The Root Microbial Assembly Mechanism Of Sedum Sedum And Its Implications For Environmental Remediation

Sedum alfredii(AE ecotype)is a key material for phytoremediation of heavy metal contaminated soils,however,there is a lack of research on the assembly mechanism of root microorganisms of AE ecotype at different growth stages.In this study,the plant was selected to investigate the differences in root microbial assembly in different parts of hyperaccumulated AE ecotype in Cd-treated and control soils at different growth stages.The main objectives of this study were:(1)to compare the growth perfoemance of hyperaccumulating AEs in Cd treated and control groups at different growth stages;(2)to investigate the microbial assemblage of the root system,roots and leaves at different growth stages(early,middle and late growth stages);(3)to investigate the differences in the community structure and functional composition of root and non-root soil microorganisms at different growth stages of AE between the different treatment groups to reveal the differences in the microbial composition of the root compartment at different growth stages.(3)To investigate the differences in the community structure and functional composition of root and bulk soil microbiome at different growth stages of AE between different treatment groups to reveal the differences in the mechanism of root microbial assembly at different growth stages;(4)To reveal the correlation between microbial assembly and root metabolites by comparing the differences in the composition of root metabolites and microorganisms of different ecotypes of Sedum alfredii between treatments.The obtained results of the study are as follows:The root length,plant dry weight and wet weight of Sedum alfredii increased in the Cd-treated group compared to the control group.On the contrary,plants in the control group grew shorter and all physiological indicators were lower than those in the treatment group.It can be seen that the soil in the treatment group was more favorable for the growth of Sedum alfredii.The content of total organic acids in plant roots increased in the Cd-treated group,where the amount of oxalic acid in plant roots and non-root soils in the Cd-treated group was much greater than its amount in the control group;the amounts of citric acid,tartaric acid and malonic acid in the root soils of the Cd-treated group first increased and then slowly decreased in the process of plant growth.The composition and abundance of root,rhizosphere,and leaf microorganisms were significantly different during plant growth,with the most significant changes in Actinobacteriota,which occupied a certain abundance in all three parts of the plant,and its proportion gradually increased with plant growth,which was most likely related to the migration of Cd from rhizosphere,root,and plant leaves.This is likely to be related to the migration of Cd from root soil-root to plant leaves.During the plant growth,the overall microbial composition did not vary much at the phylum level,and the top abundant three phyla were Firmicutes,Proteobacteria,and Chloroflexi.Among them,Actinobacteriota,Firmicutes and Proteobacteria were had a higher percentage in rhizosphere soil than in bulk soil during growth,which indicated that these three phyla were the dominant species enriched in rhizosphere soil and beneficial for plant roots to resist elevated Cd.By comparing the differential rhizosphere soil microbial composition in the three growth stages,it was observed that the relative abundance of Proteobacteria increased with plant growth,while the abundance of Actinobacteriota decreased with plant growth.At the genus level,the genera Phycicoccus,Bacillus,Streptomyces,Modestobacter,Myxococcaceae,and Intrasporangiaceae were significantly enriched in the initial rhizosphere soil,while in the Ramlibacter,Devosia,Caenimonas,and Haliangium were significantly more abundant in the rhizosphere soil at the later stage of growth than in the other two stages(p<0.01).by comparing the differences in the composition and function of microorganisms in the surrounding soil,root system,and roots of two ecotypes of Sedum alfredii at high and low concentrations.It was found that genera enriched in the inter-rhizosphere of AE Sedum alfredii at high Cd concentrations,such as Bacillus,Sphingomonas,Sphingomonas neoformans,Gemmatimonas,Cutriavidus,Nakamurella,and Nocardioides,could influence plant growth through IAA production,nitrogen fixation,biodiversity,and phosphorus solubilization,as well as help plants acquire Cd from soil.Recent evidence suggests that microbial-induced Fe carrier synthesis is usually regulated by root secretions and that microbial functions involved in Fe carrier metabolism are significantly positively correlated with soil Cd in AE,but significantly negatively correlated with soil Cd in NAE.Therefore,our results suggest that roots of AE can recruit microorganisms that synthesize iron carriers to improve Cd acquisition,leading to differences in adaptability between the two Sedum alfredii.The analysis of plant metabolome composition revealed that the expression of these functional genes was more significant in late plant nucleotide metabolism,metabolism of other amino acids,metabolism of terpenoids and polyketides,enzyme family substances,glycan biosynthesis and metabolism,and biosynthesis of other secondary metabolites.The research of this project concluded that AE Southeast Sedum can be a good material for Cd contaminated soil remediation,with high growth in high Cd concentration environment and can enrich most of the absorbed Cd in the leaves,which is most obvious in the late growth stage and convenient to handle,and the soil Cd removal efficiency reached about 30%.