Increasing soil C sequestration relies on novel understanding of natural processes and development of innovative management practices. Such understanding will be obtained by taking into consideration whole soil C as organic matter storage in top- and subsoil horizons may be controlled by contrasting processes. Indeed,organic matter in different parts of the soil profile shows specific properties concerning its nature and stability. This session invites contributions dealing with the evaluation of the importance of organic matter in top- and subsoil horizons of different soil types for biogeochemical cycling and ecosystem services, such as carbon sequestration and nutrient availability. Presentations in this session concern the nature, fate and management of organic matter at the nexus of biology, hydrology and chemistry. Experimental and modelling studies concerning the mechanisms of soil organic matter formation, its loss and impact on global biogeochemical cycling are welcome.