Effects Of Different Continuous Cropping Years On Soil Microbial Community Structure And Physical And Chemical Characteristics In The Rhizosphere Soil Of Codonopsis Pilosula

Codonopsis pilosula(Franch.)Nannf.is widely cultivated in China because of its high medicinal value.With the increase in the number of years of cultivation of Codonopsis pilosula,the problem of succession barrier of Codonopsis pilosula has become increasingly prominent,which has seriously affected the sustainable development of the Codonopsis pilosula industry,and there are few studies on the succession barrier of Codonopsis pilosula,therefore,it is crucial to elucidate the specific causes of the succession barrier of Codonopsis pilosula for the development of the Codonopsis pilosula industry.In this study,the effects of continuous crop on the interroot soil physicochemical properties,soil microbial community characteristics and soil metabolic mechanisms were analysed in plots that had been left fallow for 5 years before planting Codonopsis pilosula as a control,and Codonopsis pilosula planted fields that had been under continuous crop for 1,2,3 and 4 years,to investigate the response of inter-root soil physicochemical properties and microbial community characteristics to the number of years of continuous crop.This study was conducted to provide a theoretical basis for mitigating the barriers to continuous cropping of Codonopsis pilosula.The main results of this study are as follows:1.The incidence of root rot of Codonopsis pilosula increased significantly with the increase of years of continuous crop.In this paper,the pathogens of root rot of Codonopsis pilosula in the main production areas of Weiyuan County,Gansu Province were mainly Fusarium oxysporum,Fusarium avenaceum and Fusarium foetens,with Fusarium oxysporum being the dominant causal agent of root rot of Codonopsis pilosula.The mycelium of the different pathogens is highly adaptable to environmental factors and is able to use a variety of carbon and nitrogen sources.In addition,different pathogens are able to produce a variety of cell wall degrading enzymes during the infestation process,among which polygalacturonase(PG)enzymes are more active and are potential pathogenic factors for root rot of Codonopsis pilosula.2.With the increase in the number of years of continuous crop,the p H of the interroot soil of Codonopsis pilosula showed a tendency to decrease,while the content of salts,total nitrogen,total phosphorus and organic carbon in the soil showed an increasing trend.The activities of cellulase and alkaline phosphatase in the soil decreased significantly with increasing years of continuous crop,while the enzymatic activities of peroxidase and acid phosphatase increased significantly with increasing years of continuous crop.In addition,there was a correlation between soil enzyme activity and soil physicochemical properties,with soil catalase and acid phosphatase being the main enzymes affecting soil physicochemical properties.3.With the increase in the number of years of continuous crop,the carbon to nitrogen ratio of soil microbial biomass in the inter-root zone of Codonopsis pilosula increased significantly,and the soil respiration entropy and soil microbial entropy decreased significantly.The abundance and diversity of bacterial communities decreased,the abundance and diversity of fungal communities increased,and harmful microorganisms accumulated in the soil,leading to a decrease in the stability of microbial communities.Soil total nitrogen,fast-acting potassium,microbial biomass carbon to nitrogen ratio,soil respiration entropy,electrical conductivity,microbial biomass carbon,soil alkaline phosphatase,acid phosphatase and urease were the main factors affecting the soil bacterial community,while soil total nitrogen,fast-acting potassium,soil respiration entropy,alkaline phosphatase,neutral phosphatase and sucrase were the main factors affecting the fungal community.4.A total of 98 metabolites,mainly lipids,acids,sugars,phenols,alcohols,others,esters,amines,aldehydes,ketones and organic acids,were detected from all inter-root soil samples of Codonopsis pilosula.Of these,47 were differential metabolites.The levels of acids,phenols,amines and sugars in the soil all increased significantly with the number of years of continuous cropping.Galactose metabolism,fructose and mannose metabolism,biosynthesis of secondary metabolites,ABC transporter protein,purine metabolism,arginine and proline metabolism,biotin metabolism,arginine biosynthesis,starch and sucrose metabolism,inositol phosphate metabolism and metabolic pathways played a dominant role in the metabolic regulation of inter-root soil of Codonopsis pilosula at different years of crop succession.In addition,carbamic acid 1,palmitoleic acid,D-mannitol 2,dl-3,4-dihydroxyphenylglycol and dodecane were the main metabolites affecting the structure and diversity of bacterial communities,whereas carbamic acid 1,palmitoleic acid and dl-3,4-dihydroxyphenylglycol were the main metabolites affecting fungal communities.In conclusion,the deterioration of soil physicochemical properties,the accumulation of phenolic acid metabolites caused by the reduction of microbial metabolic activity and changes in microbial diversity and abundance during the continuous crop of Codonopsis pilosula,leading to a decrease in the stability of the microbial community were the main causes of the disorders of continuous crop of Codonopsis pilosula.