LAWRENCE — One might think that a doctoral student absorbed in the physiology of ancient plants would lead a ho-hum existence locked away in some dusty, dim room with books of fossilized leaf photos.
University of Kansas student Andrew Schwendemann recently traveled to the most-frigid ends of the Earth to locate Antarctic rocks offering a glimpse back millions of years into the evolution of plants and fungi. His derring-do work there just landed him lead authorship of an article in the renowned journal Proceedings of the National Academy of Sciences.
“It’s a big ordeal,” Schwendemann said. “We flew to Christchurch, New Zealand, to get outfitted with cold-weather gear. From there, we take a C-17 and land on a glacier on the edge of Antarctica. Then we had to go through survival school at the main U.S. base at McMurdo. Next, we flew out to our base camp, which was halfway between the coast and the South Pole. Every morning, helicopters would fly us out to the sites where we wanted to collect, and they’d pick us up at the end of the day.”
Dropped in the Antarctic wilderness, Schwendemann and his colleagues hunted for primeval rocks, called silicified peat, known to contain fossilized conifers and other plants. Each day, the team loaded burlap bags with hundreds of pounds of them, and eventually hauled their find back to the KU campus in Lawrence.
“We get these big rocks of silicified peat back into our lab, and then we use a diamond-bladed slaw to slash through them like a loaf of bread,” said Schwendemann. “Then, we dip it in hydrofluoric acid that destroys the minerals, but not the plant parts. So we’ll have these 240-million-year-old plant walls, and they’ll stick up in relief. Then we put acetone on the rock surface itself, and apply a plastic sheet. The acetone dissolves the plastic at first. After a while, the acetone evaporates and the plastic sheet hardens again.”
When peeled away, the plastic sheet clearly reveals the ancient conifer cell walls, ready to be examined under powerful microscopes.
From examining the conifer root fossils, Schwendemann discovered a more ancient connection between specialized plant root structures — called nodules — and fungi than had been known previously. The KU researcher described a mutually beneficial relationship whereby a fungus lives safely in a conifer’s root and extends into the soil, bringing the tree nutrients it wouldn’t get otherwise.
Indeed, the conifer may have evolved to grow the root nodules specifically to help fungi.
“Basically there’s a little sphere of root tissue coming off the main axis which the fungi lives in,” Schwendemann said. “It’s thought that maybe this nodule allows the fungus to live during really harsh condition where a fungus that didn’t have this special structure would have died.”
The new discovery predates the next-known appearance of this association by millions of years. The specific tie discovered by Schwendemann between conifer root nodules and arbuscular mycorrhizal fungi was present in the early Mesozoic era, the period when modern conifer families first appeared.
“Previously, the first fossil evidence of these was in the Cretaceous, maybe something like 100 million years ago,” said Schwendemann. “The ones we found were much later in the fossil record — about 240 million years old. So we pushed the origin of those structures way back.”
Schwendemann and four colleagues from KU’s Department of Ecology and Evolutionary Biology authored the discovery: Anne-Laure Decombeixa, a post-doctoral researcher; Thomas N. Taylor, Roy A. Roberts Distinguished Professor Paleobiology and Curator of Paleobotany; Edith Taylor, professor and senior curator; and Michael Krings, research associate.