| Fritillaria taipaiensis P.Y.Li is a perennial herbaceous medicinal plant of the genus Fritillaria in the family Liliaceae.Its dried bulbs are used as medicine for lung moistening,asthma calming,cough suppressing,expectorant and anti-inflammatory.F.taipaiensis was widely used as medicine resources in traditional Chinese medicine,which resulted in its wild resources being depleted and could not meet the market demand.Now it is now widely cultivated in Chongqing,Yunnan,Shaanxi and Sichuan area in order to increase its yield.Succession cropping obstacle and frequent diseases during long-term continuous cultivation of F.taipaiensis,leading to a decrease in yield and quality,which seriously reduces the benefit of F.taipaiensis production.Rhizosphere soil microbes are closely related to the stability of the rhizosphere microenvironment and crop growth by promoting soil material transformation,plant nutrient uptaking and disease resistance.So it is important to understand the role of rhizosphere microbes for nutrient management and disease control in F.taipaiensis.However,little is known about rhizosphere microorganisms in cultivated F.taipaiensis.In this thesis,the rhizosphere soil in different growth years(1,2,3 and 4 years),cultivation modes(greenhouse and field),growth periods(period of dormancy,emergence,vigorous growing and sprout tumble)and health states(healthy and diseased)of F.taipaiensis base of Chongqing Academy of Chinese Materia Medicine in Wuxi County,Chongqing were collected.Then the 16 S r RNA gene and ITS were sequenced to determine the structural composition of the bacterial and fungal communities.Soil physicochemical properties and four soil enzyme activities were also measured.The composition and distribution characteristics of rhizosphere soil microbes of F.taipaiensis were analyzed,and the roles of rhizosphere microbes in soil material transformation,plant nutrient uptake as well as the mechanisms of soil-borne diseases were further explored.The results are as follows:1.The α-diversity index(Chao1,Shannon,Pielou and PD whole tree)of fungal community was significantly reduced(P<0.05),while not significantly changed for bacterial community in soil after 4 years of continuous cultivational F.taipaiensis.Analysis of community composition showed that the abundance of bacterial such as Rhodanobacter,Streptomyces,Bacillus,Pseudomonas,Aeromicrobium and Burkholderia,were relatively higher in the 1st and 3rd years soil than in the 2nd and 4th years.The abundance of Fusarium was highest in the 3rd year at 5.78%(P<0.05).In addition,the abundance of fungi such as Alternaria,Verticillium and Colletotrichum were decreased with increasing years of cultivation.Further functional predictions showed that the abundance of bacteria with chitinolysis was decreased with increasing cultivation years.The abundance of saprophytic and symbiotic fungi were higher in the2 nd and 4th years soil than in the 1st and 3rd years(P<0.05).Assembly of bacterial and fungal communities were influenced by variable selection,dispersal limitation and undominated processes.2.The soil p H was between 4.98-6.71 in both greenhouse and field F.taipaiensis cultivation treatments.The soil p H,available potassium content,sucrase and catalase activity were higher in greenhouse cultivation than field cultivation,which were increased with 18%,39%,115% and 22% respectively(P<0.05).Additionally the Shannon,Pielou and Chao1 indices of bacterial and fungal communities were also significantly higher in Greenhouse cultivation soil than in field cultivation(P<0.05).The abundance of Candidatus＿Solibacter and Nitrospira in greenhouse soil were 1.56 and 3.99 times of field soil,respectively(P<0.05).The abundance of Pseudolabrys and Rhodanobacter in field cultivation soil were 2.67 and 9.05 times in greenhouse soil(P<0.05).The abundance of bacterial functional groups associated with nitrogen cycling and mycorrhizal fungi such as ectomycorrhizae were higher in greenhouse cultivation soil than field soil(P<0.05),while the abundance of bacterial functional groups such as chemoheterotroph and fermenter were more higher in field cultivation soil than in(P<0.05).NRI and NTI values for interspecific phylogenetic distances of bacterial and fungal communities in greenhouse cultivation soil were higher than in field soil.In both management modes,the assembly process of the bacterial communities was dominated by variable selection processes,while the fungal