Wildland fire smoke alters the composition, diversity, and potential atmospheric function of microbial life in the aerobiome

Abstract

The atmosphere contains a diverse reservoir of microbes but the sources and factors contributing to microbial aerosol variability are not well constrained. To advance understanding of microbial emissions in wildfire smoke, we used unmanned aircraft systems to analyze the aerosols above high-intensity forest fires in the western United States. Our results show that samples of the smoke contained ~four-fold higher concentrations of cells (1.02 ± 0.26 × 105 m−3) compared to background air, with 78% of microbes in smoke inferred to be viable. Fivefold higher taxon richness and ~threefold enrichment of ice nucleating particle concentrations in smoke implies that wildfires are an important source of diverse bacteria and fungi as well as meteorologically relevant aerosols. We estimate that such fires emit 3.71 × 1014 microbial cells ha−1 under typical wildfire conditions in western US forests and demonstrate that wildland biomass combustion has a large-scale influence on the local atmospheric microbial assemblages. Given the long-range transport of wildfire smoke emissions, these results expand the concept of a wildfire’s perimeter of biological impact and have implications to biogeography, gene flow, the dispersal of plant, animal, and human pathogens, and meteorology.

Bacterial Emission Factors: A Foundation for the Terrestrial-Atmospheric Modeling of Bacteria Aerosolized by Wildland Fires

“…Height above ground level ranged from 20 to 60 m during the Pile burns ( n = 3 flights), 45 to 160 m during the Knob burns ( n = 9), and 30 to 100 m during the Manning Creek burns ( n = 3). The duration of sampling lasted 5 min due to flight time restrictions, to maximize replicates, and in an attempt to maintain viability of cells deposited on filters . The characteristics of all bioaerosol sampling devices may impact results; however, the button sampler was chosen for its high collection efficiency for bacterial cells and its low sensitivity to surrounding winds such as those created by UAS rotors. , …”

“…While only viable microbes have the potential to colonize deposition environments, the transport of non-viable microbes is also relevant due to the persistence of allergenic properties for their aerosols, as well as the atmospheric implications of their activity as ice nucleation particles. 3,4,24,25 Finally, we demonstrate the utility of applying BEFs for the prediction of dispersal and deposition using a newly developed adaptive Langevin dynamics 26 model that is coupled with the fire behavior-atmosphere model WRF-SFIRE. 27 BEFs and their drivers, such as bacterial source concentrations and viability, fire behavior, and atmospheric conditions, will need to be investigated in different regions and fuel types to fully characterize wildland-fire-emitted microbes and the extent of any downwind repercussions.…”

“…Microorganisms are aerosolized and transported by winds and wind-generating atmospheric disturbances such as hurricanes and dust storms. , Recent research has revealed that wildland fires (i.e., wildfires and prescribed fires) are among the mechanisms that aerosolize microbes from terrestrial sources into the atmosphere; − however, little is known about the scale of these emissions or the distances over which they are transported. Biomass burning is responsible for the global emission of more than ∼2 Pg carbon each year, and viable microbes are a ubiquitous component of biomass fuels burned in wildland fires (i.e., vegetation and soils).…”

“…Biomass burning is responsible for the global emission of more than ∼2 Pg carbon each year, and viable microbes are a ubiquitous component of biomass fuels burned in wildland fires (i.e., vegetation and soils). Studies of both low- and high-intensity burns in US forests have shown that aerosolized concentrations of microbes in proximity to wildland fires (i.e., within 150 m) are 1–2 orders of magnitude higher than background concentrations. , The microbial assemblages associated with the smoke are dominated by bacteria and fungi, with the majority of cells inferred to be viable . This suggests that after aerosolization, species capable of surviving atmospheric transport could become established and potentially affect the environments (or hosts) in which they are deposited or inhaled.…”

Reimagine fire science for the anthropocene

“…Research is needed that targets the synergy of theoretical, experimental, and modeling approaches exploring the fundamental evolutionary processes of how organisms and communities function in dynamic and diverse fire environments. Fire allows researchers to investigate the fundamental and relative roles of traits and strategies across plant, animal, and microbial communities (27), and evaluate the influence of smoke on the function of airborne microbial communities (88), photosynthesis (89), and aquatic systems (90). A focus on fire has advanced evolutionary theory through the understanding of the evolution of plant traits and subsequent influence on the fire regime and selective environment, i.e.…”