Effects of soil O₂ on CO₂ and N₂O concentration change under extreme precipitation

Agricultural soils play an important role in global greenhouse gases emissions. Precipitation is a critical factor driving soil greenhouse gases emissions in arid and semi-arid regions; however, the mechanism of greenhouse gas generation and emission under extreme precipitation has not been well documented. The aim of this study was to determine the relationships between greenhouse gases (CO₂, N₂O) concentrations and fluxes and soil O₂ dynamics under extreme precipitation. Based on an extreme precipitation scenario (100 mm), a simulation experiment of soil column was established at the Changwu Station, and high-frequency measurements of soil O₂, CO₂, and N₂O concentrations and CO₂ and N₂O fluxes were conducted under three soil management practices (no fertilization, nitrogen fertilization, and nitrogen fertilization plus straws incorporation). The results showed that N₂O cumulative emissions in no fertilization, nitrogen fertilization, and nitrogen fertilization plus straws incorporation under extreme precipitation increased by 310%, 440%, and 190% of those under light precipitation (10 mm), respectively. However, CO₂ cumulative emissions in no fertilization, nitrogen fertilization, and nitrogen fertilization plus straws incorporation increased by 27%, 1%, and −11%, respectively, compared to that under light precipitation. The surface CO₂ and N₂O fluxes followed basically CO₂ and N₂O concentrations dynamics in the soil, and there was a significant positive correlation between soil surface fluxes and belowground concentrations. Under extreme precipitation events, soil O₂ concentrations sharply decreased and progressively recovered to the initial level, and concomitantly, soil CO₂ and N₂O concentrations peaked, showing an opposite dynamic pattern. In addition, the timing of the three gases concentrations under extreme precipitation was delayed compared to that under light precipitation events. Soil O₂ concentrations were negatively correlated with CO₂ and N₂O concentrations. Soil CO₂ concentrations followed a logistic growth pattern with decreasing O₂ concentrations, and N₂O concentrations followed an exponential growth pattern with decreasing O₂ concentrations. Therefore, soil CO₂ and N₂O production and emissions are strongly related to soil O₂ concentration dynamics during extreme precipitation events. These results will help clarify the mechanism of greenhouse gases emissions from rainfed croplands in the Loess Plateau.