Seasonal adjustment of leaf embolism resistance and its importance for hydraulic safety in deciduous trees.

Embolism resistance is often viewed as seasonally stable. Here we examined the seasonality in the leaf xylem vulnerability curve (VC) and turgor loss point (Ψ ) of nine deciduous species that originated from Mediterranean, temperate, tropical, or sub-tropical habitats and were growing on the Volcani campus, Israel. All four Mediterranean/temperate species exhibited a shift of their VC to lower xylem pressures (Ψ ) along the dry season, in addition to two of the five tropical/sub-tropical species.

An increase in xylem embolism resistance of grapevine leaves during the growing season is coordinated with stomatal regulation, turgor loss point and intervessel pit membranes.

Although xylem embolism resistance is traditionally considered as static, we hypothesized that in grapevine (Vitis vinifera) leaf xylem becomes more embolism-resistant over the growing season. We evaluated xylem architecture, turgor loss point (Ψ ) and water potentials leading to 25% of maximal stomatal conductance (g ) or 50% embolism in the leaf xylem (P ) in three irrigation treatments and at three time points during the growing season, while separating the effects of leaf age and time of season. Hydraulic traits acclimated over the growing season in a coordinated manner.