Trend of gas exchanges and water potential in 2012. Mean data ±s.e. of 3 replicates (Pn, T e WUEi) and 4 replicates (Ψ_stem). a: net photosynthesis (Pn). The values along the line indicate the temperature of the leaf blade (°C). b: leaf transpiration (T). c: intrinsic efficiency of water use (WUEi) from the ratio P_n/g_s. d: water status of the vines expressed as the water potential of the stem (Ψ_stem).