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{{Short description|Basal organ  of a vascular plant}}
{{About|the part of a plant}}
{{Redirect|Rooted|the 1969 play and TV movie adaptation|Rooted (film)|the song|Ciara discography}}
[[File:Primary and secondary cotton roots.jpg|thumb|Primary and secondary roots in a [[cotton]] plant]]
In [[vascular plant]]s, the '''roots''' are the [[plant organ|organs of a plant]] that are modified to provide anchorage for the plant and take in water and nutrients into the plant body, which allows plants to grow taller and faster.<ref name="Stevens2019">{{cite book|author=Harley Macdonald & Donovan Stevens|title=Biotechnology and Plant Biology|url=https://books.google.com/books?id=Y-fEDwAAQBAJ&pg=PA141|date=3 September 2019|publisher=EDTECH|isbn=978-1-83947-180-3|pages=141–}}</ref> They are most often below the surface of the [[soil]], but roots can also be [[aerial root|aerial]] or aerating, that is, growing up above the ground or especially above water.<ref>{{Cite journal |last1=Nguyen |first1=Linh Thuy My |last2=Hoang |first2=Hanh Thi |last3=Choi |first3=Eunho |last4=Park |first4=Pil Sun |date=2023-07-05 |title=Distribution of mangroves with different aerial root morphologies at accretion and erosion sites in Ca Mau Province, Vietnam |journal=Estuarine, Coastal and Shelf Science |volume=287 |article-number=108324 |doi=10.1016/j.ecss.2023.108324 |doi-access=free |bibcode=2023ECSS..28708324N }}</ref>

== Function ==
Roots perform several essential and specialised roles that support plant growth, development and survival. Their '''primary functions''' are anchorage, uptake (absorption) of water and dissolved minerals, and conduction of these resources to the shoot. Beyond these, roots carry out a range of important '''secondary''' and '''adaptive functions''' — storage of reserves, synthesis of growth regulators, gas exchange in waterlogged environments, facilitation of symbiotic nutrient acquisition, and vegetative propagation.<ref>{{cite web |title=Root |url=https://www.britannica.com/science/root-plant
 |publisher=Encyclopaedia Britannica |access-date=2 November 2025}}</ref>

=== Primary functions ===

'''Anchorage and mechanical support.''' Roots fix the plant in the substrate and resist mechanical forces (wind, waterflow); vigorous root systems are essential for crop stability and prevention of lodging.<ref name="Zeiger Taiz">{{cite book |last1=Taiz |first1=L. |last2=Zeiger |first2=E. |title=Plant Physiology and Development |edition=3rd |publisher=Sinauer Associates/Oxford University Press |year=2010}}</ref><ref>{{cite web |title=Roots and Root Systems (chapter) |url=https://udspace.udel.edu/bitstream/handle/19716/2830/Chapter%205.%20Roots%20and%20Root%20Systems.pdf |publisher=University of Delaware |access-date=2 November 2025}}</ref>

'''Absorption of water and mineral nutrients.''' Root epidermal cells and root hairs take up soil water and dissolved ions; these are then conducted to the shoot via the xylem. Root architecture (depth, spread) determines access to water and nutrients in different soil horizons.<ref>{{cite web |title=Root |url=https://www.britannica.com/science/root-plant
 |publisher=Encyclopaedia Britannica |access-date=2 November 2025}}</ref><ref>{{cite journal |last=Hodge |first=A. |title=Root growth, architecture and nutrient foraging |journal=Plant and Soil |year=2009 |doi=10.1007/s11104-009-0041-1 |doi-broken-date=3 November 2025 |url=https://link.springer.com/article/10.1007/s11104-009-0041-1
 |access-date=2 November 2025}}</ref>

=== Secondary and specialised functions ===

'''Storage of reserve food and water.''' Many roots (fleshy taproots, tuberous roots) accumulate carbohydrates and water that support perennial growth or regrowth after dormancy. Examples include sweet potato and carrot.<ref>{{cite web |title=Tuberous root |url=https://www.britannica.com/science/tuberous-root
 |publisher=Encyclopaedia Britannica |access-date=2 November 2025}}</ref>

'''Conduction.''' Roots conduct absorbed water, minerals and some synthesised compounds to the shoot via vascular tissues (xylem and phloem connections).<ref name="Zeiger Taiz">{{cite book |last1=Taiz |first1=L. |last2=Zeiger |first2=E. |title=Plant Physiology and Development |edition=3rd |publisher=Sinauer Associates/Oxford University Press |year=2010}}</ref>

'''Synthesis of growth regulators.''' Roots synthesise and modulate plant hormones (e.g., cytokinins, some auxin metabolism), influencing shoot development and whole-plant physiology.<ref>{{cite journal |last=Steffens |first=B. |title=The physiology of adventitious roots |journal=Frontiers in Plant Science |year=2015 |volume=170 |issue=2 |pages=603–617 |doi=10.1104/pp.15.01360 |pmid=26697895 |pmc=4734560 }}</ref>

'''Aeration and gas exchange (in aquatic/waterlogged soils).''' Specialised structures (pneumatophores, aerial roots) permit gas exchange where soil oxygen is limited, enabling respiration in mangroves and other hydrophytes.<ref>{{cite web |title=Pneumatophore |url=https://www.britannica.com/science/pneumatophore-root-system
 |publisher=Encyclopaedia Britannica |access-date=2 November 2025}}</ref>

'''Symbiotic interactions and enhanced nutrient uptake.''' Roots form mutualisms (e.g., mycorrhizae, nitrogen-fixing nodules) that greatly increase nutrient acquisition and stress tolerance. These associations remodel root architecture and function.<ref>{{cite journal |last=Ahmed |first=N. |title=How arbuscular mycorrhizal fungi enhance nutrient uptake and plant resilience |journal=Frontiers in Plant Science |year=2025 |volume=16 |article-number=e144989 |doi=10.3897/imafungus.16.144989 |doi-access=free |pmid=40162002 |pmc=11953731 }}</ref>

'''Mechanical adaptations and additional support.''' Adventitious and brace/prop roots (e.g., maize, some mangroves, banyan) provide extra support, anchorage and stability in particular environments.<ref>{{cite web |title=Maize plants and the brace roots that support them |url=https://www.researchgate.net/publication/363551213
 |access-date=2 November 2025}}</ref>

'''Vegetative propagation.''' Adventitious rooting on stems, nodes or cuttings allows many species to reproduce asexually and to regenerate after damage; this is widely exploited in horticulture.<ref>{{cite web |title=Adventitious root |url=https://www.britannica.com/science/adventitious-root
 |publisher=Encyclopaedia Britannica |access-date=2 November 2025}}</ref>

=== Notes ===

Many functions overlap: a given root can simultaneously anchor, absorb, store reserves and engage in symbiosis. Root form and function are plastic and shaped by species genetics and environmental context (soil texture, water availability, aeration and mechanical stresses).<ref>{{cite journal |last=Gutjahr |first=C. |title=Multiple control levels of root system remodelling in response to symbiosis and nutrient status |journal=Frontiers in Plant Science |year=2013 |volume=4 |page=204 |doi=10.3389/fpls.2013.00204 |pmid=23785383 |pmc=3684781 |doi-access=free }}</ref>

== Types of roots (major rooting system) ==
Plants produce a variety of root systems that differ in origin, structure and function (anchorage, absorption, storage, aeration and vegetative propagation). The two classical, broad categories are '''taproot''' and '''fibrous''' systems, but several specialised root types — notably '''adventitious''', '''aerial''', '''prop/stilt''', '''climbing/adhesive''', '''buttress''', '''tuberous''' (storage) and '''floating''' roots — are biologically and ecologically important.<ref>{{cite web |title=Root |url=https://www.britannica.com/science/root-plant
 |publisher=Encyclopaedia Britannica |access-date=2 November 2025}}</ref>

