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Identifying tipping points regulating greenhouse gas emission from soils at two forest free air co2 enrichment experiments

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  • Full or part time
    Dr S Ullah
    Dr S Yamulki
    Prof E Pendall
  • Application Deadline
    No more applications being accepted
  • Competition Funded PhD Project (European/UK Students Only)
    Competition Funded PhD Project (European/UK Students Only)

Project Description

Globally, natural ecosystems including forests are responsible for ~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. However, our understanding of the environmental controls of GHG fluxes from mature temperate forests under elevated atmospheric CO2 (eCO2) is highly uncertain due to limited understanding to accurately predict global warming potential of forests under future climates.
As soil water and carbon availability, and demand for soil nitrogen by trees increases in forests exposed to eCO2, significant shifts in GHG fluxes under future climates is expected. Unravelling the mechanistic controls of GHG production and consumption is urgently needed to accurately model the net climate benefits of forests. The aim is to disentangle the impact of eCO2 on complex, nonlinear GHG production and consumption processes across the soil-atmosphere interface to reduce uncertainty when predicting the role of forests in global warming.
We hypothesize that elevated CO2 will enhance demand for nitrogen by trees and downregulate N2O production, thus leading to a tipping point of decreased N2O emissions. We hypothesize that elevated CO2 will increase soil carbon and water availability, leading to a tipping point of increased CH4 emissions, particularly under episodic enhanced soil moisture conditions. We hypothesize that thresholds of soil water, nitrogen and carbon contents will determine the net fluxes of GHGs, and that the spatio-temporal dynamics of hydrological conditions will play a key role in predicting the ultimate global warming potential of forests with climate change.
This research sits at the interface of on-going and planned research in soil science, plant physiology, hydrology and atmospheric sciences at the BIFoR Free Air Carbon Dioxide Enrichment (FACE) facility (mature oak dominated forest), UK and EuC-FACE (mature Eucalyptus dominated forest) in Australia, to unravel previously unexplored pathways of GHG production and consumption in mature forests under eCO2. The cross disciplinary outcomes of this research links to global scale modelling of carbon and nitrogen budgets of forests under future climates, which is aligned to the grand ethos of Forest Edge.
This research will be undertaken at the FACE facility under the Birmingham Institute for Forest Research (BIFoR). GHG production and consumption will be investigated through tracing techniques (15N and 13C), while soil profiles gas concentrations and fluxes from soils will be measured using pore-air sampler and chambers. The EucFACE is also a mature forest; however, it is drier with low soil carbon compared to the BIFoR site; hence their relative strengths of GHG flux are likely to be different. Thus the student will visit the EuC-FACE (~four months) to undertake tracing experiments to compare GHG controls of the two Facilities.

Funding Notes

Full payment of tuition fees at Research Councils UK fee level for year of entry (£4,270 in 2018/19), to be paid by the University;
An annual maintenance grant at current UK Research Councils rates (national minimum doctoral stipend for 2018/19 is £14,764), to be paid in monthly instalments to the Leverhulme Trust Doctoral Scholar by the University.
All studentships will come with a minimum of £3,000 Research Training Support Grant. This can be increased up to a maximum of £12,000. Supervisors should indicate from where any further costs necessary for the project will be sourced.


Ullah, S. and T.R. Moore: 2011. Biogeochemical controls on methane, nitrous oxide and carbon dioxide fluxes from deciduous forest soils, eastern Canada. J. Geophysical Research-Biogeosciences 116, G03010, DOI: 10.1029/2010JG001525
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. J Geophysical Research: Biogeosciences, doi: 10.1002/2017JG003783
Skiba, U., Jones, S.K., Dragosits, U., Drewer, J., Fowler, D., Rees, R.M., Pappa, V.A., Cardenas, L., Chadwick, D., Yamulki, S. and Manning, A.J. 2012. UK emissions of the greenhouse gas nitrous oxide. Philos. Trans. R. Soc. B Biol. Sci. 367(1593): 1175–1185. DOI: 10.1098/rstb.2011.0356.
Pendall E, (2018) 'Fast microbes regulate slow soil feedbacks', Nature Climate Change, vol.8, no.10, pp 859-860.
Yamulki, S. & Morison, J.I.L. (2017). Annual greenhouse gas fluxes from a temperate deciduous oak forest floor. Forestry, 90, 541-552, doi: 10.1093/forestry/cpx008.

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