Leaf

The main function of a green leaf is photosynthesis, during which the energy of sunlight is converted into chemical energy of organic compounds (primarily carbohydrates). The flat, dorsiventral shape of the leaf blade creates a maximum surface area per unit volume of tissue, ensuring efficient light capture (Mauseth, 2017). Chlorophyll-containing cells of the mesophyll, especially the palisade parenchyma, contain dozens of chloroplasts in which the light and dark reactions of photosynthesis occur (Evert, 2006; Graham et al., 2014). The palisade parenchyma is oriented perpendicular to the leaf surface, contributing to more complete light absorption: each palisade cell acts as a light guide, directing photons deeper into the tissue (Karabourniotis et al., 2021). The products of photosynthesis — sucrose and other organic substances — are transported via the phloem of veins to sites of consumption or storage (roots, growing shoots, fruits).

Photosynthesis is impossible without the supply of carbon dioxide, which enters the leaf through stomata — specialized structures in the epidermis consisting of two guard cells and a stomatal pore (Evert, 2006). Together with CO₂, oxygen produced during photosynthesis and water vapor are released through open stomata. The process of water evaporation from leaves is called transpiration. It is transpiration that creates the “upper end” of the water flow in the plant: due to the cohesion of water molecules and transpirational “tension,” water rises from the roots through the xylem to the leaves (Graham et al., 2014). Transpiration also cools the leaf on hot days, preventing overheating. Regulation of stomatal opening and closing is controlled by the turgor of guard cells, which depends on the uptake of potassium ions and the concentration of CO₂ in the leaf, as well as on the phytohormone abscisic acid (ABA) under water stress (Graham et al., 2014).

In most plants, stomata are located predominantly on the lower (abaxial) side of the leaf, which reduces water loss under direct sunlight (Mauseth, 2017). In xerophytes (plants of dry habitats), sunken stomata, additional cuticular layers, and dense pubescence that reduces air turbulence at the leaf surface are common (Karabourniotis et al., 2021).

Leaf functioning is closely related to the microorganisms that inhabit it — epiphytic bacteria and fungi. This complex of microorganisms (the phyllosphere microbiome) can influence plant productivity and health, particularly through nitrogen fixation, production of phytohormones, and protection against pathogens (Yang et al., 2025). In turn, leaf structure and age determine the species composition and activity of microorganisms on its surface, creating a feedback loop.

Thus, the leaf is not just an “organic matter factory” but a multifunctional organ integrating nutrition, respiration, water balance, defense, and reproduction. Understanding this functional spectrum is necessary for the proper management of crop growth and development in agroecosystems.

A typical leaf of flowering plants (especially eudicots) consists of the following parts (Raven, 2005; Mauseth, 2017):

In monocots, differentiation into petiole and blade is often absent; they may have a sheathing base and a linear or lanceolate blade (Raven, 2005).

Based on the degree of blade dissection, two main types of leaves are distinguished (Simpson, 2019; Mauseth, 2017):

Depending on the arrangement of leaflets on the rachis, the following types of compound leaves are distinguished (Simpson, 2019; Bell, 1991):

It is important to distinguish a compound leaf from a shoot with several leaves: in the axil of a compound leaf there is only one bud, whereas on a shoot there is a bud in the axil of each leaf (Raven, 2005).

Veins are vascular bundles that permeate the leaf blade. They contain xylem (typically located above) and phloem (below) and ensure the transport of water and assimilates (Evert, 2006). The pattern of vein arrangement (venation) is an important systematic character.

Two main types of venation are distinguished in flowering plants (Simpson, 2019; Mauseth, 2017):

More detailed types of venation (brochidodromous, camptodromous, craspedodromous, etc.) are used in describing fossil leaves and in fine systematics (Hickey, 1973 as cited in Simpson, 2019).

Phyllotaxis is the order of leaf placement on the stem, determined genetically and often associated with optimization of light exposure (leaf mosaic). Main types (Simpson, 2019; Serebryakova et al., 2006):

In alternate phyllotaxis, leaf mosaic is often observed: petioles curve, and blades are arranged so as not to shade each other (Serebryakova et al., 2006).

Extensive terminology for blade shape, margin, apex, and base is used for precise leaf description (Simpson, 2019; Bell, 1991).

Blade shape is determined by the ratio of length to width and the position of the widest part:

Margin type (Simpson, 2019):

Apex shape:

Base shape:

In many plants, leaf shape changes during ontogeny (heteroblasty) — for example, juvenile ivy leaves are lobed, while adult leaves are entire, elliptic (Raven, 2005).

