BOTANY WITH BASICS OF HYDROBOTANY - 2010
11. BASICS OF PLANT HYDROECOLOGY AND PHYTOCENOLOGY
Studies of plants and animals show that under similar environmental conditions, they develop similar adaptations regardless of their taxonomic relationship. It is ecological factors that determine The Nature and characteristics of these adaptations in organisms.
The Diversity of ecological conditions and, consequently, the variety of organismal adaptations have become an objective prerequisite for creating numerous ecological classifications and identifying multiple ecological groups of organisms. Among the wide variety of environmental factors, it is quite difficult to single out the most important ones for Classification. Furthermore, relying on a single factor makes it impossible to capture all aspects of how organisms adapt to their environment.
An ecological group is a collection of organisms of different species, regardless of their taxonomic affiliation, characterized by similar adaptive features to a specific environmental factor. As a rule, an ecological group is identified based on how different organisms relate to a single factor; the ADAPTATION OF ORGANISMS to a combination of various environmental factors is expressed in their life form or ecomorph.
Ecological groups of plants can be classified based on their relationship to various environmental factors.
11.1. Classification of Environmental Factors
Broadly speaking, the environment is the sum of all physical bodies, phenomena, and energy that affect a living Organism. These elements exert their influence in different ways. Some are virtually irrelevant to the plant organism (for example, inert gases in the air). Others have a significant impact on plants; these are ecological factors.
According to traditional (classical) ecological classification, factors that influence The Development of All living organisms, including plants, are divided into abiotic (unrelated to the vital activity of organisms), biotic (resulting from such activity), and anthropogenic (caused by human activity). Some species easily tolerate significant fluctuations in certain environmental factors, while others, conversely, can only exist within narrow ranges of variation. Many factors, especially abiotic ones, are limiting factors, meaning they restrict the existence of aquatic organisms (hydrobionts).
Abiotic factors are divided into several groups:
Climatic: light, Temperature, air (its composition and movement), soil and air humidity, and precipitation.
Edaphic (soil-related) - mechanical and Chemical composition of soils, their physical properties, etc.
Topographic (or orographic) - METABOLISM/18.html">The Influence of relief features on vegetation.
Chemical factors (Water mineralization, etc.)
All these factors of inanimate nature directly or indirectly affect terrestrial plants. Aquatic plants are influenced by a different set of factors characteristic of the aquatic environment.
Biotic factors are the forms of influence that living organisms exert on one another. Every organism constantly experiences the direct or indirect Influence of other living beings, enters into relationships with representatives of its own and other species—plants, animals, microorganisms—depends on them, and in turn, influences them.
Anthropogenic (anthropic) factors are forms of human activity that lead to changes in natural ecosystems as habitats for other species or directly affect their lives.
Throughout the development of human society, hunting first, and later agriculture, industry, and transport, have profoundly altered the planet's nature. Anthropogenic pressure on Earth's biota continues to grow rapidly.
PLANT RESPONSE TO environmental impact. A living organism responds to adverse environmental conditions either through a specific action—avoiding the negative effects (for example, by changing behavior)—or by altering its state and physiological Functions, thereby acquiring tolerance to negative factors. These responses ensure the survival of the species under unfavorable conditions.
Avoiding unfavorable conditions is more characteristic of animals, which move from an adverse environment to a favorable one (Taxes, animal Migrations, etc.). Higher plants can move parts of their body into more favorable conditions through growth responses and slow changes in THE POSITION OF certain Organs (for example, by turning leaves perpendicular to the direction of incident light). Under unfavorable conditions, lower plants (Algae) can form
spores that have a strong wall and are very light, allowing them to be carried by wind and currents.
Thus, the primary "life strategy" of plants is the plasticity of structures and functions, adapting their anatomy and vital processes to the environment.
These changes can be non-heritable—Modification Variability—or heritable, resulting from Changes in the genotype.
Morphological adaptive changes can be observed at various Levels of Organization—from THE CELLULAR LEVEL to that of the whole organism (changes in size, shape, The ratio of different organs, etc.).
PHYSIOLOGICAL AND BIOCHEMICAL plasticity is manifested in changes in chemical composition, as well as the intensity and stability of physiological processes.
Adaptation manifests itself in the dynamic correspondence of the morphophysiological organization and adaptive responses of an animal or plant to the typical and primary environmental conditions in which the organism developed. Adaptive organization ensures not only the survival of the individual but also the successful existence of the species.
The influence of plants on the environment. All plants affect their environment in some way. Small crustose Lichens on rocks secrete organic acids during their life processes, thereby contributing to the biological weathering of inert inorganic matter. A special microclimate is formed under a tree canopy—shade, lower temperature, and a different composition of gases and volatile substances. Large plant communities have an even greater impact on the environment. They not only affect the environment but also other living organisms, while being influenced themselves.
Thus, a distinction is made between two concepts of plant habitat and the complex of factors acting upon it: the ecotope, which is the primary complex of physical and geographical environmental factors; and the biotope, which represents environmental conditions modified by the life activities of living organisms.
For example, dense stands of higher aquatic plants negatively affect the penetration of solar radiation into the water Column. Thus, compared to open water areas, only 40% of solar radiation reaches the water surface in areas with broadleaf cattail (50-60 % projective cover), and only 25% in areas with common reed (90-95 % projective cover). Even less solar energy penetrates into the water column. For instance, at a depth of 0.3 m in stands of floating sweet-grass with 90 % cover, only 15 % of solar energy penetrates, whereas with 60 % cover, 80 % of solar energy reaches this depth.
The absorption of a significant portion of solar radiation in the upper water layers severely restricts the distribution of photosynthetic plants within the water column. Consequently, they can only develop at relatively shallow depths in inland waters, seas, and oceans.
11.2. Ecological Factors and Ecological Groups of Plants
Water as an ecological factor. Living organisms cannot exist without water; it is an integral part of them, accounting for 40 to 90% of plant volume. Water is essential for Photosynthesis, Transpiration, enzymatic activity, the absorption and transport of soil solutions and plastic substances, Respiration, and Fertilization. Water constitutes the major part of a plant Cell. On average, Cytoplasm contains 85—90 % water, and even lipid-rich cellular Organelles such as Chloroplasts and Mitochondria contain at least 50 % water. Water in plant Cells exists in two forms: bound (constitutional) water, which is hydrogen-bonded to macromolecular structures, and free (reserve) water, which is stored in vacuoles. CARBOHYDRATES, various organic acids, etc., are usually dissolved in the reserve water, allowing it to participate in stabilizing intracellular osmotic pressure.
In different PARTS OF THE globe, the ratio between moisture input and its loss is uneven. In polar regions, deserts, the tropics, and near oceans, water evaporation reaches high levels. Regions where evaporation exceeds annual precipitation and plants experience water deficits are called arid, while regions where plants are well-supplied with moisture are called humid.
In relation to water, the following ecological groups of plants (hydromorphs) are distinguished: xerophytes, mesophytes, hygrophytes, hydrophytes, and hydatophytes. Transitional forms may exist between them.
Xerophytes (from Greek xeros — dry) are plants that grow in areas with insufficient moisture and possess adaptations that allow them to obtain water when it is scarce, limit water evaporation, or store it for periods of drought. Xerophytes are better able to regulate their water balance than other plant groups, allowing them to remain active during prolonged droughts. They are divided into two main types: succulents and sclerophytes. Succulents are fleshy plants with highly developed water-storing parenchyma in various organs. Their ROOT system is shallow but widely exten-
-ded. Examples of succulents include cacti, cactiform euphorbias, aloe, agaves, houseleeks, stonecrops, and asparagus. Sclerophytes are dry-looking plants, often with narrow, small leaves covered with hairs or a waxy coating. They have well-developed sclerenchyma, allowing them to lose up to 25% of their water content without wilting and without significant consequences. Examples of sclerophytes include feather grass, narrow-leaved meadow-grass, sheep's fescue, wormwood, and some other plants).
Mesophytes (from Greek mesos — middle) are plants that require moderate soil and air moisture for their development. This is the most numerous ecological group, comprising plants that can tolerate short and mild droughts. These plants grow under conditions of moderate moisture, moderate temperatures, and a fairly good supply of mineral nutrients. They have a well-developed root system and grow rapidly under conditions of sufficient soil fertility. Mesophyte leaf Tissues feature palisade and spongy parenchyma, a well-developed network of Veins, and medium-sized intercellular spaces.
In terms of their ability to regulate water balance, some of these plants resemble hygrophytes, while others are closer to drought-resistant forms. This group includes evergreen trees of the upper canopy of tropical rainforests, deciduous trees of savannas, summer-green deciduous species of temperate forests, understory shrubs, herbaceous plants of broad-leaved forests, plants of floodplain and moderately dry upland meadows, desert ephemerals and ephemeroids, many weeds, and most cultivated plants.
Hygrophytes (from Greek hydros — wet) are plants of wet habitats: swamps, riverbanks, lakeshores, wet meadows, and damp forests. They do not tolerate moisture deficits and are not adapted to water limitation. They are characterized by the development of hydathodes, or water Stomata, which exude liquid water droplets. Their leaves are often thin, with a poorly developed cuticle, and tissue water content reaches up to 80%. The most typical hygrophytes are herbaceous plants and epiphytes of humid tropical forests: epiphytic fern species, swamp palms, papyrus, and other plants, while in our latitudes they include marsh marigold, marsh cinquefoil, swamp sedges, common reed, cattail, and many other plants. Among crop plants, rice belongs to the hygrophytes. Characteristic Features of hygrophytes include large leaves with well-developed intercellular spaces, root systems located in the upper soil horizons, and the development of so-called respiratory roots. The Structure of leaves and stems characteristic of hygrophytes is call-
-ed hygromorphic. This structure, combined with weak stomatal regulation of transpiration, causes hygrophytes to wilt rapidly when air and soil moisture decrease.
There are transitional groups between typical hygro- and mesophytes. These are mainly marsh and meadow grasses and sedges, which are classified as hygromesophytes. Marsh herbaceous plants are also called helophytes (Fig. 11.1).
Fig. 11.1. Ecological groups of aquatic plants
Hydrophytes (from Greek hydro — water) are semi-aquatic plants that are partially submerged in water and grow along shores, in shallow waters, and in marshes. Compared to hydatophytes, they have better-developed vascular and mechanical tissues, a well-defined aerenchyma, and a relatively high rate of transpiration. This group includes plants such as common reed, marsh marigold, common water-plantain, buckbean, and other species.
Hydatophytes (from Greek hydatos — water, moisture + Greek phyton — plant) are plant species that are completely or largely submerged in water. The group of hydatophytes includes plants such as Canadian waterweed, pondweeds, hornwort, water crowfoot, and frogbit. Plants that are completely submerged in water, with only their reproductive organs rising above the surface, are called euhydatophytes (pondweeds, water milfoil, waterweed).
