Figure 1.

Nitrogen (N) content and diversity of free amino acids (FAAs) in leaves under the split-root system. (a) Diagram showing the split-root system used to simulate the spatial heterogeneity of different N forms. Two separated physical spaces where different N forms could be applied, were created in this split-root system: U. ammonium (NH₄⁺) (both compartments had NH₄⁺), U. nitrate (NO₃⁻) (both compartments had NO₃⁻), Sp. NH₄⁺ (one of the compartments had NH₄⁺), and Sp. NO₃⁻ (the other compartment had NO₃⁻); (b) leaf N content; (c) diversity of FAAs in the leaves. The mean ± SE (n = 3) are shown in the data. The different letters show that means are significantly different at p < 0.05. The different conditions to compare the analytical results obtained are shown in the Materials and Methods section.