Anectomycorrhiza (from Ancient Greek ἐκτός (ektós) 'outside' μύκης (múkēs) 'fungus' and ῥίζα (rhíza) 'root'; abbreviatedEcM;pl. ectomycorrhizae orectomycorrhizas) is a form ofsymbiotic relationship that occurs between afungalsymbiont, ormycobiont, and theroots of various plant species. The mycobiont is often from the phylaBasidiomycota andAscomycota, and more rarely from theZygomycota.^[1]

Ectomycorrhizae form on the roots of around 2% of plant species,^[1] usuallywoody plants, including species from thebirch,dipterocarp,myrtle,beech,willow,pine androse families.^[2] Research on ectomycorrhizae is increasingly important in areas such asecosystem management andrestoration,forestry, andagriculture.

Unlike othermycorrhizal relationships, such asarbuscular mycorrhiza andericoid mycorrhiza, ectomycorrhizal fungi do not penetrate theirhost'scell wall. Instead they form an entirely intercellular interfaces known as theHartig net, consisting of highly branchedhyphae forming a latticework betweenepidermal andcortical root cells.

Ectomycorrhizas are further differentiated from other mycorrhizas by the formation of a dense hyphal sheath, known as the mantle, surrounding the root surface.^[3] This sheathing mantle can be up to 40 μm thick, with hyphae extending up to several centimeters into the surrounding soil. The hyphal network helps the plant to take up nutrients including water and minerals, often helping the host plant to survive adverse conditions.^[2] In exchange, the fungal symbiont is provided with access to carbohydrates.

Although samples of ectomycorrhizas are usually taken from the surface horizon due to higher root density, ectomycorrhizas are known to occur in deep tree roots (a depth more than 2 meters), some occurring at least as deep as 4 m.^[4]

Well-known EcM fungalfruiting bodies include the economically important and edibletruffle (Tuber) and the deadlydeath caps anddestroying angels (Amanita).

Mycorrhizal symbioses are ubiquitous interrestrial ecosystems, and it is possible that these associations helped to facilitateland colonization by plants. There ispaleobiological and molecular evidence thatarbuscular mycorrhizas (AM) originated at least 460 million years ago.^[5]

EcM plants and fungi exhibit a widetaxonomic distribution across all continents (apart from Antarctica), suggesting that the EcM symbiosis has ancientevolutionary roots.^[1]Pinaceae is the oldest extant plant family in which symbiosis with EcM fungi occurs,^[6] andfossils from this family date back to 156 million years ago.^[7]

It has been proposed thathabitat type and the distinct functions of different mycorrhizas help determine which type of symbiosis is predominant in a given area.^[8] In this theory, EcM symbioses evolved in ecosystems such asboreal forests that are relatively productive but in whichnutrient cycling is still limiting. Ectomycorrhizas are intermediate in their ability to take up nutrients, being more efficient than arbuscular mycorrhizas and less so thanericoid mycorrhizas, making them useful in an intermediate nutrient situation.

Fungi are composed ofsoft tissues, makingfossilization difficult and the discovery of fungal fossils rare. However, some exquisitely preserved specimens have been discovered in the middleEocenePrinceton Chert ofBritish Columbia. These ectomycorrhizal fossils show clear evidence of aHartig net, mantle andhyphae, demonstrating well-established EcM associations at least 50 million years ago.^[7]

The fossil record shows that the more common arbuscular mycorrhizas formed long before other types of fungal-plant symbioses.^[5][9][10] Ectomycorrhizas may have evolved with the diversification of plants and the evolution ofconifers andangiosperms. Arbuscular mycorrhizas may thus have been a driving force in the plant colonization of land, while ectomycorrhizas may have arisen either in response to furtherspeciation as theEarth's climate became more seasonal and arid, or perhaps simply in response to nutritionally deficient habitats.^[10][11]

Molecular andphylogenetic analyses of fungal lineages suggest that EcM fungi have evolved and persisted numerous times from non-EcM ancestors such ashumus and woodsaprotrophic fungi.^[1] The estimates range from 7–16^[6][12][13] to ~66 independent evolutions of EcM associations.^[1] Some studies suggest that reversals back to the ancestral free-living condition have occurred,^[12] but this is controversial.^[6][10][13]

As suggested by the name, thebiomass of the mycosymbiont is mostly exterior to the plant root. The fungal structure is composed primarily of three parts: 1) the intraradical hyphae making up theHartig net; 2) the mantle that forms a sheath surrounding the root tip; and 3) theextraradical hyphae and related structures that spread throughout the soil.

