Ecological disturbances like fire restructure microbial communities and reorient their seasonal trajectories. Fungi play key roles in regulating plant biomass (i.e. fuels) through saprotrophic, mutualistic, and pathogenic interactions, so fire’s impact on fungal communities could have implications for fire regimes. Following fire, fungal compositional shifts likely occur and interact with natural seasonal turnover in fungal communities. For prescribed fires commonly set in spring, direct mortality effects of fire may be the immediate driver of fungal communities. With increasing time after fire and the onset of the growing season, however, fire related environmental changes (e.g. nutrients and edaphic conditions) may indirectly determine fungal community composition. We hypothesized that 1) fires would predictably shift fungal communities across frequently burned, pyrophilic ecosystems, and that 2) changes would be associated with direct and indirect fire effects on fungi. Specifically, we predicted that fire would initially shift fungal communities, and also drive longer term community changes correlated with nutrients. In plots with and without prescribed burning, we assessed seasonal changes in soil fungal communities in two pyrophilic ecosystems, a Longleaf pine savanna and tallgrass prairie. Using ordination, indicator species analyses, and linear models, we assessed how fire shifted fungal communities and seasonal trajectories across time.
Results/Conclusions
Fire altered fungal community structure and seasonal trajectories similarly across pyrophilic ecosystems. Fire-driven fungal community shifts persisted throughout the experiment, and were independent of co-occurring seasonal changes in adjacent, non-burned communities. Early after fire, changes were primarily driven by the presence/absence of fire, as well as fire driven changes to the environment that favored taxa able to survive in harsh, post-fire environments. Surprisingly, fire driven shifts to nutrient availability were not predictive of fungal community structure after three months, despite persistent differences between burned and non-burned fungal communities. This suggests that the early effects of fire reoriented fungal seasonal trajectories and caused longer term shifts in fungal communities. Furthermore, fire favored drought-tolerant and wood decomposing taxa at the expense of pathogenic fungi based on indicator species analysis. If changes to fungal communities correspond with broader changes in the ecological functions that regulate plant fuel loads, then fire regimes and entire ecosystems may be impacted. In summary, we demonstrated that fire drives similar changes to fungal communities across different pyrophilic ecosystems. Since disturbances like fire are expected to increase due to climate change, incorporating disturbance’s belowground impacts can improve our knowledge of the ecological processes that underpin terrestrial ecosystems.