Study On The Mechanism Of Exogenous Phenolic Acids On Beta Grape Plant Growth And Rhizosphere Soil Microbes

Autotoxicity and soil biotoic factor were the key reasons for the occurence of grape replant disease. In order to study on the mechanism of grape autotoxins, phenolic acids on soil microbes,’Beta’(Vriparia×V.labrusca cv.), one of the most common rootstock in China, were used in the present study with pot experiment under rain-shelter cultivation, and exogenous 4-hydroxybenzoic acid (4-HBA) or salicylic acid (SA) was added into soil without or with Beta grape cuttings planted. Changes of phenolic acids and soil microbes were determined. And then, model of phenolic acids on soil microbes was analyzed by comparing the differences in these two groups. Biotransformation of 4-HBA and the specific microbial groups that are involved in the metabolism of 4-HBA in the Beta grape rhizosphere soil environment was identified in a bid to explicit the mechanism of phenolic acids on soil microbes. The major results were as follows.1. Exogenous 4-HBA or SA caused shifts in the growth of Beta grape cuttings and phenolic acids in root exudates.4-HBA or SA promoted the growth of Beta grape cuttings at lower concentrations, but inhibited at higher levels. The growth of Beta grape cuttings was promoted at 0.5 mg·g-1 4-HBA or 0.25 and 0.5 mg·g-1 salicylic acid treatment, but inhibited at 1.0 and 2.0mg·g-1 4-HBA or 1.0,1.5 and 2.0 mg·g-1 SA treatment. The Beta grape root secreted more 4-HBA under exogenous 4-HBA treatment, but secreted less SA under exogenous SA treatment.2. Content of 4-HBA or SA in soil decreased under 4-HBA or SA treatment.4-HBA and SA in Beta grape rhizosphere soil was higher than that in soil without Beta grape planted. The results showed that root exudates increased the content of 4-HBA and SA in soil. However, the content of 4-HBA or SA in Beta grape rhizosphere soil was lower than that in soil without Beta grape planted under exogenous 4-HBA or SA treatment. The results showed that exogenous 4-HBA or SA may affect the root exudates characteristics, soil microbial community and function, and then, indirectly caused shifts in 4-HBA or SA content in soil.3. Exogenous 4-HBA or SA could be adsorbed by soil and degraded by soil microbes. At 72 h after treating, residual dose of 4-HBA was about 0.003%-0.09% of exogenous adding 4-HBA dose and SA was about 5.4%-23.5% of exogenous adding SA dose.4.4-HBA could be biotransformed into dimers. A new [M-H]-(m/z=273.039181) signal was found in the Beta grape rhizosphere soil treated with 4-HBA at 6 h after incubation (m/z=273.039181), and the new signal was still found until 68 h after incubation.5. Exogenous 4-HBA or SA caused shifts in the soil bacterial and fungal community structures and soil microbial functional diversity. And the shifts differed between the two designated groups. Compared to treatments in soil without Beta grape planted, lmg·g-1 and 2 mg·g-1 of 4-HBA treatments resulted in a greater decrease in the average diversity of the bacterial community diversity in soil with Beta grape planted, but a greater increase in the average diversity of the fungal community in soil with Beta grape planted. However, the bacterial and fungal community diversities increased at 0.5 mg·g-1 of 4-HBA. Comparing the treatments in two groups, the application of SA to the soil make the soil bacterial community diversity higher in soil with Beta grape planted but soil fungal community diversity higher in in soil without Beta grape planted.6. The results showed that the microorganisms responsible for 4-HBA transformation in Beta grape rhizosphere soil were identified with DNA-stable isotope probing combined with high-throughput sequencing. In all,14 phylotypes, i.e., Methylibium, Lysobacter, Methylophilaceae_uncultured, Blastococcus, Legionella, Methylophilus, Arthrobacter, Azoarcus, Azotobacter, Cupriavidus, Novosphingobium, Pseudomonas, Ramlibacter and Vogesella were identified in the 4-HBA-treated soil. Of these, species belonging to genera Arthrobacter, Azotobacter, Azoarcus, Pseudomonas, Novosphingobium, Vogesella, Lysobacter, and Methylophilaceae might also affect soil N availability.7. The results showed that the dominant fungi with the ability of phenolic acid resistance were isolated and identified in the study. In the exogenous 4-HBA treatment, five strains of fungi were selected and sequences analysis showed that they were Alternaria tenuissima, Penicillium sp., Cunninghamella elegans, Trichoderma harzianum and Penicillium chrysogenum, respectively. In the exogenous SA treatment, five strains of fungi were selected and sequences analysis showed that they were Alternaria tenuissima, Trichoderma, Penicillium, Fusarium oxysporum and Mucor circinelloides, respectively. Among them, Alternaria tenuissima showed the highest metabolic efficiency, and had a significant inhibitive effect on Beta grape plant growth. The Beta grape plant height, stem diameter and fresh weight were decreased by 14.92%,2.76% and 16.82%, respectively.