Effects Of Continuous Cropping And Soilborne Diseases On Microbial Community Structure And Soil Properties Of Panax Ginseng C.A.Meyer Rhizosphere Soil

Panax ginseng C.A.Meyer is a kind of precious Chinese herbal medicine with traditional medicine and food homology,which has high edible and medicinal value.However,due to the long planting period,problems such as continuous cropping obstacles and soilborne disease were prone to occur during the planting process,which seriously restricted the development of ginseng planting.In this thesis,the effects of continuous cropping and soilborne diseases on ginseng rhizosphere soil were studied compared with the blank control,woodland soil which didn’t planting ginseng.The effects of continuous cropping and soilborne diseases on soil physicochemical properties,soil enzyme activities and phenolic acids.At the same time two test methods culturable method and Mi Seq high-throughput sequencing method were used to explore the changes of soil microbial community structure.In order to clarify the effects of continuous cropping and soilborne diseases on ginseng rhizosphere soil,reveal the causes of soilborne disease of ginseng,and provide theoretical support for alleviating the obstacles of continuous cropping of ginseng.The main results of this study are as follows:(1)The study of soil properties showed that,the continuous cropping of ginseng led to the decrease of total nitrogen,hydrolyzable nitrogen and organic matter in ginseng rhizosphere soil,and the decrease of hydrolyzable nitrogen was more obvious in soilborne group,which decreased from 398.47 mg/kg to343.03 mg/kg compared with the blank control.Continuous cropping led to a significant decrease in the p H of ginseng rhizosphere soil,compared with the blank control(7.47),the p H of CH decreased by 2.95 units,and that of CD decreased by 1.99 units,and the soil became acidified.The available phosphorus in ginseng rhizosphere soil accumulated obviously,and the soil nutrients were obvious imbalance.Continuous cropping caused the activities of soil urease,soil acid phosphatase,soil alkaline phosphatase,soil polyphenol oxidase and soil catalase in ginseng rhizosphere soil to decrease obviously,and the activity of soil cellulase was higher in healthy ginseng group.Through a correlation analysis,it is confirmed that there was a correlation between soil physicochemical properties and soil enzyme activity.Eight phenolic acids(gallic acid,vanillic acid,syringic acid,ferulic acid,salicylic acid,benzoic acid,coumaric acid,cinnamic acid)used in this study were all detected in three samples,among which coumaric acid and salicylic acid accumulated obviously in the rhizosphere soil of disease group.(2)The analysis of soil culturable microorganisms showed that,continuous cropping led to a significant decrease in the total soil microbial community,and the proportion of fungal community in the total soil microbial community increased significantly after ginseng continuous cropping,from 0.0676%(CK)to 0.2450%(CH)and 0.0993%(CD),and the soil culturable microbial flora changed from bacterial type to fungal type.A total of 193 strains of bacteria(including Actinomycetes)was isolated from ginseng rhizosphere soil samples by various media.It was identified that 193 strains of bacteria belonged to 4 phyla,6 classes,13 orders,19 families,39 genera and 96 species.After soilborne diseases,the relative isolation frequency of Bacillus and Paenibacillus in ginseng rhizosphere soil decreased,while the relative isolation frequency of Streptomyces increased.The correlation analysis between phenolic acids and culturable bacteria showed that the accumulation of cinnamic acid led to the decrease of relative isolation frequency of Proteobacteria.(3)The analysis of data by high-throughput sequencing indicated that,continuous cropping and soilborne diseases significantly changed the microbial community structure of ginseng rhizosphere soil samples.The αdiversity index changed significantly after continuous cropping and soilborne diseases.Soilborne diseases led to a significant decrease in the relative abundance of Chloroflexi and Firmicutes in soil bacterial communities at the phylum level and the relative abundance of Ascomycetes and Basidiomycetes to decrease,while the relative abundance of Fusarium at the genus level increased.According to the Cooccurrence network analysis,it can be found there were 2 negatively related hubs in bacterial community,and there were 4 positively related hubs and 5 negatively related hubs in fungal community.The correlation analysis between environmental factors and microorganisms shows that the order of soil physicochemical properties on microbial community is HN>S-ACP>TN>S-AKP>S-PPO.The prediction of microbial community function in ginseng rhizosphere soil showed that soilborne diseases and continuous cropping significantly affected the metabolic function of microorganisms in soil.A large number of functional groups of saprophytic microorganisms have appeared in the rhizosphere soil which planted ginseng.And compared with the other two samples,the CD sample had more functional groups of Plant Pathogen.From the above results,it is inferred that the changes of physicochemical properties of soil and the soil enzyme activity,and the accumulation of coumaric acid and cinnamic acid;the soil acidification;the change of culturable microbial flora and the decrease of relative separation frequency of Bacillus and Paenibacillus;the decrease of relative abundance of Ascomycetes and Basidiomycetes,and the enrichment of functional groups of plant pathogens such as Fusarium led to the occurrence of soilborne diseases after continuous cropping of ginseng.