Divergent Responses of Soil CO2 and N2O Fluxes to Simulated Rainfall in a Restored Arid Ecosystem

Precipitation pulses refer to discrete and intermittent precipitation events that significantly influence ecosystem carbon and nitrogen cycling processes. However, the mechanisms by which different vegetation types modulate the sensitivity of carbon dioxide (CO2) and nitrous oxide (N2O) fluxes to short-term rainfall pulses remain poorly elucidated. To address this knowledge gap, we conducted a controlled rainfall simulation experiment across four representative surface types (moss-dominated biological soil crusts, Artemisia-ordosica-dominated soil, Caragana-korshinskii-dominated soil, and bare sandy soil), applying two precipitation pulses (5 mm and 10 mm) to quantify soil CO2 and N2O flux responses. The results showed that: (1) CO2 emissions increased significantly with precipitation intensity, with the 10 mm treatment producing higher mean fluxes than the 5 mm treatment. Emission peaks (1200–1600 mg m−2 h−1) occurred within 24 h after rainfall and returned to baseline levels within three days; (2) Surface cover exerted a strong regulatory effect on CO2 emissions, with moss crust soils (~400 mg m−2 h−1) and A. ordosica soils (~350 mg m−2 h−1) exhibiting CO2 fluxes 2.5–3 times higher than those of bare sandy soils (~120 mg m−2 h−1); (3) Structural equation modeling indicated that precipitation indirectly enhanced CO2 emissions by increasing soil carbon availability, with total organic carbon emerging as the strongest direct driver. Together, these findings clarify the primary controls on precipitation-induced CO2 emissions in restored desert systems and highlight the decoupled and weak short-term response of N2O, providing critical insights for managing carbon–nitrogen processes under increasing precipitation variability.