When nanoparticle and microbes meet: The effect of multi-walled carbon nanotubes on microbial community and nutrient cycling in hyperaccumulator system

Carbon nanotubes can potentially stimulate phytoremediation of heavy metal contaminated soil by promoting plant biomass and root growth. Yet, the regulating mechanism of carbon nanotubes on the rhizosphere micro-environment and their potential ecological risks remain poorly characterized. The purpose of this study was to systematically evaluate the effects of multi-walled carbon nanotubes (MCNT) on the diversity and structure of rhizosphere soil bacterial and fungal communities, as well as soil enzyme activities and nutrients, in Solanum nigrum L. (S. nigrum)-soil system. Here, S. nigrum were cultivated in heavy metal(loid)s contaminated soils applied with MCNT (100, 500, and 1000 mg kg-1 by concentration, none MCNT addition as control) for 60 days. Our results demonstrated more significant urease, sucrase, and acid phosphatase activities in MCNT than in control soils, which benefit to promoting plant growth. Also, there were significant reductions in available ni-trogen and available potassium contents with the treatment of MCNT, while the organic carbon and available phosphorus were not affected by MCNT application. Notably, the alpha diversity of bacterial and fungal com-munities in the MCNT treatments did not significantly vary relative to control. However, the soil microbial taxonomic compositions were changed under the application of MCNT. Compared to the control, MCNT appli-cation increased the relative abundances of the Micrococcaceae family, Solirubrobacteraceae family, and Con-exibacter genus, which were positively correlated with plant growth. In addition, the non-metric multidimensional scaling (NMDS) analysis revealed that the community structure of bacterial and fungal com-munities did not significantly change among all the treatments, and bacterial community structure was signif-icantly correlated with soil organic carbon. At the same time, sucrase activity had the highest relation to fungal community structure. This study highlighted soil microbes have strong resistance and adaptation ability to carbon nanotubes with existence of plants, and revealed linkage between the rhizosphere microenvironment and plant growth, which well improved our understanding of carbon nanotubes in heavy metal phytoremediation.

Automated summary

The study demonstrated that the application of MCNT increased soil enzyme activities that promote plant growth, but resulted in reductions in available nitrogen and potassium contents. Although the taxonomic compositions of soil microbes were altered by MCNT, the diversity of bacterial and fungal communities did not significantly change. The study also revealed a correlation between microbial community structure and soil organic carbon content, indicating the strong resistance and adaptation ability of soil microbes to carbon nanotubes in the presence of plants.