Root and Root System

The first thing the root provides is mechanical anchorage of the plant in the substrate. This is especially important for large woody plants that resist wind loads. A powerful system of skeletal roots, often penetrating to considerable depth, and a branched network of fine roots create a reliable support. In some tropical trees (e.g., banyan figs), special buttress roots or prop roots form, adding extra stability (Mauseth, 2017; Stern, 2020). Even in herbaceous plants, the root mass can account for up to a third of the total dry mass, indicating the significance of this function (Graham et al., 2014).

This is perhaps the best‑known function of the root. Roots absorb from the soil water with dissolved ions of macro‑ and microelements (nitrogen, phosphorus, potassium, calcium, magnesium, sulfur, iron, etc.). The main absorption zone is the zone of maturation, bearing a huge number of root hairs — outgrowths of epidermal cells. Root hairs multiply the absorbing surface many times over: for example, in a single rye plant, the total length of all root hairs may exceed 10,000 km, and the absorption area — 400 m² (Evert, 2006; Raven et al., 2005). It is important to emphasize that the uptake of mineral ions is largely an active process requiring energy (ATP). The roots themselves selectively “pump” necessary elements across cell membranes using specialized transport proteins (Graham et al., 2014).

The absorbed water and mineral salts must be delivered to the shoots, leaves, and reproductive organs. For this purpose, a conducting tissue — xylem — is formed in the central cylinder of the root. Through xylem vessels, water with dissolved ions rises upward to the above‑ground part (upward flow). In the opposite direction, from leaves to roots, organic substances (products of photosynthesis — mainly sucrose) are transported via phloem sieve tubes, necessary for the growth and activity of the root system itself (Evert, 2006; Serebryakova et al., 2006). Thus, the root is an integral link in the plant’s unified transport system.

The root is an important endocrine organ. In its meristematic zones (especially the root tip), phytohormones — cytokinins and gibberellins — are synthesized, which are then transported via xylem to the shoots, where they regulate cell division, stem growth, leaf development, and delay senescence (Mauseth, 2017; Stern, 2020). In addition, other growth regulators may be synthesized in roots, e.g., abscisic acid (especially under drought), as well as various secondary metabolites — alkaloids (e.g., nicotine in tobacco roots), which accumulate in leaves and serve for protection against herbivores (Graham et al., 2014).

Many plants store reserve nutrients in their roots, mainly starch, as well as fats and proteins. This function is particularly pronounced in biennial plants (carrot, beet, turnip, radish). In the first year of life, they form a powerful storage organ — a taproot — in which reserves are deposited, and in the second year they use them for flowering and fruiting (Graham et al., 2014). Storage roots are also characteristic of many perennials (dahlia, sweet potato, chicory). Anatomically, the storage tissue is a highly developed parenchyma of either the cortex or the secondary xylem (Serebryakova et al., 2006).

The root, like all living organs, respires. It consumes oxygen to oxidize organic substances (mainly sugars coming from leaves) and to produce ATP — the universal energy required for active ion uptake, growth, and cell division. Therefore, the soil must be sufficiently aerated. Plants growing in waterlogged soils or in water have developed special adaptations. For example, mangrove trees form pneumatophores — respiratory roots that grow vertically upward (negative geotropism). They are permeated by aerenchyma (loose tissue with large intercellular spaces) and absorb oxygen from the air through lenticels on the surface, delivering it to the underground parts of the root system (Graham et al., 2014; Beck, 2010). Without oxygen, roots quickly switch to anaerobic respiration (fermentation), leading to weakening and death.

Roots actively enter into mutually beneficial relationships with soil microorganisms:

All these functions are realized thanks to the complex morphological and anatomical structure of the root, which will be discussed in detail in the following sections. It is important to remember that the root is a heterotrophic organ: it depends entirely on the supply of carbohydrates from the photosynthesizing leaves. Limitation of photosynthesis immediately affects root growth and function (Evert, 2006).

