Tundra and boreal ecosystems encompass the northern circumpolar permafrost region and are experiencing rapid environmental change with important implications for the global carbon (C) budget. We analysed multi-decadal time series containing 302 annual estimates of carbon dioxide (CO₂) flux across 70 permafrost and non-permafrost ecosystems, and 672 estimates of summer CO₂ flux across 181 ecosystems. We find an increase in the annual CO₂ sink across non-permafrost ecosystems but not permafrost ecosystems, despite similar increases in summer uptake. Thus, recent non-growing-season CO₂ losses have substantially impacted the CO₂ balance of permafrost ecosystems. Furthermore, analysis of interannual variability reveals warmer summers amplify the C cycle (increase productivity and respiration) at putatively nitrogen-limited sites and at sites less reliant on summer precipitation for water use. Our findings suggest that water and nutrient availability will be important predictors of the C-cycle response of these ecosystems to future warming.

苔原和北方生态系统涵盖北部环极地永久冻土区，正在经历快速的环境变化，对全球碳 (C) 预算产生重要影响。我们分析了多个年代际时间序列，其中包含 70 个永久冻土和非永久冻土生态系统的 302 个年度二氧化碳 (CO ₂ ) 通量估计值，以及 181 个生态系统的 672 个夏季 CO ₂通量估计值。我们发现非永久冻土生态系统的年度CO ₂吸收量有所增加，但永久冻土生态系统并未增加，尽管夏季的吸收量也有类似的增加。因此，最近的非生长季节CO ₂损失严重影响了永久冻土生态系统的CO ₂平衡。此外，年际变化分析表明，在假定的氮限制地点和用水较少依赖夏季降水的地点，温暖的夏季会放大碳循环（提高生产力和呼吸作用）。我们的研究结果表明，水和养分的可用性将是这些生态系统对未来变暖的碳循环响应的重要预测因素。