Carbon nanotubes alter agrosystem multifunctionality

Abstract

Since the discovery of the potential of carbon nanotubes (CNTs) in agriculture to improve crop yield, many studies have been conducted to understand which effects CNTs could have on agrosystem components. However, to date, very little is known about their impacts on ecosystem functions such as biogeochemical cycles or primary production and consequently on the multifunctionality of agrosystems. In this study, we aimed at understanding the impact of CNTs in microcosms including soil bacteria and a crop plant (maize) with a special focus on H₂O, C and N cycles as well as crop nutrition and resistance. After a 6-week exposure, bacterial concentration was increased by 82% in soils exposed to 10 mg kg⁻¹; in parallel, the organic matter decomposition rate was also significantly enhanced. An increase of nitrifier abundance was quantified with archaeal amoA gene copy numbers reaching +144% in soils exposed to 10 mg kg⁻¹ of CNTs. Maize exposed to 0.1 mg kg⁻¹ of CNTs had in average 34%, 18% and 12% lower chlorophyll, tannin and phenolic compounds, respectively but no impact was detected on the biomass production. Maize plants were water-stressed after exposure to 10 mg kg⁻¹ of CNTs with a significant 17% increase of the dry matter compared to unexposed maize. CNT exposure also led to a significant decrease of H₂O flux in the system. As a result, the multifunctionality of the agrosystem was significantly decreased at 0.1 mg kg⁻¹. Structural equation modeling suggested that CNT impact on bacteria population in general, and on bacteria implied in denitrification and CO₂ emission were the main factors influencing the multifunctionality index.