Effects Of Exogenous 4-Hydroxybenzoic Acid On Nitrogen Content And Related Metabolic Microorganisms In Grape Rhizosphere Soil

Grape is one of the main tree species planted in China.Due to the continuous updating of varieties and the limitation of cultivated land area,the problem of replant disease is becoming more and more serious,which seriously affects the healthy and sustainable development of the grape industry.ρ-Hydroxybenzoic acid(4-HBA)is one of the main autotoxins secreted by grape roots.In this study,Beta grape(Beta V.riparia×V.labrusca)seedlings were used as test materials,which were planted in different fertility soils(no fertilization for long-term NK,low nitrogen fertilizer NL,high nitrogen fertilizer NH).The effects of different concentrations of 4-HBA on soil nitrogen content and related microorganisms were studied.The mechanism of self-toxic substances in grape was elucidated from the perspective of 4-HBA→N metabolism-related microorganisms→N content level.The research will further improve the theoretical system of the mechanism of grape replant disease.The main results of the experiment were as follows:1.After exogenous 4-HBA applying to the soil,the growth of Beta grape seedlings was inhibited,and the inhibitory effect was stronger with the increase of treatment concentration.2.After the application of exogenous 4-HBA into the soil,the p H of the soil changed.As the concentration of 4-HBA treatment increasing,the soil p H increased.After adding4-HBA for 31 d,the p H of the 2 mg/g 4-HBA treated NK,NL and NH soils increased by 0.60,0.65 and 0.85,respectively,compared to the 0 mg/g treatment.3.After the application of exogenous 4-HBA into the soil,the content of ammonium nitrogen in the soil increased with the increasing treatment time,while the content of nitrate nitrogen in the soil increased with the increase of treatment concentration.After adding4-HBA for 31 d,the ammonium content of 2 mg/g 4-HBA treated NK,NL and NH soils increased by 5.74 mg/kg,12.20 mg/kg and 13.56 mg/kg,respectively,compared to the 0mg/g treatment.But the nitrate nitrogen content was reduced by 14.19 mg/kg,10.00 mg/kg and 12.72 mg/kg,respectively.The results indicated that 4-HBA could promote the accumulation of ammonium nitrogen in soil and inhibit the conversion of ammonium nitrogen to nitrate nitrogen.4.Exogenous 4-HBA changed the community structure,diversity and abundance of bacteria in the soil.After adding 4-HBA for 16 d,the community diversity and abundance of bacteria in the three soils were significantly reduced.At phylum level,4-HBA promoted theabundances of Proteobacteria and Bacteroidetes in the soil,and inhibited the other dominant bacteria.Proteobacteria in NK,NL And NH soil accounted for 45%,69% and 77%,respectively,which is the main dominant bacteria in the soil.5.Exogenous 4-HBA promoted the growth of Azotobacter,Azospirillum,Paenibacillus,Rhizobium Pseudomonas,Bacillus,Ramlibacter etc.in soil have the function of nitrogen fixation,ammonification or denitrification.And inhibited the growth of Nitrospira of nitrification bacteria.