Carbon nanotubes as fertilizers: effects on tomato growth, reproductive system and soil microbial community

>Carbon nanotubes are promising materials in activating plant growth and development. In this study, we demonstrate that carbon nanotubes can significantly affect tomato growth, plant reproductive systems and the composition of soil microbiota. Tomato plants grown in soil supplemented with 50μg/ml and 200μg/ml of multi-walled carbon nanotubes (CNT) produced two times more flowers and fruits compared to plants grown in soil mixed with activated carbon or in control soil. The accumulation of CNTs in flowers of tomato plants was demonstrated by Raman spectroscopy. The effect of carbon nanotubes on microbial community of CNT-treated soil was determined by denaturing gradient gel electrophoresis (DGGE) and pyrosequencing analysis. The composition of soil microbial community was affected by the introduction of CNTs in watering practice. Phylogenetic analysis indicated that Proteobacteria and Bacteroidetes were the most dominant groups in the microbial community of soil. The relative abundances of Bacteroidetes and Firmicutes were found to increase whereas Proteobacteria and Verrucomicorbia decreased with increasing concentration of CNTs. The results of comparing diversity indices and species level phylotypes (OTUs) between samples showed that there was not a significant affect in bacterial diversity and the dominant OTUs were maintained in CNT exposed soils when compared to controls.