Root cap (calyptra) — a protective structure at the very tip of the root. It consists of living parenchyma cells that are constantly sloughed off from its surface and replaced by new cells through division of the apical meristem (Evert, 2006). The root cap performs several critically important functions:

In addition, sloughed‑off cap cells (so‑called “border cells”) continue to secrete mucilage and protect the root from pathogens (Graham et al., 2014).

Zone of cell division (apical meristem) — located directly under the root cap. Here cells divide intensively, providing root elongation and the formation of all primary tissues. Meristem cells are small, isodiametric, with dense cytoplasm, a large nucleus, and small vacuoles (Evert, 2006). A characteristic feature of the root meristem is the presence of a quiescent center — a group of cells that divide very rarely and serve as a reserve for meristem restoration upon damage (Beck, 2010; Mauseth, 2017).

Zone of elongation — here cells stop dividing but elongate greatly due to an increase in the central vacuole and stretching of cell walls. This process is the main cause of root elongation. Importantly, cells elongate selectively, which, together with gravity perception by the root cap, allows the root to grow directionally downward (positive geotropism) (Serebryakova et al., 2006).

Zone of absorption (zone of root hairs) — the region of the root where epidermal cells (rhizodermis) form thin tubular outgrowths — root hairs. A root hair is not a separate cell but an outgrowth of a single epidermal cell, increasing the absorbing surface of the root tens to hundreds of times (Graham et al., 2014). For example, in a four‑month‑old rye plant, the total number of root hairs is estimated at 14 billion, and their total absorbing surface — 400 m² (Raven et al., 2005). Hairs live only a few days, but new ones are constantly formed as the root grows. It is in this zone that the main uptake of water and mineral ions occurs. Rhizodermis cells have thin walls, not covered by a cuticle, which facilitates absorption (Evert, 2006).

Zone of conduction (branching) — the longest region, located above the absorption zone. Here root hairs are absent, and the outer layer often becomes suberized (forming an exodermis). In this zone, lateral roots are actively initiated (endogenously from the pericycle), hence it is often called the branching zone. The main function of this zone is to conduct water and mineral salts upward (via xylem) and organic substances downward (via phloem), as well as to provide mechanical strength (Serebryakova et al., 2006; Mauseth, 2017).

As the root grows, all these zones continuously shift: the root cap and division zone advance deeper into the soil, while the absorption and conduction zones follow, exploiting new volumes of ground.

The totality of all roots of a plant (main, lateral, adventitious) forms the root system. Based on origin and shape, two main types of root systems are distinguished: taproot and fibrous (Serebryakova et al., 2006; Stern, 2020).

Taproot system is characteristic of most gymnosperms and dicot angiosperms (e.g., pine, oak, sunflower, carrot). It features a well‑developed main root, which arises from the embryonic radicle. The main root is usually larger than the others, grows vertically downward (orthogropically), and persists throughout the plant’s life. Lateral roots of the first and subsequent orders branch off from it. Such a system allows the plant to penetrate deeply into the soil, extracting water from lower horizons, which is especially important in arid conditions (Evert, 2006). In many biennial crops (carrot, radish, beet), the main root becomes greatly thickened and turns into a storage organ — a taproot (Graham et al., 2014).

Fibrous root system is typical of most monocots (e.g., wheat, maize, onion, palms). Here the main root either dies early or is poorly developed and does not stand out among the others. The bulk consists of adventitious roots, which arise from the stem (usually from nodes, underground or aboveground). All roots in such a system are roughly similar in thickness, forming a dense branched network in the surface soil layer, often intertwining. A fibrous system effectively holds the fertile topsoil, preventing erosion, and quickly exploits moisture from precipitation (Stern, 2020; Beck, 2010).

There are also transitional and mixed types. For example, many perennial herbs (clover, alfalfa) develop a powerful taproot, but in addition, numerous adventitious roots grow from the stem, creating a kind of “combined” system (Serebryakova et al., 2006).

