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Mycorrhizal network#Importance at the forest community level

Introduction

The importance of mycorrhizal networks facilitation is no surprise. Mycorrhizal networks help regulate plant survival, growth, and defense. Understanding the network structure, function and performance levels are essential when studying plant ecosystems. Increasing knowledge on seed establishment, carbon transfer and the effects of climate change will drive new methods for conservation management practices for ecosystems.

Seedling establishment

Seedling establishment research often is focused on forest level communities with similar fungal species. However mycorrhizal networks may shift intra- and interspecific interactions that may alter pre-established plants physiology. Shifting competition can alter the evenness and dominance of the plant community. Discovery of seedling establishment showed seedling preference is near existing plants of con-or heterospecific species and seedling amount is abundant.^[1] Many believe the process of new seedlings becoming infected with existing mycorrhizae expedite their establishment within the community. The seedling inherit tremendous benefits from their new formed symbiotic relation with the fungi. ^[2]The new influx of nutrients and water availability, help the seedling with growth but more importantly help ensure survival when in a stressed state. ^[3]Mycorrhizal networks aid in regeneration of seedlings when secondary succession occurs, seen in temperate and boreal forests.^[1]

Seedling benefits from infecting mycorrhizae

Increase infectivity range of diverse mycorrhizal fungi
Increase carbon inputs from mycorrhizal networks with other plants
Increased area means greater access to nutrients and water
Increased exchange rates of nutrients and water from other plants.

Mature Pseudotsuga Menziesii

Several studies have focused on relationships between mycorrhizal networks and plants, specifically their performance and establishment rate.  Pseudotsuga menziesii seedlings growth expanded when planted with hardwood trees compared to unamended soils in the Oregon Mountains. P. menziesii had higher rates of ectomycorrhizal fungal diversity, richness, and photosynthetic rates when planted alongside root systems of mature P. menziesii and B. papyrifera than compared to those seedlings who exhibited no or little growth when isolated from mature trees. .^[4]P. Menziessi was the focus of another study to understand its preference for establishing in an ecosystem. Two shrub species, Arctostahphylos and Adenostoma both had the opportunity to colonize the seedlings with their ectomycorrhizae fungi. Arctostaphylos shrubs colonized P. Menziessi seedlings who also had higher survival rates. The mycorrhizae joining the pair had greater net carbon transfer toward the seedling. ^[5]The researchers were able to minimize environmental factors they encountered in order to avoid swaying readers in opposite directions.

In burned and salvaged forest, Quercus rubrum L. establishment was facilitated when acorns were planted near Q. Montana but did not grow when near arbuscular mycorrhizae Acer rubrum L. Seedlings deposited near Q.mmontana had a greater diversity of ectomycorrhizal fungi, and a more significant net transfer of nitrogen and phosphorus contents demonstrating ectomycorrhizal fungi formation with the seedling helped with their establishment. Results demonstrated with increasing density; mycorrhizal benefits decrease due to an abundance of resources that overwhelmed their system resulting in little growth as seen in Q.rubrum. ^[6]

Mycorrhizae networks decline with increasing distance from parents, but rate of survival was unaffected. Indicating seedling survival has a positive relation with decreasing competition as networks move out farther. ^[7]

One study displayed the effects of ectomycorrhizal networks in plants who face primary succession. In his experiment, Nara transplanted Salix reinii seedlings inoculated with different ectomycorrhizal species. He found that mycorrhizal networks are the connection of ectomycorrhizal fungi colonization and plant establishment. Results showed increased biomass and survival of germinates near the inoculated seedlings compared to inoculated seedlings. ^[8]

In conclusion, studies have found that association with mature plant equates with higher survival of the plant and greater diversity and species richness of the mycorrhizal fungi. However, these studies have not considered the threshold status of competing for resources and the benefit for the mycorrhizal networks.

Carbon Transfer

Carbon transfer has been demonstrated by experiments using isotopic ¹⁴C and following the pathway from ectomycorrhizal conifer seedlings to another using mycorrhizal networks.  ^[9] The experiment showed a bidirectional movement of the 14C   within ectomycorrhizae species. Further investigation of bidirectional movement and the net transfer was analyzed using pulse labeling technique with isotopes ¹³C and ¹⁴C in Ectomycorrhizal species Pseudotsuga Menziesii and Betula payrifera seedlings. ^[10]Results displayed an overall net balance of carbon transfer between the two until the second year where ^{P. Menziesii} received carbon from B. payrifera.^{[11] [12]}Detection of the isotopes was found in receiver plant shorts, expressing carbon transfer from fungus to plant tissues.

