Fungi account for around half of the living organisms in our soils, yet we tend to only notice them when a conspicuous mushroom or toadstool pops up and draws our eye. Meanwhile, scientists estimate that just below out feet, trillions of miles of fungal networks permeate the soil, transporting water and nutrients across the planet’s ecosystems and drawing carbon belowground.

Now, a team of specialists is embarking on the first worldwide effort to map these subterranean network-forming fungi by building a global database of where they occur. The project, led by the Society for the Protection of Underground Networks (SPUN) and comprising researchers from Canada, Europe and the U.S., aims to identify the world’s hotspots of underground biodiversity.

“The maps will allow us for the first time to incorporate information about fungal biodiversity into our conservation planning and decision-making,” Colin Averill, a senior scientist at ETH Zürich in Switzerland and co-founder of SPUN, told Mongabay.

As we risk overstepping Earth’s nine planetary boundaries, the environmental limits within which current life support systems operate, experts agree that focusing conservation efforts belowground could prove vital in meeting global challenges such as climate change, biodiversity loss, land use change, and pollution of the biosphere.

In addition to altering land management practices to protect fungi, conservationists are increasingly incorporating fungi into nature-based solutions to restore degraded ecosystems, remediate contaminated soils and speed the transition toward sustainable agriculture.

“An understanding of underground fungal networks is essential to our efforts to protect the soil, on which life depends, before it is too late,” Jane Goodall, renowned conservationist and adviser to the project, said in a statement.

Hotspots of fungal biodiversity

The researchers are initially drawing on the GlobalFungi database, which contains thousands of records of fungi from around the world, to build models of fungal distribution using machine learning and the latest environmental metrics. They will then use the models to predict fungal diversity in parts of the world that have not yet been surveyed.

Beginning in April 2022, the team plans to make its first field collections in the highlands of Patagonia and will spend 18 months gathering more than 10,000 soil samples from different habitats around the world. They will then use environmental DNA sequencing to find out which species occur where. The researchers will focus on potential hotspots of fungal diversity, including the Canadian tundra, the Mexican plateau, the Negev desert in the Middle East, the grasslands and high plains of Tibet, and the Russian taiga.

Networks perform crucial ecosystem roles

Mushrooms and toadstools are only one small component of fungi, equivalent to the flowers or fruits in plants. The main part of a fungus is its root system, known as mycelium, which comprises weblike threads called hyphae that extend throughout soils and other moist environments, such as rotting tree trunks, in search of nutrients.

The most notable underground fungal networks are created by mycorrhizal fungi, a type of fungi that live in a symbiotic relationship with plant roots. Their mycelia form vast, interconnected networks that soak up water, nitrogen, phosphorus and other nutrients from the soil, and pass them on to plants. In return, plants provide the mycorrhizal fungi with sugars in a process that sequesters carbon from the atmosphere into the fungi’s bodies.

The SPUN team are focusing their efforts on documenting hotspots of mycorrhizal biodiversity, in part due to their enormous role in carbon storage: ecosystems with thriving underground fungal networks have been shown to store eight times as much carbon as ecosystems without them. Furthermore, mycorrhizal networks form “super highways” for important soil microbes and have even been shown to facilitate “communication” between trees.

Nonetheless, experts say decomposer fungi must not be forgotten due to their crucial role in recycling nutrients that would otherwise remain locked up and unavailable to plants. In the process of breaking down dead organisms, decomposers emit carbon dioxide, so it is vital to keep track of their influence on the global carbon cycle.

Lynne Boddy, a fungal ecologist at Cardiff University in the U.K., who is not involved in the new mapping project, said that while the initiative is a welcome move to learn more about fungal networks and highlight the importance of underground biodiversity, it’s unclear how the scientists plan to go about mapping fungal networks at such an enormous scale.

There are estimated to be 2 million to 5 million species of fungi worldwide, only a fraction of which have been classified so far, and individual fungi range in size from tiny yeasts to enormous mycelia that cover several hectares; the largest fungus ever recorded, an Armillaria gallica found in Michigan and dubbed the “humongous fungus,” weighed more than a blue whale.

“There are networks of fungi at many different levels and at all sorts of scales,” Boddy said, “and the decomposers are as important surely as the mycorrhizal fungi … they all have networks, it’s just that mycorrhizal fungi link plants, and decomposers link dead stuff.”

Boddy also said that eDNA sequencing data doesn’t always lead to improved knowledge about the function of species. “We have to be very cautious about how we interpret species lists,” Boddy said. “Just because a species is there doesn’t necessarily mean it is important in the community; we just know that it’s there.” Maximizing ecological knowledge through collaboration with local experts, she said, will likely be key.

Averill from SPUN agrees. “What we need is a distributed network of scientists around the world who live and work in these places and know them best,” he said, adding that SPUN plans to roll out an “explorer” program to cultivate expertise and partner with local communities and conservation initiatives to collect data and protect habitats.

Restore fungi to restore ecosystems

One of the biggest questions the SPUN researchers aim to address is how fungi are affected by global threats, including expansion of industrial agriculture, deforestation, pollution, drought and climate change.

Although ecologists have recorded gradual shifts in the distribution of tree and plant species, it remains unclear whether underground fungal networks have shifted in step.

“The mosaic of mycorrhizal fungi is fundamentally changing and moving around,” Averill said. “It is being pushed around by climate, by nitrogen pollution and other drivers. The thing we really don’t know at scale is, as those trees move, are they bringing their fungi with them or are they being left behind?”

Deforestation “annihilates” soil fungi, Averill said, “and when we till soils, we are just ripping knives through the soil and we’re shredding hyphal networks, the actual bodies of the fungi.” Soil organisms are further damaged when farmers treat crops with chemical fertilizers rich in nitrogen, phosphorus and potassium, which break down the symbiosis between mycorrhizal fungi and plant roots. Research has also shown that rainfall contaminated with sulfur dioxide, nitrogen oxide and other atmospheric pollutants inhibits mycorrhizal relationships in forests.

Restoring the symbiotic relationship between mycorrhizal fungi and plant and tree roots could go a long way to restoring degraded ecosystems and transitioning away from chemical inputs in farms and other managed landscapes, according to Averill. For instance, this can be achieved in agriculture by changing practices toward no-till farming.

Actively restoring the mycorrhizal symbiosis in plantations and reforestation projects by transplanting soil also enhances tree growth and restores natural mechanisms for carbon storage both aboveground and belowground.

“There is an opportunity to fold fungal restoration and soil microbiome restoration into our concept of ecosystem restoration and forest restoration,” Averill said, “and in the process, we might build more resilient and biodiverse and productive forests and ecosystems.”

Banner image: Fungi emerging through dead wood covered in moss. Image by adege via Pixabay

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