The Hartig net is formed by an ingrowth of hyphae (often originating from the inner part of the surrounding mantle) into the root of the plant host. The hyphae penetrate and grow in a transverse direction to the axis of the root,^[14] and thus form a network between the outer cells of the root axis. In this region fungal and root cells touch, and this is where nutrient andcarbon exchange occurs.^[15]

The depth of penetration differs between species. InEucalyptus andAlnus the Hartig net is confined to theepidermis, whereas in mostgymnosperms the hyphae penetrate more deeply, into the cortical cells or theendodermis.^[2] In many epidermal types elongation of cells along the epidermis occurs, increasing surface contact between fungus and root cells. Most cortical type Hartig nets do not show this elongation, suggesting different strategies for increasing surface contact among species.^[2]

A hyphal sheath known as the mantle, which often has more biomass than the Hartig net interface, envelops the root. The structure of the mantle is variable, ranging from a loose network of hyphae to a structured and stratified arrangement of tissue. Often, these layers resemble plantparenchyma tissue and are referred to aspseudoparenchymatous.^[15]

Because the root is enveloped by the mantle it is often affecteddevelopmentally. EcM fungal partners characteristically suppressroot hair development of their plant symbiont.^[15] They can also increase root branching by inducingcytokinins in the plant.^[16] These branching patterns can become so extensive that a single consolidated mantle can envelop many root tips at a time. Structures like this are called tuberculate or coralloid ectomycorrhizas.^[15]

The mantles of different EcM pairs often display characteristictraits such as color, extent of branching, and degree of complexity which are used to help identify the fungus, often in tandem withmolecular analyses.^[15]Fruiting bodies are also useful but are not always available.^[2]

Extraradical hyphae extend outward from the mantle into thesoil, compensating for the suppression of root hairs by increasing the effective surface area of the colonized root. These hyphae can spread out singly, or in an aggregate arrangement known as arhizomorph. These composite hyphal organs can have a wide range of structures. Some rhizomorphs are simply parallel, linear collections of hyphae. Others have more complex organization, for example the central hyphae may be larger in diameter than other hyphae, or the hyphae may grow continuously at the tip, penetrating into new areas in a way that superficially resemblesmeristematic activity.^[2]

This part of the ectomycorrhiza, which is called the extraradical or extramatricalmycelium, functions largely as atransport structure. They often spread considerable distances, maintaining a large contact area with the soil.^[17] Some studies have shown a relationship between nutrient transport rates and the degree of rhizomorph organization.^[2][18] The rhizomorphs of different EcM types often have different organization types and exploration strategies, observed as different structure and growth within the soil.^[17] These differences also help identify the symbiotic fungus.

The hyphae extending outward into the soil from an ectomycorrhiza can infect other nearby plants.Experiments andfield studies show that this can lead to the formation of commonmycorrhizal networks (CMNs) that allow sharing of carbon and nutrients among the connected host plants.^[19][20][21] For example, the rare isotopecarbon-14 was added to a particular tree and later detected in nearby plants and seedlings.^[22] One study observed a bidirectional carbon transfer betweenBetula papyrifera andPseudotsuga menziesii, primarily through the hyphae of the ectomycorrhiza.^[23] However, not all plants are compatible with all fungal networks, so not all plants can exploit the benefits of established ectomycorrhizal linkages.^[22]

The shared nutrient connection through CMNs has been suggested to be involved with otherecological processes such as seedling establishment, forestsuccession and other plant-plant interactions. Some arbuscular mycorrhizas have been shown to carry signals warning plants on the network of attack by insects or disease.^[24][25]

Unlike most arbuscular mycorrhizal fungi, EcM fungi reproducesexually and produce visible fruiting bodies in a wide variety of forms.^[1] The fruiting body, or sporocarp, can be thought of as an extension of theextraradical hyphae. Itscell walls andspores are typically composed ofcomplex carbohydrates, and often incorporate a great deal ofnitrogen.^[26] Many EcM fungi can only form fruiting bodies and complete theirlife cycles by participating in an EcM relationship.

