Botany - B.Ye. Yakubenko 2017

Part Three. The Plant Kingdom (Planthae)
Chapter X. Plant Ecology. Concepts of Plant Ecology
10.1 Main Ecological Factors and Their Impact on Plants

Plant ecology is the science of the relationships between PLANTS AND THEIR environment, as well as among different plant species. Identifying the patterns in plant-environment interactions is crucial for developing crop cultivation technologies, establishing agrocenoses, introducing new plant species into cultivation, forecasting yields, and protecting plants from pests and pathogens.

Plant development is inseparable from the environment, which provides them with nutrients and energy. The environment consists of many factors, including the composition of air and soil, the presence and Abundance of flora and fauna, and industrial emissions and waste. Their roles in plant life processes vary. Plants are indifferent to certain factors, meaning their absence does not affect overall development (for example, atmospheric molecular nitrogen and light during the Cytology/cytology/16.html">Early stages of plant development); other factors are essential for normal functioning. Environmental elements necessary for plant development are called ecological plant life factors, and their collective set forms the plant environment.

Class="center">10.1 Main Ecological Factors and Their Impact on Plants

Plants are simultaneously affected by abiotic and biotic ecological factors. Abiotic factors include the following.

Climatic factors — air, Water, light, wind, heat, cosmic radiation, radioactivity, precipitation, air impurities, oxygen, carbon dioxide, solar radiation, etc.;

Edaphic factors — parent rocks, soil, acidity, salinity, biotic conditions, etc.;

Biotic factors — METABOLISM/18.html">The Influence of living organisms on one another: plants on animals, animals on plants, certain plant species on others, the influence of microorganisms, as well as The impact of humans and the technosphere on plants and the environment (human impact is often classified under anthropogenic factors).

10.1.1. Abiotic Factors. Climatic Variables

Climatic conditions play a vital role in the Development of Plants and vegetation. They are highly diverse in their composition and effects. Combining with one another, climatic elements create the climatic environment.

Air as an ecological factor. Air is a critical factor in plant life. Plants assimilate carbon dioxide, atmospheric water, and mineral dust particles from it, which allows them to build organic matter. Air affects plants through its physical properties and chemical composition. The Physical Properties of air include its transparency, density, and purity. Green plants act as the purricators of the atmospheric ocean. Therefore, Earth's plant cover is often metaphorically called the planet's Lungs.

Physical properties of air. With increasing altitude, the thinness and transparency of the air increase. This ensures better penetration of ultraviolet and infrared rays into the plant canopy, which stimulates growth intensity, flower vibrancy, and The Biosynthesis of biologically active medicinal substances in plants.

As a result of weathering, wind and soil erosion, and industrial manufacturing processes, the air becomes polluted with dust particles. Their density in the air causes haze and dust storms. Becoming covered in dust impairs the Photosynthesis process in plants and reduces their productivity.

The chemical composition of air is diverse: it contains 78.08% nitrogen, 20.95% oxygen, 0.93% argon, 0.10% hydrogen, and 0.03% carbon dioxide. There are even smaller amounts of helium, ozone, neon, krypton, xenon, and impurities such as sulfur dioxide, ammonium, flue gases, and radioactive dust. Due to continuous mixing, the Chemical composition of the air remains homogeneous, stable, and dense in the lower layers of the atmosphere.

Atmospheric nitrogen is of exceptional importance to plant life, as it is a component of Proteins. The source of nitrogen Nutrition is molecular nitrogen from the air, which plants assimilate with the help of nitrogen-fixing symbiotic Bacteria. As a result of this Symbiosis, nodules populated by bacteria appear on the roots. With their participation, atmospheric atomic nitrogen is fixed and accumulated. In this way, for example, lupine plants in the arable soil layer accumulate 150–200 kg/ha of nitrogen per growing season in the form of nitrates and nitrites suitable for plant nutrition. Nodules have also been found on the roots of alder, ginkgo, conifers, casuarinas, the coffee tree, and many other plants.

Carbon dioxide makes up 0.03% of the atmosphere, but its importance for plants is exceptionally high, as its presence is a prerequisite for photosynthesis. During photosynthesis, driven by solar energy, CO₂ and water are broken down, and the released carbon and hydrogen are used to synthesize organic matter. During the growing season, plants worldwide synthesize up to 490 billion tons of organic matter.

Atmospheric oxygen. According to V.I. Vernadsky, the content of free oxygen in the atmosphere ranges from 1.2 x 10⁵ to 2.1 x 10¹⁵ tons, while plants enrich the atmosphere by 1.2 x 10¹¹ tons annually. Thanks to this stable content, plants do not experience oxygen deficiency.

Industrial and domestic oxygen consumption leads to a decrease in its atmospheric concentration, threatening The Development of both PLANTS AND HUMANITY.

Wind and its ecological effect on plants. Wind plays a major ecological role in plant life. Its effects on plants can be direct or indirect. The Direct impact of wind manifests as mechanical action — deformation of tree crowns, branch breakage, leaf tearing, premature dropping of flowers, fruits, and seeds, as well as windbreak and windthrow. Strong winds cause trees to sway, which impairs the uptake of water and mineral salts, as well as the outflow of plastic substances.

The direct action of wind noticeably affects the anatomical and Morphological Characteristics of plants. In open areas exposed to unidirectional air masses, woody plants acquire a flag-like shape (Fig. 106), plants become stunted, and tree trunks develop eccentric wood rings. In deserts and mountains, under the constant influence of wind, shrub and subshrub species take on a streamlined cushion-like form (Fig. 107).

