Species traits and inertial deposition of fungal spores

One of the most common classes of bio-aerosols is fungal spores. While there is considerable species-specific variation in the morphological traits of fungal spores, their effect on spore dispersal is not well understood. Due to their super micron size, fungal spores deposit via inertial mechanisms. In this study, we combine experimental, theoretical, and statistical approaches to investigate the effects of spore morphology, airflow conditions, and surface structure on dry deposition of spores of forest-dwelling basidiomycete fungi. Firstly, we measured the spore aerodynamic diameter (Da) of 66 species and spore equivalent diameter (De) of 37 species. De combined with spore wall thickness was the best predictor of Da. We also derived a parameterization to calculate the spore density (ρspore); it ranged between 0.51 and 3.92 g/cm3 (mean 1.57 g/cm3). Assuming that spores are prolate-ellipsoids and using calculated values of De instead of the measured ones would under estimate ρspore. Secondly, we measured the inertial deposition of spores for 21 species in an experimental setup where spores were carried by turbulent airflow through a vertical pipe containing an obstacle (spruce twigs or a metal mesh). The deposition velocity on spruce twigs was 0.4–21 mm/s depending on the airflow velocity, spore size, and twig density. Evaluations of a three-layer deposition model suggested that the roughness length (F) of the twigs was 10–93 μm and it depended on the friction velocity. The deposition velocity of spores on the metal mesh was 24–53 times higher than that on the twigs. Spore shape did not have an unambiguous effect on Da or deposition on the mesh. Our study will facilitate the development of mechanistic dispersal models that incorporate the effect of species-specific spore traits as well as a physically realistic description of deposition to environmental surfaces.