The fruit bodies of many species take on classic, well-recognized shapes such asepigeousmushrooms andhypogeoustruffles. Most of these produce microscopicpropagules of about 10 μm that can disperse over large distances by way of variousvectors, ranging from wind tomycophagous animals.^[27] It has been suggested that animals are drawn to hypogeous fruiting bodies because they are rich in nutrients such as nitrogen,phosphorus, minerals and vitamins.^[15] However, others argue that the specific nutrients are less important than the availability of food at specific times of the year.^[26]

Surveys of fruiting bodies have been used to assesscommunity composition andrichness in many studies. However, this method is imperfect as fruiting bodies do not last long and can be hard to detect.^[28]

To form an ectomycorrhizal connection, the fungal hyphae must first grow towards the plant's roots. Then they must envelope and penetrate theroot cap cells and infect them, allowing the symbioticHartig net and associated structures to form. Both partners (plant and fungus) must follow a precise sequence ofgene expression for this to be successful. There is evidence that communication between the partners in the early stage of ectomycorrhiza occurs in some cases viavolatileorganic compounds produced only during the interaction phase,^[29] and that genes involved insecretory, apical growth, and infection processes show changes in expression early in the pre-contact phase.^[30] Thus, a complex set of molecular changes appears to take place even before the fungus and host plant make contact.

The plant hosts releasemetabolites into therhizosphere that can triggerbasidiosporegermination, growth of hyphae towards the root, and the early steps of EcM formation.^[31] These includeflavonoids,diterpenes,cytokinins,hormones and other nutrients. Some host-released metabolites have been shown to stimulate fungal growth inPisolithus, modify the branching angle of hyphae, and cause other changes in the fungus.^[31] Some fungal genes appear to be expressed before plant contact, suggesting that signals in the soil may induce important fungal genes at a distance from the plant.^[31]

Once the fungal hyphae make contact withroot cap cells, they must continue to grow inwards to theepidermal cells and multiply to form the layers that will eventually produce the mantle. Production of the fungal mantle involves theupregulation of genes responsible fortranslation andcell growth, as well as those responsible formembranesynthesis and function, such ashydrophobins.^[32] Somepolypeptides are only found when the fungus and plant have achieved symbiosis; thesesymbiosis-related (SR) proteins are termed ectomycorrhizins.^[33]

Major changes in polypeptide andmRNA synthesis happen rapidly after colonization by the fungus, including the production of ectomycorrhizins.^[2][34] Changes include theupregulation of genes that may help new membranes to form at the symbiotic interface.^[35] The effect of the mantle on root proliferation, root hair development anddichotomous branching can be partially mimicked by fungal exudates, providing a path to identifying the molecules responsible for communication.^[31]

TheHartig net initially forms from the fullydifferentiated inner layer of the mantle, and penetration occurs in a broad front oriented at right angles to the root axis,^[14] digesting through theapoplastic space. Some plant cells respond by producing stress- and defense-relatedproteins includingchitinases andperoxidases that could inhibit Hartig net formation.^[2][31] However, extensive root colonization still occurs in these plants and these hallmarks of resistance seem to diminish by about day 21 after colonization, implying that EcM fungi can suppress the defense response.^[2]

As the fungus and plant become closely connected, they begin to share nutrients. This process is also controlled by symbiosis-related genes. For example,monosaccharide uptake inAmanita muscaria requires atransporter that is only expressed when it is in a mycorrhizal association. When the transporter is expressed, leading to increased import of sugar by the fungus, the plant host responds by increasing sugar availability. The transport ofammonium andamino acids from fungus to plant is also regulated.^[32][35]

