The effects of plants on the mobilization of Cu and Zn in soil columns.

Whereas metal effects on plants have been well studied, much less is known about plant effects on metal mobilization in soils. We investigated metal mobilization and speciation with a resolution of a few cm in soil columns planted with willows (Salix viminalis). In the presence of plants, the concentration profiles of dissolved organic carbon (DOC), major ions (e.g., Ca), Cu, and Zn exhibited more variation than in the absence of plants, and both smaller and larger concentrations were observed, indicative of strong local effects. The Cu concentration in the absence and presence of plants was controlled by DOC mobilization and could be described by the same relationship. Zn mobilization was controlled by DOC and Ca in the plant-free system and by pH and Ca in the presence of plants. Cu2+ and labile Zn were reasonably well predicted by the NICA-Donnan model and were influenced by the plant-induced changes of the soil solution composition. Plant uptake reduced the dissolved Zn concentration and transpiration reduced Cu and Zn leaching.