CADMIUM-INDUCED ALTERATIONS IN NUTRIENT COMPOSITION AND GROWTH OF BETULA-PENDULA SEEDLINGS - THE SIGNIFICANCE OF FINE ROOTS AS A PRIMARY TARGET FOR CADMIUM TOXICITY

Birch seedlings (Betula pendula) were cultivated in nutrient solution with 0-2 mu M cadmium (Cd). The effects of 2-10 days of Cd exposure on root and shoot element composition [potassium (K), calcium (Ca), magn esium (Mg), phosphorus (P), sulfur (S), iron (Fe), manganese (Mn), zin c (Zn), copper (Cu), molybdenum (Mo), and Cd] and growth (as percentag e dry weight increase) were investigated. The element composition of f ine roots and remaining root parts were analysed separately to elucida te the significance of the fine roots as a primary target for Cd toxic ity. The nutrient composition of the roots was considerably altered by the Cd exposures, whereas the nutrient composition of the shoot was l ess affected. After eight days, the whole root (fine roots + remaining roots) concentrations of K, Ca, Mg, and Mn were reduced, whereas the opposite was found for Cu and Mo. The element distribution between fin e roots and remaining roots was altered by the Cd exposures. Cadmium w as accumulated in the roots and in fine roots especially. Fine roots a lso exhibited a capacity for Cu accumulation and a retainment of Ca an d S. Total plant growth was stimulated by 0.05 mu M Cd but was reduced by the 0.5-2 mu M Cd treatments. Root growth was increased by the Cd exposures and growth reductions were restricted only to the shoot. Acc umulation of Cd and Cu and a retainment of Ca and S in the fine roots together with a preference for root growth, imply that the explanation for the Cd effects obtained may include mechanisms for Cd tolerance.