旱地农田土壤N2O产生和还原过程微生物驱动机制的研究

Nitrous oxide (N2O) is a potent greenhouse gas that also depletes stratospheric ozone. The upland arable soil is the major emission source; hence, abating its N2O release is of great importance for mitigating global climate change. However, few efforts have been made to explore the microbial-driven mechanisms of N2O producing and reducing pathways, especially for the latter one. Hereby, in this project, two typical upland soils, namely the alkaline Fluvo-aquic soil from North China Plain and the acid Red soil from South China, will be selected as experimental subjects; we use selective inhibitors to differentiate the N2O producing and reducing pathways, as well as the relative contribution of AOA, AOB, nirS- and nirK-denitrifiers to N2O production via microcosm incubation. In combination of the molecular microbial ecology analysis and H218O-DNA-stable isotope probing (H218O-DNA-SIP), we intend to explore the active N2O producers and consumers in these soils, and then reveal the microbial-driven mechanisms of N2O production and consumption in upland soils. This project will provide deep insight into the microbial mechanisms of N2O emission in upland soils, and theoretical guidance for devising strategy for mitigating N2O emission in upland soils.

N2O是一种重要的温室气体，且对大气臭氧层有着强烈的破坏作用，旱地农田是N2O释放的主要来源，因此降低旱地农田N2O排放对缓解全球气候变化具有重要的意义。N2O释放是产生和还原过程的净结果，但当前关于N2O产生，尤其是还原过程微生物驱动机制的研究十分薄弱。据此，本研究以华北潮土和南方酸性红壤作为研究对象，采用选择性抑制剂区分N2O产生和还原过程通量，探明AOA、AOB、nirS和nirK型反硝化菌对产生过程的贡献率，结合微生物分子生态学手段和H218O-DNA稳定同位素探针技术（H218O-DNA-SIP）鉴别环境中负责N2O产生和还原的活性微生物，以期揭示旱地农田土壤N2O产生和还原的微生物驱动机制。研究结果有助于加深人们对旱地土壤N2O释放机理的认知，还可为设计针对性的减排措施提供理论依据。

氨氧化过程是旱地农田土壤N2O产生的重要途径，由氨氧化细菌（AOB）、氨氧化古菌（AOA）和全程氨氧化细菌（Comammox）执行。这三类功能微生物具有不同的N2O释放能力和特征，且存在明显的生态位分化现象。最近的观点认为，利用这些现象可以降低旱地农田土壤的N2O释放。然而，目前关于它们在旱地农田土壤中的N2O相对释放贡献及生态位分化的具体机制仍不明晰。本项目采用多种抑制剂结合稳定同位素探针技术，通过一系列试验明确了三种功能微生物种群对旱地农田土壤N2O释放的相对贡献，及它们的生态位分化机制。得到以下主要结论：（1）在碱性高氨旱地农田土壤中，抑制AOB促进高氨敏感型AOA进化分枝的生长，表明AOA可以适应富营养环境，这一发现挑战了传统认为AOA嗜好寡营养环境的认知；（2）需氧条件下，AOB是旱地农田土壤主要的N2O释放源，AOA的N2O释放贡献随土壤pH的下降而提高；（3）Nitrosomonas communis是酸性农田硝化作用的重要执行者；（4）生态位偏好性和种间竞争驱动了AOA和AOB之间的生态位分化现象；（5）全程氨氧化细菌对碱性旱地农田土壤的N2O释放贡献十分有限。这些研究结果加深了人们对旱地农田土壤N2O释放机理的认知，为设计合理的N2O减排农田管理措施提供了理论依据。