Nitrogen is essential inplant biochemistry, being required forchlorophyll and all proteins. In most terrestrial ecosystems nitrogen is in short supply and is sequestered in organic matter that is hard to break down. Fungal symbionts thus offer two advantages to plants: the greater range of their hyphae when compared with roots, and a greater ability to extract nitrogen from thelayer of soil in which organic matter lies.^[15][36] Net transfer of nutrients to plants requires the nutrient to cross three interfaces: 1) the soil-fungus interface, 2) the fungus-apoplast interface, and 3) the apoplast-root cell interface.^[36] It has been estimated that ectomycorrhizal fungi receive approximately 15% of the host plant'sfood product and in return provide up to 86% of a host's nitrogen needs.^[27]

Some studies have shown that if there is too much nitrogen available due to human use of fertilizer, plants can shift their resources away from the fungal network.^[37][38] This can pose problems for the fungus, which may be unable to produce fruiting bodies,^[37] and over the long term can cause changes in the types of fungal species present in the soil.^[39] In one study species richness declined dramatically with increasing nitrogen inputs, with over 30 species represented at low nitrogen sites and only 9 at high nitrogen sites.^[40]

As the hyphae of the Hartig net region become more densely packed, they press against the cell walls of the plant's root cells. Often the fungal and plant cell walls become almost indistinguishable where they meet, making it easy for nutrients to be shared.^[41] In many ectomycorrhizas the Hartig net hyphae lack internal divisions, creating amultinucleartransfer cell-like structure that facilitates interhyphal transport.^[36] The hyphae have a high concentration oforganelles responsible for energy and protein production (mitochondria andrough endoplasmic reticulum) at their tips.^[42] There are signs that transporters in both fungal and plantplasma membranes are active, suggesting a bidirectional nutrient exchange.^[41]

The structure of the EcM network depends on the availability of nutrients. When nutrient availability is low, the investment in the underground network is high relative to above-ground growth.^[43] Phosphorus is another typically limiting nutrient in many terrestrial ecosystems. Evidence suggests that phosphorus is transferred largely asorthophosphate.^[41] Some mat-forming ectomycorrhizas containribonucleases capable of rapidly degrading DNA to obtain phosphorus fromnuclei.^[36]

Extraradical hyphae, particularly rhizomorphs, can also offer invaluable transport of water. Often these develop into specialized runners that extend far from the host roots, increasing the functional water access area.^[44][45] The hyphal sheath enveloping the root tips also acts as a physical barrier shielding plant tissues from pathogens and predators. There is also evidence thatsecondary metabolites produced by the fungi act as biochemical defense mechanisms against pathogenic fungi, nematodes and bacteria that may try to infect the mycorrhizal root.^[15][46] Many studies also show that EcM fungi allow plants to tolerate soils with high concentrations ofheavy metals,^[47][48][49]salts,^[50][51]radionuclides andorganic pollutants.^[15]

Although theHartig net forms outside the root cells, penetration of plant cortical cells occasionally occurs. Many species of ectomycorrhizal fungi can function either as ectomycorrhizas or in the penetrative mode typical of arbuscular mycorrhizas, depending on the host. Because these associations represent a form of symbiosis in between arbuscular mycorrhizas and ectomycorrhizas, they are termed ectendomycorrhizas.^[52]

Ectomycorrhizal fungi are found throughoutboreal,temperate andtropical ecosystems, primarily among the dominant woody-plant-producing families.^[27] Many of the fungal families common in temperate forests (e.g.Russulaceae,Boletaceae,Thelephoraceae) are also widespread in theSouthern Hemisphere and tropicaldipterocarp forests: although the plant families are quite different in temperate and tropical forests, the ectomycorrhizal fungi are fairly similar.^[53] The types of EcM fungi are affected by soil types both in the field^[54][55] and in the lab.^[56][57]

For most types of plants and animals, species diversity increases towards the equator. This is called thelatitudinal gradient of diversity (LGD).^[58] In contrast, there is evidence that EcM fungi may be at maximum diversity in thetemperate zone.^[27][59] If this is the case, it might be explained by one or more of the following hypotheses: 1) EcM fungi may have evolved at higher latitudes withPinaceae hosts, and be less able to compete intropical climates; 2) the plants EcMs use as hosts might be more diverse in temperate conditions, and the structure of the soil in temperate regions may allow for higherniche differentiation and species accumulation; and 3) tropical EcM hosts are spread out more sparsely in small isolated forest islands that may reduce the population sizes and diversity of EcM fungi.^[59]

