Description du sujet de thèse

Impact of climate change on the composition and degradation of organic matter in permafrost peatlands.
The thesis project will address the following question: how do permafrost thawing and vegetation changes induced by climate change affect the dynamics and transfers of carbon and major nutrients (C-N-P) in Arctic ecosystems? To do this, we aim to gain a detailed understanding of the processes involved in the evolution of C-N-P cycles caused by changes in temperature and organic matter (OM) composition experimentally, by conducting in situ experiments (mesocosms in the field in the subarctic zone) and experiments under controlled conditions (microcosms in the laboratory). Particular attention will be paid to greenhouse gas emissions linked to C-N-P cycles: carbon dioxide, methane, and nitrous oxide. Arctic and subarctic permafrost zones represent a major climate issue on a global scale. These regions are a key player in controlling natural GHG emissions, which could become major sources of CO2, CH4 and N2O in the atmosphere in the coming decades, as a result of climate change and permafrost thawing. Better understanding the processes involved in these greenhouse gas emissions is crucial. The doctoral project aims to link the issue of greenhouse gas emissions in the permafrost zone with the cycling of major nutrients, which control biological activity in these regions. In particular, the vegetation changes recently observed in the Arctic are likely to modify the C-N-P composition of the plant biomass that feeds the C-N-P biogeochemical cycles in the active layer of permafrost, and by transfer, in the aquatic ecosystems to which it is connected. In order to understand how stoichiometric changes in plant litter will affect the carbon cycle along the continuum of the global ecosystem (soil, water, microbial community and plants), in situ and laboratory experiments will be designed to identify the role of different parameters on carbon emission and consumption and the transfer of nutrients to other compartments (microbial biomass, soil solution and surface water). These experiments will focus on the main processes governing the fate of carbon and nutrients in permafrost ecosystems, such as the interactions between organic matter quality and microbial decomposition versus photo-oxidation of dissolved and particulate organic matter, permafrost thawing, water saturation and temperature increase. The project is positioned on an interdisciplinary scope, mobilizing the knowledge and skills of the following disciplines: Physical Chemistry/Geochemistry/Biogeochemistry, Environmental and Molecular Microbiology/Microbial Ecology.

Contexte de travail

The proposed thesis will be carried out within the PEPR PEACE framework and between 2 laboratories (GET and CRBE). Regular meetings with the scientific managers will be organized. The PhD student will be working with teams from two laboratories, PEPR Peace partners and the Arctic station in Sweden (Abisko). This study site is part of the Climate Impact Research Center (CIRC) managed by Umeå University. Working meetings, national and international conferences are planned during the contract period.

Le poste se situe dans un secteur relevant de la protection du potentiel scientifique et technique (PPST), et nécessite donc, conformément à la réglementation, que votre arrivée soit autorisée par l'autorité compétente du MESR.