With megafires on the rise around the world, more than 24 million hectares have burned in Australia alone during the 2019-2020 bushfire season. In 2016, 534 square kilometers (53,400 hectares) of tanoak redwood forest burned in the Soberanos Megafire in California’s Big Sur region, including two sites that were already part of fire ecology studies. The biologists involved in this research saw an opportunity to investigate how communities of soil microbes respond to megafires.
So what exactly are microbes and how do they help?
A soil microbe is any microscopic organism that is present in the environment, including types of bacteria, fungi, protozoa (single-celled eukaryotic organisms), and nematodes (non-segmented roundworms). Together, they play a very important role in the cycling of micro and macro nutrients in soils, which are crucial for supporting plant and animal life. Fungi in particular have a strong symbiotic relationship with plants, with most plants relying on mycorrhizal fungal networks to make nitrogen more readily available. While we know that, in general, these microbial communities are crucial for restoring ecosystems after wildfires, what we don’t know is exactly how fires affect microbes.
“Plants are unlikely to be able to recover from megafires without beneficial fungi that supply nutrients to the roots, or bacteria that transform the additional carbon and nitrogen in the soil after the fire,” said lead author and UCR mycologist Dr. Sydney Glassman, a mycologist at the University of California and leader of the study. study. “Understanding microbes is key to any restoration effort.”
Taking soil samples from the two burned sites and one from an ecologically similar but unburned site, the team from the University of California (USA) and the University of Tokyo (Japan) set out to qualify and quantify the diversity of microbes before and after the fire. mega fire event, with a focus on bacteria and fungi in particular.
How did microbes respond to the megafire?
DNA was extracted from the soil, then fungal and bacterial samples were selected and amplified by PCR. The number of species was approximated using the amount of DNA measured in each group of microbes, called operating taxonomic units (OTUs), while species diversity was estimated by sequencing the DNA to see how many different taxonomic groups were present.
In the samples from burned areas, the number of species had decreased, where the OTU of fungi decreased by 70% and the OTU of bacteria by up to 52% in the burned areas compared to the unburned ones.
The composition of the community also changed dramatically after the megafire, where before the fire, the dominant fungi belonged to Basidiomycota (62%), Mucoromycota (25%) and Ascomycota (10%). After the megafire, Ascomyocota took over (65%), Basidiomycota fell 35%, and Mucoromycota was completely wiped out. Within the remaining species of Basiomycete, Basidioascus greatly increased yeasts, which have the ability to degrade wood components, including lignin within plant cell walls.
For bacteria, before the fire the communities were composed of Proteobacteria (84.4%) and Acidobacteria (15.6%) dominated. After the fire, Proteobacteria numbers were devastated, with Firmicutes becoming the favorite at 82%, while Acidobacteria slightly benefited (up 18%). Penicillium was one of the microbes that thrived, possibly taking advantage of the remains of fallen creatures, while some species can also eat charcoal.
The full set of their results can be found at molecular ecology.
“One of the reasons there is so little understanding of fungi is that there are very few mycologists studying them,” says Glassman, “but they really do have major impacts, especially after big fires that only increase in frequency and severity so much here. like all over the world.”