Most EcM hosts show low levels ofspecificity, and can form symbioses with many distantly related fungi.^[60] This may have evolutionary benefits to the plant in two ways: 1) the plant's seedlings are more likely to be able to form mycorrhizas in a wide array of habitats; and 2) the plant can make use of different fungi that vary in their ability to access nutrients.^[61]

EcM fungi exhibit various levels of specificity for their plant hosts, and the costs and benefits to their specialization are not well understood.^[62][63][64] For example, the suilloid group, amonophyletic assemblage containing the generaSuillus,Rhizopogon,Gomphidius and others, shows an extreme degree of specificity, with almost all of its members forming ectomycorrhizas with members of thePinaceae.^[61] However, many other fungal groups exhibit a very broad host range.^[65][66]

Host plants that aretaxonomically related have more similar EcM fungal communities than do taxa that are more distantly related.^[67] Similarly,molecular phylogenetic studies have shown that fungi derived from acommon ancestor are more likely to have hosts that are taxonomically related.^[12][68] The maturity of the host environment, orsuccessional status, may also affect the variety of EcM fungal communities present.^[67] Other indirect factors can also play a role in the EcM fungal community, such as leaf fall and litter quality, which affectcalcium levels andsoil pH.^[69]

Plants that are not native to an area often require mycorrhizal symbionts to thrive. The vast majority of arbuscular mycorrhizas are non-specific, and so plants that interact with these mycorrhizas often becomeinvasive quickly and easily. However, ectomycorrhizal symbioses are often relatively specific. Inexoticforestry, compatible EcM fungi are often introduced to the foreign landscape to ensure the success offorest plantations.^[70] This is most common ineucalypts andpines, which areobligate ectomycorrhizal trees in natural conditions.^[70] Pines were difficult to establish in the southern hemisphere for this reason,^[71] and manyEucalyptus plantations required inoculation by EcM fungi from their native landscape. In both cases, once the EcM networks were introduced the trees were able to naturalize and then began to compete with native plants.^[70]

Many EcM species co-invade without the help of human activity, however. The familyPinaceae often invade habitats along with specific EcM fungi from the generaSuillus andRhizopogon.^[62] There are also ectomycorrhiza-forming fungi withcosmopolitan distributions which can allow non-native plant species to spread in the absence of their specific EcM fungi from the native ecosystem.^[62]

Plants can compete through attacking each other's fungal networks. Dominant native plants can inhibit EcM fungi on the roots of neighboring plants,^[72] and some invasive plants can inhibit the growth of native ectomycorrhizal fungi, especially if they become established and dominant. Invasivegarlic mustard,Alliaria petiolata, and itsallelochemicalbenzylisothiocyanate were shown to inhibit the growth of three species of EcM fungi grown onwhite pine seedlings.^[73] Changes in EcM communities can have drastic effects on nutrient uptake and community composition of native trees, with far-reaching ecological ramifications.^[63]

Competition among EcM fungi is a well-documented case ofsoil microbial interactions.^{[74][75][76][77]} In some experiments, the timing of colonization by competing EcM fungi determined which species was dominant. Manybiotic andabiotic factors can mediate competition among EcM fungi, such as temperature, soil pH,soil moisture, host specificity, and competitor number, and these factors interact with each other in a complex way.^[75][76] There is also some evidence for competition between EcM fungi and arbuscular mycorrhizal fungi. This is mostly noted in species that can host both EcM and AM fungi on their roots.^[78]

Some soilbacteria, known asMycorrhiza helper bacteria (MHBs), have been shown to stimulate EcM formation, root and shoot biomass, and fungal growth.^[79][80][81] Some argue that bacteria of this kind should be considered a third component of mycorrhizas.^[82] Other bacteria inhibit ectomycorrhizal formation.^[80]