It is important to note that root system architecture (RSA) is not only a heritable trait but also a plastic parameter that changes depending on environmental conditions (water availability, soil density, nutrient availability) (Lombardi et al., 2021). Modern crop science actively seeks ways to manage the type of root system to increase drought tolerance and fertilizer use efficiency (Sui et al., 2024).

The primary anatomical structure forms from the apical meristem. On a cross‑section of a young root (in the absorption zone), three main parts are clearly visible: the rhizodermis, the primary cortex, and the central cylinder (stele) (Beck, 2010).

Rhizodermis (epiblema) — the primary covering tissue. It consists of a single layer of living thin‑walled cells, often with root hairs. The rhizodermis lacks a cuticle and freely allows water and dissolved mineral ions to pass through. Its main function is absorption (Evert, 2006). In the conduction zone, the rhizodermis usually sloughs off, giving way to the protective exodermis.

Primary cortex — the most massive part of the young root. It consists of parenchyma cells, often with intercellular spaces, and performs several functions:

The inner layer of the cortex — endodermis — is one of the key elements of the root.

Endodermis — a single‑layered cylinder of tightly packed cells that, at early stages of development, bear Casparian strips on their radial and transverse walls — local thickenings impregnated with suberin and lignin. Casparian strips are a hydrophobic barrier: they interrupt the apoplastic pathway, forcing water and dissolved ions to switch to the symplastic pathway, i.e., to pass through the plasma membrane of endodermal cells. Thus, the endodermis serves as a selective filter controlling the entry of substances into the central cylinder (Beck, 2010; Evert, 2006). In many plants (especially monocots), the endodermis later thickens further with a suberin lamella and even cellulose layers, and also has passage cells — cells that retain only Casparian strips, through which selective transport continues (Serebryakova et al., 2006).

Central cylinder (stele) includes:

This primary structure ensures efficient absorption and radial conductivity, and it persists throughout life in monocots and many herbaceous dicots.

In gymnosperms and woody (as well as many herbaceous) dicots, roots can thicken due to the activity of secondary meristems — cambium and phellogen (cork cambium) (Evert, 2006).

Cambium formation and activity. The cambium arises in the central cylinder. First, between the primary xylem and primary phloem (in parenchymatous gaps), arcuate strips of cambium appear. Then the cambium “wraps around” the ends of the xylem arms, merging into a continuous cylinder. The xylem part of the cambium deposits cells inward (secondary xylem — wood), while the phloem part deposits cells outward (secondary phloem — bast). Because the cambium deposits much more secondary xylem than phloem, the central cylinder expands greatly, compressing and gradually destroying the primary cortex (Mauseth, 2017; Serebryakova et al., 2006). In most roots, secondary xylem is rich in parenchyma cells, and the vessels are larger than in the stem; annual rings are less pronounced or absent (Beck, 2010).

Periderm formation. Simultaneously with cambial activity, phellogen (cork cambium) arises in the pericycle (or, more rarely, in the outer layers of the phloem). It deposits cork (phellem) outward — dead, suberinized cells — and living cells of phelloderm inward. Cork protects the root from water loss and pathogen entry. The entire set of cork, phellogen, and phelloderm is called periderm. As the primary cortex and rhizodermis die and slough off, the periderm becomes the outer protective layer (Evert, 2006; Raven et al., 2005).

Final result of secondary structure. In a fully developed secondary root (e.g., in apple, linden, oak), one can distinguish (from outside inward): periderm (sometimes turning into rhytidome), remnants of primary phloem, secondary phloem, cambium, secondary xylem (occupying the bulk), and in the center — primary xylem (sometimes with remnants of parenchyma). Such a structure allows the root to simultaneously perform supporting, conducting, and storage functions, as well as to achieve perennial growth in thickness (Beck, 2010).

