| Platycodon grandiflorum is a frequently used medicinal plant.It possess various values such as edible and medicinal values as well as ornamental value.P.grandiflorum is a typical continuous cropping obstacle.When P.grandiflorum is continuously cultivated for two years,its yield is reduced by 20%;when the continuous cropping P.grandiflorum for five years,its yield reduced up to 80%,and accompanied with severely diseases as well as high occurrence of pests.In order to alleviate the continuous cropping obsetacles of P.grandiflorum,we explored the cultivation pattern of P.grandiflorum intercropped with Allium fistulosum,and acquired satisfactory results.The intercropping association of P.grandiflorum with A.fistulosum increased the contents of soil available nitrogen and phosphorus,the activity of soil alkaline phosphatase and polyphenol oxidase,enhanced the ration of soil bacterial and fungal ratio.In this experiment,we tried to explore the mechanism of association of P.grandiflorum with A.fistulosum to alleviate the continous cropping obstacle of P.grandiflorum.Root exudates of P.grandiflorum and A.fistulosum were analyzed by GC-MS technique;The structure of soil microflora was determined by high-throughput Illumina Miseq platform sequencing.Metabolomics method was used to identify and analyze the metabolites of the P.grandiflorum.It is expected to clarify the alleviation mechanism of the association of P.grandiflorum intercropped with A.fistulosum from the levels of physiological perspective root exudates and rhizosphere microflora.The experiments were conducted in the Chinese Medicine Botanical Garden in Shandong Agricultural University in 2018.The experiment consisted of single P.grandiflorum cultivation,single A.fistulosum cultivation and the intercropping of P.grandiflorum with A.fistulosum according the ratio of 5:2,4:2 and 3:2.In order to simplify,they were denoted as SJG,SDC,IIJC32,IJC42,IJC52.The main findings are as follows:1.A total of 39 compounds were identified the root exudates of P.grandiflorum and A.fistulosum in all cultivation patterns.Of all compounds,the structure were identified as 4 kinds of benzenes,18 kinds of alkanes,3 kinds of fatty acids,3 kinds of amines,2 kinds of phenols,2kinds of alcohols,2 kinds of sulfur compounds,and 5 kinds of other compounds.19 compounds were shared P.grandiflorum and A.fistulosum in all cultivation patterns.The relatively percentages of the19 compounds were arranged as follow:[6-(1,1-methylenebis-(4-methyl-6-tert-butylphenol),N,N-Dimethyldodecamide,n-trihexadecane,2,4-3methyl-1,2-dihydroquino-line,2,4-tert-butylphenol,an alkane compound,octadecyl acetate,dibenzylamine,Methyl palmitate,eicosane,?-sitosterol,tetradecane,benzothiazole,rock saponin,trimethyldodecane,squalene,2-methylthiobenzothiazole,2,4-dimethyl heptane,dodecamethylcyclohexasiloxane.Except for ntrihexadecane,the relative content of the remaining compounds in 19 compounds is higher than that of P.grandiflorum and A.fistulosum,which is higher than that in the single planting of P.grandiflorum and A.fistulosum.The secretory function of the roots of P.grandiflorum increased root secretions.The intercropping of P.grandiflorum and A.fistulosum increased the total content of root exudates,benzothiophene,2-methylthiobenzothiazole,dodecamethylcyclohexasiloxane and horns.The content of beneficial sensitizing substances such as squalene increased significantly,indicating that intercropping of P.grandiflorum and A.fistulosum increased the release of beneficial allelochemicals,which was beneficial to killing soil pathogens and maintaining soil micro-ecological balance.2.The data obtained by Illumina MiSeq high-throughput sequencing was classified at 97%similarity level.Species annotation was performed on the representative sequence of OTU.All soil bacteria were annotated to 45 phylums and 659 genus,1425 species(species).A total of 45bacterial gates were detected in all treated soil samples,including the relative abundance of Acidobacteria,Proteobacteria,and Chloroflexi>10%.The bacteria of these three bacteria gates dominated the rhizosphere bacterial community structure.The soil fungi is divided into 11species at the level of the eumycota,The first dominant eumycota is Ascomycota,the relative abundance varied from 85.50%to 90.49%,and the second dominant eumycota is Basidiomycota(Basidiomycete),accounting for 5.91%-7.30%.3.The intercropping of