Stipules may be free or adnate to the petiole. They are often modified: in peas and vetches, large stipules perform a photosynthetic function; in euphorbias, they transform into spines; in Rosaceae, they sometimes appear as glands (Simpson, 2019). In species of the genus Rubia, stipules fuse with opposite leaves, forming a whorl of false leaves. In Polygonaceae, stipules fuse into a membranous sheath (ochrea) surrounding the node (Serebryakova et al., 2006).

In some cases, leaves of different shapes develop on the same plant or even on the same shoot (heterophylly). This may be associated with changes in light conditions (in aquatic plants — submerged and emergent leaves) or with age-related variability (in eucalyptus, ivy) (Raven, 2005).

Anisophylly is the development of leaves of different sizes and shapes at the same node (e.g., on plagiotropic shoots of elm, some begonias). Anisophylly is often accompanied by different potential activities of axillary buds (Simpson, 2019).

Thus, the morphological description of a leaf includes a wide range of characters that allow unambiguous characterization of a species. Knowledge of morphological terminology is necessary for working with identification keys, herbarium material, and in breeding and seed production practice.

The epidermis is a single-layered dermal tissue covering the entire leaf surface. Epidermal cells are tightly packed, lack intercellular spaces, and, except for guard cells of stomata, usually do not contain chloroplasts (Mauseth, 2017). The transparency of epidermal cells ensures unobstructed penetration of sunlight to the photosynthetic tissues. The outer walls of epidermal cells are covered by a cuticle — a layer of insoluble polymer cutin and waxes that significantly reduces unregulated water loss (transpiration) (Evert, 2006). Cuticle thickness varies from very thin in moisture-loving plants (hydrophytes) to thick, multilayered in xerophytes (e.g., oleander, pine), where it plays an important protective role (Karabourniotis et al., 2021).

Stomata are specialized structures of the epidermis consisting of two guard cells (usually bean‑shaped or dumbbell‑shaped) and a stomatal pore between them (Graham et al., 2014). Guard cells, unlike other epidermal cells, contain chloroplasts and regulate the opening and closing of the pore in response to changes in turgor pressure. The mechanism of stomatal operation is associated with active transport of potassium ions: when osmotic pressure in guard cells increases, water enters them, they bend, and the stomatal pore opens; when ions and water flow out, it closes (Evert, 2006). In most plants, stomata are predominantly on the lower side of the leaf (hypostomatic type), reducing water loss under direct solar heating. In floating leaves of aquatic plants (water lily), stomata are only on the upper side (epistomatic type), while in submerged leaves they may be completely absent (Raven, 2005).

Trichomes (hairs) — outgrowths of epidermal cells that may be unicellular or multicellular, simple or branched (glandular and non‑glandular). Trichomes perform many functions: reduce evaporation (creating a “boundary layer” of air), reflect excess solar radiation, protect against insect herbivory, and secrete various substances (essential oils, nectar) (Karabourniotis et al., 2021; Mauseth, 2017). In many xerophytes (e.g., olive, lavender), dense pubescence is an important adaptation to arid conditions.

In some plants, the epidermis contains cystoliths (cell outgrowths encrusted with calcium carbonate) or silica inclusions (phytoliths) that stiffen the leaf and protect it from being eaten (Karabourniotis et al., 2021).

The mesophyll is the parenchyma tissue located between the upper and lower epidermis. This is where the main processes of photosynthesis occur. In most eudicots, the mesophyll is differentiated into two layers (bifacial leaf) (Evert, 2006):

In monocots with narrow, linear leaves, differentiation into palisade and spongy parenchyma is often not expressed; the mesophyll consists of uniform cells with large intercellular spaces (Raven, 2005). In plants of dry habitats, an isobilateral mesophyll may form (with palisade parenchyma on both sides of the leaf), allowing efficient light use regardless of sun position (e.g., in eucalyptus) (Karabourniotis et al., 2021).

The leaf is permeated by a branched network of veins, which are continuations of the stem’s vascular system. Veins consist of xylem (typically located on the adaxial, upper side) and phloem (on the abaxial, lower side), together forming collateral vascular bundles (Evert, 2006). Xylem delivers water and dissolved minerals from the roots to the leaf, while phloem transports photosynthetic products (sucrose) to sites of consumption or storage.