Thus, root anatomy is an example of evolutionary adaptation, where the simplicity of the primary structure (radial bundle, exarch xylem) is ideally suited for absorption and radial transport, while the secondary structure is suited for perennial growth and increasing mechanical strength.

Root elongation occurs through cell division in the apical meristem and subsequent cell expansion in the elongation zone. Unlike the shoot, where the apical meristem is protected by leaf primordia, the root meristem is covered by the root cap. Inside the meristem itself lies a quiescent center — a group of cells that divide rarely but, when surrounding meristematic cells are damaged, quickly become active and restore the apex (Evert, 2006; Beck, 2010). Division of initial cells and subsequent expansion of their derivatives enable the root tip to advance tens of millimetres per day (in some grasses, up to several centimetres). At the same time, the zones themselves (division, elongation, absorption) maintain a constant length and appear to “slide” forward (Serebryakova et al., 2006).

Roots of most plants exhibit positive geotropism — they grow in the direction of the gravity vector. This allows them to penetrate the soil and use moister horizons. Gravity perception occurs in the columella — the central part of the root cap. Columella cells contain amyloplasts (statoliths) — dense starch grains that, under gravity, settle to the lower cell wall (Beck, 2010; Graham et al., 2014).

Statolith settling triggers a cascade of signals, the central link of which is the redistribution of auxin transporters (PIN proteins) in root cap cells. As a result, auxin accumulates on the lower side of the root, in the elongation zone, where at high concentrations it inhibits cell expansion. The upper side, receiving less auxin, elongates faster, and the root bends downward (Mauseth, 2017; Evert, 2006). This mechanism ensures vertical growth of the main root and sets the gravitropic set‑point angle (GSA) of lateral roots, which can vary from nearly vertical to horizontal (Lombardi et al., 2021). The set‑point angle is controlled by expression of genes such as EXOCYST70A3 and PIN4, and affects root system depth (Ogura et al., 2019).

Some roots, for example pneumatophores of mangroves, grow upward (negative geotropism), while creeping roots may be diageotropic (horizontal). Such deviations are associated with special ecological adaptations (Graham et al., 2014).

Branching is a key mechanism for increasing the absorbing surface of the root system. Lateral roots are initiated endogenously — inside the parent root, in the pericycle. The process includes several successive stages (Benková & Bielach, 2010; Dastidar et al., 2012):

Root branching is a highly plastic process. Its frequency and the positioning of lateral roots can change in response to soil moisture, nitrate and phosphate availability, and mechanical stimulation (Dastidar et al., 2012). For example, in nitrate‑rich local patches, additional branching is induced, increasing resource use efficiency (“hydropatterning”) (Orosa‑Puente et al., 2018; Lombardi et al., 2021).

Root System Architecture (RSA) is the set of spatial characteristics: penetration depth, branch angle, branching density, root diameter, and growth rate. RSA results from the interaction between the genetic program and environmental factors (moisture, density, soil pH, nutrient content) (Sui et al., 2024; Lombardi et al., 2021).

Two main types of RSA (already mentioned in Section 2) are distinguished: taproot (with a dominant main root) and fibrous (with a system of adventitious roots). However, within these types, there is enormous diversity. For example, in many cereals under drought, the growth of deeper roots (deep RSA) can be enhanced, increasing drought tolerance (Uga et al., 2013; Graham et al., 2014). Conversely, under surface moisture, a more branched but shallow RSA develops.

RSA plasticity is ensured by complex hormonal regulation, in which auxin plays a central role. It coordinates main root elongation, lateral root initiation and growth, as well as their set‑point angle (gravitropic response). Other hormones — cytokinins, ethylene, abscisic acid, and brassinosteroids — modulate stress responses (Benková & Bielach, 2010; Dastidar et al., 2012). For example, under phosphorus deficiency, main root growth is suppressed, but branching is stimulated, increasing the search area (Sui et al., 2024).

