Efficiency Of Biodegradable EDDS, NTA And APAM On Enhancing The Phytoextraction Of Cadmium By Siegesbeckia Orientalis L. Grown In Cd-contaminated Soils

Addition of biodegradable chelants can improve the bioavailability of heavy metals in the soils, then enhancing the phytoextraction of heavy metal contaminated soils. In order to choose suitable chelants and application of combinations, this study chooses Siegesbeckia orientalis L. which grew in a lead-zinc mine site in Huidong, Sichuan as a test material. The aim of this study was to investigate the efficiency of the three biodegradable NTA, EDDS and APAM in enhancing the accumulation of Cd by S. orientalis L. growing in Cd-contaminated soils though soil culture and plot experiment. The main results showed as follows:S. Orientalis L. grew in soil culture showed great tolerance characteristics of cadmium after addition of EDDS, NTA and APAM. The biomass, root surface area and root volume of S. orientalis L. of all chelants treatments showed no significantly (P>0.05) difference compared with control. At 10 mg kg-1 Cd-contaminated soil extraction experiment, treatments of chelants generally increased the POD and CAT activities in leaves, increasing 1.03-1.33 fold for POD and 1.02-1.46 fold for CAT compared with control; the Pn, Gs, Tr and Ci of S. Orientalis L. of all chelants treatments showed no significantly (P>0.05) difference compared with control; the GSH of S. orientalis L. of all chelants treatments was similar to the CAT; the soluble protein of S. orientalis L. of all chelants treatments showed no significantly ((P>0.05) difference compared wilh control. When the soils spiked up to 100 mg kg-1; the POD and CAT activities increased 0.87-1.11 fold and 0.64-1.16 fold, respectively; the Pn, Gs, Tr and Ci ofS. orientalis L. of all chelants treatments reduced significantly (P<0.05) compared with control; the GSH of S. Orientalis L. of all chelants treatments was similar to the CAT; the soluble protein concentrations in leaves of S. orientalis L. showed no difference compared with control (P>0.05).The addition of EDDS, NTA and APAM significantly (P<0.05) enhanced the Cd accumulation characteristics of roots and shoots. The Cd concentrations and accumulations of roots and shoots were in sequence APAM< EDDS< NTA. And the higher doses and earlier addition day of the chelants gained higher Cd concentrations and accumulations. At 10 mg kg-1 Cd-contaminated soil extraction experiment, the Cd concentrations and accumulations in shoots of S. orientalis L. increased 11.94-102.38% and 7.05-98.97%, respectively. The MER of all chelant treatments was 1.07-1.99 fold compared with control, reached 0.62-1.16%. When the soils spiked up to 100 mg kg-1, the Cd concentrations and accumulations in shoots of S. orientalis L. increased 10.99-61.33% and 7.54-24.94%, respectively. With the application of chelants, the MER was 1.07-1.24 fold compared with control, reached 0.62-1.16%.S. Orientalis L. grew in plot with mixed heavy metal pollution soils showed great tolerance characteristics. The application of EDDS, NTA and APAM enhanced the Cd accumulation of S. Orientalis L. The biomass of roots and shoots of all treatments were 2 and 7 fold compared with the biomass of roots and shoots S. orientalis L. grew in pot. Under the addition of 2 mmol kg-1 NTA on the 80th day, the highest accumulation in shoot of S. orientalis reached 4420.10μg plant-1.