Endris Joe, Rehm Evan
Biology Department, Austin Peay State University, 601 College St, Clarksville, TN 37044, USA.
Northern Research Station, US Forest Service, 180 Canfield St, Morgantown, WV 26505, USA.
AoB Plants. 2024 Nov 1;17(3):plae060. doi: 10.1093/aobpla/plae060. eCollection 2025 Jun.
Changing climates are creating more intense and frequent high-temperature events that could disrupt forest communities. In temperate forests, we have a relatively limited understanding of how trees are impacted by heat events, hindering our ability to predict the impacts of future heat waves. We conducted a community-level assessment of thermal safety margins in 11 hardwood tree species native to eastern North America. We used chlorophyll fluorescence to determine the critical heat tolerance of photosystem II (PSII) across 2 years in central Tennessee, USA. We focus on the temperature at which PSII first starts to decline ( ) as this is the temperature where membranes become unstable, resulting in permanent damage to these tissues. varied within the season and between years, being higher in July than June and in 2022 than 2023. also varied among species with species like and showing consistently lower heat tolerances. When compared to the record high temperature for our study site, 10 of 11 species would have experienced heat stress during at least one sample period. When compared to current year high temperatures, the risk was variable and lower across all species and sample periods. However, we found that leaf temperatures often exceeded air temperatures many species were likely heat stressed as heat tolerances were often below species-specific leaf temperatures. Indeed, four species were potentially heat stressed during every sample period. Our data highlights the importance of using leaf temperature, not air temperature to assess thermal safety margins and that community-wide stress may already occur under extreme heat conditions. As climate change intensifies, leaf temperatures will likely approach critical thresholds that lead to damage across the tree community. Understanding species-specific responses to heat stress is essential to predicting future forest dynamics and ecosystem functioning.
气候变化正在导致更强烈、更频繁的高温事件，这可能会扰乱森林群落。在温带森林中，我们对树木如何受到高温事件的影响了解相对有限，这阻碍了我们预测未来热浪影响的能力。我们对原产于北美东部的11种阔叶树种进行了群落水平的热安全边际评估。我们利用叶绿素荧光在美国田纳西州中部的两年时间里确定了光系统II（PSII）的临界耐热性。我们关注PSII首次开始下降时的温度（ ），因为这是膜变得不稳定的温度，会导致这些组织受到永久性损伤。 在季节内和年份间有所变化，7月高于6月，2022年高于2023年。 在物种间也有所不同，像 和 这样的物种耐热性一直较低。与我们研究地点的历史最高温度相比，11个物种中有10个在至少一个采样期内会经历热应激。与当年的高温相比，风险是可变的，且在所有物种和采样期内都较低。然而，我们发现叶片温度经常超过空气温度，许多物种可能受到热应激，因为耐热性往往低于物种特定的叶片温度。事实上，在每个采样期都有四个物种可能受到热应激。我们的数据强调了使用叶片温度而非空气温度来评估热安全边际的重要性，以及在极端高温条件下可能已经出现了整个群落范围的应激。随着气候变化加剧，叶片温度可能会接近导致整个树木群落受损的临界阈值。了解物种对热应激的特定反应对于预测未来森林动态和生态系统功能至关重要。
