Study On Differential Changes In The Key Rhizosphere Microorganisms Of Radix Pseudostellariae Continuous Cropping System And Its Appication

Radix pseudostellariae,a perennial tonic medicinal plant,belongs to the family Caryophllaceae having very high medicinal value.However,the phenomenon of continuous cropping retards the plantation of R.pseudostellariae.Consecutive monoculture of this plant in the same field results in serious decline in both yield and quality of underground tubers along with poor plant performance and insufficient resistance for disease and pest,which severely limits production and utilization of medicinal plant resources.Therefore,it's very necessary to explore the action mode and underlying mechanism of consecutive monoculture problems.This study investigated the mechanism of consecutive monoculture problems using kinds of system biology methods from the perspectives of soil microbial ecology.The main results and conclusions are listed as follows:The results from denatured gradient gel electrophoresis(DGGE)analysis of soil fungal community indiacted that consecutive monoculture had a significant impact on rhizospheric microbial community composition and function diversity.The diversity index and evenness index declined with the increasing years of monoculture.Furthermore,the relative abandance of Trichoderma,reported to be antagonistic microorganisms,was significantly lower in monocultured soils than in the newly planted soil.However,the opposite was true for Fusarium.The results from denatured gradient gel electrophoresis(DGGE)analysis of soil Fusarium community indicated that consecutive monoculture had a significant impact on rhizospheric Fusarium community composition.The diversity index and evenness index improved with increasing cropping year.In total,there were five kinds of Fusarium,including Fusarium oxysproum,Fusarium solani,Fusarium asiaticum,Fusarium falciforme and Fusarium foetens.Among them,the content of F.oxysporum increased in consecutively monocultured soils(two-and three-year monoculture soils).Meanwhile,real-time PCR assay confirmed the increase in abundance of F.oxysporum in consecutively monocultured soils as compared to control and newly planted soils,which was consistent with the DGGE results.Based on the results of previous T-RFLP analysis and DGGE analysis in this study,we further isolated some antagonistic and pathogenic microorganisms from the rhizosphere soils.A strain of Fusarium oxysproum harmful to R.pseudostellariae was isolated from rhizosphere soils by using potato dextrose agar(PDA).Two Trichoderma spp.(Trichoderma harzianum and Trichoderma asperellum)and two pseudomonas spp.(361,313)with the antagonistic activities against pathogen were successfully isolated from rhizosphere soils by using selective medium,respectively.Meanwhile,two Burkholderia spp.(P4,P8)were isolated as well.The results from qPCR analysis showed that the relative abundances of three groups of antagonistic microbes declined in soils under consecutive monoculture.However,the amounts of Fusarium increased with the increasing years of monoculture.Therefore,the main reasons for consecutive monoculture problems might be closely related to the decline of probiotics and the increase of pathogens under monoculture regime.Moreover,we found that the phenolic compounds mixture at the rhizosphere soil ratio could significantly promote the mycelial growth of pathogenic F.oxysporum,but inhibited the growth of beneficial Pseudomonas 361,Pseudomonas 313,Burkholderia P4 and Burkholderia P8.It suggested that the phenolic compounds mixture had a negative effect on the growth of beneficial microbes but a positive effect on pathogenic microbes.Furthermore,we found that application of novel bio-organic fertilizer containing antagonistic bacteria could effectively suppress Fusarium wilt and promote the yield of tuberous roots of R.pseudostellariae under monoculture regime.It suggested that the regulation of root microbiomes can be used to alleviate the consecutive monoculture problems of R pseudostellariae.The above-mentioned results showed that consecutive monoculture could lead to the imbalance of soil microecosystem mediated by the mixed phenolic acids exudated from the monocultured medicinal plants.On the contrary,the imbalance of belowground microbial community resulted in the poor growth of monocultured R..pseudostellariae.In conclusion,the decline in the yield of R pseudostellariae under consecutive monoculture might result from(I)the decrease of microorganisms providing beneficial functions because of the selective inhibitory effect of root exudates and(?)the increase of microorganisms with pathogenicity because of the selective promoting effect of root exudates.