Study On The Effect Of Exogenous 4-Hydroxybenzoic Acid On The Nitrogen Metabolism Of Rhizosphere Soil And Grapevine Seedlings

Grapes was the third largest fruit tree species in the world.The cultivation had a long history,and the planting area was widely distributed,and had high value of yield and output value.With the fast development of grape industry,the problem of replant disease had becomed more serious,and 4-HBA was one of autotoxins that cause replant disease in grapes.Previous studies had found that 4-HBA can affect soil nitrogen metabolism,but the specific mechanism of action was not clear.Based on the previous study in this experiment,the seedlings of Beta grape（V.riparia×V.labrusca cv.Beta）were used for test materials,which were planted in potting soil after 16 d of 4-HBA treatment.The effects of autotoxins 4-HBA on soil N content,N transformation efficiency and soil microbial community structure and function were studied and the changes of N content,N metabolism-related enzymes and gene expression levels in grape were determined.Finally,the mechanism of effect of self-toxic substances on plant N metabolism by changing soil N content in rhizosphere of grape was revealed.The main results of the study were as follows:1.When exogenous 4-HBA was added to NH（high nitrogen）soil for 16 d,the content of soil nitrogen was changed.With the increase of 4-HBA concentration,the content of NH₄⁺-N showed an increasing trend,and the content of NO₃^--N first increased and then decreased.Grape seedlings were planted in the soil after 4-HBA added for 16 days.High concentrations（2mg/g）of 4-HBA increased the NH₄⁺-N content in the grape rhizosphere soil,while the NO₃^--N content decreased.The grape autotoxins 4-HBA can reduce nitrification rate of nitrogen in the soil,and improved the immobilization rate and ammonification rate of NH₄⁺and NO₃^-.2.Grapevine seedlings were growed in the soil which added middle and high level of4-HBA for 16 days showed a decreasing trend of NO₃^--N content and an increasing trend of NH₄⁺-N content in roots after growing 15d.With the increase of 4-HBA level,the activities of NR,Ni R,GS,GOGAT and the expression levels of NR,NIR,NADH-GOGAT and Fd-GOGAT,GS_1-1,GS_1-2,GS₂genes in roots and leaves first increased and then decreased.GDH activity and GDH gene expression level decreased with the increase of 4-HBA level in roots,but increased first and then decreased in leaves.3.When exogenous 4-HBA was added to NH（high nitrogen）soil for 16 d,soil microbial community structure had changed.The abundance of Proteobacteria,Acidobacteria in bacteria significantly increased,and Actinobacteria significantly decreased.The archaea Thaumarchaeota significantly increased in low level（NHB）and decreased in high level（NHD）.The abundance of Ascomycota in fungi had decreased,while the abundance of Basidiomycota significantly increased.4.When exogenous 4-HBA was applied to NH（high nitrogen）soil for 16 days,the expression levels of microbial functional genes related to nitrogen cycling were changed.The three level of 4-HBA decreased the expression level of nxr A（nitrite oxidoreductase）gene of nitrification to a certain extent and the high level treatment decreased the gene abundance of nxr B（nitrite oxidoreductase）In nitrate assimilation into ammonium process,the low and middle level treatments significantly reduced the expression level of NR gene.Both middle and high concentration treatments significantly reduced the expression level of nas B（nitrate reductase）gene,three treatments significantly decreased the expression level of the NIT-6gene.