Trait Shifts and Vertical Redistribution Enable Nematode-Trapping Fungi to Adapt to Fire Disturbance

Fire rapidly reshapes soil environments, yet direct experimental evidence of how soil microorganisms respond through both functional trait adjustment and spatial redistribution remains limited. Here, we used nematode-trapping fungi (NTF) as a model system to test whether their response to fire is mediated by coordinated changes in functional traits and vertical redistribution. We first compared strains isolated from naturally burned habitats with those from adjacent unburned habitats and identified consistent trait shifts; we then tracked NTF dynamics in artificial soil profiles exposed to simulated fire. Strains from burned habitats produced 53-1114% more trapping structures and exhibited bait-based predation efficiencies 9-41% higher than those from unburned habitats. Conidia of fire-adapted strains were smaller, with reductions in length and width of 0.3-8.0 µm and 0.1-3.4 µm, respectively. Hyphal growth rates increased significantly in Dactylellina and Drechslerella but declined overall in Arthrobotrys. In the soil-profile microcosm experiment, simulated fire completely eliminated Arthrobotrys from the topsoil (0-5 cm), whereas Dactylellina and Drechslerella from deeper layers (10-20 cm) were subsequently detected in upper layers, indicating upward redistribution and recolonization within 7-56 days. Together, these results reveal two complementary mechanisms underlying NTF adaptation to fire: individual-level trait shifts, which likely reflect the reallocation of resources from reproductive structures to predatory traps and hyphal expansion, and community-scale vertical redistribution, which enables recolonization via deep-soil source populations. Our work provides experimental evidence that soil microorganisms cope with abrupt fire disturbance through coordinated trait shifts and vertical spatial redistribution, offering mechanistic insights that may support trait-oriented restoration management of post-fire soil ecosystems.