Environmental behavior and synergistic effects of urea-derived carbon dots on the maize-soil system

Nitrogen (N) fertilizer-induced pollution poses a significant challenge to sustainable agroecosystems. This study examines the hydrothermal conversion of urea into N-doped carbon dots (NDs) and compares the fate, transport, and environmental impacts of these NDs within the plant-soil system to those of urea. Specifically, foliar application of NDs at 10 mg/L is absorbed by maize leaves, translocated to the roots, and partially deposited onto the soil during spraying. This pathway alters rhizosphere microbial community composition and functional gene profiles, leading to increased soil nitrification, reduced denitrification, and enhanced carbon stabilization. As a result, NH₄⁺-N and NO₃^--N concentrations increase by 117.0% and 12.9%, respectively, following NDs foliar application. NDs also suppressed soil organic carbon (SOC) mineralization, thereby helping to preserve soil fertility. In parallel, NDs reduced soil emissions of CO₂, NH₃, and N₂O by 20.9%, 60.0%, and 11.2%, respectively, which mitigates the environmental footprint of nitrogen fertilizer use. NDs further enhanced maize productivity by 16.7% by promoting carbon fixation: they increased carboxylase activity and upregulated key photosynthetic electron-transport genes such as psaA and psbA. At the same time, NDs stimulated maize genes and enzyme activities involved in nitrogen uptake, translocation, and assimilation, leading to a 56.6% rise in leaf nitrogen accumulation and a 10.2% increase in grain protein content. Together, these findings illuminate how nanotechnology can support soil environmental sustainability and suggest promising pathways for advancing sustainable agriculture.