Wind facilitates the dispersal of pollen, spores, fruits, and seeds, which have evolved various adaptations for this purpose.

One manifestation of the ecological action of wind is Transpiration — the physiological process of water evaporation by living plants. Wind dries out the air and hinders plant development.

Wind is a primary cause of erosion in poorly anchored soils. Its impact is significantly moderated by vegetation. While wind sweeps across open terrain without obstruction, its effect changes markedly in areas with well-developed plant cover. Upon encountering brushwood or forest plantations, the wind changes its direction and force. Humans utilize vegetation in the fight against dust storms and dry winds by creating protective forest shelterbelts.

Light as an ecological factor. Light is of paramount importance in nature and for plant life. It drives photosynthesis, transpiration, the movement of solutions within the plant, and essential biochemical transformations. Solar energy is consumed in morphogenetic processes—seed germination, the formation and development of tillering nodes, seedling growth, internode elongation, flower and inflorescence development, and fruit ripening. All these processes require a specific amount and duration of light.

Through the utilization of solar energy, a vast amount of organic matter is synthesized, of which 2,320 billion t is produced in oceans, seas, and water bodies. On land, forest vegetation annually synthesizes 191 billion t, steppe vegetation 20 billion t, and desert vegetation 4 billion t. A large mass of organic matter is also synthesized by cultivated crops and widely utilized by humans.

Based on their light response, plants are divided into three ecological groups.

1. Light-loving (heliophilous) plants are those that require a large amount of light for optimal development, meaning they have high demands regarding both light intensity and duration. Light significantly affects plant Morphology AND ANATOMY. Therefore, Two Types of light ecologisms are distinguished.

Morphological light ecologism. It manifests as slowed SHOOT growth, weakened activity of renewal buds, dwarfism, and shoot compactness. Plants feature small, linear-lanceolate, narrowed, folded, or clustered leaves.

Anatomical light ecologism. Under the influence of light, leaves become hard, leathery, and intensely colored; their Cells are large, and Chloroplasts are small and numerous. Leaves positioned at an angle have an isolateral Structure, whereas horizontal ones have a mesophyll differentiated into spongy and palisade parenchyma (Fig. 112).

The upper epidermis features a thick cuticle, and its cells lack chloroplasts. The number of Stomata in the lower epidermis is greater than in the upper one. Plants are rigid due to the lignification of certain morphological elements and parts, which frequently form thorns or spines (acacia, hawthorn).

2. Shade-loving (sciophilous) plants are those that require shade for their development. They are typical of forest and shrub coenoses.

Morphological shade ecologism. Shade-loving plants mostly grow in height, with their vertical growth exceeding diameter growth. Shading promotes the drying, dying off, and shedding of branches, and has a detrimental effect on the formation and development of buds and shoots. Crowns are poorly developed and positioned high up. Leaves are large, wide, thin, and delicate.

Anatomical shade ecologism. Shade leaves have a single-layered epidermis without a cuticle, with stomata present in both the upper and lower epidermis. The leaf mesophyll is not differentiated into palisade and spongy parenchyma (Fig. 108). Parenchyma cells are large, with a negligible number of chloroplasts. The photosensitivity of shade-loving plant leaves is high, ensuring the utilization of the dim light that penetrates beneath tree canopies.

3. Shade-tolerant plants are those that develop best under full light but can tolerate shading without harm. Shade-tolerant plants exhibit more intensive vertical growth than diameter growth, and their crowns are denser and more compact than those of light-loving plants.

It is well known that plant development is influenced not only by the total amount of radiant energy and light intensity but also by the qualitative, spectral composition of radiation. In the north, lighting is weaker, but summer is longer than in the south. Diffuse light, which is richer in long-wave radiation, prevails here.

The duration of illumination throughout the day and night—that is, its periodic supply—is also important for plants. The reaction of plants to The ratio of day and night length is called Photoperiodism. Accordingly, three groups of plants are distinguished:

1. Long-day plants, whose flowering does not occur or is delayed if the day length is equal to or less than 12 hours: common yarrow (Achillea submillefolium L.), red clover (Trifolium pratense L.), winter rye (Secale cereale L.), cultivated oat (Avena sativa L.), and wild chicory (Cichorium intуbus L.).

2. Short-day plants, whose flowering does not occur or is delayed if the day length exceeds 12 hours: buckwheat (Fаgopуrum esculentum L.), common sunflower (Helianthus annuus L.), and garden sage (Salvia officinalis L.).

3. Day-neutral plants: common dandelion (Taraxacum officinale Webb. ex Wigg.), common daisy (Bellis perennis L.), and others.

Heat as an environmental factor. Heat is a prerequisite for plant existence. It drives plant metabolism, morphogenesis, growth, and development. The uptake of water and mineral nutrients occurs within specific soil Temperature ranges. Enzymatic activity, photosynthesis, Respiration, and the germination of seeds and spores proceed only under a specific temperature regime.

For crop cultivation, the thermal regime is of great significance rather than the absolute amount of heat and its spatial distribution. Plant productivity depends on the distribution of heat throughout the growing season. The intensity of photosynthesis increases simultaneously with rising temperature, reaching its maximum values, for example, at 20 °С in tomatoes and sugar beets, and at 30 °С in field beans.

