大气CO_(2)浓度升高背景下优化施氮对淹水稻田CH4排放的影响

Effects of optimized nitrogen application on CH4 emissions from flooded paddy fields under elevated atmospheric CO_(2) concentrations

为探讨未来气候变化条件下,合理管理氮肥以充分协调水稻产量与温室气体排放量之间的矛盾,实现低碳排放并保持水稻产量,本研究探讨了大气CO_(2)浓度升高120μmol·mol^(-1)与氮肥减施40%对淹水稻田水稻生产及CH4排放的影响及机理。利用开顶式气室(OTC)组成的CO_(2)浓度自动调控平台设置4个处理,即环境CO_(2)浓度+施氮250 kg·hm^(-2)(CK)、大气CO_(2)浓度升高120μmol·mol^(-1)+施氮250 kg·hm^(-2)(C+)、环境CO_(2)浓度+施氮150 kg·hm^(-2)(N-)、大气CO_(2)浓度升高120μmol·mol^(-1)+施氮150 kg·hm^(-2)(C+N-),分析了稻田CH4累积排放量(CAC)、水稻生物量及产量、土壤理化性质及酶活性等指标。结果表明:与CK处理相比,C+处理使CAC/产量显著提高了16.93%,N-处理使CAC/产量显著降低了13.33%,C+N-处理使CAC/产量降低了7.89%,但不显著;N-处理在一定程度上削弱了C+处理对CAC、CAC/产量、水稻生物量、土壤可溶性有机碳含量的促进作用;逐步回归分析表明,基于可溶性有机碳和硝态氮含量及土壤脲酶活性的线性模型,可解释稻田CH4累积排放64%的变异。综上,在大气CO_(2)浓度升高条件下,氮肥减施可通过影响土壤碳、氮基质及土壤脲酶活性来调节稻田CH4排放。

The aim of this study was to explore the rational management of nitrogen fertilizer under future climate change condition,achieve low-carbon emissions,and maintain rice yield.The effects and mechanisms of elevated atmospheric CO_(2) concentration(120μmol·mol^(-1))and reduced nitrogen application rate(40%)on rice production and CH4 emissions in flooded paddy fields were investigated in this study.Four treatments were set up using open-top chambers(OTCs)to automatically control the CO_(2) concentration:ambient CO_(2) concentration+nitrogen application by 250 kg·hm^(-2)(CK),elevated atmospheric CO_(2) concentration by 120μmol·mol^(-1)+nitrogen application by 250 kg·hm^(-2)(C+),ambient CO_(2) concentration+nitrogen application by 150 kg·hm^(-2)(N-),elevated atmospheric CO_(2) concentration by 120μmol·mol-1+nitrogen application by 150 kg·hm^(-2)(C+N-).The cumulative amount of CH4 emissions(CAC),rice biomass and yield,soil physicochemical properties,and enzyme activities were analyzed.The results showed that compared with CK treatment,the C+treatment significantly increased CAC/yield by 16.93%,N–treatment significantly decreased CAC/yield by 13.33%,and C+N–treatment decreased CAC/yield by 7.89%,but this was not significantly.N–treatment weakened the promoting effect of C+on CAC,CAC/yield,rice biomass,and soil-soluble organic carbon concentration to a certain extent.Stepwise regression analysis showed that the linear model based on dissolved organic carbon and nitrate nitrogen content and soil urease activity could explain 64%of the variation in cumulative CH4 emissions from paddy fields.In summary,nitrogen fertilizer reduction can regulate CH4 emissions from paddy fields under elevated atmospheric CO_(2) concentrations by affecting soil carbon,nitrogen substrates,and urease activity.