Plant ecophysiological trade-offs between different strategies for tolerating stresses are widely theorized to shape forest functional diversity and vulnerability to climate change. However, trade-offs between hydraulic and stomatal regulation during natural droughts remain under-studied, especially in tropical forests. We investigated eleven mature forest canopy trees in central Amazonia during the strong 2015 El Niño. We found greater xylem embolism resistance (\({P}_{50}\) = − 3.3 ± 0.8 MPa) and hydraulic safety margin (HSM = 2.12 ± 0.57 MPa) than previously observed in more precipitation-seasonal rainforests of eastern Amazonia and central America. We also discovered that taller trees exhibited lower embolism resistance and greater stomatal sensitivity, a height-structured trade-off between hydraulic resistance and active stomatal regulation. Such active regulation of tree water status, triggered by the onset of stem embolism, acted as a feedback to avoid further increases in embolism, and also explained declines in photosynthesis and transpiration. These results suggest that canopy trees exhibit a conservative hydraulic strategy to endure drought, with trade-offs between investment in xylem to reduce vulnerability to hydraulic failure, and active stomatal regulation to protect against low water potentials. These findings improve our understanding of strategies in tropical forest canopies and contribute to more accurate prediction of drought responses.

不同耐受压力策略之间的植物生态生理学权衡被广泛理论化，以塑造森林功能多样性和对气候变化的脆弱性。然而，自然干旱期间水力和气孔调节之间的权衡仍未得到充分研究，尤其是在热带森林中。我们在 2015 年强厄尔尼诺现象期间调查了亚马逊中部的 11 棵成熟的林冠树。我们发现了更大的木质部栓塞抵抗力（\({P}_{50}\)= − 3.3 ± 0.8 MPa) 和水力安全裕度 (HSM = 2.12 ± 0.57 MPa) 比之前在亚马逊东部和中美洲更多降水季节性雨林中观察到的。我们还发现，较高的树木表现出较低的栓塞阻力和更大的气孔敏感性，这是水力阻力和主动气孔调节之间的高度结构权衡。这种由茎栓塞发作引发的对树木水分状态的主动调节起到了反馈作用，避免了栓塞的进一步增加，也解释了光合作用和蒸腾作用的下降。这些结果表明，冠层树表现出一种保守的水力策略来忍受干旱，在木质部投资以减少水力故障的脆弱性与积极的气孔调节以防止低水势之间进行权衡。