NUTRITIONAL ALLEVIATION OF ZINC-INDUCED IRON DEFICIENCY IN INDIAN MUSTARD AND

THE EFFECTS ON ZINC PHYTOEXTRACTION

Abstract

Brassica juncea is a promising candidate for the phytoextraction of Zn, but the effectiveness of this plant

can be limited under Zn-contaminated conditions. Iron deficiency is common among plants that are grown under

conditions of excessive Zn supply, but efforts to alleviate Zn-induced Fe deficiency in B. juncea by foliarly

fertilizing with Fe have yielded mixed results. Our objectives were to determine the effects of root-applied Fe and Zn

on plant growth, the accumulation of Zn in plant tissues, and the development of nutrient deficiencies for B. juncea. In the

experiment, B. juncea (accession 182921) was supplied 6 levels of Fe-EDDHA (0.625 to 10.0 mg L- 1) and two levels of Zn

(2.0 and 4.0 mg L- 1) for three weeks in a solution-culture experiment. In a previous experiment, B. juncea suffered from

Zn-induced Fe chlorosis if plants were supplied $3.0 mg Zn L- 1 in solution culture. Nutrient solution pH decreased

with decreasing supply of Fe and increasing supply of Zn in solution, indicating that B. juncea may be an Fe-efficient plant.

To the extent that Fe deficiency was the limiting factor for plant growth, we were able to increase growth by supplying increasing

levels of Fe in solutions. If plants were supplied 2.0 mg Zn L- 1, plant growth was stimulated by increases in Fe supply, but plant

growth was not influenced by Fe treatments if plants were supplied 4.0 mg Zn L-1. Zinc concentrations in r oots and shoots were

suppressed by increasing levels of Fe in solution. Leaf concentrations of Cu, Mn, and P were suppressed also if the Fe supply in

solutions increased. Iron additions to the nutrient solution were not effective at increasing the overall phytoextraction potential of

B. juncea unless plants were supplied a phytotoxic level of Zn in solution culture. Even under these conditions, Fe additions were

effective only if supplied at low levels in solution culture (1.25 mg Fe L- 1). Results suggest that Fe fertility has limited potential for

enhancing Zn phytoextraction by B. juncea, even if plants suffer a suppression in growth from Fe deficiency.