Contribution of soil bacteria to the atmosphere across biomes.

The dispersion of microorganisms through the atmosphere is a continual and essential process that underpins biogeography and ecosystem development and function. Despite the ubiquity of atmospheric microorganisms globally, specific knowledge of the determinants of atmospheric microbial diversity at any given location remains unresolved. Here we describe bacterial diversity in the atmospheric boundary layer and underlying soil at twelve globally distributed locations encompassing all major biomes, and characterise the contribution of local and distant soils to the observed atmospheric community. Across biomes the diversity of bacteria in the atmosphere was negatively correlated with mean annual precipitation but positively correlated to mean annual temperature. We identified distinct non-randomly assembled atmosphere and soil communities from each location, and some broad trends persisted across biomes including the enrichment of desiccation and UV tolerant taxa in the atmospheric community. Source tracking revealed that local soils were more influential than distant soil sources in determining observed diversity in the atmosphere, with more emissive semi-arid and arid biomes contributing most to signatures from distant soil. Our findings highlight complexities in the atmospheric microbiota that are relevant to understanding regional and global ecosystem connectivity.

Effect of Sodium Dodecyl Benzene Sulfonate on the Production of Cloud Condensation Nuclei from Breaking Waves.

While sea spray particles are highly soluble by nature, and are thus excellent seeds for nascent cloud droplets, organic compounds such as surfactants have previously been identified within aerosol particles, bulk seawater, and the sea-surface microlayer in various oceans and seas. As the presence of dissolved surfactants within spray particles may limit their ability to act as cloud condensation nuclei (CCN), and since the abundance of CCN available during cloud formation is known to affect cloud albedo, the presence of surfactants in the marine environment can affect the local radiation balance. In this work, we added a model surfactant commonly used in households and industry (sodium dodecyl benzene sulfonate, SDBS) to a control solution of NaCl and observed its effects on the number of CCN produced by artificial breaking waves. We found that the addition of SDBS modified the number of CCN produced by a breaking wave analogue in three main ways: (I) by reducing the hygroscopicity of the resulting particulate; (II) by producing finer particulates than the control NaCl solution; and (III) by reducing the total number of particles produced overall. In addition, measurements of the absorption of ultraviolet light (λ = 224 nm) were used to quantify the concentration of SDBS in bulk water samples and aerosol extracts. We found that SDBS was significantly enriched in aerosol extracts relative to the bulk water even when the concentration of SDBS in the bulk water was below the limit of detection (LOD) of our quantitation methods. Thus, the surfactant studied will influence the production of CCN even when present in minute concentrations.