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Fungiecological relationship

Mycorrhizal networks

The fungi are real, the connections are real, and carbon does move. Whether anybody is sharing is a different question, and it is still open.

Fungi join the roots of different plants, and carbon and nutrients move along those connections — that much is measured. What is disputed is how much reaches the neighbouring plant rather than staying in the fungus, and whether anything about it resembles sharing.

This is the clearest case in NatureHQ of a story travelling much further than its evidence, and it is worth reading precisely because the underlying science is genuinely good. Almost every land plant forms a partnership with fungi at its roots, trading sugars and fats for phosphorus, nitrogen and water. In a forest those partnerships overlap, so the trees are physically joined below ground by an organism neither of them is. Field experiments have labelled carbon in one tree and recovered it in another. From there, popular books and documentaries built a picture of forests as cooperative communities in which old trees recognise their own seedlings and feed them through a fungal internet. In 2023 a systematic review examined that literature and found three headline claims — that such networks are widespread in forests, that they transfer resources in quantities that matter, and that trees preferentially nourish kin — running well ahead of the data, with citations growing more confident over time while the evidence did not. The best experiments in the field, meanwhile, describe something less comforting and more interesting than cooperation: a trade, in which each partner supplies preferentially to whoever supplies it.

In-depth coverage · 98% complete · reviewed 2026-08-30

Quick facts

What it is
Fungal hyphae linking the roots of two or more plants
What is exchanged
Plant sugars and fats for fungal phosphorus, nitrogen and water
Outcome for the plant
Runs from a large benefit to a net cost, depending on conditions
Mother tree hypothesis
Not established; citation record ran ahead of the evidence

What the "wood wide web" actually is

A physical structure, before it is anything else.

The short answer

What is the wood wide web?

Fungal threads finer than the finest root, joining the roots of different trees into a shared physical network. Carbon and nutrients move through it. Whether that amounts to trees sharing food is the part still being argued.

Take the phrase apart and four separate claims fall out of it, each with its own evidence. That plants and fungi are joined at the root: established, near-universal, ancient. That one fungal individual can connect two plants: established in many cases, though mapping which fungus links which trees in a real forest is genuinely difficult. That material moves along those connections: measured repeatedly with isotopes. That the movement constitutes trees feeding one another: not established — much of the label recovered from a receiving root sits in the fungus occupying it rather than in the plant, and nothing has shown a donor doing anything it would not otherwise do. NatureHQ treats the first three as real and the fourth as open, which is also where the field is.

Check it for yourself

Diagram

Where a fungus meets a root

The two main partnership types, and what crosses between them. Not to scale; a hypha is far finer than the finest root.

Arbuscular mycorrhizamost plant families; the hypha enters the cellroot cortex cellarbuscule — branched, inside thewall but outside the membraneEctomycorrhizapines, oaks, birches; no hypha enterssheathHartig net,between cellsWhat is exchanged at that interfacePlantsugars and fatsphosphorus, nitrogen, waterFungusThe exchange is measured. Whether either partner is doing the other a favour is a separatequestion, and the outcome for the plant runs from strongly positive to negative.
The same explanation in words

Two panels showing the interface between a fungus and a root. The left panel, arbuscular mycorrhiza — the type formed by most plant families — shows a fungal hypha approaching a root cortex cell from outside, passing through the cell wall and branching repeatedly inside it into a tree-shaped structure called an arbuscule. The label notes that the arbuscule sits inside the wall but outside the cell membrane, so the fungus never enters the living interior of the cell. The right panel, ectomycorrhiza — the type formed by pines, oaks and birches — shows no penetration at all: a sheath of fungal tissue wraps the outside of the root tip, and hyphae grow between the cortex cells, forming the network known as the Hartig net, with more hyphae extending outward into the soil. Beneath both panels a summary of what is exchanged: sugars and fats pass from the plant to the fungus, and phosphorus, nitrogen and water pass from the fungus to the plant. A closing note records that the exchange is measured, that whether either partner is doing the other a favour is a separate question, and that the measured outcome for the plant runs from strongly positive to negative.

The reason the partnership is worth having is a matter of scale. A fungal thread is a few micrometres across, far finer than the finest root hair, and it reaches into soil pores no root can enter. In exchange the plant hands over sugars and fats — a real and continuous cost, amounting in some systems to a substantial share of everything it fixes. The network in a forest is not a designed structure; it is what happens when many overlapping root systems are each colonised by fungi that are themselves spreading.

