The Diversity Characteristics Of AM Fungi In The Abandoned Ion-absorbed Rare Earth Areas And Their Effects On The Degradation Ability Of Nitrogen By Paspalum Wettsteinii

Southern Jiangxi is one of the most densely distributed areas of ion-absorbed rare earth ores in China.For many years of mining activities in the region,which has caused great destructions to the ecological environment and the soil pollution is deteriorating,these adverse factors threaten human health and social and economic development.Arbuscular mycorrhizal(AM)fungi can form symbiotic system with a lots of plants to promote the absorption of nutrients such as nitrogen and phosphorus.AM fungi combined phytoremediation as an economical and efficient remediation technique has become a hot research topic.However,the application of this technique to remediation of contaminated soil in abandoned ion-absorbed rare earth mines is still at the initial stage.In this study,the physio-chemical characteristics of soil quality of the typical abandoned ion-absorbed rare earth ores distribution areas in southern Jiangxi were tested,and the soil fertility and pollution were discussed.High-throughput sequencing technology was used to detect the diversity of AM fungi in soil,and the species with the largest proportion of the total species was obtained.The effects of AM fungi on the growth of Paspalum wettsteinii as well as the nitrogen content and enzymatic activity in rhizosphere soil were studied by indoor pot experiment.It provides a theoretical basis for soil remediation in abandoned ion-absorbed rare earth mines.Main conclusions of the study are as follows:(1)The soil of abandoned ion-absorbed rare earth mining area is acidic and the pH value ranging from 3.64 to 4.88,the contents of soil organic matter and available phosphorus were lower than 10g/kg and 15mg/kg,respectively,and the contents of available potassium were between 0.1 and 0.155g/kg,the fertility level was low,the cationic exchange capacity(CEC)was lower than the general value of 10 to 20 cmol/kg and the soil fertility is poor.The highest concentrations of heavy metal elements copper(Cu),zinc(Zn),lead(Pb),cadmium(Cd)and mercury(Hg)were exceeded the soil background standard in ganzhou city of Jiangxi province 1.36,2.34,6.87,2.44 and 1.85 times,respectively,according to the result of geoaccumulatoin index evaluation,the Pb pollution is serious,and the pollution scope is wide,the existence of greater security risks,so it should be taken extreme attention.The rare earth elements lanthanum(La),yttrium(Y)and europium(Eu)are abundant,and their contents range from 9.62 to 608.0 mg/kg,22.7 to 608.0 mg/kg and 0.13 to 16.8 mg/kg,respectively,and these soil factors hinder the plants growth normally.According to the results of principal component analysis(PCA),the main environmental factors in the soil disturbed by the mining activities of ion-absorbed rare earth minerals were ammonia,available potassium,CEC,and heavy metal elements Hg and Cu.(2)The species diversity of AM fungi in the rhizosphere soil of ion-absorbed rare earth mining areas is low and 22 species of 11 genera AM fungi were isolated from the rhizosphere soil.8 species belong to Glomus,3 species belong to Ambispora,2 species belong to Paraglomus and 2 species belong to Geosiphon,Acaulospora,Claroideoglomus,Kuklospora,Scutellospora,Gigaspora,Diversispora and Archaeospora are all found in one species,respectively.Among them,the Glomus has the most proportion was the dominant genus of AM fungi,and the dominant species were Glomus intraradices,Glomus mosseae and Glomus occultum in the research areas.Redundancy analysis(RDA)showed that ammonia,available phosphorus,available potassium and organic matter were the important factors affecting the species diversity and community structure composition of AM fungi in the soil of ionabsorbed rare earth mining areas.(3)Inoculation of three kinds of AM fungi,namely Glomus intraradices,Glomus mosseae and Glomus occultum could establish a good symbiotic relationship with Paspalum wettsteinii,enhance the mycorrhizal infection rate of plant roots,and the infection rate of mycorrhizal in plant roots was 83%,83% and 80%,respectively,to promote the growth of Paspalum wettsteinii,and increase the plant number survival.In the inoculation treatment of three AM fungi groups,the number of Paspalum wettsteinii,the length of overground roots and underground roots,the content of chlorophyll and the fresh weight were all better than that of the uninoculated treatment groups.In particular,the number of viable strains and fresh weight of inoculated Glomus intraradices were 2.84 and 4.16 times of those of uninoculated.Compared with the uninoculated groups,the inoculation of three AM fungi had no obvious effect on the nitrogenous enzyme activity in the root soil,but all of them could improve the activity of protease and urease in the soil.(4)The content of total nitrogen in the soil of AM fungi treatment groups were higher than those of non-inoculation treatment groups(155.0 mg/kg),the content of nitrate nitrogen was the highest(7.69 mg/kg)in the non-inoculation groups,and the content of ammonia was the lowest(19.90 mg/kg)in the non-inoculation groups,these indicating that AM fungi inoculation can promote the formation of inorganic nitrogen ammonia in soil,provide nitrogen needed for the growth and development of host plants,and also play a role in removing nitrogen pollutants in soil.The pH value and contents of organic matter and total phosphorus in the rhizosphere soil of Paspalum wettsteini inoculated with three AM fungi were all higher than those without inoculation.This study provides an important theoretical basis for the research and application of AM fungi species diversity,and has a good practical value in the practice of soil remediation damaged and polluted by the mining activities of ionabsorbed rare earth mines areas,and also has certain practical significance in the improvement of plant biomass.