High-severity wildfire reduces richness and alters composition of ectomycorrhizal fungi in low-severity adapted ponderosa pine forests

Ponderosa pine (Pinus ponderosa) forests are increasingly experiencing high-severity, stand-replacing fires. Whereas alterations to aboveground ecosystems have been extensively studied, little is known about soil fungal responses in fire-adapted ecosystems. We implement a chronosequence of four different fires that varied in time since fire, 2 years (2015) to 11 years (2006) and contained stands of high severity burned P. ponderosa in eastern Washington and compared their soil fungal communities to adjacent unburned plots. Using Illumina Miseq (ITS1), we examined changes in soil nutrients, drivers of species richness for ectomycorrhizal (plant symbionts) and saprobic (decomposers) fungi, community shifts, and post-fire fungal succession in burned and unburned plots. Ectomycorrhizal richness was 43.4% and sapmbic richness 12.2% lower in the burned plots, leading to long-term alterations to the fungal communities that did not return to unburned levels, even after 11 years. Differences in the post-fire fungal community were driven by pyrophilous, fire-loving fungi, including the ectomycorrhizal Ascomycete genera Pustularia and Wilcoxina, and the saprobic Basidiomycete genus Geminibasidium. Ectomycorrhizal and sapmbic fungi were intimately linked to the soil environment: depth of the organic matter, total carbon, total nitrogen, and their interaction with fire predicted ectomycorrhizal richness. Whereas total carbon, time since fire, treatment, and the interaction between time since fire and treatment predicted saprobic richness. We conclude that high-severity wildfires lead to lower ectomycorrhizal richness and significantly altered ectomycorrhizal and saprobic communities in fire-adapted ecosystems, selecting resilient and fire-adapted species, such as W. rehmii and Geminibasidium sp., thus initiating post-fire succession.

Automated summary

The study revealed that high-severity wildfires led to lower ectomycorrhizal and saprobic fungal richness, significantly altering fungal communities in fire-adapted ecosystems by selecting resilient species and initiating post-fire succession. Fire-driven changes in soil environment influenced fungal richness and community composition, indicating long-term impacts of wildfires on soil fungal dynamics.