The biogeography of plant heat tolerance and vulnerability to heatwaves

Abstract

Trees are important to humankind for the provision of resources and ecosystem services (e.g., food, wood, fodder, oxygen), including mitigation of the impacts of climate change. Climate extremes, such as high temperature events and heatwaves increasingly affect urban trees and urban greenspaces. Selecting the right tree species to survive increasing temperatures is crucial for mitigating the impacts of urban heat. Yet knowledge of heat tolerance and heatwave vulnerability among tree species remains limited. In this thesis, I aim to advance knowledge of heat tolerance of a diverse range of tree species from temperate to tropical climates. The critical temperature (Tcrit) of chlorophyll a fluorescence is a metric that has been widely used to assess thermal tolerance. For this thesis, I conducted a series of controlled-environment glasshouse studies, including heatwave exposure, to investigate the reliability of Tcrit as a heat tolerance metric among phylogenetically diverse tree and shrub species. Furthermore, I test a relatively new heat vulnerability metric, the thermal safety margin, for its accuracy and reliability in predicting species vulnerability to heatwaves. The thesis explores three overarching questions 1) Do species from different climates of origin exhibit differences in heat tolerance when grown in a common environment? 2) Does heatwave exposure result in plastic adjustment in heat tolerance? 3) Is thermal safety margin (TSM) a good metric for assessing species vulnerability to heatwaves? Overall, this thesis provides new insights into the factors shaping the heat tolerance of tree and shrub species and the reliability of TSM as a predictor of heat tolerance. I observed that leaf traits influencing Tleaf_max are an important aspect of shaping heat tolerance and its short-term acclimation to high temperatures. Furthermore, TSM is potentially useful for assessing species vulnerability to heatwaves across different locations. Such knowledge is crucial to understand the potential impact of a changing climate on trees in natural and urban systems. These findings will be an important source of information to mitigate negative impacts by selecting the right species for the right climate and urban environment.

Date of Award	2022
Original language	English