Influence of Artificial Root Exudates and Actual Root Exudates on the Microbial Community in Pyrene-contaminated Soil

Abstract

The high-throughput Illumina NovaSeq sequencing method was adopted to study the effect of artificial root exudates and Lolium perenne L. root exudates on the community structure, α and β diversity, and gene function of the bacterial communities in pyrene-contaminated soils to understand the impact of root exudates on microbial communities. The results showed that root exudates did not significantly change the composition of pyrene-contaminated soil bacterial communities. The main dominant bacterial phyla were Proteobacteria, Actinobacteria, Firmicutes, Bacteroidetes, etc. The main dominant bacterial genera were Sphingomonas, Lactobacillus, Bacillus, etc. Root exudates changed the relative abundance of dominant species to a different extent and resulted in discriminating bacteria. The genus Lachnospiraceae belonging to Proteobacteria and Ruminiclostridium belonging to Firmicutes were the biomarkers in the artificial root exudates group and the actual root exudate group, respectively. The common discriminating bacteria in both root exudate groups compared to those in the control group were polycyclic aromatic hydrocarbon (PAHs)-degrading bacteria. Root exudates selectively promoted the growth of PAHs-degrading bacteria. Root exudates had little effect on the richness and diversity of the bacterial communities in pyrene-contaminated soil. However, they significantly influenced the soil bacterial community structure, which resulted from significant changes in low-abundance species. The bacterial community structures of the two root exudate groups were similar. Root exudates decreased pyrene concentration in the soil by 14.0% (artificial root exudates) and 8.7% (actual root exudates). The promotion of pyrene degradation affected by root exudates was due to the growth promotion of PAHs-degrading bacteria and the significant increase in the abundance of some functional genes. This research can supply data for the exploration of a rhizoremediation mechanism in PAHs-contaminated soils.