Heavy-Metal Nutrition and Iron Chlorosis of Citrus Seedlings

Abstract

Excess quantities of Cu, Zn, or Mn in the nutrient soln. all caused stunting and chlorosis of citrus seedlings. Additions of chelated Fe prevented chlorosis but did not appear to eliminate the toxic effect of Cu and Zn on the roots. The Fe was much more effective against excess Mn. Analysis of plant parts showed that all of these metals accumulate in roots, even in acidic culture solution. Toxic levels of Cu in the soln. did not cause an increase in the leaf of this element but did depress the amts. of Zn, Mn, and Fe in the foliage. Increases of Zn and Mn in the culture soln. were reflected by increased amts. of these elements in the leaves. The heavy metals influence the action of one another. This indicates the desirability of considering them as a group, as single element studies could lead to erroneous conclusions regarding ion behavior. These characteristics substantiate field observations indicating that the recent widespread occurrence of acid-soil citrus chlorosis in Florida is due primarily to the toxic effect of accumulated Cu which has resulted from 15 yrs. of heavy usage of this metal in cultural practices.