Microbial Community Response to Phenolic-Exuding Plants in Hydrocarbon-Contaminated Soil

A greenhouse experiment was designed to test phenolic-exuding horticultural plant species for their phytoremediation potential in soils contaminated with polycyclic aromatic hydrocarbons (PAHs). Species included high-phenolic-exuding plants: Malus sp., Osmanthus fragrans, Sambucus nigra, Castanea pumila, Morus alba, and Myrica cerifera and low-polyphenol-exuding plants: Ziziphus jujube, Ribes aureum, and Cassia fistula. The species were planted in soil amended with benzo[a]pyrene, phenanthrene, and pyrene. After 7 months, nitrogen, phosphorus, and potassium amendments were added each month for three months. Plant roots were harvested; polyphenols were ethanol-extracted and quantified using the Folin-Ciocalteu method. Rhizosphere DNA was extracted, quantified, and the 16S rRNA gene and ITS region were sequenced for bacteria and fungi, respectively. In addition, qPCR was conducted that targeted the 16S rRNA and ITS region of bacteria and fungi, respectively. The highest and lowest concentrations of phenolics were from Sambucus nigra and Ribes aureum, respectively. There were no significant differences between 16S rRNA and ITS abundance among treatments. Sequencing showed a significant difference between the rhizosphere bacterial community compositions on a global level. Specifically, several Actinobacteria were over-represented in the low-phenolic-exuding plants, while high-phenolic-exuding plants were over-represented by several Proteobacteria. There were no significant differences between the fungal populations of treatments and all were dominated by Ascomycota. However, high-phenolic exuders had a higher abundance of Basidiomycota, than the low-phenolic exuders. Results showed that different microbial communities were selected for by high polyphenol-exuding plants and low polyphenol-exuding plants. This selection was more pronounced in bacteria than in fungi. The drastic ways in which bacteria respond to phenolic inputs highlight their importance in phytoremediation.