communities had the highest contribution from the influence of undominated processes.There was no significant difference in topological characteristics of the fungal and bacterial networks between cultivation treatments.Mantel analysis showed that p H was the main factor influencing the structure of soil bacterial and fungal communities.3.In the rhizosphere soil of F.taipaiensis at different growth periods of greenhouse and field cultivation,soil p H,organic matter and total nitrogen content all show a gradual decrease.Botryotinia was more abundant in the vigorous growing stage of F.taipaiensis under greenhouse cultivation,significantly higher than in other growth periods(P<0.05).Further functional predictions also showed that the abundance of plant pathogen fungi was 37.76% in the greenhouse cultivation,significantly higher than in other growth periods(P<0.05);the abundance of bacterial functional groups such as nitrate respiration and nitrogen respiration decreased in the sprout tumble stage,while the aromatic compound degradation functional group increased in the sprout tumble stage.The process of assembly of bacterial communities changed from variable selection to dispersal limitation in greenhouse cultivation,while no major change were observed in field cultivation and the contribution of variable selection was maintained at50%;the assembly of fungal communities were mainly influenced by undominated processes.The period of dormancy had the lowest average clustering coefficient and the vigorous growing stage had the highest network density and average path length of the bacterial networks constructed,and there were more key OTUs belonging to Candidatus＿Solibacter.The average clustering coefficient was lower for period of dormancy and sprout tumble,and the network density was higher for the period of emergence and vigorous growing stage of the fungal networks constructed,and there were more key OTUs belonging to Mortierella.4.In rhizosphere siol of healthy and diseased F.taipaiensis during the vigorous growing stage,the contents of organic matter,total nitrogen and available nitrogen,and the activities of urease,sucrase and acid phosphatase,as well as the Shannon and Pielou indices of the bacterial community and the Chao1 and PD whole tree indices of the fungal community in health were significantly higher than those in disease(P<0.05).Bacteria such as Candidatus＿Solibacter and Lysobacter,as well as fungi such as Mortierella,Aspergillus and Cladosporium were significantly higher in health than in disease(P<0.05).The abundance of functional groups of bacteria associated with chitinolysis and sulphur respiration were also significantly higher in health than in disease(P<0.05).Community construction analysis showed that the NTI value for interspecific phylogenetic distances of bacterial and fungal communities was higher in health than in disease(P<0.05),and the variable selection contributed more to the assembly of fungal communities in disease than in health.A higher proportion of negative correlations,lower average clustering coefficient and more key connecting nodes in the bacterial and fungal networks of health compared to disease;compared to the microbial network of disease,the key OTUs belonging to Aquisphaera,Haliangium,Bradyrhizobium and Mesorhizobium of the bacterial network,as well as the key OTUs belonging to Trichoderma and Exophiala,were unique to health.In rhizosphere siol of diseased F.taipaiensis during growth periods(period of emergence,vigorous growing and sprout tumble),soil enzyme activities such as urease,catalase and acid phosphatase increased to the highest at sprout tumble period(P<0.05).Chao1 and PD whole tree indices of bacterial and fungal communities increased at sprout tumble stage(P<0.05).The abundance of Candidatus＿Solibacter and Bradyrhizobium were lowest in the vigorous period(P<0.05),while Fusarium was highest in the sprout tumble period(P<0.05)than other growth periods.Further functional predictions also indicate that plant pathogen fungi were higher in the period of vigorous and sprout tumble than in the emergence period(P<0.05).The process of bacterial community assembly in the rhizosphere soil of diseased F.taipaiensis changed from a variable selection to dispersal limitation,while no major changes were observed in fungal communities and mainly influenced by undominated processes,as the growth period changed. |
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