Influence of Miscanthus x giganteus and Trifolium repens L. on microflora and PAH-degrading bacteria in contaminated technosol

Purpose Rhizodegradation is the breakdown of organic contaminants such as polycyclic aromatic hydrocarbons (PAHs) using plants and rhizospheric microorganisms. The influence of two phytoremediating plants, Miscanthus x giganteus (M x G) and Trifolium repens L., was studied on a PAH-contaminated technosol composed of soil and sediments. More specifically, microbial density and diversity were studied along with the density of the population of PAH-degrading bacteria. Methods M x G and white clover were tested in mono- and co-culture on the technosol in a mesocosm over 263 days (life cycle of M x G until its senescence). At the beginning and the end of the phytoremediation experiment, microbial density was measured by real-time PCR, targeting bacteria (16S rDNA), fungi (18S rDNA), and PAH-degrading bacteria (PAH-RHD alpha GP). Bacterial and fungal diversity were determined by metagenomic analysis. Results The M x G monoculture appeared to increase bacterial diversity compared to non-planted technosol, in contrast to other planting patterns, while fungal diversity appeared to decrease in the presence of any of the plants. Overall, the plants increased the bacterial density in the technosol, while only white clover and the co-culture increased the fungal density, with the latter having a greater impact. Concerning the degrading bacteria, only the co-culture stimulated the PAH-degrading bacterial population. This is remarkable for the PAH rhizodegradation. Conclusion Even though the co-culture seemed to decrease the microbial diversity in the technosol, this condition was the most interesting with respect to the increase of the bacterial and fungal density as well as the enhancement of the PAH-degrading bacteria in the technosol.

Automated summary

The study revealed that monoculture of Miscanthus x giganteus appeared to increase bacterial diversity in the technosol compared to other planting patterns, while white clover and co-culture increased fungal density, with co-culture having a greater impact. Additionally, only co-culture stimulated the population of PAH-degrading bacteria, showing potential for PAH rhizodegradation.