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 1,2. Conventional dogma that this is a neutral process involving ubiquitous distribution in air has been challenged by recent advances 3–5. However, the lack of standardized methods and analytical frameworks have impeded synthesis and global perspective. A key unresolved question is whether microorganisms assemble to form a taxonomically distinct, geographically variable and functionally adapted atmospheric microbiome. Here we characterized global-scale 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 processes. Fungi dominated above tropical, temperate and continental biomes whilst bacteria did so above oceans and drylands. At high altitudes bacterial diversity declined but fungal diversity was greatest. Source-tracking indicated a complex recruitment process involving local soils plus globally distributed inputs from drylands and the phyllosphere. Assemblages displayed stress-response and metabolic traits relevant to survival in air, and taxonomic and functional diversity were correlated with macroclimate and atmospheric variables. Our findings highlight a structured global atmospheric microbiome that is central to understanding regional and global ecosystem connectivity.