大气CO2浓度和温度升高下小麦季施用缓释氮肥对大豆季N2O排放的后效作用

Residual effects of slow-release nitrogen fertilizer application during the wheat growing season on N2O emission in soybean season under co-elevated atmospheric CO2 concentration and temperature

  • 摘要: 农田N2O排放是当今气候变化研究的一个热点问题, 气候变化和农田管理措施是影响N2O排放的关键因素。本研究在控制气室中设置两种气温(环境温度和环境温度+2 ℃)和两种CO2浓度400 μmol∙mol−1 (当前环境CO2浓度)和600 μmol∙mol−1, 并在各环境处理下设置小麦-大豆轮作的小麦季施用两种肥料常规尿素(C)和缓释尿素(H), 大豆季不施肥; 以控制气室内模拟的当前环境CO2浓度和温度为对照(CK), 对大豆季整个生育期N2O排放、鼓粒期和成熟期土壤铵态氮和硝态氮含量、硝化-反硝化相关酶活性进行测定, 探讨未来气候变化背景下小麦-大豆轮作系统中前茬作物施用缓释肥对后茬作物N2O排放的影响。结果表明: N2O排放主要集中在大豆生育后期。与施用常规尿素相比, 小麦季施用缓释肥在仅升高温度(ET)处理下, N2O排放总量降低38.46%, CK、仅升高CO2浓度(EC)和CO2浓度和温度协同升高(ECT)处理下施用缓释肥时N2O排放总量分别增加80.76%、82.35%和11.96%。与CK处理相比, ET处理加快了大豆鼓粒期土壤中铵态氮向硝态氮的转化, 进而提高了硝酸还原酶活性, 增加了N2O排放; EC处理对N2O排放没有显著影响。ECT处理的土壤硝态氮和铵态氮含量略有增加, 主要是硝酸还原酶活性的增加促进了N2O的排放。在常规尿素施肥时ECT与ET的N2O排放量没有显著差异。总之, 在未来气温增加时, N2O排放量增加, 合理施用缓释肥可以增加土壤中可利用的氮素, 降低N2O排放。

     

    Abstract: Farmland N2O emission is a popular topic in climate change research. Climate change (elevated CO2 concentrations and increased temperatures) and farmland management measures are key factors affecting N2O emissions in soil. Slow-release fertilizers are considered to have a positive effect on reducing N2O emissions. It is unclear how the interaction between climate change and slow-release fertilizers affects N2O emissions. Thus, we combined the local wheat-soybean cultivation model to investigate the potential impact of applying slow-release fertilizers on soil N2O emissions during the growing season of subsequent crop under elevated CO2 concentrations and increased temperatures. In this study, two air temperatures (ambient temperature and ambient temperature + 2 ℃) and two CO2 concentrations (400 μmol∙mol−1 and 600 μmol∙mol−1) were set in the controlled chambers. Two fertilizers (conventional urea and slow-release urea) were applied during the wheat season under various environmental treatments in a wheat–soybean rotation system. Still, no fertilizer was used during the soybean growing season. CK referred to the ambient CO2 concentration and temperature simulated in the controlled chamber (the ambient environmental CO2 concentration in this experiment was 400 μmol∙mol−1, and the environmental temperature was controlled by the intelligent control system to be consistent with the external environment). N2O emissions during the entire growth period of soybean, soil ammonium nitrogen and nitrate nitrogen contents, and activities of soil enzymes involved in nitrification and denitrification during the drumming and ripening stages of soybean were measured. The results indicated that N2O emissions from soybean-grown soil were mainly concentrated during the later growth period of soybeans. Compared to the application of conventional urea, the application of slow-release fertilizer in wheat-grown soil reduced total N2O emissions by 38.46% during the soybean growth period under increased temperature (ET) alone, whereas the application of slow-release fertilizer increased total N2O emissions in soybean-grown soil by 80.76%, 82.35%, and 11.96% under the CK, elevated CO2 concentration (EC) alone, and co-elevation of atmospheric CO2 concentration and temperature (ECT) treatments, respectively. Compared to the CK treatment, ET accelerated the conversion of ammonium nitrogen to nitrate nitrogen in soybean-grown soil at the seed filling stage, enhancing nitrate reductase activity and increasing N2O emissions. In addition, EC alone had no effect on N2O emissions from soybean-grown soil compared to the CK treatment. ECT resulted in a slight increase in nitrate and ammonium nitrogen contents in soybean-grown soil compared with the CK treatment, which was mainly attributed to the increase in nitrate reductase activity that might promote N2O emissions; however, there was no significant difference in N2O emissions in soybean-grown soil when ECT was compared with ET under conventional urea. In conclusion, N2O emissions did not increase with elevated CO2 concentration alone. N2O emissions were expected to increase under elevated temperatures in the future, and the rational application of slow-release fertilizers in wheat-grown soil can increase the available nitrogen content in the soil, thus reducing N2O emissions in soybean-grown soil. Our study highlights that slow-release fertilizers have greater potential to reduce N2O emissions under climate change scenarios.

     

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