Fires occur in most terrestrial ecosystems where they drive changes in the traits, composition, and diversity of fungal communities. Fires range from rare, stand-replacing wildfires to frequent, prescribed fires used to mimic natural fire regimes. Fire regime factors, including burn severity, fire intensity, and timing vary widely and likely determine how fungi respond to fires. Despite the importance of fungi to post-fire plant communities and ecosystem functioning, attempts to identify common fungal responses and their major drivers are lacking. This synthesis addresses this knowledge gap, and ranges from fire adaptations of specific fungi to succession and assembly fungal communities as they respond to spatially heterogenous burning within the landscape. Fires impact fungi directly and indirectly through their effects on fungal survival, substrate and habitat modifications, changes in environmental conditions, and/or physiological responses of the hosts with which fungi interact. Some specific pyrophilous, or "fire-loving", fungi often appear after fire. Our synthesis explores whether such taxa can be considered cosmopolitan, and whether they are truly fire-adapted, or simply opportunists adapted to rapidly occupy substrates and habitats made available by fires. We also discuss the possible inoculum sources of post-fire fungi and explore existing conceptual models and ecological frameworks that may be useful to generalize fungal fire responses. We conclude with identifying research gaps and areas that may best transform the current knowledge and understanding of fungal responses to fire.

Aim: Roots and rhizospheres host diverse microbial communities that can influence the fitness, phenotypes, and environmental tolerances of plants. Documenting the biogeography of these microbiomes can detect the potential for a changing environment to disrupt host-microbe interactions, particularly in cases where microbes buffer hosts against abiotic stressors. We evaluated whether root-associated fungi had poleward declines in diversity, tested whether fungal communities in roots shifted near host plant range edges, and determined the relative importance of environmental and host predictors of root fungal community structure.Location: North American plains grasslands. Taxon: Foundation grasses -Andropogon gerardii, Bouteloua dactyloides, B. eriopoda, B. gracilis, and Schizachyrium scoparium and root fungi. Methods: At each of 24 sites representing three replicate 17°-latitudinal gradients, we collected roots from 12 individuals per species along five transects spaced 10 m apart (40 m × 40 m grid). We used next-generation sequencing of ITS2, direct fungal culturing from roots, and microscopy to survey fungi associated with grass roots. Results: Root-associated fungi did not follow the poleward declines in diversity documented for many animals and plants. Instead, host plant identity had the largest influence on fungal community structure. Edaphic factors outranked climate or host plant traits as correlates of fungal community structure; however, the relative importance of environmental predictors differed among plant species. As sampling approached host species range edges, fungal composition converged in similarity among individual plants of each grass species. Main conclusions: Environmental predictors of root-associated fungi depended strongly on host plant species identity. Biogeographic patterns in fungal composition suggested a homogenizing influence of stressors at host plant range limits. Resultspredict that communities of non-mycorrhizal, root-associated fungi in the North American plains will be more sensitive to future changes in host plant ranges and edaphic factors than to the direct effects of climate.

Fire can impact terrestrial ecosystems by changing abiotic and biotic conditions. Short fire intervals maintain grasslands and communities adapted to frequent, low-severity fires. Shrub encroachment that follows longer fire intervals accumulates fuel and can increase fire severity. This patchily distributed biomass creates mosaics of burn severities in the landscape—pyrodiversity. Afforded by a scheduled burn of a watershed protected from fires for 27 years, we investigated effects of woody encroachment and burn severity on soil chemistry and soil-inhabiting bacteria and fungi. We compared soils before and after fire within the fire-protected, shrub-encroached watershed and soils in an adjacent, annually burned, non-encroached watershed. Organic matter and nutrients accumulated in the fire-protected watershed but responded less to woody encroachment within the encroached watershed. Bioavailable nitrogen and phosphorus and fungal and bacterial communities responded to high severity burn regardless of encroachment. Low severity fire effects on soil nutrients differed, increased bacterial but decreased fungal diversity, and effects of woody encroachment within the encroached watershed were minimal. High severity burns in the fire-protected watershed led to a novel soil system state distinct from non-encroached and encroached soil systems. We conclude that severe fires may open grassland restoration opportunities to manipulate soil chemistry and microbial communities in shrub-encroached habitats.

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