=== Taproot system ===
A taproot system is dominated by a single, vertically growing primary root (the radicle) from which lateral roots arise. Taproots often function in deep anchorage and in storage of carbohydrates and water (common in many dicotyledons and some biennials/perennials). Examples include carrot (Daucus carota), dandelion (Taraxacum) and many true dicots.<ref>{{cite web |title=Taproot |url=https://www.britannica.com/science/taproot
 |publisher=Encyclopaedia Britannica |access-date=2 November 2025}}</ref>

=== Fibrous root system ===
A fibrous root system consists of numerous, similarly sized roots that form a dense network near the soil surface. In many species this network is composed largely of adventitious roots that arise from the stem base rather than the primary radicle. Fibrous systems are effective at soil binding, rapid uptake of surface nutrients and erosion control. Typical examples are grasses (Poaceae), wheat and rice.<ref>{{cite web |title=Fibrous root system |url=https://www.britannica.com/science/fibrous-root-system
 |publisher=Encyclopaedia Britannica |access-date=2 November 2025}}</ref>

=== Adventitious roots ===
Adventitious roots arise from non-root organs (stems, nodes, leaves or callus tissue) and play multiple roles: replacing or supplementing the primary root, providing mechanical support, enabling vegetative propagation, and forming specialized root types (aerial roots, prop roots, pneumatophores). They are especially important in monocots and many cultivated plants, and are a common response to wounding, flooding or other stressors.<ref>{{cite web |last= |first= |title=Adventitious root |url=https://www.britannica.com/science/adventitious-root
 |publisher=Encyclopaedia Britannica |access-date=2 November 2025}}</ref><ref>{{cite journal |last=Steffens |first=B. |title=The physiology of adventitious roots |journal=Frontiers in Plant Science |year=2015 |volume=170 |issue=2 |pages=603–617 |doi=10.1104/pp.15.01360 |pmid=26697895 |pmc=4734560 }}</ref>

Examples and notes: in many monocots the functional root system is adventitious (forming a fibrous habit); maize (Zea mays) produces nodal brace/prop roots that stabilise the stem; banyan (Ficus spp.) develops aerial adventitious roots that may become supportive trunks; many cuttings root adventitiously during vegetative propagation.<ref>{{cite arXiv |last=Hostetler |first=A.N. |title=The development and function of brace roots in maize |year=2020 |class=q-bio.TO |eprint=2008.04783}}</ref>

== Anatomy ==
[[File:CSIRO ScienceImage 11626 Barley root.jpg|thumb|The cross-section of a [[Hordeum vulgare|barley]] root]]
Root morphology is divided into four zones: the [[root cap]], the [[apical meristem]], the elongation zone, and the hair.<ref name="Okon1993">{{cite book|author=Yaacov Okon|title=Azospirillum/Plant Associations|url=https://books.google.com/books?id=I07BKGI8rboC&pg=PA77|date=24 November 1993|publisher=CRC Press|isbn=978-0-8493-4925-6|pages=77–}}</ref> The [[root cap]] of new roots helps the root penetrate the soil. These root caps are sloughed off as the root goes deeper creating a slimy surface that provides lubrication. The [[Meristem|apical meristem]] behind the root cap produces new root cells that elongate. Then, root hairs form that absorb water and mineral nutrients from the soil.<ref name=arizona>{{cite web |title=Backyard Gardener: Understanding Plant Roots |website=University of Arizona Cooperative Extension |url=https://cals.arizona.edu/yavapai/anr/hort/byg/archive/understandingplantroots.html}}</ref> The first root in seed producing plants is the [[radicle]], which expands from the plant embryo after [[Germination|seed germination]].

When dissected, the arrangement of the cells in a root is [[root hair]], [[Epidermis (botany)|epidermis]], [[epiblem]], [[Cortex (botany)|cortex]], [[endodermis]], [[pericycle]] and, lastly, the [[vascular tissue]] in the centre of a root to transport the water absorbed by the root to other places of the plant.{{clarify|reason=need diagram |date=March 2016}}
[[File:Ranunculus Root Cross Section.png|thumb|''Ranunculus'' root cross section]]

Perhaps the most striking characteristic of roots that distinguishes them from other plant organs such as stem-branches and leaves is that roots have an ''endogenous''<ref>{{cite book | title = College Botany | volume = 1 | vauthors = Gangulee HC, Das KS, Datta CT, Sen S | publisher = New Central Book Agency | location = Kolkata }}</ref> origin, ''i.e.'', they originate and develop from an inner layer of the mother axis, such as [[pericycle]].<ref>{{cite book | title = BOTANY For Degree Students | edition = 6th | vauthors = Dutta AC, Dutta TC | publisher = Oxford University Press }}</ref> In contrast, stem-branches and leaves are ''exogenous'', ''i.e.'', they start to develop from the cortex, an outer layer.

In response to the concentration of nutrients, roots also synthesize [[cytokinin]], which acts as a signal as to how fast the shoots can grow. Roots often function in storage of food and nutrients. The roots of most vascular plant species enter into symbiosis with certain [[fungi]] to form [[mycorrhiza]]e, and a large range of other organisms including [[bacteria]] also closely associate with roots.<ref>{{Cite book|last=Sheldrake|first=Merlin|title=Entangled Life|publisher=Bodley Head|year=2020|isbn=978-1-84792-520-6|page=148}}</ref>

[[File:Kiental entre Herrsching y Andechs, Alemania 2012-05-01, DD 12.JPG|thumb|Large, mature tree roots above the soil]]

==Root system architecture (RSA)==
[[File:Tree Roots at Riverside.jpg|thumb|Tree roots at [[Cliffs of the Neuse State Park]]]]

===Definition===
In its simplest form, the term root system architecture (RSA) refers to the spatial configuration of a plant's root system. This system can be extremely complex and is dependent upon multiple factors such as the species of the plant itself, the composition of the soil and the availability of nutrients.<ref>{{cite journal| vauthors = Malamy JE |title=Intrinsic and environmental response pathways that regulate root system architecture |journal=Plant, Cell & Environment |year=2005|volume=28|issue=1 |pages=67–77 |doi=10.1111/j.1365-3040.2005.01306.x|pmid=16021787 |doi-access=free |bibcode=2005PCEnv..28...67M }}</ref> Root architecture plays the important role of providing a secure supply of nutrients and water as well as anchorage and support.

The configuration of root systems serves to structurally support the plant and compete with other plants for uptake of nutrients within the soil.<ref name=":0">{{cite journal | vauthors = Caldwell MM, Dawson TE, Richards JH | title = Hydraulic lift: consequences of water efflux from the roots of plants | journal = Oecologia | volume = 113 | issue = 2 | pages = 151–161 | date = January 1998 | pmid = 28308192 | doi = 10.1007/s004420050363 | bibcode = 1998Oecol.113..151C }}</ref> Roots grow [[Root phenotypic plasticity|in response to]] specific ecological conditions, which, if changed, can impede a plant's growth. For example, a root system that has developed in dry soil may not be as efficient in flooded soil, yet plants are able to adapt to other changes in the environment, such as seasonal changes.<ref name=":0" />

===Terms and components===
The main terms used to classify the architecture of a root system are:<ref name=Fitter>{{cite book| vauthors = Fitter AH |chapter=The ecological significance of root system architecture: an economic approach|title=Plant Root Growth: An Ecological Perspective | veditors = Atkinson D |year=1991 |pages=229–243 |publisher=Blackwell |isbn=978-0-632-02757-6 }}</ref>

{| class="wikitable"
|-Root || Root can hold the plant firmly to the ground and it absorb water and neutrients
| Branch magnitude || Number of links (exterior or interior)
|-
| Topology || Pattern of branching ([[Herringbone pattern|Herringbone]], [[Dichotomous]], [[Radial symmetry|Radial]])
|-
| Link length || Distance between branches
|-
| Root angle || Radial angle of a lateral root's base around the parent root's circumference, the angle of a lateral root from its parent root, and the angle an entire system spreads.
|-
| Link radius || Diameter of root
|}

