The positive role of root decomposition on the bioremediation of organic pollutants contaminated soil: A case study using PCB-9 as a model compound

Root decomposition keeps occurring widely in soils, particularly after plant harvest and death, and drives critical microbial ecological functions. However, its role in the destiny of soil organic pollutants and underlying mechanisms remain unclear. In this study, DNA stable isotope probing (DNA-SIP) was combined with metabolomics to investigate the mechanisms of soil polychlorinated biphenyls (PCBs) degradation in the root decomposition process by identifying the active PCBs degraders in situ and corresponding metabolites. The 2,5dichlorobiphenyl (PCB-9) degradation was improved by 7.4% in the root decomposition treatment relative to the rhizosphere treatment, and the degradation was faster in both treatments than the control after 6-week cultivation. Both root decomposition and rhizosphere treatments altered soil microbial community, changing the active PCB-9 degraders to different extents. The root decomposition treatment had the highest average phylogenetic distance index (ADI) value, indicating a competition reduction effect of root decomposition on microbial survival, and the lowest corrected average phylogenetic distance index (ADIC) value, suggesting a preference toward aerobic PCBs degraders during root decomposition. Metabolites associated with the root decomposition process critically affected both the whole microbial community and active PCB-9 degraders. Compounds related to carbohydrate and lipid metabolisms were enriched during the root decomposition process and might be important to the active PCB-9-degrading community assembly. Our results confirmed that root decomposition improved the biodegradation of organic pollutants in soil and reminded us of its importance in soil quality.

Automated summary

Root decomposition plays a significant role in enhancing the degradation of organic pollutants in soil. This study combined DNA stable isotope probing and metabolomics to investigate the mechanisms of polychlorinated biphenyls (PCBs) degradation during root decomposition. The results showed that root decomposition altered the soil microbial community and influenced the abundance of active PCB-9 degraders. Metabolites associated with carbohydrate and lipid metabolisms were found to critically affect both the whole microbial community and active PCB-9 degraders. This study highlights the importance of root decomposition in improving soil quality and biodegradation of organic pollutants.