Nutritional Alleviation of Zinc-Induced Iron Deficiency in Indian Mustard and the Effects on Zinc Phytoremediation

ABSTRACT

Indian mustard (Brassica juncea Czern) is a promising species for the phytoextraction of zinc (Zn), but the effectiveness of this plant can be limited by iron (Fe) deficiency under Zn-contaminated conditions. Our objectives were to determine the effects of root-applied Fe and Zn on plant growth, accumulation of Zn in plant tissues, and development of nutrient deficiencies for B. juncea. In the experiment, B. juncea was supplied 6 levels of iron ethylenediamine dihydroxyphenylacetic acid (Fe-EDDHA; 0.625 to 10.0 mg L^?1) and two levels of Zn (2.0 and 4.0 mg L^?1) for 3 weeks in a solution-culture experiment. 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. 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 concentration in roots and shoots was suppressed by increasing levels of Fe in solution. Leaf concentrations of Cu, Mn, and P were suppressed also as Fe supply in solutions increased. Iron additions to the nutrient solution were not effective at increasing the Zn-accumulation potential of B. juncea unless plants were supplied the higher 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.