The primary source of heat on the planet is solar radiation energy. Of exceptional importance for plant development is heat exchange between the upper soil layers, which serve as the sphere of ROOT nutrition, and the above-ground layers, which house the Organs of cosmic (aerial) nutrition. Root nutrition in many cases depends on soil temperature. At low temperatures, plants assimilate nitrogen fertilizers poorly due to the disruption of root synthetic activity. Plants in bogs that are rich in nitrogen yet wet and cold suffer from its unavailability for consumption.

Steppe and psammophytic plants possess a thick cuticle, a dense covering of hairs, thick layers of cork and bark, and shoots modified into thorns.

To complete individual phases of their developmental cycle, plants require varying amounts and durations of heat. The germination of wheat, clover, oats, and winter cress occurs at 0—2 °С, rye at 1—2, lupine at 4—5, beans at 5—6, soybean at 10, sorghum above 10, and rice at 10—12 °С. Cucumber seeds germinate at 10 °С, and date palm seeds at 30 °С. Seedlings of wheat, barley, and rapeseed emerge at 3—5 °С, and beans at 6—10 °С. Optimal temperatures for the growth of vegetative organs are 26.6 °С for field beans, and 26 °С by day and 17—18 °С at night for tomatoes. Plants that develop across wide temperature amplitudes are called eurythermal, whereas those with narrow amplitudes are called stenothermal.

Temperatures that ensure the timely and normal progression of PHYSIOLOGICAL AND BIOCHEMICAL processes in plants throughout ontogenesis are called optimal. At these temperatures, nitrogen and ash elements are assimilated more fully, and plants achieve high productivity.

Extreme low temperatures at which plant viability and the progression of all physiological processes are maintained are called minimum temperatures. Some strains of smut Fungi can withstand temperatures of —110 °С, spores of *Penicillium* and *Aspergillus* retain viability at —200 °С, and shoots of black currant remain alive even at —253 °С when cooled gradually.

Extreme high temperatures at which physiological processes cease or are heavily suppressed and the plant loses viability are the maximum temperatures.

Water as an environmental factor. Water is a component of Cytoplasm, and its content reaches up to 80–90%. Water is essential for enzymatic activity, the absorption and Transport of mineral and plastic substances, photosynthesis, respiration, and transpiration. Precipitation is of great importance for plant development. Wild and cultivated plants make fuller use of precipitation from steady, prolonged rains rather than downpours. During prolonged fine-droplet rains, up to 90% of moisture accumulates in the soil and is gradually utilized by plants.

Snow and dew, which forms on cool nights due to water vapor Condensation, are of significant ecological importance. Dew is partially absorbed by the above-ground organs of plants and partially enters the soil, where it accounts for 10—30 mm of the annual precipitation.

According to their water requirements, plants are divided into four ecological types (ecologisms).

Hydrophytes are plants that are completely or largely submerged in water. They fall into two main groups: rooted submerged plants anchored to the bottom soil (such as water soldier and vallisneria), and free-floating plants suspended in the water Column (such as bladderwort and planktonic Algae). These plants have high water requirements and inhabit marine environments, lakes, and rivers.

Hydrophytes typically exhibit heterophylly (the presence of different leaf forms), which is an adaptation to living in two environments: aerial leaves are entire, whereas submerged leaves are finely dissected (as seen in floating fern, water crowfoot, and water dropwort).

Their defining features include a poorly developed root system and mechanical tissue, highly developed aerenchyma in the stems, rhizomes, and roots, as well as an extensive network of intercellular spaces and air passages (Fig. 110), which account for 60–70% of the plant's total volume. Floating leaves feature a mesophyll differentiated into palisade and spongy parenchyma, while the epidermis possesses a cuticle and numerous stomata (400–600 per 1 mm²).

Hygrophytes are plants of permanently or temporarily waterlogged habitats, with the greater part of their body exposed to the air. They are typical of bogs, wetlands, high-altitude zones, as well as lake and river shores—meaning these plants always have an abundant supply of moisture and do not develop adaptations for water storage.

Mesophytes are plants that require moderate moisture levels for their development to support all physiological metabolic processes. They feature well-developed root systems, broad leaves, and differentiated mechanical tissue. In dicotyledons, the leaf mesophyll is divided into palisade and spongy parenchyma.

Many agricultural crops belong to the mesophyte group (cabbage, carrots, tomatoes, beets, potatoes, plums, raspberries, etc.). They exhibit varying degrees of drought tolerance.

A special category among mesophytes consists of ephemerals and ephemeroids.

Ephemerals are annual plants that complete their vegetation phase in early spring, taking advantage of warmth, moisture, and the absence of shading from other plants (e.g., early whitlow-grass, desert alyssum, clasping pepperweed). Their life cycle lasts only 1–2 months. Depending on their developmental period, they are divided into spring and autumn ephemerals, being particularly characteristic of the steppe zone.

Ephemeroids are perennial herbaceous plants with a short vegetative period followed by a long dormant phase. Many of them emerge before the leaves of trees and shrubs unfold, successfully completing their developmental cycle in a short time (e.g., species of snowdrop, corydalis, anemone, bulbous bluegrass). During the dry period, the above-ground organs of ephemeroids die off, while their underground organs—bulbs, tubers, and rhizomes—survive, providing the energy reserves for the next cycle of growth.

