A microscopic fungi may have contributed to the largest mass extinction in history — and may lead to a fungal disease increase in today’s forests due to the climate change, according to a study by a UC Berkeley professor and her collaborators in Europe.
The study, which will be published in the September issue of the journal Geology, identifies 250-million-year-old fungal marine fossils to be relatives of the modern-day fungi group Rhizoctonia, which is known to spread deadly pathogens to plants.
“The sediments contain fossils that look like the resting structures of the modern fungi Rhizoctonia,” said Cindy Looy, assistant professor of integrative biology at UC Berkeley and an author of the paper. “The interesting thing is that Rhizoctonia is partially pathogenic, which means microbes in the soil can attack and kill entire ecosystems that are under environmental stress.”
According to Looy, during the mass extinction that occurred at the close of the Permian era about 250 million years ago, ecosystems suffered environmental stresses from volcanic eruptions, which spewed carbon dioxide and methane into the atmosphere and probably destroyed some of the Earth’s ozone layer. In such an environmental crisis, fungal pathogens can become very active, and in this case, accelerate tree mortality, Looy said.
The study also acknowledges that pathogenic soil microbes found in Rhizoctonia could also accelerate the tissue damage in trees environmentally stressed from today’s increasing temperatures and drought.
“As the optimum range for plant growth moves north, the southern edges of ecosystems will be in trouble,” said Ivo Duijnstee, an adjunct assistant professor of integrative biology at UC Berkeley. “It is not easy for plants to physically move northward as their ideal climate-zone does.”
Duijnstee said it may be possible to find a higher amount of plant pathogens in these areas.
According to Looy, fungi in the group Rhizoctonia enter a resting structure when environmental conditions are not ideal. In this dormant stage, the fungi release pathogenic microbes that enter the trees and plants of the surrounding ecosystem.
“The fact that we have resting structures implies two things,” Looy said. “There is lots of soil erosion, and the pathogens are active.”
The micro-fossils found by Looy and her colleagues — Henk Visscher of Utrecht University in the Netherlands and Mark Sephton of Imperial College London — were discovered in the Alps of northern Italy among plant remains for a large coniferous forest and strung together in long chains resembling pearl necklaces.
Looy and Visscher studied the pollen and spores of the plant fossils and identified the remains within. Sephton studied the biochemistry of the remains to conclude that they were indeed fungal, disputing conclusions of other researchers that the chain-like fossils were remains of algae.
“The micro-fossils didn’t look like normal, present-day fungi,” Looy said. “But, when we realized that we were looking in the wrong place, we started to look at resting structures of fungi.”
According to Looy, the resting stages of Rhizoctonia allows it to survive extreme conditions and may be the reason why it has survived these many years, proliferating all around the world.
“Because the fungi’s fossils can be found almost everywhere in the world and in different types of plant fossils, we can say that these fungi may have played a large role in accelerating the largest mass extinction in history,” Duijnstee said.