Project highlights

  1. Pioneering the implications of a decade long elevated CO2 enrichment of forests for soil greenhouse gas production and consumption processes. 
  2. Unravelling unexplored soil-tree-microbe interactions to explain ecosystem-scale greenhouse gas fluxes from forests under changing climates. 
  3. An exciting cross-disciplinary PhD studentship that integrates soil science, forests ecology and atmospheric sciences at the only global forest BIFoR-FACE facility for mature forests in northern latitudes. 


Globally, forests are capture about 18% of the total human source carbon dioxide (CO2) emission into air, thus playing a pivotal role in climate change mitigation. However, forests are responsible for about 60% of the total nitrous oxide (N2O) gas emitted from soils, and consume ~25% of the total atmospheric methane (CH4). N2O and CH4 are potent greenhouse gases (GHG), playing a critical role in global warming. Previous research at the University of Birmingham Institute for Forest Research’s Free Air CO2 Enrichment (BIFoR-FACE) Facility for mature forests showed an initial increase in CO2 fluxes from soils, followed by reduction in CO2 fluxes by the 7th year of elevated atmospheric CO2 (eCO2) enrichment. At the same time an increase in CH4 consumption and in potential N2O emission (Sgouridis et al. 2023) was observed. Will these greenhouse gas fluxes patterns persist over the next three years of eCO2 enrichment (year 8, 9 and 10) as stable state shift responses to eCO2 enrichment and what key environmental and soil factors affect these fluxes? Answering these questions are important to accurately predict global warming potential of forests under future climates. 

Enhancement of photosynthesis rates of the forests (Gardner et al. 2021), a decrease in soil moisture, increase in fine roots biomass (Ziegler et al. 2022) and soil nutrient cycling processes (Sgouridis et al. 2023) in the first 5 years of under eCO2 enrichment are expected to persist and thus it is very likely to affect net greenhouse gas emission from soils. Therefore, unravelling the impacts of plant-soil-microbes interactions on  greenhouse gas production and consumption processes is urgently needed to accurately model the net climate benefits of forests. The aim is to disentangle the impact of eCO2 on the dynamics of GHG production and consumption at the soil-atmosphere interface, reducing uncertainties in  predicting the role of forests in global warming and climate change mitigation. 

This research sits at the interface of on-going and planned research in soil science, plant physiology, and atmospheric sciences at BIFoR-FACE), UK to unravel previously unexplored pathways of GHG production and consumption under eCO2 in a mature oak-dominated forest ecosystem. The cross disciplinary outcomes of this research links to global scale modelling of carbon and nitrogen budgets of forests under future climates.  

Aerial view showing the trees and structures of the BiFOR FACE facility in Staffordshire.

Figure 1. View of BIFoR FACE showing eCO2 arrays (coloured) and control FACE arrays.


CENTA Flagship

This is a CENTA Flagship Project

Case funding

This project is suitable for CASE funding


University of Birmingham


  • Climate and Environmental Sustainability
  • Organisms and Ecosystems


Project investigator

Sami Ullah, University of Birmingham, [email protected]


Liz Hamilton University of Birmingham, ([email protected]),

Rob Mackenzie, University of Birmingham, ([email protected])

Dr Elena Vanguelova, Forest Research UK, ([email protected])

Prof Niall McNamara, UK Centre for Ecology & Hydrology, ([email protected])

Felicity Ross, NationalTrust, ([email protected].

How to apply


This research will be undertaken at the BIFoR-FACE facility. The FACE experiment is in a mature oak dominated (Quercus robur) woodland with an upper storey of >170 years old and ≥25 m tall oak trees with a sycamore (Acer pseudoplatanus) and hazel understorey (Corylus avellana). The FACE has been established in replicate arrays (30 m diameter):  three eCO2 (+150 ppm) and three ambient CO2 (with infrastructure) (Fig 2), (Mackenzie et al. 2021). CO2-enrichment has successfully operated from 2017 during the growing seasons and will continue until end of 2026 (Hart et al. 2019). Automated GHG production and consumption will be investigated within the FACE arrays using LiCoR GHG auto-chambers attached to LiCoR CO2 and Picaro N2O and CH4 analysers. Soil profiles and gas concentrations will be measured using pore-air samplers for the isotopic signatures of the greenhouse gases and their concentrations to discern the major sources of GHG production. Soil samples will be collected at varied depths for characterizing the pathways of GHG flux potentials using 15N and 13C isotopes including the isotopomer approach for source partitioning of N2O (using a 15N Picaro analyser at UKCEH Lancaster) to understand controls on GHG fluxes over the 8th to the 10 year of eCO2 enrichment of the forest.  

