Figure 2.

Concentrations of the principal N metabolites in the xylem sap of nodulated (A) and non-nodulated (B) soybean plants treated with various N compounds. Treatments: Cont, control with N-free solution; NO₃⁻, 5 mM KNO₃; NH₄⁺, 2.5 mM (NH₄)₂SO₄; urea, 2.5 mM urea; NO₃⁻ + NH₄⁺, 2.5 mM KNO₃ + 1.25 mM (NH₄)₂SO₄. n = 3. Average ± standard error. The different letters on the top of the columns indicate significant differences in the N concentration among the treatments based on Tukey’s test (p < 0.05). Asterisks (*, **) designate significant changes according to Student’s t-test results for the same compound in the same treatment between nodulated and non-nodulated plants at p < 0.05 and p < 0.01, respectively. ND; not detected.