Abstract: 【Objective】 Experiments were carried out to investigate the autotoxicity of vanillic acid and its effect on seed germination and seedling growth of peanut, so as to reveal the response rules of rhizosphere microbes to the autotoxic substances in peanut growth period.【Method】Peanut (Arachis hypogaea L. cv Fuhua 12 150GY ) was used in this study, and petri dish method, nursery pot and pot culture experiment were adopted to explore the effect of vanillic acid on the peanut seed germination, seedling growth and rhizosphere microflora. Six vanillic acid application treatments in petri dish experiment were set with application of different vanillic acid amounts: 0, 0.01, 0.03, 0.05, 0.07, 0.09 mmol·L^-1, five treatments in nursery pot experiment were 0, 0.01, 0.03, 0.05, 0.07 mmol·L^-1, and five treatments in pot culture experiment were 0, 0.01, 0.03, 0.05, 0.07 mg·kg^-1 dry soil.【Result】(1) The seed germination ratio, germination energy and germination index were lower than CK after treatment with different concentrations of vanillic acid. When the concentration of vanillic acid was 0.09 mmol·L^-1, the seed germination ratio, germination energy and germination index respectively decreased by 39%, 66.3% and 55.9% compared with CK, and the response index (RI) reached the maximum. (2) The root length, plant dry weight, chlorophyll content, net photosynthetic rate and stomatal conductance were lower than CK after treatment with different concentrations of vanillic acid. When the concentration of vanillic acid was 0.07 mmol·L^-1, all above indexes decreased by 37.3%, 40.0%, 19.0%, 53.9% and 49.1%, respectively, compared with CK, and the response index (RI) reached the maximum. Conversely, the intercellular CO₂ concentration was the opposite of the above indexes, it went up with the increase of the concentration of vanillic acid. When the concentration of vanillic acid was 0.07 mmol·L^-1, the intercellular CO₂ concentration increased by 46.1% compared with CK. (3) when the concentration of vanillic acid ≥0.03 mmol·L^-1, the total absorption area, active absorption area and root activity were lower than CK, while the MDA content were higher than CK. When the concentration of vanillic acid was 0.07 mmol·L^-1, all above indexes respectively decreased by 22.4%, 54.2% and 40.6% compared with CK, the MDA content increased by 43.3%. (4) The number of rhizosphere actinomycetes were markedly reduced with the increase of vanillic acid concentration at the early stage of peanut, and the differences between the treatments were not significant at the late stage of peanut. The number of bacteria in different treatments were not significant difference at the early stage of peanut, and it substantially reduced with the increase of vanillic acid concentration at the late stage. A high concentration of vanillic acid (0.07 mg·kg^-1 dry soil) had inhibitory effect on rhizosphere fungal growth, and low concentration of vanillic acid (0.01 mg·kg^-1 dry soil) had a promoting effect of fungal growth. 【Conclusion】 Vanillic acid had a significant autotoxinc-effect, which inhibited the photosynthesis of peanut seedling, reduced the root activity and promoted seedling leaf malondialdehyde. In addition, the number of rhizosphere bacteria and actinomycetes decreased after treated with vanillic acid, indicating that vanillic acid inhibited the growth of rhizosphere bacteria and actinomycetes; while it promoted the growth of rhizosphere fungi at low concentration but inhibited the growth at high concentration.

Key words: vanillic acid, peanut, autotoxic substances, photosynthetic characterization, root activity, microflora