Fig. 6

Leaf-level WUE and WUEi versus VPD for NT, T1 and T2. The top panel shows the leaf-level WUE versus VPD with a fitted exponential decay equation (leaf-level WUE = 3.92 + 6.416e−1.325VPD (R2 = 0.074). The bottom panel shows the leaf-level WUEi versus VPD with a fitted parabolic equations (leaf-level WUEi = 27.08VPD2-27.45VPD + 63.32 (R2 = 0.23)