Figure 2

Tolerance indices (%) based on relative root length of different populations of  Rumex acetosa  and  Commelina communis  under four Cu treatments in hydroculture (0.25, 40, 160, and 320 μmol L^-1CuSO4, respectively; M: metallicolous; NM: non-metallicolous). Different letters on the error bars indicate a significant difference at P  < 0.05 (LSD test) under the same treatment.