Dissimilatory nitrate reduction to ammonium (DNRA) contributes to nitrogen (N) conservation, whereas denitrification and anaerobic ammonium oxidation (anammox) lead to N loss in agroecosystems. However, their relative roles in nitrate (NO₃⁻) partitioning for total dissimilatory NO₃⁻ reduction and the effects of long-term straw retention on such mechanisms remain largely unclear. In this study, after implementing straw return and N addition for seven consecutive years in a paddy field, we used ¹⁵N tracing combined with molecular biological techniques to investigate the rates of denitrification, anammox, DNRA, and their associated abundance of nosZ, hszB, and nrfA genes, respectively, as well as the characteristics of the DNRA community. The results showed that the rates of denitrification, anammox, and DNRA varied from 20.7 to 33.3, 0.12–0.34, and 0.88–3.20 nmol N g⁻¹ h⁻¹, respectively. Straw return significantly increased denitrification, anammox, DNRA activities, and the abundance of associated genes, except for the anammox hszB gene. With increasing N input rate, the denitrification rate increased (P < 0.05), the DNRA rate decreased (P < 0.05), whereas the abundance of the three functional genes did not change significantly. Compared with chronic high N addition under straw retention, low N amendment increased the DNRA-based NO₃⁻ partitioning by 61–111%, although denitrification dominated the dissimilatory NO₃⁻ reduction process. The significant increase in soil DOC:NO₃⁻ ratio (R² = 0.89), and the reduction of soil pH (R² = 0.87) and standing water NO₃⁻ concentration (R² = 0.70), promoted N conservation through DNRA. The core subset of DNRA communities (R² = 0.99), belonging to Bacteroidetes, Proteobacteria, Euryarchaeota, and Firmicutes phyla, were responsible for DNRA activities. This is the first study to examine all three dissimilatory NO₃⁻ reduction processes in response to long-term straw return and N addition. We propose that straw return with low N addition can largely favor DNRA partitioning among the three dissimilatory NO₃⁻ reduction processes through biotic and abiotic regulators.

硝酸盐异化还原为铵 (DNRA) 有助于氮 (N) 的保存，而反硝化和厌氧铵氧化 (anammox) 会导致农业生态系统中的 N 损失。然而，它们在硝酸盐 (NO ₃ ^- ) 分配以减少总异化 NO ₃ ^{- 中}的相对作用以及长期秸秆保留对此类机制的影响在很大程度上仍不清楚。本研究在稻田连续 7 年实施秸秆还田和施氮后，采用¹⁵ N 示踪结合分子生物学技术，研究了反硝化率、厌氧氨氧化、DNRA 及其相关的nosZ、hszB、和nrfA基因，以及 DNRA 群落的特征。结果表明，反硝化、厌氧氨氧化和 DNRA 的速率分别从 20.7 到 33.3、0.12-0.34 和 0.88-3.20 nmol N g ^-1 h ^{-1 变化}。除厌氧氨氧化hszB基因外，秸秆还田显着增加了反硝化、厌氧氨氧化、DNRA 活性和相关基因的丰度。随着N输入速率的增加，反硝化速率增加（P  < 0.05），DNRA速率降低（P  < 0.05），而三个功能基因的丰度没有显着变化。与秸秆保留条件下的慢性高氮添加相比，低氮添加增加了基于DNRA的NO ₃ ^-分配 61-111%，尽管反硝化作用主导了异化 NO ₃ ^-还原过程。土壤DOC:NO ₃ ^-比率（R ²  = 0.89）的显着增加以及土壤pH值（R ²  = 0.87）和静水NO ₃ ^-浓度（R ²  = 0.70）的降低，通过DNRA促进了N的保存。DNRA 群落的核心子集 (R ²  = 0.99)，属于拟杆菌门、变形菌门、Euryarchaeota 和厚壁菌门，负责 DNRA 活动。这是第一项检查所有三种异化 NO _{3 的研究}^-响应长期秸秆还田和氮添加的减少过程。我们提出，低氮添加的秸秆还田在很大程度上有利于 DNRA通过生物和非生物调节剂在三个异化 NO ₃ ^-还原过程中进行分配。