Characteristics of Cd Uptake by the Roots of Bidens tripartita L. Under Salinity and pH Variations Assessed by Applying Non-invasive Micro-test Technology

The purpose of the study was to investigate the effects of salinity and pH variations on cadmium uptake by Bidens tripartita L. roots using non-invasive micro-test technology (NMT). The results indicated that Cd 2+ influx at 300 µm from the root apexes decreased in treatments with Cd and 5 mM or 10 mM NaCl compared to Cd stress alone. However, treatments with Cd and 2.5 mM NaCl had little effect on net Cd 2+ influx compared to Cd treatments alone. Importantly, Cd treatments at pH = 4.0 markedly increased Cd 2+ influx to the roots. While it was significantly decreased when pH was adjusted to 7.0 compared to those at pH = 5.5. The results also showed that treatments with Cd in combination with 5 mM or 10 mM NaCl significantly decreased chlorophyll (Chl) a and b concentrations in leaves and root vigor of B. tripartita relative to Cd treatments alone, while there were no significant differences between Cd treatments with 2.5 mM NaCl and Cd treatments alone. A significant increase in root vigor was observed in Cd treatments at pH = 4.0 in comparison to pH = 5.5.