Heavy-Metal Nutrition and Iron Chlorosis of Citrus Seedlings

Abstract

Studies were made on the responses to differential supplies of copper, zinc, manganese, and iron shown by sweet orange and mandarin seedlings grown in vermiculite and solution cultures with the pH maintained near 4. The first three metallic ions were all found to interfere with Fe metabolism in such a way as to induce chlorosis under certain conditions. Relatively low concentrations of these elements also were toxic to roots. Copper appeared to be about 50 times as toxic as Mn and 12 to 15 times as toxic as Zn. Strongly chelated Fe prevented the development of chlorosis. It did not, however, prevent Cu toxicity in roots. It appeared to reduce slightly Zn toxicity in roots and to alleviate greatly toxicity due to Mn. Cu accumulates in roots, even to the point of toxicity, without being transported to the upper parts of the plants in increased amounts. Both Zn and Mn show marked accumulation in the roots as well as substantial distribution within the plant when these elements are increased in the nutrient solution. 12 references, 4 tables.