| Continuous cropping disturbs the balance between the microbes beneficial to plant and pathogenic microorganisms in rhizosphere soil,which have a direct and indirect adverse effect on soil and plant health.It is of great significance to study the mechanism of continuous cropping obstacle and to looking for a reasonable rotation mode to solve the problem of continuous cropping.In this study,we studied the microbial community structure and diversity of the rhizosphere soil under continuous cropping 1,3,6 years by pyrosequencing approach,compare to bulk soil,using Astragalus Mongholicus as experimental material.The dynamics of soil microbial quantity and enzyme activity,and the effects of continuous cropping obstacles on the pathogenesis of root rot,growth and quality of A.Mongholicus were analyzed.Reasonable crop rotation schema,which can play a role in alleviating the continuous cropping obstacle of A.Mongholicus was conducted a preliminary study.The results show that:1.At the end of A.Mongholicus growth,the increase of continuous cropping time resulted in the reduction of the relative abundance(RA)of Solirubrobacterales,RA of Rhizobiales,Burkholderiales,which were related to nodule formation,and Myxococcales,Xanthomonadales increased continuously,and Pseudomonas,Lysobacter related to disease was large more.In high incidence period of disease,the RA of pathogens was higher in the rhizosphere soil of A.Mongholicus continuous cropping 6 years.The results indicating that continuous cropping break the balance of soil beneficial bacteria and pathogens in rhizosphere soil of A.Mongholicus,which caused the rhizosphere soil microecological imbalance.2.The community structure and dominant flora of bacteria,fungi were affected by the continuous cropping years,sampling period and rhizosphere or not,which were more significantly affected the bacteria.Continuous cropping A.Mongholicus rhizosphere soil bacteria,fungal diversity decreased,fungal diversity and richness decreased in the growth period.The bacterial abundance of rhizosphere soil decreased in continuous cropping 6 years during the growth period.The more continuous cropping years were,the more unfavorable to the microbial diversity of rhizosphere soil.3.The increase of continuous cropping years resulted in decreased of bacteria and decreased of fungi amount in A.Mongholicus rhizosphere soil,the same with soil urease and invertase activity,while the cellulase activity was increased.During the growth of A.Mongholicus,the number of bacteria and actinomycetes increased,fungi is the opposite,while the soil urease activity increased,sucrase activity increased first and then decreased,and cellulase activity fluctuated.The composition,quantity of soil microorganisms and enzyme activities in the rhizosphere of A.Mongholicus were changed by continuous cropping,which had a negative effect on the rhizosphere soil health.4.A.Mongholicus under continuous cropping has a high incidence of root rot.The growth rate slow down and the biomass decreased.Continuous cropping 6 years is harmful to the accumulation of calycosin-7-O-?-glycoside,calycosin and formononetin.Continuous cropping increased the incidence of root rot,and inhibited growth and quality formation of A.Mongholicus were shown.5.Among the treatments of A.Mongholicus rotation with Solanum tuberosum,Avena nuda,Brassica napus,A.Mongholicus-Avena nuda-A.Mongholicus could improve the activity of acid phosphatase and urease in.rhizosphere soil of A.Mongholicus,the incidence of severe root rot was reduced,the root-shoot ratio of A.Mongholicus was increased,the content of calycosin-7-O-?-glycoside and ononin improved.That is,rotation with Avena nuda is conducive to improving the normal growth and development of A.Mongholicus and soil health,which is more suitable for alleviating the continuous cropping obstacle of A.Mongholicus. |
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