Based on size and function, we distinguish (Evert, 2006; Mauseth, 2017):

In some plants, the bundle sheath connects to the epidermis via bundle sheath extensions — strands of collenchyma or sclerenchyma that strengthen the leaf and possibly participate in lateral water transport (Karabourniotis et al., 2021).

To maintain the blade in an expanded state and withstand wind loads, the leaf contains mechanical tissues:

The anatomical structure of the leaf varies greatly depending on growing conditions (ecological plasticity):

Thus, the anatomical organization of the leaf is the result of a complex evolutionary compromise between maximally efficient photosynthesis, gas exchange, and protection against adverse factors. Understanding this organization is necessary for diagnosing stress, assessing crop condition, and justifying agronomic practices (e.g., foliar application of fertilizers, growth regulators, and protective agents).

The leaf arises exogenously on the shoot apex. In the peripheral zone of the apex (the region adjacent to the central zone), cells begin to divide more actively, and a small bump — the leaf primordium — forms on the surface (Malinowski, 2013; Serebryakova et al., 2006). The rhythmicity of primordium initiation defines the plastochron — the time interval between the initiation of two successive primordia (Serebryakova et al., 2006). The site of primordium initiation is not random: it is determined by the accumulation of auxin, which is transported to the apex by PIN1 proteins, and by inhibitory fields of previously initiated leaves (Reinhardt et al., 2003; Nakayama et al., 2012; cited in Malinowski, 2013). In dicots, the primordium initially has the shape of a cone or ridge, while in monocots it often surrounds the apex in the form of a ring (Raven, 2005).

Inside the bud, the leaf primordium undergoes a phase of intense cell division. The shape of the future leaf is established already at this stage: the leaf base forms, and the blade develops from the marginal (edge) meristem and intercalary meristems (Malinowski, 2013). In dicots, primordium growth in length occurs due to an apical meristem, and then the marginal meristem comes into play, ensuring blade expansion. In monocots, the primordium quickly envelops the apex, and the sheath forms, with the blade developing later from the distal part of the primordium (Raven, 2005). Differentiation of the vascular system (procambium → primary xylem and phloem) occurs acropetally (from base to tip) hierarchically: first large veins are initiated, then small veins, and finally blind endings (Evert, 2006; Nelson & Dengler, 1997). Differentiated protoxylem and protophloem elements may elongate as the leaf grows; in grasses, some protoxylem elements break down, forming protoxylem lacunae (cavities) (Serebryakova et al., 2006).

After emerging from the bud (or upon seed germination), the post‑bud phase begins, during which cell expansion (elongation) predominates due to water uptake and vacuole enlargement. Cell division is largely completed by this time, and further growth occurs through expansion of existing cells and, in some plants, through intercalary growth (e.g., in grasses). In dicots, in the expanding leaf, palisade parenchyma cells increase in length, and spongy parenchyma cells develop irregular shapes and intercellular spaces. In monocots (grasses), an intercalary meristem is retained at the base of each internode and at the base of the leaf blade, allowing the leaf to regrow after damage (Raven, 2005; Mauseth, 2017). Light plays a key role in expansion: in many plants, etiolated leaves (grown in darkness) have elongated internodes, reduced chloroplasts, and often an unexpanded blade.

An important process during the expansion stage is stomatal formation. In dicots, stomata mature acropetally (from base to tip); in monocots, basipetally (from tip to base) (Evert, 2006). Completion of leaf growth is accompanied by differentiation of all tissues, cuticle formation, and wax deposition.

Heterophylly is the phenomenon in which leaves of different shapes and sometimes different internal structures are sequentially formed on the same plant during ontogeny (Chitwood & Sinha, 2016; Simpson, 2019). The most striking examples are the change from juvenile (young) to adult leaves in ivy (Hedera helix), eucalyptus, acacia, and fig. In ivy, juvenile leaves are lobed, palmate; adult leaves are entire‑margined, ovate. In acacia, juvenile leaves are bipinnate, while adult leaves become phyllodes — expanded, flattened petioles that function as blades (Chitwood & Sinha, 2016; Bell, 1991).

