Underground Fungal Networks Are Longer Than the Distance to the Sun, Times a Billion

Beneath a single footstep in a healthy forest, thousands of fungal threads are quietly moving carbon, water, and nutrients between trees. New estimates suggest the total length of these underground networks could reach roughly 68 quadrillion miles, a figure so large it would span the distance from Earth to the Sun about a billion times over. The scale is staggering, and researchers are only beginning to understand what it means for climate stability and ecosystem health.

How Fungal Networks Connect Plants Across Entire Ecosystems

Mycorrhizal fungi form symbiotic relationships with the roots of most land plants, threading through the soil in filaments called hyphae. These hyphae are individually microscopic, but they accumulate into networks that operate at a planetary scale. The fungi trade mineral nutrients, particularly phosphorus and nitrogen, with host plants in exchange for sugars produced through photosynthesis. This exchange is ancient, dating back roughly 450 million years to when plants first colonized land, and it remains one of the most widespread biological partnerships on Earth. Scientists now recognize that these networks do not just link individual plants to individual fungi; they form interconnected webs that can link trees across an entire forest stand, routing resources toward seedlings in shade and away from stressed adults.

Carbon Sequestration at a Scale That Rivals Human Emissions

The climate implications of mycorrhizal networks may be their most consequential feature. According to research on underground fungal carbon transport, fungi move roughly 4 billion tons of carbon dioxide into soils each year, a flux equivalent to about 11% of annual human-related CO2 emissions. That figure puts fungal networks in the same conversation as major carbon sinks like the Amazon basin or the world's oceans. Separate work indicates that fungi stabilize the carbon they capture: by binding soil particles together into aggregates, fungal hyphae help lock organic matter away from decomposition. Studies of natural grasslands suggest that fungi stabilize up to 75% of plant-derived carbon in the soil, a share that dwarfs most other sequestration mechanisms. If those estimates hold up across biomes, protecting fungal networks could be as important to climate policy as protecting forests themselves.

Why Measuring Something This Large Is Genuinely Hard

Estimating the total length or carbon throughput of Earth's fungal networks requires extrapolating from a relatively small number of field measurements to the entire land surface. Researchers typically work at the scale of soil cores or experimental plots, and then apply scaling factors to arrive at global totals. Those scaling factors carry real uncertainty. Soil chemistry, climate, plant community composition, and disturbance history all affect how dense fungal networks grow and how much carbon they move. A persistent challenge, noted in recent reviews of mycorrhizal network complexity, is that laboratory experiments often fail to capture the environmental variability and complex species interactions that shape how these networks behave in the field. The jump from a controlled growth chamber to a boreal forest or a tropical savanna introduces compounding assumptions that researchers are still working to validate.

What Deforestation and Agriculture Do to These Networks

Fungal networks are not indestructible. Tillage physically shreds hyphae, which is one reason heavily tilled agricultural soils tend to store less carbon and need more synthetic fertilizer than minimally disturbed ones. Deforestation removes the host trees that fungi depend on, collapsing local networks within seasons. Fungicide use, soil compaction, and nitrogen overloading from synthetic fertilizers can all suppress mycorrhizal communities. The concern among ecologists is that land-use change is degrading these networks far faster than science can document their extent or function. If the 4-billion-ton carbon transport figure is roughly accurate, even a modest global reduction in fungal network coverage could represent a meaningful addition to atmospheric CO2, on top of the direct emissions from land clearance.

The Open Questions That Will Shape This Field

For all the excitement around these estimates, researchers are careful to note how much remains uncertain. The 68-quadrillion-mile figure is an extrapolation, not a direct measurement, and different modeling assumptions yield different totals. Scientists do not yet have a reliable global census of fungal species diversity below ground, which matters because different species move different amounts of carbon with very different efficiencies. There is also the question of what happens to mycorrhizal networks as the climate itself shifts: warming soils, changing precipitation patterns, and rising CO2 concentrations may alter the balance of this plant-fungus exchange in ways that are difficult to predict. Some models suggest warming could accelerate fungal decomposition of stored carbon rather than its sequestration, potentially flipping the network from a sink to a source. Resolving that question is one of the more urgent priorities in soil ecology right now, and it will require field experiments at a scale that matches the networks themselves.

Evidence rating

EMERGING — 76/100

Caveats:

• Funding for this study was not disclosed, limiting the ability to assess potential conflicts of interest.
• The study shows association between cohabitation and microbiome strain sharing, not a causal relationship.
• Results have not yet been independently replicated in a separate population.

Observational study examining gut and oral microbiome strain sharing across household relationships. The design shows association between cohabitation and microbial strain overlap but cannot establish causation. Independent replication has not been reported.

References

1. (2026). <em>Science</em>Adviser: Fantastic fungi could stretch from Earth to the Sun a billion times. AAAS Articles DO Group. https://doi.org/10.1126/science.aej8564
2. Beneath our feet lies a fungal superhighway stretching 68 quadrillion miles | ScienceDaily. ScienceDaily. https://www.sciencedaily.com/releases/2026/06/260615143306.htm
3. Steven P C de Goede, S Emilia Hannula, Boris Jansen, Elly Morriën (2025). Fungal-mediated soil aggregation as a mechanism for carbon stabilization. The ISME Journal. https://doi.org/10.1093/ismejo/wraf074
4. Adam Frew, Sandra Varga, Tamir Klein (2025). Mycorrhizal networks: Understanding hidden complexity. Functional Ecology. https://doi.org/10.1111/1365-2435.70063