Microbial biomass stoichiometry and proportion of Fe organic complexes separately shape the heterogeneity of mixotrophic denitrification and net N2O sinks in iron-carbon amended ecological ditch

文献类型： 外文期刊

第一作者： Jiang, Bi-Ni

作者： Jiang, Bi-Ni;Zhang, Ying-Ying;Wang, Yan;Liu, Hai-qin;Zhang, Zhi-Yong;Yang, Yi-Jing;Jiang, Bi-Ni;Yang, Yi-Jing;Song, Hai-Liang

作者机构：

关键词： Vegetated drainage ditch; Mixotrophic denitrification; Fe oxides; DOM fraction; Iron-carbon micro-electrolysis; Net N2O sink

期刊名称：WATER RESEARCH （ 影响因子：12.4； 五年影响因子：12.9 ）

ISSN： 0043-1354

年卷期： 2025 年 272 卷

页码：

收录情况： SCI

摘要： Coupling of iron-carbon can form a mixotrophic denitrification and is regarded as a promising solution for purifying nitrate-rich agricultural runoff. However, its prevalence and efficacy of the synergistic augmentation of nitrogen elimination and net N2O sinks remain crucial knowledge gaps in ecological ditches (eco-ditches). Here, we investigated the underlying variability mechanisms by implementing sponge iron (sFe)-coupled Iris hexagonus (IH)- or Myriophyllum aquaticum (MA)-derived biochar produced via microwave-assisted (MW) pyrolysis and conventional pyrolysis. Surprisingly, unamened eco-ditch became net N2O sink while exhibiting a significant increase in total nitrogen (TN) removal rate of 319 % (P < 0.001) compared to soil ditch. The integration of MW pyrolyzed IH-derived biochar with sFe to amend eco-ditch achieved synchronous enhancement in net N2O sinks (P < 0.01) and TN removal rate (P < 0.001), whereas the remaining amended eco-ditches that significantly intensified TN removal performance, were N2O emitters. Such heterogeneity primarily depends on Fe organic complexes (Fep) / the total reactive Fe oxides (Fed) ratio, rather than the prevailing nosZ gene, underscoring that low density metastable reactive iron plays a more important role than biological reactions during the mixotrophic denitrification process. As such, iron oxides are not necessarily a bottleneck for denitrification and contribute to N2O sinks. Conversely, microbial biomass C:(C + N), together with nirK and nosZ genes, mainly explain the TN removal heterogeneity of sFe-biochar eco-ditch. This study revisits the discrepant resilience of iron-carbon coupling to N abatement and N2O sink-induced cooling and has significant practical implications for better understanding the cascading effects of mixotrophic denitrification driven by iron-carbon interactions.

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