Words used here
Mycorrhiza
A partnership between a fungus and a plant root. The fungus supplies water and minerals; the plant supplies sugars and fats.
Hypha
A single fungal thread. A mass of them is called mycelium.
Arbuscule
The branched structure a fungus builds inside a root cell wall, where most of the exchange happens. It never crosses the cell membrane.

It is a trade, not a favour

The best experiment in this field describes a market, and it runs in both directions.

Plants and fungi each send more to whichever partner sends more back. Nobody is being generous.

Well supported

Good evidence backs this, though some details remain open.

In isotope-labelled experiments offering plants a choice of fungal partners and fungi a choice of hosts, each partner allocated resources preferentially to the more reciprocating counterpart, in both directions within the same system.

Who this applies to
Arbuscular mycorrhizas in simplified laboratory systems, including root-organ cultures.Do not extend this beyond the taxa listed — the popular version over-reaches.
Studied in
Glomeromycota, Medicago truncatula

You may have heard

“Fungi feed trees, and trees feed fungi back.”

Both halves describe a flow, and the flows are real. What the experiments show is that each side supplies preferentially to whoever supplies it — a trade that stays stable because freeloading is unprofitable, not an exchange of favours.

Why we rate it this way, and what the caveats are
Well supportedModerate confidence

A well-designed experiment with labelling in both directions and a clear result, but conducted in simplified systems and not yet extended to the forest symbioses most readers have in mind.

How far it can be extended

Ectomycorrhizal partnerships, which dominate temperate and boreal forests, involve different structures and have not been shown to behave the same way.

Caveats

  • Preferential allocation does not require either organism to be choosing anything; local responses to local conditions are sufficient.
  • Demonstrated in arbuscular systems; the ectomycorrhizal case is open.

Still unanswered

  • How either partner senses what the other is supplying.
  • Whether reciprocal reward operates in ectomycorrhizal forest trees.

Last reviewed 2026-08-30

The evidence (2 studies)

How we know

Giving a root a choice of fungi, and a fungus a choice of roots

Is the exchange between a plant and its fungus generosity, or is each side paying the better supplier?

Roots were grown in contact with more than one fungal partner at a time, and fungi with more than one host. The phosphorus each fungus delivered and the carbon each plant supplied were labelled with distinguishable isotopes, so the flows could be followed in both directions at once. Some partners were then experimentally handicapped — supplied with less phosphorus to pass on, or with a host less able to supply carbon — so that a good partner and a poor one sat side by side on the same root.

What happened

Each side sent more to whichever partner was sending more back. Plants moved carbon preferentially to the more generous fungus; fungi moved phosphorus preferentially to the more generous root. The bias appeared in both directions in the same system.

What it shows

The symbiosis is stabilised by reciprocal reward rather than by either side simply giving. That is a mechanism that keeps freeloaders from taking over, and it explains how a partnership this old survives partners that vary in quality.

What it does not show

It does not show how either partner senses the other’s contribution, and it does not license the language of choice or fairness — nothing here requires either organism to be doing anything but responding locally to local conditions. These were also simplified laboratory systems with arbuscular fungi, and the ectomycorrhizal partnerships that dominate temperate forests were not tested.

The controls — what makes this evidence rather than a story
  • Isotope labelling in both directions, so allocation could be measured rather than inferred from growth.
  • Good and poor partners were present on the same individual, removing plant-to-plant variation from the comparison.
  • Root-organ cultures were used alongside whole plants, separating what the root does from what the shoot might be directing.

From Reciprocal rewards stabilize cooperation in the mycorrhizal symbiosis

Nothing in that result requires either organism to be choosing anything. Local responses to local conditions produce it, and that is what makes it a stable arrangement rather than a fragile one: a partner that takes without giving gets less, automatically, with nobody enforcing it. Reciprocal reward is a better explanation of a partnership four hundred million years old than generosity would be, because generosity is exactly the strategy that invites exploitation.

Words used here
Biological market
A relationship in which partners allocate resources preferentially to whoever gives most in return, so that the exchange stabilises without any enforcement.

Sometimes it costs the plant more than it is worth

Being colonised by mycorrhizal fungi helps some plants a great deal and costs others.

