Figure 4.

Bioaccumulation factors (μg g⁻¹ metal shoot/μg g⁻¹ soil) in field sampled N. brachypetala populations (A); translocation factors (μg metal shoot/μg metal root) in N. brachypetala populations and N. caerulescens (Ganges) grown on hydroponics (B); Cd concentrations (μg g⁻¹) in hydroponically-grown N. brachypetala populations and N. caerulescens (Ganges) (C); Zn concentrations (μg g⁻¹) in hydroponically-grown N. brachypetala populations and N. caerulescens (Ganges) (D). Metal treatments on hydroponic plants were 1.5 μM CdCl₂ and 100 μM ZnSO₄, controls were without Cd or with 2 μM Zn. Plants were under treatment for 4 weeks. Error bars on columns in (A,B) are standard deviations based on three different ICP-MS analyses from a pool of five collected plants or five soil samples; columns with the same letters (capitals for Cd and lower case for Zn) are statistically not different (Tukey test; p < 0.05). Error bars on (C) and (D) are standard deviations based on three independent ICP analyses from a pool of 10 plants; columns with the same letters (capitals for shoots and lower case for roots) are statistically not different (Tukey test; p < 0.05) Dotted lines indicate threshold for hyperaccumulation.