Sources and traits of bacteria and fungi found in the near-surface atmosphere

Fungi and bacteria are ubiquitous in the near-surface atmosphere, and these airborne microbes can have important impacts on ecosystem and human health. Previous work has established that plant leaves and soils are the most likely sources of airborne microbes in natural, inland systems. Yet, the relative importance of these sources on the amounts and types of airborne microbes remain poorly quantified. Furthermore, not all microbes found in a source environment are equivalent in their ability to be aerosolized and persist in the near-surface atmosphere, but the specific traits associated with the capacity for aerial transport remain uncertain. To address these knowledge gaps, we collected 110 bioaerosol samples from the near-surface atmosphere in ~1 ha open savanna-like habitat fragments, and surrounding plantation forest in South Carolina, USA. We also collected samples from local leaves and soils to quantify potential bioaerosol sources. Despite the pronounced vegetation differences, the concentrations and composition of the airborne microbial assemblages in the distinct vegetation types did not differ, most likely due to substantial air mixing at this spatial scale. Foliar surfaces were more important sources of fungi and bacteria to the near-surface atmosphere than soils over the course of this study. Compared with foliar surfaces, bioaerosols were enriched in spore-forming bacteria and fungal taxa that produce fruiting bodies and smaller spores. Our work highlights that bioaerosols in the near-surface atmosphere are relatively unaffected by land-use change at small scales, and we can identify microbial traits that are important determinants of atmospheric dispersal.IMPORTANCEEach year, an estimated 10²³ fungal spores and 10²⁴ bacterial cells enter the atmosphere from terrestrial sources. These airborne microorganisms have important effects on human health and ecosystem processes, with atmospheric transport serving as a key mode of dispersal that shapes microbial distributions. We paired analyses of microorganisms in bioaerosols and local sources to address important outstanding questions about the spatial variation, sources, and traits of airborne microorganisms. We establish that the largest local sources of airborne microbes in our system are leaf surfaces, yet not all leaf-associated bacterial and fungal taxa are equally capable of dispersal through the atmosphere. Furthermore, we identified specific bacterial and fungal traits that facilitate microbial aerosolization and persistence in the atmosphere, building toward a more mechanistic understanding of microbial aerial dispersal.