Abstract
Root exudates mediate soil microbiome composition and diversity, which might further influence plant development and health. Vanillic acid from root exudates is usually referred as autotoxin of cucumber, however, how vanillic acid affect soil microbial community diversities and abundances remains unclear. In this study, vanillic acid (VA; 0.02, 0.05, 0.1, and 0.2 μmol g-1 soil) was applied to soil every other day for a total of five applications. We used Illumina MiSeq sequencing, quantitative PCR (qPCR) and PCR-denaturing gradient gel electrophoresis (PCR-DGGE) to test the effects of VA on the total fungi community composition as well as the Trichoderma and Fusarium spp. community abundances and structures in the cucumber rhizosphere. Illumina MiSeq sequencing showed that VA (0.05 μmol g-1 soil) increased the relative abundance of the fungal phylum Basidiomycota while decreasing the relative abundance of Ascomycota (P < 0.05), and not altered the diversity of the soil fungal community. VA (0.05 μmol g-1 soil) also increased the relative abundances of the fungal genera with plant pathogens, such as Conocybe and Spizellomyces spp.(P < 0.05). A qPCR analysis showed that VA (0.05 to 0.2 μmol g-1 soil) exerted promoting effects on Trichoderma spp. community abundance and stimulated Fusarium spp. abundance at low concentrations (0.02 to 0.05 μmol g-1 soil) but inhibited it at high concentrations (0.1 to 0.2 μmol g-1 soil). The PCR-DGGE analysis showed that all concentrations of VA altered the community structures of Trichoderma spp. and that the application of VA (0.02 and 0.05 μmol g-1 soil) changed the band number and the Shannon-Wiener index of the Fusarium spp. community. This study demonstrated that VA changed the total fungal community in the cucumber seedling rhizosphere and that the Trichoderma and Fusarium spp. communities showed different responses to VA.
Highlights
Autotoxicity is an intraspecific allelopathy process through which plants can inhibit their growth or that of their relatives by releasing toxic chemicals into the environment (Huang et al, 2013), as has been observed in both natural and manipulated ecosystems, agroecosystems
The relative abundance of Ascomycota was lower and the relative abundances of Fungi unclassified was higher in vanillic acid-treated soil (0.05) compared with the control soil (P < 0.05) (Supplementary Figure S2A)
Compared with the control treatment, the soil treated with 0.05 μmol g−1 soil vanillic acid (VA) had higher relative abundances of Agricomycetes and Fungi unclassified but a lower relative abundance of Leotiomycetes (P < 0.05) (Figures 1B,C)
Summary
Autotoxicity is an intraspecific allelopathy process through which plants can inhibit their growth or that of their relatives by releasing toxic chemicals into the environment (Huang et al, 2013), as has been observed in both natural and manipulated ecosystems, agroecosystems. Soil microorganisms play an important role in sustaining terrestrial ecosystem processes, and the soil microbial community abundance and diversity are sensitive to fertilization, irrigation, and plant history (Mendes et al, 2011; Bardgett and van der Putten, 2014; Zhou et al, 2017). Recent studies involving in vitro experiments or soil experiments have stressed the effects of phenolic acids, such as ferulic (Zhou and Wu, 2012b), vanillin (Zhou et al, 2018a) and p-coumaric acid (Zhou et al, 2018b), on specific microorganisms or soil microbial communities. Many phenolic acids have been identified as autotoxins from plants, root exudates, and soil (Huang et al, 2013), and the effects of these acids on the microbial communities in soil remains unclear
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