Plasticity of vulnerability to leaf hydraulic dysfunction during acclimation to drought in grapevines: an osmotic-mediated process

Previous studies have reported correlation of leaf hydraulic vulnerability with pressure-volume parameters related to cell turgor. This link has been explained on the basis of the effects of turgor on connectivity among cells and tissue structural integrity, which affect leaf water transport. In this study, we tested the hypothesis that osmotic adjustment to water stress would shift the leaf vulnerability curve toward more negative water potential ((leaf)) by increasing turgor at low (leaf). We measured leaf hydraulic conductance (K-leaf), K-leaf vulnerability [50 and 80% loss of K-leaf (P-50 and P-80); |(leaf)| at 50 and 80% loss of K-leaf, respectively), bulk leaf water relations, leaf gas exchange and sap flow in two Vitis vinifera cultivars (Tempranillo and Grenache), under two water treatments. We found that P-50, P-80 and maximum K-leaf decreased seasonally by more than 20% in both cultivars and watering treatments. However, K-leaf at -2MPa increased threefold, while osmotic potential at full turgor and turgor loss point decreased. Our results indicate that leaf resistance to hydraulic dysfunction is seasonally plastic, and this plasticity may be mediated by osmotic adjustment.