Methane consumption by forest soils: spatial variability of physical and biotic processes involved to estimate the sink of forests in Grand-Est region


Topic

The atmosphere and the soil exchange three greenhouse gases with a major contribution to radiative forcing: carbon dioxide, methane and nitrous oxide. A small change in the intensity of the net flux of these gases can have a significant impact on the composition of the atmosphere, and thus a positive (mitigation) or negative (amplification) effect on global warming. N2O production from forest soils is marginal because they are generally limited in nitrogen. A very large number of studies have addressed CO2 production (soil respiration) during the past two decades. For methane, much less studied than CO2, the net exchange results from two biotic processes with antagonistic effects (methanotrophy, methanogenesis) and depends on physical processes (diffusion, advection, dissolution, …), all more or less sensitive to the microclimate and human impacts on soil physical properties. At the global scale, forest soils are considered the main sink of methane, absorbing a large part of anthropogenic emissions and helping to mitigate climate change. Forest soils of the Grand-Est region have the double feature of being more or less hydromorphe (luvisols) and of having a silty loam texture at their surface making them particularly sensitive to compaction resulting from increased mechanization of forestry activities. Their sink strength may decrease in the future if the diffusion of atmospheric methane to the surface horizons is reduced or if a change in the flow of water increases the duration of anoxic episodes leading to methane production in deep horizons.

The objective is to assess the global forest methane sink in the Grand-Est region, and to identify the factors of evolution in the medium term and the leverage actions to preserve this ecosystem service. The project will specify the contribution of physical and biological processes in the evolution of CH4 flux on two highly instrumented sites in Lorraine (SOERE F-ORE-T) to identify dynamic drivers of production and oxidation of methane in the soil (analysis of continuous records of flux and concentration profile using a multi-layer model). Proxies (potential methanotrophy, soil porosity) easily measurable on many sites will be tested on these two sites to simulate their annual methane budget and their measurements will be expended to other forests of the Grand-Est region using all the forest plots of the RENECOFOR network and available climate data.

The subject of the thesis is central in the Deepsurf working group project by assessing the role of forest soils in the balance of a greenhouse gas with a high global warming potential, and the impact of land use on this balance. Modelling methane transport from the atmosphere to the soil and from production areas in saturated horizons to surface horizons and to the atmosphere is an important scientific issue of the project. Although the subject is centred on forest soils for feasibility reasons (limited duration of a thesis, availability of monitoring equipment, validation of the genericity of the transport model to be applied on other soil types), it is already envisaged to extend this approach to other types of soils from mild (meadow …) to strong (crops, urban soils, brownfields) anthropogenic influences, in particular through a partnership with LSE (Laboratoire Sols et Environnement – GISFI), which will be involved in the steering committee of this thesis.

 

Supervisor: Daniel Epron, UL

Co-supervisor: Caroline Plain, UL

Doctoral school: RP2E

Socio-economic challenge: implementing the future of energy and energy transition, the development of new sources of energy carriers with low carbon impact on climate change and environment and maximizing efficiency energy of industrial processes, transport and buildings.

Partner : ONF – RDI (N. Pousse)

Cooperation inside UL: Laboratoire Sols & Environnement, UMR 1120 UL -INRA, GISFI (C. Schwartz, S. Leguédois, F. Darboux, G. Séré), Biogéochimie des Ecosystèmes Forestiers (J. Ranger)

International cooperation: University of Freiburg (M. Maier)

How to apply

In order to prepare a PhD thesis within the Lorraine Université d’Excellence Program, the interested candidate should consult the PhD topics offered in each social and economic challenges.
These PhD thesis topics are proposed by faculty members or researchers accredited to supervise research.

Candidate application period: according to graduate school schedule

  • visit graduate school web site for application rules. RP2E doctoral school
  • contact adress christine.fivet (@) univ-lorraine.fr

Each candidate may submit an application on up to three separate research topics.

Application analysis period by each graduate school
The graduate school reviews the applicants for a doctoral contract in the relevant disciplines. They check the level of supervision for each supervisor and the situation of trained doctors. Each candidate will meet the laboratory director, a supervisor or a representative from the graduate school. This interview is to identify the candidate’s motivations and suitability as a candidate for the PhD project proposed by the supervisor. A recommendation will be made to the graduate school. This will summarize the strengths and/or weaknesses of the application.

PhD grants will include monthly income for the PhD student (roughly 1700 € for research only, complement can be provided for teaching missions) and environment for research in the research unit.

Please be aware that in order to offer a variety of subjects, more positions are posted here than available funding. The LUE executive committee will make the final choice on the granted funding (up to 12 positions), based on the recommendations by the doctoral schools.