Over 70% of global ecosystems remain unsampled for critical underground fungi
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Drylands including deserts, steppe regions, and grasslands, are often overlooked in ecology. This is surprising as they cover roughly 45% of the Earth’s terrestrial surface. Examples include the Kazakh steppe, the Chihuahuan Desert, and the Sahelian Acacia savanna. They may be underrepresented or biased in ecological sampling because vegetation cover is typically sparse.
view moreCredit: Yevgeniy Lechshenko / SPUN
Underground, intricate networks of soil fungi underpin the functioning of terrestrial ecosystems. Yet despite their global importance, only 30% of global ecosystems have been sampled for these fungal partners.
Arbuscular mycorrhizal fungi form important resource trade partnerships with plants. The fungi grow complex networks to help plants acquire nutrients, such as phosphorus and nitrogen. In exchange, plants provide carbon to the fungi, with roughly one billion tons of carbon transferred annually from plants to mycorrhizal fungal partners. Because these networks move massive amounts of carbon, nutrients, and water, they are often referred to as one of Earth’s circulatory systems.
In a study published in FEMS Microbiology Letters, researchers analyzed environmental DNA from the largest global dataset of arbuscular mycorrhizal fungi compiled to date. Their findings reveal a striking gap: More than 70% of the world’s ecoregions have no sequencing data for AM fungi. By mapping these gaps, the researchers highlight how data collection has been heavily skewed toward just a few regions. This month, the study was awarded “Best Study of 2025” in FEMS Microbiology Letters by the journal’s Senior Editors.
“Arbuscular mycorrhizal fungi underpin the functioning of most terrestrial ecosystems, but our data are heavily skewed toward a limited set of regions,” Dr. Justin Stewart the lead author and evolutionary biologist notes. “If we want robust predictions about biodiversity, carbon cycling, and ecosystem resilience, we need far more representative global sampling.”
Large areas of Africa, parts of Asia, boreal systems, and drylands remain severely underrepresented. The consequences extend beyond biodiversity surveys. Arbuscular mycorrhizal fungi influence plant productivity, soil aggregation, and carbon stabilization. Without more representative sampling, projections of fungal distributions and their contributions to climate mitigation and restoration targets carry substantial uncertainty. Drawing attention to these severe data gaps can encourage researchers to focus future sampling efforts in key habitats.
The study is part of an ongoing global effort led by the Society for the Protection of Underground Networks. Their mission is to map and advocate for the protection of Earth’s mycorrhizal networks. Last year, collaborators published global maps of mycorrhizal fungal diversity in Nature. These maps integrated nearly three billion DNA sequences, satellite imagery, and approximately 25,000 soil samples to generate predictive models of mycorrhizal fungal biodiversity and endemism globally.
While these models can predict biodiversity patterns globally – including in ecosystems without samples – they require validation. Uncertainty increases in areas with little or no empirical data. Underground arbuscular mycorrhizal fungal DNA data is still missing or not publicly available for more than 600 terrestrial ecosystems. Reducing this uncertainty will require targeted sampling and ground truthing campaigns across underrepresented regions.
To address this, SPUN launched the Underground Explorers Program, a decentralized and community-led initiative in which researchers and local communities collect soil samples in underrepresented ecosystems. By expanding sampling into overlooked habitats, the program aims to reduce uncertainty in global maps and generate open access data that improve predictions and forecasts of fungal biodiversity.
“Environmental DNA allows us to identify fungal species from even a teaspoon of soil,” Dr. Bethan Manley, the Lead Computational Biologist at SPUN and an author on this study. “It is one of the most reliable tools we have for documenting biodiversity belowground because it captures species of fungi that spend their whole lives out of sight in the soil, many of which are impossible to cultivate in the lab. But these environmental DNA sequencing surveys can only work once the soil is collected in the first place. Expanding sampling on the ground remains essential.”
By identifying where information is missing, the new analysis provides a roadmap for future research. Filling these gaps will clarify the biogeographic distributions of AM fungal species and strengthen their integration into environmental policy, restoration planning, and global carbon models.
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Advancing knowledge on the biogeography of arbuscular mycorrhizal fungi to support Sustainable Development Goal 15: Life on Land. FEMS Microbiology Letters
https://doi.org/10.1093/femsle/fnaf055
This work was supported by grants from the Jeremy and Hannelore Grantham Environmental Trust, Paul Allen Family Foundation, the Schmidt Family Foundation, NWO Gravity Grant MICROP (024.004.014), the European Union (ERC, Programme—HORIZON, acronym—NUCLEAR MIX, Project–101076062), and an Ammodo grant. GlobalAMFungi was supported by the Ministry of Education, Youth and Sports of the Czech Republic grant Talking microbes—understanding microbial interactions within One Health framework (CZ.02.01.01/00/22_008/0004597).
The Society for the Protection of Underground Networks (SPUN) is a science-based initiative launched in 2021 to map and advocate for the protection of the mycorrhizal communities that regulate Earth’s climate and ecosystems.
These fungi form extensive networks of mycelium in soils, where they establish intimate associations with plant roots. The fungal threads forage for nutrients in the soil and trade them with plants in exchange for carbon, with global transfers estimated to reach roughly one billion tons of carbon per year.
Credit
Loreto Oyarte Gálvez - VU Amsterdam, AMOLF, SPUN
Colored areas on the map indicate ecoregions without publicly available AM fungal sequencing data. More than 70% of terrestrial ecoregions remain unsampled for AM fungi. Across those ecoregions where sampling has occurred, the mean number of samples per ecoregion is only four, highlighting limited replication even in represented regions. These colored regions represent priority targets for future field expeditions and coordinated sampling efforts.
Credit
SPUN
Journal
FEMS Microbiology Letters
Method of Research
Data/statistical analysis
Subject of Research
Not applicable
Article Title
Advancing knowledge on the biogeography of arbuscular mycorrhizal fungi to support Sustainable Development Goal 15: Life on Land
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