Effect Of Cadmium Stress On Symbiont Combined With AM Fungi And Medicago Truncatula And The Effect Of Additional Fructose

As a soil green fertilizer,arbuscular mycorrhizal fungi(AMF),could form a mutualistic symbiont with plants to improve the growth and nutrition metabolism of plants under various stress.Meanwhile,AMF has become a research hotspot of plant combined remediation since it can increase the tolerance of host plants to heavy metals and improve the efficiency of phytoremediation.However,research on AM mycorrhizal fungi mainly focuses on the comparative study of mycorrhizal and non-mycorrhizal plants,while the physiological and biochemical mechanisms of improving host heavy metal tolerance are not fully understood,especially for remediation of soil ecosystem with different levels of contamination.Thus,this study mainly studied the physiological and biochemical changes of Medicago truncatula-AM fungal symbiont as well as soil physicochemical properties under different cadmium stresses.Based on this,GC-MS metabonomics analysis and high throughput sequencing technology were used to investigate the effects of exogenous fructose on Medicago truncatula-AM fungal symbionts under cadmium stress and their joint effects under cadmium stress.Here are the main findings:1.In the range of 0-80mg/kg Cd stress,Medicago truncatula-AM fungal symbiont showed "low promotion and high inhibition" effect on plant growth,nutrient phosphorus absorption,PSII capacity and soil organic matter nutrients.Among them,5mg/kg Cd had the optimum promotion effect on host Medicago truncatula and soil substrate while the inhabitation effection was observed after 20mg/kg;Besides,Cd was mainly concentrated in the root part of Medicago truncatula-AM fungal symbiont,and the upward translocation factor of Cd increased with the increase of Cd concentration,the maximum concentration and transport coefficient were 5.77 and 1.40 times of the control respectively at the concentration of 80mg/kg cadmium.Also,the As A-GSH antioxidant enzyme system of Medicago truncatula changed significantly under cadmium stress.With the increase of cadmium concentration,the activities of protective enzymes such as ascorbate peroxidase(APX),monodehydroascorbate reductase(MDHAR),Dehydroascorbic acid reductase(DHAR)and glutathione transferase(GST)were increased to enhance the stress resistance of Medicago truncatula to cadmium stress.2.AMF inoculation was significantly better than the exogenous addition of fructose in the growth and nutrient phosphorus content uptake of Medicago truncatula under cadmium stress.In addition,inoculation of AMF had positive effects on mercaptan metabolites such as amino acids and fatty acids in the host alfalfa rhizosphere and increased the metabolism of Ethanolamine and Homoserine in Medicago truncatula root system by 0.97 and 2.55 times,respectively compared with the control group.While,the addition of fructose showed a promotion effect on carbohydrate metabolism(increased by 1.13 folds in Isomaltose).Though exogenous fructose decreased the ? diversity of bacterial species in rhizosphere soil by 12.95%,it increased the relative abundance of Actinobacteria in rhizosphere soil by 94.60%.3.Though the combined treatment of fructose and AM fungi had no obvious synergistic effect on growth under Cd stress,it had significantly synergistic effect on phosphorus absorption,PSII ability and amino acid and fatty acid metabolism of root parts in Medicago truncatula.Exogenous fructose and AMF inoculation both had promoting effects on Y(II)and ETR of Medicago truncatula in photosynthetic system II,increased by 23.88% and 24.02%,respectively,Meanwhile,the ? microbial diversity of rhizosphere soil was increased by 21.17% under the combined treatment and the abundance of bacteria(Verrucomicrobia)related to organic matter decomposition in rhizosphere soil was increased 8.09 times(P<0.05).Additionally,the Cd accumulation content in Medicago truncatula was significantly increased compared with single AMF inoculation.The combination of fructose and AMF inoculation in phytoremediation could be beneficial to improve the cadmium accumulation of single mycorrhizal plant extraction.