Sensitivity of Tropical Forest to Heat Stress -Trop-Heat

热带森林对热应激的敏感性 -Trop-Heat

• 批准号: NE/X001172/1
• 负责人: Lina Mercado
• 金额: $ 83.07万
• 依托单位: UNIVERSITY OF EXETER
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2023
• 资助国家: 英国
• 起止时间: 2023 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FX001172%2F1
• 关键词: Sensitivity; Tropical; Forest; Heat; Stress

Tropical forests are biodiversity hotspots and important biological conservation regions. They deliver key ecosystem services such as carbon sequestration and storage, and water for electricity generation via hydropower (a large source of electricity in many tropical countries) and freshwater provision, serving the needs of millions of people and fast-growing populations in these regions. However, tropical regions have experienced the largest recent increases in heat extremes over the globe, with ongoing warming predicted to exceed the bounds of historic climate variability in the next two decades. This climate change has potentially large but poorly understood consequences for tropical forests. Recent findings suggest that these critical forests appear at substantial risk, in terms of their vulnerability and exposure to warming and its extremes. For example, extreme temperatures in lowland forest reduces tree growth and carbon storage. Furthermore, in the tropical Andes, recent warming has been associated with increased mortality of species in the warm extreme of their thermal ranges, triggering a compositional change towards warm-adapted species across all elevations. The mechanisms underpinning reduced tree growth and species compositional changes remain largely unknown. To predict species composition changes and their implications for forest function and ecosystem services, a mechanistically-informed understanding of the physiological strategies employed by thermally resilient and susceptible species is needed.At our unique warming experiments along elevation gradients in the tropics in the Colombian Andes and in Rwanda in the Albertine Ridge we obtain a range of responses to the warming treatment: some species have died, some have shown reduced growth, while others have increased their growth. Importantly, and contrary to some expectations, plant physiological responses to average site temperatures cannot predict growth patterns. Rather, preliminary evidence suggests that tree growth and survival in the North Andean region and in our experiments in Colombia and Rwanda, is related to species abilities to deal with heat stress. Multiple mechanisms may be involved in determining the ability of species to cope with heat stress, but their relative roles in different settings is unknown. In Rwanda, preliminary data suggest that the most successful species thermoregulate, cooling their leaves via high rates of evapotranspiration to cope with extreme temperature, while species that have shown reduced growth with warming reach very high leaf temperatures (ie they cannot thermoregulate). In contrast, in Colombia, the most successful species are those that emit isoprene to ameliorate heat stress suggesting enhanced thermotolerance may be a key mechanism. Overall, our results demonstrate an urgent need to understand how different tropical tree species cope with extreme rather than average temperatures. Using our experiments in Colombia and Rwanda, this project will deliver new mechanistic understanding of heat stress physiology for tropical forests and possible links to plant growth responses to warming which will inform how we understand and predict composition changes along elevation and climate gradients. We will use a holistic combination of measurements not done before in any ecosystem- thermoregulation, thermal tolerance thresholds, in situ isoprene emissions, and their thermal plasticity- to evaluate tree heat stress strategies. We will combine our experimental data with mechanistic modelling to generalise our results to other ecosystems and with data from Andean trees to determine the extent to which the new understanding of species-level heat stress strategies can explain compositional changes in Andean forest tree species. Our project will support better prediction of future biodiversity shifts and forest function, tropical forest restoration and conservation.

热带森林是生物多样性热点和重要的生物保护区。它们提供关键的生态系统服务，如碳固存和储存、水力发电用水（许多热带国家的主要电力来源）和淡水供应，满足这些地区数百万人和快速增长的人口的需求。然而，热带地区最近经历了全球极端高温事件的最大增加，预计未来20年持续变暖将超过历史气候变率的界限。这种气候变化可能对热带森林造成巨大但人们知之甚少的后果。最近的研究结果表明，这些关键的森林似乎面临着巨大的风险，就它们的脆弱性和对变暖和极端气候的暴露而言。例如，低地森林的极端温度减少了树木的生长和碳的储存。此外，在热带安第斯山脉，最近的变暖与处于其热范围温暖极端的物种死亡率增加有关，引发了在所有海拔高度向温暖适应物种的组成变化。支撑树木生长减少和物种组成变化的机制在很大程度上仍然未知。为了预测物种组成的变化及其对森林功能和生态系统服务的影响，需要对热弹性和易感物种采用的生理策略有一个机械的了解。我们在哥伦比亚安第斯山脉和卢旺达艾伯丁山脊的热带地区沿着海拔梯度进行了独特的变暖实验，我们得到了对变暖处理的一系列反应：一些物种已经死亡，一些物种的生长速度下降，而另一些物种的生长速度加快。重要的是，与一些预期相反，植物对平均地点温度的生理反应不能预测生长模式。相反，初步证据表明，在北安第斯地区以及我们在哥伦比亚和卢旺达的实验中，树木的生长和生存与物种应对热应激的能力有关。决定物种应对热应激的能力可能涉及多种机制，但它们在不同环境下的相对作用尚不清楚。在卢旺达，初步数据表明，最成功的物种通过高蒸发蒸腾速率冷却叶片以应对极端温度，而那些因变暖而生长减缓的物种则会达到非常高的叶片温度（即它们无法进行温度调节）。相比之下，在哥伦比亚，最成功的物种是那些释放异戊二烯来改善热应激的物种，这表明增强的耐热性可能是一个关键机制。总的来说，我们的研究结果表明，迫切需要了解不同的热带树种如何应对极端而非平均温度。利用我们在哥伦比亚和卢旺达的实验，该项目将为热带森林热应激生理学提供新的机制认识，并为植物生长对变暖的反应提供可能的联系，这将为我们如何理解和预测海拔和气候梯度的成分变化提供信息。我们将使用从未在任何生态系统中做过的测量的整体组合-温度调节，热耐受阈值，原位异戊二烯排放及其热塑性-来评估树木的热应激策略。我们将把我们的实验数据与机械模型结合起来，将我们的结果推广到其他生态系统，并将安第斯树木的数据结合起来，以确定对物种水平热应激策略的新理解在多大程度上可以解释安第斯森林树种的成分变化。我们的项目将有助于更好地预测未来的生物多样性变化和森林功能，以及热带森林的恢复和保护。