Fig. 1

Biomass (a), R/S (b), tree height (c), leaf area (d), root biomass (e) and stem biomass (f) under drought and well-watered conditions with low nitrogen (LN) or adequate nitrogen (AN). R/S, the ratio of root biomass to shoot biomass. 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