Thus, the root system is a dynamic structure capable of rapidly reorganizing its architecture in response to changing conditions. Understanding the molecular mechanisms of this plasticity opens up possibilities for directed modification of root systems in crops to enhance their tolerance to drought, salinity, and nutrient deficiency (Lombardi et al., 2021; Sui et al., 2024).

Roots actively release various organic compounds into the surrounding soil — root exudates (mucigel, organic acids, sugars, amino acids, phenolic compounds, enzymes). These exudates perform several functions (Evert, 2006; Raven et al., 2005):

Thanks to exudates, the rhizosphere becomes a zone of intense microbiological metabolism, accelerating element cycling and increasing the availability of nitrogen, phosphorus, iron, and other elements to the plant (Graham et al., 2014).

Mycorrhiza (from Greek mykes — fungus and rhiza — root) is a mutualistic symbiosis between the roots of most land plants (over 80% of species) and soil fungi. The fungus receives carbohydrates (sugars) and other organic substances from the plant, while the plant obtains significantly improved uptake of water, phosphorus, nitrogen, and micronutrients (Mauseth, 2017; Beck, 2010). Two main types of mycorrhiza are distinguished (Graham et al., 2014; Stern, 2020):

Mycorrhiza is particularly important for phosphorus uptake, which in soil is often in poorly available forms (bound to calcium, iron, or aluminum). Fungal hyphae penetrate soil micropores that root hairs cannot enter and secrete phosphatases and organic acids, releasing phosphate ions. In exchange, the plant supplies the fungus with carbohydrates (up to 20% of photosynthetic products may be directed to mycorrhiza) (Mauseth, 2017; Stern, 2020). The agricultural importance of mycorrhiza is very great: tillage, application of high doses of phosphorus fertilizers, and some fungicides can suppress mycorrhiza formation, reducing natural soil fertility (Graham et al., 2014).

Although atmospheric nitrogen (N₂) makes up about 78% of air, most plants cannot use it directly. However, some bacteria (primarily of the genera Rhizobium, Bradyrhizobium, as well as actinobacteria of the genus Frankia and cyanobacteria) possess the enzyme nitrogenase, which can reduce N₂ to ammonium (NH₄^\+). This process is called biological nitrogen fixation (Raven et al., 2005; Graham et al., 2014).

The most studied symbiosis is between leguminous plants (family Fabaceae) and rhizobia. The process includes several stages (Evert, 2006; Stern, 2020):

As a result, legumes can grow on soils poor in mineral nitrogen and accumulate large amounts of protein in their seeds. Moreover, after root and nodule decay, the soil is enriched with nitrogen, which is used in crop rotations (Graham et al., 2014). Similar symbioses with nitrogen‑fixing actinobacteria are formed by alder (Alnus), sea buckthorn (Hippophae), and some species of Casuarina (Beck, 2010).

It is important to emphasize that both types of symbiosis — mycorrhiza and nodules — are not passive infections but genetically programmed interactions governed by complex signaling pathways. Studies in Arabidopsis and legumes have revealed common genes controlling both types of interactions (e.g., genes responsible for perception of Nod factors were recruited from more ancient systems regulating mycorrhiza formation) (Dastidar et al., 2012; Lombardi et al., 2021).

Thus, the rhizosphere and root symbioses are the “hidden front” of plant life, largely determining plant productivity, stress tolerance, and competitiveness in natural and agricultural ecosystems.

Drought (water deficit) — one of the most powerful factors limiting plant productivity. Roots are the first to perceive water shortage. Under mild or moderate deficit, the plant may enhance the growth of deep‑penetrating roots (“drought‑tolerant” deep RSA) and increase branching in moister horizons (hydropatterning — the ability of roots to branch preferentially on the side facing a water source) (Orosa‑Puente et al., 2018). This involves changes in the expression of genes controlling the gravitropic angle (e.g., DEEPER ROOTING 1 in rice) and activation of abscisic acid (ABA) synthesis in roots, which sends a signal to the shoot, causing stomatal closure and reduced transpiration (Sui et al., 2024; Uga et al., 2013). However, under severe and prolonged drought, root growth is inhibited: cell division in the apical meristem decreases, elongation is reduced, and branching slows. Root hairs die, and the endodermis and exodermis may become further suberized to reduce water loss from the root into the dried soil (Mauseth, 2017; Graham et al., 2014).