Many ectomycorrhizal fungi rely uponmammals for thedispersal of their spores, particularly fungi withhypogeous fruiting bodies. Many species of small mammals aremycophages, eating a wide range of fungi and especially the fruiting bodies. Spores are dispersed either because the fruiting body is unearthed and broken apart, or after ingestion and subsequent excretion. Some studies even suggest that passage through an animal's gut promotes sporegermination, although for most fungal species this is not necessary.^[83][84] By spreading the fungal spores, these animals have an indirect effect on plant community structure.^[26]

Other fruiting bodies are eaten byinvertebrates such asmollusks and fly larvae, some of which are even tolerant to the toxicα-amanitin found in death caps. Below ground,nematodes andspringtails also consume fungal tissue.^[15] The ectomycorrhizal fungusLaccaria bicolor has been found to lure and killspringtails to obtain nitrogen, some of which may then be transferred to the host plant. In one study,eastern white pine inoculated withL. bicolor was able to derive up to 25% of its nitrogen from springtails.^[85]

Edible fungi are important in societies throughout the world.Truffles,porcinis andchanterelles are known for their culinary and financial importance.^[86]

Ectomycorrhizal fungi are not prominent inagricultural andhorticultural systems. Most of the economically relevantcrop plants that form mycorrhizas tend to form them with arbuscular mycorrhizal fungi.^[87] Many modern agricultural practices such astillage, heavyfertilizers andfungicides are extremely detrimental to mycorrhizas and the surrounding ecosystem. It is possible that agriculture indirectly affects nearby ectomycorrhizal species and habitats; for example, increased fertilization decreases sporocarp production.^[88][89]

In commercialforestry, thetransplanting of crop trees to new locations often requires an accompanying ectomycorrhizal partner. This is especially true of trees that have a high degree of specificity for their mycobiont, or trees that are being planted far from their native habitat among novel fungal species. This has been repeatedly shown inplantations involving obligate ectomycorrhizal trees, such asEucalyptus andPinus species.^[70] Mass planting of these species often requires an inoculum of native EcM fungi for the trees to prosper.^[88]

Sometimes ectomycorrhizal plantation species, such aspine andeucalyptus, are planted and promoted for their ability to act as asink for atmospheric carbon. However, the ectomycorrhizal fungi of these species also tend to depletesoil carbon, making this use of plantations controversial.^[90][91]

The role of ectomycorrhizas in supporting their host plants has led to the suggestion that EcM fungi could be used inrestoration projects aimed at re-establishing native plant species inecosystems disrupted by a variety of issues.^[52][92] Since the disappearance of mycorhizal fungi from a habitat constitutes a major soil disturbance event, their re-addition is an important part of establishing vegetation and restoring habitats.^[52]

Heavy metals aretoxic for living organisms. High soil concentrations of heavy metals such aszinc,copper,cadmium,lead,nickel, andchromium affect basicmetabolic processes and can lead tocell damage and death. Some ectomycorrhizal fungi are tolerant to heavy metals, with many species having the ability to colonize contaminated soils.^[93] There are also cases ofpopulations locally adapted to tolerate harsh chemical environments.^[93]

Fungi exhibitdetoxification mechanisms to reduce heavy metal concentrations in their cells. These mechanisms include reducing heavy metal uptake, sequestering and storing heavy metals within the cell,^[48] and excretion. Heavy metal uptake can be reduced bysorption and metabolic inactivation at the cell wall and apoplast level.^[93] Ectomycorrhizal fungi also have the ability tobind considerable amounts of heavy metals.^[93][94] Once inside the cell, heavy metals can be immobilized in organo-metal complexes, made soluble, transformed intometallothioneins, involved in metal sequestration and/or stored in vacuoles in chemically inactive forms.Antioxidant detoxification systems may also be in place, reducing the production offree radicals and protecting the fungal cell.^[95][96] Fungi can export metals from the cytoplasm to the apoplast, a mechanism that also occurs in plants.^[97] Ectomycorrhizal fungi can also concentrate heavy metals in their fruiting bodies.^[98] Genetic differences between populations growing in toxic versus non-toxic habitats have rarely been reported, indicating that metal tolerance is widespread. No metal-adaptedendemic taxa have been documented so far.^[94][99] There is, however, evidence for community shifts associated with heavy metals, with lower diversity associated with contaminated sites.^{[100][101][102]} On the other hand, soils naturally rich in heavy metals, such asserpentine soils, do not seem to affect the diversity of ectomycorrhizal fungal communities.^[103]

