Fig. 3.

Average value of A (a), E (b), WUE_i (c) and δ¹³C (d) in leaves. LN, low nitrogen. AN, adequate nitrogen. A, net photosynthetic rates. E, transpiration rates. WUE_i, intrinsic water use efficiency. δ¹³C, stable carbon isotope compositions. The bars indicate means ± SE (n = 12). Different letters on the bars indicate significant differences (P < 0.05) based on multiple comparisons (Tukey’s HSD test) in ANOVA. P-values of the two-way ANOVA of water (W), nitrogen (N) and their interactions (W × N) are indicated. *P < 0.05; **P < 0.01; ns, not significant