Journal Article

Surface Hydrophobicity Causes SO<sub>2</sub> Tolerance in Lichens

Markus Hauck, Sascha-René Jürgens, Martin Brinkmann and Stephan Herminghaus

in Annals of Botany

Published on behalf of The Annals of Botany Company

Volume 101, issue 4, pages 531-539
Published in print March 2008 | ISSN: 0305-7364
Published online December 2007 | e-ISSN: 1095-8290 | DOI: http://dx.doi.org/10.1093/aob/mcm306
Surface Hydrophobicity Causes SO2 Tolerance in Lichens

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  • Ecology and Conservation
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Background and Aims

The superhydrophobicity of the thallus surface in one of the most SO2-tolerant lichen species, Lecanora conizaeoides, suggests that surface hydrophobicity could be a general feature of lichen symbioses controlling their tolerance to SO2. The study described here tests this hypothesis.

Methods

Water droplets of the size of a raindrop were placed on the surface of air-dry thalli in 50 lichen species of known SO2 tolerance and contact angles were measured to quantify hydrophobicity.

Key Results

The wettability of lichen thalli ranges from strongly hydrophobic to strongly hydrophilic. SO2 tolerance of the studied lichen species increased with increasing hydrophobicity of the thallus surface. Extraction of extracellular lichen secondary metabolites with acetone reduced, but did not abolish the hydrophobicity of lichen thalli.

Conclusions

Surface hydrophobicity is the main factor controlling SO2 tolerance in lichens. It presumably originally evolved as an adaptation to wet habitats preventing the depression of net photosynthesis due to supersaturation of the thallus with water. Hydrophilicity of lichen thalli is an adaptation to dry or humid, but not directly rain-exposed habitats. The crucial role of surface hydrophobicity in SO2 also explains why many markedly SO2-tolerant species are additionally tolerant to other (chemically unrelated) toxic substances including heavy metals.

Keywords: Contact angle; hydrophilicity; hydrophobicity; lotus effect; cortex; sulphur dioxide; air pollution; water uptake; lichens

Journal Article.  5846 words.  Illustrated.

Subjects: Ecology and Conservation ; Evolutionary Biology ; Plant Sciences and Forestry

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