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Forest fires fire up the soil microbiota

Forest fire raging in the middle of the night amid a background of burning trees.

Forest fires adversely impact the soil environment

The year 2022 has seen hearing news of forest fires ravaging the US and Europe. On top of destroying homes and releasing excess carbon dioxide into the air, forest fires can have devastating impacts on soil. Severe forest fires increase the risk of soil erosion, reduce soil nutrient levels, and adversely impact watersheds. The recent fires have become such a concern in the States that the US federal government is set to direct almost $1 billion to reduce wildfire dangers.

Much more research on how forest fires impact the soil microbiota needs to be done. A single gram of soil can contain as many as 10 billion bacterial cells. The soil microbiota is also highly diverse. Variations in soil composition even within a foot of depth or width make it impossible to define a typical soil microbiome. Regardless of the soil microbiota composition, the bacteria dwelling in soil play important play important roles in cycling nutrients and elements essential for life on Earth to function.

The method for studying the impact of forest fires on the soil microbiome

As forest fires change a soil’s chemical composition and physical characteristics, it stands to reason that forest fires can also affect the types of bacteria living in the soil and how these bacteria behave. In an effort to start exploring this question, researchers from Colorado State University published a research paper on Nature Microbiology that assessed the impacts of forest fires on the soil microbiota.

To start exploring these impacts further, samples were obtained from lodgepole pine-dominated forests in Medicine Bow-Routt National Forest (Figure 1) burned by two different forest fires in 2018. For each soil sample, the researchers measured inorganic nitrogen levels, pH, and total dissolved organic carbon to assess soil chemistry. The researchers then conducted a comprehensive ‘omics pipeline by extracting nucleic acids for 16S rRNA sequencing, metagenomics assembly, and metatranscriptomics analyses. These efforts enabled the researchers to identify the bacterial species present in the soil samples and what they may have been doing at the time of sampling.

The key findings

Collecting soils at different depths enabled the researchers to show that forest fires had a greater impact on surface soil (0-5 cm depth) microbiomes than those dwelling in deep soil (>5 cm). These changes manifested themselves as reduced microbiome diversity among the surface soil microbiomes. There were three additional features regarding the reduced diversity that the authors noticed:

When checking for microbial chemistry through their metagenomics and metatranscriptomics data, the researchers also identified a series of metabolic changes that took place after a forest fire:


Topsoil plays a critical role in Earth’s biogeography. Representing the surface layer of soil, it provides the majority of organic matter for plant growth and human sustenance. Changes to this environment can have adverse impacts on agriculture and ecosystem function. The emergence of aromatic amino acids and Actinobacteria as the dominant taxon at the expense of other species may increase SOM stabilization and reduce its degradation. The results of this study point to substantial alterations of the surface soil that take place during a forest fire.


  • Paul Naphtali is the founder of GenoWrite, a life sciences communications company. He holds an MSc in Biology and went through the PhD program in Biochemistry and Biomedical Sciences, both at McMaster University. Before GenoWrite, he created Microbe Musings out of a passion for communicating microbiology research to diverse audiences around the globe and from all walks of life.

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