Copper concentration in plants and in the rhizosphere as influenced by the iron status of tomato (Lycopersicon esculentum L.)

Changes of metal concentration that occur in the rhizosphere may arise from several processes including variation in the concentration of complexing ligands, pH or redox potential that can be influenced by the Fe status of the plant. The aim of this study was to assess for both acidic and calcareous, Cu-contaminated soils how Cu concentration in plants and in the rhizosphere was affected by the Fe status of a strategy I plant species. The change of soil solution pH, total solution Cu concentration and soil redox potential was monitored for 8 days in the rhizosphere of tomato (Lycopersicon esculentum L.) in response to contrasting Fe supply. The concentration of Cu in roots was enhanced under Fe deficiency in the acidic soils. Shoot Cu however did not vary with the Fe status of the plant. The plant Fe status had little effect on rhizosphere pH, redox potential or Cu concentration in solution in either acidic or calcareous soils. Marked differences in pH and solution Cu concentration were observed between rhizosphere and uncropped soils. Roots induced an increase in pH of acidic soils and a decrease in solution Cu concentration in all soils. The decrease in solution Cu concentration in acidic soils may be explained by the increase in rhizosphere pH. The proposed device provided new data on the fate of Cu in the rhizosphere and showed a positive correlation for the four soils considered together between the total Cu concentration in soil solution and root Cu concentration.