Studies On Physi-ecological Responses And Tolerance Mechanism Of Medicago Lupulina L. To Cd Stress

With the development of modern industry, the release of heavy metals into the environment has been accelerating annually. Heavy metal contamination poses a threat to human health and life quality. So it has become a serious problem in environment and society. This problem may be partially solved by the phytoremediation which offers a cost-effective"green"method to soil remediation.In this paper, we selected Medicago lupulina L. as experimental material and studied the physi-ecological responses and tolerance mechanism of Medicago lupulina L. to Cd stress with pot experiment. The main results were as follows:(1) The seed germination and seedling growth of Medicago lupulina L. treated with Cd were studied. Seed germination rate, germination viability and germination index of the seeds had effects of promotion (within 5 mg·L-1)and inhibition (beyond 5 mg·L-1)when treated with Cd. And the growth of root was inhibited stronger than the growth of bud. The main reason for low germination rate of Medicago lupulina L. was that hard seed made it difficult to extracted water or stopped embryo to stretch. It existed the pehomenon that seeds coat inhibited germination of embryo. The inhibition effect on the seed germination was: seed coat>Cd stress (0 mg·L-1≤Cd concentration≤50 mg·L-1).(2) The fresh weight of Medicago lupulina L., above-ground and under-ground fresh weight of Medicago lupulina L. decreased with increasing Cd concentration. The permeability of cell membrane and content of MDA increased with increasing Cd concentration. With increasing Cd concentration, antioxidative enzyme activities rised at first, then fell. Plant antioxidative enzyme system not only have detoxification function but also is the reactional site of Cd2+ phyto-toxicity. The sensibility of antioxidative enzymes to Cd stress was SOD>POD>CAT.(3)Contents of different chemical forms of Cd in Medicago lupulina L. increased significantly with increasing of Cd concentration, while percentage of ethanol extractable Cd reduced and that of acetic acid extractable Cd, HCl extractable Cd and NaCl extractable Cd increased significantly.Our studies on physi-ecological responses and tolerance mechanism of Medicago lupulina L. to Cd stress and the achievement in this paper hopefully provide a theoretical basis for utilizing to restore Cd-polluted soil and phytoremediation in tail-mining wasteland.