Xerophytes are plants that thrive in conditions of high atmospheric and soil drought. They have low water requirements. In the steppe and forest-steppe zones of Ukraine, they make up a significant percentage of the floral COMPOSITION OF THE plant cover. This is facilitated by specific Anatomical and morphological adaptations, such as ericoid leaf structure (small leaf size, rolled margins, sunken and concealed stomata); leafless shoots or reduced leaves; dense felt-like pubescence (e.g., woolly mullein); the persistence of old, dead leaf remains (species of the genus Stipa, common beardgrass); leathery leaves with a cuticle gloss that scatters and reflects light, reducing radiation and overheating; excessive development of mechanical tissue; and the modification of shoots and leaves into thorns, spines, or scales (Fig. 106).

Succulents are plants equipped with specialized water-storing tissue that allows them to accumulate water during rainy periods and expend it sparingly through droughts. Based on the site of water storage, succulents are classified as stem, leaf, or root succulents.

Stem succulents (Fig. 113) feature a highly developed water-storing parenchyma within their stems (such as cacti, stapelias, and bottle trees); leaf succulents store water in their leaves (aloe, agave, bryophyllum); and root succulents store it in their roots.

Figure 113. Succulents

A distinct ecological group is formed by psychrophytes. These are plants of cold and damp habitats that develop under conditions of physiological drought caused by restricted water uptake due to low temperatures. Examples include plants of bogs and mountain slopes (purple moor-grass, marsh Labrador tea, common heather, grey Hair-grass).

Plants growing under conditions of physical drought are called cryophytes. These inhabit cold, humid environments where water crystallizes into ice or frost due to low temperatures, rendering it physically unavailable to plants (such as conifers and ericaceous plants).

10.1.2. Edaphic Conditions and Their Impact on Plant Organisms

Edaphic factors are of exceptional importance to plants because the soil acts either as the medium from which they absorb water and nutrients, or as the habitat for soil fungi, algae, invertebrates, and other organisms. Edaphic conditions are determined by the PHYSICOCHEMICAL PROPERTIES OF the soil and the organisms living within it. There are three primary types of edaphic influence on plants: 1) physical factors, 2) chemical composition of the soil, and 3) biotic factors.

Ecological Significance of the physical Properties of the soil environment. The soil cover of Ukraine is diverse and has formed with the active participation of vegetation. The mineralization of steppe plant residues resulted in The formation of chernozems (black earths), which feature a deep humus horizon (70–200 cm), a high content of nitrogen (3–8%, locally up to 12%) and carbonates (5–6%) in the arable layer, ensuring their high fertility and agricultural value.

In Polissia, characterized by a sparse and less productive plant cover, acidic, low-humus sod-podzolic soils have developed. Consequently, their impact on plant development and vegetation cover is less than optimal.

The modern plant cover of various regions is largely determined by the physical properties of the soil.

Ecological significance of soil structure, aeration, and water regime. In Polissia, under conditions of adequate or excessive moisture, poorly structured peat soils are consistently supplied with water. Water stagnation impairs the development of mesophytic vegetation and promotes swamping of the area.

In the Forest-Steppe zone, where moisture is variable, a downward flow of water occurs during spring and autumn, which is replaced by an upward flow in summer—conditions that favor the optimal development of agricultural crops and high yields.

In the Steppe zone, where precipitation is less than evaporation, water moves upward through well-structured soil. This is often accompanied by the leaching and upward transport of calcium, sodium salts, chlorine, and sulfur, leading to carbonate and sulfate soil salinization and hindered plant growth.

Soil capillarity is of vital ecological significance because it drives the upward Movement of water from lower horizons to upper ones. Drying surface layers of structured chernozems and meadow soils are supplied with water more effectively and thoroughly than unstructured sandy soils (due to inadequate capillary water transport from deeper layers). As a result, steppe vegetation on chernozems thrives and is considerably more abundant compared to sparse, low-productivity psammophytic vegetation.

Ecological impact of the chemical composition of the soil environment on plant organisms and vegetation. Plant development is largely influenced by the chemical composition of the soil. Plants acquire water, nitrogen, and ash elements from the soil, and once they die off, mineralized elements are returned to the soil.

Plants react sensitively to the presence of nitrogen, micro- and Macronutrients in the soil, which is why they serve as indicators of acidity, salinity, and the content of nitrogen, calcium, magnesium, and other elements.

Soil acidity. Soil acidity plays a vital ecological role in plant development, determined by the concentration of free exchangeable hydrogen ions in the soil solution. Soil saturation with hydrogen ions occurs during redox reactions involving carbonic and organic acids. Total, exchangeable, and actual acidity are distinguished. Actual acidity is defined as the pH value, which represents the negative logarithm of the hydrogen ion activity in an aqueous solution. Conventionally, three acidity categories are identified: acidic (pH 2.4–6.7), neutral (pH 6.7–7.0), and alkaline (pH 7–14).

Regarding PLANT RESPONSE TO soil acidity, four groups are distinguished:

I. Acidophilic, or oxyphilic, plants develop at pH 2.4–6.7. Typical representatives include: brown bog-moss (Sphagnum), cotton-grass, rye, colonial bentgrass, bracken, matgrass, sheep's fescue, flax, potato, wheat, wild strawberry, and ox-eye daisy.

II. Neutrophilic plants grow at pH 6.7–7.0 (common bean, pea, sunflower, alfalfa, flat-pea).

III. Basiphilic plants grow at pH above 7.0 (hemp, sickle medick, Ukrainian trefoil, wild rye, creeping couch grass, alkali grass, petunia, gallant soldier, saltwort, rough frankenia, white zygophyllum, saltbush).

IV. Indifferent plants are insensitive to the acidity of the soil solution and grow in both acidic and alkaline soils (lily of the valley, oak, pine, dyers' chamomile).

