How dormant soil microbes survive in a 60-year-old fire

Microscopic organisms living in soil, called microbes, are essential for a healthy planet. They help plants grow and decompose organic matter, keeping ecosystems functioning smoothly. But what happens to these vital soil microbes when human actions disrupt the environment?

Researchers at Michigan State University (MSU) are finding answers in a most unexpected place: a 60-year-old underground coal mine fire in Centralia, Pennsylvania. This “press disturbance,” as scientists call it, has been continuously burning since 1962, heating the soil above as it spreads.

The research uncovered a remarkable survival tactic used by the dormant soil microbes. The microbes essentially put their life processes on hold, allowing them to endure harsh conditions.

Diversity of soil microbes

“If you look in a gram of soil, you have tens of thousands of different bacterial species. Soil is the most diverse microbiome that we know, more diverse even than the human gut,” said Ashley Shade, an associate professor in the MSU Department of Plant, Soil and Microbial Sciences.

For seven years, Professor Shade and her colleague, Samuel Barnett, a postdoctoral scholar at the lab, analyzed soil dynamics over time in Centralia. Their annual expeditions involved collecting soil samples from fire-affected areas to understand how microbial communities adapt to the heat altering their habitat.

“We go out every October, and we take soil cores,” said Dr. Barnett. “We have a big PVC pipe that we sterilize and drive into the soil and pull out about 20 centimeters or 8 inches of soil. Then we sieve the soil to get rid of roots and rocks and the stuff we don’t want and then freeze it in liquid nitrogen and bring it to the lab.”

Active and dormant soil microbes

There are two main states of soil microbes: active and dormant. Active microbes are busybodies. They’re constantly growing, multiplying, and doing their jobs in the environment. This includes cleaning up waste, breaking down dead things, and making sure everything runs smoothly.

Dormant microbes, on the other hand, have slowed down their activity to almost a standstill. They’re not growing or reproducing, but they’re not dead either. Dormancy is basically a survival tactic that lets these microbes wait until things get better.

The experts observed a surprising change in the balance between active and dormant soil microbes in the burned areas. A large number of microbes in the soil existed in a low-activity state. These microbes survive the harsh conditions by becoming dormant.

When the environment becomes favorable again, the dormant microbes can become active and contribute to soil. The ability to switch between active and dormant states is essential for the soil to recover from the fire damages.

Critical role of dormant bacteria

This study emphasizes the critical role dormant bacteria play in the soil’s resilience. This resilience, built on both active and dormant populations, demonstrates the complex way microbial communities respond to the environment.

“Many people don’t realize that an incredible number of soil microbes are simply not active and functioning at any given time,” noted Professor Shade.

Soil microbes and climate change

Interestingly, the researchers noted a steady decrease in soil temperature within the burned areas over the seven years studied.

Even though the initial heat from the fire subsided over time, the fire’s impact on the soil’s chemistry remained. This was evident through ongoing carbon dioxide release (CO2 venting) and changes in the soil’s acidity (pH levels).

The research shows that dormant soil microbes are actively involved in keeping the environment stable and helping it recover from disruptions. They have surprising abilities to adapt to harsh conditions. Understanding how these microbial communities function is crucial as our planet faces increasing challenges from climate change.

Study significance

Centralia’s story showcases how life endures even in harsh conditions. This knowledge not only improves our understanding of microbes, but also offers possibilities for repairing environments damaged by human actions.

“If we can understand what wakes up the dormant microbes, we can try to manage the microbiome, for example, to wake up when we need it to wake up, to go to sleep potentially when we need it to go to sleep,” said Professor Shade.

As we face climate change and environmental destruction, the microbes of Centralia teach us about nature’s inherent ability to recover. By understanding and utilizing this resilience, we can work towards a better future for our planet.

The study is published in the journal Ecology Letters.

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