Copper oxide nanoparticle effects on root growth and hydraulic conductivity of two vegetable crops

Aims Root growth and water transport were evaluated for two vegetable crops of contrasting root architecture (lettuce, carrot) exposed to copper oxide nanoparticles (CuO NPs). Methods 10-day seedling root growth assays were evaluated for 16 nanometer (nm) diameter CuO NP and CuCl2 control (0.8 – 798.9 mg Cu L−1). In a separate experiment, hydraulic conductivity (Kh) of root systems not previously exposed to NP was tested using 16 and 45 nm CuO NP (798.9 mg Cu L−1) relative to CuO NP-free controls, and xylem sap was assessed by TEM-EDS for presence of CuO NPs. Results 16 nm CuO NP produced dose-dependent increases in root diameter for lettuce (+52%) and carrot (+26%) seedlings, whereas CuCl2 did not affect (lettuce) or marginally increased (carrot) root diameter. Root Kh was similarly reduced by 16 and 45 nm CuO NPs for lettuce (−46%) but not for carrot, and no Cu was identified by TEM-EDS in xylem sap. Conclusions Adverse effects of CuO NPs on root physiology and function in the early stages of growth of two key food crops are not necessarily due to Cu2+ toxicity and can be specific to crop species. In addition to triggering root thickening, reduction of root Kh signifies that CuO NPs can compromise root water transport and thus crop performance.