ECOLOGICAL PLANT GROUPS are characterized not by the extreme limits of their habitat conditions, but by the optimal values of actual soil solution acidity that ensure the normal progression of all physiological processes. High acidity and alkalinity inhibit Plant GROWTH AND DEVELOPMENT.

Ecological significance of the total nutrient content in the soil. Plant development relies on the presence of nitrogen, potassium, phosphorus, calcium, magnesium, and other macro- and micronutrients in the soil, without which plant physiological processes cannot proceed. The total content of ash elements determines the level of plant nutrition. Based on their requirements for the total nutrient content in the soil, plants are divided into three ecological groups: eutrophic, mesotrophic, and oligotrophic.

I. Eutrophic plants require rich mineral nutrition. They grow intensively and achieve high productivity. Indicators of soil eutrophy include: rice, wheat, sunflower, cucumber, beets, raspberry, nettle, alder, oak, ash, linden, celandine, European wild ginger, pumpkin, etc.

II. Mesotrophs are plants with moderate water and mineral nutrition requirements. The optimal progression of all life processes in such plants is ensured under conditions of average moisture and soil fertility levels. This ecological group includes: carrot, cabbage, plum, cherry, apple, oat, potato, millet, corn, etc.

III. Oligotrophic plants grow on infertile soils. They indicate soils with a minimal content of nitrogen and ash elements. Indicators of such soils include sphagnum mosses of raised bogs, plants of sandy areas, and high-altitude habitats, which obtain nitrogen and ash elements from atmospheric precipitation.

Ecological significance of calcium. Calcium is an essential element of mineral nutrition that ensures the normal course of metabolic processes; it neutralizes the toxic properties of oxalic acid and hydrogen ions, lessens soil solution acidity, and thereby improves Plant Growth and development.

According to their calcium requirements, the following ecological groups of plants are distinguished:

I. Calciphiles are plants that demand the presence of calcium. They grow in soils with a calcium content of at least 3%. These include: sickle medick, chalk pine, European beech, ash, lady's slipper orchid, Siberian larch. Calciphiles are characterized by low stature, xeromorphic structure, dense venation, development of mechanical tissue, and leaf reduction.

II. Calciphobes are plants that avoid rich carbonate nutrition. They react negatively to the presence of calcium salts in the soil and develop only in soils where mere traces of it are found. Typical calciphobes include various species of genera such as sphagnum, heather, matgrass, tufted hairgrass, chestnut, rosebay willowherb, sorrel, lupine, etc.

III. Indifferent plants are those that are insensitive to the presence and amount of calcium in the soil solution. They develop equally well in soils with traces of calcium and with contents of 20% or more. Occasionally, they settle on limestone (yellow sweet clover, chalk chamomile, chalk hyssop).

Ecological significance of nitrogen. Nitrogen is of great importance for plant development because it is a component of proteins, which are the carriers of living Cell structures. Based on their nitrogen nutrition requirements, plants are divided into two groups.

I. Nitrophiles are plants that require rich nitrate nutrition. They inhabit fertile soils near settlements, animal waste sites, and the humus of broad-leaved forests. Typical nitrophiles include various species of genera such as tobacco, raspberry, saltbush, hop, elder, pigweed, henbane.

II. Nitrophobes are plants that avoid rich nitrogen nutrition. They have low demands for nitrogen and ammonium compounds and develop where the concentration of such compounds is minimal. Indicators of these conditions include various species of lupine, tufted hairgrass, rosebay willowherb, horsetail, saltwort (Anabasis), wood small-reed, devil's bit scabious, tormentil, etc.

Halophytes are plants that grow under conditions of excessive soil salinity. They are characteristic of the Steppe and Forest-Steppe zones of Ukraine, as well as arid coastal regions. Moisture deficit is offset by the influx of groundwater, which carries readily soluble salts into the surface horizons or onto the surface via upward capillary currents. A specific halophytic vegetation develops on saline soils. Halophytes are low-growing, spreading across the soil surface, leafless or possessing reduced short thick leaves with highly developed water- and salt-storing parenchyma and a low chlorophyll content. The epidermis is thin, and mechanical tissue is sparse.

Soil salinity varies greatly and is caused by the accumulation of water-soluble salts such as NaCl, CaCl₂, MgCl₂, NaHCO₃, Na2SO₄, CaSO₄, MgSO₄, and others in the soil solution. As a result, chloride, carbonate, sulfate, and nitrate types of salinity occur. Each of these salinity types features a specific flora and vegetation, which simultaneously hold significant indicator value.

Psammophytes are plants of sandy habitats. They form a distinct ecological group of plants. Psammophytes exhibit a high Osmotic Pressure of cell sap (30–70 atm), which enables them to absorb water from deep horizons and survive under extreme conditions.

Helophytes are plants of bogs and waterlogged or excessively moist soils. Due to high moisture capacity and oxygen deficiency, dead plant remains do not decompose fully and are preserved in the soil as a natural biogenic body—peat.

A specific ecological group is formed by Insectivorous Plants (round-leaved, English, and lesser sundews). The latter two are rare in the bogs of Ukraine. Aldrovanda and butterwort also occur rarely. Their distinguishing feature is digestive glands, the secretion of which glistens in the sun and attracts insects; upon touching a gland, an insect sticks to it and is digested by Enzymes released by the trapping apparatus. In this way, plants obtain nitrogen compounds essential for their development.

