From Ashes to Insights: Mycorrhizal Fungi Functions in Post-Fire Landscapes

Communities in fire-affected ecosystems possess unique traits that aid survival and ecosystem recovery post-fire. As fires increase in frequency and intensity due to climate change, we enter a time increasingly influenced by fire therefore understanding the functions of these communities in forested systems is essential. While previous work has been done on the presence or absence of mycorrhizal fungi post-fire, generally using DNA-based approaches, there is limited knowledge about the functions they serve. This work aimed to identify functional traits of mycorrhizal fungi that correlate with fire regime and vegetative composition.

Thirty dry sclerophyll forest sites surrounding the Sydney basin that burned in the 2019-2020 black summer fires of Australia were selected based on historical gradients in fire severity and interval. Vegetative composition, fungal communities as well as soil carbon and nutrient availability were analysed from each site, from these, a subset of sites were selected for further study to distinguish direct (via effects on fire regimes) and indirect (via effects on nutrient availability) on mycorrhizal fungal functional traits associated with biomass production, hyphal chemistry (carbon, nitrogen, and phosphorus concentrations). For this, we harvested mycorrhizal fungal biomass using mesh in-growth bags filled with plastic resin-beads that absorb mineralized nutrients.

Available nutrients influenced mycorrhizal fungal community structure and biomass production in material collected from in-growth bags, whereas fire regime and vegetative structure had no effect. Hyphal chemistry was not significantly associated with nutrient availability, vegetative structure, or fire regime. In contrast, soil-derived data revealed significant effects of fire frequency on community structure, but no influence of nutrient availability or vegetative structure.

By integrating responses related to functional traits, fungal community composition, vegetation structure, and environmental factors, we aim to understand not only the functions that individual fungi provide in forested systems but also how these communities function collectively. We highlight the contrasting effects of fire frequency and nutrient availability on mycorrhizal communities in soil compared to those collected with mesh in-growth bags. These differences in community structure across sites likely reflect fungal growth strategies and their sensitivity to nutrient availability.