| Continuous cropping obstacles seriously affect the yield peanut(Arachis hypogaea L.)and restrict the sustainable development of peanut industry in China.The allelopathy of phenolic acids secreted by peanut roots to soil microorganisms and their growth is one of the main factors that cause peanut continuous cropping obstacles.Intercropping with reasonable crops can alleviate continuous cropping obstacles,and it is a safe,effective and ecological method.Suitable maize(Zea mays L.)//peanut can alleviate the peanut continuous cropping obstacle to a certain extent.In order to clarify the mechanism of maize-peanut intercropping alleviating peanut continuous cropping obstacle,Luhua 11 and Zhengdan 958 were used as experimental materials and peanut continuous cropping was used as control.In the plot where peanut has been planted for 10 years in Juxian County of Rizhao,we set up the intercropping patterns of maize and peanut(M2P4),3:3(M3P3),3:4(M3P4)and 4:4(M4P4)by adjusting the width,proportion and spacing of the intercropping zones of maize and peanut,and studied the effects of maize-peanut intercropping on the soil micro ecological environment and root exudates of peanut(phenolic acid)characteristics,soil physical and chemical properties and peanut yield.Through collecting maize root exudates,through a simulated culture experiment,further studied the effect mechanism of corn root exudates on the allelopathy of continuous cropping of peanut phenolic acids.The main results are as follows:1.Effects of maize-peanut intercropping on growth,yield and quality of peanutMaize-peanut intercropping significantly increased the height of main stem and the length of lateral branches,decreased the number of branches,and the border row had a greater impact;During flowering and pegging stage the dry matter weight per plant of peanut was higher than that of continuous cropping,but it was lower than that of continuous cropping peanuts during pod setting stage,pod filling stage and harvest period,and the border row was lower than that of inner row.Maize-peanut intercropping significantly reduced the number of rotten fruits per plant in peanut,and the pod yield per unit area increased by an average of 2.58%?6.46%compared to continuous cropping peanuts.The intercropping modes M2P4,M3P3,and M3P4all have certain intercropping advantages(LER>1),and M3P4 is the best,the average LER for two years is 1.12.2.Effects of maize-peanut intercropping on the phenolic acids in the rhizosphere soil of peanutMaize-peanut intercropping changed the type and content of root exudates.The results showed that caffeic acid was not detected in the rhizosphere soil of four intercropping models compared with continuous peanut in the pegging stage;In the period of flowering and pegging stage and pod setting stage,the contents of ferulic acid,benzoic acid,p-hydroxybenzoic acid,p-coumaric acid,caffeic acid,phthalic acid,cinnamic acid and vanillic acid in the intercropping peanut rhizosphere were significantly lower during the flowering stage and pod setting stage,and the decline in interaction rows was larger,which was an average decrease of36.14%,32.17%,33.33%,50.10%,66.40%,41.41%,38.34%,and 17.71%,respectively.Rotation planting of maize belt and peanut belt is beneficial to reduce the content of phenolic acids in the rhizosphere soil of inner row peanut.3.Effects of maize-peanut intercropping on chemical properties of rhizosphere soil of peanutMaize-peanut intercropping increased the activities of soil enzymes(UE,ACP,SC,CAT and?-GC)and the contents of soil nutrients(AN,AP,AK and AI)in peanut rhizosphere.In different sampling periods,the effects of maize-peanut intercropping on the chemical properties of peanut rhizosphere soil were as follows:FP>PS>PF>HS;the effects on peanut rhizosphere soil in different positions were as follows:border row>inner row.The more rows of intercropping maize,the greater the increase of enzyme activity in peanut rhizosphere soil.The M3P3,M3P4 and M4P4 of intercropping mode were higher than those of M2P4,but there was no significant difference between the effective nutrient content of peanut rhizosphere soil under different intercropping modes.Rotation planting of maize belt and peanut belt could increase the soil enzyme activity,AN,AP and AK in the middle row peanut rhizosphere to a certain extent,but had little effect on the AI.4.Effect of maize-peanut intercropping on soil microorganism in peanut RhizosphereMaize-peanut intercropping increased soil microbial biomass(MBC,MBN)and microbial activity in peanut rhizosphere during flowering and pegging stage,pod setting stage,pod filling stage and harvest period,with the largest increase in flowering and pegging stage;the effects on soil microbial biomass