Screening And Tolerance Characteristics Of Cadmium-resistant AM Fungi

In recent years,the rapid development of industrial and agricultural production activities has led to the continuous increase of heavy metal pollution in farmland soil in China,which poses a huge safety hazard to food safety and human health.Under the national strategic requirements of’Ecological Civilization Construction’and’New Rural Construction’in China,the remediation of heavy metal pollution in soil has become an urgent environmental problem to be solved in China.With the deep understanding of soil microorganisms,the potential application value of arbuscular mycorrhizal fungi（Arbuscular mycorrhizal fungi,AM fungi）in enhancing phytoremediation of heavy metal pollution has been gradually explored.AM fungi is a kind of beneficial bacteria which widely exists in soil environment and can establish symbiotic relationship with most terrestrial plants.It can help plants absorb mineral nutrients to enhance plant resistance to heavy metals,and further change the absorption,transport and distribution of heavy metals in plants to slow down soil heavy metal pollution.Remediation of heavy metal pollution in farmland by AM fungi combined with plant roots has good environmental effects and application prospects.However,there are few reports on the role and mechanism of AM fungi in fixing heavy metals,enhancing plant resistance,and detoxification of heavy metals in soil.Understanding the effects of contaminated soil environmental factors on the diversity of AM fungi and the promotion effect of tolerant bacteria on soil remediation can provide scientific and data support for the application of AM fungi in soil heavy metal pollution and ensure food security in contaminated areas.This study investigated the heavy metal pollution of wheat farmland soil in Baoding City,Hebei Province.The community diversity of AM fungi was analyzed by high-throughput sequencing to explore the influence of environmental factors on the structure of AM fungi.The isolated native AM fungal spores were subjected to soil culture experiments in artificially configured Cd-contaminated soil.According to the indicators of soil heavy metal content and morphology,wheat growth,and wheat enrichment of heavy metals,AM fungi with cadmium resistance and efficient removal of soil heavy metals were screened.The main conclusions are as follows:（1）Among the investigated heavy metal pollution（Cu,Cd,Pb,Zn）,the heavy metal Cd pollution in the study area is serious.The content of Cd in each site ranged from 0.23 to5.62 mg·kg^-1,and the exceeding rate of Cd in the contaminated area was more than 50%.The Cd content of wheat seeds also exceeded the standard,and the exceeding rates of Cd in wheat seeds at three contaminated sites were 38.3%,9.91%and 24.8%,respectively.（2）The community structure and diversity of AM fungi in soil and wheat roots were different.High-throughput sequencing results showed that the dominant genus of AM fungi in soil and wheat roots was Glomus,and AM fungi in soil were more abundant than those in roots.The dominant species of soil AM fungi was Glomus caledonium,accounting for25.72%.The dominant species of wheat roots was an unclassified species,accounting for42.53%.Redundancy analysis（RDA）of environmental factors and AM fungal community showed that heavy metal Cd pollution was the main factor affecting soil AM fungal community structure,and p H and total phosphorus（TP）had the most significant effects on AM fungal community in wheat roots.（3）In this study,soil pot experiments were carried out on the isolated Glomus constrictus（Gco）,Glomus heteromorphus（Gh）and Glomus scotchensis（Gca）.It was found that inoculation of AM fungi in artificially configured Cd-contaminated soil could effectively promote the growth of wheat biomass,reduce the concentration of heavy metal Cd in soil,and promote the transformation of heavy metal Cd to a more stable form（residual form）.Inoculation of AM fungi can promote the fixation of Cd in wheat roots and reduce the transformation of Cd to the ground.Under medium and low Cd concentrations,the removal rate of Cd in soil by inoculation of Gh could reach 18.87%～36.36%.Under high Cd concentration,the removal rate of Cd by Gca was as high as 47.81%.Gh and Gca were efficient cadmium removal tolerant strains at low and medium cadmium concentrations and high cadmium concentrations,respectively.