Life Forms of Plants Based on Climate: Predation, Parasitism Allelopathy, Symbiosis, and Commensalism
Introduction
Raunkiaer (1934), a Danish ecologist, established a classification system for living forms based on plants’ ability to survive the coldest season. Plant morphology and life history are connected to climate by the life form system. The categories are determined by where on the bud, under ideal conditions, the growing sprouts. The categories include
Therophytes: Therophytes are annual plants that reproduce by producing seeds and surviving cold temperatures or dry seasons. These plants are often far more tolerant of temperature stress than developing plants.
Hydrophytes: Water plants with roots whose buds are protected from the cold during the winter, such as water lilies.
Geophytes: Because the buds are buried in the ground, they are highly insulated. Plants having underground stems, such as bulbous plants like tulips, fall under this group.
Hemicryptophytes: Biennials and perennial grasses, for example, act as insulation for buds that are close to the ground’s surface.
Chamaephytes: Buds of chamaephytes are just a few centimeters above the ground. With certain plants, such as trailing and creeping shrubs and succulents, the buds may occasionally be protected from severe winds by snow cover.
Phanerophytes: Mainly trees and shrubs with buds on shoots that are more than 25 to 50 cm above the ground. Lanais are phanerophytes as well.
An area’s biological diversity can be represented by the relative abundance of various living types there. Therophytes are abundant in desert areas. While hemiocrytophytes predominate in grasslands, chamaephyes are more common in arctic and mountainous regions. Tropical rainforests are dominated by phanerophytes.
Ecological Responses to Biotic Elements
Natural communities of creatures can have an impact on how other species in the group function. These interactions might result in odd ecological and physiological impacts, which would have a significant evolutionary impact. A complicated interaction between competing plants, fungus, and other microorganisms for the same resources and co-inhibiting species changing other environmental parameters is what causes the majority of plants’ reactions to environmental stimuli to be complex.
Plants interact not only between members of the same species (intra-specific) but also between members of different species (inter-specific)
The following are some ways that organisms can affect other creatures:
1. Direct control over the flow of resources.
2. Unintended consequences caused by changes to the chemical or physical environment.
3. Dispersal
Organisms can have the following effects on plants:
Competition for resources
Competition is the state in which a resource supply is insufficient to meet the combined needs of two organisms, impairing the performance of either one or both. Competition could be present for nutrients, water, etc. Ecological communities are shaped in large part through competition. The leaf canopy architecture and height, transpiration rates, root morphology and distribution, nutrient uptake capacity and kinetics, and biomass portioning are the characteristics that provide competitive supremacy.
Competitive dominance for PAR is defined by foliage height and the rate at which height is obtained, and it is based on the capacity to position leaves in the light rather than in shaded areas. The most important variables in a competition between annual crops and weeds are seed size, relative growth rate, and elongation rate. Large seeds have larger cotyledons, which creates a positive feedback loop that causes them to absorb more light and develop more quickly. Water flux, plant demand, root density, and diffusion coefficients of the soil-plant system that regulate uptake in the competition are the key characteristics of water and ion uptake. When competing for the use of a resource, survival depends either on dividing the resource to cease competition or on achieving competitive superiority. A population’s density is significantly influenced by intraspecific competition, whereas interspecific competition may result in the extinction of one or both species.
Predation and Parasitism
In addition to herds of grazing mammals that destroy the plants, there are a hundred thousand species of phytophagous insects and several thousand species of parasitic fungus. Through the following mechanisms, plants deter prospective diseases and herbivores from causing excessive harm.
1. Nutritional Deficiencies: The majority of plants have relatively low protein content, which ranges from 1% in wood to over 30% in many seeds. Herbivorous insects specialize in feeding on more nutrient-dense portions. Tryptophan and methionine levels, as well as the amounts of numerous plant proteins and even sodium, are additional nutritional considerations. The quantity of food is not as important to herbivores as its quality. High-quality fodder rich in N is necessary to disintegrate the plant cellulose and transform it into animal meat.
2. Physical Barriers: A lot of plant organs contain scales, hairs, or glandular structures as their external coverings. Predators have difficulty penetrating plant tissues because of strong cuticles, thick epidermal cell walls, bands of collenchyma or sclerenchyma, or deposits of materials like silica (in grasses) or resins (in conifers). Many seeds have stiff, thick seed coverings that protect them from creatures that consume seeds.
3. Toxins: Either naturally occurring or brought on by an attack, toxins are the most striking chemical defenses. Alkaloids, tannins, cyanogens, and a variety of phenolic compounds are some of these substances. Chemicals make food difficult to digest, unpleasant to taste, or even toxic.
Based on the type of material eliminated, there are two different families of creatures that feed on plants.
Tissue feeders are creatures that remove whole cells to extract vital chemicals. Others, known as metabolic feeders, such as leaf-mining beetles and stem mining beetles, specifically remove the contents of the cells. Metabolite feeders feed on the contents of xylem, phloem, parenchymatous or other cells through systemic infection or mechanical insertion of a probe to remove material. Metabolic feeders rarely cause significant harm to plants, but tissue feeders, particularly leaf feeders, can eat away a significant section of the assimilative tissue, often resulting in complete defoliation. Mammals, mollusks, and insects are all possible tissue feeders. Tissue feeders can bite or tear their mouth parts, but they manage cellulose-based diets more discreetly.
