| American ginseng(Panax quinquefolius)has high medicinal value and economic benefit,but the continuous cropping obstacle seriously limits the sustainable development of its industry.For many years,researches on obstacles of continuous cropping of American ginseng(AG)at home and abroad mainly focused on soil changes during the growth period of AG and pathogen infection,but lacked researches on soil restoration in different years after harvest,especially in long-term rotation.Therefore,in this study,the AG cultivated fields which have been restored by rotation for 1,10,and 20 years(A1,A10,A20,respectively)are taken as the research objects,and the farmland soil without AG is taken as the control(CK).The seedling growth of AG planted in different rotation restoration soils is observed,and the soil inorganic and organic nutrients are measured and analyzed,and the soil-microbiota-AG interaction network is constructed by combining metabonomics and microbiomics research.The main contents and results are as follows:(1)Research on the ability of replanting AG in the AG cultivated soil.According to the results of the pot experiment,the survival rate of AG in the AG cultivated soil in group A1 was the lowest(45%),followed by group A10(50%),CK and A20 were 67.5%and 75%,respectively,and there was no significant difference in leaf area,height,aboveground and underground biomass of the surviving plants,which indicated that continuous cropping seriously affected the survival of AG,and the success rate of continuous cropping could be greatly improved after long-term rotation recovery in the AG cultivated soil.(2)Analysis of soil pH and nutrient change.Compared with the control,the soil pH of AG cultivated decreased significantly.It can be restored to a certain extent after20 years of rotation,but it can not be restored to CK level.?Changes of inorganic nutrients.There is no significant difference in the contents of total nitrogen,total phosphorus,alkali-hydrolyzable nitrogen and available phosphorus among different types of soils,which indicates that although soil inorganic nutrients are an important factor affecting the growth of AG,the continuous cropping obstacle is not caused by the shortage of inorganic nutrients.?Changes of organic nutrients.Compared with CK,the contents of 11 amino acids such as histidine decreased significantly and 3amino acids such as aspartic acid increased significantly in A1 soil,and 7 amino acids such as histidine,threonine and serine failed to recover after 20 years of rotation.In A1 soil,the contents of 16 kinds of sugar and sugar alcohol decreased significantly,and after a long rotation,11 kinds of them recovered to a certain extent,while 5 kinds of sugar alcohol,such as n-butanol and Melezitose,were still significantly lower than the control in A20 soil.Organic nutrients,such as amino acids and small molecular sugars,can provide certain nutrient support for the perennial plant AG during the non-growth period from late autumn to early spring.Therefore,it is speculated that the decrease of amino acids,small molecular sugars and sugar alcohols will limit the continuous cropping growth of AG in terms of nutrients,and some nutrients are still difficult to recover after 20 years of rotation,which may be one of the important reasons for the continuous cropping obstacles of AG lasting for decades.(3)Change analysis of soil metabolites.Metabolomics analysis showed that the phenolic acid content decreased significantly in the AG cultivated land,and had a certain persistence after the decrease.Amines such as monoamine,polyamine and amide,pyridine(nicotinamide)and ketone with benzene ring(acetophenone)decreased significantly in the AG cultivated land and were difficult to recover by rotation,while the contents of most fatty acids and pyruvic acid increased significantly in the AG cultivated soils of different restoration years.This metabolite change in the AG cultivated field may be an important reason for hindering the continuous cropping of AG and causing continuous cropping obstacles.(4)Study on the changes of soil metabolic pathways.Compared with CK,a total of 130 metabolic pathways showed significant differences among the three groups,and there are 35 metabolic pathways that are significantly different in the all three groups of AG cultivated ginseng.Among them,two metabolic pathways were up-regulated,namely the prodigiosin biosynthesis and the fatty acid biosynthesis related to dodecanoic acid metabolism.Other 33 metabolic pathways were down-regulated,including glycine,glucose and other amino acids and carbohydrate metabolic pathways.Therefore,the metabolic pathways of allelopathic autotoxic substances fatty acids involved in inhibiting the growth of AG are all up-regulated,while the other metabolic pathways are all down-regulated,which means that the overall metabolism of soil slows down and the soil metabolism changes in a direction unfavorable to the growth of AG.(5)Analysis of changes in soil microbial diversity and community composition.The ? diversity analysis of bacteria,fungi and non-fungi eukaryotes showed that there was no significant difference in richness and diversity among the above three AG cultivated soils groups.The ? diversity analysis showed that there were significant differences between A1 and other groups at genus level,and minority groups such as Sphingomonas,Acremonium and Gymnophrys would not return to CK level after 20 years of rotation.(6)Factor division,construction of network correlation network and screening of continuous cropping obstacle factors.There are 50,8 and 53 potential factors of short-term,mid-term and long-term continuous cropping obstacles in the AG cultivated soils of different restoration years,respectively.It is found that nearly 45.05% of the factors can be quickly recovered during the 1-10 year rotation,and the subsequent recovery speed is slow.The 53 long-term factors could not be recovered by natural rotation within 20 years,which provided the basis for soil property change for the continuous cropping obstacle of AG to exist for more than 20 years.Through correlation analysis and network analysis,it was found that microorganisms did not play a leading role in the interaction of factors of continuous cropping obstacle;Combined with the analysis of structural equation model,it shows that the allelopathy caused by the change of metabolites that are difficult to recover through rotation for a long time is an important reason for the long-term existence of continuous cropping obstacles,and 9 key factors with high correlation are found,which can be used as key elements for subsequent soil improvement of old ginseng.To sum up,this study takes the restoration of AG cultivated soil by long-time series rotation as the research object,analyzes the changes of soil micro-ecological environment by means of multi omics technology,divides the potential factors of short-term,medium-term and long-term continuous cropping obstacles,and proves that nearly half of the potential factors cannot be restored by natural rotation within 20 years,It provides a basis for the change of soil properties that the continuous cropping obstacle of AG can last for more than 20 years.The results of correlation analysis and network analysis showed that biological factors such as microorganisms did not play a leading role in the factor interaction of continuous cropping obstacles;Compared with soil microorganisms,the decline of organic nutrients may be an important factor of continuous cropping obstacles;The allelopathy caused by the changes of metabolites such as pyruvate,fatty acid and amine is an important reason for the long-term existence of continuous cropping obstacle.This study can provide data support and theoretical guidance for the follow-up soil improvement of AG cultivated land and the solution of continuous cropping obstacles of Panax medicinal plants. |
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