THERMOS:Thermal Safety Margins of Earth's Tropical Forests

膳魔师：地球热带森林的热安全裕度

• 批准号: NE/Y00163X/1
• 负责人: David Robert Galbraith
• 金额: $ 108.57万
• 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: 2024
• 资助国家: 英国
• 起止时间: 2024 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FY00163X%2F1
• 关键词: THERMOS; Thermal; Safety; Margins; Earth

Earth's tropical forests provide an array of ecosystem services, housing over 50% of global biodiversity, taking up 8-13% of annual anthropogenic CO2 emissions, recycling rainfall at continental scales and directly providing livelihoods to millions of people. The biological and ecological processes that sustain these services (e.g. photosynthesis and transpiration) are strongly climate-sensitive, such that the future large-scale functioning of tropical forests depends on keeping their climate space within safe operating limits. Currently we do not know what the safe operating temperature limits for tropical forests are nor how close they are to upper limits of temperature function. There are three main reasons for this:1) different plant processes are subject to different temperature thresholds - e.g. there are optimal temperatures for photosynthesis and also temperatures at which the photosynthetic apparatus begin to break down, but large data gaps prevent us from understanding how these limits vary across tropical forests and species2) even for species where we do know the temperature thresholds for key physiological functions (e.g. breakdown of photosynthesis machinery), we usually do not have the leaf temperature records that allow us to gauge how close tropical trees are to these thresholds. The distinction between leaf and air temperature is key here - leaf temperatures are the physiologically meaningful measure of temperature and can be substantially different to air temperatures3) we do not know what leaf-level metrics of temperature tolerance mean for the performance of the whole plant in terms of growth and mortality. It is unclear whether leaf traits can predict risk of heat-induced mortality. Temperature can affect plant performance directly (e.g. by reducing photosynthetic rate) but also indirectly by increasing the vapour pressure difference between the air and leaves (leaf-to-air vapour pressure deficit). Higher VPD increases plant water losses due to greater atmospheric demand for water but also results in reduced stomatal conductance and carbon assimilation rates. Recent studies have suggested that increasing tree mortality patterns observed in some temperate and tropical zones may be driven by increasing VPD. However, no study to date has sought to isolate the role of direct temperature effects vs. indirect VPD effects in inducing heat stress-driven mortality.THERMOS will address each of these current bottlenecks to deliver unprecedented large-scale insights into the thermal risk of tropical forests. To do this, a diverse set of complementary methodologies will be used including: 1) extensive field data collection in tropical forests in four continents to determine the high temperature thresholds of key plant processes, 2) drone-based thermal imaging to determine maximum leaf temperatures reached in different sites, 3) new extreme heating greenhouse experiments to test the ability of leaf thermal traits to predict mortality and to evaluate the importance of direct vs. indirect VPD effects in driving mortality, 4) remote sensing to determine how thermally 'safe' forests are across the Tropics and 5) analysis of forest dynamics records to evaluate the role of increasing temperature and VPD in driving increased mortality across tropical forests.

地球上的热带森林提供一系列生态系统服务，拥有全球 50% 以上的生物多样性，占每年人为二氧化碳排放量的 8-13%，在大陆范围内循环利用降雨，并直接为数百万人提供生计。维持这些服务的生物和生态过程（例如光合作用和蒸腾作用）对气候非常敏感，因此热带森林未来的大规模功能取决于将其气候空间保持在安全运行范围内。目前我们不知道热带森林的安全工作温度限制是多少，也不知道它们与温度函数上限的接近程度。造成这种情况的主要原因有三个：1) 不同的工厂流程受到不同的温度阈值 - 例如，存在光合作用的最佳温度以及光合作用装置开始分解的温度，但巨大的数据差距使我们无法了解这些限制在热带森林和物种之间如何变化2)，即使对于我们确实知道关键生理温度阈值的物种由于功能（例如光合作用机制的故障），我们通常没有叶子温度记录来衡量热带树木与这些阈值的接近程度。叶子温度和空气温度之间的区别在这里是关键 - 叶子温度是具有生理意义的温度测量，可能与空气温度有很大不同3）我们不知道叶子水平的温度耐受性指标对于整个植物的性能意味着什么生长和死亡率方面。目前尚不清楚叶子性状是否可以预测热致死亡的风险。温度可以直接影响植物的性能（例如通过降低光合速率），也可以通过增加空气和叶子之间的蒸气压差（叶子与空气的蒸气压差）来间接影响植物的性能。由于大气对水的需求增加，较高的 VPD 会增加植物的水损失，但也会导致气孔导度和碳同化率降低。最近的研究表明，在一些温带和热带地区观察到的树木死亡率增加可能是由 VPD 增加造成的。然而，迄今为止，还没有任何研究试图区分直接温度效应与间接 VPD 效应在导致热应激导致的死亡率方面的作用。THERMOS 将解决当前的每一个瓶颈，以对热带地区的热风险提供前所未有的大规模见解。森林。为此，将使用一套多样化的补充方法，包括：1）在四大洲的热带森林中进行广泛的现场数据收集，以确定关键植物过程的高温阈值，2）基于无人机的热成像以确定最高叶片温度在不同地点实现，3）新的极端加热温室实验，以测试叶片热特性预测死亡率的能力，并评估直接与间接 VPD 效应在驱动死亡率方面的重要性，4）遥感以确定热“安全”程度森林遍布热带地区和 5) 森林动态记录分析，以评估温度升高和 VPD 在推动热带森林死亡率增加中的作用。