The Response Of Soil Microbial Community And Environmental Factors To The Growth Process Of American Ginseng

American ginseng(Panax quinquefolium)is a perennial medicinal herb of Araliaceae,Panax.Its whole plant(especially root)has many medical and health functions.It is a famous medicinal and food homologous plant,which is quite popular in the market.However American ginseng faces serious continuous cropping obstacles in the process of cultivation,which restricts the sustainable development of American ginseng industry.To clarify the causes and mechanisms of continuous cropping obstacles of American ginseng is the key problem to be studied in depth.To solve this problem,we first need to understand and grasp the regularity,mechanism and interaction of soil microorganisms and soil physical and chemical environmental factors during the normal growth of American ginseng,which is also the scientific problem to be explored in this study.The study was carried out in the "2+2" cultivation mode area of American ginseng in Liuba,Shaanxi Province,the soils of annual(A),biennial(B),triennial(C),quadrennial(D)and harvested(G)of American ginseng in the same plot were taken as the different treatments,and the neighboring soils(F)that never been cultivated were taken as the control.High-throughput sequencing,Chloroform fumigation extraction capacity analysis and Conventional soil physical and chemical analysis were used to determine soil microbial community,soil microbial biomass carbon(MBC),soil nutrients and enzyme activities.The changes of soil microbial composition and structure,major species groups,soil nutrients(including MBC),soil enzymes and the relationship between soil microbial community and soil environmental factors during the cultivation of American ginseng were studied by mathematical statistics and multivariate analysis of measured datas.To explore the process and regularity of soil environment change during the growing process of American ginseng,and the relationship between this change of continuous cropping obstacles of American ginseng.The main findings are as follows:1.The results of High-throughput sequencing.Six groups of 18 soil samples obtained total of 105,680,2 effective bacterial tags and 1,439,688 effective fungal tags.An effective sequence with a similarity of more than 97%was defined as an operational taxonomic unit(OTU),and bacterial OTU was 32,224,fungal OTU was 9054.Species annotation and classification after screening low OTU content,the bacteria belong to 25 phylums,75 classes,115 orders,202 families,337 genera and 248 species.The fungal belong to 11 phylums,28 classes,57 orders,110 families,161 genera and 139 species.2.Effects of cultivation of American ginseng on soil bacterial community.① The thermal graph clustering and PCoA analysis showed that according to the composition of the bacterial community OTU,the six groups of soils can be clearly divided into four categories,unplanted American ginseng(F),planted one year(A-C),planted two years(B-D)and harvested(G)soil.② The variance analysis showed that compared with the soil non-cultivated ginseng,the Shannon-wiener index of soil bacterial community in harvested was significantly lower(P<0.05).Compared with the soil non-cultivated ginseng,the abundances of 7 phylums and 16 genera of bacteria changed significantly in harvested soil(P<0.05),including Acidobacteria,Actinobacteria,Gemmatimonadetes,Chloroflexi,Nitrospirae,Verrucomicrobia and Saccharibacteria of bacterial phylum,as well as Sphingomonas,uncultured bacterium f Gmmatimonadaceae,Luteibacter,Pseudomonas,uncultured bacterium f Nitrosomonadaceae,Rhodanobacter,Gemmatimonas,RB41,H16,Bryobacter,uncultured bacterium f Chitinophagaceae,uncultured bacterium f 0319-6A21,Candidatus solibacter,uncultured bacterium c KD-496,uncultured bacterium p Saccharibacteria and uncultured Acidobacteria bacterium of bacterial genus.3.Effects of cultivation of American ginseng on soil fungal community① The thermal graph clustering and PCoA analysis showed that according to the OTU composition of the fungal community,the soil division results of the six groups of plots were completely consistent with the results of the bacterial community division.② The variance analysis showed that compared with the soil non-cultivated ginseng,the Shannon-wiener index of soil fungi in the harvested increased,but did not reach a significant level(P>0.05).Compared with the soil non-cultivated ginseng,the abundances of 2 phylums and 14 genera of fungi changed significantly in harvested soil(P<0.05),including Ascomycota,Basidiomycota of fungal phylum,as well as Subulicystidium、Guehomyces、Tetracladium,Hypomyces,Botrytis,Cladosporium,Plectosphaerella,Geomyces,Metarhizium,Penicillium,Atractospora,Verticillium,Lecanicillium and Cyslofilobasidium of fungal genus.4.Effects of cultivation of American ginseng on soil environmental factors.The variance analysis showed that the growth of American ginseng resulted in significant changes in soil MBC,pH,total nitrogen,total phosphorus,available phosphorus,ammonium nitrogen and TOC content,as well as catalase,urease,invertase and alkaline phosphatase(P<0.05).Compared with the soil non-cultivated ginseng,the pH,MBC,total nitrogen,TOC content,catalase,urease and invertase activities of the harvested American ginseng were significantly lower(P<0.05),while the active of alkaline phosphatase and available phosphorus content increased significantly(P<0.05).The soil comprehensive fertility decreased significantly P<0.05).5.Relationship between soil microbial communities and environmental factors during cultivation of American ginseng① Monte Cario permntation text showed that 9 of the 11 soil environmental factors tested had significant effects on the composition and structure of soil bacterial community during the cultivation of American ginseng(P<0,05).The order of influence was ammonium nitrogen>pH>TOC>catalase>alkaline phosphatase>invertase>urease>available phosphorus>MBC.11 soil environmental factors all had effects on the soil during the cultivation of American ginseng.The composition and structure of fungi community changed significantly(P<0.05).The order of influence was ammonium nitrogen>TOC>pH>invertase>catalase>alkaline phosphatase>urease>available phosphorus>MBC>total phosphorus>total nitrogen.②RDA ordination charts of fungi,bacterial communities and environmental factors showed that soil TOC and ammonium nitrogen contributed the most to the first ordination axis,soil urease contributed the most to the second ordination axis.The distribution positions of soil microbial communities in annual and triennial were similar to biennial and quadrennial on the second axis,and there were significant differences on the first axis.The distribution positions of soil microbial communities between non-cultivated ginseng and harvested were similar on the first axis and different on the second axis.③The correlation analysis showed that during the growth of American ginseng,soil bacterial community diversity was significantly positively correlated with soil pH,invertase,urease,MBC and TOC(P<0.05),and negatively correlated with ammonium nitrogen(P<0.05).There was a significant negative correlation between fungal diversity and soil pH(P<0.05),and a significant positive correlation with soil ammonium nitrogen(P<0.05).④ The multivariate regression analysis showed that soil pH,ammonium nitrogen,total nitrogen,catalase,urease and alkaline phosphatase have a great influence on the abundance of bacterial community species in the soil of American ginseng.Soil total nitrogen,total phosphorus,ammonium nitrogen,pH,catalase and urease have a great influence on the abundance of the fungal community species of American ginseng.In summary,cultivation of American ginseng would lead to corresponding changes in soil microbial community structure,diversity,main species and soil environmental factors.And soil microbial communities and soil environmental factors are interrelated.Soil microbial species and quantities in soil environment may be affected by microbial growth and propagation,migration and diffusion,intra-species interaction,and may also be affected by changes in soil environmental factors.Normal soil ecological relationships and properties may be affected by changes in soil microbial community structure and environmental factors,which may further affect the normal growth and harvest of American ginseng.The continuous cropping obstacle of American ginseng is caused by the cultivation of American ginseng and only occurs for American ginseng or its related plants,so the continuous cropping obstacle of American ginseng is the result of the comprehensive action of many factors such as American ginseng itself,soil microbial community and soil physical and chemical environmental factors.