Monday, November 13, 2006 - 9:55 AM

Contribution of Whole Root System Hydraulics to Water Use Patterns of Grapevines.

David R. Smart1, Christine Stockert1, Maria Alsina del Mar2, Carme Biel2, Samual Metcalf1, Felicidad DeHerralde2, and Claudia Negron1. (1) University of California, Department of Viticulture & Enology, One Shields Ave., Davis, CA 95616-8749, (2) Institut de Recerca i Tecnologia Agroalimentaries (IRTA), Carreterra de Cabrils, E-08348 - Cabrils (Barcelona), Spain

Hydraulic efficiency in woody perennials increases as the branch conduit numbers increase with respect to those in the trunk, or as the ratio of leaf specific hydraulic conductance (Kl) or conduit diameters decrease. These physiological indicators of efficiency are relatively easily measured in trunks and stems while hydraulic efficiency of branching and conduit properties are much more challenging to evaluate in root systems. Here, we evaluated root hydraulic properties related to efficiency for a drought tolerant grape rootstock hybrid with an apparent larger root system than a drought intolerant hybrid. We examined whole root system hydraulic conductivity (Kt) using a high pressure flow meter under field conditions. The specific conductivity per cross sectional area of xylem (Ks) was determined from the hydraulic conductivity (Kh) of the trunk, graft union and all framework roots emerging from the trunk. Contrary to our expectations, Kt was the same for both hybrids, while specific conductivity was greater for segments from the drought susceptible genotype. These results indicated that physiological properties other than root hydraulics confer drought tolerance on these hybrids.