Effects Of Arbuscular Mycorrhizal Fungi On The Growth Of Maize In Rare Earth-Heavy Metal Co-Contaminated Soil

Inner Mongolia is rich in rare earth resources, the development and utilization of rare earth resources not only has brought huge economic benefits, but also caused serious ecological environmental problems to the grassland ecosystem of Inner Mongolia. Meanwhile, these ecological environmental problems are very special, uaually companied with co-contamination of rare earth elements and heavy metal elements. As a result, to protect the ecolocial environment of rare earth mining area as well as to maintain the stability of the grassland ecosystem of Inner Mongolia, finding a feasible way to restore the soil contamination caused by rare earth development and utilization is a top priority. Arbuscular mycorrhizal fungi has the potential to restore soil heavy metal pollution, nevertheless, the mechanism of AMF in restoring rare earth-heavy metal co-contaminated soil remains unknown, therefore further study is needed. In the present study, La, Ce, Pb and maize, which are the typical pollutants of soils and the model plants species of mycorrhiza, are applied in pot experiments to investigate the possible effect of AMF on the growth and La, Ce and Pb adsorption of maize grown in different degrees of Ce contaminated soil and La-Pb contaminated soil respectively. The study aims at providing scientific basis and technical support for restoring soil contamination caused by rare earth mining in China.The study is consisted of two experiments. Experiment 1 was conducted in a greenhouse to study the colonization rate, plant biomass, C:N:P, adsorption of mineral elements and Ce of maize colonized with 5 AMF species (G aggregatum、 C. etunicatum、R. intraradices、F. mosseae and G. versiforme). Tested soil contains 100mg/kg,500mg/kg and 1000mg/kg Ce. Symbiotic associations were successfully established between 5 isolates and maize grown in different degrees of Ce contaminated soil, with an average mycorrhizal colonization rate ranging from 11%～76%. Mycorrhizal colonization rate reduced with the increase of Ce concentration. AMF colonization promoted the the plant biomass and adsorption of mineral elements, however, but the promoting effect weakened as the Ce concentration increased. In 100 and 500 mg/kg Ce contaminated soils, AMF colonization significally reduced the C:P and N:P of maize, supporting growth rate hypothesis. However, in 1000 mg/kg Ce contaminated soils, AMF colonization significantly reduced C:P and N:P of maize. In addition, AMF colonization significantly enhanced Ce adsorption in the aerial part and reduced Ce adsorption in the root in 100 mg/kg and 1000 mg/kg Ce contaminated soils respectively.Experiment 2 was conducted in a greenhouse to study the colonization rate, plant biomass, C:N:P, adsorption of mineral elements, La and Pb of maize colonized with 4 AMF species (C. etunicatum、R. intraradices、F. mosseae and G. versiforme). Tested soil contains 50mg/kg,200mg/kg and 800mg/kg La-Pb compound pollutants. Symbiotic associations were successfully established between 4 isolates and maize grown in different degrees of La-Pb co-contaminated soil, with an average mycorrhizal colonization rate ranging from 37%-80%. Mycorrhizal colonization rate reduced with the increase of La-Pb compound concentration, with the minimum of mycorrhizal colonization rate reached 17%. In 50mg/kg La-Pb co-contaminated soils, AMF inoculation decreased the biomass of maize; however, In 200 and 800 mg/kg La-Pb co-contaminated soils, AMF inoculation AMF inoculation increased the biomass of maize, with the maximum biomass exceeding 105% of that of the control group. The biomass of maize decreased with the increase of La-Pb compound. AMF colonization promoted the mineral uptake of maize. Inoculated maize grown in 200 mg/kg La-Pb co-contaminated soils exhibited the best mycorrhizal effect. Among all of the mineral nutrients tested, AMF colonization significantly promoted P adsorption of maize. The promoting effect of mineral adsorption weakened as the La-Pb compound concentration increased. AMF colonization significally reduced the C:P and N:P of maize in 50,200 and 800 mg/kg Ce contaminated soils, supporting growth rate hypothesis. In 50 mg/kg La-Pb co-contaminated soils, AMF colonization significantly increased aerial part and root La uptake as well as root Pb uptake, decreased Pb uptake in the aerial part of maize. In 200 mg/kg La-Pb co-contaminated soils, AMF colonization significantly reduced La and Pb uptake in the aerial part of maize, while promoted La and Pb uptake in root of maize. Among all of the inoculation treatments in 200 mg/kg La-Pb co-contaminated soils, inoculation with R. intraradices exhibited the most obvious effect, with La and Pb in the aerial part of maize reduced by 66% and 70% respectively, while La and Pb in root of maize increased by 76% and 88% respectively. In 800 mg/kg La-Pb co-contaminated soils, AMF colonization significantly promoted La uptake in the aerial part and Pb uptake in the root of maize, nevertheless, inoculation with AMF exihibited a verying effect on the aerial Pb uptake and root La uptake of maize.Experiment results preliminary demonstrated that AMF has the potential to promote plant growth, mineral uptake, rare earth and heavy metal adsorption, thereby enhance the resistence of maize grown in rare earth-heavy metal co-contaminated soils. The study is vital to solving the ecolocial destruction problems and environmental pollution problems caused by rare earth mining in China.