Ecological Impact of Soil Biotic Factors. Plant development depends heavily on the biotic conditions of the soil environment created by animal and plant organisms. Microorganisms, nematodes, rotifers, worms, burrowers, and others thrive in aerated, warm, fertile, and cultivated soils. There are 10–100 million microorganisms, fungi, and algae per 1g of chernozem. These organisms are especially abundant in the plant rhizosphere. Each crop has its own specific microflora, unique in its quantitative and qualitative composition.

Soil fertility enhancement and the improvement of ecological conditions for plant development occur with the participation of not only microflora but also algoflora. According to E. A. Shtina, the rhizosphere of clover contains 5,400 diatoms, 90,000 green algae, and 11,000 blue-green algae per 1 g of soil. It has been calculated that the algae biomass in meadow soils is 300 kg/ha, and in forests — 20 kg/ha. The animal population of the soil is of significant ecological importance for plant development. According to E. Mishustin, 1 dm3 of soil contains 30,000 nematodes, 2,000 mites, 1,000 springtails, 500 rotifers and tardigrades, 100 crustaceans, spiders, and insects, 50 enchytraeids, and 2 earthworms.

The ecological role of fungi lies in the breakdown and mineralization of plant residues, releasing nutrients necessary for flowering plants. Under optimal conditions of moisture, warmth, and aeration, higher and flowering plants enter into symbiosis with fungi and, with their help, absorb nutrients and biocoenosis elements. The rate of nutrient uptake depends on The activity of the biological soil population, while the quantity depends on the productivity of plant communities.

Earthworms play a vital role in the soil by improving soil structure, promoting the capillary rise of moisture, breaking down soil particles as they pass through the digestive tract, and enriching these particles with calcium.

Thus, edaphic factors are highly diverse in their composition and impact on the development of plants and plant communities, which is largely determined by the physical properties, chemical composition, and biological population of the soil.

10.1.3. Orographic Conditions as an Ecological Factor

In any locality, The Effect of the aforementioned ecological factors is amplified by geographical and orographic modifications. The entire diversity of orographic influences can be reduced to the action of several factors.

The local relief influences vegetation indirectly. Its secondary effect determines the GENERAL PATTERNS OF the vertical distribution of vegetation and the specific species composition of phytocoenoses. Vegetation changes under the influence of relief. In the Forest-Steppe zone with a rugged relief, its soil-protecting role is depleted and weakened.

In flat-land (plakor) conditions of the Steppe, humus- and ash-rich chernozems develop, but depending on relief conditions, they are heated and moistened differently on slopes of various orientations: southern slopes are warmer and drier than northern ones. Therefore, the former are covered by xerophilous natural vegetation, while the latter are covered by mesophilous vegetation.

Altitude above sea level significantly affects the growth and development of plants and plant cover, especially in the mountain systems of the Carpathians and Crimea. The elevation factor is decisive and determines the variation of climatic, edaphic, and biotic factors.

With increasing altitude, air temperature drops as a result of increased heat loss from the soil surface. For every 100 m increase in altitude above sea level, the mean annual air temperature decreases by 0.5°C. This value is called the vertical temperature gradient.

Due to the lower mean annual air temperature in mountainous areas, plants bloom 2–4 days later, and their fruits and seeds ripen 5–6 days earlier. With altitude, the saturation of the air with water vapor, dust, and gas impurities decreases, making the air thinner and cleaner. As a result, illumination intensity and The amount of direct light increase, along with the proportion of blue, violet, ultraviolet, and infrared rays. This creates a specific light regime that plays a crucial role in the accumulation of medicinal substances by plants and affects their quality.

10.2. Biotic Factors and Their Impact on Plant Organisms

Relationships develop among the organisms inhabiting the biosphere in which each component affects the others directly or through altering the ecological environment, acting as a leading biotic factor. Therefore, the entire totality of diverse influences that plants, animals, and microorganisms exert on one another is called biotic factors. They are diverse, and depending on the primary biogenic factor, they are distinguished into: zoogenic, phytogenic, and microbogenic, and within these, by The Nature of action — Direct and Indirect, antagonistic and symbiotic relations, mechanical and chemical. Biotic conditions are closely related to THE CONCEPT OF biocenosis.

A biocenosis is a community of living organisms interconnected and interdependent through a shared exchange of matter and energy. They exist not in isolation, but in combination with one another and in interconnection with the environment..

The assemblage of plants inhabiting a biocenosis constitutes a phytocenosis, animals form a zoocenosis, and microorganisms form a microbocenosis. Relationships that develop within a biocenosis are called biotic, within a phytocenosis — phytocenotic, within a zoocenosis — zoocenotic, and within a microbocenosis — microbocenotic. Relationships in forests, steppes, and bogs are particularly complex and diverse due to the large number of biocenosis components and the heterogeneous influence of abiotic factors.

10.2.1. Phytogenic Factors and Their Action

Plant Parasitism. One of the categories of relationships in biocenoses is parasitism. This is a form of coexistence between different plant species where one lives at the expense of the other due to the loss of its ability to synthesize organic substances. Parasitism can be permanent or temporary. Among parasites are bacteria, fungi, and flowering plants.

Parasitic bacteria develop on cultivated and wild plant species. More than 300 species of bacteria are known to be causative agents of bacterioses. Dangerous to agricultural crops is Pseudomonas holci, which causes bacteriosis in sorghum, millet, wheat, and corn. Bacteriosis weakens plant vitality and reduces the productivity of the agrophytocenosis.

