Root-associated Microbiotas And Its Functional Characteristics Of Licorice In Northwest Region

Soil microbiotas were diverse and closely related to plant growth and development.Root-associated microbiotas mainly originated from soil and were affected by host plants and various environmental factors.However,the distribution,functional characteristics and environmental responses of the root-associated microbiotas of the medicinal plant licorice were still not clear,which impeded us from promoting the licorice plant growth and accumulation of root secondary metabolites by regulating the microbiotas.In the study,the different licorice plant ecotypes and the distribution of corresponding root-associated microbiotas in different regions of northwest China were investigated,and the regulation of root secondary metabolites by root-associated microbiotas under the influence of various factors was also elucidated;the temporal succession patterns of root-associated core bacterial communities among different growing years of licorice and the influence of environmental factors were studied.Combined with network analyses,the specificity of root-associated microbial foodwebs and its regulation of root secondary metabolites between different licorice species were studied.Meanwhile,aiming at the continuous cropping obstacle of licorice in original production area,the response of rhizobacterias to allelochemicals and its alleviating effect on allelopathy were investigated by adding exogenous allelochemicals,metagenomic sequencing,isolation of strains and potted inoculation experiments.The results were as follows:First,the plant community was clearly differentiated into five ecotypes and was primarily driven by geographic distance and soil available nitrogen based on genotyping-by-sequencing and analyses.The microbial community compositions of bulk soil,rhizosphere soil and endosphere were significantly different among distinct plant ecotypes.The results of variation partitioning analysis showed that environmental,geographical and plant factors had different effects on root-associated microbiotas,and the environmental factors accounted most for the variation in rhizosphere fungal community.Furthermore,licorice root secondary metabolites were complicatedly modulated by multiple abiotic and biotic factors;and were mostly explained by these factors in the rhizosphere model.These results indicated that environment–plant–microbiotas interactions commonly affected the root secondary metabolites.Second,the alpha-diversity of root-associated bacterial communities decreased from the bulk and rhizosphere soils to endosphere compartment,and the community composition was strongly clustered in the rhizosphere.The core-enriched taxa were various among different sampling compartments and growing years of licorice based on differential enrichment analyses,and differently core-enriched taxa displayed varied time–decay relationships.Temporal variations in soil characteristics and root secondary metabolites were distinct.Moreover,soil total potassium as a key factor was significantly correlated with root secondary metabolites and individual core-enriched taxa in the bulk and rhizosphere soils.Third,the soil protistan communities had lower alpha diversity compared with fungal and bacterial communities,but had higher stochastic processes and varied compositions among cultivated and wild licorice root-associated microbiotas.Based on the structural equation models,the single fungal and bacterial community played an important role in the regulation of root secondary metabolites,while the protistan community alone could not regulate the secondary metabolites under distinct control of variously dominated edaphic properties.The rhizosphere soil and wild licorice correspondingly had complicated networks,and the specific responsive modules from the networks had significantly positive correlations with root secondary metabolites and were mostly affected by edaphic properties.Moreover,these responsive modules directly or indirectly regulated the root secondary metabolites to varying degrees with the presence of soil protists,which closely involved the potential interactions between different groups of microorganisms.Finally,the effects of allelopathic autotoxic substances on the growth and rhizosphere microbial community of licorice were simulated by addition of exogenous glycyrrhizin in pot experiment,it was found that the exogenous glycyrrhizin inhibited licorice development,as well specifically reshaped and enriched some rhizobacterias and functions related to glycyrrhizin degradation.Moreover,Novosphingobium genus accounted for a relatively high proportion of enriched taxa and appeared in metagenomic assembly genomes.Through specific enrichment culture and purification,four strains with ability of glycyrrhizin degradation were isolated.Synthetic community were constructed based on their genomic features and their glycyrrhizin degradation efficiency.After inoculation experiment,it was found that distinct inoculants had different colonization capacities and glycyrrhizin degradation efficiencies in rhizosphere soil for alleviating the allelopathy of licorice.Notably,the single replenished N(Novosphingobium resinovorum)inoculant had the strongest alleviating effect on the allelopathy of licorice seedlings,and it was stronger than synthetic inoculants.Overall,this study revealed the differences in the distributions of root-associated microbiotas among different licorice plant ecotypes,growing years and species,as well as the specificity of its responses to external environment and regulation patterns of root secondary metabolites in licorice.Different groups of root-associated microbiotas variously contributed to the microbial foodwebs,but they jointly regulated root secondary metabolites.It was also found and verified that the specially enriched rhizobacterias had an obvious alleviating effect on licorice allelopathic autotoxicity.These results provided theoretical guidance for the selection of cultivation plots and field management measures in the future,and provided an experimental reference for solving the problem of continuous cropping obstacles of medicinal plants by using special functional rhizobacterias.