Effects Of Plant Endophytes On The Growth And Soil Properties Of Peanut Contaminated By Cadmium And Microplastics

In terrestrial ecosystems,Cd is on of the most common heavy metal pollutants in soils,which is easily absorbed,transferred and accumulated in large quantities by plants and animals due to its strong mobility,affecting normal life activities.Microplastics(MPs),as an emerging environmental pollutant,are expanding with the scope and accumulation of pollution,making soil a major convergence site.The effects of plant probiotics on plants in Cd and MPs contaminated soils are currently unknown In this study,two plant probiotic bacteria(Rhizophagus irregularis and the plant endophytic bacterium SC60)were selected to study the effects of different Cd concentrations with different species of microplastics on peanut growth,soil Cd effectiveness and uptake transport and soil properties under single and complex conditions using single and complex inoculations.The main findings were as follows:(1)Under single Cd contamination: inoculation with plant endophytes significantly increased peanut biomass,with 43.24% and 67.57% increase in above-ground biomass under single and compound inoculation,respectively,indicating that compound inoculation was better than single inoculation;main stem height and lateral branch length increased significantly,while photosynthesis and leaf SPAD values also increased significantly.Soil conductivity values and effective phosphorus content were increased.Complex inoculation with plant probiotic bacteria increased the soil effective state Cd content by 11.52%-41.89%,and peanut plants increased Cd content by 36.10%-72.53%(above ground)and 24.56%-73.68%(below ground),respectively.Inoculation with plant endophytes significantly reduced the number of bacterial OTUs,bacterial community diversity and richness;At the phylum classification level,the relative abundance of Proteobacteria and Chloroflexi increased by4.50%-9.92% and 1.48%-2.74%,respectively,while the relative abundance of Actinobacteria decreased by 6.29%-11.37%.At the genus classification level,the relative abundance of Blastococcus and Skermanella increased,while the relative abundance of Aeromicrobium decreased.Soil p H was the most important environmental factor in the change of bacterial community structure.(2)Under Cd-LDPE(low density polyethylene)complex contamination: inoculation with plant probiotic bacteria increased peanut subsoil biomass by 9.65% and 27.60%,and peanut photosynthesis and SPAD values were also significantly increased,but the effect on peanut plant morphology was not significant.The effects of soil p H,electrical conductivity,effective phosphorus and fast-acting potassium content were not significant.Complex inoculation with plant endophytes increased the soil effective state Cd content by 26.99%-38.34%,and peanut plants increased Cd content by 40.88%-83.92%(above ground)and66.91%-69.77%(below ground),respectively.Inoculation with plant endophytes changed the soil bacterial structure,and the number of bacterial OTUs,bacterial community diversity and richness decreased significantly;the community composition also changed,At the phylum classification level,the relative abundance of Gemmatimonadetes increased by 0.82%-1.44%,and that of Actinobacteria decreased by 5.83%-7.25%.At the genus classification level,the relative abundance of Sphingomonas increased,while that of Bradyrhizobium decreased significantly.Soil EC,AP and effective state Cd were the most important environmental factors affecting the change of bacterial community structure.(3)Under Cd-PBAT(butylene adipate-co-terephthalate)complex contamination:inoculation with plant endophytes had no significant effect on peanut biomass and plant morphology,leaf SPAD values did not change significantly.Soil organic carbon content significantly increased by 32.65%-54.67%,while the effects on soil p H,conductivity,effective phosphorus and fast-acting potassium content were not significant.Complex inoculation with plant probiotic bacteria increased the soil effective state Cd content by 72.60%-96.38% and increased the Cd content in peanut by 55.81%-61.03%(above ground)and 120.20%-230.01%(below ground),respectively,while inoculation reduced the translocation of Cd in peanut and reduced the transfer of Cd to the above ground.Inoculation with plant endophytes reduced the number of bacterial OTUs,bacterial community diversity and richness;At the phylum classification level,the relative abundance of Proteobacteria increased by 6.07%-6.12%,the relative abundance of Gemmatimonadetes also increased,and the relative abundance of Chloroflexi decreased by 0.31%-2.24%.At the genus classification level,the relative abundance of Skermanella increased,while that of Bradyrhizobium and KD4-96 decreased significantly.Similar to the Cd-LDPE complex contamination,soil EC,AP and effective state Cd were also the most important environmental factors affecting the changes in bacterial community structure.