The Special Report on Global Warming of 1.5 °C by the Intergovernmental Panel on Climate Change (IPCC, 2018) recently outlined the clear case for reducing net CO2 emissions globally. The report explicitly covers land use change as a pathway to achieving net CO2 emission reductions, making the creation of climate-smart soils (Paustian et al. 2016) a new challenge to society. Forests have a high potential for carbon sequestration, particularly in young, rapidly growing stands. However, to understand the full benefit of tree planting for long-term sequestration of CO2 from the atmosphere, we need to account for changes in the underlying soil carbon (C) stock, as a loss of soil C following afforestation can potentially offset any gains in aboveground C stock. There are a number of knowledge gaps to address in order to manage soils under forestry in a climate-smart fashion:
• Where within the soil does C sequestration occur, and what are turnover times of different fractions?
• What is the role of microbial communities (including mycorrhizal associations with roots) in the formation and the decomposition of sol organic matter?
• What are interactions between climate, underlying geology and vegetation that can optimise climate-smart land management?
• What is the significance of soil erosion and transport of dissolved organic matter on the net C balance of afforested sites?
This studentship addresses these key uncertainties in order to provide robust insights for land management. A strong focus will be placed on process studies to better understand the ecological and biogeochemical processes that produce observed changes under a range of soil types, vegetation cover and environmental conditions.
Through the collaboration with Forest Research, the student has access to forest sites of different ages since plantations were established, and with recorded land use and management history. By selecting plantations on land previously used for pasture, the aim is to create a data set of chronosequences for which soil C stock can be established. Control sites of continuous pasture will be used to verify potential changes in C stock and other soil parameters (e.g. pH or bulk density changes).
Transplanting soils between geographical locations is a powerful tool to separate influences of climate, geology and vegetation type. Nylon netting of different mesh size will be used to selectively allow or block access to transplanted soils by roots and/or mycorrhiza (e.g. Subke et al., 2011). Measurement of CO2 flux from these transplanted soils will then identify increased or decreased decomposition, whilst addition of common substrates (e.g. wood or plant litter) are options to focus on specific forms of organic matter affected by root and mycorrhizal priming. A novel aspect of the methodology is the measurement of natural abundance radiocarbon (14C) in soil organic matter pools and respired CO2 to determine the changes in turnover and age of carbon emissions following a transition between vegetation types. 14C determinations are subject to approval by the NERC Radiocarbon Facility, and the student would be involved in writing this application, providing valuable experience in composing and managing scientific grant applications.
Field experiments will be supplemented by lab studies using mesocosms of different plant/mycorrhizal assemblages in soils of contrasting management origins. In collaboration with Prof. D. Johnson (University of Manchester), the student will develop his/her abilities to culture plant/fungal assemblages and set up novel experiments to investigate mechanisms of organic matter formation as well as decomposition. The student would also have access to Prof. Johnson’s state-of-the-art mobile laboratory to monitor gas flux from soil cores at field sites, enabling novel short- and long-term responses to manipulations in aboveground and belowground C dynamics.
1) General field work methods, including gas flux measurements and soil transplant/mycorrhizal in-growth experiments as well as ecophysiological techniques
2) Critical laboratory skills, including elemental analysis and application of 14C in experiments and stable isotope methods (13C and 15N).
3) Numeracy, data analysis, ecological modelling & informatics. These skills will be gained through targeted training courses within the IAPETUS2 consortium and available at Stirling.
4) Complementary training in transferable skills and core scientific skills (data management, analysis, presentations, paper writing).
This PhD is part of IAPETUS2, a Doctoral Training Programme. Supervision will be provided by Dr J.-A. Subke and Dr F.X. Joly (University of Stirling), Dr Mark Garnett (SUERC, Glasgow), Prof David Johnson (University of Manchester), and Mike Perks (Forest Research).
This is a 3.5 year PhD studentship with a stipend set at the RCUK national rate (forecast to be £14,296) with an anticipated start date of October 2018.
Guo, L., Gifford, R., 2002. Soil carbon stocks and land use change: A meta analysis. Global Change Biology 8, 345-360.
IPCC, 2018. IPCC Special Report on Global Warming of 1.5ºC. www.ipcc.ch/report/sr15/
Paustian, K., Lehmann, J., Ogle, S., Reay, D., Robertson, G.P., Smith, P., 2016. Climate-smart soils. Nature 532, 49–57.
Subke, J.A., Voke, N.R., Leronni, V., Garnett, M.H., Ineson, P., 2011. Dynamics and pathways of autotrophic and heterotrophic soil CO2 efflux revealed by forest girdling. Journal of Ecology 99, 186-193.
IMPORTANT: The deadline for applications is Jan 18th 2019 at 16:00. However, serious applicants are strongly advised to get in touch by the 17th December to discuss their application. Interviews will be held in January. By the January deadline, applicants must have submitted a formal application through the Stirling University online application system: https://www.stir.ac.uk/research/research-degrees/how-to-apply-for-our-research-degrees/
TO APPLY: Please send a CV and cover letter outlining your suitability for this studentship to Jens-Arne Subke ([email protected]).
To be eligible for a full award a student must be a UK citizen or have been resident in the UK for a period of 3 years or more. Please see the RCUK Website for more details.