Comparative studies of the water relations and the hydraulic characteristics in Fraxinus excelsior, Acer pseudoplatanus and A-opalus trees under soilwater contrasted conditions

Plant water relationships and hydraulic characteristics were measured for t wo species of the genus Acer that co-occur with Fraxinus excelsior, but dif fer in their habitat preference with respect to soil moisture: Acer pseudop latanus is restricted to wet habitats, whereas Acer opalus occurs on drier sites. The data obtained showed significantly lower hydraulic conductance a nd lower vulnerability to embolism in the drought-tolerant species, Acer op alus, than in the water prefering species Acer pseudoplatanus. Similar diff erences in hydraulic conductance and xylem vulnerability to embolism were a lso found under dry acclimated conditions for Fraxinus excelsior trees, ind icating that the hydraulic differences observed might be attributable to th e contrasting soil water conditions of the sites. The possible physiologica l and ecological significance of such differences are discussed, in relatio n to habitat preference and the distribution of each species.