Mycorrhizae fungi

Discussion in 'Organic Lawn Care' started by ICT Bill, Dec 12, 2007.

  1. ICT Bill

    ICT Bill LawnSite Platinum Member
    Posts: 4,115

    In another post someone was asking to learn more about this subject. I have pulled paragraphs from several articles together, some is written by me. It is a bit technical but you have to be in order to speak about the subject.

    There are two groups of mycorrhizae fungi endo and ecto. Some endo-dependent plants include vegetables, grapes, fruit trees, berries, turfgrass, and flowers.
    Ectomycorrhizas are found almost entirely on woody perennials including trees.

    It is important to define the term rhizosphere first. Hiltner (1904) first introduced the term rhizosphere, which is derived from the Greek word ‘rhiza’, meaning root, and ‘sphere’, meaning field of influence. He defined the rhizosphere as the zone of soil immediately adjacent to legume roots that supports high levels of bacterial activity. However, more recently the term has been broadened to include both the volume of soil influenced by the root and the root tissues colonized by micro-organisms (reviewed in Pinton et al., 2001).

    The rhizosphere supports diverse bacteria that can stimulate growth of plants. Such plant growth-promoting rhizobacteria operate by a wide variety of mechanisms, including N2 fixation, enhanced solubilization of P, and phytohormone production (Vessey, 2003 ; Barrea et al., 2005 )

    For plants, there are two influential specific plant–microbe associations: mycorrhizaes and root nodulation. Mycorrhizaes are mutualistic symbioses between plant roots and soil fungi (Smith and Read, 1997 ). Over 80% of land plants are able to form mycorrhizal associations. In these associations there is a bidirectional flow of nutrients. Carbon flows out from the plant host to the fungus, and mineral nutrients flow from the fungus to the plant. It is estimated that between 4% and 20% of net photosynthate can be transferred from the plant to its fungal partner. In return, the mycorrhizae can become the primary organ acquiring mineral nutrients

    The establishment of the mycorrhizal network offers a number of basic advantages for the acquisition of mineral nutrients: fungal hyphae extend beyond the area of nutrient depletion surrounding the root; fungal hyphae greatly increase the surface area for the absorption of nutrients relative to non-mycorrhizal roots; hyphae are able to extend into soil pores that are too small for roots to enter; and some mycorrhizal fungi can access forms of N and P that are unavailable to non-mycorrhizal plants, particularly organic forms of these nutrients

    Many farming practices, including fertilizer application, cultivation, and fumigation can have deleterious impacts on communities of AM fungi (Kurle and Pfleger, 1994 ), which are known to be less diverse and abundant in conventional agricultural systems relative to organically managed and semi-natural areas

    Arbuscular mycorrhizas (AM, also called endo) are the commonest mycorrhizal group, and are found on angiosperms, gymnosperms, pteridophytes, and bryophytes. The association is very close and the fungal hyphae penetrate root cortical cells to form arbuscules to exchange nutrients and carbon. About 150–200 obligate biotrophic AM fungi have been described so far, which all belong to the Glomeromycota (Schussler et al., 2001 ).

    Over 2000 fungus species are known to be capable of forming ectomycorrhizaes, with most being basidiomycetes or ascomycetes. Hyphae penetrate into the root cortex where they ramify between cells to form a ‘Hartig net’, through which materials are exchanged. The fungus forms a mantle of hyphae on the outside of the plant root which extends into the surrounding soil. The primary function of the fungal mycelium is absorption of nutrients from the soil, and the translocation of these materials to the host. Ectomycorrhizal fungi have been shown to translocate mineral forms of N, P, and micronutrients from the soil to the host.

    Many rhizosphere fungi, including mycorrhizal fungi, are able to suppress soil-borne plant pathogens (Whipps, 2001 ). Fungi have the advantage over bacterial biocontrol agents in that they are generally more effective at spreading through the soil and rhizosphere. A variety of mechanisms are involved in the control of fungal pathogens by rhizosphere fungi, including competition for nutrients, antibiotic production, and induced resistance. In addition, many fungi are able to parasitize spores, sclerotia, or hyphae of other fungi, resulting in biocontrol.

