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== Secretions ==
== Secretions ==
Plants [[Secretion|secrete]] many compounds through their roots to serve symbiotic functions in the rhizosphere. [[Strigolactone]]s, secreted and detected by [[mycorrhiza]]l fungi, stimulate the [[germination]] of spores and initiate changes in the mycorrhiza that allow it to colonize the root. The parasitic plant, ''[[Striga (plant)|Striga]]'' also detects the presence of strigolactones and will germinate when it detects them; they will then move into the root, feeding off the nutrients present.<ref>{{Cite journal|last=Arnaud Besserer, Virginie Puech-Pagès, Patrick Kiefer, Victoria Gomez-Roldan, Alain Jauneau, Sébastien Roy, Jean-Charles Portais, Christophe Roux, Guillaume Bécard, Nathalie Séjalon-Delmas|first=|year=2006|title=Strigolactones Stimulate Arbuscular Mycorrhizal Fungi by Activating Mitochondria|url=http://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.0040226|journal=PLOS Biology|volume=|pages=|via=}}</ref><ref>{{Cite journal|last=Andreas Brachmann, Martin Parniske|first=|year=2006|title=The Most Widespread Symbiosis on Earth|url=http://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.0040239|journal=PLOS Biology|volume=|pages=|via=}}</ref> Symbiotic [[Nitrogen fixation|Nitrogen-fixing]] bacteria, such as ''[[Rhizobium]]'' species, detect compounds like [[flavonoids]] secreted by the roots of leguminous plants and then produce [[nod factor]]s which signal to the plant that they are present and will lead to the formation of [[root nodule]]s. In these nodules bacteria, sustained by nutrients from the plant, convert nitrogen gas to a form that can be used by the plant.<ref>{{Cite journal|last=Chang Fu Tiana, Anne-Marie Garneronea, Céline Mathieu-Demazièrea, Catherine Masson-Boivina, and Jacques Batuta|first=|year=2012|title=Plant-activated bacterial receptor adenylate cyclases modulate epidermal infection in the Sinorhizobium meliloti–Medicago symbiosis|url=http://www.pnas.org/content/109/17/6751.full|journal=PNAS|volume=109|pages=6751–6756|via=}}</ref> Non-symbiotic (or "free-living") nitrogen-fixing bacteria may reside in the rhizosphere just outside the roots of certain plants (including many grasses), and similarly "fix" nitrogen gas in the nutrient-rich plant rhizosphere. Even though these organisms are thought to be only loosely associated with plants they inhabit, they may respond very strongly to the status of the plants. For example, nitrogen-fixing bacteria in the rhizosphere of the [[rice plant]] exhibit [[Diurnality|diurnal]] cycles that mimic plant behavior, and tend to supply more fixed nitrogen during growth stages when the plant exhibits a high demand for nitrogen.<ref>{{Cite journal |author=Sims GK, Dunigan EP |year=1984 |title=Diurnal and seasonal variations in nitrogenase activity (C2H2 reduction) of rice roots |journal=Soil Biology and Biochemistry |volume=16 |issue=1 |pages=15–18 |doi=10.1016/0038-0717(84)90118-4|last2=Dunigan}}</ref>
Plants [[Secretion|secrete]] many compounds through their roots to serve symbiotic functions in the rhizosphere. [[Strigolactone]]s, secreted and detected by [[mycorrhiza]]l fungi, stimulate the [[germination]] of spores and initiate changes in the mycorrhiza that allow it to colonize the root. The parasitic plant, ''[[Striga (plant)|Striga]]'' also detects the presence of strigolactones and will germinate when it detects them; they will then move into the root, feeding off the nutrients present.<ref>{{Cite journal|last=Arnaud Besserer, Virginie Puech-Pagès, Patrick Kiefer, Victoria Gomez-Roldan, Alain Jauneau, Sébastien Roy, Jean-Charles Portais, Christophe Roux, Guillaume Bécard, Nathalie Séjalon-Delmas|first=|year=2006|title=Strigolactones Stimulate Arbuscular Mycorrhizal Fungi by Activating Mitochondria|url=http://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.0040226|journal=PLOS Biology|volume=|pages=|via=}}</ref><ref>{{Cite journal|last=Andreas Brachmann, Martin Parniske|first=|year=2006|title=The Most Widespread Symbiosis on Earth|url=http://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.0040239|journal=PLOS Biology|volume=|pages=|via=}}</ref> Symbiotic [[Nitrogen fixation|Nitrogen-fixing]] bacteria, such as ''[[Rhizobium]]'' species, detect compounds like [[flavonoids]] secreted by the roots of leguminous plants and then produce [[nod factor]]s which signal to the plant that they are present and will lead to the formation of [[root nodule]]s. In these nodules bacteria, sustained by nutrients from the plant, convert nitrogen gas to a form that can be used by the plant.<ref>{{Cite journal|last=Chang Fu Tiana, Anne-Marie Garneronea, Céline Mathieu-Demazièrea, Catherine Masson-Boivina, and Jacques Batuta|first=|year=2012|title=Plant-activated bacterial receptor adenylate cyclases modulate epidermal infection in the Sinorhizobium meliloti–Medicago symbiosis|url=http://www.pnas.org/content/109/17/6751.full|journal=PNAS|volume=109|pages=6751–6756|via=}}</ref> Non-symbiotic (or "free-living") nitrogen-fixing bacteria may reside in the rhizosphere just outside the roots of certain plants (including many grasses), and similarly "fix" nitrogen gas in the nutrient-rich plant rhizosphere. Even though these organisms are thought to be only loosely associated with plants they inhabit, they may respond very strongly to the status of the plants. For example, nitrogen-fixing bacteria in the rhizosphere of the [[rice plant]] exhibit [[Diurnality|diurnal]] cycles that mimic plant behavior, and tend to supply more fixed nitrogen during growth stages when the plant exhibits a high demand for nitrogen.<ref>{{Cite journal |author=Sims GK, Dunigan EP |year=1984 |title=Diurnal and seasonal variations in nitrogenase activity (C2H2 reduction) of rice roots |journal=Soil Biology and Biochemistry |volume=16 |issue=1 |pages=15–18 |doi=10.1016/0038-0717(84)90118-4|last2=Dunigan}}</ref>


