Learn about forest microbes that can survive big fires

A new study from UC Riverside shows that fungi and bacteria that can survive large fires in the Tanoac redwood forest are "cousins" of microbes that often multiply when they sense a flame.

Fires of unprecedented size and intensity, known as mega-fires, are becoming more common. In the west, climate change is causing temperatures to rise and snow to melt earlier, extending the dry season when forests are most vulnerable to fires.

Although some ecosystems have adapted to less intense fires, little is known about how plants or the associated soil microbiome respond to large fires, especially in California's charismatic redwood forests.

"Plants are unlikely to recover from a major fire without beneficial fungi to provide nutrients to the roots or bacteria to dump extra carbon and nitrogen into the soil after a fire," said Sidney Glassman, UCR mycologist and lead author of the study. "Understanding the microbes is key to any recovery effort."

The UCR team contributed to this understanding with an article in Molecular Ecology.

In addition to examining the effects of mega-fires on microbes in the Tanoac redwood forest, the study is unusual for other reasons. Soil samples were collected from the same plot in Monterey County before and immediately after the 2016 Soberanes fires.

"To get data like this, researchers have to burn the properties themselves. It's complicated to predict exactly where a burn will occur," Glassman said.

The team was not surprised to see that the fires at Sobernes had a significant impact on bacterial and fungal communities, with a 70% reduction in microbial species. However, they were surprised that some yeast and bacteria not only survived the fire but also reproduced.

The growing bacteria include actinobacteria, responsible for breaking down plant matter. The team also found an increase in Firmicutes, which are known to promote plant growth, control plant pathogens, and scavenge heavy metals from the soil.

In the fungi category, the team found a significant increase in heat-resistant Basidioascus yeast, which can break down various components in wood, including lignin, the healthy part of plant cell walls that gives them structure and protects them from insect attack.