Fossils from a Wisconsin roadcut show clearly that fungi and green plants moved from water onto land at about the same time, bolstering the theory that fungi helped plants successfully invade the land.
The newly discovered fossils - microscopic spores and threads in sediments dating from 460 to 455 million years ago - push the origin of land-based fungi back some 55 to 60 million years to about the same era that green plants invaded land, said Dirk Redecker, a postdoctoral researcher at the University of California, Berkeley.
"The presence of both organisms at the same time suggests that there could have been such an interaction, and that organisms even then were interdependent," Redecker said.
Redecker and his colleagues at the University of Wisconsin, Madison, report their discovery of the fossil fungi in the Sept. 15 issue of Science.
Plant/fungus interactions are widespread today, with between 80 and 90 percent of all green plants forming associations with so-called mycorrhizal fungi. These fungi grow around and into plant roots and help them absorb minerals and water, giving plants a substantial competitive advantage, said coauthor Linda K. Graham, a professor of botany and environmental studies at the University of Wisconsin, Madison.
"Plants without mycorrhizal fungi are competitively inferior," Graham said. "Though they won't die, in a highly competitive situation or places with a dearth of resources, mycorrhizal fungi function as an auxiliary root system to provide additional nutrients."
The researchers caution that the fossil fungi they discovered and report in Science show no evidence of an association with green plants. However, similar modern fungi from the genus Glomus form a simple association with modern liverworts and hornworts, relatives of the only group of land plants around 460 million years ago.
In addition, mycorrhizal fungi have been found in fossils as old as 400 million years, in company with later, more evol
Contact: Robert Sanders
University of California - Berkeley