Established

Specialists would state this without hedging. Multiple independent lines of evidence agree.

Meta-analysis of inoculation experiments finds plant biomass responses ranging from strongly positive to negative, varying systematically with plant functional group, fungal group and above all nutrient supply — plants already well supplied with phosphorus frequently show no benefit.

Who this applies to
Inoculation experiments, dominated by short-term pot studies with young plants.
Studied in
Glomeromycota, Basidiomycota, Tracheophyta

You may have heard

“Mycorrhizal fungi help plants grow.”

Sometimes, and substantially. But the measured range runs to negative: a fungus taking sugar from a plant that already has plenty of phosphorus is charging for a service the plant does not need. Mutualism here is an outcome that depends on conditions, not an identity.

Why we rate it this way, and what the caveats are
EstablishedHigh confidence

A large meta-analysis with a result that is systematic rather than noisy: the variation is predictable from conditions, which is stronger evidence than a uniform average would be.

How far it can be extended

The context-dependence is found across plant and fungal groups in a large pooled analysis, and the mechanism — the value of what the fungus supplies depends on how scarce it is — applies generally.

Caveats

  • Pot experiments with young plants may not represent long-lived trees in the field.
  • Biomass response is not the same as fitness.

Still unanswered

  • How outcomes are distributed for forest trees over decades, which no experiment has yet measured.

Last reviewed 2026-08-30

The evidence (2 studies)

The logic is straightforward once stated: the fungus is selling phosphorus, and the value of phosphorus depends on how scarce it is. A plant on poor soil with coarse roots gains a great deal. A well-fertilised plant that can reach its own nutrients is paying sugar for a service it does not need, and the pooled experiments show exactly that — the measured response runs from strongly positive to negative, and where a given pairing lands is predictable from conditions rather than random.

Mutualism here is an outcome, not an identity. The same fungus and the same plant can be a good partnership on one soil and a bad one on another.

Based on Being colonised by mycorrhizal fungi helps some plants a great deal and costs others.

What moves between plants, and how we know

The experiments that made this famous label carbon in one plant and look for it in another. In 1997 a field experiment using two isotopes found net transfer between birch and fir seedlings sharing ectomycorrhizal fungi. In 2016 an experiment labelled the canopies of mature spruce in a Swiss forest and recovered the label in neighbouring trees of four other species. Those are real results in real forests, and NatureHQ carries them as such.

Carbon does move between trees below ground

Well supported

Good evidence backs this, though some details remain open.

Isotope-labelling experiments in the field have detected movement of carbon between trees of different species, including between mature trees, with mycorrhizal fungi the most likely route.

Who this applies to
the temperate forest tree species tested so far
Studied in
Betula papyrifera, Pseudotsuga menziesii, Picea abies, Fagus sylvatica
Why we rate it this way, and what the caveats are
Well supportedModerate confidence

That carbon moves is well evidenced by two independent field experiments. What is far less certain is how much, by which route, and whether the receiving tree benefits at all.

How far it can be extended

Detected independently in North American and European forests, in seedlings and in mature trees, using different labelling approaches.

Caveats

  • Carbon found in a neighbour's roots may have been used by the fungi rather than by the tree.
  • Net transfers measured were small relative to a tree's total carbon budget.
  • Labelling designs struggle to exclude movement through soil rather than through fungi.

Still unanswered

  • How much of the transferred carbon is actually used by the receiving tree?
  • Is the fungus a conduit, a trader, or the main beneficiary?

Last reviewed 2026-08-09

The evidence (2 studies)

In pot experiments, plants connected by fungi respond to a neighbour being attacked

Emerging evidence

Real findings exist, but too few or too recent to be settled.

Broad bean plants connected by intact mycorrhizal mycelium produced aphid-repellent and parasitoid-attracting volatiles when a connected neighbour was infested; plants whose fungal connections were severed did not.

Who this applies to
broad bean plants with one fungal species, in pots
Studied in
Vicia faba

You may have heard

“Plants talk to each other through the wood wide web.”

A controlled pot experiment showed defensive chemistry appearing in a connected neighbour and not in a disconnected one, which is a real and careful result. Turning that into forests holding conversations skips several unanswered questions, starting with what the signal is.

Why we rate it this way, and what the caveats are
Emerging evidenceModerate confidence

The mesh design cleanly separates fungal connection from soil chemistry, which makes the result credible. It is one crop species, one fungus, in pots, with the signal itself unidentified.

