Contents
| AIR HYGIENE REPORT no. 10 | |
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Contents |
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3.1 General
Burton (1986) found that available information concerning fungi and air pollutants was sparse compared to lichens and bryophytes, was limited to plant pathogens and was based largely on short-term SO2 fumigation studies. This remains the situation, but since 1986 a few authors have discussed fungi as potential bioindicators of air pollution damage in forests (Fellner, 1989; Marx and Shafer, 1989).
Mycorrhizae (root symbioses) are responsive to effects of atmospheric deposition on forests and ectomycorrhizae in particular may be the first line of biological defense against stress for trees (Marx and Shafer, 1989). In their review of fungal and bacterial symbioses as potential biologic markers of effects of atmospheric deposition on forest health, Marx and Shafer (1989) concluded that the lack of standard techniques to assess these symbiotic associations and the paucity of base-line data on healthy forests limited their utility. References
Fellner (1989) and Fellner and Pešková (1995) proposed mycorrhiza-forming fungi as potential bioindicators of air pollution by indicating the disturbance of forest ectotrophic stability in the Czech Republic. The paper is brief but two myco-bioindication methods were proposed:
| Ecotrophic forest stability disturbance (degrees) | Ectomycorrhizal mycocoenoses impoverishment (phases) | Lignicolous mycocoenoses enrichment (phases) |
| Latent - The percentage of species of ectomycorrhizal fungi in the total count of macromycetes is decreasing to 40%, while the percentage of lignicolous species is tending to reach more than 30% | Inhibition of sporocarp production (accompanied with a decline of highly sensitive species, e.g., hydnaceous fungi) | Stimulation of sporocarp production |
| Acute - Ectomycorrhizal species contribute constantly less than 40% of the total number of macromycetes, while lignicolous species as a rule more than 40% | Reduction of species diversity (with a continuous inhibition of sporocarp production) | Increase of species diversity (with a continuous stimulation of sporocarp production) |
| Lethal - Ectomycorrhizal species contribute constantly less than 20%, while lignicolous species as a rule more than 55% of all macromycetes | Partial to total destruction of mycorrhizal mycocoenoses | Expansion of mycocoenoses |
In the Netherlands, Schaffers and Termorshuizen (1989) obtained strong negative correlations between the number of mycorrhizal fungal species on field stands of Pinus sylvestris L. and the occurrence of fruit bodies on these species with levels of NH3 and SO2. The authors were not aware if air pollution affected tree vitality which consequently altered the mycoflora or vice versa. If air pollution influences in the mycoflora modify tree vitality these associations could potentially be used as early indicators of air pollution impacts on tree vitality in forests.
The number of fungal endophytes isolated from birch leaves in Lapland decreased significantly in response to simulated acid rain treatments (Helander et al., 1993). Such sensitivity enhances the potential of these endophytes as bioindicators of air pollution.
An open chamber fumigation study in California used percentage frequencies and diversity indices to measure the effects of O3 and SO2 on leaf colonising fungi of three tree species (Fenn et al., 1989). Chronic exposure of the trees to either pollutant reduced the fungal populations and, to a lesser extent, reduced fungal diversity on the leaves.
Other studies concentrate on effects of air pollutants on host/pathogen combinations. These are generally impact assessments associated with economic crop and forest species rather than in the context of air pollution monitoring (Lorenzini et al., 1992; Wookey and Ineson, 1991; Khan and Kulshrestha, 1991; Tiedemann et al., 1991; Singh and Bharat, 1990). References
Dowding and Richardson (1990) demonstrated the suitability of leafyeasts for assessing air quality in both urban and rural areas of the non-Mediterranean countries of Europe. Leafyeasts are found on a wide variety of leaves in temperate regions and actively discharge spores at night. These properties enabled the development of a simple and effective methodology for collecting and isolating Sporobolomyces roseus, the most common leafyeast. Dowding (1994) detailed an extremely clear and concise description of a method designed for school children in a co-ordinated survey. Other advantages of using leafyeasts for air pollution monitoring are their sensitivity to SO2, their ability to provide a current assessment of air pollution and results can be obtained within one week. Furthermore, sampling work in Hamburg established quantitative relationships between leafyeast numbers and SO2 levels, where a regression line was derived between the natural logarithm of counts and mean SO2 concentration for the previous four days. Yeasts respond to SO2 levels in the range 0 to 100 µg m-3 (Dowding and Richardson, 1989). The disadvantages of the leafyeast method are its reliance on weather and seasonal conditions. Leafyeast growth is restricted to the time of year when deciduous trees are in leaf and show variations with time of year, which will vary with location and country. Sporulation is enhanced in wet conditions such that weather conditions on days immediately prior to collection affect numbers significantly. References
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