浅表层水稻土落干过程中排放氧化亚氮的关键机理探究

Nitrous oxide is an important greenhouse gas. The drying process in paddy fields usually cause a large amount of N2O emission, and the surface soil is probably the main source of N2O emission. In this project, we focus mainly on the processes of abiotic consumption, microbial production and reduction associated with N2O emission in surface paddy soil. By simulating the drying process under laboratorial condition, the soil sterilization and stable isotope labeling technology will be employed to research the diffusion and abiotic consumption process of 15N2O in surface paddy soil profile, and also the balance of N2O production and consumption will be studied in non-sterilization surface paddy soil. By the methods of the real-time PCR and the high-throughput sequencing, the responses of the abundance, composition and express activities of nitifiers and denitrifiers involved in N2O production (amoA、nirK/nirS) and reduction (nosZI/nosZⅡ) in surface paddy soil to drying process will be investigated. Conclusively, the key regulation mechanism of nitrifiers, denitrifiers and abiotic consumption in surface paddy soil on N2O emission will be explored by coupling the N2O abiotic consumption, microbial production and reduction. The due results will be of great significance in further understanding the regulating mechanism of N2O emission in paddy soil, and also it can provide scientific basis for controlling the emission of greenhouse gas N2O from paddy fields.

氧化亚氮是一种重要的温室气体，稻田水分落干过程引起N2O大量排放，且浅表层土壤可能是N2O排放的主要来源。本研究针对浅表层水稻土落干过程中N2O排放相关的非生物消纳、微生物产生和还原过程，通过模拟水分落干，采用稳定同位素标记技术系统研究外源15N2O气体在灭菌处理的浅表层水稻土中迁移扩散和非生物消纳过程，以及非灭菌处理的浅表层水稻土中15N2O产生与消纳平衡过程；进一步利用实时定量PCR与高通量测序等分子生物学技术研究浅表层土壤硝化、反硝化微生物（amoA、nirK/nirS、nosZI/nosZⅡ）种群丰度和组成、表达丰度和表达结构对水分落干过程的响应规律，揭示N2O产生与消纳过程耦合调控浅表层水稻土N2O排放的作用机制。研究结果对于深入认识稻田土壤N2O排放的调控机制具有重要的意义，也可为稻田温室气体N2O的减排控制提供科学依据。

本项目针对落干过程中浅表层水稻土为何会成为N2O排放主源，以及与之相关的N2O产生和消耗耦合过程不清的问题，通过5cm原状水稻土柱和风干土回填土柱水分控制试验，分别研究落干过程中关键功能微生物调控浅表层水稻土N2O产生和消纳平衡过程的作用机制，以及淹水条件下浅表层水稻土对N2O的消耗潜力以及微生物还原过程对N2O消耗总量的相对贡献。通过项目的实施，明确了浅表层水稻土柱在落干过程中土壤水分含量持续下降，浅层深度5cm土体内的N2O产量直接贡献于土表的N2O排放；其中硝化作用对土体内的N2O产生过程的调控强于反硝化作用，且含AOA基因的硝化微生物数量以及群落组成随水分含量的变化与N2O排放量动态变化显著相关，可认为AOA是调控落干过程N2O产生与排放的主导微生物类群。淹水厌氧状态下5cm水稻土柱能够大量截留消耗5cm土体中产生积累的N2O气体，消耗总量可达96%以上，在诸多消耗途径中，微生物还原N2O为N2的途径贡献最大，约占N2O消耗总量的64.50%~83.64%。其中nosZI基因丰度的变化比nosZⅡ与水稻土N2O消耗量和N2产量关系更为密切，且nosZI基因丰度的变化与可溶性有机碳源的消耗量也显著相关，可认为含nosZI基因的氧化亚氮还原微生物主导了淹水水稻土的N2O消耗能力。研究结果可为稻田土壤不同水分阶段N2O减排，全球气候变化研究等方面提供理论基础。