The Mechanism Of Endophytic Fungus Pseudomonas Sp. To Improve The Micro-ecological Environment Of Continuous Cropping

Peanut(Arachis hypogaea L.)is an economically and nutritionally important crop.Studies showed that the yield of peanut could reduce 10%to 40%if continuous cropping for three years and the time of continuous cropping is longer,the obstacles will be more serious.Soil allelochemical substances accumulation,soil microflora imbalance,soil enzyme activity and nutrient imbalance are four important factors of peanut continuous cropping obstacle.At present,endophytes had been proven to have wide range of ecological functions,and their roles on the improvement of ecological environment were also investigated by many scholars.However,little information about the micro-ecological environment where peanut plants growth,weather it could be changed by applying endophytic fungus and further beneficial to peanut plant growth.Therefore,in this article,on the basis of previous research,we selected an endophytic fungus to further explore its mechanism on alleviating replant obstacles of peanut.Peanut residue in the soil is considered to be an obstacle to peanut replanting.We aimed to understand the effect of applying an endophytic fungus[Phomopsis liquidambari(B3)]on accelerating peanut residue decay,improving the micro-ecological environment in the soil,and alleviating an obstacle to peanut replanting as well as its possible mechanism.We investigated the dynamics of peanut residue decay,phenolic acid concentrations,and enzyme activities during peanut growth in a pot experiment,where peanut residues were added into soil.Results showed that applying endophytic fungus B3(treatment B3+)significantly accelerated the decay of peanut residue at the peanut germination and seedling stages.In addition,the concentrations of p-hydroxybenzoic acid(4-HBA),vanillic acid(VA),and p-coumaric acid(p-CA)in treatment B3+ were significantly greater than those in CK at the germination and seedling stages.In treatment B3+,the activities of laccase,manganese peroxidase,lignin peroxidase,and polyphenol oxidase were all significantly greater than those in CK at the corresponding peanut growth period,and peanut pod yield increased by 19.9%,compared with CK.Increases in activities of soil enzymes,which were associated with decay of peanut residues in treatment B3+,should be beneficial to decay of peanut residues and accelerate conversion of harmful phenolic acid allelochemicals.A real-time quantitative polymerase chain reaction technique was used to monitor dynamics of endophytic fungus B3 during peanut growth.The above results suggested that promoting the rapid degradation of peanut residues and regulating dynamics of phenolic acids should be important mechanisms for B3 to alleviate obstacles in peanut replanting.Therefore,the aims of this study were further to study endophytic fungus B3,whether it could degrade composite phenolic acids in liquid culture and soil,in addition,the metabolic dynamics and pathways have also been investigated during degradation of single phenolic acid in liquid culture.On the other hand,the effects of artificially inoculated B3 into continuous soil containing phenolic acids,on Fusarium oxysporum f.sp Niveum(F.oxysporum)growth as well as been evaluated.The fungal metabolic pathways of phenolic acids were investigated by high performance liquid chromatography-mass spectrometry(HPLC-MS)and spectrographic analysis technique.The results showed that B3 could significant degrade composite phenolic acids in liquid culture and soil with a short time.Results also showed that vanillic acid was demethylated to protocatechuic acid,and p-Cumaric acid was first decarboxylated to 4-HBA,and then hydroxylated to protocatechuic acid.Metabolic products analysis indicated that protocatechuic acid was a common product during degradation of various phenolic acids,and then protocatechuic acid 3.4-dioxygenase play an important role to further degradation of protocatechuic acid.Besides,inoculation of B3 could significantly decreased composite phenolic acid concentration and F.oxysporum population in continuous soil,and contributed to improving soil sickness.The results showed that endophytic fungus B3 had a potential function to alleviate continuous cropping obstacles of peanut.It is necessary to further investigate the feasibility of alleviating replant obstacles of peanut by inoculating B3 and evaluate its effect.Therefore,in this article,the effect of intercropping Atractylodes lancea which inoculated endophytic fungus B3 on peanut microbial communities in rhizosphere and phyllosphere was investigated.Meanwhile,the utilization efficiency of mineral nutrition by peanut plants,peanut quality and yield as affected by intercropping system were evaluated as well.The results showed that the microbial communities were significantly affected,especially from flowering to podding stages,the abundance and diversity index of rhizosphere and phyllosphere bacteria community structures were much higher than monoculture,but reversed for rhizosphere fungi.After harvest,single row pod yield of intercropping plot increased by 44.1%,soil available N content decreased,soil available K and available P(phosphorus)content were higher than monoculture,the accumulation of total N,P and K(potassium)in peanut straw and peanut quality significantly increased.In addition,the strengthen inoculation and colonization of endophytic fungus B3 in A.lancea foliage ensured that the uniformity of different medicinal plants,on the other hand,A.lancea could also served as the source that endophytic microbial constantly release into the surrounding environment.In a word,the abundance and diversity of rhizosphere and phyllosphere bacteria communities increased in this intercropping system,rather than fungi,were positively correlated with peanut yield and quality,soil micro ecological environment and mineral nutrition transfer.In conclusion,endophytic fungus B3 had an important role on alleviating continuous cropping obstacles of peanut.The toxicity of allelochemical decreased,the utilization efficiency of mineral nutrition increased,and the micro-ecological environment of peanut plants improved might be associated closely with alleviating replant obstacles of peanut.