| Astragalus is one of the traditional Chinese medicinal materials.In recent years,due to the increasing market demand for Astragalus,the problem of continuous cropping obstacles has become more and more prominent.However,the current researches on continuous cropping obstacles of Astragalus mainly focus on prevention and treatment,and few studies reveal the potential relationship between the causes.In this study,Astragalus mongholicus was taken as the research object,combining pot experiment and incubation experiment,using highthroughput sequencing technology and high performance liquid chromatography-mass spectrometry technology.By exploring the influence of soil microbial diversity on bacterial community composition,PHBA degradation function of bacterial community and growth of Astragalus mongholicus,the relationship between microbial diversity and continuous cropping obstacles of Astragalus mongholicus was revealed.Finally,organic fertilizer was added to improve soil microbial diversity to alleviate continuous cropping obstacles.The main results of this study are as follows:(1)Dilution reduced bacterial diversity,changed the structure of bacterial community,reduced the stability and recovery of bacterial community,and weakened some of the metabolic and degradation functions of bacterial community.The α diversity of bacteria decreased significantly with the increase of inoculated soil suspension dilution,and the bacterial community structure was significantly different with different dilution.At the level of phylum,with the increase of dilution,the relative abundance of Proteobacteria and Bacteroidetes decreased while that of Actinobacteria and Firmicutes increased.At the genus level,the relative abundance of Bacillus and Brevibacillus increased with increasing dilution,while that of Lysobacter and Pseudomonas decreased.Exogenous addition of PHBA significantly reduced the α diversity of undiluted soil bacteria,and also had a significant effect on bacterial community structure.As for the species composition,at the phylum level,the relative abundance of Bacteroidetes and Acidobacteria increased while that of Bacteroidetes and Acidobacteria decreased after the addition of PHBA.The relative abundance of Nocardioides and Pseudomonas increased at the genus level,while the relative abundance of Limnobacter decreased.Lower diversity led in reduced complexity of bacterial interaction networks,reduced network stability,and reduced resilience of bacterial community after PHBA stress.In addition,the decrease of diversity weakened the degradation function of exogenous substances,and the abundance of PHBA degradation gene pca H decreased with decreasing diversity.The decrease of diversity also weakened the metabolic function of the bacterial community.Compared with the control,the cellobiose hydrolase activity of D4 and D6 decreased by 73.49% and 95.15%,the β-1,4-N-acetylglucosaminosidase activity decreased by 80.22% and 73.74%,and the β-1,4-glucosidase activity decreased by 57.65%and 83.64%,respectively.(2)High concentration of PHBA and low microbial diversity inhibited the growth of Astragalus mongholicus,and the synergistic effect of both on Astragalus mongholicus was more significant.When the PHBA concentration reached 300 mg/kg,the chlorophyll content,plant height and aboveground dry weight of Astragalus mongholicus decreased by 32.30%,25.62% and 54.84% compared with the control,respectively.Compared with D0,the aboveground dry weight of D2,D4 and D6 decreased by 22.35%,23.53% and 48.82%,respectively.At D0,the aboveground dry weight of Astragalus mongholicus with PHBA concentration of 150 and 300 mg/kg decreased by 22.35% and 45.88% compared with the control,respectively.When PHBA concentration was 300 mg/kg,the aboveground dry weight of D4 and D6 decreased by 38.26% and 37.77% compared with the control,respectively.Diversity and PHBA had a superimposed effect on the growth of Astragalus mongholicus,that is,the higher the concentration of PHBA,the lower the microbial diversity,and the more obvious the inhibition effect on Astragalus mongholicus.(3)Under natural conditions,a small decrease in microbial diversity had little effect on the PHBA degradation function of the bacterial community.However,under stress conditions,especially drought stress,a small decrease in microbial diversity also significantly weakened the PHBA degradation function of the bacterial community.In the absence of external stress,PHBA in D0 and D2 soil was completely degraded at 2 days.However,under drought stress,the degradation rate of PHBA in D0 soil reached 74.43% in 2d,while that in D2 was only31.62%.(4)Considering the changes of Astragalus mongholicus biomass,soil enzyme activity and bacterial community structure,the addition of 70% fertilizer + organic fertilizer + biochar+ humic acid had a better effect on alleviating continuous cropping obstacles of Astragalus mongholicus,which could increase aboveground biomass of Astragalus mongholicus,promote the accumulation of flavonoids and saponins in roots,and improve the activity of enzymes related to carbon,nitrogen and phosphorus cycle.At the same time,the soil microbial environment was improved.In conclusion,increasing soil microbial diversity can promote bacterial degradation of self-toxic substances in soil,so as to alleviate continuous cropping obstacles and improve the yield and quality of Astragalus mongholicus.This study will provide new ideas for the prevention and control of continuous cropping obstacles in the cultivation of medicinal plants and other plants. |
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