When a wildfire rages across a forest, the subsurface environment undergoes alterations as well. Many microorganisms die as a result of their actions. However, certain bacteria, like trees, have developed resistance to fire.
Certain fungi are classified as pyrophilous, which means “lovers of fire.” Fire-resistant fungus “appear out of nowhere, practically,” according to Tom Bruns, a mycologist at the University of California, Berkeley. This is true even in places that haven’t burnt in decades, according to Bruns. Some grow in flaming colours of orange and pink, while others are more muted. His research has shown that they are “a global phenomena,” but that “we don’t know much about them.”
Following a fire, a new research, published last month in the journal Frontiers in Microbiology, sought to determine the source of food that causes Pyronema, a genus of pyrophilous fungus, to develop in such large numbers so soon and in such large quantities. What they observed was that the damage caused by the fire itself may have provided an ideal environment for the fungus to grow. The recovery of the ecosystem, as well as the amount of carbon released into the atmosphere as a result of wildfires, might be affected as a result.
During a strong wildfire, a large amount of carbon in the top layer of soil is released into the atmosphere as carbon dioxide, but part of it remains in the soil as charcoal, which scientists refer to as pyrolyzed organic matter. The temperature drops somewhat as you go further into the soil, but it’s still high enough that any live microorganisms and insects erupted and perished, according to Monika Fischer, a postdoctoral fellow at the University of California, Berkeley who was the study’s principal author.
According to Dr. Fischer’s co-author, Thea Whitman, an associate professor of soil ecology at the University of Wisconsin-Madison and a member of the research team, charcoal is difficult for many species to decompose.
Pyronema samples gathered by Dr. Bruns’s team after the Rim fire in California in 2013 were used to grow the fungus, which allowed the researchers to determine if Pyronema can consume charcoal. The Pyronema subsisted mostly on charcoal, with three additional nutritional sources included for comparison. The fungus was then frozen in liquid nitrogen and shipped to a lab for RNA sequencing to complete the experiment.
As Dr. Fischer said, “If it’s attempting to consume the charcoal, we’d see a number of metabolic genes being switched on — which is exactly what we found.” There were also a large number of genes that were involved in breaking down the intricate ring structures that comprised charcoal.
Fungi are similar to humans in that they take in oxygen and emit carbon dioxide, the majority of which originates from the food they consume. The carbon-13-labeled emissions from the fungus, on the other hand, showed that it was indeed consuming charcoal.
Normal carbon dioxide was also detected coming out of the fungus, and it was significantly higher in concentration than the charcoal, indicating that it was consuming something other than charcoal, according to Dr. Whitman. This could have been the agar on which it was growing or carbon that had been introduced during inoculation.
Dr. Fischer provided the following explanation: “Pyronema is capable of consuming charcoal, but it does not like doing so.” According to the scientists, the fungus may first prefer the layer of dead creatures and then switch to charcoal when the situation calls for it.
According to Kathleen Treseder, an ecologist at the University of California, Irvine who was not involved in the work, “fungi are wonderful in degrading all types of chemicals.” This pyrolyzed substance makes sense, thus it seems reasonable that they would be able to break it down. Aditi Sengupta, a soil microbial ecologist at California Lutheran University who was not involved in the study, said that it would be beneficial to validate the results of the experiment outside of the lab and in the wild.
In the event that Pyronema is capable of decomposing charcoal after a fire, Dr. Fischer believes that this might open up a food supply for the next generation of bacteria and other organisms that are unable to digest charcoal, making Pyronema a key participant in post-fire recovery. And if Pyronema can accomplish it, she speculated, then maybe other fungus can as well.
“We want these types of actions to take place in the soil,” Dr. Sengupta said. While at the same time warning that “in the long run, this might result in our losing the carbon stored in the soil,” she said that Dr. Treseder explained that as a result of climate change and other human actions, wildfires are becoming more frequent and intense. “We need to understand whether carbon stored in the ground as charcoal will remain there, or if that’s not something we can really count on because the fungus can degrade it and release it as CO2,” he said.
