施肥和秸秆还田对玉麦轮作农田土壤N2排放和N2O/(N2+N2O)影响效应和机制研究

Denitrification is a primary process to close the global nitrogen cycle. Quantification of the magnitude and variation characteristics of N2 emissions from soil is the key for better understanding the nitrogen cycle in agricultural ecosystem and evaluation of nitrogen fertilizer loss due to denitrification. This project will rely on a summer maize-winter wheat rotation cropping system after long-term application of nitrogen fertilizer and/or straw. Using the method that combines the gas-flow-soil-core technique with Helium incubation and the real-time quantitative PCR technique, the emissions of N2 and N2O from soil, the abundance and activity of functional genes (bacterial amoA for nitrification and nirS, nirK, nosZ, and AnirK for denitrification) related with N2 and N2O production, and the environmental controlling factors (i.e. oxygen, moisture, temperature, nitrogen and carbon concentrations) of soil in different treatments of nitrogen fertilizer and straw incorporation will be measured for two consecutive double rotations of observation. The objectives of this project are to (1) determine the magnitudes and variation characteristics of N2 emission and the ratio of N2O/(N2+N2O) from soil, (2) identify the contributions of different functional microbes on the production of N2 and N2O from soil, and (3) assess the effects and mechanisms of long-term incorporated nitrogen fertilizer and straw on the N2 emission and the ratio of N2O/(N2+N2O) from soil. Such findings would provide the fundamental data for quantitative measurements of nitrogen fertilizer loss as N2. Also, the results of this project will provide the scientific evidence for a win-win situation of high efficiency and environmentally friendly in nitrogen fertilizer utilization.

反硝化N2排放是闭合全球氮循环的重要环节。土壤N2排放的准确定量与变化规律研究，是阐明农田氮循环过程和评估氮素反硝化损失的关键。本项目拟依托长期不同碳氮投入的夏玉米-冬小麦轮作农田实验平台，采用氦培养-直接定量N2和荧光定量PCR相结合的方法，对不同碳氮管理处理的土壤N2和N2O排放、与其产生相关的硝化、反硝化微生物关键功能基因（amoA、nirS、nirK、nosZ和AnirK等）的丰度和活性、及土壤环境因子（氧气、温湿度、碳氮底物浓度等）进行两个轮作周期的观测研究，以期明确玉麦轮作农田土壤N2排放和N2O/(N2+N2O)的变化规律、探究不同功能微生物对土壤N2和N2O产生的贡献，评价氮肥用量和秸秆还田对土壤N2排放和N2O/(N2+N2O)的影响效应和微生物机制。该成果可望为肥料氮N2排放损失的准确定量提供实验数据基础，为实现我国农业氮肥高效利用与环境友好协同提供科学依据。

土壤N2排放的准确定量与变化规律研究，是阐明农田氮循环过程和评估氮素反硝化损失的关键。本项目以长期不同碳氮投入的冬小麦-夏玉米轮作农田为研究对象，采用野外原位观测和室内控制实验相结合的方法，明确了华北玉麦轮作农田土壤N2排放和N2O/(N2O+N2)比值的季节变化特征，定量了田间土壤N2损失量，揭示了不同碳氮管理对土壤N2排放和N2O/(N2+N2O)比值变化的影响效应和微生物机制。结果表明：基于环境因子参数化的N2O/(N2O+N2)比值和原位的N2O通量和多环境因子动态的观测可用于估算田间土壤N2排放；发现施氮“热时事件”中影响土壤N2O产生的硝化和反硝化作用的贡献是动态变化的，受施氮后土壤湿度和温度的共同影响；全秸秆还田通过促进灌溉小麦田的N2O还原为N2的过程，而利于玉麦轮作农田的净温室气体减排；在夏玉米季秸秆还田通过降低反硝化nosZ基因丰度（RNA水平）而不利于N2产生，但同时增加(nirK+nirS)/nosZ比值，表明对N2O排放的促进作用大于对N2O的还原作用，而导致高的N2O/(N2O+N2)比值。本研究为解决玉麦轮作农田土壤氮收支中N2估算提供了方法支持，并完善土壤N2O排放机理认知。相关成果在国内外期刊上发表论文6篇，培养硕博士研究生4名。