Use Of Ricinus Communis L. For Phytoremediation Of Cd And Pb Assisted With Citric Acid And Arbuscular Mycorrhizal Fungi

As the research object in this paper, castor (Ricinus communis L.) is a typicaleconomic crop. The effect of citric acid and exogenous arbuscular mycorrhizal fungi(AMF) on phytoremediation of R. communis for Cd and Pb were tested in potexperiment. The potential mechanism of both treatments was also studied to providesome scientific suggestion for phytoremediation effectiveness and efficiency.In this study, castor (Ricinus communis L.), abutilon (Abutilon theophrasti), flax(Linum usitatissimum), three economic plant cultivers with multiple non-food uses,were cultivated to examine their biomass production and heavy metals uptake andchoose the appropriate plant stype when growing in Cd and Pb artificial polluted soils.Besides, the effects of citric acid on Cd and Pb’s phytoextraction and the role of AMFin R. communis’s growth were investigated. The resource utilization of plant residuesafter phytoremediation was discussed briefly. The results we acquired were asfollows:(1) R. communis grown in single Cd or Pb contaminated soils behaved well andproduced higher root and shoot yields than corresponding abutilon and flax. Cd andPb concentrations in roots, stems and leaves of R. communis were the highest amongthem and could be used for further study.(2) R. communis developed well in Cd and Pb co-contaminated soils andproduced higher root and shoot yields. Growing in polluted soils containing150mgkg-1Cd and1000mg kg-1Pb, the biomass of R. communis were higher than abutilonand flax growing in clean soils, showing great growth advantage. The order of casterorgans accumulating Cd and Pb was: root＞stem＞leaf. In practical application,castor roots’ collection and disposal cannot be ignored because Cd and Pbconcentrations in roots of R. communis were so high that they occupied the most partof the total accumulation.(3) The energy crop (R. communis) may have potential use in phytoextraction ofCd and Pb assisted with citric acid. At the dosage of10mM kg-1soil, citric acideffectively increased Cd and Pb concentrations in shoots and these parts grew normally without suffering phytotoxicity. The application of citric acid decreasedCEC values, weakened the soil adsorption of heavy metals and activated Cd and Pb inthe soil solution.(4) The soil evaluation index (SEI) increased by14%and19%with theamendment of citric acid, which indicated that the soil quality was improved, showinga certain significance for soil remediation and ecological reconstruction.(5) Mycorrhizal colonization significantly increased P concentrations andcontents in roots, stems and leaves of R. communis. Shoot dry weight of AMFinoculated plant (1.46g plant-1) significantly increased by25%compared to thenon-inoculated plant (1.12g plant-1) when the soils were artificially polluted by1mgkg-1Cd and50mg kg-1Pb. The facilitation effect weakened with increasing Pbconcentrations.(6) When the soils were artificially polluted by1mg kg-1Cd and50mg kg-1Pb,inoculation increased R. communis’s Cd and Pb phytoextraction efficiency (shootcontent/total content) from35%and27%to49%and44%, respectively.(7) Carbon-based catalyst was made by plant residues after phytoremediation andthe removal efficiency of NOxwas the same as the catalyst made by clean planttissues, showing a certain value of resource utilization.