Quantifying the gross rates of individual nitrogen (N) processes is critical for understanding the availability, retention and loss of N and its eco-environmental impacts in agricultural ecosystems. Here, we carried out a ¹⁵N tracing study to quantify the influence of soil moisture on the gross rates of ten different N processes in two intensively managed fluvo-aquic soils. Results showed that the gross N mineralization rates were insensitive to changes in soil moisture, ranging from 40 to 120% water-filled pore space (WFPS). Contrarily, the gross ammonium (NH₄⁺) immobilization rates increased exponentially with elevated soil moisture. Specifically, under high soil moisture conditions (i.e., 90–120%WFPS), the gross NH₄⁺ immobilization rates (4.04 ± 0.83 and 0.88 ± 0.28 mg N kg^− 1d^− 1 for the two soils, respectively) were nearly four times higher than those under medium or low moisture conditions (i.e., 40–80%WFPS). Meanwhile, the high WFPS reduced the gross autotrophic nitrification rates (5.92 ± 2.15 and 12.31 ± 3.83 mg-N kg^− 1d^− 1 for the two soils, respectively) to only one-third to one-half of those that were observed under medium or low WFPS. By contrast, the rates of nitrate (NO₃⁻) immobilization increased in one soil whereas they decreased in another under high moisture conditions, and the other N processes (including heterotrophic nitrification and dissimilatory nitrate reduction to ammonium (DNRA)) were negligible throughout the different WFPS. Overall, our results suggest that under highly saturated conditions, the increase in microbial NH₄⁺ immobilization and decrease in autotrophic nitrification are critical for N retention in the fluvo-aquic soils. These findings provide valuable insights into potential alterations in soil N retention or loss under future climate change scenarios, where more intensive irrigation and extreme rainfall events are anticipated.

量化各个氮 (N) 过程的总速率对于了解氮的可用性、保留和损失及其对农业生态系统的生态环境影响至关重要。在这里，我们进行了¹⁵ N 追踪研究，以量化土壤湿度对两种集约化管理的潮土中十种不同氮过程总速率的影响。结果表明，总氮矿化率对土壤湿度的变化不敏感，土壤湿度范围为 40% 至 120% 充满水的孔隙空间 (WFPS)。相反，随着土壤湿度的升高，总铵（NH ₄ ⁺）固定率呈指数增加。具体而言，在高土壤湿度条件下（即 90–120%WFPS），总 NH ₄ ⁺固定率（两种土壤分别为 4.04 ± 0.83 和 0.88 ± 0.28 mg N kg ^{− 1} d ^{− 1}）接近 4比中低湿度条件下（即 40-80%WFPS）高出数倍。同时，高 WFPS 将总自养硝化率（两种土壤分别为 5.92 ± 2.15 和 12.31 ± 3.83 mg-N kg ^{− 1} d ^{− 1}）降低至仅在低 WFPS 下观察到的三分之一至二分之一。中或低 WFPS。相比之下，在高湿度条件下，一种土壤中的硝酸盐 (NO ₃ ^- ) 固定率增加，而另一种土壤中的硝酸盐 (NO 3 - ) 固定率则降低，并且其他氮过程（包括异养硝化和异化硝酸盐还原为铵 (DNRA)）在整个过程中可以忽略不计。不同的 WFPS。总体而言，我们的结果表明，在高度饱和条件下，微生物 NH ₄ ⁺固定的增加和自养硝化作用的减少对于潮​​土中氮的保留至关重要。这些发现为未来气候变化情景下土壤氮保留或损失的潜在变化提供了宝贵的见解，预计将出现更密集的灌溉和极端降雨事件。