Among hydatophytes, there are plants whose leaves float on the water surface. Some of them float freely On the surface—pleustophytes (common duckweed, great duckweed)—while others are rooted—neustophytes (white water-lily, yellow water-lily).
The aquatic environment has several distinctive features to which plants have developed various adaptations (reduction of stomata, well-developed aerenchyma, absence of a cuticle, etc.). Higher aquatic plants are secondarily aquatic organisms—terrestrial plants that adapted to Life in water. Their species belong to very diverse and distantly related families.
The main adaptations of higher plants to an aquatic habitat include the following:
1) predominance of Vegetative Reproduction;
2) enhanced growth compared to terrestrial plants;
3) underdevelopment or absence of xylem in the stems;
4) reduction of The Root System or modification of its functions;
5) a relatively large body surface area for better gas exchange, and the lack of parenchyma differentiation into palisade and spongy;
6) heterophylly;
7) well-developed aerenchyma
8) secretion of mucilage by specialized glands, which prevents the leaching of nutrients from the plant;
9) the vast majority of higher aquatic plants are perennials.
Heterophylly (leaf dimorphism) is very common in hydatophytes. Leaves floating on the water surface are entire and larger, while submerged leaves are dissected into fine segments, with a very thin epidermis lacking a cuticle, and a thin blade without stomata (Fig. 11.2). Floating leaves, conversely, have a more complex structure: the epidermis of the upper side has a cuticle and numerous stomata, while the mesophyll is differentiated into palisade and spongy parenchyma.
The root system in floating plants is poorly developed, and the leaves have hydathodes.
Aquatic plants differ in size, and based on this trait, they are divided into two groups: microphytes and macrophytes. Microphytes are microscopic aquatic plants, namely algae. Accordingly, macrophytes are aquatic plants visible to the naked eye. Macrophytes include higher aquatic plants and lower plants—macroscopic algae (charophytes, green algae, etc.).
Fig. 11.2. Heterophylly in water buttercup: 1 — submerged leaves; 2 — emergent leaves
In lower plants (algae), the body is not differentiated into organs and tissues, unlike higher plants, which have complex vegetative and reproductive organs: stem, leaf, root, and flower.
For most algae, water is a permanent habitat, yet many algae can also live out of water. Based on their resistance to desiccation, terrestrial plants are classified into poikilohydric—unable to maintain a constant water content in their tissues—and homoiohydric—capable of maintaining constant tissue Hydration. In poikilohydric plants (blue-green and some green algae), cells shrink during desiccation without irreversible changes to their ultrastructure and, therefore, do not lose viability. Upon rehydration, they restore normal metabolism. The minimum moisture level required for the normal life of such plants varies. Its value determines, in particular, the distribution of aerophytes (aerial algae).
For homoiohydric plants, the presence of a large central vacuole is mandatory, as it stabilizes The Cell's water reserve. However, cells with large vacuoles largely lose their ability to tolerate desiccation. Homoiohydric algae include, for example, some aerial green and yellow-green algae (иіойтсйа^, Уаисйегіа^), which typically colonize environments with constant excessive moisture.
Water movement. Water movement plays a huge role in the life of aquatic plants. Absolutely stagnant, motionless water does not exist; therefore, practically all aquatic plants are inhabitants of flowing waters. In any continental and marine water bodies, relative Movement of water masses is observed, which ensures the influx of nutrients and the removal of plant waste products.
Current velocity is a factor whose significance is comparable to the Impact of Anthropogenic pollution of water bodies. Thienemann A. (1912) proposed dividing aquatic organisms into three groups based on their relation to current velocity: rheophiles, rheobionts, and rheoxenes. The group of rheophiles, capable of growing at current velocities from 0.7 to 1.2 m/s, includes floating sweet-grass (Glyceria fluitans), common reed (Phragmites australis), flowering rush (Butomus umbellatus), grassy pondweed (Potamogeton gramineus), perfoliate pondweed (Potamogeton perfoliatus), and fringed water-lily (Nymphoides peltata). Most submerged aquatic plants are rheobionts, growing in flowing waters (from 0.2 to 0.7 m/s). In stagnant and slow-flowing waters, rheoxenes are predominantly found, such as sweet flag (Acorus calamus), marsh marigold (Caltha palustris), and water violet (Hottonia palustris).
In areas with rapid currents, species diversity decreases to one or two adapted plant species, and the projective cover drops to 10-15%. In areas with slow currents, the intensity of competition among aquatic plants increases, as There is a much wider species spectrum and high projective cover (up to 100%).
Benthic algae growing in flowing water conditions have advantages compared to those growing in sluggish waters. The same level of photosynthesis can be achieved by plants under current conditions at lower light levels, which promotes the growth of larger algae with a high nutrient content. Water movement prevents the deposition of silt particles on rocks and stones, which would otherwise hinder the attachment of algal germlings, and washes away herbivorous animals from the substrate surface. Although strong currents or heavy surf can damage algae or tear them from the substrate, water movement prevents the settlement of microalgae and microscopic stages of macroalgae. As a rule, sites with intensive water movement are characterized by a significant development of benthic algae.
In the Arctic, perennial brown algae (Fucus, Laminaria) are easiest to find near the shore among boulders and rocky ledges that block the movement of ice, which could otherwise destroy the plant stands.
Light. The primary source of energy in the biosphere is solar radiation. Light energy is assimilated by phototrophic organisms (higher and lower plants), converting it into a form accessible to consumers—the chemical bond energy of organic substances.
Light is essential for The transport of nutrients within the plant, transpiration, and qualitative biochemical transformations. Solar energy is expended on morphogenetic processes: seed germination, the initiation and Development of the tillering node in grasses, seedling growth, stem formation, flower development, fruit ripening, and so on. All these processes require a certain quantity and duration of illumination.
Solar radiation plays an exceptionally important role in the functioning of aquatic ecosystems. It is linked to the behavior and distribution of aquatic organisms within the biotope. Among aquatic organisms, some develop intensively in the upper water layers, which receive the greatest amount of solar energy. These are primarily autotrophic organisms: algae, photosynthetic Bacteria, and higher aquatic plants. Through photosynthesis, they store a large amount of energy in the form of organic matter (primary production), which is then utilized by organisms of other trophic levels.
Autotrophic aquatic organisms (algae, higher aquatic plants) utilize the solar radiation spectrum in the range of 380-710 nm. It is this radiation that most effectively influences the physiological processes associated with photosynthesis in aquatic plants. This spectral region is called photosynthetically active radiation (PAR). Direct solar radiation contains 28-43% PAR, while diffuse radiation contains 50-60%.
A light ray incident on the water surface, In addition to reflection and refraction, undergoes diffraction, polarization, and spectral splitting. Furthermore, it is absorbed as it passes through the water column and is scattered by suspended particles, resulting in different amounts of solar energy reaching different depths, which causes a decrease in light intensity with depth.
An ecologically important property of water is its ability to transmit sunlight. This depends on the color and transparency of the water. Transparency is determined by the Molecular structure and concentration of dissolved organic substances—predominantly colored ones (such as humic and fulvic acids)—as well as suspended particles and planktonic organisms.
The upper layer of water, which receives sufficient light for plants to synthesize organic matter using solar energy, is called the photic zone, while the lower layer, which receives no solar
energy, is the aphotic zone. The zone of light penetration where the intensity of photosynthesis exceeds Plant Respiration is known as the euphotic zone. Its lower boundary, where photosynthesis balances respiration, is called the compensation point.
Long waves of solar radiation, which are most crucial for photobiological processes, are absorbed most intensely in water. Radiation from the blue part of the spectrum, with a wavelength of 475–480 nm, penetrates deepest through freshwater and marine columns. During photobiological reactions, the energy of solar radiation is absorbed by discrete particles called photons or quanta. Photosynthesis occurs in the spectral range of 400–900 nm in bacteria, 400–700 nm in higher green plants, and 400–660 nm in algae. Wavelengths shorter than 300 nm disrupt the molecular structure of Proteins and Nucleic Acids, thereby impairing the normal functioning of living systems. This is why the depletion and thinning of the ozone layer—which blocks precisely these quanta of solar radiation from reaching Earth—pose a serious threat to the biosphere.
Based on their light requirements, plants are divided into several ecological groups, or heliomorphs. Heliophytes (from Greek helios meaning sun + phyton meaning plant) are sun-loving plants that prefer brightly lit habitats; sciophytes (from Greek scia meaning shade) are shade-tolerant plants capable of withstanding considerable shading; and heliosciophytes are plants that thrive in well-lit areas but can also tolerate varying degrees of shade.
Sun-loving plants, or heliophytes, achieve optimal development under full sunlight. These species tolerate little to no shading—they include sweet flag (Acorus calamus), water plantain (Alisma plantago-aquatica), flowering rush (Butomus umbellatus), yellow iris (Iris pseudacorus), sacred lotus (Nelumbo nucifera), yellow water lily (Nuphar lutea), white water lily (Nymphaea alba), shining pondweed (Potamogeton lucens), perfoliate pondweed (P. perfoliatus), and greater duckweed (Spirodela polyrrhiza).
Shade plants, or sciophytes, achieve optimal development at 1/10 to 1/3 of full illumination. Aquatic sciophytes include marsh calla (Calla palustris), rigid hornwort (Ceratophyllum demersum), water horsetail (Equisetum fluviatile), quillwort (Isoëtes lacustris), water mint (Mentha aquatica), and common bladderwort (Utricularia vulgaris).
Shade-tolerant plants, or heliosciophytes, exhibit varying degrees of shade tolerance. This group includes species that grow best in good light but can endure shading without significant stress, such as water wheel (Aldrovanda vesiculosa), great fen-sedge (Cladium mariscus), marsh cinquefoil (Comarum palustre), Canadian waterweed (Elodea canadensis), floating sweet-grass (Glyceria maxima), ivy-leaved duckweed (Lemna trisulca), floating pondweed (Potamogeton natans), and water spangles (Salvinia natans).
Algae, especially microscopic ones, exhibit the highest conversion efficiency of light energy compared to other photosynthetic organisms. Many species are capable of mixotrophy and efficiently utilize low-intensity light.
Based on their light preferences, algae are divided into two groups: heliophilic and heliophobic.
Heliophilic (light-loving) algae require substantial amounts of light for normal metabolic activity and photosynthesis. This group includes most blue-green algae and a significant number of green algae that develop massively in surface water layers during the summer.
Heliophobic algae are adapted to low-light conditions. For example, most diatoms avoid the brightly lit surface layer of water; in low-transparency lakes, they develop intensively at a depth of 2–3 m, while in transparent marine waters, they thrive at depths of 10–15 m.