All components of the root architecture are regulated through a complex interaction between genetic responses and responses due to environmental stimuli. These developmental stimuli are categorized as intrinsic, the genetic and nutritional influences, or extrinsic, the environmental influences, and are interpreted by [[signal transduction pathways]].<ref name=Malamy>{{cite journal | vauthors = Malamy JE, Ryan KS | title = Environmental regulation of lateral root initiation in Arabidopsis | journal = Plant Physiology | volume = 127 | issue = 3 | pages = 899–909 | date = November 2001 | pmid = 11706172 | pmc = 129261 | doi = 10.1104/pp.010406 }}</ref>

Extrinsic factors affecting root architecture include [[Gravitropism|gravity]], light exposure, water and oxygen, as well as the availability or lack of [[nitrogen]], [[phosphorus]], sulphur, aluminium and sodium chloride. The main hormones (intrinsic stimuli) and respective pathways responsible for root architecture development include:
{| class="wikitable"
|-
| [[Auxin]] || Lateral root formation, maintenance of apical dominance and [https://academic.oup.com/plphys/article/170/2/603/6114063 adventitious] root formation.
|-
| [[Cytokinins]] || Cytokinins regulate root apical meristem size and promote lateral root elongation.
|-
| [[Ethylene]] || Promotes crown root formation.
|-
| [[Gibberellins]] || Together with ethylene, they promote crown primordia growth and elongation. Together with auxin, they promote root elongation. Gibberellins also inhibit lateral root primordia initiation.
|}

==Growth==
[[File:Root of a Tree.JPG|thumb|Roots of trees]]
Early root growth is one of the functions of the '''apical meristem''' located near the tip of the root. The meristem cells more or less continuously divide, producing more meristem, [[root cap]] cells (these are sacrificed to protect the meristem), and undifferentiated root cells. The latter become the primary tissues of the root, first undergoing elongation, a process that pushes the root tip forward in the growing medium. Gradually these cells differentiate and mature into specialized cells of the root tissues.<ref name="Russell Hertz McMillan 2013">{{cite book | vauthors = Russell PJ, Hertz PE, McMillan B | title=Biology: The Dynamic Science | publisher=Cengage Learning | year=2013 | isbn=978-1-285-41534-5 | url=https://books.google.com/books?id=dVIWAAAAQBAJ&pg=PT1365 | access-date=2017-04-24 | page=750 | url-status=live | archive-url=https://web.archive.org/web/20180121201126/https://books.google.com/books?id=dVIWAAAAQBAJ&pg=PT1365 | archive-date=2018-01-21 }}</ref>

Growth from apical meristems is known as '''primary growth''', which encompasses all elongation.
'''Secondary growth''' encompasses all growth in diameter, a major component of [[woody plant]] tissues and many nonwoody plants. For example, storage roots of [[sweet potato]] have secondary growth but are not woody. Secondary growth occurs at the [[lateral meristem]]s, namely the [[vascular cambium]] and [[cork cambium]]. The former forms [[secondary xylem]] and [[secondary phloem]], while the latter forms the [[periderm]].

In plants with secondary growth, the vascular cambium, originating between the xylem and the phloem, forms a [[cylinder (geometry)|cylinder]] of tissue along the [[Plant stem|stem]] and root.{{citation needed|date=March 2016}} The vascular cambium forms new cells on both the inside and outside of the cambium cylinder, with those on the inside forming secondary xylem cells, and those on the outside forming secondary phloem cells. As secondary xylem accumulates, the "girth" (lateral dimensions) of the stem and root increases. As a result, tissues beyond the secondary phloem including the epidermis and cortex, in many cases tend to be pushed outward and are eventually "sloughed off" (shed).{{citation needed|date=March 2016}}

At this point, the cork cambium begins to form the periderm, consisting of protective [[cork (material)|cork]] cells. The walls of cork cells contains [[suberin]] thickenings, which is an extra cellular complex biopolymer.<ref>{{cite book |doi=10.1016/B978-0-7020-2933-2.00042-3 |chapter=Cell differentiation and ergastic cell contents |title=Trease and Evans' Pharmacognosy |date=2009 |last1=Evans |first1=William Charles |last2=Evans |first2=Daphne |pages=551–562 |isbn=978-0-7020-2933-2 }}</ref> The suberin thickenings functions by providing a physical barrier, protection against pathogens and by preventing water loss from the surrounding tissues. In addition, it also aids the process of wound healing in plants.<ref>{{Cite web|title=Suberin Form & Function – Mark Bernards – Western University|url=https://www.uwo.ca/biology/faculty/bernards/research/suberin_form__function.html|access-date=2021-08-31|website=www.uwo.ca}}</ref> It is also postulated that suberin could be a component of the apoplastic barrier (present at the outer cell layers of roots) which prevents toxic compounds from entering the root and reduces radial oxygen loss (ROL) from the [[aerenchyma]] during waterlogging.<ref name="ReferenceA">{{cite journal |last1=Watanabe |first1=Kohtaro |last2=Nishiuchi |first2=Shunsaku |last3=Kulichikhin |first3=Konstantin |last4=Nakazono |first4=Mikio |title=Does suberin accumulation in plant roots contribute to waterlogging tolerance? |journal=Frontiers in Plant Science |date=2013 |volume=4 |page=178 |doi=10.3389/fpls.2013.00178 |pmid=23785371 |pmc=3683634 |doi-access=free|bibcode=2013FrPS....4..178W }}</ref> In roots, the cork cambium originates in the [[pericycle]], a component of the vascular cylinder.<ref name="ReferenceA"/>

The vascular cambium produces new layers of secondary xylem annually.<ref>{{Cite web |title=Plant Development II: Primary and Secondary Growth {{!}} Organismal Biology |url=https://organismalbio.biosci.gatech.edu/growth-and-reproduction/plant-development-ii-primary-and-secondary-growth/ |access-date=2025-10-04 |website=organismalbio.biosci.gatech.edu}}</ref> The xylem vessels are dead at maturity (in some) but are responsible for most water transport through the vascular tissue in stems and roots.
[[File:Tree branches and roots.jpg|thumb|Tree roots at Port Jackson|alt=]]
Tree roots usually grow to three times the diameter of the branch spread, only half of which lie underneath the trunk and canopy. The roots from one side of a tree usually supply nutrients to the foliage on the same side. Some families however, such as [[Sapindaceae]] (the [[maple]] family), show no correlation between root location and where the root supplies nutrients on the plant.<ref>{{cite journal |last1=van den Driessche |first1=R. |title=Prediction of mineral nutrient status of trees by foliar analysis |journal=The Botanical Review |date=July 1974 |volume=40 |issue=3 |pages=347–394 |doi=10.1007/BF02860066 |bibcode=1974BotRv..40..347V }}</ref>