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.  

The student will benefit from supervision and access to resources across three UK research institutes who are already collaborating on related GHG research in forestry.  The student will based at the University of Birmingham where a range of transferable skills training are available. Specific environmental analytical training will be provided in the operation of instruments including gas chromatography, isotope tracing and GHG flux quantification (Birmingham), laser spectroscopy (UK CEH-Lancaster) and organic matter quality (Forest Research). A placement at Forest Research at the Alice Holt Experimental station in year 1 of the project will enable contextualisation of the research plan within the UK forest management and policy needs. In addition, interactions with project members and international partners will enable knowledge exchange and lasting linkages.  

Partners and collaboration

This studentship benefits directly from access to the only global temperate forests Free Air Carbon Dioxide Enrichment (FACE) facility with extensive infrastructure (>£30million) ( and the Alice Holt forest at Forest Research( This studentship will benefit from the high experimental costs of these projects and facilities, which is beyond the funding capacity of any single PhD studentship. The involvement of the National Trust, CEH and Forest Research, UK offers significant values in terms of access to facilities. Access to Picarro analyser (>£170k) at CEH and an internship at Forest Research, UK will thus support this studentship  

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 Prof. Sami Ullah ([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 Geography and Environmental Science (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-B44  when completing the application form. 

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

Further details on BIFoR-FACE.

Possible timeline

Year 1

  • Literature review and training in analytical instruments (chromatography, colorimetry, isotopes, in situ GHG- LiCoR and Picaro analyser), GHG flux data analysis and flux quantification and experimental design at Birmingham, Forest Research and UKCEH Lancaster. Introductory visits to the BIFoR-FACE in England. 
  • Placement (3 weeks) at Alice Holt, Forest Research to learn about forest management and policy development for sustainable forestry practices. 
  • Research plan finalisation including statistical design, and launch of GHG flux quantification and publication of a literature review paper. 

Year 2

  • Continuous measurement of GHG fluxes at BIFoR-FACE with associated relevant environmental characterisation of soils using in situ sensor technology.  
  • Seasonal sampling of soils for source partitioning strengths of N2O, methanogenesis, and methanotrophy using 15N and 13C isotopes in the laboratory.  
  • Data analysis and compilation of results for publication.  

Year 3

  • Continuation of GHG flux and carbon quality characterisation research in the field and analysis of 15N-N2O in samples using laser spectroscopy at UKCEH for source partitioning. 
  • Partitioning of bacterial and fungal contribution to potential CO2 production rates in relation to soil organic matter quality characterization using an ATR-FTIR approach. 
  • Data analysis and completion of experimental work. 

 Year 4: 

  • Thesis write up, defence and publications. 
  • Wider involvement with supervisor linked project partners offering further opportunities for pooling data within a multidisciplinary data pool potentially feeding into large synthesis papers and methodologies. 

Further reading

Sgouridis, F., M. Reay, S. Cotchim, J. Ma, A. Radu and S. Ullah. (2023). Stimulation of soil gross nitrogen transformations and nitrous oxide emission under Free Air CO2 Enrichment in a mature temperate oak forest at BIFoR-FACE. Soil Biology and Biochemistry, doi:  

Gardner, A., D S Ellsworth, K Y Crous, J Pritchard, A R MacKenzie. 2021. Is photosynthetic enhancement sustained through three years of elevated CO2 exposure in 175-year-old Quercus robur?, Tree Physiology, 42:130–144;doi: 

MacKenzie A. R., S. Krause, K. Hart, R. Thomas, P. Blaen, L. Hamilton, G. Curioni, S. Quick, A. Kourmouli, D. Hannah, S. Comer-Warner, N. Brekenfeld, S. Ullah, and M. Press. 2021. BIFoR FACE: Water-soil-vegetation-atmosphere research in a temperate deciduous forest catchment, including under elevated CO2. HYDROLOGICAL PROCESSES, DOI: 10.22541/au.160157598.86879557 

Pan, Y et al.,2011. A Large and Persistent Carbon Sink in the World’s Forests. Science 333,988-993.DOI:10.1126/science.1201609 

Sgouridis, F, and S. Ullah. 2017. Soil greenhouse gas fluxes, environmental controls and the partitioning of N2O sources in UK natural and semi-natural land use types. Journal of Geophysical Research-Biogeosciences, doi: 10.1002/2017JG003783 

Morrison Ross; Rowe Rebecca L.; Cooper Hollie M.; McNamara Niall P., 2019, Multiyear carbon budget of a mature commercial short rotation coppice (SRC) willow plantation. Global Change Biology Bioenergy 11: 895-909