Soil nitrogen deficiency and poor fertility have been widely concerned in saline-alkaline paddy soil of the Yellow River Delta (YRD). NH₄⁺-N content regulated by soil organic carbon (SOC) and the rate of feammox reaction which provides a worth understanding in nitrogen (N) transformation. A 5-year field experiment was carried out to investigate the effect of straw returning and N fertilization rates on the NH₄⁺-N, microbially reducible Fe(III) (MR-Fe) and bacterial community composition in YRD. Six treatments were designed, including three straw returning rates (S0, S1 and S2, which was 0, 4500 and 9000 kg C ha⁻¹, respectively) under two N fertilization levels (N1 and N2, which was 400 and 255 kg N ha⁻¹, respectively). Our results showed that, compared with N1 level, soil NH₄⁺-N content showed no significant changes in N2 level at same straw returning rate. Under N2 level, compared with S0 and S2 rates, NH₄⁺-N content was increased by 64.8% and 50.3% in S1 rate, respectively. SOC content showed no difference between S1 and S2 treatments, which were higher than that in S0 treatment. While the labile carbon (i.e., readily oxidized organic carbon and dissolved organic carbon) was increased in S2 treatment, which promoted the dissolution of MR-Fe and increased the relative abundance of Geobacter and Anaeromyxobacter. Additionally, the structural equation models further indicated that more soil labile carbon could improve MR-Fe content and Geobacter and Anaeromyxobacter abundance, which decreased soil NH₄⁺-N content via feammox reaction. Therefore, half straw returning with the optimized N fertilization decreased NH₄⁺ oxidation and Fe reduction by supporting a more stable bacteria community structure, which played a key role in N availability and promoted the sustainable development of modern agriculture in saline-alkaline paddy soils.

黄河三角洲盐碱地水稻土壤缺氮、肥力差问题已引起广泛关注。NH ₄ ⁺ -N 含量受土壤有机碳 (SOC) 和 feammox 反应速率的调节，这为氮 (N) 转化提供了有价值的理解。进行了为期 5 年的田间试验，研究了秸秆还田和施氮量对长三角地区NH ₄ ⁺ -N、微生物可还原 Fe(III) (MR-Fe) 和细菌群落组成的影响。设计了六个处理，包括三种秸秆还田率（S0、S1 和 S2，分别为 0、4500 和 9000 kg C ha ^-1）在两种施氮水平（N1 和 N2，分别为 400 和 255 kg N ha）下⁻¹， 分别）。我们的结果表明，与N1水平相比，土壤NH ₄ ⁺ -N含量在相同秸秆还田率下N2水平没有显着变化。在N2水平下，与S0和S2率相比，S1率中NH ₄ ⁺ -N含量分别增加了64.8%和50.3%。S1和S2处理间SOC含量无差异，均高于S0处理。而S2处理中不稳定碳（即易氧化的有机碳和溶解的有机碳）增加，促进了MR-Fe的溶解，增加了地杆菌和厌氧菌的相对丰度. 此外，结构方程模型进一步表明，更多的土壤不稳定碳可以提高 MR-Fe 含量以及地杆菌和厌氧菌丰度，从而通过 feammox 反应降低土壤 NH ₄ ⁺ -N 含量。因此，优化施氮的半秸秆还田通过支持更稳定的细菌群落结构来减少NH ₄ ⁺氧化和Fe还原，这在氮的有效性方面发挥了关键作用，促进了盐碱稻田现代农业的可持续发展。