Diverse recruitment to a globally structured atmospheric microbiome

Abstract

Atmospheric transport is critical to dispersal of microorganisms between habitats and this underpins resilience in terrestrial and marine ecosystems globally. A key unresolved question is whether microorganisms assemble to form a taxonomically distinct, geographically variable, and functionally adapted atmospheric microbiome. Here we characterised globalscale patterns of microbial taxonomic and functional diversity in air within and above the atmospheric boundary layer and in underlying soils. Bacterial and fungal assemblages in air were taxonomically structured and deviated significantly from purely stochastic assembly. Patterns differed with location and reflected underlying surface cover and environmental filtering. Source-tracking indicated a complex recruitment process involving local soils plus globally distributed inputs from drylands and the phyllosphere. Assemblages displayed stressresponse and metabolic traits relevant to survival in air, and taxonomic and functional diversity were correlated with macroclimate and atmospheric variables. Our findings highlight complexity in the atmospheric microbiome that is key to understanding regional and global ecosystem connectivity.

Scientific novelty beyond the experiment

“…An earlier breakthrough with this work was made when Carslaw et al ( 1994 , 1995 ) extended the model by nitric acid; they were then able to predict a new type of polar stratospheric clouds which turned out to be important and relevant as shown by subsequent field observations and laboratory experiments. Whereas Clegg et al ( 1998 ) was not a study of microbiology, it is pertinent to determinations of habitability for planetary atmospheres given that active microbial metabolism, growth, and ecology occur in Earth's atmosphere (Archer et al, 2021 ; Hallsworth, Koop, et al, 2021 ).…”

Water is a preservative of microbes

“…Nevertheless, the findings highlighted here indicate that the effective concentration of vapour‐phase water molecules (relative humidity) can be critical to ensure survival under some circumstances. This can be critically important for microbes that inhabit surfaces (including those within soils and soil crusts; Lebre et al ., 2017) and microbes present in the atmosphere, whether attached to particles, within aerosols, or ‘free’ (Archer et al ., 2021). Such habitats are frequently dynamic; for example, there is an equilibrium between the vapour phase and condensed water.…”