Rapid warming in the Arctic threatens to amplify climate change by releasing the region’s vast stocks of soil carbon to the atmosphere. Increased nutrient availability may exacerbate soil carbon losses by stimulating microbial decomposition or offset them by increasing primary productivity. The outcome of these competing feedbacks remains unclear. Here we present results from a long-term nutrient addition experiment in northern Alaska, United States, coupled with a mechanistic isotope-tracing experiment. We found that soil carbon losses observed during the first 20 years of fertilization were caused by microbial priming and were completely reversed in the subsequent 15 years by shrub expansion which promoted an increasingly efficient carbon–nitrogen economy. Incorporating long-term stoichiometric responses in Earth system models will improve predictions of the magnitude, direction and timing of the Arctic carbon–climate feedback.

北极的快速变暖可能会向大气中释放该地区大量的土壤碳，从而加剧气候变化。养分可用性的增加可能会通过刺激微生物分解来加剧土壤碳流失，或者通过提高初级生产力来抵消碳流失。这些相互竞争的反馈的结果尚不清楚。在这里，我们介绍了在美国阿拉斯加北部进行的长期营养添加实验以及机械同位素示踪实验的结果。我们发现，在施肥的前 20 年观察到的土壤碳损失是由微生物引发引起的，并在随后的 15 年中通过灌木扩张完全逆转，这促进了越来越有效的碳氮经济。将长期化学计量响应纳入地球系统模型将改进对北极碳-气候反馈的大小、方向和时间的预测。