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Lumbricus terrestris is a large, reddish worm species widely distributed around the world (along with several other lumbricids). In some areas where it is an introduced species, some people consider it a serious pest for outcompeting native worms.


Through much of Europe, it is the largest naturally occurring species of earthworm, typically reaching 20 – 25 cm in length when extended (though in parts of southern Europe, the native species are much larger). In September 2012, a specimen was found in SW China measuring roughly 50 cm in length. In May 2016 a worm was found that was about 61cm long. It has an unusual habit of copulating on the surface at night, which makes it more visible than most other earthworms.
== Overview ==


Common names
The root is typically the part of the plant that grows into the [[soil]], although it can be aerial in waterlogged soil. Roots have two main functions, anchoring the plant to the ground, and absorbing nutrients, water, and minerals for the plant. There are two main types of roots, tap roots and fibrous roots, both of which are explained in this page. Plant root systems can be very extensive, and are harder to study than the above ground biomass. Current methods for studying root systems include: the [[harvest method]], [[isotopic analysis]], [[root ingrowth]], and [[rhizotrons]]. Roots can often have symbiotic relationships with [[Ectomycorrhizal Fungi]] and [[Arbuscular Mycorrhizal Fungi]].
Because it is widely known, Lumbricus goes under a variety of common names. In Britain, it is primarily called the common earthworm or lob worm (though that name is also applied to a marine polychaete). In North America, the term nightcrawler (or vitalis) is also used. In Canada, it is also called the dew worm, or "Grandaddy Earthworm". In the rest of the world, most references are just to the scientific name, though with occasional reference to the above names.


Although this is not the most abundant earthworm, even in its native range, it is a very conspicuous and familiar earthworm species in garden and agricultural soils of the temperate zone, and is frequently seen on the surface, unlike most other earthworms. It is also used as the example earthworm for millions of biology students around the world, even in areas where the species does not exist. However, 'earthworm' can be a source of confusion, since in most of the world, other species are more typical. For example, through much of the unirrigated temperate areas of the world, the "common earthworm" is actually Aporrectodea (=Allolobophora) trapezoides, which in those areas is a similar size and dark color to L. terrestris.
== Parts of the plant root ==
[[File:partsofroots.jpg|300px|thumb|left|Parts of the Root. Source: Biology Junction]] [[File:Root_Crosssection.jpg|300px|thumb|left|Root Cross Section. Source: Encyclopædia Britannica, Inc.]]


Biology
; Root Hairs
:The [[root hairs]] are thin hairlike structures growing from the epidermis. These help with the absorption of moisture and nutrients from the soil, which is then transported to the rest of the plant. The majority of plant water absorption happens with the root hairs. The length and shape allows them to have a large surface area while being able to go between soil particles, both of which helps with water absorption. In legume plants, they are involved in root nodule formation. 


Earthworm head
; Xylem
L. terrestris is an anecic worm. That is, it forms temporary deep burrows and comes to the surface to feed, as opposed to burrowing through the soil for its food as most other earthworms do. An unusual habit of this species is to pull leaves into the mouth of its burrow where they partially decay before being eaten. While they generally feed on plant material, they have been observed feeding on dead insects and feces.
:In vascular plants, xylem transports nutrients and water in a sap from the roots to the stem and leaves. It uses passive transportation, so it does not need an input of energy to operate. The xylem is primarily composed of dead cells, and can only flow upward. This movement is mainly driven by negative pressures.  


The natural lifespan of L. terrestris is unknown, though individuals have lived for six years in captivity.
;Phloem
:In vascular plants, phloem transports the products of photosynthesis in a sap from the chloroplast down to the roots or storage structures. The sap holds a lot of sucrose, but is water-based. The phloem is primarily composed of living cells and is able to flow in many different directions. It's flow is called translocation, and is mainly caused by positive hydrostatic pressures.  