Depending on the composition of their photoreceptor pigments, algae from different divisions exhibit maximum photosynthetic rates at different wavelengths of light. In terrestrial environments, the qualitative characteristics of light remain relatively constant, as does photosynthetic rate. When light passes through water, the red and blue parts of the spectrum are absorbed, allowing greenish light—which is poorly absorbed by chlorophyll—to penetrate deeper. Consequently, red and brown algae survive primarily at these depths, possessing accessory Photosynthetic Pigments (such as phycocyanins and phycoerythrins) that can utilize green light energy. This accounts for the vertical distribution of algae in seas and oceans: green algae generally dominate in near-surface layers, brown algae are found deeper, and red algae inhabit the deepest zones. However, this pattern
is not absolute. Many algae can survive under extreme, atypical low-light conditions or even in total darkness, accompanied by certain shifts in pigment composition or nutritional modes. For instance, under low-light conditions, blue-green algae can alter their pigment composition to favor phycobilins, causing their trichomes to shift in color from blue-green to purple. Representatives of various algal divisions (such as euglenoids) can switch to a saprophytic mode of Nutrition in the absence of light and in the presence of excess organic matter.
Only 10% of seawater has sufficient light conditions for photosynthesis. Ninety percent of water lies in absolute darkness and receives nutrients primarily via downward flux from the euphotic zone. Ultraviolet and long-wave light penetrate to lesser depths than blue-green light. Plants living near the surface, such as Ulva sp., absorb light similarly to terrestrial plants. Red algae utilize deep-penetrating yellow-green light with the aid of specialized pigments that transfer energy to chlorophyll a.
Bacterial pigment absorption extends far into the invisible range of the light spectrum (Fig. 11.3). Producers are able to survive in marine ecosystems by adapting their absorption systems to various light zones down to depths of 200 m.
Fig. 11.3. Absorption of light by algae and bacterial pigments
Other processes driven by solar energy are not directly
linked to The conversion of sunlight into the chemical energy of compounds. Light can act as an informational cue that regulates plant photoperiodic responses, synchronizing stages of their reproductive cycle via the Phytochrome pigment system.
Phototaxis is the movement of organisms in response to directional lighting. In algae, Protozoa, and some Multicellular Organisms, this manifests as migration to better-illuminated areas of water bodies. Phototaxis is most strongly stimulated by ultraviolet, violet, and blue rays of the solar spectrum.
Phototropism is manifested as A change in the growth direction of hydrobionts in response to one-sided light stimuli.
Temperature. Aquatic ecosystems are characterized by slow cooling and heating of water due to its exceptionally high heat capacity. This is caused by the expenditure of a portion of thermal energy on breaking Hydrogen Bonds within associated molecules. When air temperatures rise significantly, water becomes warmer, but its temperature never reaches that of the atmosphere because of water's high latent heat of vaporization. On hot days, The rate of water evaporation increases, leading to greater heat dissipation and preventing overheating. Conversely, when the temperature drops below 0°C and ice forms, a substantial amount of heat is released, causing the water to cool slowly. Thanks to this high heat capacity, the temperature range of the aquatic environment inhabited by hydrobionts rarely exceeds 1–35 °C. Compared to aquatic organisms, terrestrial organisms must adapt to a much wider range of ambient temperature fluctuations.
The ecological significance of temperature primarily manifests through its influence on the distribution of hydrobionts in water bodies and the metabolic rates of various life processes. Species that thrive across a wide temperature range are called eurythermal (for example, green algae of the order Oedogoniales, whose sterile filaments can be found in shallow water bodies from early spring to late autumn), whereas those adapted to a narrow range are termed stenothermal. Stenothermal organisms include cryophilic (cold-loving) algae that grow only at temperatures close to the freezing point of water. Cryophilic algae are predominantly green, blue-green, and diatoms. Developing in massive quantities, they can cause green, yellow,
blue, red, brown, or black "blooms" of snow or ice. Green snow is caused by Raphidonema nivale, red snow by Chlamydomonas nivalis, and brown snow by Ancylonema nordenskioeldii. These algae inhabit the surface layers of snow or ice and reproduce intensively at temperatures around 0°C. Only a few possess resting stages; most lack any specialized morphological adaptations to endure low temperatures.
These species share The ability to withstand freezing without Cell Structure disruption and then, upon thawing, rapidly resume vegetative growth using a minimal amount of heat.
In general, algae exhibit perhaps the widest range of temperature tolerance. They are capable of existing in extreme temperature conditions—both on The surface of ice and snow, and in hot springs with temperatures close to the boiling point of water.
Thermophilic algae grow at water temperatures of 35—52 °С, and in some cases up to 84 °С and higher, often in waters with elevated levels of mineral or organic substances (polluted hot wastewater from plants, factories, thermal power stations, or nuclear power plants). Typical inhabitants of hot waters are cyanobacteria, and to a lesser extent, diatoms and certain green algae. There are few specifically thermophilic species. Most algae found in hot springs can tolerate high temperatures but develop better under normal temperature conditions, meaning they are essentially mesothermic species.
The response of algae to the temperature factor influences their vertical distribution in water bodies. In various water bodies and watercourses, due to the absorption of solar radiation by the upper water layers, only these layers are warmed. Warm water is less dense than cold water, and wind-driven currents equalize its density only down to a certain depth. With the onset of the growing season, a period of intense solar radiation, a highly stable thermal stratification of the water column occurs in sufficiently deep, closed continental water bodies. In these water bodies, distinct water masses are formed: a warm, light surface layer—the epilimnion—and beneath it, a mass of colder, denser water—the hypolimnion. In autumn, the water cools down, and the thermal stratification disappears. Oceans and seas also feature a permanent thermocline layer. Algae can develop only in the epilimnion (specifically in the euphotic zone), with the most thermophilic and photophilic organisms settling in the well-warmed surface layers.
The impact of temperature on algae developing in the aquatic environment is profound. It is temperature that determines their geographical distribution. For instance, brown algae species of the genus Lessonia are found only within the 10 °С summer isotherm, species of the genera Laminaria, Agarum, and Alaria do not cross the 20 °С summer isotherm, and some Sargassum species live only at temperatures of 22—23 °С (Sargasso Sea). On the whole, except for widely distributed eurythermic species (such as some Fucales), a geographical zonation is observed in algal distribution: specific taxa of marine algae are restricted to certain geographical zones. Thus, large brown algae (Macrocystis) dominate in northern seas. Moving southward, red algae begin to play a more prominent role, while brown algae recede into the Background.
Geographical zonation is also well-pronounced in marine planktonic algae. Marine tropical phytoplankton is characterized by high species richness coupled with very low productivity. Dinoflagellates and chrysophytes are extremely abundant in the plankton of tropical waters. Tropical waters are poor in diatoms, which dominate in northern seas.
Among the higher aquatic Plants of Ukraine, there are thermophilic species: yellow water-lily (Nuphar lutea), white water-lily (Nymphaea alba), great yellowcress (Rorippa amphibia), floating fern (Salvinia natans), wide-leaved water-parsnip (Sium latifolium), water caltrop (Trapa natans), and Carolina mosquitofern (Azolla caroliniana)/
Chemical composition of water. Dissolved gases and mineral salts are present in water. The amount of dissolved oxygen in water is of great ecological importance. The presence of dissolved oxygen in natural waters is an essential condition for the existence of most aquatic organisms. Oxygen enters the water from the air and is released by aquatic vegetation during photosynthesis (photosynthetic reaeration).
The oxygen concentration in water depends on the temperature and the content of reducing agents (including intermediate substances formed and accumulated As a result of The activity of microorganisms that decompose organic residues). The solubility of the gas is low and temperature-dependent: at 0° С - 69,5, 10° С - 53,7, 20° С - 43,3 (мг/л). In
saltwater, oxygen solubility is 20% lower than in freshwater. Oxygen supersaturation can be observed in water bodies rich in vegetation, which enriches the water with oxygen during photosynthesis.
Factors leading to a decrease in dissolved oxygen concentration also include the respiration of living organisms. Respiration and oxidation occur continuously in water bodies, intensifying with rising temperatures, whereas photosynthesis is possible only in the presence of daylight. Furthermore, oxygen penetration from the atmosphere occurs only in the absence of ice cover. As a result of these processes, there are significant seasonal and diurnal fluctuations in dissolved oxygen content; minimum levels are observed at night and in winter in freezing water bodies.
Supplying aquatic plants with vital oxygen is challenging. Higher aquatic plants have adapted to oxygen deficiency in the aquatic environment by developing an advanced aeration system consisting of a tissue with very large intercellular spaces—aerenchyma. Often, the intercellular spaces within it exceed the size of the cells themselves. Aerenchyma consists of living, thin-walled cells. Atmospheric air enters the plant through the stomata or lenticels of organs located above the water and reaches oxygen-depleted Cells and Tissues of other organs via intercellular spaces, where it accumulates in large intercellular cavities (Fig. 11.4).
a b
Fig. 11. 4. Aerenchyma: a - cross-section of a watermilfoil stem, b - cross-section of a bur-reed leaf
In deep-water bodies, especially the World Ocean, with a well-developed thermocline, excess oxygen produced by phytoplankton is released into the atmosphere.
Inland water bodies are usually oxygen consumers rather than producers. This negative balance is partly due to the fact that under anthropogenic pressure, many pollutants act as additional oxygen consumers during the oxidation process.
Carbon dioxide is of great importance for plant life. It is essential for plant existence and necessary for photosynthesis. Freshwater and especially seawater contain significant amounts of carbon dioxide. For example, seawater contains 40-50 cm3/l (in free or bound form, which is 150 times higher than its concentration in atmospheric air). Many submerged hydrophytes are able to absorb carbon from water only in the form of С02, such as bryophytes, while helophytes absorb it from the atmosphere.
Salinity and the mineral composition of water are the most important Factors influencing the distribution of algae and higher plants.
The mineralization of marine (oceanic) waters is primarily determined by sodium and magnesium chlorides. One cubic kilometer of seawater contains about 35 million tons of solids, including 19.8 million tons of sodium chloride, 9.5 million tons of magnesium, and 6.3 million tons of sulfur,
31.0 thousand tons of bromine, 3.9 thousand tons of aluminum, 79.3 tons of manganese, 79.3 tons of copper,
11.1 tons of uranium, 3.8 tons of molybdenum, etc.
Unlike oceanic and marine waters, the fresh waters of rivers, lakes, reservoirs, and other water bodies are less saturated with dissolved salts and contain predominantly carbonates.
Depending on their Salt Tolerance, algae are classified into oligohaline, mesohaline, euhaline, ultrahaline, freshwater, and other species. Species richness (the number of species) is closely linked to water salinity.
