Combining microbial modeling and soil structure dynamics for an improved understanding of soil organic carbon and nitrogen turnover

Soil organic matter (SOM) turnover plays a major role in the global carbon cycle, but also influences soil health and fertility. Accurate modeling of SOM dynamics requires a comprehensive understanding of the interconnected biological and physical processes occurring at small spatial scales. The availability of carbon (C) and nitrogen (N) resources governs microbial growth, while microbial dynamics, in turn, affect the distribution of C and N within soils. The stabilization of microbial necromass within soil aggregates or its association with mineral surfaces and the role of living and decaying roots as sources of carbon require closer attention to evaluate their role for soil aggregation. This aggregation process in turn impacts the degradation of (potentially occluded) organic matter. We present a mechanistic model at the pore scale, which includes a microbial model that takes into account the turnover and C/N ratios of different organic matter sources. It is combined it with a cellular automaton model for simulating dynamic soil structural reorganization. The disturbance of soils following the input of organic matter of different quality, i.e. with distinct decomposition rates and/or C/N ratios is examined and compared for bulk soil and rhizosphere environments to assess their effect on soil organi carbon and nutrient storage capacity. We further elucidate the spatial and temporal dynamics of carbon use efficiency (CUE). In summary, our approach provides valuable insights into the complex processes that govern soil carbon cycling.