Arbuscular mycorrhizal (AM) fungi influence ecosystem productivity through their mutualisms with plant hosts. Despite the importance of AM fungal mutualisms in many ecosystems (e.g., grasslands), management methods used to maintain ecosystems, such as prescribed fire, seldom account for their influence on AM fungi. Given that prescribed fire management commonly manipulates both the frequency and season of fire, it is critical that we understand how variations in fire regime influence AM fungal community composition and seasonality. This work tested how fire frequency and season influenced AM fungal community structure through selection for spore traits. We hypothesized that increases in fire frequency would select for spore traits related to temperature resistance (e.g., darker pigmentation, smaller spore volume, etc.), and that this selection would be modified by fire season, with stronger effects in the Fall when AM fungal sporulation is highest. We further hypothesized that fire regime driven selection on spore traits would drive differences in AM fungal community composition. Using a tallgrass prairie restoration experiment manipulating fire frequency and season, we assessed how fire effects on AM fungal spore traits like saturation, luminance, volume, and sporulation, altered AM fungal community composition.
Fire altered AM fungal community composition through selection for specific spore traits, and this effect varied based on fire season and time since fire. In burned sites, spores were darker in color, displayed lower levels of non-white pigmentation, and were smaller in volume. This selection for spore traits also drove differences in AM fungal spore community composition between burned and no burn sites; however, this effect was dependent on time since fire. Specifically, fire effects on AM fungal spore traits and community composition were not immediately apparent after fire and took up to six months to develop. Ongoing work will assess the importance of fire season (Fall vs. Spring) on AM fungal traits and communities, and we predict that fire effects on AM fungal traits will be stronger in Fall burn plots due to higher sporulation at the end of the growing season.