Pore scale microbial biogeography across different soil types

Microbial activity in soils is influenced by the structural heterogeneity of the pore network, which governs the distribution of microbial communities, their interactions with organic matter and the characteristics of the immediate environment of microorganisms. This study investigates whether microbial activity exhibits consistent patterns across pore size classes in six soil types with diverse physical and chemical properties. Using a matric potential-based approach, we targeted small (3–10 μm) and large (30–100 μm) pores with ¹³C-labelled pyruvate to assess microbial respiration and substrate mineralisation.

The results revealed that the mineralisation of the added organic substrate was faster in the larger pores of four of the six studied soils, but that the microbial carbon use efficiency was lower compared to smaller pores, where a more efficient carbon use was observed. The exceptions were a forest soil with an abundant fungal community and a long term bare fallow soil with depleted soil organic C content and microbial biomass. Despite differences in soil properties, such as texture, organic matter content and pH, the observed patterns were consistent across most soil types, highlighting universal controls on microbial activity at the pore scale.

This work underscores the critical role of soil microstructure in shaping microbial activity and carbon cycling. The findings advance our understanding of microbial biogeography and provide insights for improving soil carbon models to better predict ecosystem responses to environmental change.