Induced Phytoremediation Of Heavy Metals Contaminated Soils By Elsholtzia Splendens And Its Biomass Compost Application

Elsholtzia splendens,a Chinese native Cu-tolerant plant,has been paying widely attention to in the phytoremediation of heavy metal(in particular Cu) contaminated soils. Investigations for about a decade show that E.splendens can be applied to the rehabilitation of Cu,Zn pollutants of in a soil due to high Cu,Zn concentrations in the shoot.Compared with the shoot,the root has further higher Cu,Zn concentrations because both Cu and Zn are difficult to be transported to the shoot of E.splendens.Addition of microbia chemical reagents[especially low molecular weight organic acids,for example[s, s]-ethylenediamine disuccinic acid(EDDS)],microbia in conjunction with chemical reagents,and so on,to the soil have enhanced Cu,Zn transportation from root to the shoot and increased the phytoremediation potential of Cu,Zn by E.splendens.But there has few successful examples of Cu,Zn concentrations in E.splendens shoot up to 1000,10000 mg kg^-1 DW(Cu,Zn hyperaccumulation levels in plant,respectively) by these inducements. Furthermore,E.splendens has accumulated a certain concentration of Cu,Zn in the shoot after a phytoremedying process of Cu,Zn pollutants in the soil.Batch disposal of E. splendens biomass after phytoremediation and its resourceful utilization are two of the sticking points that environmentally friendly phytoremediation justify itself.We have designed a series of incubation,pot,and field experiments,and mainly focused on:(1) Effect of acid production of Achromatium sp.on heavy metal uptake by Elsholtzia splendens;(2) Influences of arbuscular mycorrhizal fungus(AMF) and[s, s]-ethylenediamine disuccinic acid(EDDS) on the uptake of heavy metals by Elsholtzia splendens;(3) Influence of sulfur powder on solubility of Cu,Pb,Cd,and Zn in the soils contaminated by heavy metals;(4) Effects of sulfur powder and[s,s]-ethylenediamine disuccinic acid (EDDS) on s the uptake of soil Cu/Zn by Elsholtzia splendens; (5) Preliminary study on effect of Elsholtzia Splendens compost on plant growth in a Cu-deficient upland aoil and Cu uptake by winter wheat;(6) Effects of copper-enriched composts applied to copper-deficient soil on the yield and copper and zinc uptake of wheat;We had groped for Cu,Zn fractions in the soil pore water,the reasons of difficult Cu,Zn hyperaccumulation in E.splendens shoot by induced reagents and the application of the Cu-enriched compost made from E.splendens in a Cu-deficient soil, and the main results are shown as the following:â‘ The strain(Achromatium sp.) had produced more acid in the incubation experiment than in the pot one;The soluble Cu concentration in the soil solution was significantly positively related to its pH while the soluble Zn concentration significantly negatively to pH;The bacterium increased E.splendens shoot biomass and shoot Cu content,and increased significantly Cu cleaning-up by E.splendens from the soil polluted by heavy metals.â‘¡EDDS decreased significantly the shoot or root biomass of young E.splendens. Addition of EDDS remarkably increased shoot Cu,Zn content and Cu,Zn elimination from soil due to increasing of soluble Cu,Zn concentration in pore water.AMF inoculation affected insignificantly soil Cu,Zn fractions,shoot and root biomass of E.splendens,but increased Cu,Zn concentration in shoot,and AMF increased significantly Cu cleaning-up from the soil.Application of EDDS would increase the Cu elimination from soil contaminated by Cu,Zn in comparison with the inoculation of AMF.â‘¢The treatments of 200,300,400 mmol kg^-1 sulfur powder decreased significantly pH of soil pore water and soil pH,simultaneously increased markedly soil heavy metals' concentrations of pore water and NH₄NO₃ extractable.After 223 d of sulfur treatment,soil NH₄NO₃ extractable Cu,Pb,Cd,Zn concentrations in SH treatment were 57%,20%,91%, and 87%of their soil total concentrations,respectively.â‘£Application of 80 mmol kg^-1 or 120 mmol kg^-1 sulfur powder to the soil decreased significantly pH of soil pore water,and increased its heavy metals concentration,and increased markedly Zn and S concentration in the E.splendens shoot where there was a positively relationship at 0.01 level in the stem.Amendment of EDDS increased significantly Cu transportation from soil to E.splendens leaves.Application of sulfur powder influenced mostly Zn behavior,while EDDS affected mostly Cu,and there was no interaction between sulfur powder and EDDS.The sulfur powder in conjugation with EDDS enhanced the rehabilitation of soil contaminated by Cu,Zn.The degradation of EDDS would be affected by temperature and its half life was not a constant.80 mmol kg^-1 sulfur increased the biomass of E.splendens,while 120 mmol kg^-1 sulfur decreased notably the biomass of E.splendens.⑤Application of E.splendens tissue composts significantly increased plant height, biomass and 1000-grain weight of winter wheat(Triticum aestivum L.).The effect of 'root-stem' compost was not as good as that of 'leave' compost.The leave compost increased 1000-grain weight by 58.9%and the grain yield by one fold compared to CK. Amendment of chemical fertiliser only to the Cu-deficient soil decreased wheat 1000-grain weight,biomass and grain yield.â‘¥Application of the Cu-rich compost significantly increased plant height,biomass, grain yield,and 1000-grain weight of winter wheat(T.aestivum L.).In the pot experiment, plant height and shoot biomass in the 2%Cu-rich compost treatment increased 0.8 and 5.2 fold compared with the chemical fertiliser treatment at mature stage.Compared to chemical fertiliser CK,the 2%Cu-rich compost addition increased grain yield per pot by about 9.5 fold and 1000-grain weight by about 50%.In the field study the compost also showed stimulatory effects on plant growth and grain yield.Composting E.splendens plants grown in a Cu-contaminated soil and then applying the compost to a Cu-deficient soil may be an effective technique for the remediation of contaminated soils and re-distribution of the copper as a plant nutrient for copper deficient soils.