Optimization of irrigation water use in grapevines using the relationship between transpiration and plant water status

The study was carried out in order to evaluate the thresholds of grapevine internal water status as well as to propose an irrigation management technique that permits the uninterrupted photosynthetic process under drought conditions. The relationships between water relation, gas exchange parameters and sap flow measurements were examined in field grown grapevines (Vitis vinifera L., cv. Malagouzia) subjected to various levels of water stress. The differences in stem water potential were greater between the treatments compared to leaf water potential indicating that stem water potential represents a more reliable indicator of plant water status. Stomatal conductance and photosynthetic rate were significantly lower in stressed treatments while stomatal sensitivity to changes in vapor pressure deficit seems to be higher in stressed than in well-watered treatment. Maximum diurnal sap flow rates were recorded early in the morning in all treatments and decreased in water stressed treatments over the stress cycle. The SFTi/SFT1 ratio (SFT1 = mean daily sap flow of the fully irrigated plants; SFTi = mean sap flow of the stressed plants) also decreased in water stressed treatments. The close relationship between the SFTi/SFT1 ratio and stem water potential values could be used in developing a sap flow based technique for automatically controlling the irrigation system in field grown grapevines.