Fungi Live Large at the Poles
When British adventurers Ernest Shackleton and Robert Falcon Scott launched their legendary expeditions across Antarctica in the early 20th century, they built several small wooden structures as supply huts and way stations. Though neither man won the race to the South Pole (that distinction went to Roald Amundsen’s Norwegian expedition in 1911), they both made significant contributions to the scientific record and to our knowledge of this icy landscape. And their huts, abandoned with 18,000 artifacts, including newspaper clippings, cans of food, old clothing, photography notebooks, a century-old roll of film and even a stash of fine whisky, draw legions of scientists, historians and ecotourists each year. They have become monuments to the so-called heroic age of polar exploration, but in the past several decades, they’ve begun to show signs of decay.
It turns out that colonies of fungi, more readily associated with hot and humid climates, are partially to blame. Biochemist Roberta Farrell told me via skype from New Zealand that a chance encounter in the mid 90s between herself and conservationists in the cafeteria at Scott Base, a New Zealand research facility in Antarctica, led to an investigation into some of the sources of decay. Farrell, a professor at the University of Waikato in New Zealand, had previously worked with Robert Blanchette, an authority on the interactions between fungi and archaeological artifacts from the University of Minnesota, and together they secured grants from the New Zealand government and the U.S. National Science Foundation to research conservation of the huts. Given that the Shackleton and Scott huts were prefabricated with timber from Europe and that all of the other items contained in them were transported from England, New Zealand and other parts of the world, they figured they might find a few hitchhiker organisms native to the geographies of origin feasting on the wood.
Instead, they found a vast diversity of fungi, some of which had never been identified before anywhere else on the planet. That finding launched a series of research efforts that opened up a whole new world of fungi adapted to polar environments. When they are not consuming wood introduced by explorers, these fungi are dining on penguin guano and feathers, moss, lichens and even freshwater algae, which grow in clumps in Antarctic lakes and then dry up and blow off in tendrils. Because so many of the fungi were found in extensively degraded organic matter, including peat deposits, scientists believe they play a major role in decomposition in Antarctica. “They are running the ecosystem there,” Blanchette told me in a telephone conversation from Minnesota. “They’re the nutrient recyclers.” Without them, very little life — what there is of it in cold, dry inhospitable Antarctica — would survive, he said.
The dominant type of fungi consuming the wood of the huts were Cadophora, including C. malorum, C. luteo-olivacea, and C. fastigiata as well as several previously undescribed Cadophora species designated C. species H and C. species E. Cadophora are known as “soft-rot” fungi, for the particular brand of devastation they wreak: they grow in the inner cell walls of the wood, creating honeycomb-like chains of cavities that destroy its structural integrity and leave it soft to the touch. Soft-rot fungi often feed on wood in extreme conditions around the world, such as wood found buried in desert tombs or wood that is waterlogged or treated with preservatives. “It seems that they can exist where other fungi can’t,” said Blanchette. But they are also slow growers and, in temperate environments, they are often unable to compete for nutrients with more aggressive fungi such as brown-rot or white-rot.
No trees grow in Antarctica today, but the team speculated that Cadophora may be related to fungi that lived on the continent 200 million years ago, when forests and swamps dominated the landscape. Researchers took soil samples from areas where petrified wood is found in Antarctica’s Allan Hills and Mount Fleming in order to isolate fungi similar to those isolated from historic area sites. However, they have yet to complete a DNA analysis that would allow them to determine the relationship of currently found fungi in Antarctica to those observed in the fossil record.
