Organo-mineral interactions : nanoscale mechanisms for carbon sequestration in soils – NanoSoilC

Land uses disrupt the natural functioning of soils, leading to degradation of soil resources. At the same time, forecasts estimate that agricultural production has to be increased by 1.85-fold to meet the food demand of 9 billion people by 2050. Agro-ecological practices thus have to fulfil two main objectives simultaneously—minimize soil degradation while improving ecosystem services. Agro-ecological strategies for restoring soil functioning mainly strive to enhance the soil organic matter pool by increasing organic matter input fluxes. We argue that future agro-ecological techniques should also be geared towards increasing the residence time of organic matter in soil. This would represent a win-win strategy since long-term C storage in soils is also an issue in terms of climate change. This has been highlighted recently by the French Minister of Agriculture when proclaiming the future launch of the "4 per 1000" project at COP21.

A better understanding of the mechanisms that control organic matter stabilisation in soils is therefore needed. Mineral surfaces are suspected to play a major role in C storage in soils and the “nanoSoilC” project focuses specifically on the study of OM stabilization by organo-mineral interactions. We propose a conceptual breakthrough of organo-mineral interactions: our model no longer consider mineral surfaces as stable, but instead, subject to weathering. Weathering generates nanometric amorphous Al Si and Fe polymers with large specific surface areas and high reactivity towards organic compounds that they may stabilize on long-term timescales (Basile-Doelsch et al. 2015). The overall objective of the project is to explain the process of soil organic matter stabilization and destabilization by describing the mechanisms that control the organo-mineral interactions at the nano-scale. Organo-mineral complexes, considered at nanoscale, are called nCOMx.

We focus on mechanisms of nCOMx formation (during phases of soil formation and steady-state), and on mechanisms of nCOMx destabilization (loss of soil OM during the transition from forest to cultivated soil). These different mechanisms are addressed by complementary approaches. The project is organized in five Work Packages. nCOMx formation is addressed by experimental laboratory approaches (WP1) and field experiments (WP4). nCOMx destabilization is addressed by both laboratory (WP1) and field experiments (WP3), but also by an innovative modelling approach (WP2). WP0 is dedicated to the coordination of the project between partners.

The consortium brings together four partners (CEREGE, ECOSYS, BEF and Recyclage& Risques) representing 5 French institutes (CNRS, Aix-Marseille Université, Collège de France, INRA and CIRAD). The panel of scientists provides expertise in various disciplines. It aims to bring together the science of nanoparticles (and their characterization tools) with soil science. The overall budget requested to ANR is 690000 euros and includes training of post-doctoral fellows, PhD, and Master’s students. Outputs toward scientific communities and popularization of soil OM issues are also proposed.

Beyond the basic knowledge on soil functioning, two main outputs of this project are expected: (1) providing a hierarchy of processes controlling the C residence time to improve our capacity to understand and model long-term ecosystem services provided by organic matter in soils; and (2) providing the basis for understanding agro-ecological practices with respect to C storage and proposing innovation items. The Soils-nCOMx research project will thus be an innovative input for restoring the OM pool in cultivated soils to address two major societal issues: food security and climate change mitigation.