驱动稻田N2O排放关键过程的微生物作用机理

Nitrous oxide is an important greenhouse gas and the most important compound causing depletion of stratosphere ozone in the 21 century. Agricultural soil is an important contributor to the global N2O emission. China is the largest rice producer with about 29 million hectares of rice paddy area, which is an important N2O source. It is critical to investigate the key mechanisms of functional microorganisms in driving N2O emission from paddy soils. In this project, the advanced techniques of metogenomics, transcroptomics, microarray, SIP will be employed to study microbial molecular mechanisms of nitrogen cycling. The driving mechanisms of N2O production and consumption of paddy soils during flooding-drying process will be investigated including the key factors and their roles in controlling N2O emission, the activity of nitrifiers and denitrifiers. The effect of rice root on nitrogen transformation will also be studied by investigating nitrifying and denitrifying communities in relation to N2O emission in rhizosphere. Furthermore, the impact of fertilization on nitrogen cycling and N2O emission will be explored through testing the community compositions and abundance of denitrifying genes and their transcripts. It will be investigate that the influence of soil fertility on N2O production and comsumption, and microbial driving mechanisms on nitrogen cycling. Conclusively, this project will systematically investigate the functions of the key microbial communities in driving N2O emission including production, consumption and emission in paddy soil, and the main environmental factors. The studies will be valuable in understanding controlling greenhouse gas emission in agricultural soils.

氧化亚氮是一种重要温室气体，是21世纪最重要的消耗平流层臭氧的化合物。稻田重要的N2O排放源。本研究针对稻田排放N2O的三个关键过程（包括淹水-落干、肥料施用和水稻生长），通过根箱栽培、室内模拟和长期定位试验相结合，采用宏基因组学、转录组学、基因芯片和稳定性同位素核酸标记等先进技术，系统研究水稻土淹水-落干过程N2O产生、转化与释放的平衡机制、关键功能微生物驱动机理以及关键调控因子；揭示水稻根际和非根际土壤中硝化与反硝化微生物组成、丰度和活性差异与氮素转化和N2O释放的耦合关系；探讨长期施肥对水稻土氮素循环微生物活性表达组成和表达丰度与氮肥转化以及N2O排放特征的内在联系机理。从而系统揭示驱动稻田N2O排放的调控机制和关键微生物作用机理。本项研究的成果以及研究方法将对土壤过程与演变学科方向的发展有重要的推动作用，并为我国农田温室气体减排提供重要的科学依据。

氧化亚氮是一种重要温室气体，是21世纪最重要的消耗平流层臭氧的化合物。稻田是重要的N2O排放源。本研究针对稻田排放N2O的三个关键过程（包括淹水-落干、肥料施用和水稻生长），通过根箱栽培、室内模拟和长期定位试验相结合，采用宏基因组学、转录组学等先进技术，系统研究了驱动稻田N2O排放的调控机制和关键微生物作用机理。研究结果表明：（1）水稻土落干过程中排放的N2O主要来源0-5 cm表土层，而且落干过程中的硝化微生物与反硝化微生物的协同作用是驱动N2O产生和排放的关键微生物作用机制。淹水水稻土具有极强的N2O排放潜力，揭示了淹水稻田N2O排放量低的主要原因是反硝化底物（NO3-）浓度限制，添加外源NO3-可刺激反硝化微生物活性而产生激发效应，其中含narG的反硝化微生物种群数量和活性的响应是导致淹水水稻土N2O大量排放的主因之一。（2）干湿过程中水稻根系生长对N2O排放有显著的促进作用，在淹水-落干过程中水稻根系生长显著提高了根际区域N2O排放速率，根际土壤氨氧化细菌和含narG的硝酸还原菌的数量显著增加、硝化和反硝化微生物的强势协同作用是加速N2O排放的关键微生物驱动机制。根际土壤中属Beta-Proteobacteria的反硝化微生物丰度显著高于非根际，这些优势功能微生物可能与加速N2O排放有密切关系。（3）土壤磷素缺乏会抑制反硝化微生物表达活性，从而减少N2O排放；化学NPK肥与稻草还田结合显著提高反硝化微生物数量与活性，导致N2O释放速率显著提高。Gamma-Proteobacteria类反硝化细菌更适应于富营养型水稻土，反硝化能力强；而Beta-Proteobacteria类反硝化细菌则更适应于贫营养条件水稻土，且功能较弱。上述研究结果可为稻田温室气体（N2O） 减排和优化管理提供科学依据。