In parts of Europe, notably the Atlantic fringe of northwestern Europe, it is now locally endangered due to predation by the New Zealand flatworm (Arthurdendyus triangulatus) and the Australian flatworm (Australoplana sanguinea), two predatory flatworms accidentally introduced from New Zealand and Australia. These predators are very efficient earthworm eaters, being able to survive for lengthy periods with no food, so still persist even when their prey has dropped to unsustainably low populations. In some areas, this is having a seriously adverse effect on the soil structure and quality. The soil aeration and organic material mixing previously done by the earthworms has ceased in some areas.
;Pericycle
:The pericycle is made up of sclerenchyma or parenchyma cells in a cylindrical shape. In dicots, it gives protection to vascular bundles and strengthens the roots. In eudicots, it can create lateral roots, which grow horizontally and help anchor the plant.


;Endodermis
:The endodermis is the innermost layer of the cortex. The outer ring of the epidermis is deposited with the casparian strip, which helps stop the flow of water from around the cell membranes. This helps to regulate the water that flows into or out of the xylem, and stops gas bubbles from reaching the xylem.


The worm found in May 2016
;Apical meristem
As an invasive species in North America
:The apical meristem is full of actively dividing cells. It allows for primary growth, where the plant grows up and down!
Main article: Invasive earthworms of North America
L. terrestris is considered invasive in the north central United States. It does not do well in tilled fields because of pesticide exposure, physical injuries from farm equipment and a lack of nutrients. It thrives in fence rows and woodlots and can lead to reductions in native herbaceous and tree regrowth.


Further reading
;Root cap
McTavish, Michael J.; Basiliko, Nathan; Sackett, Tara E. (December 2013). "Environmental Factors Influencing Immigration Behaviors of the Invasive Earthworm Lumbricus terrestris". Canadian Journal of Zoology. 91 (12): 859–865. doi:10.1139/cjz-2013-0153.
:The root cap protects the growing apical meristem by secreting a mucus that eases the movement of the root through the soil.
External links
 
Kladivko EJ, Akhouri NM, Weesies G (1997). "Earthworm populations and species distributions under no-till and conventional tillage in Indiana and Illinois". Soil Biol Biochem. 29 (3–4): 613–615. doi:10.1016/s0038-0717(96)00187-3.
;Epidermis
Butt KR, Shipitalo MJ, Bohlen PJ, Edwards WM, Parmelee RW (1999). "Long-term trends in earthworm populations of cropped experimental watershed in Ohio, USA". Pedobiologia. 43: 713–719.
:The epidermis is the outerlayer of cells on the root. It absorbs water and nutrients, regulates gas exchange, stops water loss, and puts out metabolic compounds. It is covered in stomata, which is a pore that regulates water vapor and gas exchange.
Frelich LE, Hale CM, Scheu S, Holdsworth AR, Heneghan L, Bohlen PJ, Reich PB (2006). "Earthworm invasion into previously earthworm-free temperate and boreal forests". Biol Invasions. 8 (6): 1235–1245. doi:10.1007/s10530-006-9019-3.
 
Hale CM, Frelich LE, Reich PB (2005). "Exotic European earthworm invasion dynamics in northern hardwood forests of Minnesota, USA". Ecol Appl. 15 (3): 848–860. doi:10.1890/03-5345.
== Types of plant roots ==
Wikimedia Commons has media related to Lumbricus terrestris.
 
Types of Earthworms - New Zealand
[[File:rootsystems.gif|300px|thumb|left|Types of Roots. Source: National Gardening Association, Inc.]]
Earthworm Research Group (at the University of Central Lancashire):Frequently Asked Questions
;Tap Roots
NNZ-Nightcrawler
:Tap roots typically are large roots that grow downward, which other roots laterally sprout from. Some tap roots will persist for the entire plant life, but most plants will replace them with a fibrous system. [[Dicots]] are an example of plants that start with a tap root system. In some plants, like carrots, the tap root is later developed into an organ for storage. Most plants replace the tap root with the fibrous root because the tap roots grows from the radicle of the plant, which often dies after germination, forcing it to switch.  
The microfungal community of Lumbricus terrestris middens in a Linden (Tilia cordata) forest (PDF)
 
