Pyrolyzed substrates induce aromatic compound metabolism in the post-fire fungus,Pyronema domesticum

Abstract

Wildfires represent a fundamental and profound disturbance in many ecosystems, and their frequency and severity are increasing in many regions of the world. Fire affects soil by removing carbon in the form of CO2 and transforming remaining surface carbon into pyrolyzed organic material (PyOM). Fires also generate substantial necromass at depths where the heat kills soil organisms but does not catalyze the formation of PyOM. Pyronema species strongly dominate soil fungal communities within weeks to months after fire. However, the carbon pool (i.e. necromass or PyOM) that fuels their rise in abundance is unknown. We used a Pyronema domesticum isolate from the catastrophic 2013 Rim Fire (CA, USA) to ask if P. domesticum is capable of metabolizing PyOM. P. domesticum grew readily on agar media where the sole carbon source was PyOM (specifically, pine wood PyOM produced at 750 °C). Using RNAseq, we investigated the response of P. domesticum to PyOM and observed a comprehensive induction of genes involved in the metabolism and mineralization of aromatic compounds, typical of those found in PyOM. Lastly, we used 13C-labeled 750 °C PyOM to demonstrate that P. domesticum is capable of mineralizing PyOM to CO2. Collectively, our results indicate a robust potential for P. domesticum to liberate carbon from PyOM in post-fire ecosystems and return it to the bioavailable carbon pool.

Mega‐fire in redwood tanoak forest reduces bacterial and fungal richness and selects for pyrophilous taxa that are phylogenetically conserved

“…The Pyronemataceae produce sporocarps that are small orange cup fungi that appear on pyrolysed material after burning (El-Abyad & Webster, 1968). This repeated observation of fruiting on burned material suggests some capacity for using unique compounds produced through combustion, a post-fire nutrient acquisition trait as outlined in Figure 7, and was recently explored in a study on Pyronema domesticum charcoal metabolysis (Fischer et al, 2021). It is also possible that their colour or morphology makes them better adapted to post-fire scenarios; for example, many of them are orange and contain carotenoids (Carlile & Friend, 1956) which may add UV protection (Luque et al, 2012).…”

“…For example, Aspergillus and Penicillium species are also probably thermotolerant (Warcup & Baker, 1963), and some Penicillium species have been found to degrade polycyclic aromatic hydrocarbons (PAHs), such as those produced through combustion (Leitão, 2009). Another fungal example could be Pyronema , which in addition to thermotolerance may be utilize the resource acquisition strategy given the recent study on its ability to metabolize charcoal (Fischer et al, 2021) and thus fall along a gradient from thermotolerance to post‐fire resource‐acquisitive. Similarly, the yeast Basidioascus tolerates stress with its xero‐ and thermotolerance but as a yeast may also be a fast‐colonizer since it is unicellular.…”

Fire as a driver of fungal diversity — A synthesis of current knowledge

“…Some wood-inhabiting fungi reportedly have heat-resistant mycelia which can favor them in fire-prone or post-fire environments (Carlsson et al 2012). The heat pulse can also change the nutrient and substrate environment (Certini 2005) and produce necromass that may serve as a substrate for a number of specialized saprobes, such as Pyronema domesticum that metabolize PyOM (Fischer et al 2021). Clearly, there is a need to distinguish between the taxa that use pyrogenic materials and opportunists that exploit resources made available by the death of others.…”

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

“…The rapid and efficient germination of Aspergillus (in the subgenus Fumigati , including A. udagawae ) induced by high temperatures (Rhodes, 2006) and its ability to use various carbon and nitrogen sources, including ammonium and nitrate (Krappmann & Braus, 2005), may position Aspergillus to rapidly dominate after chaparral fires. Furthermore, Pyronema domesticum , a relatively well-studied pyrophilous fungus, can mineralize pyrogenic organic matter, a dominant substrate in burned environments (Fischer et al, 2021), thus potentially allowing it to take advantage of the abundant food source in this system. Finally, Geminibasidum, a recently described thermotolerant Basidiomycete yeast (H. D. T. Nguyen et al, 2013), dominated 45% of our sequences at 17 days post-fire.…”