| About 40 percent soil contaminated by heavy metals is associated with Cadmium (Cd). Cd, a high toxicity metal, is easily accumulated in soil and enlarged in the food chain and Cd contamination has negatively influenced the safety of the ecosystem. Solanum nigrum L.is an ideal plant in the restoration of soil contaminated by Cd. However, remediation capacity of Solanum nigrum L. is limited in high Cd soil. Plant growth regulators play important role in increasing stress tolerance, enhancing heavy metal accumulation, and alleviating the adverse impact of heavy metal. However, the effect of plant growth regulator on Cd remediation efficiency of S. nigrum L. remains to be unknown.3 years'pot experiments were carried out to investigate the remediation effect of S. nigrum L. on soil with single and compound contamination of Cu, Zn, Pb and Cd. It compared among compound sodium nitrophenolate, diethyl Aminoethyl hexanoate and 2,4-D in the effect of remediation on Cd contaminated soil. Optimum dosage of DA-6 screening test in different Cd contamination soil was also estimated in this study. Moreover, The combined effects of DA-6 and humic acid on Cd contamination soil were investigated to reveal the effect of DA-6 on the remediation of S. nigrum L.. The main results were indicated as follows:1. A study of S. nigrum L. in remediation of heavy metals contaminated soil.The growth of S. nigrum L. was promoted significantly by Cu, Zn, Pb and Cd compound contamination. Dry weight (DW) of roots, stems and leaves in treatment with compound contamination were highest in all treatments. Cu, Zn, Pb and Cd concentration and accumulation under the condition of compound contamination were higher than that under the single contamination. S. nigrum L. played an important role in accumulating the Cu, Zn, Pb and Cd. The accumulation coefficient (AC) was less than 0.6, whereas the shoot and root AC of Cd was nearly to 2 and above 3 respectively. The results showed that S. nigrum L. had strong enrichment capability of Cd in a variety of heavy metals.2. The effects of growth regulator on the abitity of S. nigrum L. in remediation soil seriously contaminated with Cd. The growth of S. nigrum L. was significantly restrained by 100 mg/kg Cd, showed that height and DW of S. nigrum L. were decreased under Cd treatment. However,2,4-D and DA-6 could promote the growth of S. nigrum L. and increased its resistance under Cd stress, but the accumulation of dry matter was significantly lower than the accumulation without Cd treatment. During S. nigrum L. maturity, compound sodium nitrophenolate,2,4-D and DA-6 increased the Cd accumulation on the ground by 20.93%-26.74%(p<0.05); The underground Cd accumulation increased by 0.5-1.33 times(p<0.05); and the total cumulative content increased by 24.49%-39.8%(p<0.05). The increasing order was:DA-6> 2,4-D>compound sodium nitrophenolate. Three plant growth regulators increased the activities of SOD and CAT, so the ability of scavenging superoxide free radical anion got enhanced, effects on Cd toxicity in the leaves of S. nigrum L. got alleviated and its Cd-resistant got enhanced. The application of three growth regulators significantly reduced the content of MDA and relative conductivity, increased the SPAD value. DA-6 was the most prominent one.3. A study on ability of DA-6 in enhancing remediation different Cd concentrations soil by S. nigrum L.When DA-6 was 10 mg/L, the ability of S. nigrum L. in accumulating Cd was the strongest with concentration of Cd in soil under 50 mg/kg, and the Cd accumulation in S. nigrum L. reached 81.87%.20 mg/L DA-6 was best for S. nigrum L. in remeding the soil contaminated with 100 mg/kg Cd. The aerial parts and total accumulation of Cd increased 36.38% and 34.54% respectively, and the effect of enhancing remediation was significant.There were great differences with the same dosage DA-6 on the different concentration of Cd in soil. It worked only by appropriate concentration of DA-6. On the condition of Cd concentrations in soil were 0 and 25 mg/kg, concentration of DA-6 which was 40mg/L got the least MDA content in S. nigrum L.. When Cd concentrations in soil were 10,50 and 100 mg/kg, DA-6 which were 10 and 20 mg/kg made the content of MDA lower. Treatments with appropriate concentration of DA-6 increased POD activity and SPAD value in S. nigrum L. leaves. Therefore, it enhanced the ability to resist the adverse environmental, also promoted the growth of S. nigrum L., thus improving the ability to remedy soil with Cd contaminated.4. A study on DA-6 combinated with humid acid enhancing remediation of soil contaminated by Cd.With the increase of Cd concentrations, dry matter of S. nigrum L. increased at first, and reached a peak when Cd concentrations was 25 mg/kg, then declined. Cd accumulation in S. nigrum L. shoot and root markedly improved with the increase of Cd concentration and total Cd accumulation enhanced significantly. Application of humic acid alone and combinated with DA-6 could improve the total Cd accumulation significantly. Results showed that DA-6 significantly enhanced remediation coefficiency of S. nigrum L. on Cd contaminatede soil, especially humic acid combinated with DA-6.
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