In practically every algal division, one can find species capable of living under extreme salinity conditions, as well as species inhabiting water bodies with very low mineralization. For instance, blue-green algae are predominantly freshwater organisms, yet some of their species can develop in ultrahaline waters. Among typically marine inhabitants—chrysophytes of the order Coccolithophorida (Соссоїййорйогійа^)—there are species also found in continental water bodies with very low mineralization. Diatoms are widespread in both marine and continental waters
mass; they occur in environments with varying salinity. However, specific diatom species often develop only at a specific salinity and are so sensitive to its fluctuations that they can be used as indicator organisms.
Brown algae are also highly sensitive to salinity changes. Many of them cannot grow even under slight freshening, which is why they are poorly represented in the waters of the Baltic Sea with its relatively low salinity. Red algae exhibit a similar dependence on water salinity: more than 300 species of red algae have been found in the Mediterranean Sea (salinity 37–39 ‰), 129 in the Black Sea (17–18 ‰), and 22 in the Caspian Sea (10 ‰). Green algae are predominantly freshwater organisms, with only 10% of them found in marine environments. Nevertheless, some species among them are able to withstand significant salinity and even cause "blooming" in hypersaline water bodies (e.g., Dunaliella salina, Asteromonas gracilis).
Thus, algae as a whole are characterized by a very wide amplitude of salt tolerance. As for specific species, few of them are capable of existing in water bodies with varying salinity, meaning that most algae are stenohaline species. Euryhaline species capable of surviving at different salinities are relatively few (e.g., Bangia, Enteromorpha, Dunaliella).
During the polymerization of highly active small molecules into macromolecules (for example, the conversion of glucose into starch) and during the reverse process—the Hydrolysis of high-molecular-weight compounds—the osmotic pressure within the cell can change rapidly. This mechanism ensures the resistance of certain algae species to desiccation and sharp fluctuations in water salinity.
Algae of saline water bodies—halobionts—grow at elevated salt concentrations in the water, reaching 285 g/L in lakes dominated by common salt and 347 g/L in Glauber's salt lakes. As salinity increases, the number of algal species decreases; only a few can tolerate very high salinity. Over-salted (hypersaline) water bodies are dominated by unicellular motile green algae—hyperhalophiles—whose cells lack a Cell wall and are surrounded only by the Plasmalemma (species of the genera Dunaliella, Asteromonas, Pedinomonas). These algae are distinguished by an elevated sodium chloride content in the protoplasm, high intracellular osmotic pressure (up to 250×103 hPa), the accumulation of carotenoids and
glycerol in their cells, and high lability of enzyme systems and metabolic processes. In the saline water bodies of southern Ukraine, they often develop in massive quantities, causing red or green "blooming" of saline waters.
Most species of vascular macrophytes are very sensitive to the salt concentration in water. However, the common reed (*Phragmites australis*), for example, belongs to species capable of growing under conditions of significant salinity—halophytes. This species grows along the shores of seas and bays, salt lakes, and other brackish water bodies, often in the vicinity of salt marshes. The common reed grows under conditions of chloride (up to 2.5–3%) and sulfate (up to 5%) salinity. It dies off In the second year only under conditions of severe chloride salinity (up to 5%).
An extremely halophilic species, sago pondweed (*Potamogeton pectinatus*), has been found in areas where salinity reached 16–17 ‰.
The group of glycohalophytes includes ditchgrass (*Ruppia maritima*), eelgrass (*Zostera marina*), and dwarf eelgrass (*Zostera nana*).
Halophobes include violet bladderwort (*Hottonia palustris*).
Water acidity. The Effect of an elevated concentration of hydrogen ions in water and soil exerts a toxic effect on plants, limiting the uptake of biogenic elements by root systems. In an acidic environment, the solubility of toxic substances increases. Acidification of the environment leads to changes in hydrobiocenoses, the replacement of vascular plant species by bryophytes, which results in a shift in the COMPOSITION AND PROPERTIES of the soil beneath the plants, and in some cases leads to waterlogging of the area.
Water acidity is of great importance for the vital activity of algae. According to their attitude towards environmental acidity, species are distinguished that live in alkaline waters—alkaliphiles (basophiles)—and those living in acidic waters at low pH values—acidophiles. Acidophiles, for example, include the majority of desmids (Desmidiales). The greatest species richness of desmid algae is observed in eutrophic and mesotrophic bogs under conditions of reduced acidity; however, some desmids can also occur in alkaline waters with high mineralization (e.g., *Closterium acerosum*, *C. leibleinii*). Charophytes, by contrast, are predominantly alkaliphiles. Their greatest species diversity is observed in slightly alkaline waters, although some of them
(*Chara vulgaris*) also develop in acidic waters at pH 5.0.
Most higher aquatic plants prefer a neutral environment. Acidophiles include mosses (genus *Sphagnum*), watercress (*Nasturtium officinale*), greater spearwort (*Ranunculus lingua*), water dock (*Rumex hydrolapathum*), water soldier (*Stratiotes aloides*), vesicled sedge (*Carex vesicaria*), bog bean (*Menyanthes trifoliata*), and sphagnum moss; a weak acidophile is yellow water-lily (*Nuphar lutea*), and bulbous rush (*Juncus bulbosus*). Basophiles include water crowfoots—pond water crowfoot (*Batrachium aquatile*) and circinate water crowfoot (*B. circinatum*)—Canadian waterweed (*Elodea canadensis*), submersed hornwort (*Ceratophyllum submersum*), silverweed (*Potentilla anserina*), sago pondweed (*Potamogeton pectinatus*), and others. Indifferent species can grow at various pH values—least bur-reed (*Sparganium minimum*) and narrow-leaved cattail (*Typha angustifolia*).
Nutrients. The presence in the environment of macro- and microelements, which are essential components of aquatic plant bodies, is of decisive importance for the intensity of their development. The concentration of mineral elements in ordinary natural water is quite low, so the accumulation coefficient (the ratio of elements in the biota to those in natural water) spans several orders of magnitude.
Elements and their compounds classified as Macronutrients are required by organisms in relatively large quantities. For example, nitrogen is a part of all protein molecules.
According to their requirements for nitrogen nutrition, plants are divided into nitrophiles and nitrophobes.
Nitrophiles are plants that require many easily assimilated nitrogen compounds for their development. Typical nitrophiles are violet bladderwort (*Hottonia palustris*) and floating duckweed (*Lemna trisulca*); a moderate nitrophile is European frog-bit (*Hydrocharis morsus-ranae*).
Nitrophobes are plants that avoid nitrogen-rich nutrition. They have low demands for nitrogen compounds and develop where this element is at a minimum.
Calcium is necessary for metabolism in plants. It neutralizes the toxic properties of oxalic acid and reduces the acidity of the soil solution, thereby promoting plant growth. The absence or deficiency of calcium in the soil disrupts the physiological processes of plant
vital activity and causes carbonate chlorosis. This element is used in large quantities by marine and freshwater algae that deposit "sheaths" of calcium salts around their bodies (some red and charophyte algae).
Based on their relationship to calcium, plants are divided into the following ecological groups: calciphiles, calciphobes, and indifferent plants.
Calciphiles are plants that have high demands regarding the calcium content in the environment. Among vascular macrophytes, Canadian waterweed belongs to calciphiles.
Calciphobes are plants that avoid carbonate-rich nutrition. These include sphagnum mosses, water chestnut (*Trapa natans*), and others.
Indifferent plants are those that are neutral to the presence of calcium in the environment (soil).
Microelements are essential for plants in very small quantities, yet they are of paramount importance to their vital activity, as they form part of many crucial Enzymes. Although the plant's requirement for microelements is low, their concentration in the surrounding environment is likewise low. Microelements frequently act as limiting factors. They comprise 10 elements: Fe, Mn, Zn, Cu, B, Si, Mo, Cl, V, and Co (iron, manganese, zinc, copper, boron, silicon, molybdenum, chlorine, vanadium, and cobalt).
Elements such as copper, manganese, zinc, and fluorine, found in water bodies in trace amounts, play a significant role in the life of aquatic organisms (influencing growth, respiration, metabolism, nutrition, reproduction, etc.). When the concentrations of these substances in water increase to certain levels, they become toxic to hydrobionts.
In plant organisms, copper is a component of oxidase enzymes and the protein plastocyanin. An excess of copper compounds exerts a toxic effect. Submerged plants accumulate heavy metals (Mn, Cu, Cr) 4–9 times more than emergent and floating-leaved plants.
Iron and manganese ions occur in natural waters in the form of bicarbonates, sulphates, chlorides, and phosphates, with iron also present in humic complexes. Iron deficiency in the soil or impaired iron uptake stunts plant development and leads to chlorosis and other pathological anomalies. An excess of iron also exerts an adverse effect on plants.
Algae from different divisions have varying requirements for macro- and microelements. For instance, the normal development of diatoms requires rather substantial amounts of silicon, which is utilized to build their frustules. In the absence or deficiency of silicon, the diatom frustules become thinner.
11.3. Ecological Significance of Biotic Factors
Interactions develop among living organisms inhabiting the atmosphere, lithosphere, and hydrosphere, whereby each component influences the others directly or through modifications of the ecological environment, thus acting as a biotic factor. Consequently, the entire aggregate of diverse and indirect influences exerted by plants, animals, and microorganisms upon one another is referred to biotic factors. They are exceptionally varied and encompass phytogenic, zoogenic, and microbogenic actions, giving rise to Direct and Indirect, antagonistic and symbiotic relationships, as well as mechanical and chemical effects.
Phytogenic factors are influences exerted by neighboring plants—both direct (mechanical contacts, Symbiosis, parasitism, epiphyte colonization) and indirect (phytogenic modifications of the plant habitat, manifested as the interception of water, soil nutrients, carbon dioxide, and light required for photosynthesis, etc.).
Zoogenic factors are animal influences (grazing, trampling, and other mechanical impacts, flower pollination, seed dispersal, and indirect effects on the environment).
Mycogenic factors are the influences of Fungi (parasites and symbionts).
Aquatic phytocoenoses are characterized by a specific species composition that includes both higher and lower plants. Complex phytocoenotic relationships, driven by phytogenic factors, are established among them.
Among the plant kingdom, there are species belonging to facultative or obligate heterotrophs that obtain preformed organic matter. These include Saprophytes, parasites, and carnivorous plants.
The saprophytic mode of nutrition involves utilizing organic matter from dead PLANT AND ANIMAL remains. This nutritional strategy is widely known in algae but also occurs in angiosperms.
Plant parasitism is a form of co-existence between different organisms,
in which one organism, having lost the ability to synthesize organic substances, lives at the expense of another. Parasitism can be permanent or temporary. Parasites settle on the surface or within the plant's body and feed on its sap. They lack a true root system or have a heavily reduced one, which is replaced by haustoria (root suckers) through which parasites absorb water, plastic substances, and Vitamins. Parasites include bacteria, fungi, and flowering plants.
