| Phytoremediation is used for the remediation of heavy metal contaminated soils by using plants which have high accumulation capacity and can transfer heavy metals in the soil to the plant body. As an emerging technology, phytoremediation has been widely recognized with its unique advantages. Currently, the potential to repair the heavy metal polluted soil of some plants, nevertheless, researches on phytoremediation of Cd polluted soil are not many, which still remain at the field screening stage. Renascent herb Kyllinga brevifolia Rottb is wide spreading, with strong vitality and fast growth rate, and has certain ability of lead accumulation, but there have been little researches on Cd accumulation and tolerance of K. brevifolia.In this research, we used the two ecotypes of K. brevifolia as test material, via pot and rhizosphere-bag experiment, studied the growth, Cd concentration, Cd accumulation, subcellular distribution, Cd chemical forms, NPT concentration, GSH concentration and PC concentration in plants and physicochemical property of soil. The main results are as follows:(1) The biomass of the two ecotypes of K. brevifolia reduced with the increasing of Cd concentrations, and the descend range of ME (mining ecotype) was greater. Cd concentration of shoots and roots of two ecotypes, and NME (non-mining ecotype) had a larger increase. NME showed a great accumulation ability at 200 mg·kg-1 Cd treatment. K. brevifolia accumulated most of the Cd it absorbed in the roots. Bioaccumulation coefficient of the two ecotypes were near to or larger than 1, showed that the ability of the plant to absorb Cd from soil is strong.(2) The pH and DOM in the rhizosphere soil of the two ecotypes of K. brevifolia were larger than that of non-rhizosphere soil. The pH in rhizosphere soil of ME increased 0.06～0.18, and that of NME increased 0.03-0.19. The concentration of DOM in rhizosphere soil of NME reached the maximum 100.82 mg·kg-1 at 200 mg·kg-1 Cd treatment, which was 1.39 times of that in rhizosphere soil of ME. The rangeability of DOC in rhizosphere soil of ME was a little smaller, which ranged from 25.12～85.04 mg·kg-1. The main existing forms of Cd in rhizosphere soil of the two ecotypes of K. brevifolia were exchangeable Cd and Cd bound to Fe-Mn oxides, and the concentration of the different forms of Cd increased with the increase of Cd concentration. Concentration of exchangeable Cd in rhizosphere soil of the two ecotypes were larger than that in non-rhizosphere soil, and exchangeable Cd in rhizosphere soil of NME was larger than ME, indicating that the ability to activate and absorb Cd of NME was greater than ME.(3) The Cd distributed mainly in cell wall (24.02%-53.54%) and soluble fraction (20.01%-55.64%) of the two ecotypes of K. brevifolia. Cd mainly existed with pectinate, protein, and phosphate, chemical forms of Cd such as ethanol-extractable Cd and deionized water-extractable Cd were lower, indicating that the plant was able to limit the transportation of Cd absorbed into roots to shoots of the plant. In addition, concentrations of chemical forms that had great mobility capacity such as ethanol-extractable Cd in NME was larger than that in ME, which provided foundation for the Cd accumulation advantage of NME.(4) The NME of K. brevifolia had strong complexing ability for Cd, and complexing ability of roots was stronger than shoots. Under different Cd conditions, a large quantity of NPT, GSH and PC were induced, and the concentration of sulfhydryl compounds increased with the increase of Cd concentration. Sulfhydryl compounds complexed with Cd, thus inducing the hurt to plant, enhancing the tolerance to Cd, and boosting the Cd accumulation capacity of K. brevifolia, which offered theoretical foundation for the reparation of K. brevifolia in the Cd contaminated soil. |
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