Divergence in response of lettuce (var. ramosa Hort.) to copper oxide nanoparticles/microparticles as potential agricultural fertilizer

CuO particles can be used as an agrochemical with slow and controlled release of micronutrients but, their size- specific effects have not been well elucidated. In this study, soil-grown lettuce was exposed to CuO nanoparticles (nCuO) and CuO microparticles (mu CuO) at 0, 200, and 400 mg Cu/kg for 60 days. At harvest, nCuO released 82.2% and 117.7% more Cu ions, as well as 48.7% and 75.3% more DTPA-extractable Cu than mu CuO at 200 and 400 mg/kg, respectively. CuO treatments induced higher copper accumulated in lettuce roots but did not change shoot's Cu content or cause oxidative stress. nCuO treatments increased shoot's biomass by 16.3-19.1%, while mu CuO showed no improvement to the biomass. The beneficial effects on lettuce by nCuO may be attributed to its modification in plant photosynthesis system with increased transpiration rate and higher stomatal conductance. Results indicate that nCuO can be a promising agrochemical fertilizer to increase crop production.