How do pore size and microbial mobility shape necromass distribution in soils ?

Soil organic carbon (SOC) sequestration is closely linked to the functioning of microbial communities present in soil microenvironments. However, it is unclear how the distribution of microbial communities or carbon resources within soil pore space influences the formation and long-term storage of microbial necromass. Using a cellular automaton simulating the exploration of pore space by bacterial cells, we estimated the relative production of necromass in different soil pore sizes, taking into account (i) the initial distribution of carbon resources used by microbial cells, (ii) soil moisture, and (iii) the microbial biomass recycling threshold. We show that carbon resources located in macropores are consumed more rapidly than those located in narrow pores. Microbial mobility appears to be highly dependent on the pore context: it is advantageous in connected macropores but becomes costly and inefficient in confined micropores, reducing carbon-use efficiency. Necromass tends to accumulate preferentially in small pores, where reduced connectivity limits its recycling. These results highlight the importance of soil spatial organization and water status in regulating microbial carbon fluxes and suggest that explicit integration of pore heterogeneity and microbial functional traits is essential for improving soil carbon dynamics models.