Evidence for Wildland Fire Smoke Transport of Microbes from Terrestrial Sources to the Atmosphere and Back

Smoke from wildland fires contains viable microbes and cell concentrations higher than typical ambient air, yet little is known about the sources and sinks of smoke-borne microorganisms. Data from molecular-based surveys suggest smoke-borne microorganisms originate from material associated with the vegetation and underlying soils that becomes aerosolized during combustion, however, the sources of microbes in smoke have not yet been experimentally assessed. To elucidate this link, we studied high-intensity forest fires in the Fishlake National Forest, Utah, USA and applied source-sink modeling to assemblages of 16S rRNA gene sequences recovered from samples of smoke, vegetation, and soil. Our results imply that 70% of the bacteria in smoke originated from the local aspen (Populus tremuloides)(33%) and soil (37%) communities. In comparison, 42% of bacteria in air sampled prior to the fires could be attributed to these terrestrial sources. When the bacterial assemblages in smoke were modeled as sources to the local communities, they contributed an average of 25% to the terrestrial sinks versus an estimated contribution of <4% from ambient air. Our results provide support for the role of wildland fire in bacterial dispersal and the working hypothesis that smoke is an environmental reservoir of microbial inocula for receiving ecosystems.