Toxic Effects of Exogenous Cadmium on Tomato and Its Toxicity Threshold
The toxic effects of exogenous Cd on the length and the fresh weight of roots, and the height and the fresh weight of the aerial part of tomato, a Cd-sensetive crop, were studied by field experiments. The toxicity thresholds of Cd(EC10)for root length, plant height and the fresh weight of tomato were calculated based on the regression equations between soil available Cd(0.10 mol/L CaCl2extractable) and root length, plant height and the fresh weight of aerial parts of tomato. The difference between the EC10 values derived from field experiments and those derived from greenhouse experiments were discussed. The results showed that low concentration of exogenous Cd may promote whereas higher concentration of exogenous Cd will inhibit the growth of tomato. The toxicity thresholds of Cd(EC10, expressed as soil available Cd) for root length, plant height and the fresh weight of aerial parts of tomato varied greatly in different soils. The EC10 values were 0.13 mg/kg to 5.22 mg/kg for root length, 0.14 mg/kg to 9.34 mg/kg for plant height and 0.02 mg/kg to 4.13 mg/kg for the fresh weight of aerial parts.The maximum difference between the EC10 values derived from field experiments and from greenhouse experiments was 103.25 times for the fresh weight of aerial parts and 2.85 times for root length. At most circumstances, the difference of EC10 values from field experiments and greenhouse experiments was within 5 times. Some EC10 values from greenhouse experiments were higher than those from field experiments while the others were on the contrary.