Chapter 9 - Influence of willow (Salix viminalis L.) roots on soil metal chemistry: Effects of clones with varying metal uptake potential

Abstract

Various Salix clones show differing efficiencies of metal uptake. Some clones accumulate certain metals to a significant extent, while excluding others. The chapter aims to find out if the tendency to have low or high uptake of Zn, Cd, or Cu was because of the varying composition of root exudates. A study of pH, Cd, Cu, or Zn organic acids and peptides in root exudates from different Salix clones was performed using a rhizobox-like method containing control soil or soil amended with Zn, Cd, or Cu. The study shows that the release of metals from soil colloids differs between metals, as well as between willow clones with different properties of metal accumulation. Most of these mechanisms are found in low accumulators. Mechanisms involving pH seem to be important for both Cd and Cu accumulation. High pH decreases Cd release in soil with low Cd content and an increase in pH decreases the release of Cu from soil with high Cu levels by low-Cu-accumulating clones. In the case of Zn, organic acids and/or peptides seem to be important in reducing Zn uptake in soil with a low Zn content, while increasing pH functions as a mechanism to decrease Zn uptake in soil with a high Zn content. Thus, rhizosphere processes may partly account for the differences in the ability of willow clones to accumulate Cd, Zn, and Cu.