The ecological role of parasitic fungi manifests in the depletion or death of cultivated plants due to their absorption of nutrients or destruction of the crop.

In nature, plant semiparasitism is quite widespread. Semiparasites are plants that settle on others, drawing partial nourishment from them while independently producing a portion of the nutrients necessary for their development (white mistletoe, eyebright, cow-wheat, yellow rattle).

One of the important forms of biotic relationships is symbiosis, which represents a form of coexistence between different organisms from which both components derive mutual benefit. An example of symbiosis is the coexistence of legumes with nitrogen-fixing bacteria residing on their roots (Fig. 113). Nodule bacteria fix free atmospheric nitrogen into salts of nitric and nitrous acid, which are accessible for consumption by higher plants. Upon their death, the soil is enriched with nitrogen. Therefore, legumes are a key element in crop rotation.

There are many saprophytic plants. Their impact on the environment is also based on nutrition, but unlike parasitic plants, Saprophytes obtain nutrients not from living plants (or animals), but from their dead remains. Saprophytes affect other plants by mineralizing plant residues and enriching phytocenoses with nitrogen and ash elements. Over 70% of the plants making up phytocenoses utilize nutrients extracted by saprophytic fungi from fallen leaves, branches, trunks, and fruits. Thus, saprophytes significantly influence the development of natural and cultivated cenoses.

In addition to the direct impact of biotic factors, plants often experience secondary, or indirect, influences that are more complex in nature and occur through various pathways,

Different plant species exert a noticeable influence on one another through chemical action, releasing substances that stimulate or inhibit growth and development—in other words, allelopathically. Specifically, plants release volatile or droplet-liquid substances that produce this effect. For instance, in vetch-oat mixtures, root exudates from oats stimulate seed germination and vetch development, just as grasses play a stimulating role in fescue-clover mixtures.

An inhibitory role is played by colins, the amounts of which vary among different plant species; wheat releases them in larger quantities than corn and potatoes do. They "cleanse" the soil of weeds, even such stubborn ones as wild oat and field mustard.

10.2.2. The Impact of Animals on Plant Organisms and Vegetation

Every phytocenosis is inhabited by animal organisms to a certain degree. Herbivores (horses, elk, deer, zebras, gazelles, elephants, etc.) have adapted so closely to coexisting with plants that they can no longer survive without them. As a result of the grazing of the herbage, the species composition becomes poorer, valuable forage species disappear, weeds emerge, the proportion of sod-forming species increases, and land productivity declines.

Great damage is caused to agriculture by voles (mice), which gnaw at the roots of wheat, rye, and barley, and consume fruits and seeds.

Plant development is significantly influenced by birds—on the one hand, they consume large quantities of forest plant fruits and seeds (jays, crossbills, capercaillies, nutcrackers), which would otherwise be sufficient to afforest many hundreds of hectares; on the other hand, they destroy numerous harmful insects and perform a sanitary role in forests and gardens (cuckoos, hoopoes, swallows, kestrels, buzzards, woodpeckers, etc.). Certain losses are inflicted on farms by flocks of sparrows that feed on a portion of the grain and sunflower harvest. However, the regrettable experience of China, where an attempt was once made to eradicate these birds, proved that they ultimately do more good than harm to agriculture.

10.2.3. Anthropogenic Factors

This is one of the most powerful factors. Human activity, armed with various technological means, has an especially massive impact on nature. For instance, as a result of the mass felling of numerous forest stands, the ecological balance of ecosystems is disrupted, and the floristic composition of the forest changes—hygrophytes disappear from the herb layer, and the proportion of species with a xeromorphic structure increases.

Burning vegetation has been practiced since ancient times. People burn herbage to improve pasture quality, get rid of thorny shrubs, halt the encroachment of forests, and destroy harmful insects, snakes, and the like. In the steppes of Ukraine, the burning of stubble and the destruction of post-harvest cereal pests are still practiced today.

The grazing of herbivores has a substantial impact on plant development. Animals trample plants, destroy the turf, expose the soil surface, and valuable medicinal plants disappear from the herb layer.

Anthropogenic impact manifests itself through the drainage of swamps and marshy lands, which lowers the groundwater table, alters air and thermal regimes, and modifies plant cover. The plant cover undergoes noticeable changes under the influence of mineral fertilizers and plant protection products against pests and pathogens, as well as radioactive and chemical pollution, which significantly affects the quality of medicinal raw Materials.

10.2.4. Historical Factors

The Evolution of the plant world and the Current state of flora across various climatic zones are largely associated with historical factors— geogenic, climatogenic, and biogenic.

According to scientists, during the Devonian and Carboniferous periods, modern continents formed a single or poorly fragmented landmass on our planet. This is supported by the humid, warm tropical climate and uniform tropical vegetation that at the time occupied vast areas of the tropics and adjacent territories in both hemispheres.

The modern diversity and Geographical Distribution of floras and vegetation are driven by climatogenic changes that took place on Earth's surface in the past.

The Emergence of angiosperms is closely linked to the biogenic influence of historical factors. Plant evolution was determined by their biological characteristics: the interaction between plants and animals through the development of various adaptations for pollination and seed dispersal, resulting in a more viable generation that ensured the flourishing of the species and its dissemination across the globe. The influence of historical factors explains the origin and distribution of many species in the contemporary flora of continents and regions.

10.3. PLANT LIFE FORMS

In the course of evolution, diverse plant forms emerged, reflecting their adaptation to variable terrestrial living conditions. They acquired morphological and anatomical distinctions and Specificity in response to environmental factors. The FEATURES OF PLANT morphological structure that reflect their adaptations to environmental conditions are called plant life forms or biomorphs. Plant life forms developed over a long period under the influence of physical and geographical factors, meaning they have their own history.

