The ability of forests to withstand, and recover from, acute drought stress is a critical uncertainty regarding the impacts of climate change on the terrestrial carbon (C) cycle, but it is unclear how drought responses scale from individual trees to whole forests. Here, we assembled a dataset of tree-ring chronologies co-located within the footprint of eddy covariance towers across North America and Europe, with the aim of quantifying the sensitivity of tree radial growth versus gross primary productivity (GPP) during and following drought. We found that drought induced a large decoupling across C cycle processes, whereby GPP was relatively resistant to water stress despite large reductions in tree-ring widths. This decoupling also occurred in the year following drought (i.e., a ‘drought legacy effect’), and was similar in magnitude in response to both summer and winter droughts. By modeling whole-forest C turnover time, we show that a radial growth-GPP decoupling has important ramifications for the forest C cycle, especially if the C not used to support radial growth is instead allocated towards pools with short residence times. Our results demonstrate that quantifications of drought impacts that rely solely on C uptake are missing this fundamental pathway through which drought alters the forest C cycle and the resulting feedbacks to the climate system.

森林承受急性干旱胁迫并从中恢复的能力是气候变化对陆地碳 (C) 循环影响的关键不确定性，但尚不清楚干旱响应如何从单棵树木扩展到整个森林。在这里，我们汇集了位于北美和欧洲的涡流协方差塔足迹内的树木年轮年表数据集，目的是量化树木径向生长与干旱期间和之后的总初级生产力 (GPP) 的敏感性。我们发现干旱在 C 循环过程中引起了很大的脱钩，尽管年轮宽度大幅减少，但 GPP 对水分胁迫具有相对抵抗力。这种脱钩也发生在干旱之后的一年（即“干旱遗留效应”），并且在应对夏季和冬季干旱时的幅度相似。通过对全森林 C 周转时间进行建模，我们表明径向生长-GPP 解耦对森林 C 循环具有重要影响，特别是如果不用于支持径向生长的 C 被分配给停留时间短的池。我们的研究结果表明，仅依赖于 C 吸收的干旱影响的量化缺少干旱改变森林 C 循环以及由此产生的对气候系统的反馈的基本途径。