Passive water control at the surface of a superhydrophobic lichen
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Some lichens have a super-hydrophobic upper surface, which repels water drops, keeping the surface dry but probably preventing water uptake. Spore ejection requires water and is most efficient just after rainfall. This study was carried out to investigate how super-hydrophobic lichens manage water uptake and repellence at their fruiting bodies, or podetia. Drops of water were placed onto separate podetia of Cladonia chlorophaea and observed using optical microscopy and cryo-scanning-electron microscopy (cryo-SEM) techniques to determine the structure of podetia and to visualise their interaction with water droplets. SEM and optical microscopy studies revealed that the surface of the podetia was constructed in a three-level structural hierarchy. By cryo-SEM of water-glycerol droplets placed on the upper part of the podetium, pinning of the droplet to specific, hydrophilic spots (pycnidia/apothecia) was observed. The results suggest a mechanism for water uptake, which is highly sophisticated, using surface wettability to generate a passive response to different types of precipitation in a manner similar to the Namib Desert beetle. This mechanism is likely to be found in other organisms as it offers passive but selective water control.
KeywordsApothecium Cryo-SEM Lichens Soredium Super-hydrophobicity Water uptake
Scanning electron microscope
Cryogen, typically at liquid nitrogen temperature
Frames per second
The authors would like to thank H.J. Ensikat for technical assistance in SEM and performing of the cryo-preparation of the specimen, W. Barthlott for providing parts of the technical equipment for the studies performed at Bonn University (both Nees-Institut für Biodiversität der Pflanzen, Bonn University, Germany) and the EPSRC for funding NJS and CAEH under grants EP/E063489/1 and EP/H00704/1.
Conflict of interest
The authors declare that there are no conflicts of interest.
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