Carbonaceous nanomaterials (CNMs) have gained remarkable attention from both academia and industry due to their extraordinary properties and promising application potential. With their rapid increase in production and use, CNMs will enter the environment where they are predicted to accumulate in soils. Published studies have reported negative effects of CNMs on plants and soil microbial communities, suggesting that CNMs could pose risks to terrestrial ecosystems. However, there is limited long-term research into CNM effects on agriculturally-important soil-grown crop species and their interactions with soil microorganisms. In this mesocosm study, we determined the comparative effects of three types of CNMs (multi-walled carbon nanotubes, graphene and carbon black, at three concentrations each) on plant growth and yield, and on root nodule nitrogen fixation potential, for soybean plants grown to full reproductive maturity in soil within a climate-controlled greenhouse. Soybean seedlings were pre-grown in peat pods, inoculated with nitrogen-fixing bacteria <i>Bradyrhizobium japonicum</i> USDA 110, and transplanted into individual pots containing sandy-clay-loam agricultural soil that was either un-amended (control) or amended with CNMs. Plant growth was periodically nondestructively monitored by measuring stem length and leaf canopy, and counting leaves, flowers and pods. Environmental parameters, including soil water content, conductivity, and temperature were also monitored regularly. Plants were harvested at one of two stages: intermediate (before reproduction) or final (full maturity, before senescence). Plant tissue measurements included wet and dry biomass, moisture content, leaf total reactive oxygen species concentration, leaf chlorophyll content, macro/micronutrient concentrations, root nodule count, nitrogen fixation potential and nodule ultrastructure. While effects varied with CNM type and concentration, the results point to CNMs exerting significant dose-dependent effects on soil-grown soybean, with particular impacts on its symbiosis with nitrogen-fixing bacteria. Our findings suggest that, where CNMs enter soils similarly to the conditions of this study, these nanomaterials could interfere with not only the production of an agriculturally important crop, but also with nitrogen sourcing and soil fertility.

Effects of carbonaceous nanomaterials on soil-grown soybean and its symbiosis with nitrogen-fixing bacteria: A mesocosm study

253rd National Meeting (2017)

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