Benificial bacteria and
mycorrhiza (Gk. μυκός,
mykós, "fungus" and ριζα,
riza, "roots",[SUP]
[1][/SUP] pl.
mycorrhizae or
mycorrhizas) is a
symbiotic (generally
mutualistic, but occasionally weakly
pathogenic) association between a
fungus and the roots of a
vascular plant.[SUP]
[2][/SUP][FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]In a mycorrhizal association, the fungus colonizes the host plant's roots, either
intracellularly as in
arbuscular mycorrhizal fungi (AMF or AM), or
extracellularly as in
ectomycorrhizal fungi. They are an important component of
soil life and
soil chemistry.[/FONT]
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[h=2]Contents[/h] [hide] [/FONT]
- [FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]1 Mutualist dynamics[/FONT]
- [FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]1.1 Sugar-water/mineral exchange[/FONT]
- [FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]1.2 Mechanisms[/FONT]
- [FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]1.3 Disease and drought resistance and its correlation to Mycorrhizae[/FONT]
- [FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]1.4 Colonization of barren soil[/FONT]
- [FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]1.5 Resistance to toxicity[/FONT]
- [FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]2 Occurrence of mycorrhizal associations[/FONT]
- [FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]3 Types of mycorrhiza[/FONT]
- [FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]3.1 Endomycorrhiza[/FONT]
- [FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]3.2 Ectomycorrhiza[/FONT]
- [FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]3.3 Ericoid mycorrhiza[/FONT]
- [FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]4 Discovery[/FONT]
- [FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]5 See also[/FONT]
- [FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]6 References[/FONT]
- [FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]7 External links[/FONT]
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Mutualist dynamics[edit][/FONT][/h][FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]Mycorrhizae form a
mutualistic relationship with the roots of most plant species. While only a small proportion of all species has been examined, 95% of those plant families are predominantly mycorrhizal.[SUP]
[3][/SUP] They are named after their presence in the plant's
rhizosphere (root system).[/FONT]
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Sugar-water/mineral exchange[edit][/FONT][/h][FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]This mutualistic association provides the fungus with relatively constant and direct access to
carbohydrates, such as
glucose and
sucrose.[SUP]
[4][/SUP] The carbohydrates are translocated from their source (usually leaves) to root tissue and on to the plant's fungal partners. In return, the plant gains the benefits of the
mycelium's higher absorptive capacity for water and mineral nutrients due to the comparatively large surface area of mycelium: root ratio, thus improving the plant's mineral absorption capabilities.[SUP]
[5][/SUP][/FONT]
[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]Plant roots alone may be incapable of taking up
phosphate ions that are
demineralized in soils with a
basic pH. The
mycelium of the mycorrhizal fungus can, however, access these phosphorus sources, and make them available to the plants they colonize.[SUP]
[6][/SUP] Nature, according to C.Michael Hogan, has adapted to this critical role of phosphate, by allowing many plants to recycle phosphate, without using soil as an intermediary. For example, in some dystrophic forests large amounts of phosphate are taken up by mycorrhizal hyphae acting directly on leaf litter, bypassing the need for soil uptake.[SUP]
[7][/SUP]
Inga alley cropping, proposed as an alternative to
slash and burn rainforest destruction,[SUP]
[8][/SUP] relies upon Mycorrhiza within the
Inga Tree root system to prevent the rain from washing
phosphorusout of the soil.[SUP]
[9][/SUP] In some cases, the transport of water, carbon, and nutrients could be done directly from plant to plant through
mycorrhizal networks that are underground hyphal networks created by mycorrhizal fungi that connect individual plants together.[SUP]
[10][/SUP][/FONT]
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Suillus tomentosus, a fungus, produces specialized structures, known as tuberculate ectomycorrhizae, with its plant host
lodgepole pine (
Pinus contorta var.
