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Substantial amounts of primary biological aerosolized particles (PBAP) areemitted into the atmosphere each year. Cloud droplets are formed by the condensation of water vapor on nucleation sites such as aerosolized particles. Recent findings in atmospheric research indicate that PBAP may play an important role in climate by contributing to the formation of cloud and precipitation-sized droplets by acting as cloud condensation nuclei. This dissertation analyzes the hydration of commonly detected PBAP, fungal spores and pollen grains, inside an environmental scanning electron microscope (ESEM), in order to elucidate their potential role in atmospheric droplet formation. Experiments focus on determining the hygroscopicity, surface wettability, and droplet formation by particles with varying surface features. The ability of PBAP to act as cloud condensation nuclei depends on the morphological and chemical characteristics of the particle. For example, the size, shape, or presence of soluble materials, may impact the critical supersaturation at which these particles are able to condense water on their surfaces, in addition to the mechanics of droplet formation. Fungal spores examined in this study exhibit distinct variations in the chemical nature of the spore surface, owing to differences in dispersal modes (active or passive). The pollen grains examined exhibit morphologically diverse, and possess various surface architectures including a range of aperture types. Observations inside the ESEM indicate that certain distinguishing characteristics of pollen grains and fungal spores may enhance or hinder surface wettability and droplet formation. For example, actively dispersed basidiospores exhibited rapid growth and expansion of large droplets, likely due to the presence of hygroscopic sugars on their surfaces. Surface features of pollen grains, such as the presence of pores or furrows, dictated surface wettability and the internal uptake of water by pollen. These findings indicate that certain taxonomic groups may exhibit distinct properties that allow them to act as efficient nuclei for the condensation of water vapor in the atmosphere. This research has implications for the emission of biological particles in regions supporting large populations of actively dispersing fungi and plants, and heightens the importance of the sustainability of these types of ecosystems.

The bird’s nest fungi (Agaricales, Nidulariaceae) package a millions spores into sporangia (referred to as peridioles) that are splashed from their basidiomata by the impact of raindrops. Peridioles are splashed from flute-shaped basidiomata at speeds of 1 to 5 meters per second (11 mph). This study examines the mechanism of peridiole ejection and funicular cord function in Cyathus and Crucibulum using high-speed video. The funicular cord is a highly-extensible bundle of hyphae whose tensile strength is maximized by the modification of clamp connections. The funicular cord remains in a condensed form during flight with an adhesive pad exposed on the projectile surface. The cord unravels when the pad sticks to surrounding vegetation and acts as a brake that quickly reduces the velocity of the projectile. This elaborate mechanism tethers peridioles in a perfect location for browsing by an herbivore and is viewed as a beautiful adaptation for a coprophilous fungus.