The angiosperm flora includes numerous parasitic and hemiparasitic species. This group comprises species of dodder (Cuscuta), broomrapes (Orobanchaceae), and toothwort (Lathraea). They parasitize herbaceous and shrubby plants, and some target trees.
Hemiparasites are plants that attach to other hosts, deriving partial nutrition from them while independently producing nutrients through their own photosynthesis (e.g., bastard toadflax, European mistletoe, white mistletoe, etc.).
Plants exert a substantial influence on animals. Over 500 plant species are known to derive nutrition at the expense of animals, particularly insects. They form a specific group of carnivorous (insectivorous) plants. These are green plants possessing specialized adaptations for capturing and digesting various small animals, most frequently insects. In this way, they Supplement their autotrophic nutrition with a form of heterotrophic nutrition. Such plants are most commonly found in nitrogen-deficient soils, where preformed organic matter serves primarily as a source of nitrogen nutrition. These plants attract insects using specific coloration, scent, and sugary secretions, capture them using specialized passive or active trapping mechanisms, and subsequently secrete specific enzymes that ensure intracellular Digestion.
In Ukraine, carnivorous plants from the sundew family occur—specifically sundews (Drosera rotundifolia, D. longifolia). Sundews contain substances that exert a paralytic effect on insects (Fig. 11.5). Upon adhesion, the marginal tentacles of the sundew bend toward the prey, and secretion is intensified.
Sundew leaves contain chlorophyll and carry out photosynthesis. If deprived of animal prey, the plant does not necessarily die, yet it develops very slowly. The absorption of breakdown products is facilitated by secretory glands connected to the plant's Vascular System.
Fig. 11.5. Round-leaved sundew (Drosera rotundifolia):
1 - general habit, 2 - flower, 3 - individual leaf, 4 - half of the tentacles bent toward the center where an insect is located
Bladderworts (Utricularia) possess specialized trapping apparatuses. These are branched basal leaves of pitcher-like shape (Fig. 11.6). Their margins bear bristles that prevent insects from escaping the trap. An insect that enters the trap dies and is dissolved by enzymes secreted by the leaf, while its Body Fluids are absorbed by the absorptive cells lining the trap walls.
More than 400 species of angiosperm plants are known to acquire nutrients in a similar manner.
Plant symbiosis is a form of coexistence between different organisms from which both components derive mutual benefit. Symbiosis is very common in nature and can be either obligate or facultative.
Obligate symbiosis is observed between legumes and free-living nitrogen-fixing bacteria. Root nodule bacteria fix atmospheric nitrogen into nitrates, which become accessible for consumption by higher plants. In turn, the bacteria receive ready-made Organic compounds from the legumes in the course of their metabolic activity. Humans utilize these symbiotic relationships between plant organisms in Practical Applications. Legume crops enrich the soil with nitrogen, after which these plots are used to sow cereal crops that lack this capability.
Fig. 11.6. Bladderwort (Utricularia)
1 - general view; small bladders develop in large numbers on the submerged stem;
2 - magnified view of a bladder; 3 - sectional view of a bladder showing the valve (a), hairs (b), and absorbing cells (c);
4 - absorbing cells under high magnification
Mycorrhiza is the symbiotic association between the roots of Higher Plants and non-pathogenic fungi. The mycotrophic type of nutrition is characteristic of plants that form mycorrhizae on their roots and obtain nutrients from the soil via fungal hyphae that are symbiotically linked with the root system.
In such a relationship, both partners benefit one another. The majority of woody plants and many herbaceous species are capable of forming symbioses with fungi. Typically, fungi infect young roots, in which case root hairs fail to develop. The fungus receives organic compounds from the higher plant and, in return, ensures the availability of water and mineral nutrients for the plant. The fungus assists the higher plant in assimilating poorly soluble humus substances. Through its enzymatic system, the fungus promotes Carbohydrate Metabolism and activates the Enzymes of the higher plant. The phenomenon of mycorrhiza is widespread in nature.
Cases of algae coexisting with other organisms are of particular interest. Most commonly, algae utilize living organisms as a substrate. Based on The Nature of the substrate inhabited by fouling algae, they are classified into epiphytes, which live on plants, and epizoites, which live on animals. For instance, species of the genera Cladophora or Odontoripis can be found on the calcareous shells of Mollusks, while some green, blue-green, and diatom algae are common in sponge fouling communities. In fouling communities, loose and short-lived associations are established between the host plant and the fouling plant.
Algae can also inhabit the tissues of other organisms—either extracellularly (in mucus, algal intercellular spaces, or sometimes within the walls of dead cells) or intracellularly. Algae that live within the tissues or cells of other organisms are called endophytes. Extracellular and intracellular algal endophytes form rather complex symbioses, known as endosymbiosis. These are characterized by permanent and robust connections between the partners. Endosymbionts can include various algae such as blue-green, green, brown, and red algae, but most frequently, endosymbioses occur between unicellular green or yellow-green algae and unicellular animals. The participating algae are referred to as zoochlorella and zooxanthellae.
Yellow-green and green algae also form endosymbioses with multicellular organisms, such as freshwater Sponges, hydras, and others. Distinctive endosymbioses between blue-green algae and Protozoans or certain other organisms are termed synthyanoses. This gives rise to a morphological complex called a cyanome, with the blue-green algae within it known as cyanelles.
The highest degree of development in symbiotic relationships is characterized by the strict constancy of the components within the symbiotic system. For example, colonies of a specific species, *Anabaena azollae*, invariably inhabit the body of the freshwater fern Azolla (*Azolla giliculoides*), regardless of where it grows. All attempts to infect Azolla with representatives of other genera or species of blue-green algae have been unsuccessful. This indicates a specific physiological interrelationship between the participants of this symbiosis.
The endosymbiotic lifestyle generally leads to morphological changes in the symbionts. For instance, in the blue-green
alga *Aphanocapsa*, which lives in the Tissues of the marine sponge *Aplisilla*, The cell wall is significantly thinner than in free-living species of blue-green algae. Algae that act as intracellular endosymbionts undergo even more drastic alterations: they lose their cell walls, the structure of their flagella becomes simplified, and the stigma disappears, often making it impossible to determine the algal taxonomic affiliation.
Among the symbioses formed by algae, the most compelling is their symbiosis with fungi, which resulted in The Emergence of a distinct group of plant organisms known as lichens. This symbiosis demonstrates a unique biological unity that led to the appearance of a fundamentally new organism. At the same time, each lichen partner retains the traits of its respective organismal group. Lichens represent the only proven case of a new organism originating from the symbiosis of two distinct entities.
Competition. The development of individual algal species can also be influenced by competitive interactions. For instance, brown algae of the genus *Fucus* typically inhabit the intertidal zone and experience periodic (sometimes up to two days) drying out. Lower down, in the permanently submerged zone, dense thickets of other brown and red algae are generally found. However, in areas where these thickets are less dense, *Fucus* can also grow at greater depths.
Allelopathy refers to the chemical influence exerted by one plant species on another through physiological exudates. Plants release volatile or liquid droplet substances whereby some species stimulate or inhibit the development of others.
Benthic algae, for example, begin to exert mutual influence from the moment of spore settlement and germination. It has been experimentally proven that zoospores of *Laminaria* do not germinate in the vicinity of thallus fragments of the brown alga *Ascophyllum*.
Microorganisms release marasmins—physiologically active substances that induce wilting and Aging in plants. Furthermore, microorganisms and fungi produce Antibiotics, Gibberellins, and highly toxic Alkaloids. Bacteria that produce antibiotics may poison themselves at high concentrations, yet stimulate their own growth at negligible ones.
Consequently, plant organisms are capable of regulating population sizes and balancing interrelationships among coenobionts within communities through stimulating and inhibitory exudates.
Zoogenic factors. Animals exert a significant influence on plant life. Relationships between them primarily develop on The basis of nutrition.
In most cases, algae act as primary producers of organic matter within ecosystems. Therefore, the most critical factor limiting algal development in a specific ecosystem is the presence of consumers that feed on algae. For instance, the development of communities dominated by *Laminaria* species off the Atlantic coast of Canada is limited by sea urchins, which feed primarily on these algae. In tropical coral reef waters, there are areas where fish completely graze away soft-thallused green, brown, and red algae, leaving hard-walled blue-green algae untouched. Gastropods also feed mainly on algae. Crawling along the bottom, they consume microscopic algae and seedlings of macroscopic species. Mass proliferation of these mollusks can cause severe disruption in littoral algal communities.
Phytophilous fish include the grass carp (*Ctenopharyngodon idella*), which consumes aquatic plants (predominantly higher plants) and is therefore referred to as the "white amur." The grass carp has been acclimatized in Ukraine and is utilized in polyculture fish farming.
Biocoenotic relationships between entomophilous plants and pollinating animals are exceptionally important. During pollination, insects feed on nectar or pollen. To obtain nectar or pollen, they must penetrate the flower. In such entomophilous plants, the flower is structured in such a way that while gathering nectar, insects get their bodies dusted with pollen and transfer it to the stigmas of other flowers they visit. This is how cross-pollination takes place.
11.4. Anthropogenic Factors
Like any other living organism, humans act as a biotic factor within a biocenosis, influencing the remaining organisms of the ecosystem they inhabit.
Human impact on nature can be either deliberate or spontaneous (accidental). Deliberately, humans breed new plant varieties and animal breeds, eradicate "harmful" species, and create novel biocenoses. However, humanity's understanding of ecosystem functioning has not always allowed for accurate predictions regarding the consequences of anthropogenic environmental intervention. As a rule, conscious human impact on nature yields positive results in the early stages. Later on, negative consequences for ecosystems emerge: the predatory overexploitation of commercial species; ill-conceived species introductions that compete with native flora and fauna, thereby altering ecosystems; land plowing that destroys natural biocenoses and reduces species diversity; and the pollution of aquatic ecosystems through agricultural chemicals, among others.
Accidental impacts refer to those that were neither planned nor foreseen: the most dangerous ecological catastrophes include industrial accidents in the coal, oil, and gas extraction sectors, as well as in metallurgical, chemical, petrochemical, and microbiological facilities. Among the largest ecological disasters of the last century is the 1986 Chornobyl Nuclear Power Plant accident, which, in addition to its immediate consequences (the loss of personnel and liquidators, along with radioactive site contamination), triggered radioactive fallout that significantly increased the risk of Cancer among the European population.
Natural disasters occurring within environments already transformed by human activity (such as earthquakes, dry winds, tornadoes, and floods) represent major factors of accidental destructive impact.
