Leaf Thermoregulation and Carbon Dynamics in Forests Under Elevated CO₂ and Warming

With rising atmospheric CO₂ concentrations and increasing global temperatures, climate change is driving profound transformations in the functioning of forests. Forest ecosystems play a central role in regulating the global terrestrial carbon and water cycles, yet their resilience to ongoing climatic extreme events remains uncertain.

A critical but often overlooked aspect of this response is the ability of plants to regulate leaf temperature under fluctuating environmental conditions. During extreme heat, plants may be able to cool their leaves enough to remain below critical mortality thresholds. Yet, recent evidence shows that as heat events become more intense and prolonged, tropical forests are nearing dangerous thermal limits while temperate forests experience increased heat stress Moreover, elevated CO₂ levels may further exacerbate this problem by increasing leaf temperatures and heightening the risk of leaf scorching, due to shifts in leaf functioning independent of heat events. Thus, understanding how forests balance heat, water, and carbon dynamics, from individual leaves to entire canopies, is essential for predicting their future stability and their capacity to mitigate climate change.

To investigate this research question, this PhD will install ‘leaf-heaters’ in state-of-the-art Free-Air CO₂ Enrichment (FACE) facilities, which exposes mature natural woodlands to both warming and elevated CO2 conditions. This research will be conducted at BIFoR-FACE in UK (temperate), AmazonFACE in Brazil (tropical) and EucFACE in Australia (Eucalyptus), where forest plots have been submitted to high CO₂ for the past 9, 1 and 13 years, respectively. By experimentally manipulating temperature, the student will be able to understand the mechanisms driving leaf thermoregulation in different species, climates, and under contrasting CO₂ levels and test whether there is an interaction between CO₂ and warming. Findings from this experimental setup in natural settings will help predict forest functioning under climate change and guide global forest management strategies.

The Doctoral Researcher will be mainly based at the University of Birmingham (UK) within the Birmingham Institute of Forest Research (BIFoR) and School of Geography, Earth and Environmental Sciences with collaboration and research support for fieldwork at AmazonFACE (Manaus, Brazil) and at EucFACE (Sydney, Australia). Key objectives of this studentship are: 1) Install leaf heaters across the 3 FACE sites, inducing local increase in temperatures. 2) Assess changes in gas exchange, leaf temperature, critical thresholds and leaf traits (e.g. light absorptance, chlorophyll fluorescence) under elevated CO₂ and hotter conditions. 3) investigate the changes in carbon storage dynamics across the growing season.

The student will gather data on photosynthetic capacity, carbon storage (e.g. non-structural carbohydrate dynamics), and leaf thermal thresholds. The primary objective is to quantify the effects of heat and CO₂ on carbon uptake in different tree species, in order to estimate the total potential carbon storage of different forest types under changing climates. This information will identify which species are most efficient at capturing carbon during high temperatures and low water availability under variable [CO₂], aiding predictions of the responses of contrasting forest types to climate change. These findings will support policy making and forestry management, including efforts to conserve tropical, temperate and eucalyptus forests, as well as utilise their role in mitigating global climate change.

The PhD student will be co-supervised by Dr. Alice Gauthey (University of Birmingham, UK), Dr. Sophie Fauset (University of Plymouth, UK), Prof. Kristine Crous (Western Sydney University, AUS), Prof. Tomas Domingues (University of Sao Paulo, BR) and Prof. Roger Dixon (University of Birmingham, UK).