Abstract The southeastern US has experienced an increase in the number of extreme heat events since the 1970s, due in part to global change. Despite rising temperatures, greater variability in weather has also led to more freeze events across parts of the Southeast, particularly during El Nino winters. Structural variation in forest stands and plant functional diversity can lead to localized micrometeorological differences that may alter the recovery of different forests from these temperature-induced disturbances. This variation can lead to differences in energy and entropy dynamics, which drive the metabolic response of these systems. Using thermodynamic metrics, we quantified metabolic energy and entropy production in response to extreme heat and freeze events at three longleaf pine savanna sites spanning an edaphic moisture gradient (i.e., xeric, intermediate, mesic). The sites also differed in anthropogenic legacy, with soil tillage occurring at the intermediate site, resulting in greater woody species abundance in the understory and overstory. We found that energy reserves in this ecosystem were built during low precipitation periods and when temperatures were below 20°C. The mesic site, which had the highest plant functional diversity, exhibited an adaptive capacity to temperature extremes by maintaining low metabolic activity throughout temperature disturbances, while the intermediate and xeric sites started with high metabolic activity that gradually declined by ~15% with prolonged temperature extremes. Response to these temperature extremes was a function of hydrological drivers, as lower water availability reduced energy reserves during cold periods and photosynthetic activity during heatwaves – especially at the intermediate and xeric sites as a result of the high energy demand of oaks in the overstory. As climate change continues to alter weather patterns across the globe, it becomes increasingly important to assess metabolic resilience to greater weather variability as a function of ecosystem structure.

中文翻译：

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森林结构和组成驱动长叶松稀树草原极端温度期间代谢能和熵动力学的差异

摘要 自 1970 年代以来，美国东南部的极端高温事件数量有所增加，部分原因是全球变化。尽管气温上升，但天气的更大变化也导致东南部部分地区发生更多冰冻事件，尤其是在厄尔尼诺冬季。林分的结构变化和植物功能多样性会导致局部微气象差异，这可能会改变不同森林从这些温度引起的干扰中恢复。这种变化会导致能量和熵动力学的差异，从而驱动这些系统的代谢反应。使用热力学指标，我们量化了跨越土壤水分梯度的三个长叶松稀树草原地点响应极端高温和冰冻事件的代谢能和熵产生（即，旱、中、中）。这些地点在人为遗产方面也不同，在中间地点进行土壤耕作，导致林下和上层林木物种的丰度更高。我们发现，该生态系统的能量储备是在降水量较少的时期和温度低于 20°C 时建立的。中性位点具有最高的植物功能多样性，通过在整个温度扰动过程中保持低代谢活动，表现出对极端温度的适应能力，而中性和干旱位点以高代谢活动开始，随着极端温度的延长逐渐下降约 15% . 对这些极端温度的反应是水文驱动因素的函数，由于较低的可用水量减少了寒冷时期的能量储备和热浪时期的光合作用活动——尤其是在中间和干旱地区，这是由于上层橡树的高能量需求。随着气候变化继续改变全球的天气模式，评估作为生态系统结构功能的更大天气变化的代谢恢复力变得越来越重要。