===Regulation===
There is a correlation of roots using the process of [[plant perception (physiology)|plant perception]] to sense their physical environment to grow,<ref>{{cite journal | vauthors = Nakagawa Y, Katagiri T, Shinozaki K, Qi Z, Tatsumi H, Furuichi T, Kishigami A, Sokabe M, Kojima I, Sato S, Kato T, Tabata S, Iida K, Terashima A, Nakano M, Ikeda M, Yamanaka T, Iida H | display-authors = 6 | title = Arabidopsis plasma membrane protein crucial for Ca2+ influx and touch sensing in roots | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 104 | issue = 9 | pages = 3639–44 | date = February 2007 | pmid = 17360695 | pmc = 1802001 | doi = 10.1073/pnas.0607703104 | bibcode = 2007PNAS..104.3639N | doi-access = free }}</ref> including the sensing of light,<ref>{{cite press release |title=UV-B light sensing mechanism discovered in plant roots |url=https://phys.org/news/2008-12-uv-b-mechanism-roots.html |work=phys.org |publisher=San Francisco State University |date=8 December 2008 }}</ref> and physical barriers. Plants also sense gravity and respond through auxin pathways,<ref>{{cite journal | vauthors = Marchant A, Kargul J, May ST, Muller P, Delbarre A, Perrot-Rechenmann C, Bennett MJ | title = AUX1 regulates root gravitropism in Arabidopsis by facilitating auxin uptake within root apical tissues | journal = The EMBO Journal | volume = 18 | issue = 8 | pages = 2066–73 | date = April 1999 | pmid = 10205161 | doi = 10.1093/emboj/18.8.2066 | pmc = 1171291 }}</ref> resulting in [[gravitropism]]. Over time, roots can crack foundations, snap water lines, and lift sidewalks. Research has shown that roots have ability to recognize 'self' and 'non-self' roots in same soil environment.<ref>{{cite journal | vauthors = Hodge A | title = Root decisions | journal = Plant, Cell & Environment | volume = 32 | issue = 6 | pages = 628–40 | date = June 2009 | pmid = 18811732 | doi = 10.1111/j.1365-3040.2008.01891.x | doi-access = free | bibcode = 2009PCEnv..32..628H }}</ref>

The correct environment of [[Aeration|air]], mineral [[nutrients]] and [[water]] directs plant roots to grow in any direction to meet the plant's needs. Roots will shy or shrink away from dry<ref>{{cite journal|last1=Carminati|first1=Andrea|last2=Vetterlein|first2=Doris|last3=Weller|first3=Ulrich|last4=Vogel|first4=Hans-Jörg|last5=Oswald|first5=Sascha E. | name-list-style = vanc |title=When roots lose contact |journal=Vadose Zone Journal |date=2009 |volume=8|issue=3|pages=805–809|doi=10.2136/vzj2008.0147|bibcode=2009VZJ.....8..805C }}</ref> or other poor soil conditions.

[[Gravitropism]] directs roots to grow downward at [[germination]], the growth mechanism of plants that also causes the shoot to grow upward.<ref>{{cite journal | vauthors = Chen R, Rosen E, Masson PH | title = Gravitropism in higher plants | journal = Plant Physiology | volume = 120 | issue = 2 | pages = 343–50 | date = June 1999 | pmid = 11541950 | pmc = 1539215 | doi = 10.1104/pp.120.2.343 }}
</ref>
Different types of roots such as primary, seminal, lateral and crown are maintained at different gravitropic setpoint angles i.e. the direction in which they grow. Recent research show that root angle in cereal crops such as barley and wheat is regulated by a novel gene called Enhanced Gravitropism 1 (EGT1).<ref>{{cite journal |last1=Fusi |first1=Riccardo |last2=Rosignoli |first2=Serena |last3=Lou |first3=Haoyu |last4=Sangiorgi |first4=Giuseppe |last5=Bovina |first5=Riccardo |last6=Pattem |first6=Jacob K. |last7=Borkar |first7=Aditi N. |last8=Lombardi |first8=Marco |last9=Forestan |first9=Cristian |last10=Milner |first10=Sara G. |last11=Davis |first11=Jayne L. |last12=Lale |first12=Aneesh |last13=Kirschner |first13=Gwendolyn K. |last14=Swarup |first14=Ranjan |last15=Tassinari |first15=Alberto |last16=Pandey |first16=Bipin K. |last17=York |first17=Larry M. |last18=Atkinson |first18=Brian S. |last19=Sturrock |first19=Craig J. |last20=Mooney |first20=Sacha J. |last21=Hochholdinger |first21=Frank |last22=Tucker |first22=Matthew R. |last23=Himmelbach |first23=Axel |last24=Stein |first24=Nils |last25=Mascher |first25=Martin |last26=Nagel |first26=Kerstin A. |last27=De Gara |first27=Laura |last28=Simmonds |first28=James |last29=Uauy |first29=Cristobal |last30=Tuberosa |first30=Roberto |last31=Lynch |first31=Jonathan P. |last32=Yakubov |first32=Gleb E. |last33=Bennett |first33=Malcolm J. |last34=Bhosale |first34=Rahul |last35=Salvi |first35=Silvio |title=Root angle is controlled by EGT1 in cereal crops employing an antigravitropic mechanism |journal=Proceedings of the National Academy of Sciences |date=2 August 2022 |volume=119 |issue=31 |article-number=e2201350119 |doi=10.1073/pnas.2201350119|doi-access=free |pmid=35881796 |pmc=9351459 |bibcode=2022PNAS..11901350F }}</ref>

Research indicates that plant roots growing in search of productive nutrition can sense and avoid soil compaction through diffusion of the gas [[ethylene]].<ref>{{cite journal |last1=Pandey |first1=Bipin K. |last2=Huang |first2=Guoqiang |last3=Bhosale |first3=Rahul |last4=Hartman |first4=Sjon |last5=Sturrock |first5=Craig J. |last6=Jose |first6=Lottie |last7=Martin |first7=Olivier C. |last8=Karady |first8=Michal |last9=Voesenek |first9=Laurentius A. C. J. |last10=Ljung |first10=Karin |last11=Lynch |first11=Jonathan P. |last12=Brown |first12=Kathleen M. |last13=Whalley |first13=William R. |last14=Mooney |first14=Sacha J. |last15=Zhang |first15=Dabing |last16=Bennett |first16=Malcolm J. |title=Plant roots sense soil compaction through restricted ethylene diffusion |journal=Science |date=15 January 2021 |volume=371 |issue=6526 |pages=276–280 |doi=10.1126/science.abf3013 |pmid=33446554 |bibcode=2021Sci...371..276P |hdl=1874/418726 |url=https://nottingham-repository.worktribe.com/output/5234573 |hdl-access=free }}</ref>
[[File:ArabidopsisLatRoot.jpg|thumb|Fluorescent imaging of an emerging lateral root]]

== Shade avoidance response ==

In order to avoid shade, plants utilize a shade avoidance response. When a plant is under dense vegetation, the presence of other vegetation nearby will cause the plant to avoid lateral growth and experience an increase in upward shoot, as well as downward root growth. In order to escape shade, plants adjust their root architecture, most notably by decreasing the length and amount of lateral roots emerging from the primary root. Experimentation of mutant variants of ''[[Arabidopsis thaliana]]'' found that plants sense the Red to Far Red light ratio that enters the plant through photoreceptors known as [[phytochrome]]s.<ref name=":02">{{cite journal | vauthors = Salisbury FJ, Hall A, Grierson CS, Halliday KJ | title = Phytochrome coordinates Arabidopsis shoot and root development | journal = The Plant Journal | volume = 50 | issue = 3 | pages = 429–38 | date = May 2007 | pmid = 17419844 | doi = 10.1111/j.1365-313x.2007.03059.x | doi-access = free }}</ref> Nearby plant leaves will absorb red light and reflect far-red light, which will cause the ratio red to far red light to lower. The phytochrome PhyA that senses this Red to Far Red light ratio is localized in both the root system as well as the shoot system of plants, but through knockout mutant experimentation, it was found that root localized PhyA does not sense the light ratio, whether directly or axially, that leads to changes in the lateral root architecture.<ref name=":02" /> Research instead found that shoot localized PhyA is the phytochrome responsible for causing these architectural changes of the lateral root. Research has also found that phytochrome completes these architectural changes through the manipulation of auxin distribution in the root of the plant.<ref name=":02" /> When a low enough Red to Far Red ratio is sensed by PhyA, the phyA in the shoot will be mostly in its active form.<ref name=":1">{{cite journal | vauthors = van Gelderen K, Kang C, Paalman R, Keuskamp D, Hayes S, Pierik R | title = Far-Red Light Detection in the Shoot Regulates Lateral Root Development through the HY5 Transcription Factor | journal = The Plant Cell | volume = 30 | issue = 1 | pages = 101–116 | date = January 2018 | pmid = 29321188 | pmc = 5810572 | doi = 10.1105/tpc.17.00771 | bibcode = 2018PlanC..30..101V }}</ref> In this form, PhyA stabilize the [[transcription factor]] HY5 causing it to no longer be degraded as it is when phyA is in its inactive form. This stabilized transcription factor is then able to be transported to the roots of the plant through the [[phloem]], where it proceeds to induce its own transcription as a way to amplify its signal. In the roots of the plant HY5 functions to inhibit an auxin response factor known as ARF19, a response factor responsible for the translation of PIN3 and LAX3, two well known auxin transporting [[protein]]s.<ref name=":1" /> Thus, through manipulation of ARF19, the level and activity of [[auxin]] transporters PIN3 and LAX3 is inhibited.<ref name=":1" /> Once inhibited, auxin levels will be low in areas where lateral root emergence normally occurs, resulting in a failure for the plant to have the emergence of the lateral root primordium through the root [[pericycle]]. With this complex manipulation of Auxin transport in the roots, lateral root emergence will be inhibited in the roots and the root will instead elongate downwards, promoting vertical plant growth in an attempt to avoid shade.<ref name=":02" /><ref name=":1" />

