Wildfire impacts on soil microbes can cause long-lasting effects to ecosystem

Over the past decades, fire seasons are getting longer and extreme wildfires have become more frequent, more intense and larger.

Smoke from hundreds of wildfires burning out of control in Canada this month affected air quality in many U.S. states and even reached Western Europe. Last spring, two fires near Table Rock State Park and Caesars Head State Park in Upstate South Carolina burned more than 15,000 acres.

Fire leaves a dramatic and noticeable impact on the landscape — scorched trees, missing canopies and a forest floor devoid of plants and shrubs.

But it has underground impact as well.

“Within the context of fire ecology, we know a lot about plants and a lot about animals. We know a bit less about microbes,” said Antonino Malacrino, an assistant professor in the Clemson University Department of Biological Sciences. “Some studies show that if you have a severe wildfire, the soil microbiome is impacted. You can see the signature of that fire in the soil microbiome even after decades.”

But very little information is known about what happens after a fire to the microbial community in terms of diversity, composition and the ecological processes that drive the assembly of the microbial community.

Wildfires impact soil

A study by Malacrino and his colleagues analyzed the effect of fire on the ecological processes driving the structure and diversity of the microbial community in soil after a fire. They used an approach called meta-analysis, through which they re-analyze data from several studies and use it to answer broader questions.

Malacrino and the other researchers analyzed data from more than 2,600 soil samples from 19 previous studies of wildfires and found that bacteria and fungi are impacted differently. Clemson’s Palmetto 2, the University’s primary high performance computing resource, was pivotal in analyzing the large amount of data. Researchers found a decrease in diversity of fungal species. The diversity of bacteria may not change after a fire, but dominance of a few species increases.

“Instead of having a more even community, we have some taxa, some species that dominate it,” he said.

Both bacteria and fungi experienced decreases in dispersal.“If dispersal is constrained, the ecosystem might be slower in recovery,” he said.

Finally, the scientists analyzed the proportion of generalists and specialists there were in the community. They found an increase in specialist microbes for both bacteria and fungi. Generalists are able to thrive in a wide variety of environmental conditions while specialists can thrive only in a narrow range of environmental conditions.

“All these things together suggest that after a fire the soil microbial communities can become more homogeneous, which is not a good thing for the environment. If we have a very homogeneous community, we have lower ecological resilience and the ecosystem can take way longer to recover fully, if it is able,” Malacrino said.

Even if a fire doesn’t destroy all of the above ground community, it does disrupt the microbiome below ground and the interactions within it. That change actually increases the ability of some plant pathogens to cause a disease because the plants are weaker and the microbiome cannot fully protect them.

Since the plant community is severely impacted, new plants colonize the area. But they are small and grow quickly, increasing the likelihood of having additional wildfires in the future until the plant community is more stable.

Changes dynamics

“It changes all of the dynamics within the plant and animal communities and the cycling of nutrients, so everything is impacted. The entire functioning of the ecosystem is impacted,” Malacrino said. “Fire is a fundamental ecological process in many ecosystems. It becomes dangerous when it is too strong and is out of control. This is becoming more frequent because of global changes in temperatures and in weather patterns.” 

Detailed findings of the study can be found in the journal Global Change Biology in an article titled, “Fire limits soil microbial dispersal and differentially impacts bacterial and fungal communities.”

Malacrino said his lab, in collaboration with the Clemson Experimental Forest, will continue to study how fire impacts the function of the soil microbiome and what the consequences are for plant and ecosystem health.