The ericoid mycorrhiza is a mutualistic relationship formed between members of the plant family Ericaceae and several lineages of mycorrhizal fungi. This symbiosis represents an important adaptation to acidic and nutrient poor soils that species in the Ericaceae typically inhabit, [1] including boreal forests, bogs, and heathlands. Molecular clock estimates suggest that the symbiosis originated approximately 140 million years ago. [2]
Ericoid mycorrhizas are characterized by fungal coils that form in the epidermal cells of the fine hair roots of ericaceous species. [3] Ericoid mycorrhizal fungi establish loose hyphal networks around the outside of hair roots, from which they penetrate the walls of cortical cells to form intracellular coils that can densely pack individual plant cells. [3] However, the fungi do not penetrate plasma membranes of plant cells. Evidence suggests that coils only function for a period of a few weeks before the plant cell and fungal hyphae begin to degrade. [3]
The coil is the site where fungi exchange nutrients obtained from the soil for carbohydrates fixed through photosynthesis by the plant. Ericoid mycorrhizal fungi have been shown to have enzymatic capabilities to break down complex organic molecules. [4] [5] This may allow some ericoid mycorrhizal fungi to act as saprotrophs. However, the primary function of these enzymatic capabilities is likely to access organic forms of nutrients, such as nitrogen, whose mineralized forms are in very limiting quantities in habitats typically occupied by ericaceous plants. [5]
The majority of research with ericoid mycorrhizal fungal physiology and function has focused on fungal isolates morphologically identified as Rhizoscyphus ericae, in the Ascomycota order Helotiales, [3] now known to be a Pezoloma species. [7]
In addition to Rhizoscyphus ericae, it is currently recognized that culturable Ascomycota such as Meliniomyces (closely allied with Rhizoscyphus ericae), Cairneyella variabilis , Gamarada debralockiae and Oidiodendron maius form ericoid mycorrhizas. [3] [8] [9] [10] The application of DNA sequencing to fungal isolates and clones from environmental PCR has uncovered diverse fungal communities in ericoid roots, however, the ability of these fungi to form typical ericoid mycorrhizal coils has not been verified and some may be non-mycorrhizal endophytes, saprobes or parasites. [11] [12] [13] [14]
In addition to ascomycetes, Sebacina species in the phylum Basidiomycota are also recognized as frequent, but unculturable, associates of ericoid roots, [11] [12] and can form ericoid mycorrhizas. [15] Similarly, basidiomycetes from the order Hymenochaetales have also been implicated in ericoid mycorrhizal formation. [16]
The ericoid mycorrhizal symbiosis is widespread. Ericaceae species occupy at least some habitats on all continents except Antarctica. [17] A few lineages within the Ericaceae do not form ericoid mycorrhizas, and instead form other types of mycorrhizas, including manzanita (Arctostaphylos), madrone (Arbutus), and the Monotropoidiae. [3] The geographic distribution of many of the fungi is uncertain, primarily because the identification of the fungal partners has not always been easy, especially prior to the application of DNA-based identification methods. [3] Fungi ascribed to Rhizoscyphus ericae have been identified from Northern and Southern Hemisphere habitats, but these are not likely all the same species. Some studies have also shown that fungal communities colonizing ericoid roots can lack specificity for different species of ericoid plant, suggesting that at least some of these fungi have a broad host range. [13] [14]
Ericoid mycorrhizal fungi form symbioses with several crop and ornamental species, such as blueberries, cranberries and Rhododendron. Inoculation with ericoid mycorrhizal fungi can influence plant growth and nutrient uptake. [18] However, much less agricultural and horticultural research has been conducted with ericoid mycorrhizal fungi relative to arbuscular mycorrhizal and ectomycorrhizal fungi.
The Ericaceae are a family of flowering plants, commonly known as the heath or heather family, found most commonly in acidic and infertile growing conditions. The family is large, with c. 4250 known species spread across 124 genera, making it the 14th most species-rich family of flowering plants. The many well known and economically important members of the Ericaceae include the cranberry, blueberry, huckleberry, rhododendron, and various common heaths and heathers.
