Distinct and synergistic roles of bacteria, fungi, and extracellular polymeric substances in soil aggregation

Microbial extracellular polymeric substances (EPS) are key chemical bonding compounds in soil, yet their capacity to form and stabilize soil aggregates independently of microbial processes remains unclear. Here, we used a controlled microcosm experiment with selective biocide treatments to disentangle the roles of EPS and soil microbiota in aggregation. We found that bacterial-dominated soil produced substantial polysaccharide-rich EPS, which facilitated microaggregate formation. However, despite elevated EPS-polysaccharide concentrations, aggregates lacking fungal cellular integrity and activity rapidly disintegrated upon wetting. This suggests that fungal hyphal networks are critical for macroaggregate stability, likely through a combination of physical enmeshment and continuous production of protein-rich EPS. While EPS represent promising soil management tools, their effectiveness critically depends on the presence of active, interacting microbial communities.