Research of Arabidopsis has led to the discovery of how this auxin mediated root response works. In an attempt to discover the role that [[phytochrome]] plays in lateral root development, Salisbury et al. (2007) worked with ''Arabidopsis thaliana'' grown on agar plates. Salisbury et al. used wild type plants along with varying protein knockout and gene knockout Arabidopsis mutants to observe the results these mutations had on the root architecture, protein presence, and gene expression. To do this, Salisbury et al. used GFP fluorescence along with other forms of both macro and microscopic imagery to observe any changes various mutations caused. From these research, Salisbury et al. were able to theorize that shoot located phytochromes alter auxin levels in roots, controlling lateral root development and overall root architecture.<ref name=":02" /> In the experiments of van Gelderen et al. (2018), they wanted to see if and how it is that the shoot of ''A.&nbsp;thaliana'' alters and affects root development and root architecture. To do this, they took ''Arabidopsis'' plants, grew them in [[Agar|agar gel]], and exposed the roots and shoots to separate sources of light. From here, they altered the different wavelengths of light the shoot and root of the plants were receiving and recorded the lateral root density, amount of lateral roots, and the general architecture of the lateral roots. To identify the function of specific photoreceptors, proteins, genes, and hormones, they utilized various ''Arabidopsis'' knockout mutants and observed the resulting changes in lateral roots architecture. Through their observations and various experiments, van Gelderen et al. were able to develop a mechanism for how root detection of Red to Far-red light ratios alter lateral root development.<ref name=":1" />

==Types==
{{Unreferenced section|date=March 2010}}
A true root system consists of a '''primary root''' and '''secondary roots''' (or [[lateral roots]]).
* the diffuse root system: the primary root is not dominant; the whole root system is fibrous and branches in all directions. Most common in [[monocots]]. The main function of the fibrous root is to anchor the plant.

===Specialized===
[[File:Prop roots of Maize plant.jpg|thumb|Stilt roots of maize plant]]
[[File:Pearl Millet Adventitious root.jpg|alt=Microscope image of a ross section of a pearl millet root, a circular fluorescent blue root containing a bright blue inner region (stele) with several smaller lateral roots emerging|thumb|Cross section of an adventitous crown root of pearl millet (''Pennisetum glaucum)'']]
[[File:Adventitious roots on Odontonema aka Firespike.jpg|thumb|Roots forming above ground on a cutting of an ''Odontonema'' ("Firespike")]]
[[File:Mangroves.jpg|thumb|Aerating roots of a [[mangrove]]]]
[[File:Root tip.JPG|thumb|The growing tip of a fine root]]
[[File:Aerial root.jpg|thumb|Aerial root]]
[[File:Socratea exorriza2002 03 12.JPG|thumb|The stilt roots of ''[[Socratea exorrhiza]]'']]
[[File:Visible roots.jpg|thumb|Visible roots]]