Although it goes beyond the rhizosphere area, it is to note that some plants secrete [[allelopathy|allelochemicals]] from their roots which inhibit the growth of other organisms. For example, [[garlic mustard]] produces a chemical which is believed to prevent [[Mutualism (biology)|mutualism]]s forming between the surrounding [[tree]]s and mycorrhiza in [[Mesic_habitat|mesic]] [[North America]]n [[Temperate broadleaf and mixed forest|temperate forests]] where it is an [[invasive species]].<ref>{{Cite journal | author = Stinson KA, Campbell SA, Powell JR, Wolfe BE, Callaway RM, Thelen GC, Hallett SG, Prati D, Klironomos JN | year = 2006 | title = Invasive plant suppresses the growth of native tree seedlings by disrupting belowground mutualisms | journal = PLoS Biology | doi = 10.1371/journal.pbio.0040140 | pmid = 16623597 | pmc = 1440938 | volume = 4 | issue = 5 | pages = e140 | postscript = <!-- Bot inserted parameter. Either remove it; or change its value to "." for the cite to end in a ".", as necessary. -->{{inconsistent citations}} | last2 = Campbell | last3 = Powell | last4 = Wolfe | last5 = Callaway | last6 = Thelen | last7 = Hallett | last8 = Prati | last9 = Klironomos}}</ref>
Although it goes beyond the rhizosphere area, it is to note that some plants secrete [[allelopathy|allelochemicals]] from their roots which inhibit the growth of other organisms. For example, [[garlic mustard]] produces a chemical which is believed to prevent [[Mutualism (biology)|mutualism]]s forming between the surrounding [[tree]]s and mycorrhiza in [[Mesic_habitat|mesic]] [[North America]]n [[Temperate broadleaf and mixed forest|temperate forests]] where it is an [[invasive species]].<ref>{{Cite journal | author = Stinson KA, Campbell SA, Powell JR, Wolfe BE, Callaway RM, Thelen GC, Hallett SG, Prati D, Klironomos JN | year = 2006 | title = Invasive plant suppresses the growth of native tree seedlings by disrupting belowground mutualisms | journal = PLoS Biology | doi = 10.1371/journal.pbio.0040140 | pmid = 16623597 | pmc = 1440938 | volume = 4 | issue = 5 | pages = e140 | postscript = <!-- Bot inserted parameter. Either remove it; or change its value to "." for the cite to end in a ".", as necessary. -->{{inconsistent citations}} | last2 = Campbell | last3 = Powell | last4 = Wolfe | last5 = Callaway | last6 = Thelen | last7 = Hallett | last8 = Prati | last9 = Klironomos}}</ref>

Revision as of 15:09, 15 March 2017

An illustration of the rhizosphere.[1] A=Amoeba consuming bacteria; BL=Energy limited bacteria; BU=Non-energy limited bacteria; RC=Root derived carbon; SR=Sloughed root hair cells; F=Fungal hyphae; N=Nematode worm

