Synergistic effects of photoinduced reactive oxygen species and electrons enhance nitrous oxide emissions from...

Agricultural soils are the primary source of global anthropogenic nitrous oxide (N₂O) emissions, which are significantly enhanced by sunlight. Previous studies attribute this phenomenon to increased plant photosynthesis and elevated soil temperature. However, this explanation does not account for the phenomenon persisting in temperature-controlled bare soils, indicating the unclear mechanism driving soil N₂O emissions. By constructing photoelectrically enhanced soil using titanium dioxide nanoparticles (TiO₂ NPs), the present study demonstrated the role of the inherent photochemical properties of soil in enhancing N₂O emissions. Specifically, photoinduced reactive oxygen species (ROS) and electrons from soil synergistically increased N₂O emissions. Photoinduced electrons accounted for 83.4 %-92.9 % of the enhanced N₂O emissions, while ROS contributed 7.1 %-16.6 %, indicating that enhanced N₂O emissions were primarily driven by accelerated denitrification by photoinduced electrons. This was evidenced by the decreased ratio of N₂O-to-nitrate (NO₃^-) and increased expression of the narG and nosZ genes. TiO₂ NPs amplified soil N₂O emissions by 3.7 %-28.0 % and enhanced 7.2 %-22.0 % NO₃^- reduction, demonstrating the role of TiO₂ NPs in extending the capacity of soil to emit N₂O and promote nitrogen loss. This effect has long been overlooked in soil environments. This present study uncovers previously overlooked photochemical reactions in soil that influence N₂O emissions, offering insights into the mechanisms by which sunlight drives these emissions. It also highlights the need to consider the impact of photochemical properties of engineered materials on soil systems.