P.grandiflorum and A.fistulosum significantly changed root metabolites of P.grandiflorum.The most common metabolites of IJC32 were 734 species,of which 685 metabolites were down-regulated and 49 were up-regulated,of which 142metabolites were annotated into 39 metabolic pathways.,There were 612 differential metabolites in IJC42,532 metabolites of which were down-regulated,and 80 metabolites were up-regulated.Similarly,362 different metabolites were found in IJC52 intercropping,196 metabolites of which were up-regulated and 166 were down-regulated.Tyrosine metabolism,Riboflavin metabolism,Methane metabolism,Aminoacyl-tRNA biosynthesis,Cysteine and methionine metabolism(cysteine and methionine metabolism),Ubiquinone and other terpenoid-quinone biosynthesis,Stilbenoid,diarylheptanoid and gingerol biosynthesis(synthesis of stilbene,diarylheptanol and gingerol),Galactose metabolism(glutathione metabolism),Sulfur metabolism,Porphyrin and chlorophyll metabolism,morphine and sucrose metabolism,Inositol phosphate metabolism,Diterpenoid biosynthesis(Biosynthesis of biosynthesis),Biosynthesis of unsaturated fatty acids,Flavonoid biosynthesis,Phenylpropanoid biosynthesis,Ami Noacyl-tRNA biosynthesis(aminoacyl biosynthesis)is a common differential metabolic pathway for P.grandiflorum and/or A.fistulosum.4.The intercropping of P.grandiflorum and/or A.fistulosum increased the activities of SOC,POD and CAT of P.grandiflorum significantly,and decreased the content of malondialdehyde.The malondialdehyde content inIJC52intercropping was the lowest,only 2.4nmol·g-1,indicating that the intercropping of P.grandiflorum with A.fistulosum can alleviate the continuous cropping obstacle of P.grandiflorum.this suggested that the intercropping of P.grandiflorum with A.fistulosum is suitable to alleviate continuous cropping obstacles of P.grandiflorum.5.The yield of P.grandiflorum was 3351.15 kg/hm~2,suggesting the intercropping of P.grandiflorum with A.fistulosum significantly increased the yield of P.grandiflorum.The highest yield of IJC32 was 5319.19 kg/hm~2,which was 58.73%higher than that of the single cropping of P.grandiflorum.there were no significant difference existed in the yield of P.grandiflorum among different intercropping association of P.grandiflorum with A.fistulosum.Considering the incropping of IJC52 decreased the lateral root number,it is satisfactory intercropping pattern.6 P.grandiflorum could be used as medicine and food.Soluble sugar is an important edible index of P.grandiflorum.Platycodon-D,total phenol and flavonoids are the indicators for measuring the quality of P.grandiflorum.Different intercropping patterns had significant effects on soluble sugar of P.grandiflorum.The highest content of sobluble sugar was found in IJC32intercropping system,470.23 mg/g,followed by IJC42,which was 463.07 mg/g.There was no significant difference between IJC52 and SJG in the content of soluble sugar.This indicated that the intercropping effect on soluble sugar content of P.grandiflorum is significant.The effect of intercropping on the contents of platycodin-D,total phenols and flavonoids was similar.The intercropping pattern of IJC32 and IJC42 reduced the content of flavonoids and total phenols.The contents of flavonoids and total phenols in IJC52 intercropping pattern was higher than in single cultivation of P.grandiflorum.The content of platycodin-D in the intercropping patterns was lower than in single cultivation of P.grandiflorum,and the highest content was found in the intercropping of IJC52,8.47 mg/g.Considering the yield and quality of P.grandiflorum,The intercropping pattern,the five row P.grandiflorum intercropped with two row A.fistulosum was the optimum intercropping pattern.Intercropping of P.grandiflorum with A.fistulosum significantly increased the yield of A.fistulosum,which was increased from 12.89%to 17.21%Among them,IJC52 had the highest yield,10080 kg/hm~2,and IJC32 had the lowest.Conclusion:The intercropping of P.grandiflorum with A.fistulosum increased the content of beneficial root secretions of P.grandiflorum.Sulfur-containing compounds inhibited the growth of pathogenic bacteria in soils,promoted the growth of beneficial bacteria,reduced the overall microbial abundance,weakened the physiology of the roots of the P.grandiflorum,and thus changed Metabolism level of roots of Platycodon grandiflorum... |
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