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Mosses, rock-weathering, and global environmental change: is the present the key to the past (and future?)


Project Description

This exciting project links geological and ecological research to investigate the role of bryophytes in terrestrial weathering and biogeochemical cycling. This process is important for modern ecosystems, but also has significant potential ‘deep time’ implications because bryophytes were likely a component of the first terrestrial ecosystems ~450 million years ago. Data from fieldwork at sites across Scotland will be used to help resolve controversy over whether bryophytes were responsible for enhancing chemical rock weathering and bringing down atmospheric CO2 towards modern levels in the early Palaeozoic (Lenton et al., 2012 vs Quirk et al., 2015).

Growth of vegetation during the ‘greening of the continents’ ~420 million years ago has been suggested to be the cause of dramatic Earth System changes. These changes may have included enhanced chemical rock weathering leading to atmospheric CO2 drawdown and consequent climate cooling (e.g. Berner, 1992), as well as phosphorus export to oceans (Lenton et al., 2012) and binding of sediment leading to trapping of mud and creation of the first meandering rivers (Davies and Gibling, 2010). But there are doubts and debates over which types of organisms were responsible for the biggest chemical and environmental revolutions: were apparently massive atmospheric CO2 and O2 changes driven by the first bryophytes (Ordovician), or the first vascular plants (Silurian), or larger trees (middle Devonian - Carboniferous)?

Not enough is currently known about the effects of bryophytes (and the complete ’bryosphere’; Lindo & Gonzales, 2010) on rock weathering to determine whether or not they are as significant to terrestrial ecosystems and global biogeochemical cycling as vascular plants and their mycorrhizal fungi. Investigation of active processes in the field and in the lab is needed for us to begin to understand this. To advance current knowledge, this PhD will:

• Describe relationships between bryophyte species’ distributions and underlying geology, particularly where mosses are growing directly on bedrock. Investigate associations between species and abundances of particular minerals. This requires both field analysis and laboratory experimentation.
• Determine the efficiency of mosses at extracting elements such as phosphorus from a variety of rock types, including for example phosphorus from apatite inclusions in Lewisian Gneisses.
• Elucidate the processes by which mosses could enhance rock weathering, including examining whether mosses and/or associated microbial communities (the complete bryosphere) actually cause purported enhanced chemical rock weathering.
• Measure how deep into rock the effects of moss weathering can penetrate: only fractions of a millimetre, or several centimetres into the rock? This is crucial because restriction of any enhancement of chemical weathering to sub-millimetre depths would drastically limit the potential of these non-vascular plants to bring about big biogeochemical changes.


This PhD will thus (1) document the diversity of lithophilic bryophytes at selected sites across Scotland, including the beautiful North West Highlands (Lewisian Gneiss), Midland Valley (Carboniferous basaltic volcanics and limestones) and Aberdeenshire (Granites), and (2) measure the effects of the bryosphere, on chemical weathering at each of these sites. This will be achieved by analysing field samples, field experimentation, and also by conducting experiments in controlled conditions.

Through this project the student (coming from a bioscience, geoscience, or chemistry background) will learn field and laboratory skills that span the earth and life sciences. Analysis techniques will include confocal and electron microscopy and microanalysis (SEM-EDS) combined with geochemistry (ICP-AES and XRF). The student will work in an interdisciplinary environment, benefitting from the activities and facilities of two research active Schools and our new QUADRAT Doctoral Training Programme. There will be opportunity to collaborate with government agencies, and ultimately this project will provide the basis for an exciting career in either applied or academic research.


APPLICATION PROCEDURE:

• Apply for Degree of Doctor of Philosophy in Geology
• State name of the lead supervisor as the Name of Proposed Supervisor
• State the exact project title on the application form

Application closing date is 12:00pm (GMT) on 22 February 2019. Applications received after this time will NOT be considered. Additionally, incomplete applications will NOT be considered.

When applying please ensure all required documents are attached:

• All degree certificates and transcripts (Undergraduate AND Postgraduate MSc-officially translated into English where necessary)
• CV
• 2 References (Academic, where possible)

Informal inquiries can be made to Dr A Brasier () with a copy of your curriculum vitae and cover letter. All general enquiries should be directed to the Postgraduate Research School ()

Funding Notes

This is a joint studentship between the School of Biological Sciences & the School of Geosciences. This studentship provides stipend, Home/EU Fees & a £1K p.a. RTSG (Research Training & Support Grant).

References

Berner, R.A., 1992. Weathering, plants, and the long-term carbon cycle. Geochimica et
Cosmochimica Acta 56 (8), 3225–3231.

Davies, N.S., Gibling, M.R., 2010. Cambrian to Devonian evolution of alluvial systems:
the sedimentological impact of the earliest land plants. Earth Science Reviews 98
(3–4), 171–200.

Lenton, T.M., Crouch, M., Johnson, M., Pires, N. and Dolan, L., 2012. First plants cooled the Ordovician. Nature Geoscience, 5(2), p.86.

Lindo, Z., & Gonzalez, A. (2010). The Bryosphere: An Integral and Influential Component of the Earth's Biosphere. Ecosystems, 13(4), 612-627

Quirk, J., Leake, J.R., Johnson, D.A., Taylor, L.L., Saccone, L. and Beerling, D.J., 2015. Constraining the role of early land plants in Palaeozoic weathering and global cooling. Proc. R. Soc. B, 282(1813), p.20151115.

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