Soil microbial–fauna trophic and non-trophic interactions: global patterns and implications for soil carbon stabilization

Ecological interactions between soil organisms, trophic (TIs) and non-trophic (NTIs), underpin soil carbon (C) dynamics. However, our knowledge of how these interactions are discussed in the scientific literature remains limited. We conducted a systematic literature review to identify studies examining interactions between soil microorganisms and soil fauna (micro-, meso-, and macrofauna) through trophic pathways (e.g., feeding on bacteria or fungi) and non-trophic mechanisms, including facilitation, inhibition, mutualism, and competition. The search yielded a total of 9136 potential studies, of which 339 were preliminarily selected. The countries leading research on this topic were China (12%) and the United States (9%). Most studies (54%) evaluated TIs, 39% NTIs, and the remaining 7% evaluated both interaction types. After identifying the most common keywords, we obtained three clusters. Cluster 1 was associated with biodiversity and ecosystem functioning, with a focus on nematodes' influence on microbial communities. Cluster 2 encompassed studies on soil properties and microbial community structure, emphasizing interactions between ecosystem engineers (soil macrofauna) and microorganisms. Cluster 3 addressed biogeochemical cycles, including C and nitrogen dynamics, with particular emphasis on collembolan and fungal communities. The most frequent keywords associated with microorganisms were bacteria and fungi, each appearing in 21 studies. Regarding soil fauna, 34 studies evaluated collembolans, 22 earthworms and 18 nematodes. Soil fauna could alter microbial communities through grazing or predatory activities (TIs), physical disturbance and bioturbation (NTI), and the formation of mutualistic relationships (NTIs). Therefore, increasing our understanding of soil microbial-fauna interactions is critical to identify possible mechanisms driving soil C stabilization.