Terrestrial ecosystem carbon (C) sequestration plays an important role in ameliorating global climate change. While tropical forests exert a disproportionately large influence on global C cycling, there remains an open question on changes in below-ground soil C stocks with global increases in nitrogen (N) deposition, because N supply often does not constrain the growth of tropical forests. We quantified soil C sequestration through more than a decade of continuous N addition experiment in an N-rich primary tropical forest. Results showed that long-term N additions increased soil C stocks by 7 to 21%, mainly arising from decreased C output fluxes and physical protection mechanisms without changes in the chemical composition of organic matter. A meta-analysis further verified that soil C sequestration induced by excess N inputs is a general phenomenon in tropical forests. Notably, soil N sequestration can keep pace with soil C, based on consistent C/N ratios under N additions. These findings provide empirical evidence that below-ground C sequestration can be stimulated in mature tropical forests under excess N deposition, which has important implications for predicting future terrestrial sinks for both elevated anthropogenic CO₂ and N deposition. We further developed a conceptual model hypothesis depicting how soil C sequestration happens under chronic N deposition in N-limited and N-rich ecosystems, suggesting a direction to incorporate N deposition and N cycling into terrestrial C cycle models to improve the predictability on C sink strength as enhanced N deposition spreads from temperate into tropical systems.

陆地生态系统碳（C）固存在改善全球气候变化方面发挥着重要作用。虽然热带森林对全球碳循环产生了不成比例的巨大影响，但随着全球氮 (N) 沉积的增加，地下土壤碳储量的变化仍然是一个悬而未决的问题，因为氮供应通常不会限制热带森林的生长。我们通过在富含 N 的原始热带森林中进行了十多年的连续 N 添加实验，量化了土壤 C 固存。结果表明，长期氮添加使土壤碳储量增加了 7% 到 21%，这主要是由于碳输出通量降低和物理保护机制没有改变，有机质的化学成分没有变化。一项荟萃分析进一步证实，过量氮输入引起的土壤碳固存是热带森林中的普遍现象。值得注意的是，基于在 N 添加下一致的 C/N 比，土壤 N 固存可以与土壤 C 保持同步。这些发现提供了经验证据，表明在过量 N 沉积的成熟热带森林中可以刺激地下 C 固存，这对于预测未来人类活动 CO 升高的陆地汇具有重要意义₂和N沉积。我们进一步开发了一个概念模型假设，描述了在 N 限制和富 N 生态系统中，在慢性 N 沉积下土壤 C 封存是如何发生的，这表明将 N 沉积和 N 循环纳入陆地 C 循环模型以提高对 C 汇强度的可预测性的方向随着增强的氮沉积从温带扩散到热带系统。