Abstract: A pot experiment was conducted to study the physiological responses of Brassia campestris to cadmium (Cd), lead (Pb), and their combined pollution. When treated with Cd alone, the plant nitrate reductase activity and root vigor all increased at lower Cd but decreased at higher Cd, suggesting that B. campestris had definite Cd-tolerance capability at lower concentration Cd but was damaged by higher concentration Cd. In treatments Pb alone and Pb + Cd, the nitrate reductase activity and root vigor all decreased with increasing concentrations of Pb and Cd. When treated with Cd or Pb alone, the free proline content in B. campestris roots increased with increasing concentrations of Cd and Pb, and was signi ficantly higher when treated with Cd than with Pb, which further confirmed the h igher toxicity of Cd. The root proline content was higher when treated with Pb + Cd than with Pb or Cd alone, suggesting that the combined pollution of Cd and P b promoted the accumulation of proline in roots, and Pb enhanced the Cd toxicity . The mechanisms of Cd-Pb interaction are deserved to be further studied.

Key words: Dryland, Straw mulch, Winter wheat, Effects of irrigation and N fertilization