Smaller-scale anthropogenic impacts include the accidental Introduction of animals and weed seeds into new natural zones and territories.
Technogenic and urbogenic processes are particularly harmful.
By digging canals and constructing reservoirs, humans create new habitats for aquatic organisms that often differ fundamentally from the region's original water bodies in hydrological and thermal regimes. Currently, the productivity levels of many inland water bodies are frequently determined less by natural conditions than by social and economic relations. Wastewater discharges often lead to the depletion of species composition and the death of aquatic vegetation, or alternatively, to the mass proliferation of specific species. The former occurs when toxic substances are discharged into a water body, while the latter results from the enrichment of the water with nutrients (especially nitrogen and phosphorus compounds) in mineral or organic forms—a process known as anthropogenic eutrophication of water bodies. In many cases, the spontaneous enrichment of water bodies with nutrients occurs on such a
scale that the water body, functioning as an ecological system, becomes overloaded with them. This results in excessive, explosive algae growth—known as water "blooming".
Algae, particularly aerophytic and soil-dwelling species, can also be affected by atmospheric emissions of toxic industrial waste. Often, the consequences of unintentional or targeted human intervention in ecosystem dynamics are irreversible.
Along with nitrogen compounds, phosphates contribute to the anthropogenic eutrophication of water bodies. However, due to their low mobility in the soil, phosphorus compounds pose a lower environmental risk.
11.5. Plant Life Forms
A life form (ecomorph, biomorph) refers to the outward appearance and biological traits of plants that reflect their adaptation to specific environmental conditions.
Various classifications of Morphology/18.html">PLANT LIFE FORMS exist, the most popular being the system proposed by C. Raunkiær (1906–1907). This system is based on traits that characterize how plants survive unfavorable seasons (whether cold or dry) depending on the position of their renewal buds relative to the soil surface and snow cover.
C. Raunkiær identified five main life forms: phanerophytes, chamaephytes, hemicryptophytes, cryptophytes, and therophytes.
In phanerophytes, the buds overwinter or endure dry periods "in the open", located relatively high above the ground (trees, shrubs, woody lianas, epiphytes); consequently, they are usually protected by specialized scales that shield the growing apex and young leaf primordia from moisture loss.
In chamaephytes, the buds are situated close to the soil surface or no higher than 20–30 cm above it (subshrubs, dwarf shrubs, creeping plants). In cold and temperate climatic zones, these buds overwinter beneath the snow.
In hemicryptophytes, the renewal buds lie at the soil level or are embedded slightly into the soil or the litter of fallen leaves and plant debris. These are perennial herbaceous plants.
Cryptophytes are represented either by geophytes, which have renewal buds buried at some depth in the soil (rhizomes, tubers, and bulbs), or by hydrophytes, whose renewal buds overwinter underwater.
Cryptophytes comprise aquatic geophytes.
In therophytes, all vegetative parts die off by the end of the season, leaving no overwintering buds. They regenerate the following year from seeds.
C. Raunkiær established a correlation between life forms and climate. Phanerophytes dominate in the humid tropics, hemicryptophytes in the temperate zone, therophytes in deserts, and chamaephytes in tundras and deserts.
Over the course of plant evolution, life forms also shifted. The earliest land plants that transitioned from water to land were low-growing plants resembling modern herbaceous species. Later, large tree-like forms evolved, including ferns standing 30–45 meters tall, alongside herbaceous ferns that have survived to the present day. Gymnosperms represent a predominantly woody group. Flowering plants exhibit the greatest diversity of life forms. Throughout evolution, angiosperms progressed from relatively short, thick-trunked, sparsely branched rosette trees (resembling modern palms and papaya trees) to large, true trees with well-developed trunks and crowns; from trees down to shrubs, subshrubs, and various grasses. Herbaceous plants are particularly well-adapted to colonizing new ecological niches.
11.6. Plant Strategies
There are various ways plant populations survive within communities and ecosystems, a concept characterized by the term "plant strategies." Based on plant strategy types within communities, L.G. Ramensky in 1938 identified three primary types: violents, patients, and explerents. Violents are "lion" species that thrive in favorable, undisturbed habitats; they are dominants and edifiers of plant communities with broad realized niches that approach the dimensions of their fundamental niches. These are robust plants with well-developed root systems, allowing them to control edaphic and light resources. Violents lack specialized adaptations for surviving adverse conditions and respond to environmental degradation by shrinking in size; they react negatively to disturbances because they lack seed banks or vegetative bud banks. Patients are "camel" species—plants of harsh habitats capable of enduring adverse conditions through specialized physiological and biochemical survival mechanisms.
stress tolerance. Explerents, or wanderer species («jackals»), exhibit high seed productivity, largely enhanced by intensive vegetative reproduction. As a rule, these are plants with a shortened life cycle. Explerents possess weak competitive ability, inhabit disturbed habitats, and form the earliest stages of autogenic successions.
In 1979, J. Grime, unaware of Ramensky's earlier work, redescribed these exact Three types of strategies under the names of competitors (C-strategists), stress-tolerators (S-strategists), and ruderals (R-strategists). J. Grime identified three primary types of strategies, noting the existence of secondary strategy types, which makes the classification of plants rather conditional. Currently, the Ramensky-Grime strategy types represent one of the most popular frameworks for plant strategies.
There is another system of plant strategies based on the ratio of energy allocated to reproductive effort versus the Maintenance of the vegetative state, known as the McLeod-Pianka strategy types. McLeod was the first scientist to address the existence of plant strategy types back in 1884, distinguishing the categories of «proletarians» and «capitalists». English researcher E. Pianka in 1970 practically rediscovered McLeod's strategy types by developing THE CONCEPT OF two polar types, K and r, which are differentiated by the proportion of life energy used for reproduction. In the first case (K), the plant's primary life energy is directed toward maintaining vegetative activity (growth and sustaining the organism in its adult state), whereas in the second case (r), a large amount of energy is used for reproduction, for the «production» of numerous offspring scattered at random, allowing the species to survive through a powerful «seed bank».
The most common higher aquatic plants in Ukraine can be classified into the following types:
K-strategists (violents) — common reed, broadleaf cattail, yellow water-lily, shining pondweed, and floating pondweed;
S-strategists (patients) — lesser duckweed, white water-lily, lakeshore bulrush;
R-strategists (explerents) — curled pondweed, multi-root duckweed, water plantain.
Many species are transitional between two or even three strategic types. For example, rigid hornwort and spiked water-milfoil are S-R-strategists, while perfoliate pondweed falls into the mixed KRS group.
11.7. Plants as Indicators of Natural Environment Changes
The complex of environmental factors in a habitat strictly determines which organisms can live in a given place and which cannot. By applying this principle in reverse, one can draw Conclusions about a habitat based on the organisms living within it. The scientific field of assessing environmental habitat factors using living organisms, their populations, and communities is called bioindication. Those living organisms whose vital functions correlate so closely with specific environmental factors that they can be used for their assessment are called bioindicators. The expanded concept of a bioindicator includes not only biological systems proper, but also their structures (species populations, communities) and traits whose functions correlate with specific environmental factors.
Bioindication Methods are widely used to assess anthropogenic impacts on nature. The environmental factor itself can only be judged indirectly through bioindication results. When assessing environmental pollution, it complements traditional physicochemical studies by analyzing the biological consequences of anthropogenic factors.
Due to the biological characteristics of plants, phytoindication is distinguished as a major, separate branch of bioindication. PLANTS AND THEIR communities are used to assess various factors of anthropogenic impact: disturbance of natural landscapes, air pollution by gaseous substances (lichens, certain conifer species), aquatic environment pollution by industrial and municipal wastewater, and others. There are significant methodological differences in using higher and lower plants of various taxonomic positions as phytoindicators.
The quality or degree of water pollution based on aquatic plant composition is assessed in two ways: 1) using indicator organisms; 2) by comparing community structures in areas with varying degrees of pollution against a control site. In the first approach, the presence, absence, or relative Abundance of indicator species or groups—evaluated using pre-established systems of indicator organisms—is used to classify a water body or its specific section into a particular water quality Class. In the second approach, conclusions are drawn by comparing the composition of aquatic vegetation across different parts of a water body subject to varying levels of pollution.
For instance, in the aquatic phytocenoses of the Ustia River—which flows through the city of Rivne and receives municipal wastewater from the regional center—the number of submerged plant species varies significantly across different sections (ranging from 10–12 species in relatively clean water areas down to 1–2 in polluted ones). Among the species identified in the river, Eurasian water-milfoil, white water-lily, ivy-leaved duckweed, and shining pondweed proved to be the most sensitive to pollution. Their presence or absence serves as a reliable indicator of river water quality. Overall, submerged plants, having maximum contact with the aqueous medium, are considered the most sensitive to water pollution, whereas helophytes—emergent coastal plants—are the most resistant.
The degree of organic pollution in water bodies determines their saprobity (from *sapros*, meaning rotten), and the branch of hydroecology that studies such pollution is known as saprobiology.
The species structure of hydrobiont communities, depending on their sensitivity to organic water pollution, is clearly expressed at the biocenotic level. Therefore, in 1908, German researchers R. Kolkwitz and M. Marsson concluded that the decomposition of organic matter present in wastewater occurs in a stepwise manner. Consequently, water bodies or their zones are classified into poly-, meso-, and oligosaprobic According to the degree of organic pollution.
In the polysaprobic zone, located close to the wastewater discharge point, the Breakdown of Proteins and carbohydrates occurs under anaerobic conditions. This zone is characterized by an almost complete absence of free oxygen, the presence of undecomposed proteins, significant concentrations of hydrogen sulfide and carbon dioxide, and a reducing nature of biochemical processes. The number of algal species capable of thriving in this zone is relatively small, but they occur in massive quantities.
In the mesosaprobic zone, pollution is less pronounced: undecomposed proteins are absent, hydrogen sulfide and carbon dioxide are present in small amounts, and oxygen is available in noticeable quantities, although the water still contains ammonia, Amino Acids, and amides. The mesosaprobic zone is subdivided into alpha- and beta-mesosaprobic subzones. The former contains ammonia, amino acids, and amides, yet dissolved oxygen is already present. This subzone is inhabited by blue-green algae of the genera Oscillatoria and Phormidium. The Mineralization of organic mat-
ter proceeds primarily via aerobic oxidation, particularly driven by bacteria. The subsequent mesosaprobic subzone is characterized by the presence of ammonia and its oxidation products—nitric and nitrous acids. Amino acids are absent, hydrogen sulfide is found in negligible amounts, dissolved oxygen is abundant, and mineralization occurs through the Complete oxidation of organic matter. Algal species diversity is higher here than in the preceding subzone, whereas organism abundance and biomass are lower. The most characteristic taxa for this subzone include diatoms of the genera Melosira, Diatoma, and Navicula, as well as green algae from the genera Cosmarium, Spirogyra, Cladophora, and Scenedesmus.
