| Cd is toxic and can damage the physiology of plants when present in excess in the soil,posing a severe threat to human health and ecological safety.The mining and smelting of non-ferrous metals,the discharge of industrial waste,and the inappropriate use of fertilizers have led to the regional distribution of Cd pollution in China.Therefore,Cd pollution exists in farmland near tailings and factories,and it can even be highly concentrated.China is a large consumer of grain,and the primary solution to the problem of food shortage is to use existing farmland to produce more grain.Therefore,the contradiction between limited arable resources and high Cd pollution in regional farmland is an urgent problem that needs to be solved in agricultural resource utilization.Among the many remediation methods,bioremediation technology has economic and environmental advantages.Among them,hyperaccumulator plants and arbuscular mycorrhizal fungi(AMF)are the main forces in soil Cd pollution bioremediation technology,but so far,evidence of their synergistic effect is limited.Therefore,we innovatively designed a planting system called"Rhizophagus intraradices-Solanum nigrum L.-Glycine max L."to construct a powerful underground network by connecting Solanum nigrum L.with Glycine max L.through Rhizophagus intraradices,and we studied the effects of inoculation with Rhizophagus intraradices and intercropping on the distribution and transfer of Cd in plants and soil,plant physiology,soil properties,and bacterial diversity.Our goal is to provide a new system for the microbial-plant joint technology to control and improve heavy metal Cd pollution in soil,and to create a sustainable development model of"production and restoration in parallel."Our research results confirmed that intercropping and Rhizophagus intraradices inoculation can improve the physiological status and Cd tolerance of plants in high Cd pollution land,and reduce soil Cd pollution and improve soil quality.The main research results are as follows:1.The combination of intercropping and Rhizophagus intraradices also reduced the Cd concentration in the soil,and transformed Cd in the soil into a stable form that is not easily utilized by plants and microorganisms,limiting the flow of Cd to plants and creating a suitable microenvironment for plant and microbial growth.In addition,inoculation with Rhizophagus intraradices can significantly reduce the Cd content in plants,while intercropping can significantly reduce the Cd concentration in the soil.Therefore,the combination of intercropping and Rhizophagus intraradicess can allow more Cd to accumulate in the turnip of the intercropping system,especially in the roots,and reduce the Cd concentration of soybean grains in the intercropping system.The Cd concentration in the grains of soybeans under this treatment was 56%lower than that of soybeans without endophytic fungus inoculation.2.Intercropping and Rhizophagus intraradices inoculation can offset the negative effects of intercropping and resist Cd stress by promoting plant growth through the advantages of Rhizophagus intraradices,such as increasing net photosynthesis rate,electron transfer rate,and chlorophyll content.Under intercropping and Rhizophagus intraradices inoculation,the transpiration rate of soybean was the highest at 3.93mmol/m~2/s at the Cd 80 level,and the maximum fluorescence parameter and PSII maximum photochemical quantum yield were also the highest at the Cd 80 level.In addition,intercropping and Rhizophagus intraradices inoculation can significantly increase the inoculation effect and tolerance index of Solanum nigrum L.The tolerance index of soybean and Solanum nigrum L.under intercropping and Rhizophagus intraradices inoculation were the highest values in the treatment group,58.59%and86.96%,respectively.Moreover,the intercropping effect of soybean was higher than that of Solanum nigrum L.,and inoculation with Rhizophagus intraradices reduced the intercropping effect.3.The combination of intercropping and Rhizophagus intraradices can improve the plant’s antioxidant defense.Under Cd stress,the content of glutathione in soybean leaves and the activity of catalase in turnip leaves reached the highest level with the combination treatment of intercropping and Rhizophagus intraradices.They were 23.68%and129.12%higher than those of plants without Rhizophagus intraradices inoculation,respectively.The increase of antioxidant enzymes and non-enzymatic substances can alleviate Cd-mediated oxidative stress,which was manifested as a reduction in the number of phagosomes in the ultrastructure and a decrease in the content of malondialdehyde(MDA).4.The combination of intercropping and Rhizophagus intraradices can combine the advantages of both,increasing organic acid content,soil enzyme activity,and reducing soil p H and farmland pollution index.Intercropping of Solanum nigrum L and soybean significantly increased soil phosphatase activity,promoted the expression of bacterial energy metabolism and secondary metabolite biosynthesis pathways.Inoculation with Rhizophagus intraradices increased the total nitrogen,total phosphorus,and available phosphorus contents of the soil under Cd stress,and increased the organic acid content by increasing the lactate and pyruvate contents,which in turn lowers the soil p H.Inoculation with Rhizophagus intraradices can also increase soil enzyme urease and catalase activity and enhance soil bacterial diversity.5.The combination of intercropping and Rhizophagus intraradices can increase bacterialα-diversity index(Shannon,Simpson).The combination of intercropping and endophytic fungus mainly increased the abundance of Acidobacteria,Firmicutes,Patescibacteria,Cyanobacteria,and Nitrospirae bacteria at the phylum level.The combination of intercropping and endophytic fungus can also increase the abundance of functional genus levels such as Subgroup＿6,Sphingomonas,and Nocardioides,which have multiple functions such as phosphorus solubilization and heavy metal tolerance.Among them,species such as Subgroup＿6 and RB41 were closely related to surrounding species.These functional bacteria,in combination with Rhizophagus intraradices,indirectly improved soil quality by regulating nutrient content and soil enzyme activity.In summary,the"Rhizophagus intraradices-Solanum nigrum-Soybean"planting system can serve as a biological remediation mode for high-Cd polluted areas.It not only reduces the toxicity of heavy metals on target plants,but also gradually repairs Cd-polluted soil year by year.In addition,soybean feed is an economic crop that can make up for the economic losses during local pollution remediation.This paper expands the application range of mycorrhizal technology and intercropping patterns in polluted land,providing technical reference for the application and promotion of ecological restoration. |
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