The fungi findings led conservationists with New Zealand’s Antarctic Heritage Trust to get to work reducing moisture in and around the huts. This was no small task. As temperatures rise above freezing during the brief Austral summer, ice melts to water and moisture accumulates inside the wooden walls of the huts, which allows the fungi to proliferate. The huts were meant to last a couple of years, not a century. “They were pretty cheap and cheerful in their construction. There were lots of ways for water to get into them,” Gordon McDonald, a conservationist with the Trust for 14 years, told me. In their effort to stem the tide, McDonald and other conservationists with the Trust have taken apart floors — some of which bore knife marks from cutting seal meat — dried them and put them back together again. They have removed over a hundred years of snow and ice from under the floors and around the walls. They have built perimeter dams around the huts down a half meter into the permafrost. They have replaced the most damaged pieces of wood entirely. Some of this work was done at temperatures that dipped to 13 degrees below zero and in total darkness.
Blanchette and Farrell, meanwhile, ventured further afield. They wanted to know if the fungi they had identified were confined mostly to the historic huts, where there is a lot of humidity and human traffic in summer — hot bodies, boots and backpacks — or were they a critical feature of the larger Antarctic environment? Were the novel species native to Antarctica or were they recent migrants from somewhere else that simply hadn’t been catalogued yet? To answer these questions, they decided they needed to study more pristine Antarctic soils, some untouched by human activity. So they sampled remote locations in ice-free mountainous regions and dry valleys around the continent: at Mt. Fleming, which contains significant amounts of fossilized wood, Allan Hills, McKelvey Valley in the Upper Dry Valleys as well as the Lake Fryxell Basin in the McMurdo Dry Valleys. What they found was a wide diversity of fungi in Antarctic soils, and a high degree of overlap with the Cadophora causing degradation in the huts and artifacts. In all, they identified 71 different fungal taxa. This finding seemed to support their hypothesis that fungi play a meaningful role as decomposers in the larger Antarctic ecosystem.
So how do fungi, more often associated with temperate climes, survive the extreme polar environment? Many of the Antarctic fungi are highly pigmented, which gives them UV protection and helps them absorb solar energy. (In fact, many conservationists mistook the fungi in the cabins for soot at first, said McDonald.) The majority are also cold-tolerant rather than cold-loving: cold-tolerant organisms are capable of growth at 0 degrees Celsius, but grow optimally above 15 degrees Celsius, while true psychrophiles grow best below 15 degrees Celsius. Cold tolerance is thought to allow the Antarctic fungi to withstand the freeze-thaw cycles and wide ranges of temperatures that are feature of the polar climate. “If we take these fungi and put them into the lab, under the best of conditions, they can degrade [wood] quite fast. They have the potential for rapid decay,” said Blanchette. They are only limited by the degree-days above zero Celsius.
Farrell also found that the Cadophora produce nearly as many aerial spores in winter as in summer, which means the hardy fungi can reproduce and disperse even in the most extreme conditions. One of Farrell’s then graduate students, Dr. Shona Duncan, further found that the Cadophora produce different cellulose-degrading enzymes for breaking down wood in the coldest and the warmest months, which suggests they may be remnants from a period when Antarctica was warmer and, over time, have evolved adaptations to colder temperatures. Or it’s possible they have been versatile generalists all along. “This is something that we’ve been looking at, and what makes these fungi so special? How can they survive so well?” said Blanchette.
The fungi that call Antarctica home today are likely to be around a while longer. The fact that most of them are cold-tolerant rather than cold-loving means they should persevere and even thrive as temperatures rise with global climate change — unless and until warming allows some of their more aggressive decomposer fungi cousins to crowd the scene.
In the meantime, they will continue to pose a challenge for conservationists and scientists working to preserve Shackleton’s and Scott’s huts. The reconstruction efforts and dams are meant to keep the huts dry for the next forty years. But, Farrell wonders, how soon will hungry Cadophora or some other soft-rot fungi find their way in? Much like the explorers who conquered this continent, they are hardy, daring creatures — survivors of extremes.
I Contain Multitudes is a series of videos, educational materials, and articles produced by HHMI and inspired by a New York Times bestselling book by Ed Yong. It explores the fascinating powers of the microbiome: the world of bacteria, fungi, and other microbes that live on and within other organisms, including ourselves.
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