Seasonal variation of airborne fungal diversity and community structure in urban outdoor environments in Tianjin, China

Abstract

Airborne fungi are ubiquitous in human living environments and may be a source of respiratory problems, allergies, and other health issues. A 12 months study was performed to investigate the diversity, concentration and community structure of culturable airborne fungi in different outdoor environments of Tianjin City, using an HAS-100B air sampler. A total of 1,015 fungal strains belonging to 175 species and 82 genera of Ascomycota 92.5%, Basidiomycota 7%, and Mucoromycota 0.3% were isolated and identified using morphological and molecular analysis. The most abundant fungal genera were Alternaria 35%, Cladosporium 18%, Penicillium 5.6%, Talaromyces 3.9%, Didymella 3%, and Aspergillus 2.8%, while the most frequently occurring species were A. alternata (24.7%), C. cladosporioides (11%), A. tenuissima (5.3%), P. oxalicum (4.53%), and T. funiculosus (2.66%). The fungal concentration ranged from 0 to 340 CFU/m³ during the whole study. Environmental factors, including temperature, relative humidity, wind speed, and air pressure exerted a varying effect on the presence and concentration of different fungal taxa. The four analyzed seasons showed significantly different airborne fungal communities, which were more strongly influenced by air temperature and relative humidity in spring and summer, whereas wind speed and air pressure had a stronger effect in autumn and winter. Fungal communities from green and busy sites did not show significant differences over the four analyzed seasons, which may be due to the effect of the surrounding environments characterized by high human activities on the air of the relatively small parks present in Tianjin. The present study provided valuable information on the seasonal dynamics and the environmental factors shaping the diversity and concentration of the analyzed outdoor airborne fungal communities, which can be of help for air quality monitoring, microbial contamination control, and health risk assessment in urban environments.

Keywords: airborne fungi; environmental factors; fungal diversity, concentration, and community structure; green and busy urban areas; outdoor environments; seasonal variation.

Figure 1

Schematic diagrams of Tianjin Municipality location in China, and distribution of Tianjin total and central districts. Detailed eight sampling locations and coordinates in NanKai, HeBei, HePing, and HeXi districts are marked in the diagram.

Figure 2

Krona Chart indicating the taxonomic identification and relative abundance of fungi isolated from Tianjin air.

Figure 3

Strains of the dominant fungal species isolated each month.

Figure 4

Venn Diagrams showing the diversity of fungal genera isolated at each district and site (green vs. busy).

Figure 5

Seasonal variation of airborne fungal concentrations at district level, in Tianjin.

Figure 6

Average colony concentration in different seasons, at city level (*p < 0.05 spring vs. summer, **p < 0.05 spring vs. winter).

Figure 7

Variances of fungal communities in four sampling seasons and effects of environmental factors on the airborne fungal diversity. (A) 3D PCoA plot of airborne fungal communities in four seasons based on Bray–Curtis distance (ANOSIM, p = 0.001, r = 0.5360). (B) Distance-based Redundancy Analysis of the fungal communities, with symbols coded by seasons. (C) Number of shared and unique fungal genera among four seasons. The numbers are indicated in the respective circles and bars. (D) Comparison of top-fifteen abundant fungal genera in four seasons. Differences in the genera abundance as evaluated by Kruskal-Wallis test. (E) Differences of top-fifteen abundant fungal genera between two seasons based on Post hoc Dunn’s test. In the sub-figures, T, RH, WS and AP refer to “temperature,” “relative humidity,” “wind speed” and “air pressure,” respectively. The value p is indicated as: *p < 0.05, **p < 0.01, ***p < 0.001.

Figure 8

Correlation Heat Map of the detected 82 fungal genera and four environmental factors (AP = Air Pressure, RH = Relative Humidity, T = Temperature and WS = Wind Speed). Different colors infer to Spearman’s correlation coefficients (r). The value p is indicated as: *p < 0.05, **p < 0.01, ***p < 0.001.

Figure 9

Fungal community composition in the air of green (G) and busy (B) sites from four seasons. The relative abundance of fungal genera <5% were merged as “others” in the bar plots. For each season, statistical differences between fungal communities in green and busy sites were indicated as p-values, which were derived from ANOSIM. The number of common and unique airborne fungal genera in green and busy sites of Tianjin was displayed in the Venn diagram.