Description of the continuous nature of organic matter in models of soil carbon dynamics

Abstract : The understanding of soil organic matter (SOM) dynamics has considerably advanced in recent years. It was previously assumed that most SOM consisted of recalcitrant compounds, whereas the emerging view considers SOM as a range of polymers continuously processed into smaller molecules by decomposer enzymes. Mainstreaming these new insights in current models is challenging because of their ill-adapted framework. We propose the C-STABILITY model to resolve this issue. Its innovative framework combines compartmental and continuous modelling approaches to accurately reproduce SOM cycling processes. Model theoretical simulations highlight the role of SOM accessibility on its turnover. They reveal how enzyme depolymerization, decomposer community succession and carbon use efficiency are key drivers of SOM composition and quantity during decomposition and at steady-state. The mathematical structure of C-STABILITY may be tailored to different scales and is open to alternative formulations, thus offering a promising foundation for enhancing carbon cycling predictions.