The roots, or parts of roots, of many plant species have become specialized to serve adaptive purposes besides the two primary functions{{clarify|reason=there's no intro section|date=March 2016}}, described in the introduction.
* '''Adventitious roots''' arise out-of-sequence from the more usual root formation of branches of a primary root, and instead originate from the stem, branches, leaves, or old woody roots. They commonly occur in [[monocot]]s and pteridophytes, but also in many [[dicot]]s, such as [[clover]] (''Trifolium''), [[ivy]] (''Hedera''), [[strawberry]] (''Fragaria'') and [[willow]] (''Salix''). Most aerial roots and stilt roots are adventitious. In some conifers adventitious roots can form the largest part of the root system. Adventitious root formation is enhanced in many plant species during (partial) submergence, to increase gas exchange and storage of gases like oxygen.<ref>{{cite journal |last1=Ayi |first1=Qiaoli |last2=Zeng |first2=Bo |last3=Liu |first3=Jianhui |last4=Li |first4=Siqi |last5=van Bodegom |first5=Peter M. |last6=Cornelissen |first6=Johannes H. C. |title=Oxygen absorption by adventitious roots promotes the survival of completely submerged terrestrial plants |journal=Annals of Botany |date=October 2016 |volume=118 |issue=4 |pages=675–683 |doi=10.1093/aob/mcw051|pmid=27063366 |pmc=5055620 }}</ref> Distinct types of adventitious roots can be classified and are dependent on morphology, growth dynamics and function.<ref>{{cite journal |last1=Lin |first1=Chen |last2=Ogorek |first2=Lucas León Peralta |last3=Liu |first3=Dan |last4=Pedersen |first4=Ole |last5=Sauter |first5=Margret |date=11 January 2023 |title=A quantitative trait locus conferring flood tolerance to deepwater rice regulates the formation of two distinct types of aquatic adventitious roots |journal=New Phytologist |volume=238 |issue=4 |pages=1403–1419 |doi=10.1111/nph.18678|pmid=36519256 |doi-access=free |bibcode=2023NewPh.238.1403L }}</ref><ref>{{cite journal |last1=Maric |first1=Aida |last2=Hartman |first2=Sjon |date=11 March 2023 |title=The leaf sheath promotes prolonged flooding protection by giving rise to specialized adventitious roots |journal=New Phytologist |volume=238 |issue=4 |pages=1337–1339 |doi=10.1111/nph.18824|pmid=36905344 |doi-access=free |bibcode=2023NewPh.238.1337M }}</ref>
* '''Aerating roots''' (or '''knee root''' or '''knee''' or '''pneumatophores'''): roots rising above the ground, especially above water such as in some [[mangrove]] genera (''[[Avicennia]], [[Sonneratia]]''). In some plants like ''Avicennia'' the erect roots have a large number of breathing pores for exchange of gases.
* '''[[Aerial roots]]''': roots entirely above the ground, such as in ivy (''Hedera'') or in [[epiphyte|epiphytic]] [[orchid]]s. Many aerial roots are used to receive water and nutrient intake directly from the air – from fogs, dew or humidity in the air.<ref name="deficit">{{cite journal|last1=Nowak|first1=Edward J.|last2=Martin|first2=Craig E.| name-list-style = vanc |title=Physiological and anatomical responses to water deficits in the CAM epiphyte ''Tillandsia ionantha'' (Bromeliaceae) |journal=International Journal of Plant Sciences |date=1997 |volume=158 |issue=6 |pages=818–826 |jstor=2475361 |doi=10.1086/297495 |bibcode=1997IJPlS.158..818N |hdl=1808/9858 |hdl-access=free }}</ref> Some rely on leaf systems to gather rain or humidity and even store it in scales or pockets. Other aerial roots, such as [[mangrove]] aerial roots, are used for aeration and not for water absorption. Other aerial roots are used mainly for structure, functioning as prop roots, as in [[maize]] or anchor roots or as the trunk in [[strangler fig]]. In some Epiphytes – plants living above the surface on other plants, aerial roots serve for reaching to water sources or reaching the surface, and then functioning as regular surface roots.<ref name="deficit" />
*'''[[Canopy root]]s/arboreal roots''': roots that form when tree branches support mats of epiphytes and detritus, which hold water and nutrients in the canopy. They grow out into these mats, likely to utilize the available nutrients and moisture.<ref>{{cite journal | vauthors = Nadkarni NM | title = Canopy roots: convergent evolution in rainforest nutrient cycles | journal = Science | volume = 214 | issue = 4524 | pages = 1023–4 | date = November 1981 | pmid = 17808667 | doi = 10.1126/science.214.4524.1023 | bibcode = 1981Sci...214.1023N }}</ref>
* '''Coarse roots''': roots that have undergone secondary thickening and have a woody structure. These roots have some ability to absorb water and nutrients, but their main function is transport and to provide a structure to connect the smaller diameter, fine roots to the rest of the plant.
* '''Contractile roots''': roots that pull bulbs or corms of [[monocot]]s, such as [[hyacinth (plant)|hyacinth]] and [[lily]], and some [[taproot]]s, such as [[dandelion]], deeper in the soil through expanding radially and contracting longitudinally. They have a wrinkled surface.<ref>{{cite book |doi=10.1201/9780203909423 |title=Plant Roots |date=2002 |isbn=978-0-203-90942-3 |editor-last1=Waisel |editor-last2=Eshel |editor-last3=Beeckman |editor-last4=Kafkafi |editor-first1=Yoav |editor-first2=Amram |editor-first3=Tom |editor-first4=Uzi |last1=Pütz |first1=Norbert |chapter=Contractile Roots |pages=975–987 }}</ref> 
* '''Coralloid roots''': similar to root nodules, these provide nitrogen to the plant. They are often larger than nodules, branched, and located at or near the soil surface, and harbor nitrogen-fixing [[cyanobacteria]]. They are only found in [[cycad]]s.
* '''[[Dimorphic root system]]s''': roots with two distinctive forms for two separate functions
* '''[[Fine root]]s''': typically primary roots <2&nbsp;mm diameter that have the function of water and nutrient uptake. They are often heavily branched and support mycorrhizas. These roots may be short lived, but are replaced by the plant in an ongoing process of root 'turnover'.
* '''Haustorial roots''': roots of parasitic plants that can absorb water and nutrients from another plant, such as in [[mistletoe]] (''Viscum album'') and [[dodder]].
* '''Propagative roots''': roots that form adventitious buds that develop into aboveground shoots, termed [[Basal shoot|suckers]], which form new plants, as in [[Asclepias syriaca|common milkweed (''Asclepias syriaca'')]], [[Cirsium arvense|Canada thistle (''Cirsium arvense'')]], and many others.<ref>{{cite journal|first1=Deana|last1=Namuth-Covert|first2=Amy|last2=Kohmetscher|url=https://ohiostate.pressbooks.pub/crpsoil2422t/chapter/3-3-vegetative-forms-of-reproduction/|title=3.3 Vegetative Forms of Reproduction: Modified Roots|journal=Principles of Weed Control|location=[[Montreal]]|publisher=[[Pressbooks]]|quote=Examples of plants with modified roots: Common milkweed (''Asclepias syriaca'') and Canada thistle (''Cirsium arvense'').|access-date=October 13, 2024}}</ref>
*'''Photosynthetic roots''': roots that are green and photosynthesize, providing sugar to the plant. They are similar to [[phylloclade]]s. Several orchids have these, such as ''[[Dendrophylax]]'' and ''[[Taeniophyllum]]''.
* '''[[Proteoid root]]s''' or cluster roots: dense clusters of rootlets of limited growth that develop under low [[phosphate]] or low [[iron]] conditions in [[Proteaceae]] and some plants from the following families [[Betulaceae]], [[Casuarinaceae]], [[Elaeagnaceae]], [[Moraceae]], [[Fabaceae]] and ''[[Myricaceae]]''.
* [[Root nodule|'''Root nodules''']]: roots that harbor nitrogen-fixing soil bacteria. These are often very short and rounded. Root nodules are found in virtually all [[legume]]s.
* '''Stilt roots''': adventitious support roots, common among [[mangrove]]s. They grow down from lateral branches, branching in the soil.
* '''Storage roots''': roots modified for storage of food or water, such as [[carrot]]s and [[beet]]s. They include some [[taproot]]s and tuberous roots.
* '''Structural roots''': large roots that have undergone considerable secondary thickening and provide mechanical support to woody plants and trees.
* '''Surface roots''': roots that proliferate close below the soil surface, exploiting water and easily available nutrients. Where conditions are close to optimum in the surface layers of soil, the growth of surface roots is encouraged and they commonly become the dominant roots.
* '''Tuberous roots''': fleshy and enlarged lateral roots for food or water storage, e.g. [[sweet potato]]. A type of storage root distinct from taproot.

==Depths==
[[File:Exposed mango tree roots.jpg|thumb|Cross section of a [[mango]] tree]]
The distribution of vascular plant roots within soil depends on plant form, the spatial and temporal availability of water and nutrients, and the physical properties of the soil. The deepest roots are generally found in deserts and temperate coniferous forests; the shallowest in tundra, boreal forest and temperate grasslands. The deepest observed living root, at least {{Convert|60|m}} below the ground surface, was observed during the excavation of an open-pit mine in Arizona, US. Some roots can grow as deep as the tree is high. The majority of roots on most plants are however found relatively close to the surface where nutrient availability and aeration are more favourable for growth. Rooting depth may be physically restricted by rock or compacted soil close below the surface, or by anaerobic soil conditions.

===Records===
[[File:Tree roots2.jpg|thumb|[[Ficus]] tree with [[buttress root]]s]]
{| class="wikitable"
|-
! Species
! Location
! Maximum rooting depth (m)
! References<ref>{{cite journal | vauthors = Canadell J, Jackson RB, Ehleringer JB, Mooney HA, Sala OE, Schulze ED | title = Maximum rooting depth of vegetation types at the global scale | journal = Oecologia | volume = 108 | issue = 4 | pages = 583–595 | date = December 1996 | pmid = 28307789 | doi = 10.1007/BF00329030 | bibcode = 1996Oecol.108..583C }}</ref><ref>{{cite journal | vauthors = Stonea EL, Kaliszb PJ |date=1 December 1991 |title=On the maximum extent of tree roots |journal=Forest Ecology and Management |volume=46 |issue=1–2 |pages=59–102 |doi=10.1016/0378-1127(91)90245-Q|bibcode=1991ForEM..46...59S }}</ref>
|-
| ''[[Boscia albitrunca]]''
| Kalahari desert
| 68
| Jennings (1974)
|-
| ''[[Juniperus monosperma]]''
| Colorado Plateau
| 61
| Cannon (1960)
|-
| ''[[Eucalyptus]]'' sp.
| Australian forest
| 61
| Jennings (1971)
|-
| ''[[Acacia erioloba]]''
| Kalahari desert
| 60
| Jennings (1974)
|-
| ''[[Prosopis juliflora]]''
| Arizona desert
| 53.3
| Phillips (1963)
|}

