Zinc toxicity on growth and nutrition of Eucalyptus maculata and Eucalyptus urophylla in nutrient solution

Abstract

The objective of this work was to evaluate the effect of excessive doses of Zn on growth and nutrition of eucalyptus in a greenhouse experiment. Seedlings of Eucalyptus maculata and Eucalyptus urophylla were grown in pots containing 2 L of Clark's nutrient solution, adding increasing levels of Zn, in μM: 0, 400, 800, 1,200 and 1,600 supplied as ZnSO₄. After five weeks, plants exhibited internerval chlorosis, dark roots and growth inhibition, even in lower metal levels. The critical metal dose in the solution, for 10% reduction of shoot dry matter, was 170.3 μM and 73.0 μM in E. maculata and E. urophylla, respectively. The plant critical toxicity levels were 853 mg kg^-1 in E. maculata and 697.8 mg kg^-1 in E. urophylla. These results indicate that E. maculata is more tolerant to Zn than E. urophylla. High levels of Zn reduced concentrations of Fe and Ca in shoot dry matter to levels considered deficient for the growth of both species. Translocation of Fe from roots to shoots was also reduced, independently of the species, of 21% in control to 2% in 1,600 μM Zn, indicating strong relationship among dry matter reduction and induced Fe-deficiency in plants.