The Screening Of High Cadmium Concentration Plants And Preliminary Study On Comprehensive Phytoremediation

With the application of electroplating, organic pesticides, sewage irrigation and a series of human activities, cadmium residues in the soil for a long-term which has brought a serious threat for the survival of animals and plants. A variety of repair methods adopted by the human to control environment pollution by heavy metals,among these methods, phytoremediation is a hot point of research. Heavy metals were extracted, fixed, decomposed and volatilized by plants to reduce or remove heavy metals in the soil.Phytoremediation is a green remediation technology, not only costs less, but also can't result secondary pollution to the environment. In this paper,Impatiens balsamina L.and Allium tuberosum Rottler were regarded as the experimental materials, the hydroponics and pot experiment were conducted to investigated the seed germination, seeding growth, the structure of adult plant, and physiological resistance and Cd accumulation laws of the adult plant infected by AM fungi under different concentrations of cadmium stress which aimed at digging out the potential of phytoremediation. The main research contents and results are as follows:(1)Cadmium stress promoted seeds germination of Impatiens balsamina L. and Allium tuberosum Rottler at low concentrations while inhibited germination at high concentrations. The germination index and vigor index decreased at high concentrations of cadmium stress and difference with the controls significantly(P <0.05), the root length and shoot length shortened with the increasing of cadmium concentration of two plants. Under 300 mg·kg-1cadmium stress, the root length and shoot length of two plants reduced by 70.33%, 97.03% compared with the control,and the shoot length respectively reduced by 66.33%, 65.58% which showed that the inhibitory effect of cadmium stress on root is more stronger than that of the shoots.(2) After infected by AM fungi, the two plants had different physiologicalresponses to different Cd concentrations stress. The SOD activity of two plants increased firstly and then decreased,and reached the maximum at 300 mg·kg-1 Cd stress. The POD activity of Impatiens balsamina L. increased firstly and then decreases and increased again at last,reaching the maximum at 300 mg · kg-1.However, the POD activity of Allium tuberosum Rottler firstly increased and then decreased and reached the maximum at 250 mg·kg-1 Cd stress. The CAT activity decreased firstly and then increased which was contrary with that of Allium tuberosum Rottler, and the CAT activity of two plants reached the maximum at 300 mg·kg-1 Cd stress. The antioxidant enzyme activities of AM fungi infection were higher than control group. AM fungi reduced the contents of MDA and proline at high Cd concentration stress, The root length and shoot length of two species infected AM fungi were longer than the control group which indicated that AM fungi enhanced the antioxidant enzyme activity, reduced lipid peroxidation, enhanced plants tolerance to cadmium and alleviated the toxicity of cadmium on plants.(3)Under 300 mg·kg-1 cadmium stress, the Cd accumulation ability of two plants had difference. The cadmium content distribution in Impatiens balsamina L is:root > stem > leaf, and in Allium tuberosum Rottler is: the aboveground part> the underground part, cadmium content in the underground part of Impatiens balsamina L was less than that of Allium tuberosum Rottler while the cadmium conten in aboveground in Impatiens balsamina L was higher than that of Allium tuberosum Rottler. The transport factor of two plants were 0.34, 0.2, the bioconcentration factor in Impatiens balsamina L reached maximum at 0.44 under 250 mg·kg-1 Cd stress, the transport factor and bioconcentration factor was less than 1 and did not achieve the hyperaccumulator plant standard. Cd concentrations in soil and Impatiens balsamina L cadmium had a significant positive correlation between, both of two were increased with cadmium stress concentration strengthen. High Cd stress significantly reduced the individual plant biomass of the two plants. For Impatiens balsamina L, AM fungi increased the underground cadmium content while reduced that of aboveground part.In a word, AM fungi reduced the total cadmium accumulation of Impatiens balsamina L.(4)Under the low concentration(50 mg·kg-1) and high cadmium concentration stress, the cadmium distribution in roots of Impatiens balsamina L at subcellular level showed the tendency of cell sap > cell wall > organelles. 50 mg·kg-1 cadmium stress,the cadmium content of cell sap, cell wall and cell organelles respectively 45%,16.8%, 6.6% and respectively accounted for 25.87%, 4.9%, 2.9% in that of 300 mg · kg-1 cadmium stress. It was showed that although the total amount of Cd concentration was creased in every subcellular part under high Cd stress, the Cd absorption capacity of the subcellular fractions decreased. because of the serious cell damage.(5)High cadmium stress destroyed the vessel structures of Impatiens balsamina L. In cross section, the vessel splited and could not form a complete closed structure,moreover, the derangement of fibrous tissue shrivelled; In the vertical, the vessel shrunken, the pitch increased, and the whole structure was loose and messy which suggested that it has linked to Cd destroyed the wall material structure and influenced microtubule arrangement of the destruction.