Willows have been shown to be promising for Cd phytoextraction. Nevertheless, plant responses to Cd are still not clearly understood. We investigated the effects of Cd accumulation on morphological parameters, and Cd allocation in leaves by autoradiography in Salix viminalis grown in hydroponics with increasing concentrations of Cd (0-200 μM) to assess the effect of Cd localization on plant performance.
Willow was highly tolerant to Cd, with only an 18% shoot and no significant root biomass reduction at 20 μM Cd, although Cd concentration in shoots exceeded 100 mg kg^-1. At 50 μM significant reduction in root and shoot biomass and total root length, as well as change in root architecture was observed. At 100 μM, S. viminalis exhibited strong stress symptoms, whereas 200 μM impaired survival. Cadmium accumulation and the intensity of visible phytotoxicity symptoms on the leaves increased from 3 to 50 μM and then decreased at higher concentrations.
At all Cd concentration exposure Cd was localized mainly in the tips and edges of the younger leaves, whereas it was mainly located at the base of the older leaves. This localization coincided with visible necrotic spots and indicated that Cd tolerance had been exceeded.