Figure 6.

Effect of pH clamping of rhizosphere pH on Al resistance. A, Examples of root growth of two maize varieties grown in unbuffered full nutrient solutions at pH 4.0 (white circles), pH 4.0 solutions buffered with 2.5 mm Homopipes (black circles), and unbuffered pH 6.0 full nutrient solutions (black triangles). Similar results were obtained for the remaining four cultivars examined in this study (data not shown). B, Comparison of RRG and Al resistance (based on Al inhibition of root growth) under conditions where the rhizosphere pH remained pH clamped at pH 4 with 2.5 mm Homopipes (white bars) or is unbuffered (striped bars). The RRG between control and Al-treated (39 μm Al³⁺) plants in buffered and unbuffered conditions was calculated over a 3-d period as described in “Materials and Methods.” The RRG between buffered and unbuffered control conditions is shown in black. Vertical bars indicate the SEM.