Photograph of respiratory roots (pneumatophores) of a mangrove tree growing vertically upward from the water. author::Peripitus[https://commons.wikimedia.org/wiki/User:Peripitus] https://commons.wikimedia.org/wiki/File:Pneumatophore_overkill_-_grey_mangrove.JPG CC BY-SA 3.0

Waterlogging (flooding, hypoxia) — an equally dangerous factor because roots require oxygen for respiration. In waterlogged soil, O₂ diffusion slows drastically, leading to hypoxia or anoxia. Roots switch to anaerobic respiration (fermentation), which yields 18 times less ATP than aerobic respiration. As a result, active ion transport ceases, cell division and growth stop, and cortical cells may die (Graham et al., 2014). Adaptations to waterlogging include the formation of aerenchyma — a loose tissue with large intercellular spaces that facilitates oxygen diffusion from above‑ground parts to the roots. In some plants (e.g., mangroves, rice), special respiratory roots — pneumatophores — grow vertically upward, supplying underground parts with oxygen (Raven et al., 2005; Beck, 2010). Also, under hypoxia, the development of adventitious roots, which arise closer to the surface where more oxygen is available, may be induced (Stern, 2020).

Soil temperature affects the rate of cell division in the meristem, enzyme activity, and respiration intensity. Each species has its own temperature optimum for root growth (usually around +20…+25 °C). When temperatures drop below +5…+10 °C, root growth slows sharply, and during frosts (in sensitive species) may completely stop, with cells dying. Temperatures above +35…+40 °C also inhibit roots due to protein denaturation and membrane disruption (Mauseth, 2017). Perennial plants of temperate regions are adapted to seasonal fluctuations: in autumn, root growth stops, a dormant period ensues, and in spring it resumes when the soil warms up (Serebryakova et al., 2006).

Root growth in dense, stony, or compacted soil (e.g., after heavy machinery traffic) is hindered. The root cap secretes less mucigel, cells in the elongation zone are compressed, reducing elongation rate. However, the plant can partially overcome mechanical impedance by sinuous growth, seeking cracks and pores, and by altering cell wall stiffness (under the influence of ethylene and auxin) (Evert, 2006). Branching may be suppressed, and the root system becomes poorer, negatively affecting water and nutrient uptake (Raven et al., 2005).

Most crop plants prefer a neutral or slightly acidic soil reaction (pH 6.0–7.0). Under strong acidification (pH < 5.0), the mobility of toxic aluminum (Al³⁺) and manganese (Mn²⁺) ions increases, damaging root meristems, inhibiting cell expansion, and reducing calcium and magnesium uptake (Graham et al., 2014). In addition, the growth of beneficial bacteria and mycorrhizal fungi is suppressed in acidic environments. Plants can adapt to acid soils by secreting organic acids (citric, malic) that bind Al³⁺ into non‑toxic chelates, and by increasing proton pump activity to maintain homeostasis (Sui et al., 2024; Mauseth, 2017).

Under alkalization (pH > 8.0), the availability of iron, manganese, zinc, and phosphorus decreases, leading to chlorosis and retarded root growth.

High salt concentrations (especially NaCl) in the soil create osmotic stress — water enters roots with difficulty — and ion imbalance (excess Na⁺ and Cl^-). Roots respond to salinity by reducing cell elongation, suppressing branching, and thickening the cell walls of the endodermis and exodermis to enhance the barrier function (Sui et al., 2024). In salt‑tolerant species (halophytes), mechanisms exist for removing Na^\+ from the cytoplasm into the vacuole (via Na⁺/H^\+ antiporters) or secreting salts through salt glands on the shoot surface (Raven et al., 2005). Auxin and ABA play key roles in reorganizing root growth under salinity, causing the root to bend away from areas with high salt concentration (halotropism) (Lombardi et al., 2021).

