Airborne Bacteria Are Influenced by Surrounding Soil, Litter and Vegetation at a Forest Campsite.

Contact with natural environments is increasingly linked to human well-being, yet the environmental sources shaping forest airborne microbiota remain poorly resolved. Here, we examined the relationship between the forest aerobiome and nearby ground reservoirs, focusing on litter and surface soil in a recreational forest. Bacterial communities were compared among air, litter and soil at a campsite spanning two vegetation types: a secondary broadleaf forest with diverse understory and a conifer plantation with sparse understory. Air was continuously sampled for 1 week using membrane filtration, and litter and surface soil were collected adjacent to each air sampler. We identified 6146 amplicon sequence variants across 19 phyla. Habitat (air, litter, soil) was the primary driver of community composition. Airborne communities were significantly distinct from both litter and soil and showed lower diversity. Although dominant higher taxa were shared across habitats, airborne assemblages were compositionally distinct at the genus and amplicon sequence variant levels, whereas litter and soil were more similar to each other. Nonetheless, substantial genus-level overlap between air and ground habitats was detected in both vegetation types. These findings indicate that litter and soil act as important, but incomplete, environmental reservoirs of forest airborne bacteria in recreational settings.