Caveats

  • Both experiments are pot studies with crop species and a single fungal partner.
  • Neither design can separate a signal that was sent from a compound leaking into a shared conduit and being overheard.
  • The nature of the transmitted signal is unknown.
  • No demonstration that this operates at meaningful scales in a wild ecosystem.

Still unanswered

  • What is the signal?
  • Does anything comparable happen in a forest, where networks are far more complex?

Last reviewed 2026-08-09

The evidence (2 studies)

How we know

A mesh that lets a fungus through but not a root

If one plant is attacked, can a neighbour joined to it only by fungal threads respond before it is attacked itself?

Pairs of tomato plants were grown in pots divided by mesh. In one treatment the mesh had pores large enough for fungal hyphae to pass but too small for roots. In another the pores were too small even for hyphae. In a third the pairs were left unconnected. One plant of each pair was then infected with a leaf blight, and several days later the untouched neighbour was tested for defence gene activity and then challenged with the same pathogen.

What happened

Neighbours connected by hyphae switched on defence genes and subsequently suffered less disease. Neighbours whose hyphal connection was blocked did not.

What it shows

Something that changes a receiving plant’s defences moves along a fungal connection between two plants. The mesh design makes that a fairly clean result about the route.

What it does not show

It does not show that anything was sent. A compound leaking from a stressed plant into a shared conduit, and a neighbour detecting it, produces this result without any signalling on the donor’s part — the difference between being addressed and being overheard, which this design cannot separate. It also does not show that the effect occurs in a forest: these were two crop plants in a divided pot with one fungal partner.

The controls — what makes this evidence rather than a story
  • Roots were physically excluded in every treatment, so a root-to-root route cannot explain the result.
  • Mesh treatments differed only in pore size, holding soil, water and pot geometry constant.
  • Uninfected donor pairs were included, so the response is to the infection rather than to the presence of a neighbour.

From Interplant communication of tomato plants through underground common mycorrhizal networks

Words used here
Isotope labelling
Feeding a plant carbon dioxide made with an unusual form of carbon, so that anything built from it afterwards can be identified as having come from that plant.

The problem nobody has solved

A label found in a root can be in the plant, or in the fungus threaded through it.

When labelled carbon turns up in a neighbouring tree, much of it is sitting in the fungus rather than in the tree.

Contested

Researchers actively disagree, and the disagreement is substantive.

Reanalysis of isotope-labelling experiments found that most label recovered from a receiving plant’s roots was accounted for by fungal tissue occupying those roots rather than by carbon incorporated into plant tissue, and that net transfer into recipient plants, where resolvable, was small relative to the recipient’s own carbon budget.

Who this applies to
Isotope-tracing experiments on plant-to-plant carbon movement through shared fungal networks.Do not extend this beyond the taxa listed — the popular version over-reaches.
Studied in
Glomeromycota, Tracheophyta

You may have heard

“Trees share food through the wood wide web.”

Carbon does move along fungal connections. Whether it arrives in the neighbouring tree, in what quantity, and whether the neighbour is any better off are separate questions — and the measurement that would answer them struggles to tell carbon inside a root from carbon inside the fungus filling it.

Why we rate it this way, and what the caveats are
ContestedModerate confidence

The measurement problem is real and has never been fully resolved: a label in a root can be in the plant or in the fungus growing through it. Later work using methods that separate the compartments better has reached a range of conclusions, and a 2023 review found the citation record running well ahead of the underlying data.

How far it can be extended

Some ectomycorrhizal systems have since reported larger fluxes, and the magnitude remains disputed rather than settled in either direction.

Caveats

  • That carbon moves through the network is not in dispute. What is disputed is how much reaches plant tissue and whether it matters to the recipient.
  • A quantity too small to affect a mature tree may still matter to a seedling in deep shade.

Where researchers disagree

  • Field labelling of mature trees has recovered substantial quantities of label in neighbours, while reanalyses of pot experiments conclude that net transfer into plant tissue is minimal — and the two are hard to compare because the methods resolve the plant–fungus boundary differently.
  • Whether the fungus should be treated as an intermediary or as a destination is itself unsettled, and it changes what "transfer between trees" means.

Still unanswered

  • How much transferred carbon is incorporated into recipient plant tissue under field conditions.
  • Whether transfer is ever large enough to affect the survival or growth of the receiving plant.

