Root development of the Zinc-hyperaccumulator plant Thlaspi caerulescens as affected by metal origin, content and localization in soil

Penetration into and exploitation of contaminated soils by roots of hyperac cumulator plants is a prerequisite for efficient removal of heavy metals, i .e. efficacy of phytoextraction. This work was undertaken to study the deve lopment of roots of the Zn-hyperaccumulator Thlaspi caerulescens under vari ous conditions of soil contamination. Rhizoboxes were constructed with a re movable plastic front cover, and filled with soils containing different amo unts and forms of metals (Zn, Cd and Pb). Treatments were: homogeneous soil profile, superposition of three layers, inclusion of contaminated soil int o uncontaminated soil, or inclusion of uncontaminated soil into uniformly c ontaminated soil. Four seedlings were transplanted into each rhizobox, and development of the root system was periodically recorded for 133 days. At h arvest, the biomass and size of the rosette of aerial parts were determined . The aerial biomass/root length fraction as well as the kinetics of root d evelopment varied according to the presence and localization of Zn. The dis tribution and morphology of roots at harvest were strongly dependent upon t he metal content and form in soil. Roots exhibited a high affinity for the Zn-contaminated patches and showed two distinct morphologies according to t he concentration of Zn in soil.