Labile Carbon from Artificial Roots Alters the Patterns of N₂O and N₂ Production in Agricultural Soils

Labile carbon (C) continuously delivered from the rhizosphere profoundly affects terrestrial nitrogen (N) cycling. However, nitrous oxide (N2O) and dinitrogen (N-2) production in agricultural soils in the presence of continuous root C exudation with applied N remains poorly understood. We conducted an incubation experiment using artificial roots to continuously deliver small-dose labile C combined with N-15 tracers to investigate N2O and N-2 emissions in agricultural soils with pH and organic C (SOC) gradients. A significantly negative exponential relationship existed between N2O and N-2 emissions under continuous C exudation. Increasing soil pH significantly promoted N-2 emissions while reducing N2O emissions. Higher SOC further promoted N-2 emissions in alkaline soils. Native soil-N (versus fertilizer-N) was the main source of N2O (average 67%) and N-2 (average 80%) emissions across all tested soils. Our study revealed the overlooked high N-2 emissions, mainly derived from native soil-N and strengthened by increasing soil pH, under relatively real-world conditions with continuous root C exudation. This highlights the important role of N2O and N-2 production from native soil-N in terrestrial N cycling when there is a continuous C supply (e.g., plant-root exudate) and helps mitigate emissions and constrain global budgets of the two concerned nitrogenous gases.