The presence and structure of lichens under rocks

In the deserts, the environmental conditions are so extreme that life finds excellent allies in the rocks to get ahead. This is the case of the communities of microorganisms and lichens that inhabit the stony pavement of the Namib desert (Namibia), whose composition and spatial structure have recently been analyzed by an international research team in which researchers from the National Museum of Natural Sciences participate. (MNCN) and the Institute of Natural Resources and Agrobiology of Salamanca (IRNASA), both of the CSIC. Thanks to this work, they have been able to see how the microorganisms that are located under small quartz fragments of the stony pavement are organized (hypolithic colonization) and show for the first time the presence of lichens in these same habitats.

“For this work, we sampled in two areas of the Namibian desert, on the coast, where there are frequent morning coastal fogs, and in inland, more arid areas, to determine the differences that exist between the microbial communities located under quartz pebbles in both environments. The surprise was that in coastal areas, we detected lichens at the rock-soil interface”explains the MNCN researcher Asunción de los Ríos.

lichens

Lichens are organisms that arise from the symbiosis between a fungus and at least one photosynthetic component, an algae and/or a cyanobacteria (capable of photosynthesis). The organization and structure that this association acquires gives them protection against desiccation and high solar radiation, making them exceptionally resistant to different adverse environmental conditions and capable of forming part of ecosystems in extreme environments around the planet.

In the hypolithic lichens described in this work, the structure is modified with respect to those that grow on the rock. In hypolithic lichens, the algae need less protection from fungi because the quartz under which they hide protects them from ultraviolet radiation. Under the rock, in addition to being protected, the lichens can better retain the moisture that comes from the fog or dew, favoring their activity. In the Namib desert, many of the semitransparent quartz rocks of the pavement are colonized on the part that is in contact with the ground, forming a green patina under them.

“It was already known that, in the interior areas of the desert, these hypolithic communities were mostly dominated by cyanobacteria. With this work, one of the objectives was to assess whether this hypolithic colonization had a similar spatial organization and composition in coastal areas, where lichens colonize the rock surface, and in very arid areas in the interior of the desert. The data obtained has allowed us to confirm that there are many structural differences, especially due to the development of lichens under the stones in the coastal zone”exposes the MNCN researcher Asunción de los Ríos.

hypolithic colonization

“We have also shown that the hypolithic colonization of lichens is not an extension of the lichens that grow on the dorsal surface (epilithic), but that there are specific species that dominate each of the habitats”points out Isaac Garrido, also from the MNCN. “The composition of the bacteria present in the hypolytic communities of both locations also differs taxonomically and functionally”clarifies the IRNASA researcher, Ángel Valverde.

The description of this new habitat for lichens highlights the great adaptability of microorganisms and the importance of fog and dew in the colonization of desert areas. This increases the record of possible places to search for life forms in extreme terrestrial environments or even on other planets or satellites, since, if there is or was life on them, it is most likely that it was also hidden.

Font: MNCN CSIC

Reference article: https://www.mncn.csic.es/es/Comunicaci%C3%B3n/describen-por-primera-vez-la-presencia-y-estructura-de-liquenes-bajo-las-rocas