latifolia). These structures have in turn been shown to host
nitrogen fixing bacteria which contribute a significant amount of
nitrogen and allow the pines to colonize nutrient-poor sites.[SUP]
[11][/SUP][/FONT]
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Mechanisms[edit][/FONT][/h]
[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]The mechanisms of increased absorption are both physical and chemical. Mycorrhizal mycelia are much smaller in diameter than the smallest root, and thus can explore a greater volume of soil, providing a larger surface area for absorption. Also, the cell membrane chemistry of fungi is different from that of plants (including
organic acidexcretion which aids in
ion displacement[SUP]
[12][/SUP]). Mycorrhizas are especially beneficial for the plant partner in nutrient-poor soils.[SUP]
[13][/SUP][/FONT]
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Disease and drought resistance and its correlation to Mycorrhizae[edit][/FONT][/h][FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]Mycorrhizal plants are often more resistant to diseases, such as those caused by microbial soil-borne
pathogens. Prof. Dr. Anton Muhibuddin from University of Brawijaya (UB) - Indonesia found that AMF (Arbuscular Mycorrhizae Fungi) was significantly correlated with soil water content and soil chemical fertility variable such as, organic carbon, total phosphorus and CEC, however it was not significantly correlated with pH. AMF was also significantly correlated with soil biological fertility variable such as, soil fungi and soil bacteria, including soil disease. Furthermore, AMF was significantly correlated with soil physical variable, but only with water level and not with aggregate stability.,[SUP]
[14][/SUP][SUP]
[15][/SUP] and are also more resistant to the effects of drought.[SUP]
[16][/SUP][SUP]
[17][/SUP][SUP]
[18][/SUP][/FONT]
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Colonization of barren soil[edit][/FONT][/h][FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]Plants grown in sterile
soils and growth media often perform poorly without the addition of
spores or hyphae of mycorrhizal fungi to colonise the plant roots and aid in the uptake of soil mineral nutrients.[SUP]
[19][/SUP] The absence of mycorrhizal fungi can also slow plant growth in early succession or on degraded landscapes.[SUP]
[20][/SUP] The introduction of alien mycorrhizal plants to nutrient-deficient ecosystems puts indigenous non-mycorrhizal plants at a competitive disadvantage.[SUP]
[21][/SUP][/FONT]
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Resistance to toxicity[edit][/FONT][/h][FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]Fungi have been found to have a protective role for plants rooted in soils with high metal concentrations, such as
acidic and
contaminated soils.
Pine trees inoculated with
Pisolithus tinctorius planted in several contaminated sites displayed high tolerance to the prevailing contaminant, survivorship and growth. One study discovered the existence of
Suillus luteus strains with varying tolerance of
zinc. Another study discovered that zinc-tolerant strains of
Suillus bovinus conferred resistance to plants of
Pinus sylvestris. This was probably due to binding of the metal to the extramatricial
mycelium of the fungus, without affecting the exchange of beneficial substances.[SUP]
[21][/SUP][/FONT]
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Occurrence of mycorrhizal associations[edit][/FONT][/h][FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]At around 400 million years old, the
Rhynie chert contains the earliest fossil assemblage yielding plants preserved in sufficient detail to detect mycorrhizas - and they are indeed observed in the stems of
Aglaophyton major.[SUP]
[22][/SUP][/FONT]
[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]Mycorrhizas are present in 92% of plant families studied (80% of species),[SUP]
[23][/SUP] with
arbuscular mycorrhizas being the ancestral and predominant form,[SUP]
[23][/SUP] and indeed the most prevalent symbiotic association found in the plant kingdom.[SUP]
[4][/SUP] The structure of arbuscular mycorrhizas has been highly conserved since their first appearance in the fossil record,[SUP]
[22][/SUP] with both the development of ectomycorrhizas, and the loss of mycorrhizas,
evolving convergently on multiple occasions.[SUP]
[23][/SUP][/FONT]
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Types of mycorrhiza[edit][/FONT][/h]
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[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]Arbuscular mycorrhizal
wheat[/FONT]
[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]Mycorrhizas are commonly divided into
ectomycorrhizas and
endomycorrhizas. The two types are differentiated by the fact that the hyphae of ectomycorrhizal fungi do not penetrate individual
cells within the root, while the
hyphae of endomycorrhizal fungi penetrate the cell wall and invaginate the
cell membrane. Additionally, many plants in the order
Ericales form a third type,
ericoid mycorrhizas, while some members of the Ericales form arbutoid and monotropoid mycorrhizas.[SUP]
[24][/SUP][SUP]
[25][/SUP] All
orchids are
myco-heterotrophic at some stage during their lifecycle and form
orchid mycorrhizas with a range of basidiomycete fungi.[/FONT]