Figure 3. Nitrate and ammonium uptake into intact roots.

¹⁵N incorporation into attached, freshly excavated roots of fertilized (+140 kg urea N ha⁻¹) and unfertilized field grown 3-month-old plants when supplied with 1 mM N NH₄ ¹⁵NO₃ (▪) or ¹⁵NH₄NO₃ (□) for 30 and 120 min. Roots treated with protonophore, CCCP, prior to incubation indicate passive influx (PI). Bars represent mean±standard error (n = 4). ^A,a indicate significance difference between fertilized and unfertilized uptake for NH₄ ⁺ and NO₃ ⁻; * indicate significance difference between NH₄ ⁺ and NO₃ ⁻ uptake at P<0.05 (ANOVA, Tukey's post hoc test).