Root-induced changes in the rhizosphere of plants. II. distribution of heavy metals across the rhizosphere in soils

Abstract

Three experiments were carried out using the rhizobox system to determine the distribution of heavy metals (Cu, Zn, Mn, and Fe) across the rhizosphere of barley (Hordeum vulgare L., var. Dorirumugi). The movement of ⁶⁵Zn, ⁵⁴Mn, and ⁵⁹Fe within the rhizosphere was also investigated. The solubility of heavy metals was evaluated by using double acid (H₂SO₄ + HCl) extractant. The results indicated that the rhizobox system provides quantitative information on the area of rhizosphere concerning the heavy metal distribution. The increase of the pH at the vicinity of the roots tended to decrease the amount of soluble Cu and Zn. In spite of the increase of the pH, the solubility of Mn and sometimes of Fe was increased in the rhizosphere. However, it remains to be determined whether the increase in soluble Mn was due to root excretion or microbial activity.

Key Words:

• bulk soil
• rhizobox
• rhizosphere pH
• sewage sludge
• ⁵⁴Mn•⁵⁹Fe•⁶⁵Zn