Saprotrophic Capabilities of Neurospora crassa on Charred Plant Biomass

Neurospora crassa is a popular model organism for laboratory research, yet its natural ecology remains mysterious. Its proliferation on charred plant biomass (wood and grasses) in fire-affected environments is often linked to the heat tolerance or heat-/chemical-induced germination of N. crassa spores; however, this link is not consistent across ecosystems or substrate types. Another possible, yet unvalidated, explanation is that N. crassa has an enhanced capacity for degrading charred (i.e., pyrolyzed) plant biomass. We assessed this adaptation for N. crassa by quantifying the decay of wood and grasses that were pyrolyzed to relevant extents (untreated, heated at 225°C or 350°C for 20 min) and by comparing this decay with non-fire-associated fungi. Neurospora crassa did not have an enhanced ability to degrade pyrolyzed substrates. Additionally, N. crassa struggled to degrade any wood substrate (< 6% mass loss) but did degrade untreated grasses (> 20% mass loss). These results, paired with chemical analyses of substrates pre- and post-decay, support a fire-response strategy for N. crassa, rather than a fire-adaptive ability to degrade charred substrates. This fungus likely proliferates on charred biomass by rapidly colonising heat-sterilised substrates after heat- or smoke-induced spore germination and then consuming unpyrolyzed lignocellulose beneath a charred exterior.