Figure 2. Nitrate and ammonium uptake with increasing N supply.

Dry biomass (A) and total plant N content (B) for shoots and roots of sugarcane plants used for ¹⁵N labelling experiment with increasing N supply rates. Nitrogen treatments correspond to low (0.4 mM), intermediate (1 mM) and high (10 mM) N supply. Bars represent mean±standard error (n = 20). Data from three commercial sugarcane varieties were pooled. Uptake of ¹⁵N into shoots (C, E, G) and roots (D, F, H) of plants grown at low (0.4 mM N) (C, D), intermediate (1 mM N) (E, F) and high (10 mM N) (G, H) N supply. ¹⁵N was supplied to plants as either ¹⁵NH₄NO₃ (○) or NH₄ ¹⁵NO₃ (▪) at concentrations from 0.2 to 3.2 mM ¹⁵N for 24 h. Data represent mean±standard error (n = 3). * indicate significance difference between NH₄ and NO₃ uptake at P<0.05 (ANOVA on ln transformed data, Tukey's post hoc test).