| The rhizosphere microbial community plays important roles in plant growth,soil nutrient cycling,and regulation of plant metabolism.Astragalus membranaceus(Fisch.)Bge.var.mongholicus(Bge.)Hsiao(A.mongholicus)is a commonly used medicinal material,and its growth and active ingredient are usually affected by farming methods and management methods.At present,the distribution composition,functional characteristics and influencing factors of A.mongholicus rhizosphere microbial community are not clear,which limits the growth and quality of A.mongholicus by regulating the rhizosphere microbial community.This study centered around the rhizosphere microbial community of A.mongholicus,the diversity and changes of rhizosphere microbial communities under different root parts,crop rotation,intercropping,fertilization and irrigation management were studied which based on high-throughput sequencing and metagenomics technology.The correlation analysis was carried out based on the growth of A.mongholicus,the content of effective ingredients,soil chemical properties and enzyme activities in the field experiment.The change of rhizosphere microbial community under different influence factors and the correlation with the growth and quality of A.mongholicus were analyzed.This study provided a theoretical basis for the formation mechanism of geoherbalism,continuous cropping obstacles and relieving methods,standardized planting and management methods.The results are as follows:1.The plant and soil samples among five main production areas of A.mongholicus were collected.The diversity and association with environmental factors of bacterial communities in different parts(bulk soil,rhizosphere,rhizoplane and endosphere)were compared.The results indicated that the yield and active ingredient content of A.mongholicus in Fengzhen and Wuchuan were higher.The diversity and composition of bacterial communities in various root parts were obviously different,which significantly affected by the geographical location(longitude,latitude),climate factors(mean annual precipitation),soil properties(SOM,AP,TK and AK),season and other factors.The growth and quality of A.mongholicus were influenced by environmental factors and significantly associated with rhizosphere bacterial community diversity.The results indicated that the rhizosphere bacteria were significantly regulated by environmental factors in different origins and regulated the growth and accumulation of active components of A.mongholicus,which is one of the formation mechanisms of geoherbalism.2.The composition,function and differential metabolic pathway of A.mongholicus rhizosphere microbial community under continuous cropping and crop rotation treatment were analyzed based on metagenomics technology.The results found that continuous cropping caused a significant reduction in rhizosphere bacterial community diversity,the abundance of pathogen,such as Rhizoctonia solani,Fusarium oxysporum and Fusarium acuminatum were significantly increased.Root rot was serious,which is the main reason of continuous cropping obstacles.Crop rotation with Avena sativa L.improved the diversity of rhizosphere bacterial communities and the abundance of some beneficial bacteria,which can effectively inhibit the growth of pathogenic bacteria and alleviate the continuous cropping obstacles of A.mongholicus.Continuous cropping reduced the soil nitrogen metabolism function,and crop rotation improved invertase activity in nitrate reduction,nitrification and nitrogen fixation.The enhancement of nitrogen metabolism was beneficial to the root nitrogen fixation of A.mongholicus and alleviating the continuous cropping obstacles.3.The growth,active ingredient content,soil chemical properties,soil enzyme activity and rhizosphere microbial diversity under different intercropping methods were compared in the 2-year field experiment.The results found that A.mongholicus intercropping with Avena sativa L.significantly increased the growth and the content of active ingredients,soil nutrient contents and enzyme activities.Intercropping improved the bacterial community diversity and decreased the rhizosphere fungal community diversity,the abundance of beneficial bacteria,such as Bacillus,Cyanobacteria,Anaerolineaceae and nitrogen-fixing bacteria were increased.Intercropping inhibited the growth of the pathogens,which is a reasonable intercropping method conducive to the growth of A.mongholicus and relieving continuous cropping obstacles.4.The growth,active ingredient content,soil chemical properties,soil enzyme activity and rhizosphere microbial diversity under different proportions of chemical fertilizer and organic fertilizer application were compared in the 2-year field experiment.The results found that 75% chemical fertilizer-25% organic fertilizer application and 50% chemical fertilizer-50% organic fertilizer application significantly increased the growth and the content of active ingredients of A.mongholicus,soil organic matter,total nitrogen content and soil enzyme activity were significantly increased.Fertilization significantly affected the rhizosphere bacterial and fungal community diversity of A.mongholicus,mixed application of chemical fertilizer and organic fertilizer improved the rhizosphere bacterial diversity and the abundance of some beneficial bacteria and nitrogen-fixing bacteria.The abundance of pathogen,such as Rhizoctonia solani and Fusarium were significantly decreased,which is benefit to the growth of A.mongholicus and improve the sustainable utilization of the soil.5.The growth,active ingredient content and rhizosphere bacteria diversity under different irrigation periods and irrigation times were compared in the 2-year field experiment.The results found that irrigation once in July significantly increased the dry weight and root length of A.mongholicus root,the accumulation of calycosin-7-O-β-glucoside and formononetin were increased.The rhizosphere bacterial community diversity was increased,and the abundance of some bacteria that could improve plant stress resistance,such as Verrucomicrobia,Nitrospira and Planctomycetes were increased,which is benefit to the growth of A.mongholicus.The results indicated that delaying the irrigation period and reducing the irrigation times can effectively improve the yield and quality of A.mongholicus.In conclusion,this study explored the formation mechanism of geoherbalism by studying the influencing factors of rhizosphere microbial community of A.mongholicus,and provided a new perspective for environment-plant-microbial community interaction to improve plant growth quality.The reason of A.mongholicus continuous cropping obstacles was studied,and this study proposed that A.mongholicus crop rotation or intercropping with Avena sativa L.was an effective mitigation of continuous cropping obstacles.At the same time,the water and fertilizer management methods conducive to the growth,quality and the sustainable utilization of soil were explored.These findings provided a certain theoretical reference for the selection of suitable planting sites and field management measures for A.mongholicus in the future.These results had a good theoretical innovation and application prospect for the standardized ecological cultivation of high-quality A.mongholicus and promoting the development of A.mongholicus production. |
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