In vascular plants, the root is the organ of a plant that typically lies below the surface of the soil. Roots can also be aerial or aerating, that is, growing up above the ground or especially above water. Furthermore, a stem normally occurring below ground is not exceptional either (see rhizome). Therefore, the root is best defined as the non-leaf, non-nodes bearing parts of the plant's body. However, important internal structural differences between stems and roots exist.
1 Evolutionary history 2 Definitions
2.1 Anatomy 2.2 Architecture
5.1 Depth records
6 Environmental interactions 7 Economic importance 8 See also 9 Notes 10 References 11 External links
Evolutionary history Further information: 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 million years ago. 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. Definitions The first root that comes from a plant is called the radicle. A root's four major functions are 1) absorption of water and inorganic nutrients, 2) anchoring of the plant body to the ground, and supporting it, 3) storage of food and nutrients, 4) vegetative reproduction and competition with other plants. In response to the concentration of nutrients, roots also synthesise 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 mycorrhizae, and a large range of other organisms including bacteria also closely associate with roots.
Large, mature tree roots above the soil
The cross-section of a barley root
When dissected, the arrangement of the cells in a root is root hair, epidermis, epiblem, 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.[clarification needed]
Perhaps the most striking characteristic of roots (that makes it distinguishable from other plant organs such as stem-branches and leaves) is that, roots have an endogenous origin, i.e. it originates and develops from an inner layer of the mother axis (Such as Pericycle). Whereas Stem-branching and leaves (those develop as buds) are exogenous, i.e. start to develop from the cortex, an outer layer. Architecture
In its simplest form, the term root architecture 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
The configuration of root systems serves to structurally support the
plant, compete with other plants and for uptake of nutrients from the
soil. Roots grow to specific 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
Branch magnitude: the number of links (exterior or interior). Topology: the pattern of branching, including:
Herringbone: alternate lateral branching off a parent root Dichotomous: opposite, forked branches Radial: whorl(s) of branches around a root
Link length: the distance between branches.
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 categorised as intrinsic, the genetic and nutritional influences, or extrinsic, the environmental influences and are interpreted by signal transduction pathways. The extrinsic factors that affect root architecture include 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:
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.
Growth from apical meristems is known as primary growth, which
encompasses all elongation.
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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.
Stilt roots of
Roots forming above ground on a cutting of an Odontonema ("Firespike")
Aerating roots of a mangrove
The growing tip of a fine root
The stilt roots of Socratea exorrhiza
The roots, or parts of roots, of many plant species have become specialized to serve adaptive purposes besides the two primary functions[clarification needed], 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
monocots and pteridophytes, but also in many dicots, 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.
Aerating roots (or knee root or knee or pneumatophores or Cypress
knee): roots rising above the ground, especially above water such as
in some mangrove genera (Avicennia, Sonneratia). In some plants like
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 60 metres below the ground surface, was observed during the excavation of an open-pit mine in Arizona, USA. 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. Depth records
Species Location Maximum rooting depth (m) References
Boscia albitrunca Kalahari desert 68 Jennings (1974)
Juniperus monosperma Colorado Plateau 61 Cannon (1960)
Acacia erioloba Kalahari desert 60 Jennings (1974)
Prosopis juliflora Arizona desert 53.3 Phillips (1963)
Environmental interactions Certain plants, namely Fabaceae, form root nodules in order to associate and form a symbiotic relationship with nitrogen-fixing bacteria called rhizobia. Due 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. Economic importance
Roots can also protect the environment by holding the soil to reduce soil erosion
The term root crops 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 and horseradish. Spices obtained from roots
include sassafras, angelica, sarsaparilla and licorice.
Roots on onion bulbs
Absorption of water
Fibrous root system
^ Retallack, G. J. (1986). "The fossil record of soils". In Wright, V.
P. Paleosols: their Recognition and Interpretation (PDF). Oxford:
Blackwell. pp. 1–57. Archived (PDF) from the original on
^ Hillier, R.; Edwards, D.; Morrissey, L.B. (2008). "Sedimentological
evidence for rooting structures in the Early Devonian Anglo–Welsh
Basin (UK), with speculation on their producers". Palaeogeography,
Palaeoclimatology, Palaeoecology. 270 (3–4): 366–380.
^ College Botany, Volume-1 by HC Gangulee, KS Das and CT Datta,
revised by S Sen, New Central Book Agency, Kolkata
^ BOTANY For Degree Students, 6th Ed, by AC Dutta, Revised by TC
Dutta. Oxford University Press
^ Malamy, J. E. (2005). "Intrinsic and environmental response pathways
that regulate root system architecture". Plant, Cell &
Environment. 28: 67–77. doi:10.1111/j.1365-3040.2005.01306.x.
^ a b Caldwell, M. M.; Dawson, T. E.; Richards, J. H. (1998).
"Hydraulic lift: consequences of water efflux from the roots of
plants". Oecologia. 113 (2): 151–161.
^ Fitter, A. H (1991). "The ecological significance of root system
architecture: an economic approach". In Atkinson, D.
Dennis D.Baldocchi and Liukang Xu. 2007. What limits evaporation from
Mediterranean oak woodlands – The supply of moisture in the soil,
physiological control by plants or the demand by the atmosphere? Vol
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Brundrett, M. C. (2002). "Coevolution of roots and mycorrhizas of land
plants". New Phytologist. 154 (2): 275–304.
Chen, R.; Rosen, E.; Masson, P. H. (1999). "
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