外源氮对潮土本底N2O排放的激发效应研究

The development of sustainable agriculture in China faces great challenges to maintain crop yield while mitigating N2O emissions from agricultural soils. In recent years, numerous isotopic tracing studies showed that exogenous N application can not only induce substantial direct N2O emissions but also have a significant priming effect on the N2O emission from native soil, which results in an increased risk of greenhouse gas emission. However, the mechanisms behind the priming effect are unclear. This project focuses on fluvo-aquic soil, and 15N tracing studies will be carried out to evaluate the changes of mineral N contents and N2O emissions from native soil after exogenous N application; assess the impact of exogenous N addition on native N2O production pathways and functional microbes’ abundances; and investigate the effect of crop-soil interaction on the primed N2O emission. The mechanisms of the priming effect will be subsequently elucidated from the aspects of 1) changes of N2O production substrates from native soil, 2) microbial regulatory mechanisms, and 3) botanic regulatory mechanisms. This project will facilitate further understanding of the relationships between N application and N2O emission, help to optimize N2O emission simulation, and promote the establishment of regional mitigation actions.

在保障作物产量的同时降低农田N2O排放是我国可持续农业发展面临的重要挑战。近年来国内外同行及申请人进行的同位素示踪研究发现，外源氮施用除导致大量的N2O直接排放外，还会显著激发土壤本底N2O排放，从而进一步加剧温室气体排放风险。然而，关于外源氮激发土壤本底N2O排放的机制尚不明确。本项目拟选取黄淮海粮食产区主要土壤类型潮土为研究对象，结合15N同位素示踪技术，分析外源氮施用后土壤本底无机氮含量及N2O排放的变化；研究外源氮对土壤本底N2O产生途径及相关功能微生物丰度的影响；探究施用外源氮后作物生长参与对土壤本底N2O排放的影响。进而分别从1）本底N2O产生底物变化、2）微生物调节机制和3）植物调节机制三个方面阐释外源氮对潮土本底N2O排放激发效应的产生机制。本项目的实施可为进一步明确施氮与N2O排放的关系，优化N2O排放估算模型，制定区域减排措施提供参考依据。

调控农田N2O排放对我国可持续农业的发展具有重要意义。近年来研究发现外源氮施用除导致大量N2O直接排放外，还会显著激发土壤本底N2O排放。但外源氮激发土壤本底N2O排放的机制目前尚不明确。本项目以潮土为研究对象，综合运用15N稳定性同位素技术，分别从底物产生、微生物驱动和植物调节三个角度，总结外源氮对本底N2O排放的影响及其机制。主要研究结果如下：1）15N示踪及库稀释试验显示，低氮土壤和高氮土壤施氮后本底N2O排放分别比对照处理提高了1.41倍和5.65倍；在等量外源氮投入下，高氮土壤本底N2O排放显著高于低氮土壤，表明高氮土壤的本底N2O排放风险更高；与未施氮处理相比，施氮后两天内土壤初级矿化量增加了33.0%−98.5%，表明外源氮施用对土壤氮素初级矿化的促进作用为激发本底N2O排放提供了底物条件；2）通过探究外源氮施用对N2O排放途径及其功能微生物的影响发现，施氮所激发的本底N2O排放量中有61.79%−78.19%来自硝化过程；施氮后土壤氨氧化细菌（AOB）基因丰度显著提高，且多元分析表明AOB基因丰度对N2O排放总量及本底N2O排放影响显著，表明外源氮施用主要通过提升AOB活性来促进总N2O排放及本底N2O排放；3）通过研究植物生长参与对N2O排放来源的影响发现，外源氮与作物的交互作用对N2O排放及其来源影响显著，与未种植作物相比，种植作物显著降低了土壤N2O排放总量，但是来自土壤本底N2O排放比例显著增加，说明植物生长与外源氮对土壤氮素周转及本底N2O排放具有协同促进作用。综上所述，外源氮施用会促进土壤氮素初级矿化量增加，为本底N2O排放提供底物，进而在AOB的介导下，主要通过硝化过程将矿化的本底氮素转化为N2O排放，导致外源氮对土壤本底N2O排放的激发效应。作物生长参与可协同外源氮施用促进N2O排放的激发过程。本项目研究成果可为优化N2O排放估算模型，制定区域减排措施提供参考依据。