Lethal Psi: Characterising critical embolism thresholds for Amazon tree survival

Lethal Psi：描述亚马逊树木生存的关键栓塞阈值

• 批准号: NE/X001164/1
• 负责人: David Robert Galbraith
• 金额: $ 83.7万
• 依托单位: University of Leeds
• 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%2FX001164%2F1
• 关键词: Lethal; Psi; Characterising; critical; embolism

The Southern Amazon faces the greatest climatic threat of all Amazon regions. This region is drier and warmer than 'core' areas of the Amazon and has been subject to the most pronounced drying and warming trends. It is also the region of the Amazon where increases in tree mortality have been most marked and where atmospheric measurements suggest forests are no longer acting as a carbon sink but as a net source of carbon to the atmosphere. Given that Southern Amazon is at the front line of the Amazon's battle against climate change, it is essential that we better understand how resistant its forest species are to climate stress.In Lethal Psi, we will construct a new 1-hectare drought experiment to better understand the physiological survival limits of southern Amazon trees. It has become increasingly clear that the process of hydraulic failure plays an important role in drought-induced tree mortality. Water is transported from the soils to the canopy under tension. As drought ensues and the soil dries, the tension in the xylem vessels that transport water intensifies and this can lead to the formation of air bubbles (embolism) in xylem vessels, disrupting water transport to the canopy and ultimately resulting in tree death. While this process is understood in general terms, one critical current knowledge gap is that we don't know the thresholds in embolism formation that result in the death of tropical trees. This lack of understanding of the physiological thresholds that result in death constitutes a key uncertainty for accurately modelling tree mortality under climate change. Determining the hydraulic thresholds of tree death is not an easy task and requires monitoring tree hydraulic status up to the point of death. In Lethal Psi, we track key indicators of hydraulic function (e.g. leaf water potentials and sap flux) from the beginning of our imposed drought all the way to the death of the tree to quantify how loss of xylem conductance translates into mortality risk. While other drought experiments have been set up in Amazonia, these did not monitor embolism status before and during the mortality process and were thus unable to provide insights into physiological thresholds of survival. Up to now, drought experiments have only been set up northeastern Amazonia, where annual rainfall is almost twice that of our study site and where changes in climate have been much less pronounced than in southern Amazonia. Given their ecotonal nature and the rapid climate change experienced in southern Amazonia, we expect that trees in this region are much closer to their climatic limits and will experience much more accentuated mortality under imposed drought than observed in northeastern experiments. Ultimately, we plan to use the newly acquired field data to develop improved mortality functions that we will apply more broadly across southern Amazonia to better predict drought mortality risk of this critically important region. This will be done by updating a unique trait-based model specifically developed to simulate Amazon forests and their responses to environmental change.

亚马逊南部面临着所有亚马逊地区中最大的气候威胁。该地区比亚马逊的“核心”地区更干燥和温暖，并且受到最明显的干燥和变暖趋势的影响。这也是亚马逊地区树木死亡率增加最明显的地方，大气测量表明森林不再作为碳汇，而是作为大气的净碳源。鉴于亚马逊南部处于亚马逊应对气候变化的前线，我们必须更好地了解其森林物种对气候压力的抵抗力。在《致命心灵指数》中，我们将构建一个新的1公顷干旱实验，以更好地了解亚马逊南部树木的生理生存极限。越来越清楚的是，水力破坏过程在干旱引起的树木死亡中起着重要作用。在张力作用下，水从土壤输送到冠层。随着干旱的加剧和土壤的干燥，木质部导管中运输水的张力加剧，这可能导致木质部导管中形成气泡（栓塞），破坏水向树冠的运输，最终导致树木死亡。虽然这个过程是一般性的理解，目前的一个关键知识差距是，我们不知道栓塞形成的阈值，导致热带树木死亡。对导致死亡的生理阈值缺乏了解，这构成了准确模拟气候变化下树木死亡率的一个关键不确定性。确定树木死亡的水力阈值不是一件容易的事，需要监测树木的水力状态，直到死亡。在Lethal Psi中，我们跟踪从我们施加的干旱开始到树木死亡的水力功能的关键指标（例如叶水势和汁液通量），以量化木质部传导性的损失如何转化为死亡风险。虽然在亚马逊河流域进行了其他干旱实验，但这些实验并没有监测死亡过程之前和期间的栓塞状态，因此无法深入了解生存的生理阈值。到目前为止，干旱实验只建立在亚马逊东北部，那里的年降雨量几乎是我们研究地点的两倍，气候变化比亚马逊南部要小得多。考虑到亚马逊河流域南部的生态交错性和快速的气候变化，我们预计这一地区的树木更接近其气候极限，并且在干旱下的死亡率将比在东北部实验中观察到的要高得多。最终，我们计划使用新获得的实地数据来开发改进的死亡率函数，我们将更广泛地应用于亚马逊南部，以更好地预测这一至关重要地区的干旱死亡率风险。这将通过更新一个独特的基于特征的模型来实现，该模型是专门为模拟亚马逊森林及其对环境变化的反应而开发的。