Heterophylly is regulated by internal mechanisms related to meristem age and phytohormonal status. MicroRNAs play a key role: miR156 is highly expressed in the juvenile phase and suppresses SPL (SQUAMOSA PROMOTER BINDING PROTEIN LIKE) transcription factors, whereas with age miR156 levels decline, allowing SPL factors to activate adult‑type genes (e.g., miR172, which suppresses juvenile traits) (Chitwood & Sinha, 2016; Yang et al., 2013). Sugars (photosynthetic products) have also been shown to promote the decline in miR156 levels and accelerate the phase transition (Yang et al., 2013). In many woody plants, heterophylly may extend over years, and the transition to the adult leaf type often coincides with the ability to flower.

Heterophylly should not be confused with heterophylly (sometimes the same term is used, but in a narrow sense, heterophylly refers to changes in leaf shape depending on external conditions, e.g., in aquatic plants).

After the leaf reaches its maximum size, senescence processes begin. Externally, this is manifested by yellowing or reddening of the blade due to chlorophyll degradation and the unmasking of carotenoids and anthocyanins (Graham et al., 2014). Inside cells, chloroplasts break down, protein synthesis declines, hydrolytic enzymes break down macromolecules, and valuable substances (amino acids, sugars, ions) are translocated from the leaf into the stem and roots (Evert, 2006). The process of leaf detachment (abscission) occurs in the abscission zone located at the base of the petiole. In dicotyledonous woody plants, two layers differentiate in this zone: the separation layer (whose cells become mucilaginous and break down) and the protective layer (cork cells that form the leaf scar after leaf fall) (Raven, 2005). In monocots and many herbaceous plants, an abscission zone may not form, and leaves die gradually, remaining on the stem.

The initiators of senescence and leaf fall are changes in photoperiod (shortening day length), temperature, and the internal balance of phytohormones: a decrease in auxin levels and an increase in ethylene and abscisic acid (Evert, 2006). In deciduous trees and shrubs, leaf fall has important adaptive significance: it sharply reduces the transpiring surface in winter, when roots cannot supply water from frozen soil, and also prevents branch breakage by snow weight (Graham et al., 2014).

Leaf lifespan varies from a few weeks in ephemerals to 20–30 years in some conifers (e.g., in Bunge’s pine, stone pine) (Serebryakova et al., 2006). Deciduous plants shed all leaves annually, while evergreens (many conifers, evergreen oaks, laurel) have leaves that live from 2 to 5 or more years, with old leaves falling gradually as new ones form (Raven, 2005). Leaf lifespan is an important adaptation to environmental conditions: in cold or dry climates, it is advantageous to have long‑lived leaves because the cost of their construction is amortized over several seasons. In tropical rainforests, conversely, many trees renew their foliage annually (often during the dry season), although they are considered evergreens (Graham et al., 2014).

Thus, leaf ontogeny is a complex multi‑stage process that includes an embryonic phase, a phase of expansion and differentiation, and then senescence and death. Heterophylly and leaf fall are crucial adaptive mechanisms ensuring plant survival and reproduction in changing environmental conditions.

Light is the main factor determining photosynthetic activity. Within a single species, and sometimes within a single crown, leaves develop that differ significantly in anatomy depending on light exposure (Aneja et al., 2025).

The anatomical differentiation of sun and shade leaves is determined not only genetically but also occurs phenotypically during development. Transferring a plant from shade to light leads to the formation of sun leaves on new shoots, but old leaves do not restructure (Aneja et al., 2025). Some species exhibit heterophylly associated with changes in illumination as the plant grows (e.g., ivy, fig).

Water regime is the second most important factor determining the evolution of leaf anatomical structure. With respect to water, plants are divided into three main ecological groups: hydrophytes (aquatic plants), mesophytes (plants of moderately moist habitats), and xerophytes (plants of dry habitats) (Raven, 2005).

Temperature affects the leaf at all levels — from membranes to the whole organ. In cold climates (high mountains, polar regions, taiga), evergreen plants develop small, leathery leaves, often with a waxy bloom (e.g., lingonberry, bearberry). In many arctic species, stomata are sunken, and the cuticle is thick, also protecting against desiccation by cold winds (Aneja et al., 2025). In conifers (spruce, pine), needle‑like leaves have a thick cuticle, sclerenchymatous hypodermis, and resin canals, increasing frost resistance (Evert, 2006). In hot climates, many plants, conversely, form thinner leaves with high water content, facilitating cooling through transpiration. Leaf fall in the temperate zone is an adaptation to winter frosts: shedding leaves prevents water loss from frozen soil and mechanical damage from snow (Graham et al., 2014).

