Effects of exposure to carbon nanomaterials on soil microbial communities: A global meta-analysis

Carbon nanomaterials (CNMs) are extensively employed in diverse fields and will inevitably be discharged into the soil to affect the soil microbial community. Numerous related studies have investigated the effects of exposure to CNMs on soil microbial communities, yet a consensus on their effects still needs to be discovered. This study conducted a global meta-analysis by synthesizing 474 pairs of experiments from 20 screened publications in the literature from 2000 to 2022. The findings indicate that: exposure to CNMs significantly reduced microbial biomass carbon (MBC) by 17.02% and increased soil Shannon index by 2.63% (p < 0.05), which had no significant effect on soil microbial community composition and only reduced the proportion of Proteobacteria by 6.83%. The type of CNMs was one of the important influencing factors. The exposure to multi-walled carbon nanotubes (MWCNTs) significantly reduced the soil MBC (p < 0.05). It reduced the proportion of Acidobacteria, Bacteroidetes, and Proteobacteria in soil, which had less effect on soil microbial diversity and was more suitable as a crop growth promoter. The exposure of single-walled carbon nanotubes exhibited a comparable impact on soil microbial biomass as MWCNTs while significantly increasing soil microbial diversity. The exposure of fullerene (C-60) had no significant effect on soil microbial biomass but significantly decreased microbial diversity (p < 0.05). In addition, soil pH, CNMs exposure dose, and exposure time significantly affect the effects of CNMs (p < 0.05). This research recommends that CNMs be used in high pH soil with high electrical charge intensity while avoiding exposure doses exceeding 1000 mg/kg and limiting exposure time to 50-100 days to minimize long-term exposure effects on the soil. MWCNTs are less toxic to microbial communities compared with the other CNMs and are more suitable as crop growth promoters. In conclusion, CNMs show great potential for promoting agricultural production.