The ancient rock paintings in Mount Mahia are in danger from lichens that cause rapid erosion of the rocks. Prof. Irit Nir and Prof. Ariel Kushmaro from Ben Gurion University also participated in the study
Fungi and lichens threaten the petroglyphs in the Negev desert, eroding ancient art by chemical and mechanical means. Archaeology, desert, fungi, lichens, microbiology, soil
Mount Mahia in the Negev desert in southern Israel is famous for its ancient rock art. Since at least the third millennium BC, the hunters, shepherds and traders who roamed the Negev left thousands of carvings, known as 'petroglyphs', on the rocks. Many of them depict domesticated animals such as goats, goats, horses, donkeys and camels, although some also include abstract forms. These petroglyphs are usually engraved with patina, a thin natural black coating that forms on limestone rocks.
Fungal threats to petroglyphs
A study published in Frontiers in Fungal Biology revealed that the petroglyphs house a community of rare fungi and lichens. Unfortunately, these species may pose a serious threat to rock art in the long term.
Fungi and lichens threaten the petroglyphs in the Negev desert, eroding ancient art by chemical and mechanical means. Archaeology, desert, fungi, lichens, microbiology, soil
"We show that these fungi and lichens may contribute significantly to the gradual erosion and damage caused to the petroglyphs," said Laura Rabakhin, a doctoral student at the Vienna Academy of Art in Austria and lead author of the study.
"They are able to secrete different types of acids that can dissolve the chalk in which the petroglyphs are engraved. In addition, the fungi can penetrate and grow inside the stone grains, causing additional mechanical damage."
Research methods and findings
Ravakhin and her colleagues took samples from a petroglyph site in the central-western mountains of the Negev. Here, only 87 mm of rain falls on average per year, and the temperatures on the surface of the rocks can rise up to 56.3 degrees Celsius in the summer. The researchers scraped samples from the desert varnish (patina) near the petroglyphs, from rocks without desert varnish (patina) and from the soil near the sampled (sampled) rocks. They also left open petri dishes near the rocks to trap spores in the air.
The authors identified fungi and lichens collected by two complementary methods. First, they repeatedly grew fungal material or spores from rocks or soil on plates with one of two different growth media until they obtained pure cultures for barcoding (suitable for identification or sequencing?) DNA. Second, they performed direct DNA sequencing of fungal material found in rock or soil samples, without growing them first. The second method can identify strains that do not grow in culture.
Both methods showed that the diversity and abundance of species (fungal species) on petroglyph-bearing rocks was low compared to soil, suggesting that few species can withstand the local extremes of dryness and temperature.
DNA barcoding (identification?) of pure cultures revealed that the petroglyphs harbor many species of fungi from the genera Alternaria, Cladosporium, and Coniosporium, while direct sequencing revealed additional species from the genera Vermiconidia, Knufia, Phaeotheca, and Devriesia. All of these except Alternaria and Cladosporium are microcolonial fungi, known to thrive in hot and cold deserts around the world. Lichens of the genus Flavoplaca were also abundant.
"Microcolonial fungi are considered very dangerous for stone paintings. For example, they are considered a probable cause of the weathering of the cultural heritage preserved in stone in the Mediterranean region," said Rabakhin.
"Lichens are also known to cause stone to wear down and therefore pose a potential threat to cultural heritage preserved in stone."
In the soil and surrounding air, the researchers found mainly various cosmopolitan fungi, which are known to be able to survive in harsh desert conditions by producing drought-resistant spores.
Impact and conservation challenges
Can anything be done to protect the petroglyphs from their slow but destructive erosion by the observed microcolonial fungi and lichens? That's unlikely, the authors warned.
"It seems that these natural weathering processes cannot be stopped, but the speed of the weathering process largely depends on whether and how the climate will change in the future. What we can do is monitor the microbial communities over time and, most importantly, document these precious works of art in detail," said Rabakhin's academic supervisor Prof. Katia Streflinger, lead author of the study.