Long-Term\nEffects of Multiwalled Carbon Nanotubes and Graphene on Microbial\nCommunities in Dry Soil

Little\nis known about the long-term effects of engineered carbonaceous nanomaterials\n(ECNMs) on soil microbial communities, especially when compared to\npossible effects of natural or industrial carbonaceous materials.\nTo address these issues, we exposed dry grassland soil for 1 year\nto 1 mg g<sup>–1</sup> of either natural nanostructured material\n(biochar), industrial carbon black, three types of multiwalled carbon\nnanotubes (MWCNTs), or graphene. Soil microbial biomass was assessed\nby substrate induced respiration and by extractable DNA. Bacterial\nand fungal communities were examined by terminal restriction fragment\nlength polymorphism (T-RFLP). Microbial activity was assessed by soil\nbasal respiration. At day 0, there was no treatment effect on soil\nDNA or T-RFLP profiles, indicating negligible interference between\nthe amended materials and the methods for DNA extraction, quantification,\nand community analysis. After a 1-year exposure, compared to the no\namendment control, some treatments reduced soil DNA (e.g., biochar,\nall three MWCNT types, and graphene; <i>P</i> < 0.05)\nand altered bacterial communities (e.g., biochar, carbon black, narrow\nMWCNTs, and graphene); however, there were no significant differences\nacross the amended treatments. These findings suggest that ECNMs may\nmoderately affect dry soil microbial communities but that the effects\nare similar to those from natural and industrial carbonaceous materials,\neven after 1-year exposure.