How do microbes return after a wildfire?

A recent study led by the University of California, Irvine has investigated how microbes re-establish their presence after the disturbance of a wildfire.

The researchers found that the re-establishment of microbial communities is strongly influenced by dispersal mechanisms.

Environmental shifts

Ecological upheavals, like wildfires, severely disrupt microbial communities. A deeper understanding of this can potentially allow researchers to predict how microbes might react to significant environmental shifts. 

The research, now published in mSystems, suggests that microbial succession post wildfires is predominantly driven by dispersal mechanisms like wind and rain.

Focus of the study

Over the last few decades, the frequency and extent of major ecological disturbances like wildfires have been increasing.

“We know with climate change and human activity we’re disturbing our ecosystems more and more,” said study lead author Kristin Barbour. “Microbes, especially those in the surface soil, perform a number of really key ecosystem processes, like carbon and nitrogen cycling.” 

Bacteria and fungi, she said, break down the dead and decaying plant matter on the floor of a field or forest. 

How the research was conducted 

Over a year, the researchers observed how bacterial and fungal communities resurfaced in the leaf litter of a burned field. 

The team noted that these communities underwent changes in accordance with seasonal shifts and the regrowth of plants. 

Surprisingly, air-driven dispersal was a major factor in the return of these microbial entities.

Wind, rain, and soil

A significant revelation of the study was that the majority of fungal species made their comeback primarily due to dispersal via wind or rain. 

Bacterial communities, however, were influenced by both airborne dispersal and the deeper layers of soil, known as bulk soil.

In the initial months after the wildfire, before any visible plant regrowth, the bacteria predominantly originated from the bulk soil. 

These findings indicate that there is an intricate relationship between surface and deeper soil layers in the recovery process post disturbances.

The Loma Ridge fire

Kristin Barbour, who is a PhD student at UC Irvine, initially aimed to study microbes in relation to droughts. But an unforeseen wildfire at Loma Ridge, close to Irvine, changed the focus of her research. 

Barbour saw the fire as an opportunity to investigate the repercussions of a phenomenon growing increasingly common due to climate change and human activities.

How the research was conducted 

The team studied two distinct ecosystems post-fire: a semi-arid grassland and a coastal sage scrub. 

Utilizing four unique configurations of dispersal bags, they sought to understand microbial movement. These bags were either porous, letting microbes move freely, or sealed, keeping microbes isolated. 

Some were filled with burned leaf litter, while others had glass slides to capture migrating microbes.

Microbial responses 

By analyzing these bags at five different intervals over a year, the researchers observed the microbial activity on the leaf litter. 

They discovered that microbial responses varied depending on the environment, challenging the ability to generalize the findings.

Recurring patterns 

However, the experts noted some recurring patterns. When it came to microbes entering the soil surface, 34% of the bacteria and 42% of the fungi were driven primarily by dispersal from the air.

The study also revealed that in the first few months after the fire, before plants had re-emerged, the soil beneath the leaf litter explained the largest share of immigrating bacteria. 

The study of how microbes move through the environment is an emerging area of research, said Barbour, but one that’s intimately connected to larger issues of how big disturbances change the environment. 

“There’s a lot of exciting work being done right now, looking at dispersal and at microbial communities out in the environment.”

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