Location in soil pores as determinant of resource accessibility for microarthropods

Trophic interactions among soil-living organisms occur predominantly within the soil pore network and are essential for soil functioning. The access of animal consumers to microorganisms is likely determined by the dimension of soil pores in which microorganisms are located and the body size of consumers. However, experimental evidence for size segregation is lacking for many soil organisms, notably microarthropods, which are key players in the soil food web. Here, we tested how the location of microorganisms in pores with different neck diameters influences their accessibility to microarthropods, and whether this accessibility varies with the consumer’s body size. By adding 13C sodium pyruvate solution to intact soil cores at different matric potential, we labelled microbial communities in different pore size classes and traced their consumption by three species of Collembola (Hexapoda), which was done by measuring the 13C incorporation into animal tissue after four-weeks of incubation. Collembola incorporated labelled C from each of the pore size treatments (4–13, 13–41 and 41–931 µm), indicating that microorganisms are not fully physically protected from consumption by microarthropods, even in pores that are smaller than their body width. However, the incorporation of 13C into Collembola tissue increased with pore neck diameter, suggesting that the physical environment limited the access of Collembola to resources. Overall, our findings suggest that resource accessibility is constrained by the body size of consumers, potentially shaping the trophic niches of microarthropods and influencing soil element dynamics at the pore scale.