The thin hairiness surface plays an important role in Seirophora villosa performances

High salt concentrations in the environment lead to a decrease in hydric potential affecting water availability in poikilohydric organisms such as lichens, causing rapid dehydration, ionic imbalances and the inhibition of photosynthesis. Consequently, lichens have developed various morphological, structural and physiological mechanisms to respond and adapt to these stresses and thus acquire tolerance. In this study, our aim is to evaluate the role of a morphological trait as the thin hairiness on thallus surface adopted by Seirophora villosa, a Mediterranean epiphytic macrolichen, to withstand the effects of sea water by continuous exposure to marine aerosol. In the lab, we exposed thalli of S. villosa with and without microscopic hair to 0, 0.5, and 1 M NaCl. Thalli were repeatedly sprayed on the upper surface with each solution until fully hydrated and once dehydrated, sodium concentrations were determined by atomic absorption spectrophotometry. Therefore, we compared the photobiont susceptibility to treatments using chlorophyll fluorescence tools for detecting PSII damage and monitoring the rate of water loss for each thallus. The mycobiont susceptibility was detected using conductivity methods as (bio-)markers/indicators of membrane damage. Our results elucidated that the lichen’s surface/volume ratio is increased by the presence of highly branched laciniae covered by a thin hairiness that not only increases the absorption surface but can also keep out part of the salt depositions sprayed on the thallus surface. Furthermore, this structural form plays a main role slowing down thallus dehydration allowing prolonged period of photosynthetic activity also with low water content, during drought periods.