The root is able to “scan” the soil for nutrient availability and reorganize its architecture to search most effectively:

When encountering an obstacle (stone, compacted layer), the root may bend or, more rarely, form aerial roots that bypass the barrier. This is also associated with local auxin redistribution and response to pressure (thigmotropism) (Evert, 2006). Light, although usually not reaching roots (except for aerial roots), can in experimental conditions inhibit root growth (negative phototropism), which is rarely relevant in natural settings.

Thus, environmental factors act on the root in a complex manner, through common signaling networks (auxin, ethylene, ABA, brassinosteroids, nitrate‑specific sensors). Understanding these mechanisms allows breeders to create varieties with optimized root systems for specific soil‑climate conditions — so‑called “climate‑ready crops” (Lombardi et al., 2021; Sui et al., 2024).

The plant maintains a relative equilibrium between the mass of the root system and the mass of the shoot. This equilibrium can change depending on environmental conditions. Root:shoot ratio is an important adaptation indicator. For example, under drought or nitrogen deficiency, the plant directs more assimilates to the roots, stimulating their growth to improve water supply and nutrient foraging. Conversely, under shading or excess nitrogen, most resources go to the shoot (Raven et al., 2005; Stern, 2020). Maintaining this balance is the result of complex hormonal and nutrient signaling.

The root absorbs water and dissolved ions from the soil and transports them via xylem to the above‑ground part. This upward flow is provided by two mechanisms (Evert, 2006; Graham et al., 2014):

Thus, the root does not “push” water upward but rather “pulls” it from below thanks to leaf activity. However, root pressure is important for refilling xylem vessels after winter and for sap rise in low‑stature plants (Mauseth, 2017).

The root is a heterotrophic organ. It is incapable of photosynthesis (with rare exceptions — some orchids) and therefore depends entirely on the supply of organic substances, primarily sucrose, from the above‑ground part. Sucrose is produced in leaves during photosynthesis and transported via phloem sieve tubes downward to the roots. In roots, sucrose is used for respiration (generating ATP needed for active ion transport, cell division, and synthesis) and serves as a starting material for the formation of starch, cellulose, and other substances (Raven et al., 2005; Evert, 2006).

If the supply of assimilates from leaves decreases (e.g., due to shading or leaf diseases), root growth slows or stops, and old roots may die. Conversely, enhanced photosynthesis stimulates root system development (Mauseth, 2017).

The root and shoot continuously exchange hormonal signals that coordinate their growth and development (Benková & Bielach, 2010; Dastidar et al., 2012):

Root‑shoot interaction is not a one‑way dictate but a system with feedback. If the root is damaged for any reason (e.g., by pests or waterlogging), the supply of cytokinins and water decreases, leading to inhibition of shoot growth, yellowing, and leaf abscission. Conversely, if the shoot is damaged (e.g., grazed by animals), the supply of auxin and assimilates ceases, inhibiting root growth and branching (Mauseth, 2017). This system allows the plant as a whole to optimize resource allocation in a constantly changing environment.

The root‑shoot connection is established at the earliest stages of ontogeny. In the seed embryo, even before germination, the rudimentary root (radicle) and shoot (plumule) are formed, connected by the hypocotyl. The vascular system links them into a continuous whole (Evert, 2006). Many plants also exhibit sympodial growth, where lateral shoots develop from axillary buds and themselves form new adventitious roots, further tightly linking root and shoot systems (Serebryakova et al., 2006).

