Drivers of the terrestrial methane sink under land use change

Atmospheric methane (CH4) concentrations have increased consistently over the Holocene, with an accelerated increase in atmospheric burden of this greenhouse gas in recent decades mostly due to anthropogenic activities (e.g. Ciais et al 2013). Aerated soils represent an important sink for atmospheric methane, as consortia of protobacteria utilise methane as a source of metabolic energy, thus mitigating current atmospheric CH4 increases. The strength of this terrestrial greenhouse gas sink is linked to the form of vegetation and land management, so that any changes in land use can have significant impacts on the greenhouse gas balance of contrasting land uses (Tate et al. 2012). Forest soils generally show higher CH4 oxidation rates than grasslands and agricultural land use forms, but the exact mechanisms underlying this pattern have not been conclusively researched (Tate 2015). Significant current changes in forest cover in the UK are therefore likely to impact on the soil CH4 sink strength.
We currently lack an understanding of the role of plant-soil interactions in the oxidation of atmospheric methane. The activity and composition of soil microbial communities is directly influenced by plant composition and productivity, but no data exist that link the strength of the terrestrial methane sink to vegetation cover.

Key research questions:
The proposed PhD project will investigate two key elements of the terrestrial methane sink, which address important gaps in our understanding of the land surface – atmosphere greenhouse gas balance:
1) Role of Land Use: The aim is to quantify rates of methane oxidation across key land uses in the UK (initially) and world-wide. Particular focus is given to land use types undergoing significant change at present, such as afforestation of former pasture land and forest removal from wetlands.
2) Interaction of vegetation and methane oxidation: Microbial activity in the soil has been clearly linked to carbon supply to fungi and bacteria in the rhizosphere (i.e. the part of the soil directly influenced by the presence and activity of roots). This project will address specifically the impact of plant C allocatrion belowground on soil CH4 oxidation.
The work will combine field surveys (across contrasting land use types) with controlled environment studies to obtain relevant data on both ‘natural’ gas exchanges and advanced process understanding. Experiments in field and lab will separate impacts of soil temperature and moisture from biotic interactions and the crucial influence of changes in atmospheric CH4 concentrations.
Results will provide an important foundation for future model development for realistic forecasting of the soil greenhouse gas budget, where microbial methane oxidation in response to atmospheric concentration change and vegetation effects is not yet considered.

References
Ciais, P., Sabine, C., Bala, G., et al. 2013. Carbon and Other Biogeochemical Cycles. In: Stocker, T.F., et al. (Eds.), Climate Change 2013: The Physical Science Basis. Cambridge University Press, Cambridge.
Tate K.R., 2015. Soil methane oxidation and land use change – from process to mitigation. Soil Biology and Biochemistry 80, 260-272.
Tate, K.R., Walcroft, A.S., Pratt, C., 2012. Varying atmospheric methane concentrations affect soil methane oxidation rates and methanotroph populations in pasture, an adjacent pine forest, and a landfill. Soil Biology & Biochemistry 52, 75-81.

Application
The deadline for applications is Friday February 10th with interviews for candidates in Edinburgh between the 21st - 24th February, 2017. Please send a CV (including two referees’ names) and cover letter to [Email Address Removed]