Abstract:
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 (CO
2, N
2O) concentrations and fluxes and soil O
2 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 O
2, CO
2, and N
2O concentrations and CO
2 and N
2O fluxes were conducted under three soil management practices (no fertilization, nitrogen fertilization, and nitrogen fertilization plus straws incorporation). The results showed that N
2O 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, CO
2 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 CO
2 and N
2O fluxes followed basically CO
2 and N
2O concentrations dynamics in the soil, and there was a significant positive correlation between soil surface fluxes and belowground concentrations. Under extreme precipitation events, soil O
2 concentrations sharply decreased and progressively recovered to the initial level, and concomitantly, soil CO
2 and N
2O 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 O
2 concentrations were negatively correlated with CO
2 and N
2O concentrations. Soil CO
2 concentrations followed a logistic growth pattern with decreasing O
2 concentrations, and N
2O concentrations followed an exponential growth pattern with decreasing O
2 concentrations. Therefore, soil CO
2 and N
2O production and emissions are strongly related to soil O
2 concentration dynamics during extreme precipitation events. These results will help clarify the mechanism of greenhouse gases emissions from rainfed croplands in the Loess Plateau.