==Evolutionary history==
{{Further|Evolution of plants#Evolution of roots}}
The fossil record of roots—or rather, infilled voids where roots rotted after death—spans back to the late [[Silurian]], about 430&nbsp;million years ago.<ref name="Retallack1986">{{cite book |chapter=The fossil record of soils | vauthors = Retallack GJ |title=Paleosols: their Recognition and Interpretation |pages=1–57 | veditors = Wright VP |publisher=Blackwell |location=Oxford |year=1986 |chapter-url=http://blogs.uoregon.edu/gregr/files/2013/07/paleosols1986fossilrecordofsoils-1vqnwyo.pdf |url-status=live |archive-url=https://web.archive.org/web/20170107005159/http://blogs.uoregon.edu/gregr/files/2013/07/paleosols1986fossilrecordofsoils-1vqnwyo.pdf |archive-date=2017-01-07 }}</ref> Their identification is difficult, because casts and molds of roots are so similar in appearance to animal burrows. They can be discriminated using a range of features.<ref name=Hillier2008>{{cite journal | title=Sedimentological evidence for rooting structures in the Early Devonian Anglo–Welsh Basin (UK), with speculation on their producers | year = 2008 | doi = 10.1016/j.palaeo.2008.01.038 | vauthors = Hillier R, Edwards D, Morrissey LB | journal=Palaeogeography, Palaeoclimatology, Palaeoecology | volume=270 | pages=366–380 | issue=3–4 | bibcode = 2008PPP...270..366H }}</ref> The evolutionary development of roots likely happened from the modification of shallow [[rhizomes]] (modified horizontal stems) which anchored primitive vascular plants combined with the development of filamentous outgrowths (called [[rhizoid]]s) which anchored the plants and conducted water to the plant from the soil.<ref>{{cite book |doi=10.1201/9780203909423 |title=Plant Roots |date=2002 |isbn=978-0-203-90942-3 |editor-last1=Waisel |editor-last2=Eshel |editor-last3=Beeckman |editor-last4=Kafkafi |editor-first1=Yoav |editor-first2=Amram |editor-first3=Tom |editor-first4=Uzi |last1=Kenrick |first1=Paul |chapter=The Origin of Roots |pages=1–20 }}</ref>

==Environmental interactions==
[[File:Cycas revoluta coralloid roots.JPG|thumb|Coralloid roots of ''[[Cycas revoluta]]'']]
Light has been shown to have some impact on roots, but it's not been studied as much as the effect of light on other plant systems. Early research in the 1930s found that light decreased the effectiveness of [[Indole-3-acetic acid]] on adventitious root initiation. Studies of the pea in the 1950s shows that lateral root formation was inhibited by light, and in the early 1960s researchers found that light could induce positive [[gravitropic]] responses in some situations. The effects of light on root elongation has been studied for [[monocotyledonous]] and [[dicotyledonous]] plants, with the majority of studies finding that light inhibited root elongation, whether pulsed or continuous. Studies of ''[[Arabidopsis]]'' in the 1990s showed negative [[phototropism]] and inhibition of the elongation of root hairs in light sensed by [[phyB]].<ref name=jpp1997>{{cite journal |last1=Kurata |first1=Tetsuya |title=Light-stimulated root elongation in Arabidopsis thaliana |journal=Journal of Plant Physiology |date=1997 |volume=151 |issue=3 |pages=345–351|doi=10.1016/S0176-1617(97)80263-5 |bibcode=1997JPPhy.151..346K |hdl=2115/44841 |hdl-access=free }}</ref>

Certain plants, namely [[Fabaceae]], form [[root nodules]] in order to associate and form a symbiotic relationship with nitrogen-fixing bacteria called [[rhizobia]]. Owing to the high energy required to fix nitrogen from the atmosphere, the bacteria take carbon compounds from the plant to fuel the process. In return, the plant takes nitrogen compounds produced from ammonia by the bacteria.<ref>{{cite book |author=Postgate, J. |year=1998 |title=Nitrogen Fixation |edition=3rd |publisher=Cambridge University Press |location=Cambridge, UK}}</ref>

Soil temperature is a factor that effects [[root initiation]] and length. Root length is usually impacted more dramatically by temperature than overall mass, where cooler temperatures tend to cause more lateral growth because downward extension is limited by cooler temperatures at subsoil levels. Needs vary by plant species, but in temperate regions cool temperatures may limit root systems. Cool temperature species like [[oats]], [[rapeseed]], [[rye]], [[wheat]] fare better in lower temperatures than summer [[Annual plant|annuals]] like [[maize]] and [[cotton]]. Researchers have found that plants like cotton develop wider and shorter [[taproot]]s in cooler temperatures. The first root originating from the seed usually has a wider diameter than root branches, so smaller root diameters are expected if temperatures increase root initiation. Root diameter also decreases when the root elongates.<ref name=encyclopedia>{{Cite book|last=Lal|first=Rattan|url=https://books.google.com/books?id=627Qopsj7bsC|title=Encyclopedia of Soil Science|date=2006|publisher=CRC Press|isbn=978-0-8493-5054-2|language=en}}</ref>

==Plant interactions==
Plants can interact with one another in their environment through their root systems. Studies have demonstrated that plant-plant interaction occurs among root systems via the soil as a medium. Researchers have tested whether plants growing in ambient conditions would change their behavior if a nearby plant was exposed to drought conditions.<ref name=":2">{{cite book |last1=Chamovitz |first1=Daniel |title=What a Plant Knows: A Field Guide to the Senses: Updated and Expanded Edition |date=2017 |publisher=Farrar, Straus and Giroux |isbn=978-0-374-53712-8 |oclc=1041421612 }}{{page needed|date=January 2025}}</ref>
Since nearby plants showed no changes in [[stoma]]tal aperture researchers believe the drought signal spread through the roots and soil, not through the air as a volatile chemical signal.<ref name=":3">{{cite journal | vauthors = Falik O, Mordoch Y, Ben-Natan D, Vanunu M, Goldstein O, Novoplansky A | title = Plant responsiveness to root-root communication of stress cues | journal = Annals of Botany | volume = 110 | issue = 2 | pages = 271–80 | date = July 2012 | pmid = 22408186 | pmc = 3394639 | doi = 10.1093/aob/mcs045 }}</ref>

==Soil interactions==
Soil microbiota can suppress both disease and beneficial root symbionts (mycorrhizal fungi are easier to establish in sterile soil). Inoculation with soil bacteria can increase internode extension, yield and quicken flowering. The migration of bacteria along the root varies with natural soil conditions. For example, research has found that the root systems of wheat seeds inoculated with ''[[Azotobacter]]'' showed higher populations in soils favorable to ''Azotobacter'' growth. Some studies have been unsuccessful in increasing the levels of certain microbes (such as ''[[P. fluorescens|P.&nbsp;fluorescens]]'') in natural soil without prior sterilization.<ref name=Bowen>{{cite journal |vauthors=Bowen GD, Rovira AD |title= Microbial Colonization of Plant Roots |journal=Annu. Rev. Phytopathol. |date=1976 |volume=14 |issue= 1 |pages=121–144|doi= 10.1146/annurev.py.14.090176.001005 |bibcode= 1976AnRvP..14..121B }}</ref>

Grass root systems are beneficial at reducing [[soil erosion]] by holding the soil together. [[Perennial]] grasses that grow wild in rangelands contribute organic matter to the soil when their old roots decay after attacks by beneficial [[fungi]], [[protozoa]], bacteria, insects and worms release nutrients.<ref name=arizona/>

Scientists have observed significant diversity of the microbial cover of roots at around 10 percent of three week old root segments covered. On younger roots there was even low coverage, but even on 3-month-old roots the coverage was only around 37%. Before the 1970s, scientists believed that the majority of the root surface was covered by microorganisms.<ref name=arizona/>

==Nutrient absorption==

Researchers studying [[maize]] seedlings found that calcium absorption was greatest in the [[Apical meristem|apical]] root segment, and potassium at the base of the root. Along other root segments absorption was similar. Absorbed potassium is transported to the root tip, and to a lesser extent other parts of the root, then also to the shoot and grain. Calcium transport from the apical segment is slower, mostly transported upward and accumulated in stem and shoot.<ref>{{cite book |doi=10.1016/B978-0-444-89104-4.50007-4 |chapter=The Development of Absorption and Transport Systems in the Corn Root: Structural and Experimental Evidence |title=Plant Roots and their Environment |series=Developments in Agricultural and Managed Forest Ecology |date=1991 |last1=Danilova |first1=M.F. |last2=Mazel |first2=YU.A. |last3=Jitneva |first3=N.N. |last4=Telepova |first4=M.N. |volume=24 |pages=17–24 |isbn=978-0-444-89104-4 }}</ref>