Last reviewed 2026-08-30

The evidence (4 studies)

This is why a question that sounds simple has stayed open for thirty years. A root in a forest is thoroughly occupied by fungus. Recover a label from that root and you have found carbon that left the donor tree — but if it stopped at the fungus, nothing moved between trees at all: the fungus was simply paid twice. A 1999 reanalysis concluded that most of the label recovered in these experiments was accounted for by fungal tissue, and while later field work using better methods has found larger fluxes, the boundary has never been cleanly resolved.

A second problem is not about measurement at all. Even a demonstrated flow into recipient tissue would not establish provisioning: resources move down gradients, and a large tree in full light beside a small one in shade is a gradient. Getting from "carbon moved" to "a tree fed another tree" requires the donor to be doing something it would not otherwise do, and no experiment has shown that.

What the reviews found, and why it matters beyond forests

The idea that "mother trees" deliberately feed their own seedlings is not supported by the evidence

Contested

Researchers actively disagree, and the disagreement is substantive.

Systematic and critical reviews find that three widely repeated claims — that common mycorrhizal networks are ubiquitous in forests, that they transfer resources to seedlings in quantities that matter, and that mature trees preferentially supply related seedlings — are not supported by the primary literature, and that citation patterns have amplified positive results.

Who this applies to
the temperate forest systems where the idea originatedDo not extend this beyond the taxa listed — the popular version over-reaches.
Studied in
Pseudotsuga menziesii, Betula papyrifera, Picea abies

You may have heard

“Forests are connected by a wood wide web through which mother trees feed their young.”

The underlying observation — carbon moving between trees below ground — is real. The elaboration into deliberate, kin-directed nurture came from popular books and documentaries rather than from the measurements, and two independent reviews have now found the specific claims unsupported. It is an unusually clear case of a story travelling faster than its evidence.

Why we rate it this way, and what the caveats are
ContestedModerate confidence

Two independent reviews reached similar conclusions, which is significant. They are reviews rather than new data, researchers in the field dispute their framing, and absence of strong evidence is not proof the phenomena are absent.

How far it can be extended

The reviews concern the specific systems the original claims were built from. Extending either the claim or its rebuttal to forests generally would repeat the error being criticised.

Caveats

  • This does not mean fungal networks are fictional, or that carbon does not move between trees.
  • The reviews are literature analyses, not new field measurements.

Where researchers disagree

  • Researchers associated with the original work dispute the reviews' framing and argue that the evidence base is stronger than the reviews allow.
  • Field experiments do detect below-ground carbon movement, so the disagreement is about scale, direction and function rather than about whether anything moves at all.

Still unanswered

  • How common are common mycorrhizal networks in real forests?
  • What experiment could show whether transferred resources actually benefit a receiving seedling?

Last reviewed 2026-08-09

The evidence (3 studies)

The 2023 review did something unusual and useful: as well as assessing the evidence, it traced how the studies had been cited. Positive results were cited far more often than negative ones, and several claims had drifted well beyond what the original papers reported — a body of literature becoming more confident with each retelling while the underlying measurements stayed where they were. That mechanism is not specific to forests, and it is the most transferable thing on this page.

The popular claims, checked

Words used here
Citation bias
The tendency for results supporting an appealing conclusion to be cited more often than results that do not, which makes a body of evidence look more one-sided than it is.

A hundred and forty years of arguing about the same soil

The measurements have accumulated steadily. What has swung is the interpretation, twice.

  1. 1885

    First observation

    Frank names the mycorrhiza

    Albert Bernhard Frank, examining the roots of forest trees, described the fungal sheath around them and proposed that the two organisms were living together to mutual advantage. He coined the word, and the suggestion that a tree might depend on a fungus was treated as eccentric for decades.

  2. 1997

    Landmark experiment

    Carbon is tracked moving between trees in a forest

    A field experiment using two carbon isotopes found net transfer between birch and Douglas fir seedlings sharing ectomycorrhizal fungi, with the direction following the shading. It is the study everything downstream rests on, and it was published with a companion piece in the same issue titled "The wood-wide web" — the phrase, and the framing, arrived together.

