The Enhancement Of Compound Plant-derived Activator On Phvtoextraction And Its Effects Evaluation

Chelate-assisted phytoextraction is a technique which involves applying chemical chelating agents,which could form complexes with target elements and promote the bioavailability of heavy metals in soil,thus increase the efficiency of phytoextraction.However,chemical chelating agents are resistant in the soil and have risks of leaching and may have negative effects on soil ecosystem.Therefore,it is urgent to develop a kind of environmental-friendly and cost-effective chelator with high efficiency.In this study,extraction of fruit residue was combined with biodegradable chelator(GLDA)and biosurfactant(tea saponin)to develop a new compound plant-derived activator(CPA).Soil culture experiment was conducted to investigate the performance of CPA,and the remediation benefit was evaluated based on plant growth,physico-chemical properities,soil microbial community and leaching risks.The main results are as follows.(1)Eleven kinds of common fruits were selected as the test materials.After the fruits residue extraction were obtained,their extractability on heavy metals from soil was determined.The results showed that the highest extraction efficiency of cadmium and lead of lemon residue extraction was 39.4%and 33.9%respectively,which was significantly higher than other fruits.According to the soil extraction experiment,the optimal ratios of volume lemon extract residue,GLDA and tea saponin to extract Cd and Pb was 15:4:1 and 15:2.5:2.5.The extractability of CPA on the insoluble cadmium and lead minerals was 311.1-490.8 and 8.65-56.2 times of pure water,proving that the CPA had great potential on mobilization of soil heavy metals and minerals.(2)Pot experiment was conducted to investigate the effect and mechanism of CPA on the phytoextraction by S.alfredii.The results showed that the CPA could promote the growth of plants in two consecutive seasons(plant biomass increased by 52.1%and 33.5%),and increase the accumulation of cadmium(43.2%and 54.7%)and lead(34.7%and 69.5%)in the shoots.After the harvest in the second season,there was no significant difference in soil pH between treatments(P<0.05).Compared with control treatment,soil dissolved organic carbon content increased significantly(59.4%),while water soluble,acid soluble and reducible cadmium and lead content decreased significantly under the application of CPA.Therefore,CPA could improve the bioavailability of heavy metal forms in soil and promote the absorption of cadmium and lead by S.alfredii,as well as improve the biomass and phytoextraction efficiency of plants.(3)To investigate the environmental effects of CPA and chemical chelating agent(EDTA)and biodegradable chelating agent(NTA),a six-month pot experiment was conducted.Compared with control group,EDTA and NTA significantly reduced plant biomass and Fv/Fm(15.4%2.1%)and Φ(Ⅱ)(7.2%,6.5%)to weaken the PS Ⅱ activities(P<0.05).While Fv/Fm,Φ(Ⅱ,qP and NPQ merely presented significant change under treatment of CPA and it could enhance plant growth(21.7%),indicating CPA didn’t influence photosynthesis of S.alfredii.Compared with EDTA,CPA increased the content of soil organic matter(10.9%)and cation exchange capacity(15.3%)(P<0.05),which improved soil fertility quality.The application of EDTA inhibited the activity of soil microorganism and lowered microbial biomass,while CPA did not have negative impact on the soil microbial biomass and microbial community,which was similiar with CK treatment.Overall,the bacterial community under CPA treratment was dominated by Proteobacteria,Chlorflexi,Acidobacteria and Actinobacteria.The dominated families were Gemmataceae,Opitutaceae,Ellin6075,OM27 and Pasteurellaceae.In addition,the leaching risk of CPA was significantly lower than EDTA and NTA(P<0.05).In conclusion,CPA was an environmental-friendly,economical and efficient activator,which could enhance growth of plants,improve the soil quality,merely disturb the soil bacterial community and pose slight leaching risk to environment.