Wetting dry soil triggers emission of nitric oxide (NO), which can harm air quality and influence ecosystem N balance. NO released after wetting may be derived from two primary mechanisms: (1) abiotic decomposition of nitrite (NO₂⁻) present in the dry soil and (2) biologically-mediated production of NO. The relative contributions of these mechanisms to NO emission are challenging to partition. To differentiate the two mechanisms, we made continuous observations of NO emission from a range of soils that varied in texture, pH, and exchangeable cations. We coupled NO gas exchange measurements with automated, non-destructive high-resolution sampling of inorganic N species via microdialysis. We identified two distinct phases of NO production (1) an initial phase that reached its maximum less than 30 min after rewetting; and (2) a second phase lasting up to 36 h. The magnitude of the initial phase of NO production was correlated with the initial nitrous acid concentration (calculated from NO₂⁻ concentrations and soil pH) and soil exchangeable calcium. The second phase of NO emission coincided with a peak in NO₂⁻ that preceded NO₃⁻ accumulation. Together, these results suggest that NO emissions following wetting are defined by an initial pulse of abiotic NO formation mediated by soil acidity at mineral surfaces, followed by a prolonged pulse of NO emission driven by a lag between the biological processes of ammonia oxidation and nitrite oxidation. These results can inform mechanistic models of NO emissions from soils to improve predictions of the terrestrial N cycle and atmospheric chemistry.

湿润干燥的土壤会引发一氧化氮 (NO) 的排放，这会损害空气质量并影响生态系统的氮平衡。润湿后释放的 NO 可能来自两种主要机制：(1) 亚硝酸盐 (NO ₂ ^-) 存在于干燥土壤中和 (2) 生物介导的 NO 生产。这些机制对 NO 排放的相对贡献很难划分。为了区分这两种机制，我们对一系列质地、pH 值和可交换阳离子不同的土壤中的 NO 排放进行了连续观察。我们通过微透析将 NO 气体交换测量与无机 N 物种的自动化、非破坏性高分辨率采样相结合。我们确定了 NO 产生的两个不同阶段 (1) 初始阶段在再润湿后不到 30 分钟达到最大值；(2) 持续长达 36 小时的第二阶段。NO 产生的初始阶段的大小与初始亚硝酸浓度相关（从 NO ₂ ^-浓度和土壤 pH 值）和土壤可交换钙。NO 排放的第二阶段与NO ₃ ^-积累之前的 NO ₂ ^-峰值一致。总之，这些结果表明，润湿后的 NO 排放是由矿物表面土壤酸度介导的非生物 NO 形成的初始脉冲定义的，然后是由氨氧化和亚硝酸盐氧化的生物过程之间的滞后驱动的延长的 NO 排放脉冲. 这些结果可以为土壤 NO 排放的机制模型提供信息，以改进对陆地氮循环和大气化学的预测。