A mycorrhiza is a symbiotic association between a fungus and a plant. The term mycorrhiza refers to the role of the fungus in the plant's rhizosphere, its root system. Mycorrhizae play important roles in plant nutrition, soil biology, and soil chemistry.
An endophyte is an endosymbiont, often a bacterium or fungus, that lives within a plant for at least part of its life cycle without causing apparent disease. Endophytes are ubiquitous and have been found in all species of plants studied to date; however, most of the endophyte/plant relationships are not well understood. Some endophytes may enhance host growth, nutrient acquisition and improve the plant's ability to tolerate abiotic stresses, such as drought and decrease biotic stresses by enhancing plant resistance to insects, pathogens and herbivores. Although endophytic bacteria and fungi are frequently studied, endophytic archaea are increasingly being considered for their role in plant growth promotion as part of the core microbiome of a plant.
An arbuscular mycorrhiza (AM) is a type of mycorrhiza in which the symbiont fungus penetrates the cortical cells of the roots of a vascular plant forming arbuscules.
Root hair, or absorbent hairs, are outgrowths of epidermal cells, specialized cells at the tip of a plant root. They are lateral extensions of a single cell and are only rarely branched. They are found in the region of maturation, of the root. Root hair cells improve plant water absorption by increasing root surface area to volume ratio which allows the root hair cell to take in more water. The large vacuole inside root hair cells makes this intake much more efficient. Root hairs are also important for nutrient uptake as they are main interface between plants and mycorrhizal fungi.
Glomeromycota are one of eight currently recognized divisions within the kingdom Fungi, with approximately 230 described species. Members of the Glomeromycota form arbuscular mycorrhizas (AMs) with the thalli of bryophytes and the roots of vascular land plants. Not all species have been shown to form AMs, and one, Geosiphon pyriformis, is known not to do so. Instead, it forms an endocytobiotic association with Nostoc cyanobacteria. The majority of evidence shows that the Glomeromycota are dependent on land plants for carbon and energy, but there is recent circumstantial evidence that some species may be able to lead an independent existence. The arbuscular mycorrhizal species are terrestrial and widely distributed in soils worldwide where they form symbioses with the roots of the majority of plant species (>80%). They can also be found in wetlands, including salt-marshes, and associated with epiphytic plants.
Myco-heterotrophy is a symbiotic relationship between certain kinds of plants and fungi, in which the plant gets all or part of its food from parasitism upon fungi rather than from photosynthesis. A myco-heterotroph is the parasitic plant partner in this relationship. Myco-heterotrophy is considered a kind of cheating relationship and myco-heterotrophs are sometimes informally referred to as "mycorrhizal cheaters". This relationship is sometimes referred to as mycotrophy, though this term is also used for plants that engage in mutualistic mycorrhizal relationships.
Nitrogen nutrition in the arbuscular mycorrhizal system refers to...
The mycorrhizosphere is the region around a mycorrhizal fungus in which nutrients released from the fungus increase the microbial population and its activities. The roots of most terrestrial plants, including most crop plants and almost all woody plants, are colonized by mycorrhiza-forming symbiotic fungi. In this relationship, the plant roots are infected by a fungus, but the rest of the fungal mycelium continues to grow through the soil, digesting and absorbing nutrients and water and sharing these with its plant host. The fungus in turn benefits by receiving photosynthetic sugars from its host. The mycorrhizosphere consists of roots, hyphae of the directly connected mycorrhizal fungi, associated microorganisms, and the soil in their direct influence.
A mycorrhizal network is an underground network found in forests and other plant communities, created by the hyphae of mycorrhizal fungi joining with plant roots. This network connects individual plants together. Mycorrhizal relationships are most commonly mutualistic, with both partners benefiting, but can be commensal or parasitic, and a single partnership may change between any of the three types of symbiosis at different times.