Exotic Earthworms in Minnesota Hardwood Forests (PDF)
;Fibrous Roots
Wise, Scott (2 September 2012). "Biologists trying to figure why giant earthworm grew so big". CBS 6, WTVR-TV. Retrieved 15 May 2013.
:Fibrous roots grow out of the stem and are made up of many thin branching roots. This can spread widely in the soil, sometimes becoming larger than the above ground plant. This type of root system can be seen in [[monocots]], such as grasses.
 
;Adventitious Roots
:Although tap roots and fibrous roots are the primary root system seen, adventitious roots are sometimes seen. These roots arise from the stem or a leaf, often being seen on plants that have an underground stem. Some of these roots are aerial, being completely or partially above the soil. Examples of plants that have these roots are mangroves, bamboo, and corn.  
 
;Other Specialized Roots Systems
:There are various other specialized root systems that are not as common to see. For example, some parasitic plants have root projections called haustoria, which penetrate the hosts tissues and absorb its nutrients. Another example of a specialized root system is pneumatophores, which can be seen on swamp plants. These roots are aerial and allow for gas exchange in the water-logged soil.
 
== Citations ==
 
*Gyssels, G., et al. “Impact of Plant Roots on the Resistance of Soils to Erosion by Water: a Review.” Progress in Physical Geography, vol. 29, no. 2, 2005, pp. 189–217.
*Cannon, William Austin. “A Tentative Classification of Root Systems.” [[Ecology]], vol. 30, no. 4, 1 Oct. 1949, pp. 542–548.
*Glinski, J. Soil Physical Conditions and Plant Roots. CRC Press, 2018.
*Russell, Robert Scott. Plant Root Systems: Their Function and Interaction with the Soil. English Language Book Society and McGraw-Hill, 1982.
*Esau, K. 1965. Plant Anatomy, 2nd Edition. John Wiley & Sons. 767 pp.
*Beeckman, Tom; De Smet, Ive (2014). "Pericycle". Current Biology. 24 (10): R378–9
*Britannica, The Editors of Encyclopaedia. “Root.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 13 Apr. 2018
*Sutton, R. F.; Tinus, R. W. (1983). "Root and root system terminology". Forest Science Monograph. 24: 137.
*Coutts, M. P. (1987). "Developmental processes in tree root systems". Canadian Journal of Forest Research. 17: 761–767. doi:10.1139/x87-122

Latest revision as of 12:05, 29 April 2021

Overview

The root is typically the part of the plant that grows into the soil, although it can be aerial in waterlogged soil. Roots have two main functions, anchoring the plant to the ground, and absorbing nutrients, water, and minerals for the plant. There are two main types of roots, tap roots and fibrous roots, both of which are explained in this page. Plant root systems can be very extensive, and are harder to study than the above ground biomass. Current methods for studying root systems include: the harvest method, isotopic analysis, root ingrowth, and rhizotrons. Roots can often have symbiotic relationships with Ectomycorrhizal Fungi and Arbuscular Mycorrhizal Fungi.

