Variation in stomatal behaviour and gas exchange between mid-morning and mid-afternoon of north-south oriented grapevines (Vitis vinifera L. cv. Tempranillo) at different levels of soil water availability

A 3-year study was conducted to examine leaf gas exchange response of Vitis vinifera L. (cv. Tempranillo) grapevines growing in the central Iberian Peninsula as a function of soil water availability. Net CO2 assimilation rate (A), stomatal conductance (gs) and transpiration (E) of leaves were measured at the east and west side of vines planted in north/south orientated rows. Soil water availability was varied by three different irrigation treatments at 0.45, 0.30 and 0.15 of ETo and a fourth non-irrigated treatment. Approximately 60% of the variation in gs over 3 years was due to changes in soil water content (θv); the correlation between the two was closer when examined on a season by season basis. Net CO2 assimilation rates were significantly correlated with gs. Stomatal conductance decreased by approximately 25-30% when measured 15:00 h (west side of vines) compared to 09:00 h (east side of vines); reductions in A were even greater than those in gs. Leaf E increased approximately by 15-25% from morning to afternoon. The reduction in A and gs from morning to afternoon was observed even in irrigated vines but absolute differences increased with decreasing soil water. This occurred when maximum daily gs was less than 200 mmol m−2 s−1. These responses indicate that in hot areas training systems and row orientation, which minimize exposed leaf, area in the afternoon should be recommended.