Soil carbon storage is an important function of terrestrial ecosystems. Soil contains more carbon than plants and the atmosphere combined. Understanding what maintains the soil carbon pool is important to understand the current distribution of carbon on Earth, and how it will respond to environmental change. While much research has been done on how plants, free-living microbial decomposers, and soil minerals affect this pool of carbon, it is recently coming to light that mycorrhizal fungi—symbiotic fungi that associate with roots of almost all living plants—may play an important role in maintaining this pool as well. Measurements of plant carbon allocation to mycorrhizal fungi have been estimated to be 5 to 20% of total plant carbon uptake, and in some ecosystems the biomass of mycorrhizal fungi can be comparable to the biomass of fine roots. Recent research has shown that mycorrhizal fungi hold 50 to 70 percent of the total carbon stored in leaf litter and soil on forested islands in Sweden. Turnover of mycorrhizal biomass into the soil carbon pool is thought to be rapid and has been shown in some ecosystems to be the dominant pathway by which living carbon enters the soil carbon pool.
An ectomycorrhiza is a form of symbiotic relationship that occurs between a fungal symbiont, or mycobiont, and the roots of various plant species. The mycobiont is often from the phyla Basidiomycota and Ascomycota, and more rarely from the Zygomycota. Ectomycorrhizas form on the roots of around 2% of plant species, usually woody plants, including species from the birch, dipterocarp, myrtle, beech, willow, pine and rose families. Research on ectomycorrhizas is increasingly important in areas such as ecosystem management and restoration, forestry and agriculture.
Ectomycorrhizal extramatrical mycelium is the collection of filamentous fungal hyphae emanating from ectomycorrhizas. It may be composed of fine, hydrophilic hypha which branches frequently to explore and exploit the soil matrix or may aggregate to form rhizomorphs; highly differentiated, hydrophobic, enduring, transport structures.
Dark septate endophytes (DSE) are a group of endophytic fungi characterized by their morphology of melanized, septate, hyphae. This group is likely paraphyletic, and contain conidial as well as sterile fungi that colonize roots intracellularly or intercellularly. Very little is known about the number of fungal taxa within this group, but all are in the Ascomycota. They are found in over 600 plant species and across 114 families of angiosperms and gymnosperms and co-occur with other types of mycorrhizal fungi. They have a wide global distribution and can be more abundant in stressed environments. Much of their taxonomy, physiology, and ecology are unknown.
John William Gibson Cairney (1959–2012) was an eminent Scottish–Australian mycologist and Director of the UWS Centre for Plants and the Environment. Cairney specialised in mycorrhizal biology and ecology, particularly of ericoid- and Ectomycorrhiza. Cairney contributed significantly to mycorrhizal research, publishing over 150 manuscripts and serving as the associate editor, editor or on the advisoral panel for numerous scientific journals including: New Phytologist, Plant and Soil, Mycological Research and the Journal of Soils and Sediments.
Cairneyella is a genus of at least two ericoid mycorrhizal and root-associated fungi that is, to date, endemic to Australian plants, mostly from the family Ericaceae. It has been demonstrated to form typical ericoid mycorrhizal coils in hair roots and is known to enhance the growth of ericaceous seedlings. The genus is named in honour of John Cairney, an Australian-Scottish mycologist.
Orchid mycorrhizae are endomycorrhizal fungi which develop symbiotic relationships with the roots and seeds of plants of the family Orchidaceae. Nearly all orchids are myco-heterotrophic at some point in their life cycle. Orchid mycorrhizae are critically important during orchid germination, as an orchid seed has virtually no energy reserve and obtains its carbon from the fungal symbiont.
Leohumicola verrucosa is a heat-resistant, endophytic, ericoid mycorrhizal soil fungus. Its species name refers to rough, warty or spine-like ornamentations on its aleurioconidia. L. verrucosa was first described from samples of soil exposed to fire; among these it was especially abundant in regularly burned blueberry fields in eastern Canada. L. verrucosa forms mycorrhizal relationships with a wide variety and distribution of species in the Ericaceae family.
Mucoromycota is a division within the kingdom fungi. It includes a diverse group of various molds, including the common bread molds Mucor and Rhizopus. It is a sister phylum to Dikarya.
The Serendipitaceae are a family of fungi in the order Sebacinales. Species do not produce visible basidiocarps, but form septate basidia on thin, trailing hyphae. Species are mycorrhizal, forming associations with a wide range of plants. Most species have only been detected through environmental DNA sampling or laboratory cultures. The family currently contains the single genus Serendipita.