To save endangered trees, researchers in South America recruit an army of fungi

Mycorrhizal fungi live in symbiosis with plants, providing them with nutrients necessary to thrive and potentially playing a key part in preserving threatened species.Although research into mycorrhizae has so far been sparse in Latin America, efforts are gaining momentum, with experts studying how the fungi could help save the Colombian black oak, an endangered, endemic species.In Huila, Colombia, local communities are successfully working with researchers on a black oak restoration project using seeds “inoculated” with fungi.

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It’s a sunny July day during an otherwise exceptionally rainy season in the lush green mountains of Huila, in Colombia’s eastern Andes. Adriana Corrales, her assistant and a local guide climb through the dense cloud forest. Above them, birds sing and monkeys howl through the canopy of ancient Colombian black oaks (Trigonobalanus excelsa), an endangered tree species. But the researchers keep their eyes on the ground.

“All this forest above us, and we are here looking down,” says Corrales, a fungi ecologist and expedition leader at the Society for the Protection of Underground Networks (SPUN), a nonprofit research organization mapping fungi worldwide. For the last two years, the group has been searching in Colombia’s black oak forests for mycorrhizae, a type of fungi that establishes a unique symbiosis with plants that’s fundamental to keeping forests alive.

Most plants worldwide are associated with these fungi. Mycorrhizae grow around roots, forming vast networks of thin, cotton-like filaments that extend into the lower soil levels and reach the litter fall. Through this system, the fungi can break down organic matter, such as dry leaves, and even mine minerals in rocks and deliver water and essential nutrients directly to plants’ roots. In return, the roots provide the fungi with sugars, essential for their survival.

The high-altitude cloud forests of Huila, cut down to open space for coffee farms, used to be covered by black oak trees. Image by Sofia Moutinho for Mongabay.

“The fungi form a microbiome on the plant’s roots in the same way that microbes in our gut help us digest food,” Corrales says. “We have these bacteria in our gut that break down the food we eat so we can absorb it. In this case, the fungi digest the food in the soil and bring the nutrients to the plant in exchange for sugar.”

Although researchers have been looking into this symbiosis since the late 19th century, no single genome of tropical mycorrhizal fungi from South America has ever been sequenced, compared to hundreds elsewhere. Among the reasons are lack of funding and difficulty accessing areas with fungi. But Corrales and other experts plan to change that.

Studying and understanding the local mycorrhizal fungi, they say, is fundamental to preserving local endangered plant species, like the endemic Colombian black oak. Its genus is thought to represent the oldest type of oak in the world. Scientists think the species is a remnant of an old oak lineage established up to 100 million years ago in what is today North America.

It’s believed that this oak once covered most of Colombia’s high-altitude regions. After centuries of deforestation for timber and agriculture, the black oak has become endangered and can be found only in five areas of Colombia in fragmented patches, covering a combined area smaller than 50,000 hectares (124,000 acres), according to a conservation assessment.

A fungi hotspot

Every now and then, the buzz of a chainsaw echoes through the patch of forest where Corrales and her colleagues, armed with liquid nitrogen, a hammer and some plastic bags, sample fungi to understand their role in protecting the black oak. The area is flanked by Huila’s encroaching coffee farms.

Researcher Antony Ortiz Suarez finds a decomposer fungus in Huila’s black oak forests. Image by Sofia Moutinho for Mongabay.

“Oh, this one is so beautiful! Spectacular!” Corrales yells as she cuts a purple-capped mushroom, the size of her pinky finger, from the ground. Finding a mushroom indicates that there’s a whole unseen organism underground. “It looks like they are made of sugar candy,” she says.

This particular species of mycorrhizal fungus is a new-to-science species in the genus Russula, which Corrales previously discovered in Panama. In the 15 years she spent there studying fungi, she found a total of 20 new-to-science species.

When the experts find mushrooms, they first inspect them with the naked eye. Then they smell them. Some mushrooms of the Russulaceae family smell like fish, while others, like those of the genus Lactarius, have a hint of honey or maple syrup. Sometimes the researchers even bite off a little piece of the mushroom and then spit it out to avoid poisoning. “This one is bitter,” Corrales tells her assistant after brushing her lips with a fat-stemmed yellow mushroom.

At night, back at their hotel bungalows in the jungle, they store their finds in plastic boxes out on the balcony. They then use a surgical knife to cut off a piece of each mushroom for detailed DNA analysis.

These samples are sent to labs in the U.S. to sequence their genomes and run them against international databases of the DNA of all known fungi species. This kind of analysis, called DNA barcoding, helps researchers classify the species — or indicates that they may have encountered a new-to-science species and classify them.

Adriana Corrales collects soil around a black oak tree with a plastic hammer and a PVC tube. Image by Sofia Moutinho for Mongabay.

The complete genome can also reveal different characteristics of the species, such as their functions, what kinds of nutrients they obtain more effectively, and how they might interact with the trees around them. Corrales says she hopes to sequence the DNA of up to 200 mycorrhizal fungi species with funding from the Joint Genome Institute (JGI), a U.S. Department of Energy research center at the Lawrence Berkeley National Laboratory.

To identify potential fungi connections to trees, Corrales’s team also collects soil samples from around the black oaks.

A single tree can be connected to several fungi species. It’s been estimated that a spoonful of soil can contain up to 100 meters (330 feet) of mycorrhizal threads. Corrales has found about 250 different kinds of mycorrhizae in soil samples taken near Colombian black oaks, many of which she says might be unique to the region and new to science.

