Project highlights

  • The project will examine how increasing temperature and elevated atmospheric CO2 affect gas exchange, at the leaf level. This study aims to quantify the water-use efficiency of mangroves under future climate conditions to improve model predictions for forest ecosystems.  
  • Experiments will be performed both in (1) natural conditions within a newly restored mangrove habitat in Dubai, and (2) in controlled conditions at the Wolfson glasshouses. 
  • The PhD student will develop skills in plant ecophysiology and remote sensing, utilising UAVS equipped with hyperspectral and thermal cameras, with opportunities to network internationally and participate to outreach activities.  

Overview

Drought and heat are major contributors to forest mortality, with hydraulic failure being the primary physiological mechanism behind drought-induced tree death. During periods of drought, the xylem —the column responsible for water transport— can rupture, resulting in the formation of air bubbles (known as embolism). These embolisms obstruct water flow through the xylem, leading to reduced water transport and, ultimately, tree mortality (Sperry and Tyree, 1988). In addition to drought, heat and atmospheric water stress severely impact tree physiology, reducing photosynthesis and causing tissue death, which can further disrupt the hydraulic system and increase embolism formation, particularly in the leaf (Grossiord et al., 2020; Marchin et al., 2022). Despite its significance, the independent effect of heat on plant health is understudied, largely due to the difficulty in isolating heat stress from drought stress in natural conditions. 

With climate change, carbon dioxide (CO2) levels are expected to rise significantly, potentially reaching 550 ppm by 2050 (compared to 420 ppm today). While elevated CO2 can contribute to warming through greenhouse effects, it also stimulates photosynthesis (Gardner et al., 2022), enhancing the forests’ role in carbon sequestration. However, tree species adapted to drier habitats (xeric) may exhibit greater resistance to heat and drought but may be less efficient at carbon uptake than species from more temperate (mesic) environments.  

Mangrove ecosystems are vital habitats for wildlife and provide essential ecosystem services for coastal communities, such as wave mitigation. However, rising CO2, increased temperatures, and increased salinity due to sea-level rise are facilitating the expansion of mangroves in saltmarsh communities and can lead to widespread mangrove mortality (Gauthey et al., 2022). There is a critical gap in our understanding of how mangrove ecosystems respond to climate change. Therefore, this study would explore the effects of elevated CO2 and temperatures on the water and carbon dynamics of mangrove species.  

This project is part of the BIFoR Global theme.

View of mangrove forest in Australia (credit: Alice Gauthey) showing Rhizophera spp. growing close to the water using aerial roots.

Figure 1: View of mangrove forest in Australia (credit: Alice Gauthey) showing Rhizophera spp. growing close to the water using aerial roots. 

Host

University of Birmingham

Theme

  • Climate and Environmental Sustainability
  • Organisms and Ecosystems

Supervisors

Project investigator

Co-investigators

How to apply

Methodology

Field Measurements:
Gas exchanges, including carbon uptake (photosynthesis) and water loss (stomatal conductance), will be measured using a Licor-6800 at the mangrove forests along the Dubai coastline. The study will focus on (1) adult trees and (2) newly planted seedlings. These measurements will help evaluate the efficiency of planting efforts in terms of carbon storage. Additionally, canopy temperature and spectral reflectance will be recorded using drone imaging to assess thermal and drought stress across a large forest scale. 

Laboratory Experiment:
In a subsequent phase, a laboratory experiment will be conducted with seedlings of various mangrove species that exhibit contrasting water-use strategies. These seedlings will be grown under varying temperatures, CO2 concentrations, and water regimes. Measurements of photosynthesis and stomatal conductance will be collected, complemented by analyses of leaf morphological and anatomical traits to provide a comprehensive understanding of each species’ responses to environmental conditions. 

Training and skills

DRs will be awarded CENTA Training Credits (CTCs) for participation in CENTA-provided and ‘free choice’ external training. One CTC can be earned per 3 hours training, and DRs must accrue 100 CTCs across the three and a half years of their PhD.  

The student will receive training in two key areas: (1) methods used to measure plant physiological traits, such as gas exchange, and (2) remote sensing techniques. Both PI’s are experts in plant ecophysiology and plant hydraulics and have extensive collaborations with colleagues managing or working on remote field sites. This network will provide the student with valuable resources and opportunities, fostering the development of long-lasting professional collaborations.  

Further details

 For any enquiries related to this project please contact Dr. Alice Gauthey ([email protected]).  

 To apply to this project:  

  • You must include a CV with the names of at least two referees (preferably three) who can comment on your academic abilities.  
  • Please submit your application and complete the host institution application process via: https://sits.bham.ac.uk/lpages/LES068.htm.   Please select the PhD Geography and Environmental Science (CENTA) 2025/26 Apply Now button. The CENTA Studentship Application Form 2025 and CV can be uploaded to the Application Information section of the online form.  Please quote CENTA 2025-B34 when completing the application form.  

 Applications must be submitted by 23:59 GMT on Wednesday 8th January 2025.   

Possible timeline

Year 1

  • Develop a detailed research plan  
  • Plan fieldwork campaigns and begin preparations for glasshouse experiments.  
  • Train in techniques necessary for conducting physiological measurements and UAV operations. Conduct fieldwork in Dubai to quantify photosynthesis, stomatal conductance, canopy temperature and spectral reflectance 

Year 2

  • Perform measurements in the glasshouse to quantify photosynthesis, stomatal conductance, and morphological and anatomical traits. 
  • Data analysis and begin writing research publications 

Year 3

  • Continue data analysis and focus on writing the thesis and research publications. 
  • Explore the possibility to repeating fieldwork or glasshouse campaigns if any issues arise. 

Further reading

Gardner, A., Ellsworth, D.S., Crous, K.Y., Pritchard, J. and MacKenzie, A.R., 2022. Is photosynthetic enhancement sustained through three years of elevated CO2 exposure in 175-year-old Quercus robur?. Tree Physiology, 42(1), pp.130-144. 

Gauthey, A., Backes, D., Balland, J., Alam, I., Maher, D.T., Cernusak, L.A., Duke, N.C., Medlyn, B.E., Tissue, D.T. and Choat, B., 2022. The role of hydraulic failure in a massive mangrove die-off event. Frontiers in Plant Science, 13, p.822136. 

Grossiord, C., Buckley, T.N., Cernusak, L.A., Novick, K.A., Poulter, B., Siegwolf, R.T.W., Sperry, J.S., and McDowell, N.G. (2020). Plant responses to rising vapor pressure deficit. New Phytol 226, 1550–1566. https://doi.org/10.1111/nph.16485. 

Marchin, R.M., Backes, D., Ossola, A., Leishman, M.R., Tjoelker, M.G., and Ellsworth, D.S. (2022). Extreme heat increases stomatal conductance and drought‐induced mortality risk in vulnerable plant species. Global Change Biology 28, 1133–1146. https://doi.org/10.1111/gcb.15976. 

Sperry, J.S., and Tyree, M.T. (1988). Mechanism of Water Stress-Induced Xylem Embolism. Plant Physiology 88, 581–587. https://doi.org/10.1104/pp.88.3.581.