Carbon (C) and nitrogen (N) are closely coupled to regulate the cycle of soil organic carbon (SOC) and its feedback to climate change in terrestrial ecosystem. However, the response of SOC content to N input in different soil types on time scales is still less understood. Here, we did a meta-analysis by collecting global farmland data across 60 years based on soil taxonomy, as well as our long-term field agricultural experiment from 2006 to 2019 (total number of observations, n = 301). The results showed that N addition promoted the increase of SOC content on an average of 9.1% in agrosystem, but varied considerably in different soil types (5.2%–12.0%). The SOC content of Alfisols and Mollisols soils showed a significant increasing response along the time scale. Furthermore, random forest model and structural equation model analysis indicated that climate factors and soil types indirectly affect the temporal response of SOC to N application through soil properties such as TN and C:N. This study emphasizes that the temporal response of SOC content to long-term N addition depends on soil type, with an scale-up effect in soil types with relative high SOC content (like Alfisols and Mollisols), which provides a new perspective for better understanding the C sequestration as the consequence of coupling effect of C and N in farmland system under long-term human activities.

碳（C）和氮（N）紧密耦合，调节土壤有机碳（SOC）的循环及其对陆地生态系统气候变化的反馈。然而，对不同土壤类型中 SOC 含量在时间尺度上对 N 输入的响应仍然知之甚少。在这里，我们根据土壤分类收集了 60 年的全球农田数据，以及我们从 2006 年到 2019 年的长期田间农业试验（观察总数，n = 301），进行了荟萃分析。结果表明，N添加促进了农业系统SOC含量的增加，平均增加了9.1%，但不同土壤类型（5.2%~12.0%）差异较大。Alfisols 和 Mollisol 土壤的 SOC 含量在时间尺度上显示出显着增加的响应。此外，随机森林模型和结构方程模型分析表明，气候因素和土壤类型通过土壤特性如 TN 和 C:N 间接影响 SOC 对施氮的时间响应。本研究强调 SOC 含量对长期 N 添加的时间响应取决于土壤类型，在 SOC 含量相对较高的土壤类型（如 Alfisols 和 Mollisol）中具有放大效应，这为更好地理解提供了新的视角长期人类活动下农田系统碳氮耦合效应导致的碳固存。