硝化作用是农田生态系统的重要过程。2015年底，可以进行一步硝化的comammox的发现，颠覆了人们对传统两步硝化过程近百年的认知，并引发众多关于comammox在硝化过程中相对贡献的深入思考。本项目拟以小麦-玉米和小麦-大豆两种轮作模式长期定位试验田为研究对象，运用定量PCR、高通量测序、稳定同位素核酸探针（DNA-SIP）等分子生物学技术，研究农田土壤中comammox在不同轮作模式下丰度和群落结构的年际变化，以及传统硝化微生物和comammox生态位差异，分析comammox对硝化作用的相对贡献，探索轮作模式农田土壤中的主导硝化路径及其微生物学机制。项目的实施有助于深入了解农田土壤中氮素转化机制，为农田尺度氮素养分管理、面源污染防控及温室气体减排提供理论依据。

Nitrification is an essential process in agricultural ecosystems. The classical two-step nitrification, the oxidation of ammonia to nitrate via nitrite, is radically challenged by the recent discovery of complete ammonia oxidation (comammox). The first report of comammox has triggered many scientific issues and deeply thoughts concerning relative contributions of comammox to nitrification since 2015. The aim of this study is to examine the distribution of comammox, the niche differentiation of conventional nitrifiers and comammox, as well as the relative contributions of comammox to nitrification in agricultural soils under two long-term various crop rotations: wheat-maize and wheat-soybean. A combination of molecular methods, such as DNA-based stable-isotope probing (DNA-SIP), real-time quantitative PCR, and high-throughput sequencing, will be used to identify contributions of conventional ammonia oxidizers and comammox to nitrification. Results from this research will significantly improve our fundamental understanding of nitrogen transformation in agricultural soils, and will provide important scientific evidence for nitrogen fertilizer management, thus help mitigate agricultural non-point pollution and nitrous oxide emissions.