Resilience not yet apparent in soil fungal communities of the boreal forest from one to five years after wildfire across a severity gradient

Wildfires are natural disturbances characteristic of boreal forests. However, fire regimes around the world are changing, with effects on fire frequency and fire severity. Here, we present data from one and five years post-fire across 40 different sites from the boreal forest of the Northwest Territories and Alberta, Canada, asking the following questions: (1) Do the factors that structure post-fire soil fungal communities change over time? (2) Is there evidence for resilience in fungal community composition across different burn severities? (3) Do fire-enriched taxa change one vs. five years post-fire? Factors correlated with fungal community composition remain largely the same five years post-fire, with a declining correlation with burned/unburned, and an increasing association with vegetation community composition. This suggests that the immediate effects of fire on fungal community composition wane or diverge with time, while the influence of longer-term effects of fire, such as changes in vegetation, increases. Fungal communities failed to demonstrate resilience in community composition five years post-fire, in contrast to our findings for bacterial communities, and suggesting that fungal communities may be more closely tied to soil properties and vegetation communities that take longer to recover post-fire. Finally, we identify and classify fire-responsive fungi into different response types, based on their enrichment or depletion one vs. five years post fire. Persistent fire responders include taxa from the genera Penicillium, Coniochaeta, and Calyptrozyma, and the family Venturiaceae, but different taxa within a single genus respond differently to fires, underscoring that generalizations even at relatively fine taxonomic levels may be inappropriate, and that the mere presence of traits that may be relevant to post-fire success are insufficient alone to guarantee post-fire abundance. Future manipulative and observational studies will help us continue to dissect the multiple factors and traits structuring fungal responses to fires.