陕北马铃薯农田滴灌条件下土壤N2O排放的微生物调控机理

N2O emission from cropland soil is a major contributor to the global warming effect. As a fourth largest food crop in China, potato is characterized by high consumption of water and fertilizer, and large planting area. Nevertheless, study on the mechanism and regulation of N2O emission from potato cropland soil is still a weak area. Northern Shaanxi is one of optimal regions for potato growth in China. Drip irrigation is one of the primary ways for the potato cultivation model of high yield and efficiency in this region. Accordingly, there is imperative to study the regulation of N2O emission from soil in potato cropland of northern Shaanxi under the drip irrigation. Based on the previous study, we focus on the scientific problems of the main pathway for N2O emission from soil and the regulation mechanism of key functional microbe for N2O emission, using typical soil in irrigated potato cropland of northern Shaanxi as research object, by an in-situ experiment, adopting the method of gas chromatography-isotope ratio mass spectrometry, and combining the technology of high-throughput sequencing, we systematically study 1) characteristics of N2O emission from soil and its main pathways, 2) responses of soil N2O emission to soil environmental factor, and 3) regulation effects of key functional microbe for the N2O emission under the drip irrigation. In order to elucidate the main microbial pathways of N2O emission form soil, and to reveal the regulation mechanism of key functional microbe of N2O emission under the drip irrigation, which could provide scientific basis for effective reducing N2O emission from cropland soil for typical cultivation model of potato in northern Shaanxi.

农田土壤N2O排放是全球温室效应的主要贡献者，马铃薯作为我国第四大粮食作物，其水肥用量高，种植面积大，但马铃薯农田土壤N2O排放的机理与调控研究尚属薄弱领域。陕北是我国马铃薯优生区，滴灌栽培是当地马铃薯高产高效栽培的主要方式，因此，迫切需要明确陕北马铃薯农田滴灌条件下土壤N2O排放的调控机理。申请人在前期研究基础上，拟针对滴灌条件下土壤N2O排放的主要途径及关键功能微生物对N2O排放的调控机理这一科学问题，以陕北典型马铃薯滴灌农田土壤为研究对象，通过田间原位试验，利用气相色谱-稳定同位素比率质谱方法结合高通量测序技术，系统研究滴灌条件下土壤N2O排放特征及主要途径、土壤N2O排放对环境因子的响应，硝化和反硝化功能微生物对土壤N2O排放的调控效应。阐明土壤N2O排放的主要微生物途径，揭示关键功能微生物对N2O排放的调控机理，为我国陕北典型马铃薯栽培模式实现农田土壤N2O有效减排提供科学依据。

农田土壤是全球N2O的主要人为排放源，目前，马铃薯农田土壤N2O排放的内在机理研究尚属薄弱领域。本项目以陕北滴灌马铃薯农田土壤为研究对象，系统研究滴灌条件下土壤N2O排放的微生物调控机理。结果表明：（1）在整个生育期，膜下滴灌处理的土壤平均N2O浓度较露地滴灌高11.26%-46.31%，但由于地膜的阻隔作用，膜下滴灌处理的土壤N2O总排放量较露地滴灌低12.32%–41.03%。N2O同位素特征值（δ18O、δ15N和SP值）的变化范围显示，硝化微生物介导的硝化作用是陕北滴灌马铃薯农田土壤N2O排放的重要微生物途径；（2）N2O通量与土壤氮素（NH4+、NO3-、DIN、DON、TN）含量和土壤温度呈正相关，与土壤C/N比和pH值呈负相关，与土壤含水量的相关度较低。N2O同位素特征值对土壤环境因子的响应程度低于N2O通量对土壤微环境的响应。与露地滴灌相比，膜下滴灌处理提高了土壤温度，增加了土壤氮素含量，有助于增强硝化微生物的硝化作用，促使N2O的产生。并且，滴灌条件下土壤水分不是N2O通量变化的限制因子；（3）膜下滴灌处理下，amoA-AOB、amoA-AOA、narG、napA、nirK、nirS、norB和nosZ功能基因丰度、功能微生物的OTU数量及α多样性指数均高于露地滴灌。不同处理对AOA以及narG、napA和nosZ型反硝化功能微生物的群落结构有明显影响，而AOB和nxrB型硝化微生物群落对土壤微环境的变化不敏感。硝化和反硝化功能基因丰度同N2O通量、土壤氮素含量呈正相关。膜下滴灌处理提高了硝化和反硝化功能微生物丰度（nxrB除外），并改变了硝化和反硝化关键微生物的群落结构，有助于N2O的产生，但由于地膜的阻隔作用，N2O排放量低于露地滴灌。本研究可为陕北地区典型马铃薯栽培模式下，通过定向调控土壤关键功能微生物特性实现N2O有效减排提供理论依据。