Temporal-spatial variations of fungal composition in PM2.5 and source tracking of airborne fungi in mountainous and urban regions.

Fungi are ubiquitous in air and their composition is potentially important for human health. Exposure to fungal allergens has been considered as a significant risk factor due to the prevalence and severity of asthma in humans. However, temporal-spatial variations and potential sources of airborne fungi aerosol have been poorly understood. In this study, 48 PM2.5 samples were collected at two sampling sites in Xi'an from April 2018 to January 2019. High-throughput sequencing technology was used to determine the diversity and abundance of fungal composition in all samples. Microbial samples were also collected from leaf-surface and soil to identify the potential sources of fungal aerosols. Results showed that the species richness of fungi in summer and autumn inclined to be higher than that in spring and winter in mountainous and urban regions. Airborne fungal species richness and diversity at Mt. Qinling sampling site were significantly higher compared to Yanta urban sampling site, except in winter. These variations in fungal composition were significantly related to season and location. The influence of atmospheric pollutants (PM2.5, ozone, sulfur dioxide and carbon monoxide) on the richness and diversity of airborne fungal composition was higher than meteorological factors (temperature, relative humidity and wind speed). Moreover, it was observed that the leaf-surface was the primary local source of airborne fungi during all seasons at both sampling sites. Back trajectories arriving at both sampling sites showed that a considerable part of airborne fungi might have come from other regions by medium or long-range airflow. This study will provide an important reference for studying the source and temporal-spatial variations of fungal aerosols and further provide basic background data for human health exposure assessment.