A global study published in Science estimates that the top 15 centimeters of Earth's soils contain a vast network of arbuscular mycorrhizal fungi. The mapping reveals the importance of grasslands, the fungi's contribution to the carbon cycle, and the potential damage caused by intensive agriculture.
Most of the body of themushrooms It is not found in the cap mushrooms we see above.ground, but in tiny webs of webs that penetrate the soil. A new global study estimates for the first time the dimensions of one of the largest biological infrastructures on Earth: the networks of arbuscular mycorrhizal fungi, which live in partnership with the roots of most terrestrial plants.
According to the study, published in the journal Science, the top 15 centimeters of the world’s soil contains about 110 quadrillion kilometers of living webs – 110 thousand trillion kilometers. If they could be laid out in a straight line, their length would be almost a billion times greater than the distance between the Earth and the sun.
The huge number is not a direct measurement of all the cold in the world, but an estimate based on soil samples, microscopic measurements and climate models. Machine learningDespite the uncertainties involved in global mapping, the study provides the first quantitative picture of the hidden fungal infrastructure that nourishes plants and transfers carbon to the soil.
A partnership more than 450 million years old
Arbuscular mycorrhizal fungi interact with about 70% of terrestrial plant species. Their thin webs penetrate soil volumes that plant roots have difficulty reaching, drawing water and minerals, including phosphorus and nitrogen, from there.
In return, the plants transfer carbon compounds they have produced through photosynthesis to the fungi. This partnership is very ancient, and likely played an important role in the establishment of the first plants on land more than 450 million years ago.
The webs, called hyphae, are ten to fifty times thinner than a human hair. With them, the fungus can greatly increase the search area of the root system. In healthy soils, the web may expand the plant's nutrient collection area by up to a hundredfold and provide a large portion of the phosphorus it needs.
More than 16 thousand soil samples
To prepare the map, the researchers collected data from more than 16 cores and soil samples taken from thousands of sites, including forests, Grasslands, deserts, tundra and agricultural areas.
Existing data wasn't enough to cover every region of the planet, so the team combined information on climate, vegetation, and soil chemistry into machine learning models that estimated web densities even in places not directly sampled.
To calculate mass and length, it is necessary to know not only how many webs are present in a given volume of soil, but also their diameter. At the AMOLF Institute for Biophysics in Amsterdam, researchers operated a robotic imaging system that performed more than 300 measurements of living webs grown in the laboratory.
Combining the measurements revealed that the networks contain about 300 million tons of carbon. The researchers created maps at a resolution of one square kilometer for most of the continents covered by vegetation, along with uncertainty maps that clarify where predictions are less well-founded due to a lack of samples.
Grasslands are a global hotspot
One might expect the densest networks to be found in rainforests, where the above-ground biomass is enormous. But the map paints a different picture: natural grasslands contain an estimated 40% of the global arbuscular mycorrhizal fungi infrastructure.
Particularly high densities were observed in the flooded grasslands of South Sudan, the Florida Everglades, and the Tibetan Plateau. On average, natural grasslands had web densities more than a third higher than those in tropical broadleaf forests.
The figure highlights that carbon and biodiversity conservation is not just a matter for forests. Grasslands store much of their carbon below ground, in roots, soil and in partnerships with fungi. As a result, they may be more resilient than forests to rapid carbon loss from fires, storms or canopy damage.
About four billion tons of carbon dioxide per year
The new study focused on the density and biomass of the webs, but it also builds on previous estimates of carbon flow between plants and fungi. According to the researchers, arbuscular mycorrhizal fungi transfer an amount of carbon equivalent to about four billion tons of carbon dioxide to the soil each year.
This does not mean that all of this carbon remains in the soil permanently. Some of it is used for fungal respiration, some is transferred to other organisms, and some is returned to the atmosphere. However, the flow demonstrates the centrality of fungi inThe carbon cycle And in transferring energy from the plants to the underground system.
The researchers say fungi are often overlooked in climate and conservation policies because they are difficult to see and measure. The new map is intended to provide a basis for monitoring, comparing regions, and identifying underground systems in need of protection.
In agricultural lands, low density was found in about half of
One of the worrying findings is that in large agricultural areas, the predicted network density is on average about 50% lower than in similar natural systems.
The study does not prove which agricultural practice is responsible for the decline. However, deep and frequent plowing can tear the webs, heavy use of phosphorus and nitrogen fertilizers can reduce the plant's dependence on the fungus, and fungicides can harm soil communities.
When networks are thinner, soil may lose some of its ability to transport nutrients, maintain a stable structure, store carbon and help plants cope with drought and other stresses. The researchers emphasize that more research is needed to separate the effects of climate, soil types, crops and tillage practices.
The map can serve as a basis for studies that will examine whether reduced tillage, cover crops, crop rotations, and more moderate use of fertilizers and fungicides allow the networks to recover.
Not every network is an "Internet of Trees"
Public interest in fungal networks has given rise to the nickname "Wood Wide Web" and the idea that trees use fungi to transmit food, warnings, and assistance to other plants.
There is evidence that mycorrhizal networks connect roots and that materials can pass through them. However, there is insufficient evidence to describe the network as a deliberate or altruistic communication system in which trees "decide" to help each other.
The current study also does not examine message transmission between plants. It estimates the length, mass, and distribution of a particular type of fungal web. Its importance is in establishing a global baseline, not in proving claims about social behavior in trees.
First map, but not yet complete
The model provides estimates per square kilometer of vegetated areas, but the quality of the predictions depends on the density of sampling. Large areas, especially in parts of the tropics, deserts, and countries where ecological research is limited, are still underrepresented.
In addition, the estimate focuses on mushrooms Arbuscular mycorrhiza and in the topsoil. It does not include all fungal species, deeper networks, or other types of mycorrhizal fungi.
Despite the limitations, the researchers see the map as a first step toward incorporating fungi into soil health assessment, restoration, and ecological systems, in agricultural planning and climate policy. It shifts the discussion from the general question of whether fungi are important to a more focused question: where are the densest networks located, where are they being damaged, and how can they be protected.
Questions and Answers
What are arbuscular mycorrhizal fungi?
These are soil fungi that live in partnership with plant roots. They transfer water and minerals to the plant, and in return receive carbon compounds created by photosynthesis.
How did the researchers arrive at a length of 110 quadrillion kilometers?
They combined measurements of web density in more than 16 soil samples with microscopic measurements of web diameter and machine learning models. The result is a global estimate, not a direct measurement of each web.
Why are grasslands so important?
According to the model, about 40% of the global biomass of these fungi is found in grasslands. Herbaceous plants have extensive root systems and may transfer a relatively high proportion of their carbon to their fungal partners.
Are mushrooms permanently burying four billion tons of carbon every year?
No. This is an estimate of the amount of carbon dioxide equivalent transferred from plants to fungi and soil. Some of the carbon is stored, but some is consumed and released again.
Why are networks thinner in agriculture?
The study found a link between agricultural land and lower density, but did not pinpoint a single factor. Ploughing, over-fertilisation, fungicides and simple cropping patterns are among the possible explanations.
Does the study prove the existence of an "Internet of Trees"?
No. It maps the density of webs and their biomass. Questions about the transfer of food or signals between plants require other experiments, and the evidence for broad claims in the field is still limited.
The scientific article and original publications
For the scientific article:
Global density and biomass of arbuscular mycorrhizal fungal networks
For the original publication by SPUN and EurekAlert:
First global map of mycorrhizal fungi reveals the scale of underground networks
For the interactive map of the fungal infrastructure:
