Shift in soil fauna feeding mode with litter quality across global forests (Tsurikov et al.)

Soil fauna regulates litter decomposition and soil organic matter transformation, acting as both litter and microbial feeders. Whether these feeding modes shift along environmental gradients remains unclear. We tested if microbivory increases with decreasing litter quality and in colder climates, both factors limiting detritus digestion by fauna. Using stable isotope composition (δ¹³C, δ¹⁵N) of 7,408 soil invertebrate samples from 228 forest sites across temperate to tropical biomes, we determined δ¹⁵N values are positively associated with litter C:N ratio and mean annual temperature, indicating a shift from detritivory toward microbivory under low litter quality with additional modulation by climate. In contrast, δ¹³C values showed no consistent association with litter C:N ratio or climate, reflecting context dependent microbial carbon routing. Our findings highlight litter quality as the primary driver of the detritivory-to-microbivory shift in soil fauna, with implications for predicting changes in climate and plant communities on carbon cycling in terrestrial ecosystems