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Drivers of the dynamics of mineral elements' availability in soils

Animators: Noémie Janot et Nicolas Fanin 

The evolution of agricultural and silvicultural practices, in particular the supply of organic matter of various origins, results in an increased solicitation of the soil's ability to recycle nutrients. Moreover, this evolution takes place on soils that are sometimes already heavily disturbed and contaminated by ancient practices and industrial activities. Added to this are the effects of climate change (temperature, humidity) which will exacerbate the extremes and stress the resilience of the soil in the years to come. In this context, we study the mid- to long-term evolution of major and trace elements availability in natural and cultivated soils.

Our research aims to (i) understand, (ii) quantify and (iii) prioritize the drivers controlling the availability of elements for living organisms, whether these drivers come from climate (temperature, rainfall, wind), abiotic processes (soils physico-chemistry, mineralogy), living organisms (soils organisms, plants) or human activities (land use change, agricultural practices). We also study the links between this availability and the transfer to other ecosystem compartments (hydrosphere, atmosphere).

Modelling the interactions between organic matter and major and trace elements' availability

Our first line of research concerns the links between soil biological activity and the availability of nutrients and contaminants, depending on the pedoclimatic context and the nature of reactive mineral phases. In particular, we seek to understand how the quality of organic matter (chemical composition, stoichiometry) influences its biodegradability and its reactivity towards the elements of interest, to determine the impact of various organic matter inputs on major and trace elements’ availability. We emphasize the functional role of soil microbial communities during the recycling of organic matter to go further in understanding the ecological mechanisms controlling the decomposition process and the (un)coupling between biogeochemical cycles. Finally, we want to characterize the effects of contaminants on biological activity in soils and their impact on the mineralization of organic matter and the availability of major and trace elements.

Short- to long-term evolution of elements availability

This second line of research aims to study the temporal dynamics of the availability of elements during crop changes, after tillage or amendment inputs, depending on the nature of the plants or the composition of the microbial communities. (specific diversity, functional group). These approaches allow us to predict the availability during transitions (slow evolutions) as well as ruptures (abrupt change in land use). In particular, we study the evolution of the identified drivers when adding recycled organic matter, which can be a potential source of soil contaminants. We also seek to determine the impact of changes in climatic parameters (temperature, water regime) on the availability of elements, in particular via the modification of physico-chemical parameters and the biotic compartment of the soil, or via the contribution of mineral and organic particles subject to wind erosion.

The challenge of this research is to combine all of these processes to build models of the dynamics of the availability of elements over time, at the scale of the plot, depending on land use and climate.

Predicting elemental availability at the global scale

This third line of research aims to study the transfer of elements between different ecosystems (edge) or between different compartments (wind erosion, leaching) to quantify elementary fluxes and evaluate their impacts on the availability of soil elements. In particular, we seek to transpose the mechanisms identified at the parcel scale into models describing the availability of elements at the global scale. One of the main objectives is to extrapolate the parametrization developed at the scale of sites to several pedo-agro-climatic contexts, by coupling the mechanistic models of availability with spatialized databases, to determine how the global food/forestry production can be impacted by the availability of trace and major elements.