Differential effects of carbon nanotube and graphene on the tomato rhizosphere microbiome

Application of carbonaceous nanomaterials (CNMs) to the soil-plant system can affect plant physiology, with positive results ranging from enhanced seed germination and root system development to improved stress tolerance. The underlying mechanisms are not fully understood. Plant rhizosphere microbiomes at the soil-root interface are strongly influenced by the host plant and play a key role in the plant hosts development and health. Yet few studies have characterized changes in plant rhizosphere microbiomes following applications of CNMs to the soil-plant system. Here we investigated the effects of multi-walled carbon nanotube (CNT) and graphene on microbial communities in the ectorhizosphere of tomato plants versus surrounding bulk soil. Pot experiments were conducted where tomato plants were exposed to CNT or graphene at 200 mg/kg soil for four weeks. Ectorhizosphere and bulk soils were then collected and analyzed for physicochemical properties and microbiome structure and function. While graphene had a limited impact on the tomato rhizosphere microbiome, CNT significantly increased microbial alpha diversity, induced greater divergence of beta diversity, enhanced microbial interactions, and potentially impacted community functions such as aromatic compound degradation, antioxidant synthesis, and redox cofactor biosynthesis. Furthermore, CNT induced stronger and/or unique microbiome alterations in the tomato rhizosphere compared to bulk soil. Our findings reveal the differential modulating effects of two widely-used CNMs on plant rhizosphere microbiomes and highlight an imminent need to understand complex plant root-microbe interplays in the CNM-impacted rhizosphere. These results have implication for realizing the full potential of phytoapplication of CNMs toward improved and sustainable plant production.