Plant thermoregulation through transpirational cooling is important when facing heat stress and is suggested as an active mechanism to maintain lower leaf temperature during heatwaves. However, whether the role of cooling through transpiration is constrained in drought-prone habitats for the sake of hydraulic safety remains largely unknown. To evaluate the influence of plant water use characteristics on transpiration-based thermoregulation, we compared responses to natural and experimental heatwave conditions of two sand dune shrub species commonly used in dune revegetation projects but inherently differ in xylem hydraulics and water-use strategies. Salix gordejevii adopts a conservative water-use strategy and has low xylem native embolism and Caragana microphylla uses water less frugally and suffers high degrees of xylem native embolism. Under natural conditions, S. gordejevii exhibited lower transpiration levels, higher leaf temperature and had greater leaf thermotolerance with regard to cell membrane thermostability than C. microphylla. During the experimental heatwave, neither species increased cooling through transpirational water loss and maintained stable leaf water status and xylem embolism levels, suggesting that water conservation for hydraulic integrity is possibly a higher priority than transpirational cooling in sand dune shrubs experiencing heatwaves. This study provides evidence that the water-use behavior of shrubs from water-limited sand dunes prioritizes protection against water stress over heat stress.

当面临热胁迫时，植物通过蒸腾冷却进行温度调节很重要，并且被认为是热浪期间维持较低叶片温度的积极机制。然而，出于水力安全的考虑，在干旱多发的栖息地中，通过蒸腾作用进行冷却的作用是否受到限制，在很大程度上仍是未知数。为了评估植物水分利用特性对基于蒸腾的温度调节的影响，我们比较了两种沙丘灌木物种对自然和实验热浪条件的响应，这两种沙丘灌木物种常用于沙丘植被重建项目，但在木质部水力学和用水策略方面存在内在差异。黄柳采取保守的用水策略，具有低木质部原生栓塞和小叶锦鸡儿节俭地用水，并遭受高度的木质部天然栓塞。在自然条件下，S. gordejevii表现出较低的蒸腾水平、较高的叶片温度，并且在细胞膜热稳定性方面比C. microphylla具有更高的叶片耐热性。在实验性热浪期间，这两个物种都没有通过蒸腾失水来增加降温，也没有保持稳定的叶水状态和木质部栓塞水平，这表明在经历热浪的沙丘灌木中，水力完整性的保水可能比蒸腾降温更重要。这项研究提供的证据表明，来自限水沙丘的灌木的用水行为优先于防止水分胁迫而不是热胁迫。