Deep beneath the tropical forest floor and invisible to the eye, millions of fungal species are playing a critical role in the fight against climate change, yet most of them remain unknown to science. Mycorrhizal fungi are essential to climate regulation. Ectomycorrhizal fungi facilitate the drawdown of over 9 billion tons of CO₂ annually (over 25% of yearly fossil fuel emissions and help Earth’s forests function by regulating nutrient cycles, enhancing stress tolerance, and even breaking down pollutants.
However, it is estimated that only 155,000 of the roughly 2-3 million fungal species on the planet have been formally described. A study published in Current Biology shows that as much as 83% of ectomycorrhizal species are so-called dark taxa.
Dark taxa are species that are known only by their DNA sequences and can’t be linked to named or described species.
Laura van Galen, a microbial ecologist working with the Society for the Protection of Underground Networks (SPUN) and ETH University, Switzerland, and lead author of the study, says, “Environmental DNA has enormous potential as a research tool to detect fungal species. Still, we can’t include unnamed species in conservation initiatives. How can you protect something that hasn’t yet been named?”
Most mycorrhizal fungi in the wild are found using environmental DNA (eDNA), genetic material that organisms shed into their surroundings. Scientists extract fungal eDNA from soil and root samples, sequence that DNA, and then run those sequences through a bioinformatics pipeline that matches a sequence with a described species. For dark taxa, there are no matches, just strings of As, Gs, Cs, and Ts.
The study highlights that underground hotspots of unknown mycorrhizal species are found in tropical forests of Southeast Asia and Central and South America, in tropical forests and shrublands of Central Africa, and in the Sayan montane conifer forests of Mongolia, among other regions.
Moreover, many fungi are symbiotic with endangered plants.
“We’re at risk here,” says van Galen. “If we lose these host plants, we might also be losing really important fungal communities that we don’t know anything about yet.”
Co-author Camille Truong, a mycorrhizal ecologist at SPUN and research scientist at the Royal Botanic Gardens Victoria in Australia, says one way to reduce the dark taxa problem is to collect, study, and sequence mushrooms and other fungi.
Researcher van Galen further highlights that most of the research on ectomycorrhizal fungi has been focused on the Northern Hemisphere, but mid-latitude and southern-hemisphere regions show signs of being home to many unknown species.
“This means there is a mismatch in resources and funding. We need to bridge this gap and facilitate more tropical researchers and those from southern-hemisphere regions to focus on identifying these super-important fungi,” he says.
The researchers emphasize the need to pay attention to fungi in the soil so that “we can understand the species and protect them and conserve them before we lose them.”
“The technology is available – what’s missing is attention,” says van Galen.
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