The Weird and Wonderful World of Fungal Symbiosis
Mycorrhizal fungi, ancient and ubiquitous organisms, have fascinated researchers for decades and continue to baffle and surprise with the many forms they take and functions they perform in all kinds of ecosystems. Ancient organisms, thought to be one of the main vehicles for allowing plants to colonise land, these microbes are at once one of the most simple and complex life-forms on the planet. Being truly symbiotic, this group of fungi forms associations with host plants from all of the phyla, and over 80% of all plant families. This relationship serves to supply the fungal partner with carbon and to allow the host plant to access otherwise unavailable water and nutrients. In addition, the host plant benefits with improved protection from stresses both biotic (i.e. pest and disease) and abiotic (i.e. drought, soil pollution). Mycorrhizas perform important ecosystem services, such as the production of Glomalin, a binding compound that improves soil structure, alleviating erosion and compaction.
‘Mycorrhiza’, a word coined by Albert Bernhard Frank in 1885 describes the actual union of fungus (‘myco’) and plant root (‘rhiza’) and this association can expand the surface uptake area of plant roots by up to 700 times. Thus, the strands of mycorrhizal hyphae (the ‘body’ of the fungus) associated with a single tree, if arranged in one long line, would stretch around the globe. Fossil finds indicate mycorrhizal fungi existed as long as 450 million years ago and over this course of time, a range of distinct fungi have evolved to associate with specific host plants via specialised structures and hyphal arrangements.
Evidence suggests that Mychorizzal fungi existed as long as 450 million years ago!
Orchid mycorrhizae penetrate the plant’s root cells and there form intricate coiled structures termed pelotons. They are unique in both form and function, particularly in that this type of fungus supplies carbon to its plant partner at the early stages of growth. Some evidence also suggests an ability of orchid mycorrhizas to derive carbon from neighbouring trees via a common mycelial network linking trees and orchids.
Ericoid Mychorrizal Fungi (EMF)
As their name suggests, ericoid mycorrhizal fungi (EMR) are specialists associating with plants of the family of Ericaceae. Great morphological differences from other types of mycorrhizal fungi mean that this type of fungus can survive in the absence of a plant host if given adequate nutrition. Evidence suggests that ERM have saprotrophic traits, giving them the ability to recycle nutrients from materials such as leaf litter, in order to supply their host plants.
Evidence suggests that Ericoid Mycorrhizal Fungi have the ability to recycle nutrients from materials such as leaf litter in order to supply their host plants with nutrients.
Arbuscular Mychorizzal Fungi (AMF)
With over 230 known species, the arbuscular mycorrhizal fungi (AMF) are one of the most studied group. Arbuscules are specialist structures designed for nutrient and water exchange within the plant root, giving AMF great efficiency. Much less host specific than orchid and ericoid mycorrhizas, AMF can be used in the form of bio-fertilisers to support development, health and yield of garden plants as well as commercial crops.
In contrast to the above types of endomycorrhizal fungi, the hyphae of ectomycorrhizas to not penetrate the root cortex. These organisms form fruiting bodies and are associated with tree species around the world. Relatively host specific, these fungi will generally be found associated with only a few tree types. Although not fully understood and defined, this selectivity is one that helps passionate mushroom hunters around the world by turning certain tree species into ‘sign posts’ for types of edible mushrooms.
Ever expanding and continuing research projects into mycorrhizas and soil microbiota help us to gain a better understanding of this fascinating subject, but much remains to be learned about the underground life of plants and fungi.
Holding a BSc in Commercial Horticulture, Jamie joined PlantWorks in 2014. Working for the company as Science and Project Manager, Jamie build on her knowledge of plant science and commercial production systems to develop mycorrhizal products for horticultural and arable farming systems. She is particularly interested in the in vitro production of arbuscular mycorrhizal fungi.
Abbott, L. (2015), Soils are alive. E-book available at: http://www.soilhealth.com/soils-are-alive/
Dearnaley, J.D.W. (2007), Further advances in orchid mycorrhizal research. Mycorrhiza, Vol. 17, Issue 6, pp. 475-486.
Smith, S. and Read, D., (2008), Mycorrhizal Symbiosis. 3rd edition. E-book available at: http://www.sciencedirect.com/science/book/9780123705266