Project highlights

  • Quantifying the effects of photorespiration on plant carbon uptake under current and future atmospheric CO2 concentrations, which will inform how increases in atmospheric CO2 concentrations will impact photorespiratory CO2 release in plants and thereby improve our qualitative and quantitative understanding of the CO2 fertilisation effect in natural ecosystems.  
  • Experiments will be performed under controlled glasshouses conditions and in the natural environment at the BIFoR-FACE facility, a multi-institutional forest research network with a wide range of training opportunities. 
  • Gaining skills in specialised plant physiology techniques (gas exchange and chlorophyll fluorescence), as well as cutting-edge stable carbon isotope techniques in one of the leading labs in the UK.   


Photorespiration is an essential metabolic pathway that occurs in all organisms that undertake photosynthesis (Eisenhut et al., 2019). It is thought that photorespiration lowers the efficiency of C3 photosynthesis, the dominant photosynthetic pathway of most plants in the UK, by ~25% through the release of previously fixed carbon as CO2 (Timm and Hagemann, 2020). Photorespiration can negatively impact carbon uptake under high temperatures and low CO2 concentrations, but it can also have a positive impact under contrasting conditions (Busch, 2020). It is therefore not immediately obvious what the net impact of photorespiration is on the carbon gain of plants. The magnitude of this effect is currently highly debated: on one hand, the impact of photorespiration is considered large, due to its ‘wasteful’ consumption of ATP and NAD(P)H, and release of CO2 and ammonia that requires refixing inside the plant (Eisenhut et al., 2019). An increase in atmospheric CO2 concentration would thus result in a large CO2 fertilisation effect. On the other hand, Busch (2020) showed that CO2 released from photorespiration does not actually account for large losses in net CO2 uptake, as CO2 diffusion resistances moderate the effect of the photorespired CO2 as some of this CO2 is refixed. This, in turn, would limit the CO2 fertilisation effect under future climates. It is therefore important to accurately quantify the impact of photorespiration on net photosynthesis under current and future CO2 concentrations to capture both the basic physiology and the capacity of plants to acclimate to new environmental conditions.  

To date, the net effect of photorespiration on carbon uptake has not been quantified across the environmental conditions a leaf operates under. By integrating over conditions when photorespiration is beneficial and when it is detrimental, this research will determine if overall photorespiration has a positive or negative effect on carbon uptake. Ultimately, it will improve our understanding of photosynthetic efficiency under elevated and current atmospheric CO2 concentrations. The research will be conducted in controlled glasshouse conditions to improve our mechanistic understanding of photorespiration and at the BIFoR-FACE facility to quantify the real-life impact of photorespiration on plants in the natural environment. 

Aerial view of the CO2 fumigation towers at the BIFoR-FACE facility.

Figure 1: Aerial view of the BIFoR-FACE facility. The experimental plots are surrounded by towers emitting CO2 to expose the plants inside the plots to atmospheric CO2 concentrations expected in about 50 years. This experiment simulates a climate change scenario to study the response of a forest ecosystem to future CO2 concentrations ( 


University of Birmingham


  • Climate and Environmental Sustainability
  • Organisms and Ecosystems


Project investigator

Florian Busch (The University of Birmingham, [email protected])


Diego Marquez (The University of Birmingham, [email protected])

Christine Foyer (The University of Birmingham, [email protected])

How to apply


A chlorophyll fluorometer will be used to tell us the average conditions that the plant is operating under, including the temperature and light intensity that it is photosynthesising at, therefore the amount of carbon that the plant is taking up under these conditions. Concomitantly, gas exchange data will be collected on the plants (light response and CO2 response curves) to estimate the net effect of photorespiration on CO2 uptake. In the laboratory and CO2 -controlled greenhouses, these will be conducted under ambient and low O2 conditions, with the latter demonstrating the conditions under which photorespiration is suppressed.  

The above measurements will be supplemented by stable carbon isotope measurements to quantify the biochemical flux of carbon into the photorespiratory pathway. These measurements can be performed in both the controlled conditions (laboratory and greenhouse), as well as in the field at the BIFoR-FACE facility. Mathematical modelling will tie together the experimental work. 

Training and skills

Students will be awarded CENTA2 Training Credits (CTCs) for participation in CENTA2-provided and ‘free choice’ external training. One CTC equates to 1⁄2 day session and students must accrue 100 CTCs across the three years of their PhD.  

This project will require the student to gain skills in plant physiological techniques, coupled with mathematical modelling of photosynthetic processes. The lead supervisor Florian Busch is an expert in photosynthetic gas exchange, chlorophyll fluorescence and photosynthetic carbon isotope discrimination. The student will be trained in these techniques and couple the experimental results to mechanistic modelling to achieve a skill-set that covers the key areas of modern plant physiology.  

Partners and collaboration

This project will be performed in collaboration with the Birmingham Institute of Forest Research (BIFoR) and its Free Air CO2 Enrichment (FACE) facility, a world-leading, multi-institutional experiment (>£20M investment). The studentship will benefit from this huge investment in infrastructure and collaborative community of researchers and students. In turn, the project will contribute to the BIFoR community.  

Further details

Further details on how to contact the supervisor for this project and how to apply for this project can be found here: 

For any enquiries related to this project please contact Florian Busch ([email protected]).

To apply to this project: 

  • You must include a CENTA studentship application form, downloadable from: CENTA Studentship Application Form 2024. 
  • 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: Please select the PhD Bioscience (CENTA) 2024/25 Apply Now button. The CENTA application form 2024 and CV can be uploaded to the Application Information section of the online form.  Please quote CENTA 2024-B1  when completing the application form. 

Applications must be submitted by 23:59 GMT on Wednesday 10th January 2024. 

Possible timeline

Year 1

  • Training in experimental research skills (continued training in chlorophyll fluorescence and gas exchange techniques, in-depth training for measuring carbon isotope discrimination in plants) 
  • Detailed development and finalisation of research plan 
  • Quantifying the impact of photorespiration on net CO2 uptake in oak seedlings in controlled glasshouse environments (ambient and elevated CO2) 

Year 2

  • Quantifying the net impact of photorespiration in oak trees of BIFoR-FACE 
  • Estimation of biochemical photorespiratory fluxes with carbon isotope techniques 
  • Data analysis and writing of publications 

Year 3

  • Mathematical modelling of photosynthetic and photorespiratory carbon fluxes 
  • Using experimental data to derive a better mechanistic understanding of the impact of photorespiration on net CO2 uptake with the use of models 
  • Data analysis and writing of publications 

Year 4:  

  • Thesis write-up, writing of publications 

Further reading

BUSCH, F. A. 2020. Photorespiration in the context of Rubisco biochemistry, CO2 diffusion and metabolism. The Plant Journal, 101, 919-939. 

EISENHUT, M., ROELL, M.-S. & WEBER, A. P. M. 2019. Mechanistic understanding of photorespiration paves the way to a new green revolution. New Phytologist, 223, 1762-1769. 

TIMM, S. & HAGEMANN, M. 2020. Photorespiration—how is it regulated and how does it regulate overall plant metabolism? Journal of Experimental Botany, 71, 3955-3965.