Journal of Integrative Agriculture ›› 2026, Vol. 25 ›› Issue (6): 2580-2594.DOI: 10.1016/j.jia.2026.01.010

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非饱和带中反硝化与亚硝酸盐氧化的并行发生：来自中国天津硝酸盐δ¹⁵N和δ¹⁸O的同位素证据

  

  • 收稿日期:2025-05-05 修回日期:2026-01-13 接受日期:2025-10-27 出版日期:2026-06-20 发布日期:2026-05-07

Parallel denitrification and nitrite oxidation in the unsaturated zone: Isotopic constraints from nitrate δ15N and δ18O in Tianjin, China

Dongmei Xue1*, Jinglei Wang1*, Lanxin Xiang1, Xiaoxian Peng1, Ke Jin2#, Yunting Fang3#, Xiangzhen Li4, Yidong Wang1, Zhongliang Wang5   

  1. 1 Tianjin Key Laboratory of Water Resources and Environment, Tianjin Normal University, Tianjin 300387, China

    2 Institute of Grassland Research, Chinese Academy of Agricultural Sciences, Huhhot 010010, China

    3 Key Laboratory of Forest Ecology and Management, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110016, China

    4 College of Resources and Environment, Fujian Agriculture and Forestry University, Fuzhou 350002, China

    5 Tianjin Key Laboratory of Aquatic Science and Technology, Tianjin Chengjian University, Tianjin 300384, China

  • Received:2025-05-05 Revised:2026-01-13 Accepted:2025-10-27 Online:2026-06-20 Published:2026-05-07
  • About author:Dongmei Xue, E-mail: xuedongmei@tjnu.edu.cn; Jinglei Wang, E-mail: 17861007620@163.com; #Correspondence Ke Jin, E-mail: jinke@caas.cn; Yunting Fang, E-mail: fangyt@iae.ac.cn * These authors contributed equally to this study.
  • Supported by:

    This work was financially supported by the National Natural Science Foundation of China (42361144860, 41973017 and 32071861).

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摘要：

反硝化作用是缓解生态系统人为硝酸盐（NO3-）累积的关键过程，而NO3- 同位素组成（δ¹⁵N 与 δ¹⁸O）是识别氮来源与转化过程的有效示踪手段。反硝化过程常叠加亚硝酸盐（NO2-）氧化产生的同位素效应，导致δ15N-NO₃⁻与δ18O-NO₃⁻同步富集，形成低于或高于1的Δδ¹⁸O:Δδ¹⁵N轨迹。本研究以非饱和带为研究对象，比较了Δδ¹⁸O:Δδ¹⁵N轨迹低于或高于1两组条件下，反硝化过程中的Δδ¹⁸O:Δδ¹⁵N轨迹变化、功能基因（narG、napA、nxrA）及代谢碳源特征。结果表明，NO3- 还原是导致Δδ¹⁸O:Δδ¹⁵N轨迹变异的主要因素，两组轨迹间NO3- 还原同位素效应（15εNO3 reduction与15εNO3 reduction）差异显著，而NO2- 氧化过程的同位素效应（15εnxr 和 18εnxr）无显著差异。在Δδ¹⁸O:Δδ¹⁵N轨迹低于1的组别中，碳源因其低分子量与简单结构，有助于更高效的电子产率，从而促进NO3- 还原；相反，在轨迹高于1的组别中，碳源的高分子量与复杂结构导致电子产率降低，进而下调三个功能基因（narG、napA、nxrA）的表达。轨迹低于1的组别在15εNO3 reduction、15εNO3 reduction、亚硝酸盐氧化比例以及narG、napA与nxrA基因拷贝数方面均显著高于另一组，表明该组在细胞水平的NO3- 还原活性更强。本研究系统阐明了同位素效应、NO3- 还原酶与NO2- 氧化还原酶活性以及代谢碳源对反硝化过程的综合影响。该发现对理解陆地生态系统氮循环中Δδ¹⁸O:Δδ¹⁵N轨迹的形成机制具有重要意义，并为通过优化碳源添加策略以强化反硝化、实现地下水保护提供了理论依据，同时证明Δδ¹⁸O:Δδ¹⁵N轨迹可作为评估陆地环境反硝化效能的有效示踪指标。

Abstract:

Denitrification plays a critical role in mitigating anthropogenic nitrate (NO3–) accumulation in ecosystems.  The isotopic composition of NO3– (δ15N and δ18O) serves as a powerful tracer for identifying N sources and transformation processes.  Denitrification often superimposed on the isotope effects of NO2– oxidation, resulting in parallel enrichment of δ15N- and δ18O-NO3– (Δδ18O:Δδ15N trajectory) that causes them to be either below or above 1.  This study compared the Δδ18O:Δδ15N trajectory during denitrification, functional genes (narG, napA, and nxrA), and carbon sources from metabolites in the Δδ18O:Δδ15N trajectories below or above 1 in unsaturated zones.  The results revealed that NO3– reduction was more important for variation in the Δδ18O:Δδ15N trajectory because the difference in isotope effects (15εNO3 reduction and 18εNO3 reduction) between the two Δδ18O:Δδ15N trajectory groups was significant, whereas the difference in isotope effects (15εnxr and 18εnxr) upon NO2– oxidation was not.  Carbon sources in the group with Δδ18O:Δδ15N trajectories below 1 facilitated more efficient electron production to promote NO3– reduction because of their low molecular weight and simple structure.  Conversely, the lower electron production efficiency due to the high molecular weight and complex structures of carbon sources in the group with Δδ18O:Δδ15N trajectories above 1 downregulated the expression of the three functional genes (narG, napA, and nxrA).  The group with Δδ18O:Δδ15N trajectories below 1 showed significantly higher levels of 15εNO3 reduction, 18εNO3 reduction, NO2– oxidation ratio, and copy numbers of narG, napA, and nxrA genes compared to the other group, revealing that NO3– reduction at the cellular level was more active in the former group.  This study elucidated the integrated influence of isotope effects, NO3– reductase and NO2– oxidoreductase activities, and carbon sources from metabolites.  These findings are significant for understanding the Δδ18O:Δδ15N trajectories of N cycling in terrestrial ecosystems and support groundwater conservation by improving carbon supplementation approaches that stimulate denitrification, with Δδ18O:Δδ15N trajectories serving as effective tracers for assessing denitrification performance in terrestrial environments.

Key words: denitrification , NO2– oxidation , Δδ18O:Δδ15N trajectory , NO3– reductase , NO2– oxidoreductase , carbon sources