Assessing Grapevine Water Status by Integrating Vine Transpiration, Leaf Gas Exchanges, Chlorophyll Fluorescence and Sap Flow Measurements

A precise knowledge of the grapevine responses to increasing level of water stress is of the utmost relevance for an effective application of deficit irrigation strategies in viticulture. Against this background, a study was conducted on potted grapevines subjected to two ten-day drought cycles to assess their water status by integrating the information derived from different physiological indexes including whole-plant transpiration (measured gravimetrically and with sap flow sensors), leaf gas exchanges and chlorophyll fluorescence. When soil water availability was not limited, vine transpiration rate was determined mainly by environmental factors and ranged between 0.5 and 2 L day−1 m−2 of leaf surface. Transpiration was affected by the soil water availability only when water stress became evident (midday stem water potential < −1 MPa), with vines showing a strong limitation of the stomata functioning (stomatal conductance < 0.05 mol m−2 s−1) and, consequently, low transpiration rates (