Rhizosphere pH measurement
For rhizosphere pH measurement, seedlings were hydroponics with 0.5 mM KNO3 + 50 µM Fe, 15 mM KNO3 + 50 µM Fe, 0.5 mM KNO3-Fe (-Fe solution supplemented with 200 µM ferrozine), 15 mM KNO3-Fe (-Fe solution supplemented with 200 µM ferrozine) treatments. The pH was measured daily with a pH electrode (PHS-3C, INESA Scientific Instrument Co., Ltd, Shanghai, China). Each treatment contained 10 biological replicates.