Remediation Of Cd-contaminated Soil By Cannabis Sativa L. Mycorrhizal Symbionts

Cadmium(Cd)is a common trace element with persistence in agroecosystems.Cd is absorbed by plants through roots and affects the safety of humans and other organisms through bio chain enrichment and biomagnification effects.Therefore,remediation of Cd-contaminated soils to avoid human health hazards is an urgent issue to be addressed.Arbuscular mycorrhizal fungi(AMF)can affect the accumulation and transport of heavy metals through a variety of direct or indirect mechanisms,to improve the tolerance of host plants.In this study,we investigated the growth status of mycorrhizal symbionts,enrichment transport capacity,differentially expressed genes in roots,and rhizosphere by inoculating AMF(Rhizophagus intraradices,Ri)with a high concentration of Cd(80 mg·kg-1)contaminated soil and hemp(Cannabis sativa L.)as the host plant.soil,and root secretion of organic acids to investigate the response strategy of AMF-hemp at the physiological,biochemical,and molecular levels.To improve the efficient utilization of Cd contaminated soil through AMF hemp joint remediation technology,provide technical support for the purpose of production and remediation of heavy metal contaminated soil,and jointly obtain ecological and economic benefits.The main research results are as follows.1.The root system of hemp inoculated with Ri formed a good symbiotic relationship,and the spores in the soil were full.The mycorrhizal infection rate was greater than 33.3%,and the tolerance index was higher than 60%.It significantly increased the biomass of various organs of hemp and improved the root morphology.Compared with uninoculated,the inoculation treatment significantly improved photosynthetic gas exchange parameters,chlorophyll fluorescence parameters,and light energy utilization efficiency of leaves,and the maximum net photosynthetic rate and light saturation point increased by 3.5% and 14.7%,respectively;PCA analysis revealed that Ri alleviated the inhibition of photosynthesis in hemp by Cd stress mainly through regulating net photosynthetic rate,PSII reaction center,and photosynthetic electron transfer rate.Meanwhile,it significantly reduced leaf Cd concentration(73.0%reduction)and TF(stem+leaf)/root,increased root Cd concentration(68.9% increase)and BCFroot/soil,and increased total Cd absorption from plants.2.Inoculation with Ri reduced the rhizosphere soil p H under Cd stress;the total Cd concentration in the rhizosphere soil was reduced by 8.5% compared to the uninoculated treatment.The DTPA-Cd concentration in the uninoculated treatment was25.1 mg·kg-1,accounting for 31.8% of the total Cd concentration,while the DTPA-Cd concentration in the inoculated treatment was 30.2 mg·kg-1,accounting for 39.2% of the total Cd concentration.Similarly,inoculation with Ri reduced the proportion of reducible-Cd and residual-Cd states and increased the proportion of exchangeable-Cd and oxidizable-Cd in the rhizosphere soil.From the analysis of organic acid composition of rhizosphere soil,inoculation with Ri treatment mainly affected DTPACd and oxidizable-Cd by affecting ethylmalonic acid,citric acid,and succinic acid;malic acid,and citric acid were significantly and positively correlated with exchangeable-Cd(P<0.05).3.The transcriptome of Cd-stressed hemp roots inoculated with Ri was determined by RNA-seq,and the results showed that,compared with the uninoculated treatment,inoculation with Ri up-regulated several genes related to signaling pathways,For example,the calcium signaling pathway and MAPK signaling pathway;differentially expressed genes were enriched in several metabolic pathways,mainly including ascorbate and aldehyde metabolism,glutathione metabolism,interconversion of pentose and glucuronide and amino acid metabolic pathway,while upregulating genes encoding cell wall-related genes.Transcription factors involved in hormone regulation,signal transduction,and stress resistance were mainly activated.Inoculation of Ri affected root enrichment transport capacity and thus root tolerance mainly by mediating the ascorbate-glutathione pathway,ABC transporter.