Atmospheric transport and mixing of biological soil crust microorganisms

Biological soil crusts (BSCs) are created where a diverse array of microorganisms colonize the surface and upper few millimeters of the soil and create a consolidated crust. They were originally described from arid ecosystems where vascular vegetation is naturally sparse or absent. They have since been discovered in all terrestrial ecosystems. Where present, they perform a variety of important ecological functions, including the capture and accumulation of water and essential plant nutrients, and their release in forms useful to vascular plants. They also stabilize the soil surface against wind and water erosion. BSC organisms include fungi (free-living, lichenized, and mycorrhizal), archaea, bacteria (cyanobacteria and chemotrophic and diazotrophic bacteria), terrestrial algae (including diatoms), and bryophytes (mosses and worts). BSC organisms reproduce primarily asexually via thallus or main body fragmentation or production of asexual spores that are readily dispersed by water and wind. Asexual and sexual propagules of BSC organisms are commonly lifted into the air with vast quantities of dust from the world's arid areas. BSC organisms and/or their propagules have been detected as high as the stratosphere. Some have also been detected in the mesosphere. Airborne dust, microorganisms, and their propagules contribute to the formation of essential raindrop and snowflake nuclei that, in turn, facilitate precipitation events. While airborne in the atmosphere, they also reflect the sun's rays passing laterally through the troposphere and stratosphere at dawn and dusk, often causing brilliant colors at sunrise and sunset.