Arctic and alpine tundra ecosystems are large reservoirs of organic carbon^1,2. Climate warming may stimulate ecosystem respiration and release carbon into the atmosphere^3,4. The magnitude and persistency of this stimulation and the environmental mechanisms that drive its variation remain uncertain^5,6,7. This hampers the accuracy of global land carbon–climate feedback projections^7,8. Here we synthesize 136 datasets from 56 open-top chamber in situ warming experiments located at 28 arctic and alpine tundra sites which have been running for less than 1 year up to 25 years. We show that a mean rise of 1.4 °C [confidence interval (CI) 0.9–2.0 °C] in air and 0.4 °C [CI 0.2–0.7 °C] in soil temperature results in an increase in growing season ecosystem respiration by 30% [CI 22–38%] (n = 136). Our findings indicate that the stimulation of ecosystem respiration was due to increases in both plant-related and microbial respiration (n = 9) and continued for at least 25 years (n = 136). The magnitude of the warming effects on respiration was driven by variation in warming-induced changes in local soil conditions, that is, changes in total nitrogen concentration and pH and by context-dependent spatial variation in these conditions, in particular total nitrogen concentration and the carbon:nitrogen ratio. Tundra sites with stronger nitrogen limitations and sites in which warming had stimulated plant and microbial nutrient turnover seemed particularly sensitive in their respiration response to warming. The results highlight the importance of local soil conditions and warming-induced changes therein for future climatic impacts on respiration.

北极和高山苔原生态系统是有机碳的大型库^1,2。气候变暖可能会刺激生态系统呼吸并将碳释放到大气中^3,4。这种刺激的强度和持久性以及驱动其变化的环境机制仍然不确定^5,6,7。这妨碍了全球陆地碳气候反馈预测的准确性^7,8。在这里，我们综合了来自 28 个北极和高山苔原地点的 56 个开顶室原位变暖实验的 136 个数据集，这些实验的运行时间不到 1 年到 25 年。我们发现，空气温度平均升高 1.4 °C [置信区间 (CI) 0.9–2.0 °C]，土壤温度平均升高 0.4 °C [CI 0.2–0.7 °C]，会导致生长季生态系统呼吸增加 30 % [CI 22–38%] ( n  = 136)。我们的研究结果表明，生态系统呼吸的刺激是由于植物相关呼吸和微生物呼吸的增加 ( n  = 9)，并且持续了至少 25 年 ( n  = 136)。变暖对呼吸作用的影响程度是由变暖引起的当地土壤条件变化（即总氮浓度和 pH 值的变化）以及这些条件中与环境相关的空间变化（特别是总氮浓度和碳：氮比。氮限制较强的苔原地区以及变暖刺激植物和微生物养分周转的地区似乎对变暖的呼吸反应特别敏感。结果强调了当地土壤条件和变暖引起的变化对未来气候对呼吸影响的重要性。