Effects Of Phenolic Acid And Saponin Autotoxic Substances On Rhizosphere Soil Microorganisms During Continuous Cropping Of Panax Notoginsen

Large-scale intensive cultivation has made continuous cropping soil obstacles more serious for Panax notoginseng in Yunnan.Autotoxic substances can promote the occurrence of continuous cropping soil obstacles.Phenolic acids and saponins exert a strong autotoxic effect on P.notoginseng.In this study,we take P.notoginseng as the research object,based on UPLC-MS/MS,the contents of six phenolic acids and saponins of P.notoginseng rhizospheric soil were tested.Based on Illumina Mi Seq high-throughput sequencing technology,16S was used for bacteria and ITS was used for fungi to sequence soil microorganisms in P.notoginseng rhizosphere,the variation in the microbial diversity in the rhizospheric soil was used as an index to explore the interactions between phenolic acids and saponins with the soil microorganisms of the P.notoginseng rhizospheric.The field investigation results showed:（1）the contents of benzoic acid（BA）,ferulic acid（FA）and vanillic acid（VA）in the soil planted with P.notoginseng were higher than those in the control soil.The contents of p-hydroxybenzoic acid（p-HA,）,syringic acid（SA,）and ferulic acid（FA）were the highest in 2-year-old diseased rhizospheric soil（S-2Y）.The contents of saponins Rd,Rg₂,Rg₁,Re,Rb₁ and R₁ in rhizospheric soil increased significantly in the presence of P.notoginseng disease.（2）Continuous P.notoginseng cropping significantly changed the microbial community structure,which showed that significantly increased bacterial Chao1 index and Shannon index and decreased fungal Shannon index.（3）A correlation analysis showed that p-HA was significantly positively correlated with plant pathogens Fusarium and Ilyonectria.Ginsenosides Rg₂,Rb₁ were significantly positively correlated with Plectosphaerella and Ilyonectria.（4）A correlation analysis of soil environmental factors associated with fungal and bacterial communities showed that available potassium（AK）,total nitrogen（TN）,organic matter（OM）and hydrolysable nitrogen（HN）were most strongly correlated with soil microorganisms.Six phenolic acids（BA,FA,SA,p-HA,VA,p-CA）and six saponins（Rd,Rg₂,Rg₁,Re,Rb₁,and R₁）were added to the rhizospheric soil of P.notoginseng,after 72 h and 74 h culture,respectively.The effects of the added autotoxic substances on the microorganisms and their degradation were studied.The results showed that:（1）Exogenous phenolic acids and saponins significantly change the soil bacteria and fungi community structure.VA significantly reduced the bacterial Shannon index.Para-HA,FA,SA and VA significantly increased the fungal Chao1 index.Exogenous saponins significantly increased the fungal Chao1 index.（2）Phenolic acids and saponins significantly changed the abundance of P.notoginseng rhizospheric soil bacteria and fungi,and increased the abundance of common pathogens causing root rot.BA and p-CA significantly increase the abundance of Ilyonectria;Ginsenoside Re and notoginseng saponin R₁ significantly increased the abundances of Alternaria.（3）P.notoginseng rhizospheric soil microorganisms can degrade phenolic acids and saponins rapidly.The degradation rate of phenolic acids was ranked as:p-CA>BA>p-HA>VA.The degradation rate of saponins was ranked as:Rd>Rg₁>R₁>Re>Rg₂>Rb₁.Phenolic acids and saponins could change the microbial community structure of P.notoginseng rhizospheric soil and promote the growth of common plant pathogenic fungi,leading to soilborne crop diseases.The interaction between soil microorganisms with phenolic acids and saponins in P.notoginseng rhizospheric was the main factor affecting the rhizospheric microflora of P.notoginseng.The effects of phenolic acids and saponins on mycelial growth and spore germination rate of Fusarium solani and Fusarium equiseti were also studied.The results showed that BA and FA significantly promoted mycelial growth and spore germination of Fusarium solani.Four phenolic acid significantly promoted spore germination of Fusarium equiseti.After 9 days of culture,ginsenoside Rb₁ and notoginsenoside R₁ significantly promoted the mycelial growth of Fusarium solani.Ginsenosides Re and Rg₂ significantly promoted spore germination of Fusarium solani.Notoginseng saponin R₁ significantly promoted spore germination of Fusarium equiseti.