Stem and whole-plant hydraulics in olive (Olea europaea) and kiwifruit (Actinidia deliciosa)

A field study and an experiment under controlled conditions using pressure-flux relationships were conducted to compare the stem and whole-plant conductance in olive (Olea europaea) and kiwifruit (Actinidia deliciosa) species. Anatomical observations were also made on one-year-old stem to determine the conductive area of vessels (Aves) and the total xylem area (Axyl). Results show that Aves of kiwifruit twigs was *2.5-fold of that in olive twigs, and the hydraulically weighted mean diameter was up to threefold that of the olive ones. One-year-old olive twigs had lower hydraulic conductivity (k) than the kiwifruit, while values of leaf-specific conductivity (i.e. k normalised per unit leaf area) were higher than the kiwifruit (i.e. *49 and 29 9 10-6 kg m-1 s-1 MPa-1, respectively). In the field experiment, the flux of sap (heat balance method) and differences in water potential through the soil–plant system (DP) were used for both species to calculate the whole-plant conductance that was normalised per unit leaf area (leaf-specific whole-plant conductance, Kplant,LA). Values of Kplant,LA are attributable to the combined effect of the DP and anatomical features of conduits. Olive species showed a larger DP (2.4 MPa at midday) than the kiwifruit (0.5 MPa) which contributed tolower Kplant,LA in Olea than the Actinidia plants. This information, combined with vessel density data, contributes to explain differences amidst olive and kiwifruit species, in terms of susceptibility to some drought-related hydraulic impairments induced by the Mediterranean environment.