Michaela Reay

Picture of Michaela Reay

Postgraduate Student


I graduated from the University of Bristol in 2015 with an MSci (Hons) in Chemistry. I completed my masters research project in the OGU under the supervision of Professor Richard Evershed. The project was titled ‘Investigating the emergence of agriculture in the prehistoric Baltic States via biomolecular and stable isotope proxies applied to absorbed residues in pottery’.

In November 2015, I returned to Bristol for my PhD as part of DOMAINE (Dissolved Organic Matter IN freshwater Ecosystems), supervised by Professor Richard Evershed (University of Bristol) and Professor Davey Jones (Bangor University) and funded by NERC. My PhD is titled ‘Tracing fertiliser nitrogen in a grassland system using novel 15N-stable isotope approaches’

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Grassland systems grazed by livestock cover ca. one fifth of the terrestrial world, and the relationship between animals, plants and the soil is central to nutrient cycling in these ecosystems.  Urine patches in these systems represent areas of high nutrient cycling, and also areas susceptible to leaching losses. High nitrogen inputs into the wider environment have negative impacts on ecosystem and human health.  It is therefore important to understand the role grazed pastures have in nitrogen inputs into catchment waterbodies. This requires an improved understanding of the transport and transformation of urinary-N in a plant-soil system, and determination of the composition of nitrogen leached from such ecosystems.

As part of my PhD project, an ecosystem-scale approach to the grassland system will use 15N-tracer methods to determine the fate of 15N-fertiliser following application, grazing and subsequent re-application as urine. The work will build on existing compound specific 15N-stable isotope probing using gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS) approaches using amino acids and involves the development of a 15N-SIP method for amino sugars, to decouple bacterial and fungal N-assimilation dynamics in soil. This will build into an ecosystem-scale evaluation of the partitioning of nitrogen fertiliser and estimate the nitrogen use efficiency of the grassland ecosystem as a whole.

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3. Reay, M.K., Charteris, A.F., Jones, D.L., Evershed, R.P., 2019. 15N-amino sugar stable isotope probing (15N-SIP) to trace the assimilation of fertiliser-N by soil bacterial and fungal communities. Soil Biology and Biochemistry. https://doi.org/10.1016/j.soilbio.2019.107599.

2. Reay, M. K., Yates, C. A., Johnes, P. J., Arthur, C. J., Jones, D. L., & Evershed, R. P., 2019. High resolution HPLC-MS confirms overestimation of urea in soil by the diacetyl monoxime (DAM) colorimetric method. Soil Biology and Biochemistryhttps://doi.org/10.1016/j.soilbio.2019.04.015

1. Reay, M., Knowles, T., Jones, D. & Evershed, R.P., 2019, ‘Development of alditol acetate derivatives for the determination of 15N-enriched amino sugars by gas chromatography-combustion-isotope ratio mass spectrometry’Analytical Chemistry.

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