华北平原农田土壤反硝化和硝化的产物比与调控机制

The project focus on the possibilities for reducing soil N2O emission by altering the product stoichiometry of denitrification/ nitrification in soils. The inverstigation will be conducted in the North China Plain, the major vegetable and food grains production area, where two cropping systems, a typical wheat-maize rotation and intensive vegetable production system are chosen.With several long-term field experiments and robotized incubation system to indentify the factors that control the product stoichiometry of denitrification /nitrification under different management practices; to evaluate the effect of managements on nitrifier/denitrifier community composition, dominant species, gene types and gene expression using molecular biology techniques; to quantify the N loss by combining the analysis of stoichiometry with field scale N2O flux measurement; and finally to understand the mechanisms of management practices for N2O emission mitigation in the region by the reduction of the product stoichiometry of nitrification/denitrification. The objectives of the present project are, by combination of soil biochemical processes and N2O emissions in situ with the composition and gene expression of nitrifier/denitrifier community, to have a better understanding the mechanism of N2O production and regulation in typical farmlands of the region, and to find out the effective measures for both mitigation of N2O emission to the atmosphere and control of nitrogen loss in agricultural field in the region.

控制硝化和反硝化过程的产物比是实现N2O减排的重要途径之一。在我国粮食和设施蔬菜主产区华北平原，选择主要粮食作物种植体系和高投入的设施菜田土壤为研究对象,以多点长期定位试验为基础，利用引进的专用设备(土壤自动培养测定系统)，研究典型管理措施条件下硝化和反硝化过程产物比发生规律及影响因子；利用分子生物学技术，揭示不同管理方式对土壤中硝化、反硝化菌组成结构、优势种群、基因类型与基因表达的影响规律；探索利用硝化、反硝化过程的产物比，并结合田间N2O通量观测，进行氮损失定量的途径；阐明利用田间管理技术，通过降低硝化、反硝化产物比，实现本地区典型农田土壤N2O减排的调控机理。本研究将田间温室气体排放、土壤过程和相关微生物优势功能种群及基因表达有机联结起来，从理论上深入认识该区典型农田土壤N2O 的产生与调控机制；在实践上为提出适合该地区N2O 减排和控制氮素损失的水肥管理措施提供科学依据。

在我国粮食和设施蔬菜主产区华北平原，选择主要粮食作物种植体系和高投入的设施菜田土壤为研究对象,以多点长期定位试验为基础，利用引进的专用设备(土壤连续培养自动监测系统)，研究了管理措施对硝化和反硝化过程产物比发生规律的影响；利用分子生物学技术，揭示不同管理方式对土壤中硝化、反硝化菌组成结构、优势种群与基因表达的影响规律；探索利用反硝化过程产物比进行氮损失定量的可能性；提出利用田间管理技术，实现本地区典型农田土壤N2O减排途径。主要结果如下：.1）设施菜田土壤中N2O产生的主导过程是反硝化过程。在大田条件下，主要来自于硝化过程和与硝化过程相耦合的反硝化过程。硝化和反硝化过程均导致NO2-过渡性积累，与N2O的产生有显著相关。以NO2-为底物的化学反硝化也对N2O产生有一定作用，特别是在酸性土壤上。.2）分析了硝化基因（amoA）与反硝化基因（narG, nirS, nirK, nosZ）的表达。高通量测序的结果表明，在设施菜田土壤长期施用有机肥导致厚壁菌门，特别是芽孢杆菌是导致N2O排放的主要功能类群。.3）土壤反硝化产物比受氧浓度、水分含量、碳源的有效性和氮形态等因素的影响，一般在0.14~0.71之间。利用产物比并结合田间N2O的通量观测数据，可以大致估计土壤反硝化过程氮的气态损失量。.4）提出了华北大田土壤的减排措施：避免施肥造成的局部高铵浓度；在保证作物产量的前提下，用硝态氮肥代替铵态氮肥；用铵态氮肥的同时施用硝化抑制剂。.5）建立全球农田土壤N2O排放的全新数据库，明确了pH是全球N2O排放的主要控制因子之一，发展了农田N2O排放的估算方法。.本项目为提出适合该地区N2O 减排和控制氮素损失的水肥管理措施提供了科学依据。