The physiological response of plants to water stresses has been a focus in understanding plant-atmosphere feedback. Tropical forests are particularly noteworthy for their remarkable diversity and dynamics. However, a deep understanding of physiological response and associated mortality risk of tropical trees with different leaf phenology under drought is still deficient. In this study, we combined sap flow measurements and a plant hydraulic model to present the water utilization of four canopy trees (two deciduous trees and two evergreen trees) in a Panamanian seasonal tropical forest during the 2016 El Niño drought. The results showed that the transpiration () of deciduous trees rapidly decreased with intensifying soil drought during the dry season, while evergreen trees still maintained high and increased with the increase of atmospheric dryness (vapor pressure deficit (VPD)). During the wet season, the of both deciduous and evergreen trees was jointly driven by increasing soil moisture (SWC) and reducing VPD. The differential pattern during the dry season is closely related to the difference in leaf phenology, with deciduous trees greatly reducing canopy stomatal conductance () through defoliation, and thereby maintaining leaf water potential (Ψ) and reducing water loss. Additionally, deciduous trees demonstrated a slow increase in the difference between midday (Ψ) and predawn (Ψ) leaf water potential (i.e. lower hydraulic sensitivity (σ)) compared to evergreen trees. Evaluation of mortality risk under changing water stresses further indicated that all trees exhibited high hydraulic failure risk (HFR) under decreasing SWC scenarios. Moreover, deciduous trees displayed a much higher stomatal closure risk (SCR) than evergreen trees. These differences in response and σ suggest a key role of the coordination between stomatal regulation and plant hydraulics in mediating physiological response to water stresses. More investigation and mechanism illumination will facilitate the prediction of tropical forest response to drought.

中文翻译：

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2016年厄尔尼诺干旱期间四种不同叶物候的热带树冠树木的用水和死亡风险


植物对水分胁迫的生理反应一直是理解植物-大气反馈的焦点。热带森林因其显着的多样性和活力而特别引人注目。然而，对不同叶物候的热带树木在干旱条件下的生理反应和相关死亡风险的深入了解仍然不足。在这项研究中，我们结合了液流测量和植物水力模型，展示了 2016 年厄尔尼诺干旱期间巴拿马季节性热带森林中四棵树冠树（两棵落叶树和两棵常绿树）的水利用情况。结果表明，旱季期间，随着土壤干旱的加剧，落叶乔木的蒸腾量迅速下降，而常绿乔木的蒸腾量仍然保持较高水平，并随着大气干燥度（蒸气压赤字（VPD））的增加而增加。在雨季，落叶树和常绿树的生长受到土壤湿度（SWC）增加和 VPD 减少的共同驱动。旱季的差异格局与叶片物候的差异密切相关，落叶乔木通过落叶大大降低冠层气孔导度（），从而维持叶片水势（Ψ），减少水分流失。此外，与常绿树相比，落叶树在中午（Ψ）和黎明前（Ψ）叶水势之间的差异缓慢增加（即较低的水力敏感性（σ））。对水胁迫变化下死亡风险的评估进一步表明，在 SWC 减少的情况下，所有树木都表现出较高的水力破坏风险 (HFR)。此外，落叶树比常绿树表现出更高的气孔关闭风险（SCR）。 这些响应和 σ 的差异表明气孔调节和植物水力学之间的协调在调节对水分胁迫的生理反应中发挥着关键作用。更多的调查和机制阐明将有助于预测热带森林对干旱的反应。