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 (A (ves)) and the total xylem area (A (xyl)). Results show that A (ves) of kiwifruit twigs was similar to 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. similar to 49 and 29 x 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 (Delta P) were used for both species to calculate the whole-plant conductance that was normalised per unit leaf area (leaf-specific whole-plant conductance, K (plant,LA)). Values of K (plant,LA) are attributable to the combined effect of the Delta P and anatomical features of conduits. Olive species showed a larger Delta P (2.4 MPa at midday) than the kiwifruit (0.5 MPa) which contributed to lower K (plant,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.