Effects Of Arbuscular Mycorrhizal Fungi On Interactions Of Rare Earth Emement And Heavy Metal

In recent years,the extensive exploration of rare earth resources and application in the agriculture have resulted in the migration of more and more rare earth elements（REE）into the environment,the heavy metals associated with rare earth mining are also transferred and enriched in the surrounding soil,agricultural land,and water bodies of the mining area.Therefore,soils in rare earth mine and surrounding area are generally characterized by the co-contamination of REE and heavy metals.There are significant interactions between REE and heavy metals in the soil-plant system,which change its environmental behavior in soil,phytotoxicity and risks to the ecosystem,and affect plant-microbial remediation.At present,studies have shown that arbuscular mycorrhizal（AM）fungi can promote phytoremediation of soils contaminated by heavy metals or REEs,but it is unclear the effects of AM fungi on the interaction of REE and heavy metals,and roles,mechanisms and factors of AM fungi under the interaction of REE and heavy metals when they exist in the soil simultaneously.Greenhouse pot experiments were conducted in this study.Light rare earth element Lanthanum（La）,Cerium（Ce）and heavy metal Cadmium（Cd）,the main pollution elements in rare earth mine tailings,were selected to simulate single element and La-Cd co-contaminated soils with different concentrations(La:0,100,and 500 mg·kg^-1;Cd:0,5 and 10 mg·kg^-1),single element and Ce-Cd co-contaminated soils with different concentrations(Ce:0,100,and 500 mg·kg^-1;Cd:0,5 and 10 mg·kg^-1).The experiments were conducted to investigate the effects of AM fungi Claroideoglomus etunicatum on AM colonization rate,plant height,biomass,nutrient uptake,C:N:P stoichiometric ratios,REEs（La and Ce）and Cd uptake,antioxidant enzyme system,osmotic adjustment substance and chlorophyll contents of maize.The results indicated:（1）Symbiotic associations were successfully established between C.etunicatum and maize,the AM colonization rates ranged from 21.3%to 34.7%or 19.2%to31.3%in single element and La-Cd co-contaminated soils or Ce-Cd co-contaminated soils with different concentrations.（2）With AM fungi inoculation,maize biomass was significantly increased by11.3%to 57.6%in combined La and Cd treatment with different concentrations compared to single-metal treatment,whereas maize biomass was significantly decreased by 68.3%to 69.7%in combined Ce and Cd treatment with moderate concentration compared to single Cd treatment.（3）AM fungi inoculation could to some extent improve nutritional status and change the C:N:P stoichiometric ratios of maize grown on La-Cd-co-contaminated soil and Ce-Cd-co-contaminated soil with different levels.（4）Compared to single La treatment,shoot La concentrations of maize were significantly decreased by 52.2%and 90.3%in combined treatment of La and Cd with low and moderate concentrations,respectively,translocation rate of La was significantly increased by 129.0%in dual-metal treatment with low concentration;With AM fungi inoculation,shoot La concentrations in dual-metal treatment with low and moderate concentrations were decreased by 87.8%and 91.1%,respectively,translocation rate of La was significantly increased by 115.3%in dual-metal treatment with moderate concentration.Compared to single Cd treatment,shoot and root Cd concentrations were significantly decreased by 65.5%and 58.7%in dual-metal treatment with low concentration,respectively,only shoot Cd concentrations in dual-metal treatment with moderate concentration were significantly increased by 70.1%;With AM fungi inoculation,only shoot Cd concentrations were significantly increased by 48.3%in dual-metal treatment with moderate concentration.（5）Compared to single Ce treatment,only root Ce concentrations of maize were significantly decreased by 69.4%in combined treatment of Ce and Cd with moderate concentration;With AM fungi inoculation,root Ce concentrations were decreased by51.0%in dual-metal treatment with moderate concentration.Compared to single Cd treatment,shoot Cd concentrations were significantly increased by 24.0%and 61.0%in dual-metal treatment with low and moderate concentrations,respectively,translocation rate of Cd was significantly increased by 45.2%in dual-metal treatment with moderate concentration;With AM fungi inoculation,shoot Cd concentrations were significantly increased by 33.8%and 138.8%in dual-metal treatment with low andmoderate concentration,respectively,and translocation rate of Cd was significantly increased by 88.5%.（6）Compared to single metal treatment,the MDA contents in combined treatment of La and Cd and combined treatment of Ce and Cd with moderate concentration were significantly decreased;Compared to single Cd treatment,the decrease of PRO content was inhibited in combined treatment of La and Cd with low concentration,the contents of soluble sugar were significantly increased by 72.7%in combined treatment of Ce and Cd with moderate concentration.The preliminary experiment demonstrates that AM fungi inoculation can significantly affect the interaction of coexistence of REE and heavy metal in co-contaminated soils depending on the type and concentration of compound pollutants.Further systematic research should focus on the mechanisms of AM fungi on the interaction of REEs and heavy metal to provide a theoretical basis for vegetation restoration of co-contaminated soil.