Terrestrial ecosystem respiration increases exponentially with temperature, constituting a positive feedback loop accelerating global warming. However, the response of ecosystem respiration to temperature strongly depends on water availability, yet where and when the water effects are important, is presently poorly constrained, introducing uncertainties in climate–carbon cycle feedback projections. Here, we disentangle the effects of temperature and precipitation (a proxy for water availability) on ecosystem respiration by analysing eddy covariance CO₂ flux measurements across 212 globally distributed sites. We reveal a threshold precipitation function, determined by the balance between precipitation and ecosystem water demand, which separates temperature-limited and water-limited respiration. Respiration is temperature limited for precipitation above that threshold function, whereas in drier areas water limitation reduces the temperature sensitivity of respiration and its positive feedback to global warming. If the trend of expansion of water-limited areas with warming climate over the last decades continues, the positive feedback of ecosystem respiration is likely to be weakened and counteracted by the increasing water limitation.

陆地生态系统呼吸随温度呈指数增长，构成加速全球变暖的正反馈回路。然而，生态系统呼吸对温度的响应在很大程度上取决于水的可用性，但水效应在何时何地很重要，目前受到的限制很差，这给气候-碳循环反馈预测带来了不确定性。在这里，我们通过分析全球 212 个站点的涡度相关 CO₂ 通量测量值，解开温度和降水（水可用性的代理）对生态系统呼吸的影响。我们揭示了一个阈值降水函数，该函数由降水和生态系统需水之间的平衡决定，它区分了温度限制和水限制呼吸。对于高于该阈值函数的降水，呼吸作用是温度限制的，而在较干燥的地区，水的限制降低了呼吸作用的温度敏感性及其对全球变暖的正反馈。如果过去几十年来随着气候变暖而扩大水资源限制区的趋势继续下去，生态系统呼吸的正反馈可能会被日益增加的水资源限制所削弱和抵消。