In the oligosaprobic zone, hydrogen sulfide is absent, carbon dioxide levels are low, oxygen concentrations approach normal saturation, and dissolved organic matter is virtually non-existent. This zone is characterized by high algal species diversity, though their individual abundance and biomass remain insignificant.
According to the Czech scientist V. Sládeček, who compiled a checklist of higher aquatic plants within the saprobic system in 1973, vascular macrophytes develop predominantly in the oligosaprobic and beta-mesosaprobic zones.
The Use of algae as indicator organisms in geology and legal practice relies on the presence among them of A large number of stenotopic species, which require a specific combination of environmental conditions unique to a particular biotop, outside of which they cannot survive. In contrast, widely distributed eurytopic species, capable of living in diverse biotopes, are unsuitable as indicator organisms. Furthermore, the application of algae as indicators in geology is facilitated by their ancient evolutionary origin and the ability of certain forms to be preserved in the fossil record.
11.8. Higher Aquatic Plants in Ornamental Aquaculture
The Significance of higher aquatic plants in ornamental aquaculture is often just as crucial as that of fish and other aquatic animals. This is because, alongside macrophytes' involvement in the transformation of organic compounds and the oxygenation of water, higher aquatic plants play an invaluable aesthetic role in aquaculture. It is precisely through plants functioning as decorative elements that any aquarium achieves an aesthetic and appealing appearance. For certain fish species, plants in a spawning aquarium
serve as a spawning substrate or nest-building material, while various ornamental aquaculture organisms (such as fish fry, small fish, and crustaceans) find shelter within the dense plant thickets.
The Significance of the decorative component of aquarium plants is confirmed by popular trends in fishkeeping that focus primarily on creating a harmonious composition of aquatic plants and modeling specific natural biotopes of individual macrophyte groups. In such areas, other decorative aquaculture objects become secondary and are treated as complementary Components of the aquarium biotope.
Tropical plants are predominantly used in decorative aquaculture. These amphibious and true aquatic plants are best suited for cultivation and propagation because most of them exhibit steady year-round growth with no dormancy periods. The range of decorative aquatic plants is constantly expanding due to the introduction and acclimatization of new species, as well as the breeding efforts of aquarists. Some of these plants are quite undemanding in cultivation, requiring little effort to grow and propagate, while others are extremely challenging to cultivate in decorative aquaculture. The main environmental factors to consider when growing plants in decorative aquaculture include lighting, the physical and Chemical properties of the water, and the species composition of hydrobionts. Thus, decorative plants have specific maintenance requirements: bright or moderate lighting, temperatures within 20–30°C, water quality close to that of the natural water body where the species originates, and the absence of active pests such as herbivorous fish and other animals that damage or uproot plants. Accordingly, the Main criteria for selecting plants for a decorative aquarium are their ability to adapt to the conditions of an artificial water body (the aquarium), an attractive appearance, and dimensions proportional to the size of the aquarium itself.
Creating an aquascape using higher plants requires a thorough understanding of their biology, growth and propagation characteristics, and requirements for basic maintenance conditions. Plant arrangements can be based on the aquarist's personal preferences or the species composition of a specific natural biotope being modeled in the aquarium, but the Selection must take into account the feasibility of keeping them together in a limited volume under defined parameters
of the environment. For instance, co-cultivating plants that require relatively low water temperatures (20–25°C) with comparatively thermophilic plants that thrive at 26–30°C in the same aquarium is only possible by reaching a certain compromise. The best approach is to select species with similar temperature requirements. Even more critical parameters of the aquatic environment for aquatic plants are pH levels and total water hardness. Keeping plant species together that are naturally adapted to diametrically opposed parameters is quite problematic. At the same time, decorative aquaculture allows for the effective maintenance of plants that require varying light intensities or current speeds. In such cases, shade-loving plants are planted in dimly lit areas of the aquarium (the side and rear walls) or in the shadow of tall, robust plants that require bright illumination. Since areas of relatively strong water Circulation can be created in the aquarium using aeration or filtration equipment, a similar approach can be taken when arranging plants with different water flow requirements.
Aquatic plants grown in decorative aquaculture are divided into the following groups: floating on the water surface (unrooted, with emergent or submerged leaves), short-stemmed (mostly rooted, aquatic or amphibious), and long-stemmed (mostly unrooted, amphibious, more rarely aquatic).
True aquatic plants, which are capable of developing exclusively in an aquatic environment, comprise a relatively small group of species. The most widespread are Representatives of the families Hydrocharitaceae (genera Egeria, Elodea, Hydrilla, Hydrocharis, Lagarosiphon, Limnobium, Blyxa, Ottelia, and Vallisneria), Nymphaeaceae, Aponogetonaceae, Potamogetonaceae, Ceratophyllaceae, Haloragaceae (Myriophyllum), and Amaryllidaceae (Crinum).
The majority of aquarium plants consist of bog (amphibious) plants that grow both in water and above it in natural conditions (different ecophases). Depending on seasonal water level fluctuations, these plants adapt by forming leaf blades of a different shape than those in the submerged ecophase. The growth rates of plants in a terrestrial environment usually significantly exceed the speed
of growth in water; therefore, the decorative aquaculture market is dominated by plants grown in humid greenhouses. At the same time, the assortment of decorative plants is constantly replenished with new species from natural tropical and subtropical water bodies. Among the fast-growing plants of this group are representatives of the families Amaranthaceae (Alternanthera), Boraginaceae (Bacopa, Hemianthus), Acanthaceae (Hygrophila), Onagraceae (Ludwigia), Campanulaceae / Lobelioideae (Lobelia), and Lythraceae (Rotala, Ammannia, Nesaea). These plants belong to long-stemmed, unrooted species.
Short-stemmed bog plants also feature fairly high growth rates compared to true aquatic macrophytes. The most common genera in aquariums are Echinodorus, Cryptocoryne, and Anubias, alongside aquatic ferns and mosses, which occupy a distinct niche in aquariums.
Among the various native distribution ranges of decorative plants, some are particularly striking or characteristic of a specific taxonomic group. These very biotopes are most frequently modeled in decorative aquariums—simulations of coastal areas of natural water bodies. Let us examine some of them.
1. The Río Guaporé River (Brazil). The forests surrounding it remain untouched by the negative impacts of civilization to this day. The substrate in many coastal areas consists of fine white sand, with the greatest diversity of plants observed in silted areas with a slow current. Large species of Echinodorus (Echinodorus paniculatus, E. grandiflorus) are widespread along the banks, as well as low-growing species that are better suited for aquarium cultivation but require fairly bright lighting (Echinodorus tenellus, E. bolivianus). Amphibious Ludwigia (Ludwigia sedoides) are also common in periodically flooded areas near the shoreline. Among true aquatic plants, the most characteristic of the transparent shallows of this biotope are Cabomba (Cabomba furkata), Limnophila (Limnophila indica), and Eichhornia (Eichhornia diversifolia, E. azurea, E. crassipes). Ottelia (Ottelia brasiliensis) is found in relatively deep areas (up to 2 m). Floating plants are mainly represented by Limnobium and Salvinia.
2. The floodplain Regions of the Río Sipapo (Venezuela). The waters of this river
are characterized by high turbidity. Heavy loams with a high iron content predominate among the substrates. Bacopa, Tonina, and Eichhornia (Eichhornia diversifolia) are most common in coastal areas. As in other South American water bodies, Echinodorus species are widespread here, with some growing in periodically flooded areas, others in a semi-submerged state, and a much smaller number of species growing fully submerged.
3. The rivers of the Uruguay River basin (Argentina). The greatest diversity and abundance are observed in areas with clayey soils and depths of up to 2 m. Numerous species of Cabomba, Myriophyllum, and Ludwigia dominate the shores under weak currents. Hygrophila and Eichhornia azurea are characteristic of areas with fast currents. Nymphoides colonize relatively deep areas. The relatively transparent water of such rivers and streams Supports the growth of Eleocharis, Myriophyllum, and Egeria.
4. Rivers and standing water bodies of Central Africa. The chief ornament of decorative aquariums originating from these waters is plants of the genus Anubias. Most species are bog plants that grow on the surface or in a semi-submerged state, while some are capable of developing underwater without emerging onto land. Lighting conditions vary greatly across different locations, so most Anubias are well adapted to shade while also growing well under bright light. Ferns, Ammannia, and Crinum are also found in these water bodies and coastal strips.
5. East African tectonic lakes: Lake Malawi and Lake Tanganyika. Aquatic plant biotopes are located in the reed zone and the littoral zone (areas with minimal water fluctuations). Spiral eelgrass (Vallisneria spiralis), coontail (Ceratophyllum demersum), Myriophyllum, and pondweeds are characteristic of these waters at depths of 0.5–4 m. Hydrilla (Hydrilla verticillata) and naiads (Najas horrida, N. marina) are relatively rare in water bodies of this type.
6. The river biotope of Madagascar. Sandy soils with significant clay inclusions give the rivers and other water bodies of this island a characteristic clay-turbid coloration. The most striking representatives of the island's aquatic flora are Aponogeton. Species growing in temporary, frequently drying water bodies or those developing in fast-flowing streams are rarely cultivated in aquariums due to their pronounced dormancy periods. Such plants occasionally find their way from natural biotopes into the pet store network. The centerpiece of an artificially created biotope (aquarium) of this type is the Madagascar lace plant (Aponogeton madagascariensis), which is one of the most popular plants in aquarium keeping.
7. The stream biotope of South Asia. Small water bodies in this region, the water of which is predominantly weakly acidic and has a low calcium and magnesium salt content, serve as the natural habitat for representatives of the genus Cryptocoryne—popular and widely distributed aquarium plants. Like most tropical amphibious plants, Cryptocorynes are found submerged, on the banks near water bodies, or in flooded areas. Clay soils with high iron content predominate in such places, with some areas consisting of silt deposits. The physicochemical composition of water in these streams changes very little throughout the year, which gives rise to certain Biological features of Cryptocorynes: under decorative aquaculture conditions, unfavorable circumstances or significant fluctuations in water parameters can trigger a rather unpleasant phenomenon known as "Cryptocoryne rot" (cryptocoryne disease). Hygrophila, ferns, mosses, and water lilies also grow in the water bodies of South Asia.
Lately, the propagation and cultivation of higher aquatic plants in artificial conditions (greenhouses, pools) for decorative aquaculture needs has increasingly surpassed harvesting them from their natural habitats. Thus, it can be argued that modern fishkeeping, in addition to its primary purpose, holds the prospect of contributing to the conservation of species diversity in natural water bodies subjected to anthropogenic impact. Another achievement of decorative aquaculture is the breeding of new plant species and varieties that do not exist in the wild but have long won popularity in aquariums.
