Fig. 4. Dependence of log concentration of Cu in plant tissue on the log of (a) effective Cu concentration, C_E, before growth, (b) effective Cu concentration, C_E, after growth, (c) soil solution Cu, before growth, (d) soil solution Cu, after growth, (e) CaCl₂–extracted Cu, (f) Cu E value, and (g) total soil Cu. The quadratic regression equations and regression coefficients are shown. Free Cu²⁺ activities were not determined (below method detection limit).