German naturalists A. Humboldt and A. Grisebach were the first to propose distinguishing plant life forms. They established the fundamental approaches to systematizing these forms. Their system is based on external morphological and structural traits, which is why it is referred to as physiognomic.

Later, classifications were proposed by J. Warming, C. Raunkiaer, V. Alekhin, O. Drude, I. Schmithüsen, I. Serebryakov, and others. These systems took into account not just one, but several traits and properties—ecological, morphological, biological, ontogenetic, etc. However, none of these systems fully satisfies the modern demands of plant geography.

The most popular and widely recognized Classification of plant life forms is C. Raunkiaer's system, in which plant life forms are distinguished by THE POSITION OF renewal buds relative to the soil surface and by the physiological response of plants to seasonal environmental changes. According to this classification, plant life forms are divided into the following groups—phanerophytes, chamaephytes, hemicryptophytes, cryptophytes, and therophytes (Fig. 114).

These life forms are further divided into categories depending on the placement and protection of renewal buds and other features, resulting in a well-structured system of life forms created by C. Raunkiaer that encompasses plants of both tropical and extra-tropical regions.

Phanerophytes are a life form of plants in which the renewal buds are located high above the soil surface (at least 25 cm) and are protected in various ways during the winter. These include trees, shrubs, lianas, and epiphytes.

Trees are perennial plants with a woody trunk that bears renewal buds and persists throughout the entire life of the plant.

Shrubs are a plant life form in which branching begins near the soil surface, and among the numerous above-ground shoots, it is difficult to single out a main trunk by either height or thickness. Shrubs do not form a distinct crown. Their renewal buds are located relatively close to the soil surface.

Shrubs can live up to 100 years, with each individual shoot or ramet completing its life cycle within 2–40 years. Thanks to first-order renewal buds, new above-ground shoots emerge, thereby extending the overall lifespan of the shrub. Shrub height typically ranges from 0.6 м to 6.0 м, which does not entirely fit C. Raunkiaer's classification system.

Lianas are plants that require physical support for their development, characterized by long, flexible stems. Upon finding a suitable support, a liana climbs into the tree canopy, occasionally spreading from one tree to another and sometimes suppressing the growth of its host plant. While scarce in temperate and moderately cold zones, lianas are abundant in tropical and subtropical rainforests. In our region, notable woody lianas include Clematis vitalba, cultivated grapevine, hardy kiwi, tara vine, purple kiwi, arguta vine, and Chinese magnolia vine, all of which hold nutritional and medicinal value.

Epiphytes are plants that grow on other plant species, using them merely as a physical substrate rather than a source of nutrients. Epiphytes are characteristic of tropical rainforests, where they find optimal conditions for growth—sufficient warmth, humidity, and distinct lighting—allowing them to develop a high degree of diversity. In temperate and moderately cold zones, epiphytes are mainly represented by mosses and Lichens, while ferns and certain flowering plants occur rarely, restricted to areas with a well-developed layer of fine soil.

Chamaephytes are a plant life form featuring perennial shoots that do not die back in winter, with dormant renewal buds located near the soil surface or elevated up to 25–30 см. These buds are protected from low temperatures by protective scales, litter, or snow cover. Chamaephytes comprise small shrubs and subshrubs, such as bilberry, lingonberry, heather, western blackberry, cloudberry, marsh Labrador tea, and bog bilberry, the fruits of which are used in medicine and dietary nutrition.

Hemicryptophytes are plant life forms comprising perennial herbaceous and, rarely, woody plants whose renewal buds lie at the soil surface, protected by dead plant debris or a layer of soil. They are particularly characteristic of open habitats, meadows, forest edges, savannas, prairies, and rock outcrops. This group includes grasses and sedges that form dense turf; they often produce shoots with buds sheltered by litter and insulated by snow in winter. Hemicryptophytes are highly diverse and encompass various forms: rosette plants (plantain, primrose, dandelion, shepherd's purse), hemimorphic rosette plants (avens, bugle, hawksbeard, peach-leaved bellflower), and non-rosette plants (toadflax, common lambsquarters, amaranth, meadow vetchling). Each of these forms is further divided into finer categories based on traits such as runner formation, sympodial or monopodial branching, and laminar or scale-like leaves.

Cryptophytes are a composite plant life form in which renewal buds develop at a certain depth beneath the soil surface. During extreme conditions, plants in this group periodically shed their above-ground parts (or they die back), while the renewal buds remain safely buried in the soil. These renewal buds are borne on rhizomes, bulbs, root tubers, or corms. Examples include bulbous plants (amaryllis, corydalis, onion), stem-tuber plants (potato, yam), and root-tuber plants (orchids, dahlia).

Therophytes are a plant life form whose entire life cycle is completed within a single year, without the formation of persistent renewal buds. They are typical of regions with unstable moisture regimes or arid climates—such as steppes, deserts, and semi-deserts—as well as open habitats in other zones. Therophytes include annuals that flourish abundantly after rainy periods, revitalizing deserts, semi-deserts, and steppes. This group also includes stem succulents, parasitic, hemiparasitic, twining, and other specialized plant forms.

The plant life forms examined, along with their variations in genetic origin and eco-physiological properties, correspond most comprehensively to the physiographic conditions of habitats across all botanical-geographical zones.