Beneath every square meter of forest soil runs a network of fungal filaments, denser than any human-made circuit. These mycorrhizal fungi form symbiosis with roughly 80 percent of all land plants: the plant supplies sugar, the fungus unlocks nutrients and water. What biologists have only grasped in full dimension over recent years is a third service this partnership provides: it extracts massive amounts of carbon from the atmosphere and locks it in soil. The figures cited in a 2023 study exceed the CO2 uptake of all of Earth's forests or oceans combined.
What 13 Billion Tonnes Mean
A meta-analysis published in Current Biology, led by Toby Kiers from Vrije Universiteit Amsterdam and Katie Field from the University of Sheffield, evaluated 194 datasets from 61 research papers. Result: land plants transfer approximately 13.12 billion tonnes of CO2 equivalents annually to their fungal partners. This corresponds to approximately 36 percent of annual global emissions from fossil fuels, according to the team's calculations.
For comparison: forests bind approximately 7.6 billion tonnes of CO2 per year net, according to World Resources Institute estimates, after accounting for forest fires and logging emissions. Oceans absorb roughly 8.8 billion tonnes of CO2 annually, according to the US atmospheric agency NOAA. The amount transferred to fungi exceeds both individual values. However, the figure describes what is transferred, not necessarily what remains permanently stored. The authors themselves emphasize their estimate is conservative and the final net storage capacity remains undetermined.
The key mechanism is glomalin: a glycoprotein produced by arbuscular mycorrhizal fungi that acts like a natural adhesive. It binds soil minerals into stable aggregates, protecting enclosed carbon from microbial breakdown. Studies published in Functional Ecology in 2026 demonstrate that glomalin can hold carbon in soil for decades to centuries.
Toby Kiers and Mapping the Invisible
Toby Kiers is an evolutionary biologist and co-founder of SPUN, the Society for the Protection of Underground Networks. Founded in 2021, the organization coordinates 137 researchers worldwide who map local mycorrhizal networks to create a global "Underground Atlas." In January 2026, SPUN launched the Underground Advocates Program, bringing together scientists and legal experts to translate findings into concrete conservation action.
In April 2026, Kiers received the Tyler Prize for Environmental Achievement, a 250,000-dollar award considered the Nobel Prize for the environment. She is the youngest woman ever to receive it. Kiers' core thesis: climate protection focused on forests and oceans while ignoring the ecosystem beneath the soil surface misses half the picture.
In Comparison: Why Underground Ecosystems Were Overlooked
Forests were long underestimated before the IPCC designated them as priority carbon sinks beginning in 2001. The same applies to wetlands: peatlands globally store approximately 550 billion tonnes of carbon according to estimates from the International Peatland Conservation Group, twice as much as all forests combined. Yet peatlands were considered harmful for decades and were drained. Fungal networks appear in no national greenhouse gas registry and hold no official status in any protection regime.
SPUN has systematically documented this situation. The Underground Atlas reveals: mycorrhizal hotspots, regions with particularly diverse and dense fungal communities, frequently coincide with biodiversity hotspots for plants and animals. This means protecting mycorrhizal networks and protecting visible species diversity would largely align in practice. What is missing is legal protection status.
What Intensive Agriculture Does
The good news carries a serious downside. Intensive farming with frequent ploughing mechanically destroys fungal networks, as fine hyphae rupture faster than they can regrow. Chemical fertilizers reduce crop dependence on fungal symbiosis: roots can absorb nutrients directly and no longer need fungal partners. According to SPUN research, organically managed fields contained 27 identifiable key species of mycorrhizal fungi. In conventionally managed fields in the same area: none.
Certain herbicides and fungicides further inhibit spore germination. Glyphosate and azoxystrobin are considered particularly harmful to mycorrhizal communities. Kiers views protecting underground networks not simply as a biodiversity project but as a climate issue: when cropland loses its mycorrhizal community, it simultaneously loses part of its carbon storage capacity.
The extent to which restoration measures can recover fungal communities remains under investigation. SPUN aims to achieve global protection status for major fungal hotspots by 2030, analogous to what exists for old-growth forests and coral reefs. Whether this succeeds depends on political will, which Kiers is currently building through the Underground Advocates Program.