Rhizosphere Microbial Diversity,Ecological Function And Plant-Microbial Interaction Mechanism Of Salt-Tolerant Ecological Floating Bed Halophyte Sesuvium Portulacastrum

Bioremediation refers to the treatment of naturally organisms to decompose harmful substances into less toxic or non-toxic substances,such as phytoremediation and microbial remediation.Among them,phytoremediation refers to the use of specific plants and their rhizosphere microbial metabolic activities to absorb,accumulate or degrade the pollutants in the environment to purify and restore the environment.In phytoremediation process,in addition to the role of absorption and conversion of pollutants plant itself,plant-coupling microorganisms also play an important role,a large number of microorganisms living in the rhizosphere of plants play a different role in the process of pollution remediation by coupling with plant roots.This study was based on the fact that the seawater ecological floating bed construction technology of the Sesuvium portulacastrum has been widely used,systematically studied the interaction between plant roots and microorganisms during the beginning of the construction to the stable operation period.The high-throughput sequencing method was used to investigate the structure and diversity of the whole microbial and the specific functional microorganisms(sulfate-reducing bacteria and denitrifying bacteria)community.The function prediction of the whole microbial community and the quantitative analysis of specific functional gene content were carried out.Finally,the plant-microbial interaction was analyzed by measuring the species and relative content of organic acids in root exudates.The main results are as follows:(1)The study of the whole microbial community structure identified to 20 phyla,40 classes,82 orders,186 families and 438 genera.There was little difference in ZOTU between sampling sites,the number of Arcobacter was higher than the rest of ZOTU.In terms of microbial community diversity,microbial community diversity in different months showed seasonal cyclical changes over time,temperature,dissolved oxygen,ammonia and inorganic phosphorus concentration had significant effects on sample diversity.According to the prediction of community function,the main function of the microbial community was chemoheterotrophy,and showed the function of methanol oxidation,methylotrophy and hydrocarbon degradation.(2)Study of the structure and diversity of microbial communities with sulfate reduction and denitrification functions,the results showed that a total of 2 phyla,3 classes,3 orders,3 families and 7 genera were identified as sulfate-reducing bacteria,the denitrifying functional microorganisms with nirS gene identified into 2 phyla,4 classes,8 orders,10 families and 15 genera,the denitrifying functional microbes with nirK gene identified into 2 phyla,3 classes,6 orders,8 families and 15 genera.The type of sulfate-reducing bacteria ZOTU varied greatly between various locations,but higher abundance ZOTU remain unchanged.The ZOTU number of denitrifying bacteria with nirK gene in the non-rhizosphere region was higher than that in the rhizosphere region,and the denitrifying bacteria with nir S gene were opposite.The dominant abundance of denitrifying bacteria with nirS gene in summer was higher than that in winter,and the community structure showed periodic changes characteristics.In the community of denitrifying bacteria with the nirK gene,the relative abundance of the dominant group gradually decreased over time.In winter,the richness and diversity of denitrifying bacteria with nirS gene of the samples under the floating bed was higher than non-floating bed areas.Most of the nirK samples under the floating bed showed lower community diversity than non-floating bed areas.(3)Determination of the organic acid component of the root exudates of the S.portulacastrum showed that the number of organic acids and the relative contents of propionic acid,malic acid,butyric acid and valeric acid showed an increasing trend from the beginning of the construction to the stable operation period.Correlation analysis between the relative concentration of root exudates and microbial community structure data showed that the change of oleic acid content was significantly correlated with the Simpson index of microbial community,the content of pentanoic acid has influence on the difference in the structure of the sample community.No correlation was found between the relative content of root exudates and the remaining community structure data and the relative abundance of dominant groups.