    Overall, it is the loss of carbon compounds from roots that drives the development of enhanced microbial populations in the rhizosphere when compared with the bulk soil (Grayston et al., 1996 ). This phenomenon is widespread across all plant species as a general process, although the compounds lost from different plant species, or even cultivars of particular species, can vary markedly in quality and quantity. Conversely, the micro-organisms in the rhizosphere can influence plants in a variety of ways, for example affecting plant growth, nutrition, development, susceptibility to disease, resistance to heavy metals.
     
  2. Nate@TLCS

    Nate@TLCS LawnSite Member
    Posts: 97

    So these fungi enhance the absorbtion of nutrients to the host plants. ?
     
  3. Kiril

    Kiril LawnSite Fanatic
    Posts: 18,308

  4. ICT Bill

    ICT Bill LawnSite Platinum Member
    Posts: 4,115

    Nate,
    They, in most instances, make nutrients that are not plant available and turn them into a plant available form. They also enhance nutrient uptake by "extending" the root rhizosphere into the soil
     
  5. ICT Bill

    ICT Bill LawnSite Platinum Member
    Posts: 4,115

    There are some plants that are non mycorrhizal for instance:
    Beet, Orchid, Protea, Carnation, Rush, Sedge, Heath, Rhododendron, Azalea

    There are some plants like the wild mustard on the east coast that actually kills mycorrhizae fungi as it encroaches into areas. The wild mustard has become a true invasive here in the mid atlantic. The mustard plant retards or kills the plants by poisoning the fungi and breaking the symbiotic bond with the existing plant in the area making it much easier for the mustard plant to take over an entire forests
     
  6. Smallaxe

    Smallaxe LawnSite Fanatic
    Posts: 10,082

    The picture that forms in my mind about what is happening here in the symbiosis is: The root hair of the plant grows out and sucks up the water and nutrient that it can.
    I had read that only 'root hairs', which are also microscopic, can absorb the nutrients and moisture. Visible roots have already lost that ability.

    So as a root hair matures and depletes the rhizosphere of nutrients, 2 things are happening. The root continues to grow to eventually send out its own root hairs and secondly, AM fungus surrounds the original root and penetrates it as well then starts to add food and water.
    I would imagine that the fungus takes over once the root hair has extended beyond the fertile region.

    Is that a fair assessment or is there a clearer way to look at it?
     
  7. Kiril

    Kiril LawnSite Fanatic
    Posts: 18,308

    Those people who have an interest in microscopy might find this a useful tool.

    http://virtual.itg.uiuc.edu/software/

    Download Here

    There are quite a few other very cool open source projects of this type which I have been playing around with for years. Rock on open source. :)
     
  8. mdvaden

    mdvaden LawnSite Bronze Member
    Posts: 1,946

    To simplify it for the average reader yes.

    That's why you will commonly see short phrases like "mycorrhizal fungi may increase water or nutrient uptake in trees by as much as 10 to 50 times or more".

    And basically, whatever you can find to purchase - which are quite a few species of it - are beneficial, otherwise they wouldn't be on the market long at all.

    Experts also writed that you can make your own additive batch with many more species than you can buy.

    By the way, you might want to bookmark the microscopic images. The image properties seem to indicate illegal hotlinking to another website. And you never know when an image will vanish due to that.

    Mycorrhizal fungi can be a better way to "feed" plants, and is a large part of the basis for my large tree feeding advice page.

    Fertilizer can damage them, so I explained further how to approach fertilizing so as not to have to abandon fertilizing altogether. It's all in the technique.
     
  9. Kiril

    Kiril LawnSite Fanatic
    Posts: 18,308

    Your right, they are hot linked, which I don't normally do (and block on my own websites), however in this case I wanted to avoid any potential copyright issues. I'll leave it up to them to decide if they want to stop the hot linking.

    The links to the source page are provided in the event they are pulled/blocked.

    BTW, all the above images can be found in various google caches with the right search phrase. :)
     
  10. mdvaden

    mdvaden LawnSite Bronze Member
    Posts: 1,946

    One option you might scrounge for - some images on usda sites have no copyright if they are federal property. The US government can't copyright. So like the pruning advice page that the USDA / Forest Service has, you can copy and paste all that text verbatim into your website if you like. The images will depend on if the USDA or feds are using them, or if they are theirs. If I see no copyright notice or credit given to someone outside the USDA, I'll copy the file for future use. :)
     

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