| Sunflower(Helianthus annuus Linn.)is one of the main oil crops and cadmium(Cd)-rich crops in China.As the last link of phytoremediation,how to safely dispose of heavy metal-enriched plant biomass is considered to be an important factor for measuring the true success of phytoremediation.This study takes a sunflower S606 as the research object,and 16 S r DNA was used to analyze the diversity of endophytic bacteria in sunflower.The endophytic strains were screened out from sunflowers through microbial tests,and the endophytic strains were used to extract cadmium in the sunflowers.Two strains with better extraction effects were selected for the next optimization experiment of the extraction system.By changing the conditions of the extraction system,using strains to extract cadmium from sunflowers,the best conditions and methods for strains to extract cadmium from sunflowers were explored.The cadmium-containing leaching solution and sunflower residue are separated reasonably,the cadmium concentration in sunflower before and after leaching and the change of matter concentration with toxic and harmful are measured.To get the comprehensive evaluation of feasibility about the strains on the best conditions for extracting cadmium in sunflower and to achieve the safety of disposal biomass after phytoremediation.The main conclusions are as follows:(1)Using high-throughput sequencing to find that the bacterial abundances in sunflower leaves and stems were 13 phyla and 28 families,respectively.Different strains are screened out according to microbial culture experiment.The used screening endophytes showed different effects on the extraction of sunflower cadmium,and J14,J15 and J16 showed better cadmium leaching effects.After 16 S r DNA identification results,J14(Enterobacter roggenkampii)and J15(Kosakonia cowanii)were selected as experimental strains,and their growth logarithmic phases were 2 h and 1.5 h,respectively.(2)By analyzing the chemical form of Cd in sunflower before leaching,sunflowers are mainly composed of protein-bound Cd(F3)and insoluble phosphoric acid Cd(F4).Among them,the largest proportion in sunflower leaves is insoluble phosphoric acid Cd,7.56 mg/kg(sunflower dry leaves),1.98 mg/kg(sunflower fresh leaves);and the largest proportion in sunflower stems is protein-bound Cd,3.66mg/kg(sunflower dry stems)and 2.10 mg/kg(sunflower fresh stems).By changing the extraction system conditions,the cadmium concentration of the four forms of water-soluble Cd(F2),protein-bound Cd(F3),and insoluble phosphoric acid Cd(F4)and oxalic acid Cd(F5)in sunflower stem extracting by J14 and J15 was much lower,comparing with primary concentration of various forms of cadmium in sunflower stems before treatment.The removal rate of cadmium exceeds 50% in water-soluble Cd,and insoluble phosphoric acid Cd and oxalic acid Cd.(3)The results of this study show that the response surface design experiment can predict cadmium remove in sunflower extracted by J14 and J15 well.The optimum conditions of removal rate of sunflower stem are that the p H of the extraction solution is 7,the liquid volume is 59.52 m L,and the temperature is 25 ℃according to the experiment results from J14.Under the optimum conditions,the removal rate of biomass cadmium is 46.29%,which is basically in line with the theoretical value of 48.34%.The optimum conditions of removal rate of sunflower stem are that the p H of the extraction solution is 5,the liquid volume is 75 m L,and the temperature is 25 ℃ according to the experiment results from J15.Under the optimum conditions,the removal rate of biomass cadmium is 43.26%,which is basically in line with the theoretical value of 48.62%.(4)Under the optimum extraction conditions,the sunflower stems were preprocessed by acid-base and cellulase,and then use microorganism to leaching.The results showed that pretreatment of sunflower by endophyte extraction greatly improved the removal rate of Cd.Among them,the J14 extracting single-cellulase pretreatment and acid-alkaline enzyme combination pretreatment of sunflower stems increased the removal rate of cadmium by 22.73% and 46.62% than the optimized condition extraction.The J15 extracting single-cellulase pretreatment and acid-alkaline enzyme combination pretreatment of sunflower stems increased the removal rate of cadmium by 23.11% and 43.90% than the optimized condition extraction.In summary,the combination of acid-alkali enzyme pretreatment is better than single enzyme pretreatment for the extraction of Cd in sunflower stems.The pretreatment of biomass improves the removal efficiency of Cd in sunflower stems by endophyte.Provide a theoretical basis for the study of microbial cadmium leaching of polluted sunflower,and realize the reuse of polluted sunflower as fertilizer. |
PDF Full Text Request