Water relations and hydraulic characteristics of three woody species co-occurring in the same habitat

Three woody species typically encroaching the Karstic region of Trieste ( Northeastern Italy) i.e. Cotinus coggygria L., Prunus mahaleb L. and Fraxinus ornus L., have been measured for diurnal and seasonal time courses of leaf conductance to water vapour, transpiration and water potential (Psi(L)), as well as whole-plant, shoot and root hydraulic resistance (R-plant, R-shoot and R-root, respectively) in view of investigating the impact of plant hydraulics on water stress resistance. F. ornus suffered the highest Psi(L) drop in July and September due to the high R-plant measured in this species. Positive significant relations were found of R-plant and Psi(L) to R-root in all three species studied, thus suggesting that root hydraulics is a major determinant of plant hydraulics and water stress resistance. The increasing R-root (and R-plant) from C. coggygria to P. mahaleb to F. ornus provided a possible explanation for the typical temporal sequence of expansion of the three species into degraded areas.