| Root exudates are the carriers of plant roots and soil in the process of material,energy and information transmission.When plants are stressed by heavy metals,they adapt to the adversity by changing the production and accumulation of root exudates.However,root exudates can change the rhizosphere environment and affect the migration and transformation of heavy metals in the soil.After complexing with heavy metals,root exudates can increase their bioavailability and promote plant absorption.When phytoremediation of Cd-contaminated soil with the hyperaccumulating plant Sedum plumbizincicola,the role of root exudates of Sedum plumbizincicola in the remediation process can provide new ideas for the remediation of Cd contaminated soil.In this study,Sedum plumbizincicola was used as the test material to explore the changes in the composition and content of Sedum plumbizincicola root exudates under Cd stress,and the components of the root exudates of Sedum plumbizincicola could improve the bioavailability of soil Cd.The components of the remediation efficiency of Sedum plumbizincicola or the combination of different components provide a certain way to reveal the possible mechanism of Cd resistance or Cd hyperaccumulation of Sedum plumbizincicola,and to strengthen the remediation of Sedum plumbizincicola with mild Cd contaminated soil.reference.The main findings are as follows:(1)According to the analysis of GC-TOF-MS,the root exudates of Sedum plumbizincicola consist of 155 kinds of metabolites,including organic acids,amino acids,carbohydrates,fatty acids,amines,lipids,alcohols and others.Under Cd stress,33 kinds of root exudates were identified as differential metabolites,including malic acid,glycolic acid,glutaric acid,glycine,alanine,isobutylamine,urea,etc.The changes of differential metabolites indicate that Cd stress also affected the metabolism of organic acid,lipid and amino acid.Analysis of differential metabolite metabolic pathways showed that there were13 metabolic pathways related to low-Cd treatment and 6 metabolic pathways related to high-Cd treatment.Among them,five metabolic pathways are the key pathways with the highest correlation with Cd stress,mainly amino acid metabolism.(2)Among the root exudates,the p H of the soil treated with the same concentration of citric acid and malic acid decreased significantly within a week compared with CK.The soil DTPA-Cd treated with citric acid and Sedum plumbizincicola root exudates stock solution The content increased significantly on the 3rd day after the start of the test.The effect of different content of citric acid,glycine and fructose treatment on paddy soil p H reduction and Cd activation is citric acid>glycine>fructose.Among them,the soil p H of citric acid treatment significantly decreased by 0.25～ on the first day after the test started.1.00 unit,the soil DTPA-Cd content increased by35.14%～66.21%;the performance of each treatment to purple soil was citric acid≈glycine>fructose,and the soil p H of citric acid and glycine treatment decreased by 0.21～0.27,0.22～ 0.27 units,soil DTPA-Cd content increased by 13.31%-20.59%,16.58%-21.55%,respectively.Among the compound treatments,only the compound treatments of citric acid and glycine had better effects in paddy soil and purple soil,but the effects of each treatment in paddy soil were higher than those in purple soil.(3)Compared with CK,in the root exudate components,under the same concentration of malic acid,succinic acid and citric acid,the biomass of Sedum plumbizincicola was observably add up to27.07%～44.79%,moreover,the Cd content in the shoots Significantly increased by 23.55%～35.18%.Compared with ACK,CG2 treatment had the best effect in different citric acid concentration or compound treatment with glycine.The biomass of Sedum plumbizincicola was significantly increased by 25.98%,and the Cd content of the above ground was significantly increased by 17.88%.Compared with the control group,each treatment promoted the conversion of residual Cd in the soil to weakly acid-extracted and reducible Cd,and improved the activity and bioavailability of Cd in the soil.Among them,the soil Cd effectiveness of the same concentration of citric acid,glycine and fructose treatment and CG2 treatment were all greater than 50%.In addition,in each treatment with the same concentration,the total amount of Cd in the soil treated with citric acid was significantly reduced to 14.84% compared with CK,and the restoration efficiency of Sedum plumbizincicola was 34.95%;in different citric acid concentrations or combined with glycine,CA1 and Compared with ACK,the total amount of Cd in the soil treated by CG2 was reduced by20.46% and 20.39%,respectively.The restoration efficiency of Sedum plumbizincicola was 46.16% and 46.11%,respectively. |
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