Fraxinus ornus L. as well as the influence of K-leaf on gas exchange rates and plant water status. With this aim, K-leaf, leaf conductance to water vapour (g(L)). leaf water potential (Psi(leaf) ) and leaf mass per area (LMA) were measured in F.ornus trees, growing in 21 different sites with contrasting water availability. Plants growing in and sites had lower K-leaf, g(L) and Psi(leaf) than those growing ill sites with higher water availability. On the contrary. LMA was similar in the two groups. The K-leaf values recorded in sites with two different levels of soil water availability were constantly different levels each other regardless of the amount of precipitation recorded over 20 days before measurements. Moreover, K-leaf was correlated with g(L) values. Our data suggest that down-regulation of K-leaf is a component of adaptation of plants to drought-prone habitats. Low K-leaf implies reduced gas exchange which may, in turn, influence the climatic conditions which may, in turn, influence the climatic condition on a local/regional scale. It is concluded that leaf hydraulics and its changes in response to resource availability should receive greater attention in studies aimed at modelling bioshpehre-atmosphere interactions.
