Advancing our understanding of how biotic and abiotic processes control soil organic matter stocks, stability, stabilisation mechanisms, biochemical transformations, and loss from terrestrial ecosystems remains a major focus in biogeochemistry today. This session aims to facilitate discussions that improve our understanding of how complex biotic and abiotic processes interact in the terrestrial ecosystem, in particular during periods of natural- or anthropogenic-induced change and across a range of scales from molecular, profile, plot, landscape, and global scales to control soil organic matter dynamics. Furthermore, the session welcomes submissions that focus on: (a) relationship of soil organic matter transformations with length and intensity of weathering processes that modify minerals and create a distinct soil matrix in which biological processes take place; (b) dynamics of soil organic matter in deep soil layers using experimental and modeling approaches and (c) plant-soil interactions on soil carbon and nutrient cycling. This session will contribute to improving our understanding and future predictive capabilities of carbon dynamics in the earth system by bringing together scientists working on improving our mechanistic understanding of key soil organic matter processing, with the explicit goal of promoting inclusion of the interplay of biology, climate, geochemistry and pedology into large-scale model frameworks.