Researchers found that partial deficiencies of K or P did not change the [[fatty acid]] composition of [[phosphatidyl choline]] in ''[[Brassica napus L.]]'' plants. Calcium deficiency did, on the other hand, lead to a marked decline of [[polyunsaturated]] compounds that would be expected to have negative impacts for integrity of the plant [[membrane]], that could effect some properties like its permeability, and is needed for the [[ion]] uptake activity of the root membranes.<ref>{{cite book |doi=10.1016/B978-0-444-89104-4.50008-6 |chapter=Properties of Root Membrane Lipids as Related to Mineral Nutrition |title=Plant Roots and their Environment |series=Developments in Agricultural and Managed Forest Ecology |date=1991 |last1=Diepenbrock |first1=W. |volume=24 |pages=25–30 |isbn=978-0-444-89104-4 }}</ref>

==Economic importance==
[[File:Roots and Soil Erosion.jpg|thumb|Roots can also protect the environment by holding the soil to reduce soil erosion.]]
[[File:World Primary Crops Harvested Area By Commodity Group.svg|thumb|Roots and tubers are some of the most widely harvested crops in the world.]]
The term [[root crop]]s refers to any edible underground plant structure, but many root crops are actually stems, such as [[potato]] tubers. Edible roots include [[cassava]], [[sweet potato]], [[beet]], [[carrot]], [[rutabaga]], [[turnip]], [[parsnip]], [[radish]], [[Yam (vegetable)|yam]] and [[horseradish]]. Spices obtained from roots include [[sassafras]], [[angelica]], [[Smilax regelii|sarsaparilla]] and [[licorice]].

[[Sugar beet]] is an important source of sugar. [[Yam (vegetable)|Yam]] roots are a source of [[estrogen]] compounds used in [[birth control pill]]s. The fish [[poison]] and [[insecticide]] [[rotenone]] is obtained from roots of ''[[Lonchocarpus]]'' spp. Important medicines from roots are [[ginseng]], [[aconitum|aconite]], [[Syrup of ipecac|ipecac]], [[gentian]] and [[reserpine]]. Several legumes that have nitrogen-fixing root nodules are used as green manure crops, which provide nitrogen fertilizer for other crops when plowed under. Specialized [[bald cypress]] roots, termed knees, are sold as souvenirs, lamp bases and carved into folk art. [[Indigenous peoples of the Americas|Native Americans]] used the flexible roots of [[Picea glauca|white spruce]] for basketry.

[[Tree]] roots can heave and destroy [[concrete]] sidewalks and crush or clog buried pipes.<ref>{{Cite news|last=Zahniser |first=David |date=2008-02-21|title=City to pass the bucks on sidewalks?|url=https://www.latimes.com/archives/la-xpm-2008-feb-21-me-sidewalk21-story.html|access-date=2023-03-30|journal=[[The Los Angeles Times]]|language=en-US}}</ref> The aerial roots of [[strangler fig]] have damaged ancient [[Maya architecture|Mayan]] [[temple]]s in [[Central America]] and the temple of [[Angkor Wat]] in [[Cambodia]].

Trees stabilize soil on a slope prone to [[landslides]]. The [[root hair]]s work as an anchor on the soil.

[[Vegetative propagation]] of plants via cuttings depends on adventitious root formation. Hundreds of millions of plants are propagated via [[cuttings (plants)|cuttings]] annually including [[chrysanthemum]], [[poinsettia]], [[carnation]], ornamental [[shrub]]s and many [[houseplants]].

Roots can also protect the environment by holding the soil to reduce soil erosion. This is especially important in areas such as [[sand dunes]].
[[File:OnionBulbRoots.jpg|thumb|right|Roots on onion bulbs]]

== See also ==
* [[Absorption of water]]
* [[Cypress knee]]
* [[Drought rhizogenesis]]
* [[Fibrous root system]]
* [[Mycorrhiza]] – root symbiosis in which individual hyphae extending from the mycelium of a fungus colonize the roots of a host plant.
* [[Mycorrhizal network]]
* [[Plant physiology]]
* [[Rhizosphere]] – region of soil around the root influenced by root secretions and microorganisms present
* [[Root cutting]]
* [[Auxin|Rooting powder]]
* [[Stolon]]
* [[Tanada effect]]
* [[Taproot]]

== References ==
{{Reflist|30em}}

== Further reading ==
{{Refbegin}}
* {{cite journal | vauthors = Baldocchi DD, Xu L | title = What limits evaporation from Mediterranean oak woodlands–The supply of moisture in the soil, physiological control by plants or the demand by the atmosphere? | journal = Advances in Water Resources | date = October 2007 | volume = 30 | issue = 10 | pages = 2113–22 | doi = 10.1016/j.advwatres.2006.06.013 | bibcode = 2007AdWR...30.2113B }}
* {{cite journal | last1 = Brundrett | first1 = M. C. | year = 2002 | title = Coevolution of roots and mycorrhizas of land plants | journal = New Phytologist | volume = 154 | issue = 2| pages = 275–304 | doi = 10.1046/j.1469-8137.2002.00397.x | pmid = 33873429 | doi-access = free | bibcode = 2002NewPh.154..275B }}
* {{cite web | last = Clark | first = Lynn | name-list-style = vanc | date = 2004 | url =http://www.eeob.iastate.edu/classes/bot404/docs/404root104.pdf | archive-url = https://web.archive.org/web/20060103160847/http://www.eeob.iastate.edu/classes/bot404/docs/404root104.pdf | archive-date = 3 January 2006 | title = Primary Root Structure and Development – lecture notes }}
* {{cite journal | vauthors = Coutts MP | year = 1987 | title = Developmental processes in tree root systems | journal = Canadian Journal of Forest Research | volume = 17 | issue = 8| pages = 761–767 | doi=10.1139/x87-122| bibcode = 1987CaJFR..17..761C }}
* {{cite journal | vauthors = Raven JA, Edwards D | date = 2001 | title = Roots: evolutionary origins and biogeochemical significance. | journal = Journal of Experimental Botany | volume = 52 | issue = Suppl 1 | pages = 381–401 | doi = 10.1093/jxb/52.suppl_1.381 | pmid = 11326045 }}
* {{cite journal | vauthors = Schenk HJ, Jackson RB | year = 2002 | title = The global biogeography of roots | journal = Ecological Monographs | volume = 72 | issue = 3| pages = 311–328 | doi=10.2307/3100092| jstor = 3100092 }}
* {{cite journal | vauthors = Sutton RF, Tinus RW | year = 1983 | title = Root and root system terminology | journal = Forest Science Monograph | volume = 24 | page = 137 }}
* {{cite journal | vauthors = Phillips WS | year = 1963 | title = Depth of roots in soil | journal = Ecology | volume = 44 | issue = 2| page = 424 | doi=10.2307/1932198| jstor = 1932198 | bibcode = 1963Ecol...44..424P }}
* {{cite journal | vauthors = Caldwell MM, Dawson TE, Richards JH | date = 1998 | title = Hydraulic lift: consequences of water efflux from the roots of plants. | journal = Oecologia | volume = 113 | issue = 2 | pages = 151–161 | doi = 10.1007/s004420050363 | pmid = 28308192 | bibcode = 1998Oecol.113..151C }}
{{Refend}}

== External links ==
{{Commons category|Roots}}
{{Wikiquote}}
* [https://web.archive.org/web/20090425083339/http://ualr.edu/botany/ Botany – University of Arkansas at Little Rock]
* {{YouTube|7WID7ObQPjE|Time-lapse photography of root growth}}

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{{Botany}}
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[[Category:Plant roots| ]]