Fig. 7
Leaf-level WUE versus PAR (upper) and leaf-level WUEi versus VPD for PAR groups (PAR in μmol/m2s) (group 1: PAR <=500; group 2: PAR > 500 and <=1500; group 3: PAR > 1500 and <= 1500; and group 4: PAR > 2500). The top panel shows the leaf-level WUE versus PAR with a fitted parabolic equation (leaf-level WUE = -5.74 × 10−7PAR2 + 2.90 × 10−3PAR + 2.99 (R2 = 0.13). The bottom panel shows the leaf-level WUEi versus VPD for the four PAR groups with fitted parabolic equations (when PAR < = 2500: leaf-level WUEi = 50.28VPD2-92.19VPD + 97.44 (R2 = 0.27) and when PAR > 2500: leaf-level WUEi = -35.59VPD2 + 147.73VPD-20.45 (R2 = 0.37)