PhD thesis in Soil Sciences : Study of the links between biodiversity, soil structure and soil functioning

Scientific context and objectives of the thesis  Environmental forcing from human activities alters the soil's organo-mineral matrix, soil organisms, and the biotic-abiotic interactions that underpin the ecological functions of soils necessary for healthy ecosystems. Preserving soils and the biodiversity they support, and restoring their functions when degraded, are therefore major challenges for all soils worldwide. However, numerous challenges and scientific gaps need to be addressed to tackle this issue. Soil biodiversity plays a crucial role in maintaining soil structure and associated functions, as soil organisms and biological activity influence porosity and aggregation through the decomposition of organic matter, root activity, exudates, and bioturbation. Recent advances in 3D imaging have improved our understanding of the links between soil structure, organic matter dynamics, and flux transfers. However, the effect of biodiversity and trophic and non-trophic interactions on soil physical structure remains poorly characterized, as the data enabling these characterizations are fragmented, limited to single sites, or focused on isolated soil properties (physical and biological soil properties are still rarely characterized at the same sites). Conversely, bioturbation morphologies depend on pedoclimatic conditions and soil management practices, and we do not know to what extent these different morphologies can impact soil functions such as water infiltration and gas transfer. Furthermore, soil structure is still frequently considered static, without taking into account the lifespan of the biostructures created and the seasonal variations they undergo. This thesis aims to contribute to answering the following question: what is the impact of biological actors (e.g., roots, soil meso- and macrofauna), as agents of soil stabilization and restructuring, on soil functioning? This thesis project will be carried out within the framework of the PEPR Sols Vivants, whose mission is to produce knowledge on the role of soil organisms and their multiple interaction networks in the multifunctionality of soils, for a diversity of soil types, uses and management methods, in order to meet the challenge of preserving and improving soil health. Work environment The successful candidate will be hosted within the Info&Sols Research Unit (INRAE ​​Orléans), under the supervision of Isabelle Cousin (PhD Director) and Marine Lacoste (Co-supervisor). The PhD will also be supervised by Guénola Péres (UMR SAS, Co- director) and Maha Chalhoub (BRGM, Co-supervisor). The Info&Sols unit's scientific project is structured around three main research areas: 1) Soil status, functioning, and monitoring; 2) Soil quality, health, ecosystem services, and impacts; and 3) Environmental data management. Main missions The PhD candidate will be tasked with exploring the links between soil biodiversity, soil structure, and soil function, focusing on water and gas transfer properties. Specifically, he/she will be responsible for: • Designing a conceptual model linking transfer properties and biodiversity characteristics. • Acquiring data on the physical properties of soils and the characteristics of soil biodiversity across metropolitan France (fieldwork conducted during a campaign in spring 2027, and laboratory experiments). • Processing the acquired data to extract indicators characterizing the soil. • Creating and sharing a dataset compliant with FAIR principles. • Analyzing the dataset to deduce links between biodiversity and soil function. Application procedures Funding for the PhD is secured. The PhD supervisors will select candidates after reviewing their applications, and interviews will be offered on November 12 or 13, 2026. Following these interviews, candidates will be ranked, and the PhD topic will be offered to them in order of their ranking until one of the candidates accepts it The successful candidate will be enrolled at the University of Orléans, within the EMSTU Doctoral School.