Diversity and temperature sensitivity of organic matter in Morvan forest soils under climatic constraints: evolution of soil respiration and control factors

Started in october 2021

Funding: doctoral grant

Supervisor: Olivier Mathieu ; co-supervisor : Mathieu Thévenot

Defended the 25 november 2024

Abstract

Current climate change and shifts in land use and management are likely to alter the dynamics of soil organic matter decomposition and associated carbon fluxes. Forest ecosystems account for 40 % of the organic carbon stock on continental surfaces and are therefore a priority for research. Locally, the Morvan, a mid-mountain region covered by 45 % forest, appears to be more sensitive to climate change than the surrounding plains. In this context, this study focused on the dynamics of organic carbon in temperate forest soils in the face of climate change. This work was mainly carried out on the Mont Beuvray site, a forested massif located in the southern part of the Morvan Regional Natural Park. Soil samples representing the spatial diversity of the massif were taken for each tree species (beech, Douglas fir, silver fir, spruce). The molecular diversity of organic matter was characterised by pyrolysis coupled with gas chromatography-mass spectrometry (Py-GC-MS). The results suggest that organic matter in soils under silver fir is more readily degradable than that in soils under Douglas fir. The temperature sensitivity of soil respiration was assessed by measuring the Q10 parameter, with values ranging from 2.3 to 3.0. A higher value was observed for beech (2.8 ± 0.1) compared to conifers (2.6 ± 0.1). This suggests that with climate change, soils under deciduous species could emit more CO2 than soils under conifers. The observed variability in this Q10 parameter is mainly explained by the interaction between the molecular composition of organic matter and the activity of microorganisms (extracellular enzymatic activities). These results will help to better assess and anticipate changes in the dynamics of organic matter in mid-mountain forest soils.

Keywords

soil organic matter, forests, carbon stocks, soil respiration, molecular diversity, climatic constraints

Thesis advisory panel

Sylvie Dousset (université de Lorraine, département de géosciences, LIEC)
Heike Knicker (Department of Biogeochemistry Plant and Microbial Ecology, IRNAS-CSIC)

jury

Laurence Mansuy-Huault – université de Lorraine – reviewer
Laurent Augusto –INRAE, Villenave d’Ornon – rapporteur
Anne Jaffrezic –Institut Agro Rennes Angers – examinatrice
Stéphane Follain –Institut Agro Dijon – examinateur
Olivier Mathieu – université de Bourgogne – directeur de thèse
Mathieu Thevenot – université de Bourgogne – co-directeur de thèse
Jean Lévêque – université de Bourgogne – invité

extrait:

lien_externe:

titre:

Diversité et réactivité des matières organiques des sols forestiers du Morvan : évolution de la respiration des sols et facteurs de contrôle sous contrainte climatique

date_de_debut_these:

octobre 2021

nom:

Bonnefoy-Claudet

date_de_debut_these_numerique:

202110

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kc_raw_content:

Diversity and temperature sensitivity of organic matter in Morvan forest soils under climatic constraints: evolution of soil respiration and control factors

Started in october 2021

Funding: doctoral grant

Supervisor: Olivier Mathieu ; co-supervisor : Mathieu Thévenot

Defended the 25 november 2024

 

Abstract

Current climate change and shifts in land use and management are likely to alter the dynamics of soil organic matter decomposition and associated carbon fluxes. Forest ecosystems account for 40 % of the organic carbon stock on continental surfaces and are therefore a priority for research. Locally, the Morvan, a mid-mountain region covered by 45 % forest, appears to be more sensitive to climate change than the surrounding plains. In this context, this study focused on the dynamics of organic carbon in temperate forest soils in the face of climate change. This work was mainly carried out on the Mont Beuvray site, a forested massif located in the southern part of the Morvan Regional Natural Park. Soil samples representing the spatial diversity of the massif were taken for each tree species (beech, Douglas fir, silver fir, spruce). The molecular diversity of organic matter was characterised by pyrolysis coupled with gas chromatography-mass spectrometry (Py-GC-MS). The results suggest that organic matter in soils under silver fir is more readily degradable than that in soils under Douglas fir. The temperature sensitivity of soil respiration was assessed by measuring the Q10 parameter, with values ranging from 2.3 to 3.0. A higher value was observed for beech (2.8 ± 0.1) compared to conifers (2.6 ± 0.1). This suggests that with climate change, soils under deciduous species could emit more CO2 than soils under conifers. The observed variability in this Q10 parameter is mainly explained by the interaction between the molecular composition of organic matter and the activity of microorganisms (extracellular enzymatic activities). These results will help to better assess and anticipate changes in the dynamics of organic matter in mid-mountain forest soils.

 

Keywords

soil organic matter, forests, carbon stocks, soil respiration, molecular diversity, climatic constraints

 

Thesis advisory panel

Sylvie Dousset (université de Lorraine, département de géosciences, LIEC)
Heike Knicker (Department of Biogeochemistry Plant and Microbial Ecology, IRNAS-CSIC)

 

jury

Laurence Mansuy-Huault – université de Lorraine - reviewer
Laurent Augusto –INRAE, Villenave d’Ornon - rapporteur
Anne Jaffrezic –Institut Agro Rennes Angers - examinatrice
Stéphane Follain –Institut Agro Dijon - examinateur
Olivier Mathieu – université de Bourgogne - directeur de thèse
Mathieu Thevenot – université de Bourgogne - co-directeur de thèse
Jean Lévêque – université de Bourgogne - invité