Although widespread metal tolerance seems to be the norm for ectomycorrhizal fungi, it has been suggested that a few fungi such asPisolithus tinctorius,^[104]P. albus^[105] and species in the genusSuillus^{[106][107][108]} can become adapted to high levels of Al, Zn, Cd and Cu.Suillus luteus andS. bovinus are good examples, with known ecotypes adapted to Zn, Cd and Cu.^{[93][106][109][110]}

EcM fungi have been found to have beneficial effects in several types of polluted environments, including:

• High salt: A number of studies have shown that certain EcM fungi can help their hosts survive highsoil salinity conditions.^{[50][51][111]}

• Radionuclides: Many species of ectomycorrhizal fungi, including theCortinariaceae, canhyperaccumulateradionuclides^[112]

• Organic pollutants: Some EcM species are capable of decomposingpersistent organic pollutants (POPs) such asorganochlorides andpolychlorinated biphenyls (PCBs). Chemicals that can be detoxified by EcM fungi, either alone or in association with their host plant, include2,4-dichlorophenol andtetrachloroethylene.^[15][113]

Ectomycorrhizal communities can be affected by increased CO₂ and the consequent effects ofclimate change. In some studies, elevated CO₂ levels increased fungal mycelium growth^[114] and increased EcM root colonization.^[115] Other EcM associations showed little response to elevated CO₂.^[116]

Increased temperatures also give a range of responses, some negative,^[117] and others positive.^[54] The EcM response todrought is complex since many species provide protection against rootdesiccation and improve the ability of the roots to take up water. Thus, EcMs protect their host plants during times of drought, although they may themselves be affected over time.^[116]

As the importance of below-ground organisms to forest productivity, recovery and stability becomes clear,conservation of ectomycorrhizas is gaining attention.^[88] Many species of EcM fungi inEurope have declined, due to factors including reduced tree vitality, conversion of forests to other uses,pollution andacidification of forest soils.^[88][118] It has been argued that conservation of ectomycorrhizas requires protection of species across their entire host range and habitat,^[88] to ensure that all types of EcM communities are preserved.^[28]

TheNorthwest Forest Plan, which governsland use onfederal lands in thePacific Northwest region of the United States, includes provisions for studying endangered fungi and developing strategies to manage and protect them. The European Council for the Conservation of Fungi was founded in 1985 to promote research on and attention to endangered fungi.^[119] In 2018, the Council collaborated with theKew Royal Botanic Gardens to produce the State of the World's Fungi Report, 2018.^[120]

Conservation strategies include the maintenance of: 1) refuge plants and reservoir hosts to preserve the EcM fungal community after harvesting; 2) mature trees to provide seedlings with a diverse array of EcM fungi; and 3)old-growth stands that have diverse macro- andmicrohabitats and support varied EcM fungal communities.^[121] Preservation of naturalforest floor constituents and retention of woody debris and substrates may also be important. In one study concerningDouglas-fir seedlings, removal of forest floor debris and soil compaction decreased EcM fungal diversity and abundance by 60%.^[122] Removal of pinegrass similarly reduced the diversity and richness of EcM fungi.^[23] Some strategies, such asprescribed burns, have different effects on different types of EcM communities, ranging from negative^[123] to neutral or positive.^[121][124]

Largeex situ culture collections of fungi, including ectomycorrhizal fungi, are maintained throughout the world as insurance against genetic loss. However, these collections are incomplete.^[125]

• Mycorrhizae and changing climate
• Orchid mycorrhiza

Scholia has a profile forEctomycorrhiza(Q3047120).

• Mycorrhizal Associations: The Web Resource Comprehensive illustrations and lists of mycorrhizal and nonmycorrhizal plants and fungi
• Mycorrhizas – a successful symbiosis Biosafety research into genetically modified barley
• International Mycorrhiza Society International Mycorrhiza Society
• MycorWiki a portal concerned with the biology and ecology of ectomycorrhizal fungi and other forest fungi.

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