Halophytes are plants of saline soils (salt marshes, mangroves). Their leaves have specialized salt glands (e.g., in sea lavender, mangroves Avicennia) that actively excrete excess salts onto the leaf surface; salts are then washed off by rain or fall off with old leaves (Karabourniotis et al., 2021). In some halophytes, leaves become fleshy (succulent), storing water and diluting salts. Anatomically, halophytes often develop isobilateral mesophyll and multi‑layered epidermis (Yang et al., 2025).

In nitrogen‑poor soils (bogs, rocks), some plants have evolved toward carnivory — capturing and digesting small animals. Trap leaves are an example of extreme morphofunctional specialization. In sundew (Drosera), leaves are covered with glandular hairs that secrete sticky mucus and enzymes; in Venus flytrap (Dionaea), the leaf can snap shut when sensitive hairs are stimulated; in Nepenthes (Nepenthes), leaves are shaped like a pitcher with a lid (Graham et al., 2014; Mauseth, 2017). All carnivorous plants retain the ability to photosynthesize, and the traps provide them with additional nitrogen.

The phyllosphere microbiome (bacteria, fungi, algae on the leaf surface) can both suppress the plant and stimulate its defense responses. Some epiphytic bacteria contribute to nitrogen fixation or phytohormone synthesis (Yang et al., 2025). Under air pollution (sulfur dioxide, ozone, heavy metals), leaves are often damaged: stomatal function is impaired, chlorophyll degrades, and necrosis develops. Visible leaf changes (chlorosis, spotting, premature leaf fall) can serve as indicators of air quality (Yang et al., 2025).

The root system and leaves are in a state of functional mutual control. Roots supply leaves with water and dissolved mineral nutrients (primarily nitrogen, phosphorus, potassium) via the xylem — the upward flow (Evert, 2006). Under water deficit, roots synthesize abscisic acid (ABA), which is transported via xylem to leaves and causes stomatal closure, thereby limiting transpiration (Graham et al., 2014). In turn, leaves supply roots with organic substances (sucrose) via the phloem — the downward flow. Photosynthetic products are necessary for root growth, ion uptake, and amino acid synthesis (Evert, 2006).

The stem (shoot axis) serves as the physical and conductive connection between leaves and roots. The stem’s vascular bundles, through leaf traces, connect to the leaf veins (Raven, 2005; Evert, 2006). At the node, one or several leaf traces depart from the stem stele and head into the leaf base; above this node, a leaf gap remains in the stele — a parenchyma region where vascular bundles are absent (Esau, 1977; cited in Evert, 2006). Nodal structure (number of leaf traces and gaps) is an important systematic character for some families.

In the plant, there is a continuous flow of assimilates from their sites of production (sources) to sites of use or storage (sinks) (Evert, 2006). Leaves, especially mature ones, are the main donors of organic carbon. Sinks include growing shoot tips and roots, developing leaves, flowers, fruits, and storage organs (tubers, rhizomes, bulbs). Distribution of assimilates among different sinks is regulated by hormonal signals and plant demands. For example, during grain filling in cereals, source–sink relationships are restructured so that assimilates from the flag leaf and leaves below it are directed primarily to the ear (Mauseth, 2017). Senescing leaves, before falling, remobilize their stored substances (nitrogen, phosphorus, potassium, sugars) to young growing parts — a phenomenon called reutilization (Raven, 2005). A balanced source–sink system is a critical condition for high yield in agricultural crops.

Phyllotaxis (leaf arrangement) is the order of leaf attachment to the stem, determined genetically and ensuring optimal spatial placement of leaf blades. Main types: alternate (spiral), opposite (two leaves per node, often decussate), and whorled (three or more leaves per node) (Simpson, 2019). Phyllotaxis matters for light capture, gas exchange, and mechanical stability of the shoot. It has been established that phyllotaxis is controlled by auxin and PIN1 proteins, which create zones of high auxin concentration on the apex, initiating primordium formation (Reinhardt et al., 2003; Malinowski, 2013).

Leaf mosaic is the mutual arrangement of leaves (often on plagiotropic shoots) such that blades do not shade each other but fill gaps between neighboring leaves (Serebryakova et al., 2006). Leaf mosaic is achieved through different petiole lengths, petiole bending, and different blade orientations. This phenomenon is particularly pronounced in plants of the forest understory and in many creeping herbs. The main external factor inducing leaf mosaic is light: the petiole bends toward better illumination, turning the blade toward the light (Serebryakova et al., 2006).

