Spring 2024


Charred tree trunks in a forest after a wildfire.
Photo courtesy of Thea Whitman


In Controlled Burn (Grow, fall 2018), Erik Ness introduced readers to the Charcoalator, a small furnace that sustains tiny fires under controlled conditions. Associate professor of soil science Thea Whitman and colleagues in her lab use the apparatus to expose organic matter to oxygen deprivation at 300–600 degrees Celsius and then see how these conditions influence soil microbes and the carbon cycle. The idea is to better understand what happens to carbon stores in the soil after wildfires strike.

Whitman and her team are also conducting these studies in the field. In a recently published paper, they examined soil bacterial communities at one and five years after a wildfire swept through a boreal forest in northern Canada. The research team focused on taxa (groups) of bacteria that, according to their laboratory studies, either survive fire, grow quickly postfire, or thrive in the post-fire environment.

The study, led by graduate student Dana Johnson MS’21, found that only a small number of bacterial taxa survived the fire. Many taxa detected in the first year were instead from the fast-growing groups, especially following severe fire. These bacteria likely take advantage of the low numbers of competing bacteria and feed on the plentiful carbon sources left behind, such as dead microbes and fine roots. However, these fast-growing taxa almost disappeared by the five-year increment. Taxa that thrive in the postfire environment took over after the first year, possibly because of their greater tolerance for fire-induced changes in soil properties, such as shifts in acidity or alkalinity or alterations in organic matter makeup.

The researchers also determined that the post-fire bacterial communities, although changed, could still readily feed on organic matter and release carbon dioxide into the air when respiring. So, shifts in soil bacteria post-fire did not hinder the microbiome’s ability to cycle carbon.

“Where, when, and how fires burn is changing,” says Whitman. “We need to understand how soil microbes are affected by fires, since they perform so many essential functions. They play important roles in nutrient cycling, which, in turn, affects which plants reestablish in the years following a fire. We’ve had a pretty good understanding of fire ecology for plants for decades. This study takes a strong step in the direction of establishing the importance of microbial responses to fires.”

This article was posted in Basic Science, Changing Climate, Follow-Up, Healthy Ecosystems, Spring 2024 and tagged , , , , , , , .