Effects Of Electro-mediated On Secretion Of Low Molecular Weight Organic Acids And Accumulation Of Cd And Pb In Rhizosphere Of Sedum Plumbizincicola And Pogonatherum Crinitum

Electrokinetic-assisted phytoremediation（EKAPR）can synergistically exert the advantages of electrodynamics and phytoremediation,and has a good effect on soil heavy metal remediation.However,the current research involves fewer plant species,and the secretion of low molecular weight organic acids（LMWOAs）and the morphological evolution of heavy metals in the rhizosphere of hyperaccumulators in the EKAPR system are not yet clear.In this paper,the EKAPR system was constructed with the typical Cd hyperaccumulator Sedum plumbizincicola and Pb hyperaccumulator Pogonatherum crinitum in the heavy metal contaminated farmland soil of Huize lead-zinc mine area in Yunnan Province.The relationship between the secretion of LMWOAs in the roots of hyperaccumulators and the morphological changes of Cd and Pb in soil was studied,and the possible mechanism of Cd and Pb enrichment in hyperaccumulators under electric mediation was analyzed.（1）13 kinds of organic acids such as oxalic acid,succinic acid and alpha-ketoglutaric acid were detected by GC-MS.Twelve organic acids including acetic acid,L-malic acid and citric acid were detected in the root exudates.The common products of LMWOAs in the rhizosphere of two hyperaccumulators included oxalic acid,tartaric acid,malic acid,citric acid,succinic acid and acetic acid.（2）Under electric mediation,the secretion of oxalic acid in Sedum plumbizincicola was the most obvious,with a maximum increase of 19 times.The secretion content of LMWOAs in roots was tartaric acid>malic acid>oxalic acid>citric acid>acetic acid.The secretion of citric acid and oxalic acid increased with the increase of voltage.The content of LMWOAs in roots was oxalic acid>acetic acid>citric acid>tartaric acid>malic acid.（3）The distribution of Pb and Cd in soil changed under electric mediation.Cd accumulated to the cathode region under the electric field,and the effective Cd content increased with the voltage gradient.Weak acid extractable Cd increased by21.97%-120.48%,and the proportion of residual Cd decreased.The content of Pb decreased under electric mediation,and the effective state Pb anode area>cathode area,and both increased.The proportion of weak acid extracted Pb did not change significantly with the voltage gradient.Suitable electric mediation promoted the growth of Sedum plumbizincicola and Pogonatherum crinitum,and promoted the enrichment of Cd and Pb,respectively.The biomass of Sedum plumbizincicola and Pogonatherum crinitum increased by 13.58%-56.63%and 12%-135.8%,respectively.（4）After exogenous addition of three LMWOAs,the content of available Cd and Pb in soil and the proportion of weak acid extractable state increased,while the proportion of residual Cd and Pb decreased.The removal effect of Cd was tartaric acid>oxalic acid>malic acid,and the best effect on the enrichment of Cd in Sedum plumbizincicola was the addition of 1 mmol·L^-1malic acid.The biomass of Pogonatherum crinitum increased by 9.64%-51.12%.The best effect of biomass increase was adding 3 mmol·L^-1apple.Electroporation can promote the excessive accumulation of Cd and Pb in plants by promoting the secretion of low molecular weight organic acids from plant rhizosphere to change soil Cd and Pb and promote plant growth.