Does competition between hydrogen and methane consumption by soil microbes lead to climate impacts?


   UK CEH

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  Dr Julia Drewer  No more applications being accepted  Competition Funded PhD Project (Students Worldwide)

About the Project

Summary

Emissions of hydrogen (H2) can act as a secondary greenhouse gas that distorts the atmospheric methane (CH4) sink. Soil bacteria can utilise H2 and CH4, but ecological mechanisms underpinning this competition remain poorly understood.

Project background

Hydrogen (H2) is likely to play an increasingly important role in decarbonizing global energy systems. However, leaks may increase atmospheric hydrogen, and atmospheric chemistry modelling indicates this will lead to increases in methane (CH4), among other gases (Sand et al., 2023), offsetting some of the benefits from reduced greenhouse gas emissions. The climate impacts from hydrogen leakage depend upon its atmospheric lifetime, largely determined by its main sink: uptake by soil microbes. This soil sink’s global magnitude and the microbial processes involved are both highly uncertain. There is an analogous soil sink of methane, and the consumption of hydrogen and methane by microbes in soils may be closely related. This raises the prospect of a coupled system, where changes in the atmospheric levels of one gas may have implications for the other.

Hence an improved quantification of the soil sink and understanding of its response to a changing climate is needed as well as an understanding of interactions with other greenhouse gases. Many soil microbes utilize H2 as an energy source but emission of H2 from soils is also possible via microbial processes. The current understanding of these processes is severely understudied due to the logistical difficulties and technical restraints of H2 flux measurements, as well as prior irrelevance. This project aims to quantify soil H2 cycling in soils in relation to CH4 cycling, investigating the response to soil moisture, temperature, H2 concentrations, pH, and soil microbial communities using laboratory incubations. In addition, direct field measurements of CH4 and H2 will inform on within-field spatial and temporal variability and effects of land-management. It is known that forest ecosystems exhibit higher H2 uptake rates than agroecosystems (Ehhalt and Rohrer, 2009). However, the exact mechanisms steering these different performances are unknown, but a combination of biological and physicochemical attributes is expected to contribute to this biological sink (Baril et al. 2022). This project aims to integrate soil physicochemical parameters and microbial diversity patterns into a series of correlation and multivariate analyses to relate their variation to trace gases flux. Controls and variations of soil H2 uptake rates will be defined for implementation into global models.

Research questions

  1. Under which conditions will soil microbes utilize hydrogen (H2) over methane (CH4)?
  2. Does uptake/emission of H2 interfere with CH4 flux measurement methodology?
  3. What is the relative size and identity of the main microbial groups involved in H2 and CH4 consumption?
  4. Does competition between H2 and CH4 uptake by soil microbes lead to a higher global warming potential (GWP) for H2?

Methodology

This project will require a large degree of practical work, and also elements of modelling. The student will use gas chromatography (GCs) and quantum cascade lasers (QCLs) to measure H2 and CH4 fluxes from soils via the flux chamber method. These measurements will be carried out at a variety of local field sites as well as in controlled laboratory conditions. These experiments will be designed in order to establish links between fluxes of these gases and the drivers within soils that control microbial behaviour. Microbial samples will be taken from measured soils, and analysis will be carried out to identify microbial populations and their sensitivities to environmental drivers of H2 and CH4 uptake/emission. 

Microbial populations involved in H2 and CH4 consumption will be identified via DNA metabarcoding methods, and quantified via qPCR and/or ddPCR.

The descriptions of the H2 and CH4 soil sinks in the UKCA model will be updated, based on the analysis of the observations. Modelling with updated soil sinks will allow the global climate impacts of these new schemes to be quantified, by calculating changes in H2 and CH4 lifetimes, and as a result, differences in their GWPs and hence their net climate impacts. 

Timetable:

Year 1 will include a literature review, instrument training, method development and setting up of laboratory and field measurements for H2. 

Year 2 will focus on microbial analysis and model development as well as continuing with laboratory and field measurements. Statistical and modelling training as well as other transferable skills training will be provided throughout.

Year 3 will focus on data analysis, modelling and academic writing of papers and chapters.

Training

A comprehensive training programme will be provided comprising both specialist scientific training and generic transferable and professional skills.

  • Flux measurements of H2 & CH4 using Gas Chromatography (GC) PDHID and Quantum Cascade Laser (QCL) instruments (UKCEH).
  • Statistical analysis using R software (UKCEH)
  • Soil microbial sampling and analysis techniques (University of Essex)
  • Molecular microbial ecology (University of Essex)
  • Global modelling with UKCA (NCAS training course – to be taken in year 1 or 2) (University of Edinburgh)
  • Academic writing training will be given and the student will be encouraged to submit manuscripts to academic journals (University of Edinburgh)

Requirements

  • Good environmental science background in ideally trace gas fluxes as well as soil microbes
  • Good numerical skills and aptitude for statistics or coding
  • Background in chemistry, physics, biology or other physical science
  • Willingness to carry out regular field work activities
  • Good people skills including the ability to work as part of a team

Please apply via the E4 DTP website: https://www.ed.ac.uk/e4-dtp/how-to-apply/supervisor-led-projects/project?item=1612

Biological Sciences (4) Chemistry (6) Environmental Sciences (13)

References

References
Baril, X., Durand, A.-A., Srei, N., Lamothe, S., Provost, C., Martineau, C., Dunfield, K., Constant, P., 2022. The biological sink of atmospheric H2 is more sensitive to spatial variation of microbial diversity than N2O and CO2 emissions in a winter cover crop field trial. Science of The Total Environment. https://doi.org/10.1016/j.scitotenv.2022.153420
Bay, S.K., Dong, X., Bradley, J.A., Leung, P.M., Grinter, R., Jirapanjawat, T., Arndt, S.K., Cook, P.L.M., LaRowe, D.E., Nauer, P.A., Chiri, E., Greening, C., 2021. Trace gas oxidizers are widespread and active members of soil microbial communities. Nat Microbiol. https://doi.org/10.1038/s41564-020-00811-w
Derwent, R.G., Simmonds, P.G., O’Doherty, S., Manning, A.J., Spain, T.G., 2023. High-frequency, continuous hydrogen observations at Mace Head, Ireland from 1994 to 2022: Baselines, pollution events and ‘missing’ sources. Atmospheric Environment. https://doi.org/10.1016/j.atmosenv.2023.120029
Meredith, L.K., Commane, R., Munger, J.W., Dunn, A., Tang, J., Wofsy, S.C., Prinn, R.G., 2014. Ecosystem fluxes of hydrogen: a comparison of flux-gradient methods. Atmos. Meas. Tech. https://doi.org/10.5194/amt-7-2787-2014
Sand, M., Skeie, R.B., Sandstad, M. et al. A multi-model assessment of the Global Warming Potential of hydrogen. Commun Earth Environ 4, 203 (2023). https://doi.org/10.1038/s43247-023-00857-8

 About the Project