An investigation of the relationships between mineral nutrition and the phytoextraction of zinc by Indian mustard (<i>Brassica juncea</i> Czern.)
Zinc is the heavy metal occurring in the greatest concentrations in the majority of wastes in modern, industrialized communities and is a common metal found at metal-polluted sites. Phytoextraction is a plant-based remediation technology aimed at the removal of metals from contaminated sites through the use of metal-accumulating plants. Although Indian mustard (Brassica juncea Czern.) has been identified as a moderate accumulator of Zn, little is known about the Zn-phytoextraction potential of this plant and whether or not mineral nutrition could be used to improve plant growth and Zn accumulation under Zn-contaminated conditions. The objectives of this research were to determine how the Zn phytoextraction potential of B. juncea is affected by: (a) the concentration of Zn in the nutrient medium; (b) the alleviation of Zn-induced Fe deficiency; (c) the molar % ratio of NH 4+ to NO3− and (d) the concentration of N and P in the nutrient medium. The pH of nutrient solutions generally decreased with: increasing Zn supply; decreasing Fe supply; and increasing proportion of NH4+-N in nutrient solutions. The ability of B. juncea to phytoextract Zn increased with increasing Zn supply initially, but then leveled off because the increase in shoot Zn concentration was accompanied by a suppression of shoot growth. Zinc-induced Fe deficiency was found to limit the effectiveness of B. juncea to phytoextract Zn, and increased P fertility appeared to exacerbate this problem. Alleviating Fe deficiency with root applied Fe-EDDHA had a limited effect on increasing Zn phytoextraction because Zn accumulation was suppressed with increasing Fe supply. Plants concentrated more Zn in shoots and roots if plants were supplied a high proportion of NO3 −, and increasing NH4+ nutrition enhanced growth. Zinc phytoextraction was maximized if plants were supplied 90% NO3−-N and 10% NH4 +-N. Zinc accumulation in shoots increased with increasing N and P supply, but the effect of N was greater. To the extent that N was a limiting factor for growth, N additions increased plant growth, but growth was not effected by P nutrition. Increased N fertility can increase Zn phytoextraction, but the effect of P nutrition is limited.
0775: Environmental engineering