In the soil beneath our feet, a vast, uncharted world of fungal diversity shapes the health of our planet, and scientists are just beginning to map its contours.
Imagine an underground internet connecting trees and plants across continents—a biological network that influences how forests draw down carbon, cycle nutrients, and withstand environmental change. This isn't science fiction; it's the realm of ectomycorrhizal fungi, mysterious organisms that form symbiotic relationships with most woody plants. Yet, despite their ecological importance, we've only begun to understand where these fungi thrive and why their distribution matters. Recent research reveals that less than 10% of the most critical fungal diversity hotspots currently fall within protected areas, leaving these vital ecosystems vulnerable to destruction 8 .
Ectomycorrhizal (EcM) fungi represent a unique class of fungi that form symbiotic relationships with the roots of various trees and woody plants. Unlike their relatives that penetrate plant cells, EcM fungi envelop root tips with a dense sheath called a mantle and form a network known as the Hartig net between root cells 7 . This structure creates an extensive interface for nutrient exchange: the fungi provide their host plants with water, nitrogen, phosphorus, and other essential minerals from the soil, while receiving carbon in the form of sugars from the plant in return 2 7 .
These fungal networks connect multiple trees together, facilitating resource sharing and communication across forest ecosystems.
These fungal partnerships are crucial for the health of approximately 2% of plant species worldwide, including many ecologically and economically important trees such as pines, oaks, birches, and eucalypts 7 . Though this percentage seems small, these host species dominate vast stretches of Earth's forests and play disproportionate roles in global carbon cycles .
The ecological significance of these fungi extends far beyond individual plant relationships. Their extraradical hyphae—filaments that extend from the root mantle into the surrounding soil—can connect multiple trees together, forming what scientists call common mycorrhizal networks 7 . These networks have been shown to facilitate the transfer of resources and chemical signals between plants, earning them the popular nickname "the wood wide web" 8 .
For decades, the distributions of EcM fungi remained largely mysterious, with knowledge limited to scattered observations of mushroom fruiting bodies. This changed dramatically with advances in DNA sequencing technology and the creation of global soil metabarcoding databases such as GlobalFungi and the Global Soil Mycobiome consortium 1 3 .
In a groundbreaking 2025 study published in Nature, researchers analyzed 2.8 billion fungal DNA sequences from nearly 25,000 soil samples across 130 countries . Using machine learning algorithms, they generated the first high-resolution global maps of mycorrhizal fungal diversity, revealing patterns that often contradict what we see aboveground.
Unlike most organisms that show highest diversity near the equator, EcM fungi display greatest richness in northern latitudes and southern regions of South America and Australia, with lowest diversity near the equator 6 .
Interactive visualization of ectomycorrhizal fungal hotspots worldwide
The revolution in DNA sequencing has revealed a startling fact: most EcM fungi represent "dark taxa"—species known only from their DNA sequences, without formal scientific names or descriptions 1 3 . Of the estimated 2-3 million fungal species on Earth, only about 155,000 have been formally described, meaning over 90% of fungal diversity remains undocumented 1 3 .
This taxonomic void creates significant problems for conservation. Without formal names, species cannot be included on Red Lists or receive legal protection 1 . The International Code of Nomenclature for algae, fungi, and plants currently requires physical type specimens to officially recognize new fungal species, making it nearly impossible to name dark taxa known only from DNA sequences 1 3 .
The global mapping of fungal diversity has revealed an alarming conservation crisis: the hotspots of fungal diversity rarely overlap with protected areas, and most face significant threats from human activities.
| Region | AM Fungal Hotspots Protected | EcM Fungal Hotspots Protected |
|---|---|---|
| Asia | 2.2% | 11.3% |
| Europe | 19.6% | Data not specified |
| Global Average | <10% | <10% |
The 2025 analysis published in Nature identified specific threats to critical fungal hotspots:
Only 1.5% of EcM fungal diversity hotspots overlapped with plant hotspots, indicating that conservation strategies focused solely on aboveground diversity will miss critical underground ecosystems 6 .
To understand how scientists are uncovering these hidden patterns, let's examine the methodologies behind the groundbreaking 2025 global mapping study published in Nature .
Researchers compiled a globally distributed collection of nearly 25,000 soil samples from 130 countries, drawing from GlobalFungi, GlobalAMFungi, and Global Soil Mycobiome consortium databases .
Laboratory technicians extracted and sequenced fungal DNA from each sample, generating >2.8 billion DNA sequences. They focused on specific genetic markers—the internal transcribed spacer (ITS) for EcM fungi and small subunit (SSU) rRNA for AM fungi .
Bioinformaticians clustered sequences into operational taxonomic units (OTUs) for EcM fungi using a 97% similarity threshold, and into virtual taxa (VT) for AM fungi .
Ecologists applied rarefaction and extrapolation approaches to estimate species richness from the sequence data, accounting for varying sampling depths across locations .
Data scientists trained random forest machine-learning algorithms to predict global fungal diversity patterns based on environmental variables from the sample locations .
Researchers defined biodiversity hotspots as areas in the upper 95th percentile of predicted richness and rarity values globally .
The analysis revealed that the most species-rich communities of EcM fungi contain more than 60 OTUs per sample . The models predicted major EcM fungal richness hotspots throughout northern forest ecosystems and specific regions of the Southern Hemisphere .
OTUs per sample in richest communities
Overlap between plant and fungal hotspots
DNA-based identification of fungal communities from soil samples
Predictive modeling using environmental variables
Repository of fungal DNA sequences
Metric combining richness and endemicity
As the field advances, researchers are proposing concrete steps to address the challenges identified in these global surveys:
In priority darkspots, particularly tropical regions and undersampled temperate forests 1
Connecting existing collections with sequence data 1
Integrating fungal diversity into conservation planning 8
These approaches aim to make the invisible world of fungal diversity visible to policymakers, land managers, and conservationists through tools like the Underground Atlas, which allows users to explore fungal diversity patterns anywhere on Earth at a resolution of 1 kilometer 8 .
Studying the biogeography of ectomycorrhizal fungi is far more than an academic exercise—it's essential for understanding and protecting the ecological processes that sustain life on land. These hidden networks:
Linking plants across forest ecosystems 7
"When we disrupt these critical ecosystem engineers, forest regeneration slows, crops fail, and biodiversity aboveground begins to unravel."
The mapping of fungal biogeography represents a critical step toward recognizing these vital organisms in our conservation efforts and land management strategies—ensuring that the hidden half of nature's partnerships receives the attention and protection it deserves.