Editing Mycorrhiza (section)

===Sugar-water/mineral exchange===

[[File:Mycorrhiza.svg|thumb|In this mutualism, fungal hyphae (E) increase the surface area of the root and uptake of key nutrients while the plant supplies the fungi with fixed carbon (A=root cortex, B=root epidermis, C=arbuscle, D=vesicle, F=root hair, G=nuclei).]]

The mycorrhizal mutualistic association provides the fungus with relatively constant and direct access to [[carbohydrate]]s, such as [[glucose]] and [[sucrose]].<ref name="Harrison MJ.">{{cite journal |last=Harrison |first=M. J. |date=2005 |title=Signaling in the arbuscular mycorrhizal symbiosis |journal=Annu Rev Microbiol |volume=59 |pages=19–42 |pmid=16153162 |doi=10.1146/annurev.micro.58.030603.123749}}</ref> 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, partly because of the large surface area of fungal hyphae, which are much longer and finer than plant [[root hair]]s, and partly because some such fungi can mobilize soil minerals unavailable to the plants' roots. The effect is thus to improve the plant's mineral absorption capabilities.<ref name="Selosse">{{cite journal |last1=Selosse |first1=M. A. |last2=Richard |first2=F. |last3=He |first3=X. |last4=Simard |first4=S. W. |date= 2006 |title=Mycorrhizal networks: des liaisons dangereuses? |journal=Trends in Ecology and Evolution |volume=21 |pages=621–628 |pmid=16843567 |doi=10.1016/j.tree.2006.07.003 |issue=11|bibcode=2006TEcoE..21..621S }}</ref>

Unaided plant roots may be unable to take up [[nutrient]]s that are chemically or physically [[Immobilization (soil science)|immobilised]]; examples include [[phosphate]] [[ions]] and [[micronutrient]]s such as iron. One form of such immobilization occurs in soil with high [[clay]] content, or soils with a strongly [[pH|basic pH]]. The [[mycelium]] of the mycorrhizal fungus can, however, access many such nutrient sources, and make them available to the plants they colonize.<ref name="Li">{{cite journal |last1=Li |first1=H. |last2=Smith |first2=S. E. |last3=Holloway |first3=R. E. |last4=Zhu |first4=Y. |last5=Smith |first5=F. A. |date=2006 |title=Arbuscular mycorrhizal fungi contribute to phosphorus uptake by wheat grown in a phosphorus-fixing soil even in the absence of positive growth responses |journal=New Phytologist |volume=172 |pages=536–543 |pmid=17083683 |doi=10.1111/j.1469-8137.2006.01846.x |issue=3 |doi-access=free}}</ref> Thus, many plants are able to obtain phosphate without using soil as a source. Another form of immobilisation is when nutrients are locked up in organic matter that is slow to decay, such as wood, and some mycorrhizal fungi act directly as decay organisms, mobilising the nutrients and passing some onto the host plants; for example, in some [[dystrophic]] forests, large amounts of phosphate and other nutrients are taken up by mycorrhizal [[hypha]]e acting directly on [[leaf litter]], bypassing the need for soil uptake.<ref>{{cite book |last=Hogan |first=C.M. |date=2011 |chapter-url=http://www.eoearth.org/article/Phosphate?topic=49557 |chapter=Phosphate |title=Encyclopedia of Earth |editor1=Jorgensen, A. |editor2=Cleveland, C.J. |publisher=National Council for Science and the Environment. |location=Washington DC |archive-url=https://web.archive.org/web/20121025180158/http://www.eoearth.org/article/Phosphate?topic=49557 |archive-date=2012-10-25 }}</ref> ''[[Inga alley cropping]]'', an [[agroforestry]] technique proposed as an alternative to [[slash and burn]] rainforest destruction,<ref name=Elkan>{{cite web |last=Elkan |first=D. |title=Slash-and-burn farming has become a major threat to the world's rainforest |work=[[The Guardian]] |date=21 April 2004 |url=https://www.theguardian.com/society/2004/apr/21/environment.environment }}</ref> relies upon mycorrhiza within the root system of species of ''[[Inga]]'' to prevent the rain from washing [[phosphorus]] out of the soil.<ref name=RFS>{{cite web |work=rainforestsaver.org |url=http://www.rainforestsaver.org/what-is-it-all-about/what-is-inga-alley-cropping/ |title=What is Inga alley cropping? |archive-url=https://web.archive.org/web/20111101062913/http://www.rainforestsaver.org/what-is-it-all-about/what-is-inga-alley-cropping |archive-date=2011-11-01 }}</ref>

In some more complex relationships, mycorrhizal fungi do not just collect immobilised soil nutrients, but connect individual plants together by [[mycorrhizal networks]] that transport water, carbon, and other nutrients directly from plant to plant through underground hyphal networks.<ref name=Simard2012>{{cite journal |last1=Simard |first1=S.W. |author2=Beiler, K.J. |author3=Bingham, M.A. |author4=Deslippe, J.R. |author5=Philip, L.J. |author6=Teste, F.P. |title=Mycorrhizal networks: mechanisms, ecology and modelling. |journal=Fungal Biology Reviews |date=April 2012 |volume=26 |issue=1 |pages=39–60 |doi=10.1016/j.fbr.2012.01.001 |bibcode=2012FunBR..26...39S }}</ref>

''[[Suillus tomentosus]]'', a [[basidiomycete]] fungus, produces specialized structures known as tuberculate ectomycorrhizae with its plant host [[lodgepole pine]] (''Pinus contorta'' var. ''latifolia''). These structures have been shown to host [[nitrogen fixation|nitrogen fixing]] [[bacteria]] which contribute a significant amount of [[nitrogen]] and allow the pines to colonize nutrient-poor sites.<ref name=paul07/>