Parts of the plant root

Parts of the Root. Source: Biology Junction
Root Cross Section. Source: Encyclopædia Britannica, Inc.
Root Hairs
The root hairs are thin hairlike structures growing from the epidermis. These help with the absorption of moisture and nutrients from the soil, which is then transported to the rest of the plant. The majority of plant water absorption happens with the root hairs. The length and shape allows them to have a large surface area while being able to go between soil particles, both of which helps with water absorption. In legume plants, they are involved in root nodule formation.
Xylem
In vascular plants, xylem transports nutrients and water in a sap from the roots to the stem and leaves. It uses passive transportation, so it does not need an input of energy to operate. The xylem is primarily composed of dead cells, and can only flow upward. This movement is mainly driven by negative pressures.
Phloem
In vascular plants, phloem transports the products of photosynthesis in a sap from the chloroplast down to the roots or storage structures. The sap holds a lot of sucrose, but is water-based. The phloem is primarily composed of living cells and is able to flow in many different directions. It's flow is called translocation, and is mainly caused by positive hydrostatic pressures.
Pericycle
The pericycle is made up of sclerenchyma or parenchyma cells in a cylindrical shape. In dicots, it gives protection to vascular bundles and strengthens the roots. In eudicots, it can create lateral roots, which grow horizontally and help anchor the plant.
Endodermis
The endodermis is the innermost layer of the cortex. The outer ring of the epidermis is deposited with the casparian strip, which helps stop the flow of water from around the cell membranes. This helps to regulate the water that flows into or out of the xylem, and stops gas bubbles from reaching the xylem.
Apical meristem
The apical meristem is full of actively dividing cells. It allows for primary growth, where the plant grows up and down!
Root cap
The root cap protects the growing apical meristem by secreting a mucus that eases the movement of the root through the soil.
Epidermis
The epidermis is the outerlayer of cells on the root. It absorbs water and nutrients, regulates gas exchange, stops water loss, and puts out metabolic compounds. It is covered in stomata, which is a pore that regulates water vapor and gas exchange.

Types of plant roots

Types of Roots. Source: National Gardening Association, Inc.
Tap Roots
Tap roots typically are large roots that grow downward, which other roots laterally sprout from. Some tap roots will persist for the entire plant life, but most plants will replace them with a fibrous system. Dicots are an example of plants that start with a tap root system. In some plants, like carrots, the tap root is later developed into an organ for storage. Most plants replace the tap root with the fibrous root because the tap roots grows from the radicle of the plant, which often dies after germination, forcing it to switch.
Fibrous Roots
Fibrous roots grow out of the stem and are made up of many thin branching roots. This can spread widely in the soil, sometimes becoming larger than the above ground plant. This type of root system can be seen in monocots, such as grasses.
Adventitious Roots
Although tap roots and fibrous roots are the primary root system seen, adventitious roots are sometimes seen. These roots arise from the stem or a leaf, often being seen on plants that have an underground stem. Some of these roots are aerial, being completely or partially above the soil. Examples of plants that have these roots are mangroves, bamboo, and corn.
Other Specialized Roots Systems
There are various other specialized root systems that are not as common to see. For example, some parasitic plants have root projections called haustoria, which penetrate the hosts tissues and absorb its nutrients. Another example of a specialized root system is pneumatophores, which can be seen on swamp plants. These roots are aerial and allow for gas exchange in the water-logged soil.

Citations

  • Gyssels, G., et al. “Impact of Plant Roots on the Resistance of Soils to Erosion by Water: a Review.” Progress in Physical Geography, vol. 29, no. 2, 2005, pp. 189–217.
  • Cannon, William Austin. “A Tentative Classification of Root Systems.” Ecology, vol. 30, no. 4, 1 Oct. 1949, pp. 542–548.
  • Glinski, J. Soil Physical Conditions and Plant Roots. CRC Press, 2018.
  • Russell, Robert Scott. Plant Root Systems: Their Function and Interaction with the Soil. English Language Book Society and McGraw-Hill, 1982.
  • Esau, K. 1965. Plant Anatomy, 2nd Edition. John Wiley & Sons. 767 pp.
  • Beeckman, Tom; De Smet, Ive (2014). "Pericycle". Current Biology. 24 (10): R378–9
  • Britannica, The Editors of Encyclopaedia. “Root.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 13 Apr. 2018
  • Sutton, R. F.; Tinus, R. W. (1983). "Root and root system terminology". Forest Science Monograph. 24: 137.
  • Coutts, M. P. (1987). "Developmental processes in tree root systems". Canadian Journal of Forest Research. 17: 761–767. doi:10.1139/x87-122