Effects Of Aqueous Extract Of American Ginseng On Soil Microbial Community, Nutrient And Enzyme Activities

American ginseng(Panax quinquefoium)is a perennial medicinal herb belonging to the family of Araliaceae,Panax.It is a valuable traditional Chinese medicine and health care product,and usually rooted in medicine,therefore it played an important role in treatment and health care and was cherished and favored in the market by people.However,the problem of continuous cropping obstacle in the process of American ginseng has long plagued the agriculture and restricted the sustainable development of the industry.Studies have shown that the growth of medicinal plants will produce some allelochemicals in the soil environment,continuous cropping obstacles and the emergence of allelochemicals in the soil are closely related.In order to understand and solve the problem of continuous cropping obstacle of American ginseng,this study was to extract the water soluble matter in the soil under the influence of American ginseng to deal with the "new soil"(the soil adjacent to the American ginseng).We measured soil microbial community structure and diversity,soil microbial biomass carbon(MBC),soil nutrient and the change of soil enzymes after soil water treatment with different age and different concentration were determined by using terminal restriction fragment length polymorphism(T-RFLP),chloroform fumigation extraction-capacity analysis and conventional method.Finally,the data were analyzed by multivariate statistical methods.Based on the cultivation mode of American ginseng "2 + 2"(That is to say,the seedlings were grown for two years after transplanting,and then transplanted in third years.After transplanting,American ginseng continued to grow for about two years)in Liuba County of Shaanxi Province,the effects of water-soluble substances on the soil environment were studied from the aspects of cultivation of American ginseng,continuous growth for two years,age of participants and concentration of soil water extract.And to lay the foundation for revealing the causes and the mechanism of the synergistic barrier of American ginseng.The main results are as follows:1.The effects of aqueous extract of American ginseng on soil microbial community.① In general,the aqueous extract of American ginseng decreased the diversity of soil bacteria and fungi community.② Compared with the annual ones,the biennial soil water extract increased the diversity of the bacterial community,decreased the diversity of the fungal community,and the composition of the bacteria and fungi community changed greatly;compared with the third year,the four-year-old soil water extract brought the diversity of bacteria and fungal communities decreased,and the structural changes of bacteria and fungi were smaller.③ Compared with the annual,three years old soil water extract increased the diversity of the bacterial community,but the diversity of the fungal community did not change significantly,and the composition of the bacteria and fungi community changed greatly.④ The concentration of water extract had significant effect on bacterial community diversity,has no significant effect on fungal communities;and with the change of concentration,the structure and composition of soil bacterial community changed little,but the composition and structure of fungal community changed greatly.2.The effects of water extract from American ginseng on soil microbial biomass carbon in new soils.① The water extract of American ginseng can promote the increase of soil MBC content.② Compared with annual,biennial soil water extract makes the new soil MBC content increased significantly;but four years old compared with the three years,the change is not significant.③ Compared with the annual,three years old soil water extract significantly increased the soil MBC content.④ The concentration of water extract had a extremely significant effect on the content of MBC in new soil.The different concentrations of water extract increased the content of MBC in new soil,and the higher the concentration,the stronger the effect.3.The effects of water extracts from American ginseng on soil nutrients in new soil.① The water extracts of American ginseng increased the content of total nitrogen,ammonium nitrogen,organic carbon and pH,decreased the content of available phosphorus,and improved the soil fertility generally.② Compared with annual,the biennial soil water extracts significantly reduced the total nitrogen and available phosphorus content,significantly increased the content of organic carbon and pH,and decreased soil fertility;compared with the triennial ones,four years old soil water extracts significantly increased the total nitrogen,total phosphorus,ammonium nitrogen,available phosphorus and organic carbon the content,but significantly decreased the pH,increase soil fertility.③Compared with the annual,triennial soil water extract significantly reduced the content of total nitrogen and available phosphorus,significantly increased the content of ammonium nitrogen and pH,and decreased the soil fertility.④ The change of water extracts concentration had significant effect on soil total nitrogen,pH value and soil fertility.4.The effects of water extracts from American ginseng on soil enzyme activities in new soil.① The water extracts of American ginseng decreased the activity of catalase,urease and alkaline phosphatase in the soil,and increased the activity of invertase.②the activity of alkaline phosphatase invertase;compared with the the triennial soil water extracts,four years old extracts significantly increased the activity of invertase enzyme and catalase,urease activity decreased siCompared with the annual soil water extracts,biennial extracts significantly decreased gnificantly.③ Compared with the annual soil water extracts,the triennial extracts reduced the activity of catalase significantly,increased the activity of alkaline phosphatase significantly.④ The concentration of water extracts had a significant effect on the invertase activity,and the higher the concentration,the stronger the enhancement effect.5.The effects of soil water extracts from American ginseng on the relationship between soil microbial communities and environmental factors in new soil.① The NMDS ordination and environmental factors fitting results further proved that American ginseng soil water extracts changed bacterial and fungal community structure;bacterial and fungal community similarity character bureau is determined by the composition of species,but at the same time,it is significantly related to the complex changes of different environmental factors.②)In the two years of continuous growth of American ginseng,soil water extracts can cause different changes in the composition and structure of bacterial and fungal communities.And this change is significantly related to the complex changes of some environmental factors.③ The soil water extracts of different ages can also cause different changes in the composition and structure of bacteria and fungal communities.The difference between the annual and three years of treatment is also reflected in the complex changes of environmental factors.It can be concluded that the water soluble substances in the soil of American ginseng can significantly change the structure and diversity of microbial community,and change the MBC,nutrients and enzyme activities of soil.Based on past experience and relevant research results,it is clear that this change is not conducive to the growth of American ginseng.Continuous cropping obstacle of American ginseng is likely to be along the growth of American ginseng → the release of substances in the soil→causing negative changes in the soil environment→ not conducive to the growth of American ginseng.