Crown architecture (the overall shape and structure of the shoot system) determines the efficiency of light use and space by trees and shrubs. In crown formation, leaves play not only a photosynthetic but also a mechanical role: they create load on branches and influence their orientation. Shoot branching, branch angle, and internode length are all interrelated with phyllotaxis and leaf morphology (Serebryakova et al., 2006). In conifers (spruce, pine), whorled branching and needle‑shaped leaves contribute to even distribution of snow load. In deciduous trees, the leafless period reduces wind resistance and the risk of branch breakage during winter storms (Graham et al., 2014).

The plant as an integrated system is characterized by correlations — mutual influences and dependencies between growth and development of different organs. The following correlations involving the leaf are known (Serebryakova et al., 2006):

The leaf secretes physiologically active substances that influence the growth and differentiation of surrounding tissues. For example, developing leaves are a powerful source of auxin, which stimulates procambium formation and differentiation of xylem and phloem in the stem (Malinowski, 2013). Leaf primordia induce the formation of leaf traces and influence the pattern of stem branching. All this underscores the unity of the shoot system and the impossibility of considering the leaf separately from the shoot.

Leaf Area Index (LAI) is a dimensionless quantity equal to the ratio of leaf area (one side) to the ground area they occupy (Graham et al., 2014). For example, at LAI = 3, the total leaf area is three times greater than the field area. LAI is a crucial indicator of crop canopy structure: it determines the absorption of photosynthetically active radiation (PAR), transpiration, and potential productivity.

The optimal LAI value depends on the crop, climate, and cultivation technology. If LAI is too low (sparse stand), solar energy is not fully utilized; if LAI is too high (dense stand), lower leaves become severely shaded, their photosynthesis decreases, and the risk of disease increases due to poor ventilation (Graham et al., 2014; Ritonga et al., 2023). Modern precision agriculture uses LAI calculations to adjust seeding rates, timing and doses of nitrogen fertilization, and for yield forecasting using satellite and UAV imagery.

For most field crops (wheat, maize, soybean, potato), maximum productivity is achieved at LAI values in the range of 3–5 (Graham et al., 2014). Leaf formation and lifespan can be regulated by agronomic practices: irrigation, nitrogen fertilization, growth regulators (e.g., retardants that increase leaf thickness and chlorophyll content) (Ritonga et al., 2023).

Foliar fertilization — application of fertilizers by spraying leaves, bypassing root uptake. This method is widely used in vegetable, fruit, and ornamental production due to rapid absorption of elements (nitrogen, potassium, micronutrients, some phosphorus compounds) (Evert, 2006). Foliar feeding is effective:

Nutrient uptake through the leaf depends on cuticle structure, stomata, and the presence of hydathodes — water stomata through which solution absorption may occur (Evert, 2006). To improve efficiency, surfactants (wetting agents) are added to working solutions to enhance wetting and penetration through the cuticle (Graham et al., 2014).

Visual leaf analysis is a classic and most accessible method for assessing mineral nutrition and phytosanitary status of plants.

Diagnosis by leaf appearance:

Leaf analysis can be supplemented by chemical analysis of leaves (determination of nitrogen, phosphorus, potassium, and micronutrient content). For this, average leaf samples are taken from a specific canopy layer at the stage of maximum vegetative mass development (Evert, 2006).

Leaves are not only the basis of plant productivity but also a valuable resource for humans.

Plant leaves (especially of trees) serve as bioindicators of air pollution. Under exposure to sulfur dioxide, ozone, nitrogen oxides, and heavy metals, characteristic necrosis, chlorosis, and premature leaf fall appear on leaves (Yang et al., 2025). Stomatal density, cuticle thickness, and pigment content in leaves measured in urban and industrial areas allow assessment of anthropogenic load. In modern environmental monitoring, methods based on chlorophyll fluorescence and spectral reflectance of leaves are widely used.

Modern breeding aims to create cultivars with optimal leaf canopy architecture: in cereals — with erect leaves (reducing shading), in legumes — with modified leaf shape and size to increase lodging resistance (Ritonga et al., 2023). Genes responsible for leaf angle (e.g., OsSPL14/IPA1 in rice), leaf shape and curling (homeobox KNOX genes), and leaf lifespan (genes controlling senescence) have been studied (He et al., 2016; Ritonga et al., 2023; Nakayama et al., 2025). Genome editing using CRISPR/Cas9 allows targeted modification of leaf traits, opening new horizons for creating cultivars with desired productivity and resilience.