RARE-EARTH ELEMENTS AND PLANT-GROWTH .3. RESPONSES OF CORN AND MUNGBEAN TO LOW CONCENTRATIONS OF CERIUM IN DILUTE, CONTINUOUSLY FLOWING NUTRIENT SOLUTIONS

Corn (Zea mays cv. Hycorn 82) and mungbean (Vigna radiata cv. Berken) plants were grown for 16 d in dilute nutrient solutions containing con stant cerium (Ce) concentrations from 0 to 1.31 mu M. Corn root growth was increased approx. 2 fold at Ce concentrations 0.63 mu M. However, the total dry matter production of corn was not significantly increas ed by Ce addition. With mungbean, the addition of as little as 0.19 mu M Ce to the nutrient solution caused significant reductions in the dr y weight of root (26%), shoot (48%) and total plant (44%). The younges t leaves of mungbean plants in the treatments containing 0.63 mu M Ce displayed symptoms of manganese (Mn) deficiency. These leaves containe d deficient Mn concentrations (5 mg/kg). Tissue concentrations of othe r nutrients in mungbean and all essential elements in corn were within ranges where healthy growth would be expected. The concentrations of Ce measured in the roots and shoots of mungbean were higher than in co rn. Roots of both species accumulated much higher concentrations of Ce than the shoots. Cerium accumulated in the oldest leaves of both plan t species. These patterns of distribution were similar to those report ed previously for lanthanum.