11.9. Basics of Phytocenology
The concept of phytocenology. A collection of organisms interconnected and mutually conditioned by a general exchange of matter and energy is called a biocenosis. Plants inhabiting a biocenosis form a phytocenosis, animals form a zoocenosis, and microorganisms form a microbocenosis.
A phytocenosis, or plant community, is a collection of plant organisms in a relatively homogeneous area that interact with each other, with animals, and with the environment. Combinations resulting from the cohabitation of numerous species of higher and lower plants frequently occur. A phytocenosis is the fundamental unit of vegetation. Every phytocenosis is characterized by a specific species composition. The MORPHOLOGICAL STRUCTURE OF a phytocenosis is determined by the spatial distribution of the plants.
A phytocenosis is a dynamic system characterized by seasonal and multi-annual variability of its components under the influence of ecological conditions.
The science that studies plant communities (phytocenoses) is phytocenology. It is a branch of geobotany and biogeocenology (many botanists treat phytocenology as synonymous with geobotany).
A mature plant community is characterized by a specific floristic composition, structure, coenotic relationships, and the ecological plasticity of its components. Consequently, a phytocenosis also features distinct stratification, coverage, abundance, vitality, physiognomy, periodicity, species constancy, and so forth.
The components of a phytocoenosis differ in their level of participation within the community, primarily regarding phytomass production and projective cover. Dominants are the prevailing species that, owing to optimal conditions, develop intensively and occupy a leading position in the community in terms of both individual count and phytomass. Their number varies and depends on the STRUCTURE OF THE coenoses, their floristic composition, and age. In the vertical profile of aquatic plant communities, dominants of the emergent, floating-leaf, and submerged tiers are distinguished. Such plant communities are termed polydominant. Communities where individual species account for 80–90% are called monodominant, while those with two co-prevailing species are termed bidominant.
In coenoses of emergent and aquatic-shore plants, narrowleaf cattail (Typha angustifolia), broadleaf cattail (Typha latifolia), and common reed (Phragmites australis) typically dominate, defining the overall physiognomy of the watercourse.
Plant species that play an important role in the community's composition—though less substantial than that of the dominants in the same tier—are called co-dominants. For instance, in stagnant or slow-flowing water bodies of Ukrainian Polissia, within communities of small free-floating plants, duckweed (Lemna minor) is the dominant, while greater duckweed (Spirodela polyrhiza) acts as the co-dominant.
Based on their impact on the phytocoenotic environment, a distinction is made between edificators—species that control the relational regime of the community and shape it (they may, but do not necessarily have to, dominate in the community)—and companion species (asectators), which have little influence on microenvironment creation within the community. For example, sedge acts as an edificator in sedge-forb communities. Bittersweet nightshade (Solanum dulcamara) or marsh forget-me-not (Myosotis scorpioides) can serve as asectators in littoral helophyte phytocoenoses.
Aquatic phytocoenoses predominantly consist of a small number of species, especially in water bodies with low water transparency. Frequently, they comprise just a single species or feature very minor participation from others. These are pure or nearly pure single-tiered phytocoenoses of a single species (such as stands of common reed or narrowleaf cattail).
Species-poor, simplified communities are quite widespread among all groups of aquatic plants, and in water bodies with low water transparency, they predominate over more complexly organized communities. In water bodies with high transparency, alongside single-species single-tiered coenoses, one encounters coenoses with one or several dominant species accompanied by a large number of associated species segregated into multiple tiers.
A synusia is an ecologically and spatially segregated part of a plant community (phytocoenosis). It consists of plants belonging to one or several ecologically similar life forms; sometimes, a synusia may be formed by a single population.
Vertical structure of phytocoenoses. The vertical differentiation of a plant community resulting from plant life forms contrasting in height is termed stratification, and the ecologically segregated structural parts are called tiers.
Stratification is a characteristic feature of a plant community. Under unfavorable environmental conditions, single-tiered communities develop, whereas optimal conditions foster multi-tiered ones.
In the vertical differentiation of aquatic plant communities, three main tiers are distinguished:
- the emergent tier, with sub-tiers (or strata) according to height: tall, medium, and low emergent plants;
- the floating tier, comprising free-floating and rooted plants with floating leaves;
- the submerged tier, with sub-tiers (or strata) according to height: tall, se
rodniakh and small bottom-dwelling plants (grasses).
The distribution of plants across tiers is determined by their environmental demands. Species with similar requirements regarding light conditions, mineral nutrition, and other factors grow in the same tier; in other words, these species are ecologically equivalent.
Plant community stratification is of great biological significance. Thanks to it, species with diverse ecological requirements can settle and coexist within a limited area, giving rise to stable phytocoenoses characterized by high productivity.
Abundance. A characteristic feature of a plant community is the abundance of a species—the quantitative participation of its individuals in The formation of the coenosis. It depends on the biological Properties of the species, habitat conditions, and phytocoenotic traits, and can be expressed by the number of individuals per unit area, the mass of organic matter, the area of dispersal, and other metrics.
The abundance of a species depends on the intensity of its life processes and its ability to develop photosynthetic and absorptive surfaces. As a result, they easily compete with other plants for light, water, and mineral nutrients, achieving significant development.
Species abundance is promoted by seed and vegetative reproduction. The flora of water bodies is typically dominated by perennial plants with robust rhizomes capable of intensive vegetative reproduction, which outcompete other plants. An example is Canadian waterweed (Elodea canadensis), which earned the moniker "water pest" due to its rapid vegetative reproduction.
Phytocoenotic properties of species also determine their abundance within the community, which is brilliantly illustrated by the interrelationships between species of different tiers. Tall and dense stands of emergent aquatic plants significantly influence the development of submerged plants through light competition, regeneration energy, and species vitality. Higher aquatic plants, as a result of water saturation with physiological secretions and other competitive traits, suppress algal development.
Cover. This reflects the geometric structure of a phytocoenosis. It is a characteristic feature of the phytocoenosis, reflecting plants' struggle for space and the rational Utilization of Light, moisture, heat, and mineral nutrition. Species that reach the upper tiers and develop a vast aerial nutrition surface synthesize more organic matter and energy than those growing beneath them. They at
tain high abundance and play a crucial role in community structure and the nutrient cycle. The heterogeneity of cover is associated with the tiered distribution of community species and seasonal climatic shifts.
Cover is a spatially expressed value of the horizontal PROJECTION OF THE aboveground plant organs onto the land surface they occupy. A distinction is made between projective and true cover. Projective cover is the proportion of a species' cover relative to the total cover of the community. Cover is most frequently expressed as a percentage. True cover is formed by the bases of plant stems (for instance, after mowing a grass stand). True cover will always be less than projective cover.
Vitality (vigor) is the level of a plant's physiological state that ensures the realization of its genetically encoded GROWTH AND DEVELOPMENT program. This is one of the characteristic features indicating THE ECOLOGICAL AND phytocoenotic adaptation of its components to life within a plant community. A 5-point scale is frequently used to denote species vitality:
5 - the species finds optimal conditions within the plant community, exhibits luxuriant development, and shows enhanced fruiting and flowering;
4 — this species has everything necessary for development and completes the cycle with fructification and active seed shedding;
3 — the species shows good vegetative development, but does not complete its full life cycle (fails to reach its typical size and does not produce seeds);
2 — the species develops normally at first with vigorous vegetative growth, but does not fruit;
1 — the species exhibits poor vegetative growth from the very beginning, does not fruit, and is severely suppressed.
The vitality of a species within a phytocenosis is determined by its competitive ability, resistance to diseases and pests, capacity for symbiosis with other organisms, and adaptation to fluctuating conditions of air-soil and water-mineral nutrition.
The periodicity of plant development in a phytocenosis is manifested through changes in its aspects.
Aspect — the external appearance of a phytocenosis, its physiognomy during a specific period of its development.
The aspect is determined by the appearance of all species inhabiting the community. It is frequently defined by the participation of a species and the developmental stage
of its vegetative and Generative organs. The physiognomy of many aquatic plant communities in lakes and reservoirs is determined by the vegetation and flowering of water lilies (yellow water-lily and white water-lily), the fruiting of cattails, etc.
Physiognomy possesses a certain dynamism — in the temperate zone, it changes several times throughout the growing season (seasonal aspect).
Chronological aspectness is driven not only by biological properties (fruiting and flowering periods), but also by ecological conditions. For instance, the appearance, flowering, or fruiting of individual species on sandy shoals of the Dnipro River are determined by the time they emerge from under water and the onset of optimal soil-air conditions.
Species constancy. This characteristic feature of vegetation is determined by the degree of a species' distribution across various sites of a given phytocenosis.
Thus, in a submerged plant community dominated by clasping-leaf pondweed, the latter species is found in all 20 studied sites of the community, sago pondweed in 10, rigid hornwort in 7, and Eurasian water-milfoil in 2 sites. Consequently, the constancy of these species in the phytocenosis varies: expressed in percentages, it is 100% for clasping-leaf pondweed, 50% for sago pondweed, 35% for hornwort, and 10% for water-milfoil.
Plant species found in the majority (over 50%) of the investigated sites of a given phytocenosis are called constant species. Species occurring in 25% of the studied sites are referred to as accessory species, while those with a constancy of less than 25% are considered accidental. In detailed vegetation studies, the number of investigated sites should be at least 20 units for each phytocenosis.
Species distribution. Within a phytocenosis, species are distributed in various ways. Most individuals of one species are more or less evenly spread across the entire area, those of another form clustered patches, and those of a third occur in groups or patches. This trait is governed by the biological CHARACTERISTICS OF THE species and the nature of its habitat conditions.
Control Questions and Assignments
1. How do habitat conditions affect the plant organism?
2. How are ecological factors classified, and what is their role in plant development?
3. What ecological groups of plants exist with respect to light, water, and temperature?
4. What adaptations do plants develop in relation to an aquatic environment?
5. How does The chemical composition of water affect plants?
6. What is the ecological significance of biotic factors for plants?
7. How does human activity impact aquatic plants?
8. Which algae serve as indicators of different saprobic zones?
9. What are plant strategies?
10. What types of aquatic plant strategies are distinguished?
11. What is The Role of aquatic plants in ornamental aquaculture?
12. Which plant species are most commonly used for aquascaping ornamental aquariums?
13. WHAT IS A phytocenosis? Name the characteristics of a phytocenosis.
14. What are the floristic Composition and Structure of a phytocenosis?
15. What is meant by the vitality of a species?
16. Which species are referred to as dominants, co-dominants, edificators, and asectators?
17. Explain the meaning of the terms: synusiae, abundance, cover, stratification (layering), and aspect.
Last update: 07/08/2026
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