Effects of elevated CO₂ treatment on expression levels of FER, LeFRO1, and LeIRT1 in tomato roots cultured with FeEDTA (A) or hydrous Fe(III)-oxide (B) medium. Relative expression levels were calculated and normalized with respect to α-tubulin mRNA. Treatments are the same as in Figure 1. Data are means ± sd (n = 5). *, Significant differences (P < 0.05) between ambient and elevated CO₂ treatments at each time point.