Herbivores that prey on plants cause defoliation and consume fruits and seeds. Plant tissue is damaged during defoliation. The plant may regrow if the grazing stops, but it may also be killed if it continues. Grazing lowers a plant’s biomass, fitness, and competitiveness within the community. The grazing of photosynthetic tissues or pathogen damage severely reduces productivity. Plants make up for loss physiologically by increasing the rate of photosynthetic activity in the remaining leaves or morphologically by producing new leaves. New leaves get their carbon from the roots. The breakdown of protein and other non-storage substrates occurs if the plants are substantially injured and there are insufficient reserves or enough remaining leaf area to resynthesize carbs. The loss of meristems is the morphological issue with regeneration. Grass has a continually active basal meristem, which may develop new tissue from the base, whereas a dicot leaf cannot replace the lost tissues. Due to this, grasses produce excellent lawns. Predation on seeds has several effects. Predation slows plant growth on the one hand, but if seed ingestion serves as a means of seed dissemination, it may also be useful.
The majority of parasites are bacteria. When a parasitic fungal infection affects the entire body, cells near the infection site frequently die as a result of the hypersensitivity phenomenon. In the dying cells, phytoalexins—chemicals that can prevent the growth of fungi—accumulate. In reaction to a known attack, phytoalexins are a type of inducible chemical defence.
When an organism is parasitic, it either inhabits or feeds on another one, or briefly interacts with it during its life cycle. Host plants can be either hemiparasite, which performs photosynthesis at a decreased rate but still receive a portion of the reduced carbon from the host, or holoparasites, which are unable to produce photosynthesis and obtain all of their reduced carbon from the host. The hemiparasite Aceuthobium sp. and the holoparasite Cuscuta sp. both infect vascular plants as parasites. The adventitious roots of parasites that penetrate the conducting parts of the host stem through haustoria enable the growth of the parasites on other plants. Higher plants’ roots contain full-blown root parasites such as Orabanche, Epifagus, and others. The partial root parasite is the santalum album. There are around 4000 parasitic angiosperms, which are divided into 22 families. Epifagus virginiana on Figus grandifolia is an example of a specialist parasite that only attaches to one host species, while Cuscuta sp. is an example of a generalist parasite that can attach to a variety of hosts. Through a secondary organism, typically mycorrhizae, epiparasites are linked to their host.
Allelopathy
When a plant produces chemicals that are harmful to another plant, this is known as allelopathy. Simple organic acids, polyacetylenes, unsaturated lactones, tannins, flavonoids, derivatives of cinnamic acid, steroids, terpenoids, amino acids, glucosides, and other substances might be considered allelopathic compounds.
The following procedures cause the release of these chemicals:
Withering: Allelopathic substances are emitted as a result of plant material decomposing during withering.
Exudation: Plants exude these substances from their underground organs.
Production: Toxic substances that are released into the atmosphere prevent other plants from budding, expanding, or establishing themselves.
Allelopathic substances can drain from both living and dead plant cells. Allelopathic substances work by obstructing cell division and membrane function, which prevents nutrients from being absorbed. It has been discovered that allelopathy is beneficial by deterring predators and pathogens as well as negatively impacting rivals. Allelopathic substances, which have unique effects on their seedlings and function as a sort of intraspecific competition, can also produce autotoxicity. Numerous mechanisms are used to endure allopathy. Plants either avoid the chemical, put up with its toxicity, or work to counteract it. Dormancy, which controls germination at the lowest chemical concentration, enables avoidance. Deep-rooted seedlings avoid toxicity. Toxins are compartmentalized in the apoplast, in non-sensitive cytoplasm, or into vacuoles, and localized in glandular trichomes to develop tolerance to allelochemicals. One component of the cell wall that can include toxins is ferulic acid, which is used to make lignin. Additionally, toxins can be eliminated through excretion or conjugation with carbohydrates and amino acids. Other biotic adaptations have been created to the advantage of the species or of both species. These changes include:
Mutualism: The connection is considered beneficial when there are benefits for both types of organisms. For the survival of the organisms as well as for the benefit of both, close and necessary contact is required in such partnerships. Mutualism could be:
Interaction between pollinators and plants: Pollinators eat plants and assist in plant reproduction in exchange.
Dispersal: Animals help spread the population by consuming the fruits and seeds of plants.
Symbiosis
When two different species work together for their mutual benefit, the relationship is known as a symbiotic association, and the involved species are known as symbionts. Examples of symbiotic relationships include phycobiont and mycobiont affiliations in lichen, rhizobium associations in root nodules, and mycorrhizal relationships in various species. Ectosymbiosis, like the mycorrhizal connection, is when two species live apart from one another. Endosymbiosis, on the other hand, is when one organism lives inside the other, like algal cells within the fungal matrix in lichens and rhizobium bacteria in plant root nodules.
Commensalism
The association is known as commensalism, and the participating species are commensals, when it benefits one species while harming or not benefiting the other. The main example of plants growing on other plants without using any nutrients is epiphytism. Epiphytes grow on plants with unique roots that have velamen to absorb water from the atmosphere in tropical forests. Despite being vascular plants with roots in the ground, lianas rely on huge trees for support to obtain the necessary light to produce food. In woods, these relationships are extremely prevalent. Living roots and leaves of higher plants provide a steady supply of nutrients to soil microbes. This is another illustration of commensalism.