极端降水条件下土壤中O_(2)浓度对CO_(2)和N_(2)O浓度变化的调控作用

Effects of soil O_(2)on CO_(2)and N_(2)O concentration change under extreme precipitation

在干旱和半干旱区,降水是农田土壤温室气体排放的重要驱动因素,但极端降水条件下温室气体(CO_(2)、N_(2)O)浓度、排放特征及其与土壤O_(2)动态变化的关系尚不清楚。针对3种土壤管理措施(不施肥、施氮肥、秸秆还田),模拟极端降水(单次100 mm)条件下,高频率监测3种管理措施土壤O_(2)、CO_(2)和N_(2)O浓度及其地表CO_(2)、N_(2)O通量。与对照(单次10 mm)相比,极端降水条件下不施肥、施氮肥、秸秆还田3种处理N_(2)O累积排放量分别增加310%、440%和190%;CO_(2)累积排放量分别增加27%、1%和−11%;地表CO_(2)、N_(2)O通量与土壤CO_(2)、N_(2)O浓度动态变化基本一致,并存在显著正相关关系(P<0.05)。极端降水后土壤中O_(2)浓度呈现先降低后升高的趋势,而CO_(2)、N_(2)O浓度变化则呈相反趋势;土壤中CO_(2)、N_(2)O浓度与O_(2)浓度均呈显著负相关关系(P<0.05);但随着O_(2)浓度的降低,CO_(2)呈生长曲线型增长,而N_(2)O呈指数型增长。极端降水条件下土壤中O_(2)、CO_(2)和N_(2)O浓度变化达到峰值的时间较早。极端降水在促进土壤O_(2)浓度消耗的同时,也促进了土壤温室气体的产生与排放。本研究结果为明确雨养区农田土壤温室气体的排放机制提供了理论支撑。

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_(2)O) 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_(2)O concentrations and CO_(2)and N_(2)O fluxes were conducted under three soil management practices(no fertilization,nitrogen fertilization,and nitrogen fertilization plus straws incorporation).The results showed that N_(2)O 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_(2)O fluxes followed basically CO_(2)and N_(2)O 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_(2)O 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_(2)O concentrations.Soil CO_(2)concentrations followed a logistic growth pattern with decreasing O_(2)concentrations,and N_(2)O concentrations followed an exponential growth pattern with decreasing O_(2)concentrations.Therefore,soil CO_(2)and N_(2)O 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.