Identifying Functional Impacts of Heat-Resistant Fungi on Boreal Forest Recovery After Wildfire

Abstract

Fungi play key roles in carbon (C) dynamics of ecosystems: saprotrophs decompose organic material and return C in the nutrient cycle, and mycorrhizal species support plants that accumulate C through photosynthesis. The identities and functions of extremophile fungi present after fire can influence C dynamics, particularly because plant-fungal relationships are often species-specific. However, little is known about the function and distribution of fungi that survive fires. We aim to assess the distribution of heat-resistant soil fungi across burned stands of boreal forest in the Northwest Territories, Canada, and understand their functions in relation to decomposition and tree seedling growth. We cultured and identified fungi from heat-treated soils and linked sequences from known taxa with high throughput sequencing fungal data (Illumina MiSeq, ITS1) from soils collected in 47 plots. We assessed functions under controlled conditions by inoculating litter and seedlings with heat-resistant fungi to assess decomposition and effects on seedling growth, respectively, for black spruce (Picea mariana), birch (Betula papyrifera), and jack pine (Pinus banksiana). We also measured litter decomposition rates and seedling densities in the field without inoculation. We isolated seven taxa of heat-resistant fungi and found their relative abundances were not associated with environmental or fire characteristics. Under controlled conditions, Fayodia gracilipes and Penicillium arenicola decomposed birch, but no taxa decomposed black spruce litter significantly more than the control treatment. Seedlings showed reduced biomass and/or mortality when inoculated with at least one of the fungal taxa. Penicillium turbatum reduced growth and/or caused mortality of all three species of seedlings. In the field, birch litter decomposed faster in stands with greater pre-fire proportion of black spruce, while black spruce litter decomposed faster in stands experiencing longer fire-free intervals. Densities of seedlings that had germinated since fire were positively associated with ectomycorrhizal richness while there were fewer conifer seedlings with greater Day et al.Functions of Post-Fire Fungi heat-resistant fungal abundance. Overall, our study suggests that extremophile fungi present after fires have multiple functions and may have unexpected negative effects on forest functioning and regeneration. In particular, heat-resistant fungi after fires may promote shifts away from conifer dominance that are observed in these boreal forests.

Material Legacies and Environmental Constraints Underlie Fire Resilience of a Dominant Boreal Forest Type

“…Fluctuating populations of seed or seedling consumers will add stochasticity to observed recruitment patterns (Zwolak and others 2012 ; Olnes and Kielland 2017 ). Overall, more experimental studies are needed to understand the role of biotic interactions on seedling recruitment and post-fire plant composition, including differential responses of tree species to mutualists or pathogens (for example, Day and others 2020 ). At the very least, our study provides evidence of granivory/herbivory as a species-specific biological hurdle that requires additional seed inputs to overcome for successful seedling recruitment.…”

“…There was 100% mortality of trees at most plots, making it easy to determine seedlings that had germinated after fire. Some individuals of aspen likely resprouted from rhizomes/suckers, although the majority were from seed (Day and others 2020 ). We measured variables indicative of seedbed conditions.…”

Rapid bacterial and fungal successional dynamics in first year after chaparral wildfire

“…This evidence suggests that pyrophilous microbes in systems that have evolved with wildfire (Dove et al, 2021) might have fire adaptations analogous to plants (Rundel, 2018) and, thus, probably follow successional dynamics akin to plants. Pyrophilous microbes have traits that allow them to survive fires (e.g., heat resistant spores, sclerotia; Day et al, 2020; Petersen, 1970) and the post‐fire environment (e.g., xerotolerance, affinity for nitrogen mineralization, and affinity for aromatic hydrocarbon degradation; Fischer et al, 2021; Nelson et al, 2022; Steindorff et al, 2021). Moreover, since heat from fire often penetrates only the top few cm of soil (Neary et al, 1999; Pingree & Kobziar, 2019), like plants, secondary succession may be initiated by surviving microbes that make up the spore bank (Baar et al, 1999; Glassman et al, 2016).…”

Rapid bacterial and fungal successional dynamics in first year after Chaparral wildfire

“…Together, evidence suggests that pyrophilous microbes likely evolved under the same fire regime as the ecosystems they inhabit (Dove et al, 2021) and likely have fire adaptations analogous to plants (Rundel, 2018). Pyrophilous microbes have traits that allow for the survival to fire (i.e., heat resistant spores, sclerotia) (Day et al, 2020;Petersen, 1970) and the post-fire environment (i.e., xerotolerance, decomposition of nitrogen and aromatic hydrocarbons) (Fischer et al, 2021;Nelson et al, 2021;Steindorff et al, 2021). However, most research is based on single time-point sampling (Dove & Hart, 2017;Pressler et al, 2019); thus, the successional trajectory of pyrophilous microbes is nearly unknown.…”

“…This evidence suggests that pyrophilous microbes in systems that have evolved with wildfire (Dove et al, 2021) might have fire adaptations analogous to plants (Rundel, 2018) and, thus, likely follow successional dynamics akin to plants. Pyrophilous microbes have traits that allow them to survive fires (e.g., heat resistant spores, sclerotia) (Day et al, 2020;Petersen, 1970) and the post-fire environment (e.g., xerotolerance, affinity for nitrogen mineralization, and affinity for aromatic hydrocarbon degradation) (Fischer et al, 2021;Nelson et al, 2022;Steindorff et al, 2021). Moreover, since heat from fire often penetrates only the top few cm of soil (Neary et al, 1999;Pingree & Kobziar, 2019), like plants, secondary succession may be initiated by surviving microbes that make up the spore bank (Baar et al, 1999;Glassman et al, 2016).…”