When ectomycorrhizal fungi receiver end of the plant has limited sunlight availability, there was an increase in carbon transfer, indicating a source-sink gradient of carbon among plants and shade surface area regulates carbon transfer.^[13]

Water Transfer

Isotopic tracers and fluorescent dyes have been used to establish the water transfer between conspecific or heterospecific plants. The hydraulic lift aids in water transfer from deep-rooted trees to seedlings. Potentially indicating This could be a problem within drought-stressed plants which form these MN with neighbors. The would depend on the severity of drought and tolerance of another plant species.^[14]

1. Perry, D.A; Bell (1992). "Mycorrhizal fungi in mixed-species forests and tales of positive feedback, redundancy, and stability. The ecology of mixed-species stands of trees". Blackwell, Oxford: 145–180.
2. Simard, Suzanne W.; Perry, David A.; Jones, Melanie D.; Myrold, David D.; Durall, Daniel M.; Molina, Randy (1997-08). "Net transfer of carbon between ectomycorrhizal tree species in the field". Nature. 388 (6642): 579–582. doi:10.1038/41557. ISSN 0028-0836. {{cite journal}}: Check date values in: |date= (help)
3. PERRY, D. A.; MARGOLIS, H.; CHOQUETTE, C.; MOLINA, R.; TRAPPE, J. M. (1989-08). "Ectomycorrhizal mediation of competition between coniferous tree species". New Phytologist. 112 (4): 501–511. doi:10.1111/j.1469-8137.1989.tb00344.x. ISSN 0028-646X. {{cite journal}}: Check date values in: |date= (help)
4. SIMARD, SUZANNE W.; PERRY, DAVID A.; SMITH, JANE E.; MOLINA, RANDY (1997-06). "Effects of soil trenching on occurrence of ectomycorrhizas on Pseudotsuga menziesii seedlings grown in mature forests of Betula papyrifera and Pseudotsuga menziesii". New Phytologist. 136 (2): 327–340. doi:10.1046/j.1469-8137.1997.00731.x. ISSN 0028-646X. {{cite journal}}: Check date values in: |date= (help)
5. Horton, Thomas R; Bruns, Thomas D; Parker, V Thomas (1999-06). "Ectomycorrhizal fungi associated with Arctostaphylos contribute to Pseudotsuga menziesii establishment". Canadian Journal of Botany. 77 (1): 93–102. {{cite journal}}: Check date values in: |date= (help)
6. Dickie, Ian A.; Koide, Roger T.; Steiner, Kim C. (2002-11). "Influences of Established Trees on Mycorrhizas, Nutrition, and Growth of Quercus rubra Seedlings". Ecological Monographs. 72 (4). {{cite journal}}: Check date values in: |date= (help)
7. Onguene, N.; Kuyper, T. (2002-02). "Importance of the ectomycorrhizal network for seedling survival and ectomycorrhiza formation in rain forests of south Cameroon". Mycorrhiza. 12 (1): 13–17. {{cite journal}}: Check date values in: |date= (help)
8. Nara, Kazuhide (2006). "Ectomycorrhizal networks and seedling establishment during early primary succession". New Phytologist. 169 (1): 169–178.
9. Reid, C. P. P.; Woods, Frank W. (1969-03). "Translocation of C^(14)-Labeled Compounds in Mycorrhizae and It Implications in Interplant Nutrient Cycling". Ecology. 50 (2): 179–187. doi:10.2307/1934844. ISSN 0012-9658. {{cite journal}}: Check date values in: |date= (help)
10. READ, Larissa; LAWRENCE, Deborah, "INTERACTIONS BETWEEN WATER AVAILABILITY AND NUTRIENT CYCLING IN DRY TROPICAL FORESTS", Dryland Ecohydrology, Kluwer Academic Publishers, pp. 217–232, ISBN 1402042590, retrieved 2018-12-15
11. SIMARD, SUZANNE W.; JONES, MELANIE D.; DURALL, DANIEL M.; PERRY, DAVID A.; MYROLD, DAVID D.; MOLINA, RANDY (1997-11). "Reciprocal transfer of carbon isotopes between ectomycorrhizal Betula papyrifera and Pseudotsuga menziesii". New Phytologist. 137 (3): 529–542. doi:10.1046/j.1469-8137.1997.00834.x. ISSN 0028-646X. {{cite journal}}: Check date values in: |date= (help)
12. Newman, E.I. (1988), "Mycorrhizal Links Between Plants: Their Functioning and Ecological Significance", Advances in Ecological Research, Elsevier, pp. 243–270, ISBN 9780120139187, retrieved 2018-12-15
13. Francis, R.; Read, D. J. (1984-01). "Direct transfer of carbon between plants connected by vesicular–arbuscular mycorrhizal mycelium". Nature. 307 (5946): 53–56. doi:10.1038/307053a0. ISSN 0028-0836. {{cite journal}}: Check date values in: |date= (help)
14. "Common mycorrhizal networks provide a potential pathway for the transfer of hydraulically lifted water between plants". Journal of Experimental Botany. 58 (12): 3484–3484. 2007-07-13. doi:10.1093/jxb/erm266. ISSN 0022-0957.

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