Inhibition of Soil Respiration By Copper Oxide Nanoparticles Is Controlled By Cu Availability across Management Systems.

The fungicidal application of nano-sized copper oxide (CuO) to annual cropping systems and inadvertent drift to surrounding ecosystems may lead to the long term accumulation of Cu in soils. The impact of CuCl₂, 16 nm CuO, 45 nm CuO, and bulk-CuO applied at rates of 0, 10, 100, and 1000 mg Cu kg^-1 soil on soil respiration (CO₂ flux) from pedogenetically similar alluvial soils (Mollic Haploxeralfs and Mollic Xerofluvents), differing in long-term (23 year) management (conventional, organic, no-input, grassland, and forest), was evaluated over 75 days. The effects of Cu form and exposure concentration on soil respiration were further evaluated by quantifying available Cu²⁺ as part of a sequential extraction procedure. At the lowest exposure dose (10 mg kg^-1), Cu application stimulated soil respiration regardless of form, whereas soil respiration was significantly impaired only at the highest exposure dose (1000 mg kg^-1) of CuCl₂, across all management systems. These results indicate that over 75 days, the response of soil respiration to Cu application depends primarily on Cu form and exposure dose rather than management history.