    Net transfer of carbon between ectomycorrhizal tree species in the field

  3. 1999

    Challenge

    The measurement problem is stated, and largely ignored

    A reanalysis asked how much of the label recovered from a receiving plant was actually in the plant rather than in the fungus occupying its roots, and concluded that most of it was fungal and that net transfer into plant tissue was small. The objection was methodological, unglamorous and never answered; the field moved on.

    Changes how the 1997 result reads

    It does not dispute that label moved. It disputes what "reached the neighbouring tree" means when a root is full of fungus, which is a question the original design could not settle and which still has no clean answer.

    The magnitude and control of carbon transfer between plants linked by a common mycorrhizal network

  4. 2011

    Landmark experiment

    The relationship turns out to be a market

    Offering plants a choice of fungal partners and fungi a choice of hosts, with both flows isotope-labelled, showed each side allocating preferentially to whichever partner reciprocated. Nobody was being generous; the partnership is stabilised by both sides paying for delivery.

    Reciprocal rewards stabilize cooperation in the mycorrhizal symbiosis

  5. 2016

    Replication

    Whole canopies are labelled in a mature forest

    Rather than seedlings in pots, the canopies of mature spruce in a Swiss forest were labelled and the tracer recovered in neighbouring trees of four other species. It is the strongest field evidence that substantial quantities move, in real trees, at real size.

    Belowground carbon trade among tall trees in a temperate forest

  6. 2023

    Reinterpretation

    The citations are audited, and found running ahead of the data

    A systematic review examined the three headline claims — that these networks are widespread in forests, that transfer matters, and that trees favour kin — and traced how the underlying studies had been cited. Positive results were cited far more often than negative ones, and claims had strengthened with repetition rather than with evidence.

    Changes how the 1997 result reads

    The 1997 experiment is not overturned by this and the review does not attempt to overturn it. What is reframed is everything built on top of it: a modest, carefully bounded field result became a settled account of how forests work without the intervening evidence ever arriving.

    Positive citation bias and overinterpreted results lead to misinformation on common mycorrhizal networks in forests

What is still unknown

  • How common are linked networks in real forests?

    Why it matters: Almost every downstream claim depends on this, and it is much harder to establish than it sounds — mapping which fungal individual connects which trees is genuinely difficult.

  • Does carbon that reaches a seedling actually get used by the seedling?

    Why it matters: It is the difference between trees sharing and fungi taking a cut. Current labelling methods struggle to tell them apart.

    What would settle it: A labelling design that can track carbon into plant tissue rather than into the root zone.

  • Does reciprocal reward operate in the ectomycorrhizal partnerships that dominate temperate forests?

    Why it matters: The market experiments were done in arbuscular systems in the laboratory. The forest symbiosis everybody is arguing about is a different structure, and has not been tested the same way.

Claims about this, checked

Things people have heard, and what the evidence actually supports.

The research behind this page

22 studies, newest first. Each one has a page explaining what it found and what it could not show.

2023Nature Ecology & Evolution

Positive citation bias and overinterpreted results lead to misinformation on common mycorrhizal networks in forests

Three widely repeated claims — that such networks are widespread in forests, that resources move through them to seedlings in useful quantities, and that mature "mother trees" preferentially nourish their kin — are supported by far less evidence than their popularity suggests.

2023New Phytologist

Re-examining the evidence for the mother tree hypothesis – resource sharing among trees via ectomycorrhizal networks

The reviewed evidence does not support preferential transfer to kin at ecologically meaningful levels; isotope-labelling designs frequently cannot distinguish transfer through fungi from transfer through soil or from fungal uptake itself.

2021New Phytologist

Root traits as drivers of plant and ecosystem functioning: current understanding, pitfalls and future research needs

Root systems are far more functionally varied than the shoot traits used to classify plants would suggest, and the widely used framework of a single fast-to-slow economics axis does not describe roots well: thin roots and thick mycorrhizal-dependent roots represent genuinely different strategies rather than points on one line.

2016Science

Belowground carbon trade among tall trees in a temperate forest

The label appeared in the fine roots of neighbouring trees of different species, indicating substantial carbon movement below ground.

2015New Phytologist

Mycorrhizal ecology and evolution: the past, the present, and the future

The great majority of land plant species form mycorrhizas, in several structurally distinct types with independent evolutionary origins.

2014Nature

Belowground biodiversity and ecosystem functioning

Soil hosts an extraordinary and incompletely described diversity of organisms.

