Mycorrhizal Fungi

Photo: Amaranthus&Allyn

Latest Update 27th July 2015.

Mycorrhizal Fungi 
  • Mycorrhizal Fungi live in the soil or in leaf litter and colonise the roots of vascular plants.  This relationship is symbiotic (mutualistic) which means it is formed for the mutual benefit of fungi and plants.
  • Most plants can form a mutualistic relationship with mycorrhizal fungi.  They provide the fungi with a relatively constant and direct supply of food in the form of carbohydrates.
  • In return, plants benefits from the fungi's higher capacity to absorb water, nitrogen and mineral nutrients from the soil through their mycelium, a root like structure made up of large numbers of branching hyphae which are much finer and penetrate further into the ground than the plants own roots.
  • These hyphae exude enzimes into the surrounding soil which break down soil particles and organic material to produce plant nutrients which are then transported to the host plant's roots.
  • The photograph above shows a small pine tree seedling grown in a glass box revealing the level of white, finely branched mycorrhizal hyphae that are attached to its roots.
  • Mycorrhizal fungi form mutualistic relationships with most plants (95% of those examined so far), unfortunately the brassicas and beets are not included.
  • Here is a List of mycorrghizal and other plants types, describing their relationship with the fungi.  It shows:-
    • Micorrhizal plants which have an arbuscular (intracellular) relationship.
    • Ectomycorrhizal plants which have an ectomycorrhizal (extracellular) relationship.
    • Non Micorrhizal plants which have no relationship with the fungi.
  • The intracellular relationship is one where mycorrhizal hyphae enter the plant's roots and produce arbuscules.  Their structure greatly increases the contact surface area between the hyphae and the cell cytoplasm to facilitate the transfer of nutrients between them.
  • The extracellular relationship is one where mycorrhizal hyphae take the form af a sheath covering the root tip and a Hartig net of hyphae surrounding the plant cells within the root cortex. 
  • Plants hosting mycorrhizal fungi are often more resistant to diseases, such as those caused by microbial soil-borne pathogens.  They are also able to flourish with lower fertiliser use than other plants and are better able to withstand drought.
  • Individual plants may have relationships with more than one fungi, and each fungi may have relationships with more than one plant.  These linkages enhance the "colonies" capacity to the benefit of all.  If a plant or a fungus dies for any reason, the colony will probably continue to prosper.
  • Mycorrhizal fungi can live for many years, and as they take up carbon from the host plant, they are sequestering it into the soil from the atmosphere.
  • It is said that if mycorrhizal fungi were used in large scale agriculture, it would significantly mitigate the loss of soil carbon due to modern farming practices which do not replace lost organic materials in the soil.
Summary. 
  • A large proportion of the global plant population is capable of forming these enormously beneficial mutualistic relationships with mycorrhizal fungi. 
  • In simple terms, the plant is supplied with minerals including trace elements and nitrogen in a readily assimilated form as food.  
  • In return carbon and water are photosynthesised to produce hexose, which is passed to the fungi to be transformed into complex carbohydrates for use as their food.
  • Fungi and plants which group together in colonies share resources and help each other control unfriendly microorganisms.
  • In a garden situation, a no dig policy is beneficial as it allows these colonies to mature over time to the long term benefit of plants grown where the soil is least disturbed.
  • Fungal spores are commercially available and you can help these colonies get established by dusting the roots of new cuttings and seedlings as you plant them in your garden beds.
  • Mycorrhizal fungi are an important agent for healthy and productive plant growth, and the take up of important phytochemicals in edible crops.  Our good health depends on it.
  • You can help develop colonies of fungi by spraying the soil with aerated compost tea.
Information from.