Rhizosphere Concentrations of Zinc and Cadmium in a Metal Contaminated Soil After Repeated Phytoextraction By Sedum Plumbizincicola

Abstract

A growth chamber pot experiment and a field plot experiment were conducted with the installation of rhizobags to study the effects of repeated phytoextraction by Sedum plumbizincicola on the bioavailability of Cd and Zn in the rhizosphere and bulk soil. Repeated phytoextraction gave significantly lower Cd and Zn concentrations in both rhizosphere and bulk soil solutions compared with soil without repeated phytoextraction. The depletion rates of NH₄OAc-extractable Zn in rhizosphere soil in each treatment (L-PS, L-NPS, H-PS, and H-NPS) were 59.7, 18.0, 16.3, and 18.6%, respectively. For NH₄OAc-extractable Cd, the depletion rates in treatments L-PS, L-NPS, H-PS, and H-NPS were 6.67, 29.4, 40.3, and 41.4%, respectively. Plant shoot biomass decreased in the order H-PS > H-NPS > L-PS > L-NPS, with dry weights of 0.56, 0.42, 1.43, and 1.21 g pot⁻¹, respectively. Plant Cd uptake increased with increasing aqua-regia extractable metal concentrations. The NH₄OAc extraction procedure was satisfactory to predict the bioavailability of Cd and Zn in rhizosphere soil in terms of shoot uptake by S. plumbizincicola with positive correlation coefficients of 0.545 (p < 0.05) and 0.452 (p < 0.05), respectively. The field study results show a slight decrease in water soluble and NH₄OAc-extractable metals, a trend similar to that found in the pot experiment.

KEY WORDS::

• Zn
• Cd
• repeated phytoextraction
• Sedum plumbizincicola
• rhizosphere properties