and microbial activity in peanut rhizosphere were as follows:border row>inner row;Rotation planting of corn belt and peanut was beneficial to increase soil microbial biomass and microbial activity in inner row.Maize-peanut intercropping increases the abundance of fungi and bacteria in the peanut rhizosphere soil.Phenolic acids are negatively correlated with the Shannon,ACE and Chao indexes of bacteria and fungi,but there are certain differences in the degree of response of different types of phenolic acids to microbial diversity:phthalic acid,benzoic acid and cinnamic acid were significantly negatively correlated with bacterial diversity;ferulic acid and caffeic acid were significantly negatively correlated with fungal diversity;P-hydroxybenzoic acid,p-coumaric acid and vanillic acid were significantly negatively correlated with fungal and bacterial diversity.The abundance of Alternaria in the rhizosphere soil of the intercropping peanut is significantly lower than that of continuous cropping,which is the main pathogen of peanut fruit rot;Both Mortierellales and Motierella of the intercropping peanuts at the pegging stage showed an increasing trend,both of which could form mycorrhizal symbiota with plant roots;But sphingomonas in the rhizosphere soil of intercropping peanuts is significantly higher than that of continuous cropping peanuts,which is a rich new type of microbial resources that can be used for aromatic compounds(phenolic acid)biodegradation.Different bacterial genera and fungal genera have a certain correlation with soil microbial biomass,microbial activity,soil enzyme activity,nutrient content and other indicators,and their correlation tends to be opposite to the content of phenolic acids.5.MRE alleviate allelopathy of phenolic acids in continuous cropping peanut soilMRE can alleviate the allelopathy of phenolic acids(cinnamic acid,phthalic acid,p-hydroxybenzoic acid mass ratio 4:10:7)to the soil micro-ecological environment to a certain extent.Compared with the treatment with phenolic acids,all indexes of soil treated with maize root exudates were increased;MRE significantly reduced the allelopathy index of low-concentration phenolic acids on soil indicators,and the allelopathy index of soil microbial biomass(MBC,MBN),microbial activity,enzyme activity and nutrient content decreased by an average of 27.06%,26.61%,30.51%and 24.49%respectively.The effects of phenolic acids and maize root exudates on the soil micro-ecological environment have a certain time effect:the allelopathy of phenolic acids tends to increase first and then weaken,while the influence of MRE on the allelopathy of phenolic acids gradually weakened.6.Interaction between MRE and phenolic acids on peanut seed germination and pathogenic bacteriaTwo concentrations(0.75 mmol·L-1,1.5 mmol·L-1)of cinnamic acid,phthalic acid,p-hydroxybenzoic acid and a mixture of three phenolic acids(cinnamic acid,phthalic acid,p-hydroxybenzoic acid the mass ratio of benzoic acid is 1:1:1),which inhibits the growth of peanut germs.The allelopathy effect of the mixture of three phenolic acids is the strongest,and the higher the concentration,the stronger the inhibition effect.MRE promote the growth of peanut germs,reduce the inhibitory effect of phenolic acids on peanut germs,and have a greater effect on the allelopathy of low concentration(0.75 mmol·L-1)phenolic acid treatments.Phenolic acids all inhibited the growth of peanut root rot Fusarium colonies,and there was a certain concentration effect;High concentrations of p-hydroxybenzoic acid and a mixture of three kinds of the substance having a phenolic acid treatment promoted the growth of anthrax.MRE can inhibit the growth of two pathogens.Adding MRE increases the allelopathy of phenolic acids on peanut root rot Fusarium anthracis and anthracnose,and reduces the phenolic acids on peanut anthracnose positive effect.Maize-peanut intercropping can reduce the types and contents of phenolic acids in peanut rhizosphere soil by increasing the microbial diversity,microbial activity of peanut rhizosphere soil,and changing certain microbial populations,etc.,thereby alleviating its activity on soil microorganisms,enzyme activity and nutrient content,reduce soil-borne diseases,thereby alleviating peanut continuous cropping obstacles;MRE inhibit the growth of peanut root rot Fusarium anthracis and anthrax,and also play an important role in alleviating the allelopathy of phenolic acids on the soil micro-ecological environment and autotoxicity to peanuts;The intercropping modes M3P4 is the best intercropping mode that is most conducive to alleviating the obstacles of continuous cropping of peanut and ensuring economic benefits. |
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