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地区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，以及通过水力发电（许多热带国家的主要电力来源）和淡水供应来发电，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地球仪上最大的极端高温增加，预计未来20年持续变暖将超过历史气候变化的界限。这种气候变化可能对热带森林造成巨大但知之甚少的后果。最近的调查结果表明，这些关键森林在脆弱性和受变暖及其极端情况影响方面似乎面临着很大的风险。例如，低地森林的极端温度降低了树木的生长和碳储存。此外，在热带安第斯山脉，最近的变暖与处于其温度范围的温暖极端的物种的死亡率增加有关，引发了所有海拔地区的物种组成向适应温暖的物种转变。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，需要对热适应性和敏感性物种所采用的生理策略有一个机械上的了解。在我们独特的变暖实验中，我们在哥伦比亚安第斯山脉的热带地区和卢旺达的艾伯丁山脉进行了沿着海拔梯度的变暖实验，我们获得了一系列对变暖处理的反应：有些物种已经死亡，有些物种的生长速度减缓，而另一些物种的生长速度加快。重要的是，与一些预期相反，植物对平均站点温度的生理反应不能预测生长模式。相反，初步证据表明，在北安第斯地区和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。多种机制可能参与决定物种科普热胁迫的能力，但它们在不同环境中的相对作用尚不清楚。在卢旺达，初步数据表明，最成功的物种温度调节，通过高蒸发速率冷却叶片以科普极端温度，而那些随着变暖而减少生长的物种达到非常高的叶温（即它们不能温度调节）。相比之下，在哥伦比亚，最成功的物种是那些排放异戊二烯，以改善热应力表明增强耐热性可能是一个关键的机制。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科普极端而不是平均温度。 利用我们在哥伦比亚和卢旺达的实验，该项目将提供对热带森林热应激生理学的新的机械理解，以及与植物生长对变暖的反应的可能联系，这将告知我们如何理解和预测沿着海拔和气候梯度的成分变化。我们将使用一个整体组合的测量之前没有做过任何生态系统-温度调节，耐热阈值，原位异戊二烯排放量，以及它们的热塑性-来评估树木热应力策略。我们将联合收割机我们的实验数据与机械建模，以概括我们的结果，以其他生态系统和数据从安第斯山脉的树木，以确定在何种程度上的新的理解物种水平的热应力策略可以解释安第斯森林树种的成分变化。我们的项目将支持更好地预测未来的生物多样性变化和森林功能，热带森林恢复和保护。