2013Ecology Letters

Underground signals carried through common mycelial networks warn neighbouring plants of aphid attack

Neighbours connected by intact fungal networks began producing aphid-repellent and parasitoid-attracting volatiles; those with severed connections did not.

2011Science

Reciprocal rewards stabilize cooperation in the mycorrhizal symbiosis

Plants directed more carbon to the fungal partners that delivered more phosphorus, and fungi directed more phosphorus to the roots that supplied more carbon.

2010PLoS ONE

Interplant communication of tomato plants through underground common mycorrhizal networks

Uninfected plants connected to an infected neighbour by fungal hyphae activated defence genes and resisted subsequent infection better than unconnected controls.

2010Trends in Ecology & Evolution

Explaining evolution of plant communication by airborne signals

The evidence best supports volatiles having evolved for within-plant signalling, with neighbouring plants acting as eavesdroppers on a cue rather than as addressees of a signal.

2010Ecology Letters

A meta-analysis of context-dependency in plant response to inoculation with mycorrhizal fungi

The response of a plant to being colonised ranged from strongly positive to negative, and the variation was systematic rather than noise: it depended on which plant, which fungus, and above all on nutrient supply.

2009Plant and Soil

Carbon flow in the rhizosphere: carbon trading at the soil–root interface

A substantial share of photosynthetically fixed carbon is released below ground by several distinct processes, of which passive leakage along a concentration gradient is a major one.

2007Proceedings of the National Academy of Sciences

Within-plant signaling by volatiles leads to induction and priming of an indirect plant defense in nature

Undamaged leaves downwind of damaged ones on the same plant increased nectar secretion and attracted more ants; blocking the airflow abolished the effect even though the leaves remained vascularly connected.

2006Annual Review of Plant Biology

The role of root exudates in rhizosphere interactions with plants and other organisms

Roots release a substantial fraction of fixed carbon into the soil as a chemically diverse exudate.

2002Ecological Monographs

The global biogeography of roots

Roots are overwhelmingly shallow.

2000Oecologia

Communication between plants: induced resistance in wild tobacco plants following clipping of neighboring sagebrush

Tobacco plants near clipped sagebrush suffered significantly less herbivore damage over the season, and the effect travelled through the air rather than through soil or root contact.

2000New Phytologist

Numerical and physical properties of orchid seeds and their biological implications

Orchid seeds are among the smallest of any flowering plant — often a few micrograms, essentially an embryo in a thin coat with no endosperm.

1999Journal of Experimental Botany

The magnitude and control of carbon transfer between plants linked by a common mycorrhizal network

Most of the transferred label was accounted for by carbon sitting in the fungal tissue inside the recipient root, not by carbon incorporated into the recipient plant.

1997Nature

Net transfer of carbon between ectomycorrhizal tree species in the field

Labelled carbon moved between birch and Douglas fir in both directions, with a modest net transfer to the shaded fir.

1995Cambridge University Press

Terrestrial Orchids: From Seed to Mycotrophic Plant

Orchid seeds contain an undifferentiated embryo and essentially no food reserve, and in nature germination requires infection by a compatible fungus that supplies carbon and minerals.

1991Forest Ecology and Management

On the maximum extent of tree roots

Lateral spread commonly reaches several times the radius of the crown, and in open-grown trees roots have been traced far outside the canopy edge.

1983Science

Rapid changes in tree leaf chemistry induced by damage: evidence for communication between plants

Undamaged plants sharing air with damaged ones increased their defensive phenolic compounds within a day or two, relative to controls in separate chambers.

This page is a stop on a longer route

A guided journey reads several subjects in a deliberate order, with an argument for why one follows another. You can join in the middle.

Where to go from here

Each of these follows from something on this page — a relationship in the evidence, a claim people ask about, or the next mechanism along.

How complete this page is, and what it is still missing

NatureHQ publishes its own gaps. This page is at 98% completeness against what we would call a finished subject, and was last reviewed on 2026-08-30. It carries 12 claims and answers 15 mapped search questions.

  • The response from researchers whose work the 2023 reviews criticised deserves fuller treatment; this page currently states the critique more fully than the reply.
  • Orchid and ericoid mycorrhizas work differently again and are covered only on the orchid page.
  • Nothing here covers how mycorrhizal communities change under fertilisation, drought or nitrogen deposition, which is where much of the current research is.