Corrales’s analysis has found the soil samples here to be very acidic and high in phosphorus, generally uncommon in nutrient-poor tropical soils. She says the fungi might be helping the oaks absorb the phosphorus and thrive in the adverse acidic soils. “The fungi change the biochemical composition of the soil to benefit the oak,” she tells Mongabay.

Using fungi for conservation

Research into mycorrhizal fungi’s links with endangered tree species could help conservation efforts. A 2019 review of 26 studies found that adding mycorrhizae to plants can enhance ecological restoration outcomes, increasing the number of species in plant communities by 30%.

Two years ago, in partnership with Colombia’s University of the Rosary and the Swiss nonprofit Franklinia Foundation, Corrales and local community members started a black oak restoration project. They collected tree seeds and “inoculated” them with mycorrhizae. They then planted about 3,000 of these seeds in greenhouse pots filled with fungi-rich soil from the forest. Although previous attempts to grow black oak from seeds had been unsuccessful, Corrales says the fungi present in the soil made the seedlings grow strong.

Researchers collect soil samples to run DNA analysis to identify the fungi species associated with black oaks. Image by Sofia Moutinho for Mongabay.

“The black oak is an umbrella species for fungi: one single plant can be related to hundreds of fungi,” she says. “The plant cannot survive without the fungi, and the fungi cannot survive without the plant.”

To date, community members have replanted 424 black oaks in forest fringes, deforested lands and near water bodies. Nelly Salazar Asturillo, who owns a small organic coffee farm outside the town of Pitalito, in southern Huila, helped grow 90 saplings in her backyard, which were distributed to other locals. Asturillo’s family keeps an intact 19-hectare (47-acre) black oak forest on her land. “By preserving the oak, more and more birds are around, and it doesn’t get as hot as before,” she says. “For many years, we haven’t seen beehives around, and now the bees are also coming back.”

Fungi ecologist Adriana Corrales prepares a mushroom of the genus Cortinarius for DNA analysis. Image by Sofia Moutinho for Mongabay.

Lucia Urbano, another local coffee farmer, used to cut and burn black oaks to make charcoal for sale. A few years ago, as she tells it, she went up the mountain and asked nature for forgiveness, before establishing a 25-hectare (62-acre) reserve on her property and planting 40 black oak saplings. “Looking back at the deforestation, lack of water and climate change, I became more aware of the need to preserve the trees,” she says. “I have children and grandchildren and worry about their future here.”

Latin America boosts fungi research

In Argentina, Valeria Faggioli, a biologist at the National Agricultural Technology Institute, has been studying mycorrhizal fungi associated with the endangered monkey puzzle tree (Araucaria araucana) in remnants of the Atlantic Forest close to the famed Iguazú Falls. The monkey puzzle tree almost went extinct due to logging, and the commercial trade in wild-sourced specimens has been prohibited since 1990.

Faggioli says she hopes to isolate the spores of the fungi present in monkey puzzle forests to multiply them in the lab and inoculate seeds for reforestation projects. “Whatever we have lost due to land use and deforestation during the last centuries remains in the preserved forest soil,” Faggioli says. “Any attempt to restore degraded lands will demand going to the origins of the native habitat.”

Coffee farmer Nelly Salazar Asturillo shows a preserved patch of black oak forest in her backyard. She helped grow 90 saplings of the endangered tree species on her property. Image by Sofia Moutinho for Mongabay.

In Chile, César Marín, a fungi ecologist at Santo Tomas University, is studying how fungi partner with the alerce tree (Fitzroya cupressoides), an iconic local endangered species. Alerce is the largest tree species in South America, growing up to 50 m (164 ft) tall. Marín has been collecting fungi at Alerce Costero National Park around the longest-living specimen of this tree, believed to be the oldest tree alive worldwide, at 5,400 years old. Chile aims to reforest 100 hectares (250 acres) of alerce in its national parks over the next three years; Marín says the fungi he’s collecting can help achieve this goal.

“More and more studies have shown it is a triple alliance between plants, fungi and the bacteria that absorb nutrients and pass them on to the fungi,” Marín tells Mongabay.

He adds more reforestation projects need to be based on fungi. Some research has shown that in certain conditions, such as in soils with high levels of phosphorus, the same mycorrhizal fungi that are helpful to trees can turn parasitic, damaging the plants. “It all depends on each place and context; that is why we need serious studies.”

Two unidentified specimens of a mushroom of the genus Russula, collected in Huila’s black oak forests and probably new to science. Image by Sofia Moutinho for Mongabay.

David Janos, a retired mycorrhizae expert at the University of Miami, agrees. Janos says moving soils around can be dangerous and potentially spread diseases and parasites. He also notes that the community of fungi that trees need to grow might change over time. “There will always be the question of whether the right kind of mycorrhiza is present in a reforestation effort,” Janos says, highlighting the importance of using native fungi whenever possible.

Most researchers agree that for a balanced and healthy ecosystem, we need to preserve both the trees and the fungi they partner with. “It is a mutualistic relationship that has to be taken into account in any restoration project. But often, projects ignore what is underground,” Corrales says. “We need to develop a more ecosystemic vision of forests. If the black oak disappears, the fungi also do, and if the fungi disappear, so will the oaks.”

Citation:

Neuenkamp, L., Prober, S. M., Price, J. N., Zobel, M., & Standish, R. J. (2019). Benefits of mycorrhizal inoculation to ecological restoration depend on plant functional type, restoration context and time. Fungal Ecology, 40, 140-149. doi:10.1016/j.funeco.2018.05.004

Banner image: According to researchers in Colombia, studying and understanding local mycorrhizal fungi fundamental to preserving local endangered plant species. Image courtesy of Sofia Moutinho.

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