The rhizosphere is the narrow region of soil that is directly influenced by root secretions and associated soil microorganisms.[2] Soil which is not part of the rhizosphere is known as bulk soil. The rhizosphere contains many bacteria that feed on sloughed-off plant cells, termed rhizodeposition, and the proteins and sugars released by roots. Protozoa and nematodes that graze on bacteria are also more abundant in the rhizosphere. Thus, much of the nutrient cycling and disease suppression needed by plants occurs immediately adjacent to roots.[3]

Secretions

Plants secrete many compounds through their roots to serve symbiotic functions in the rhizosphere. Strigolactones, secreted and detected by mycorrhizal fungi, stimulate the germination of spores and initiate changes in the mycorrhiza that allow it to colonize the root. The parasitic plant, Striga also detects the presence of strigolactones and will germinate when it detects them; they will then move into the root, feeding off the nutrients present.[4][5] Symbiotic Nitrogen-fixing bacteria, such as Rhizobium species, detect compounds like flavonoids secreted by the roots of leguminous plants and then produce nod factors which signal to the plant that they are present and will lead to the formation of root nodules. In these nodules bacteria, sustained by nutrients from the plant, convert nitrogen gas to a form that can be used by the plant.[6] Non-symbiotic (or "free-living") nitrogen-fixing bacteria may reside in the rhizosphere just outside the roots of certain plants (including many grasses), and similarly "fix" nitrogen gas in the nutrient-rich plant rhizosphere. Even though these organisms are thought to be only loosely associated with plants they inhabit, they may respond very strongly to the status of the plants. For example, nitrogen-fixing bacteria in the rhizosphere of the rice plant exhibit diurnal cycles that mimic plant behavior, and tend to supply more fixed nitrogen during growth stages when the plant exhibits a high demand for nitrogen.[7]

Although it goes beyond the rhizosphere area, it is to note that some plants secrete allelochemicals from their roots which inhibit the growth of other organisms. For example, garlic mustard produces a chemical which is believed to prevent mutualisms forming between the surrounding trees and mycorrhiza in mesic North American temperate forests where it is an invasive species.[8]

Biological control

Trichoderma

See also

References

  1. ^ Giri, B.; Giang, P. H.; Kumari, R.; Prasad, R.; Varma, A. (2005). "Microbial Diversity in Soils". Microorganisms in Soils: Roles in Genesis and Functions. Soil Biology. Vol. 3. pp. 19–55. doi:10.1007/3-540-26609-7_2. ISBN 3-540-22220-0.
  2. ^ "Microbial Health of the Rhizosphere". Archived from the original on March 12, 2007. Retrieved 5 May 2006. {{cite web}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
  3. ^ "The Soil Food Web". USDA-NRCS. Retrieved 3 July 2006.
  4. ^ Arnaud Besserer, Virginie Puech-Pagès, Patrick Kiefer, Victoria Gomez-Roldan, Alain Jauneau, Sébastien Roy, Jean-Charles Portais, Christophe Roux, Guillaume Bécard, Nathalie Séjalon-Delmas (2006). "Strigolactones Stimulate Arbuscular Mycorrhizal Fungi by Activating Mitochondria". PLOS Biology.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  5. ^ Andreas Brachmann, Martin Parniske (2006). "The Most Widespread Symbiosis on Earth". PLOS Biology.
  6. ^ Chang Fu Tiana, Anne-Marie Garneronea, Céline Mathieu-Demazièrea, Catherine Masson-Boivina, and Jacques Batuta (2012). "Plant-activated bacterial receptor adenylate cyclases modulate epidermal infection in the Sinorhizobium meliloti–Medicago symbiosis". PNAS. 109: 6751–6756.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  7. ^ Sims GK, Dunigan EP; Dunigan (1984). "Diurnal and seasonal variations in nitrogenase activity (C2H2 reduction) of rice roots". Soil Biology and Biochemistry. 16 (1): 15–18. doi:10.1016/0038-0717(84)90118-4.
  8. ^ Stinson KA, Campbell SA, Powell JR, Wolfe BE, Callaway RM, Thelen GC, Hallett SG, Prati D, Klironomos JN; Campbell; Powell; Wolfe; Callaway; Thelen; Hallett; Prati; Klironomos (2006). "Invasive plant suppresses the growth of native tree seedlings by disrupting belowground mutualisms". PLoS Biology. 4 (5): e140. doi:10.1371/journal.pbio.0040140. PMC 1440938. PMID 16623597Template:Inconsistent citations{{cite journal}}: CS1 maint: multiple names: authors list (link) CS1 maint: postscript (link) CS1 maint: unflagged free DOI (link)

Further reading

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