Thus, the root and shoot form a single functional system where the exchange of water, minerals, organic substances, and hormones ensures integrity, homeostasis, and adaptive plasticity of the plant. Understanding these interrelationships is necessary for agronomic practice: transplanting, fertilization, irrigation, canopy management, and stress mitigation.

Soil tillage dramatically affects root development. Plowing and loosening create a favourable structure for growth — reduce density, improve aeration, and facilitate root penetration. However, long‑term conventional plowing can lead to the formation of a plough pan — a compacted horizon that roots cannot penetrate. Therefore, no‑till and minimum tillage are becoming increasingly widespread; they preserve soil channels from roots and earthworms, promoting the formation of a deep and penetrating root system (Graham et al., 2014; Mauseth, 2017).

Fertilizers. Localized application (e.g., starter doses of phosphorus and nitrogen directly in the seed zone or in rows) stimulates localized root branching (“enrichment”), accelerating the development of young plants. The use of slow‑release fertilizers promotes more even root system development throughout the growing season. Conversely, uniform surface application followed by incorporation can lead to an excessively shallow root system (Raven et al., 2005).

Irrigation. The irrigation regime directly determines root architecture. Frequent surface irrigation stimulates the development of a fibrous system in the topsoil, increasing the crop’s dependence on dry periods. In contrast, infrequent deep irrigation or drip irrigation promotes deep root penetration and the formation of a drought‑tolerant phenotype (Lombardi et al., 2021; Stern, 2020).

Biopreparations. Commercial preparations containing mycorrhizal fungi (e.g., Glomus spp.) or nitrogen‑fixing bacteria (rhizobia for legumes, associative nitrogen fixers for cereals) can significantly increase the absorbing surface of roots and improve the uptake of phosphorus, nitrogen, and micronutrients. Biopreparations are especially effective on poor soils and in organic farming systems (Graham et al., 2014; Mauseth, 2017).

Traditional breeding for productivity often “selected against” a vigorous root system because plants with a compact shoot and small root mass were easier to harvest and gave a higher harvest index. However, modern programmes are returning to the idea of “targeted breeding for root architecture” (Lombardi et al., 2021). Candidate genes controlling penetration depth (DEEPER ROOTING 1 — DRO1, EXOCYST70A3, PIN4), lateral root set‑point angle (GSA), and branching density have been identified (Sui et al., 2024; Ogura et al., 2019).

Marker‑assisted selection (MAS) allows selection of plants with desired alleles of these genes without lengthy field trials. For example, introgression of the DRO1 allele from the cultivar ‘Kinandang Patong’ into the rice genome increased root system depth and drought tolerance (Uga et al., 2013).

Genome editing (CRISPR/Cas9) opens unprecedented opportunities for precise modification of RSA. Plants with edited regulatory genes have already been obtained (e.g., knockout of the ERF13 gene, which suppresses the synthesis of very‑long‑chain fatty acids, accelerating lateral root emergence through the cortex) (Sui et al., 2024). In addition, editing genes responsible for the synthesis and perception of auxin, cytokinins, and abscisic acid allows tuning of the root system to specific stress conditions.

Key target genes for RSA improvement (Sui et al., 2024, table):

Different genotypes of the same species can have dramatically different RSA. For example, in Arabidopsis there are “haplogroups” with deep and shallow root systems, adapted to different rainfall regimes (Ogura et al., 2019). Similarly, in wheat, maize, rice, and soybean, contrasting root architecture varieties have been identified. Therefore, agronomists and breeders need to select varieties with the type of RSA that best matches the soil‑climate conditions of a particular farm: for arid regions — deep, well‑branched roots (DRO1 alleles, strong gravitropism); for humid, fertilised conditions — a more compact but efficiently absorbing system (Lombardi et al., 2021; Sui et al., 2024).

Despite progress, challenges remain:

Nevertheless, root system management is one of the most promising directions of the “new green revolution” aimed at creating crops that are resilient to climate change and resource‑efficient (Sui et al., 2024; Lombardi et al., 2021).