Why mycorrhizal fungi matter for forests and climate
Plants route an estimated 13.12 gigatons of carbon dioxide equivalent to mycorrhizal fungi every year, roughly 36% of annual fossil fuel emissions, according to a 2023 analysis in Current Biology led by Heidi Hawkins of the University of Cape Town. How long that carbon stays underground is still being studied, since some remains in fungal tissue while the fungus lives and after it dies, and some returns to the air through respiration. "Mycorrhizal fungi represent a blind spot in carbon modelling, conservation, and restoration," Katie Field, professor of plant-soil processes at the University of Sheffield and a co-author of the study, said in a statement.
The fungi also track closely with how fast forests grow. Across more than 13,000 trees in 15 European countries, differences in ectomycorrhizal fungal communities were linked to a threefold difference in tree growth rates, even after accounting for climate, stand age, and nitrogen deposition, researchers reported in The ISME Journal in 2022. The authors wrote that it may be too early to say whether the fungi drive that growth or reflect soil conditions that favor it.
Where mycorrhizal partnerships are found
Climate largely sets which partnership dominates a forest. Ectomycorrhizal trees prevail where cold or dry seasons slow decomposition, especially at high latitudes and elevations, and arbuscular mycorrhizal trees dominate warm tropical forests with little seasonal change, according to the 2019 Nature study that mapped forest symbioses from more than 1.1 million inventory plots.
In 2025, SPUN released the Underground Atlas, built from more than 2.8 billion fungal DNA sequences sampled in 130 countries. Its maps flag hotspots of fungal richness in places such as the foothills of Ethiopia's Simien Mountains and the Cerrado savanna of central Brazil, and the accompanying study found that only 9.5% of these hotspots lie within protected areas.
Mycorrhizal fungi risks and challenges
Land use changes the soil these fungi depend on. Croplands carry roughly half the arbuscular mycorrhizal network density of wild ecosystems. "Fungi have been ignored in climate and conservation for too long," Toby Kiers, SPUN's executive director, said when the study was released.
Researchers also disagree over how much trees share through these networks. In a 2023 review in Nature Ecology & Evolution, University of Alberta associate professor Justine Karst and her co-authors found too little field evidence to show that shared fungal networks are widespread in forests, and no peer-reviewed field study showing that mature trees preferentially send resources to their offspring through them, the researchers wrote. Karst said in a University of Alberta statement that "many popular ideas are ahead of the science."
The future of mycorrhizal fungi in forest restoration
Restoration teams are beginning to plan for what lives below the seedlings they put in the ground. In the UK, Forest Research is testing ways to speed the return of woodland fungi to former farmland, including planting shrubs and trees that partner with arbuscular fungi alongside species that rely on ectomycorrhizal ones.Β
SPUN's global maps now give those efforts a reference point for what healthy underground communities look like in a given place. "This study is an exciting step towards understanding how this planetary circulatory system operates," biologist Merlin Sheldrake, a co-author of the 2026 Science study, said in a statement, "and suggests ways that we can better work with fungi to help address many of the unfolding challenges of our times, from food security to climate change."
