Ammonium treatments altered soil nitrogen dynamics and plant N uptake. (a) Diagram of pot-grown tomato plants where water, low NH4+(6.5 μg NH4+-N g-1 soil), and high NH4+ (65 μg NH4+-N g-1 soil) treatments were injected into buried soil rings. (b) and (c) NH4+-N and NO3--N concentrations per gram of patch soil in the three treatment groups at 5, 29, 53, and 96 hrs after injection. (d) and (e) atom percent 15N in roots and shoots 5, 29, 53, and 96 hrs after injection of the three treatment groups with 15N labeled NH4+ fertilizer. Data represent the mean ± SEM of 3 biological replicates. Within each graph, means followed by different letters are significantly different from one another at P < 0.05 (two-way ANOVA with Tukey-Kramer HSD test).