华北典型农田土壤硝化反硝化过程及N2O排放对生物炭施用的响应机制

N2O is one of the most important greenhouse gases, and agriculture soils are the main emission sources. In recent years, biochar has been increasingly seen as an effective measure to increase soil nutrient availability and mitigate greenhouse effect, yet its effect on the mechanism of soil N2O production processes--nitrification and denitrification is not clear. We intend to study the effects of biochar on soil nitrification and denitrification and N2O fluxes by the combined research methods of field experiment and laboratory incubation experiment under the winter wheat-summer maize rotation system in the typical crop field in North China Plain. The soil N2O fluxes are continuously monitored using static chamber-gas chromatography method in the field experiment, and the effects of biochar on soil nitrifying bacteria, denitrifying bacteria communities are determined using quantitative PCR, T-RFLP and cloning technology. 15N isotope tracer and acetylene inhibition methods are used to further study the relative contributions of key microbiological processes including autotrophic nitrification, heterotrophic nitrification and denitrification to N2O emission under biochar addition in the laboratory incubation experiment. The relationships between N2O fluxes and the corresponding functional microbial communities during nitrification processes and denitrification processes are also to be studied. The above research will help to clarify the mechanism of biochar application on soil nitrification and denitrification microbial communities, and on the reduction effect and mechanism of soil N2O, and it would provide scientific basis for the management of N2O emission from crop field in North China Plain.

N2O是重要的温室气体之一，农业土壤是其最主要的排放源。近年来施用生物炭被视为能够增加土壤养分、缓解温室效应的有效措施，然而其对土壤N2O产生的重要途径—硝化反硝化作用的影响机理尚不明确。本项目拟以冬小麦-夏玉米轮作体系下的华北典型农田为研究对象，采用田间定位实验与室内培养实验相结合的研究方法，研究施用生物炭对土壤硝化反硝化过程及N2O排放的影响。田间定位实验采用静态箱-气相色谱法连续观测土壤N2O的排放规律，采用定量PCR、T-RFLP和克隆测序技术研究生物炭输入对土壤硝化反硝化细菌群落的影响；室内培养实验采用15N同位素示踪和乙炔抑制相结合的研究方法，深入研究自养硝化、异养硝化和反硝化对N2O排放的贡献，硝化反硝化进程中N2O排放与相关功能微生物群落之间的关系。以上研究有助于阐明施用生物炭对相关微生物群落的影响机理以及对N2O的减排效果及机制，为我国华北农田N2O排放管理提供科学依据。

本研究以华北农田为研究对象，采用田间定位实验与室内培养实验相结合的研究方法，开展了施用生物炭、秸秆和有机肥对N2O的减排效果和作用机制的研究。主要结果如下：.（1）三年的田间定位实验表明，小麦季N2O累积排放量在0.60-1.98kgha-1yr-1之间，玉米季N2O累积排放量在0.53-1.73kgha-1yr-1之间，整个轮作周期N2O年均排放量为2.17-4.17kgha-1yr-1。小麦季，N2O排放生物炭处理降低了16.6%，秸秆还田、秸秆还田+生物炭处理分别升高了73.2%和95.2%；玉米季，生物炭处理N2O累积排放量降低了20.0%，秸秆还田、秸秆还田+生物炭处理分别升高了29.4%和52.0%。生物炭主要通过促进AOB和抑制nirK基因丰度来降低N2O排放；秸秆和生物炭+秸秆处理主要通过抑制氨氧化细菌AOB和nosZ基因丰度增加N2O排放。.（2）通过盆栽实验，研究了生物炭和有机肥联合施用对N2O的作用效果和机制。生物炭和有机肥联合施用可以降低土壤N2O排放，同时降低了nirS和nosZ基因的丰度，AOB中的亚硝化螺菌属Nitrosospira是N2O排放的主要贡献者，土壤水分，pH，铵态氮，硝态氮主要通过影响AOB和反硝化菌从而影响N2O排放。.（3）利用同位素示踪和乙炔抑制法，研究了添加生物炭对硝化、反硝化和异养硝化作用的影响及各个过程对N2O的相对贡献。自养硝化、异养硝化、反硝化对N2O的贡献分别为77.4%~81.9%，0.68%~0.85%和17.1%~25.7%。生物炭对反硝化产生的N2O有巨大的减排潜力，高通量测序表明，生物炭刺激了nirK和nosZ的微生物群落产生和还原N2O的能力，并显著改变了其群落组成。.（4）应用同位素特征值法溯源N2O的排放途径，从N2O分子形成过成阐述生物炭对硝化反硝化的影响。(NH4)2SO4作为氮源，添加生物炭前期降低了硝化作用的贡献，后期提升了硝化作用的贡献，对反硝化作用而言，培养前期促进了反硝化作用的贡献，培养中后期抑制了反硝化作用的贡献。KNO3作为氮源，添加生物炭，在培养前期降低了硝化作用的贡献，在培养中后期促进了硝化作用的贡献，对于反硝化作用而言，前期促进了反硝化作用的贡献，中后期抑制了反硝化作用的贡献。 .以上研究为华北农田土壤N2O减排和农业废弃物的资源化利用提供了科学依据。