Experimental evidence that soil fauna drives plant root exudation patterns

Soil fauna is an essential component of soil. However, its influences on root exudates are unknown. Through both direct and indirect interactions, soil fauna can affect the dynamics of interactions between plants, microbes, and soil environments. In this study, we used an original approach called EcoRoots, which features rhizoboxes with sorption traps and allows exudates on roots to be sampled with minimum soil and plant disturbance. We designed an experiment to determine the effect of springtails ( Folsomia candida W.), earthworms ( Lumbricus terrestris L.), or both on plant root metabolites of Poa annua L., a gramineous species. After nine weeks of experiments, soil fauna increased the nutrients in soil, but P. annua growth was reduced mainly in the presence of earthworms. With regard to P. annua exudation, we found specific assemblages depending on the fauna identity, with the interaction between springtails and earthworms bringing different exudates than the sum of the two single treatments. Plants in presence of soil faunal groups produced a higher richness of exudate metabolite than without soil fauna. We also found that earthworms had the greatest influence on metabolite patterns. The changes in root exudation were associated with differences in abiotic factors and microorganism communities, suggesting that both direct and indirect effects might explain these patterns. Nevertheless, distinguishing the mechanisms involved in the process remains complex. To conclude, we strongly recommend studying living soil or more real ecosystems to advance our understanding of root exudation and, more globally, soil interactions and ecology, whether in natural or agricultural ecosystems. • Presence of soil fauna modify metabolomics of Poa annua root exudates • Earthworms induce greater changes in rhizodeposition than Collembola • Soil fauna addition led to specific metabolomics patterns • Sampling living soils is crucial for understanding real exudation processes.