Drought deciduous

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Geoffroea decorticans is both cold and drought deciduous: it loses its leaves in winter as well as during particularly dry summers Geoffroea decorticans0.jpg
Geoffroea decorticans is both cold and drought deciduous: it loses its leaves in winter as well as during particularly dry summers

Drought deciduous, or drought semi-deciduous plants refers to plants that shed their leaves during periods of drought or in the dry season. This phenomenon is a natural process of plants and is caused due to the limitation of water around the environment where the plant is situated. [1] In the spectrum of botany, deciduous is defined as a certain plant species that carry out abscission, the shedding of leaves of a plant or tree either due to age or other factors that causes the plant to regard these leaves as useless or not worth keeping over the course of a year. Deciduous plants can also be categorised differently than their adaptation to drought or dry seasons, which can be temperate deciduous during cold seasons, and in contrast to evergreen plants which do not shed leaves annually, possessing green leaves throughout the year.

Contents

Botany

Ambrosia dumosa a is a type of Drought Deciduous plant among the Microphyllous species. This is an example when the plant is at a transitional state of progressing abscission and preparing to flower. Ambrosia Dumosa.jpg
Ambrosia dumosa a is a type of Drought Deciduous plant among the Microphyllous species. This is an example when the plant is at a transitional state of progressing abscission and preparing to flower.

In botany, deciduous is a description of plants that carry out a process which lead to the loss of leaves during a certain time annually. This process of shedding leaves is known as abscission. [2] Deciduous plants represent a variety of plant species among trees, shrubs and herbs. The causes of this phenomenon can vary depending on where the plant or the whole ecosystem is situated at. The characteristics of season, climate, temperate and rainfall of a certain region are all considered as factors that may have influenced the plants to be deciduous or influencing plants to have evolved as deciduous plants.

Cold deciduous species include deciduous plant species that will undergo abscission annually or at a seasonal basis. Cold deciduous plant species focus on conserving its nutrient to survive through the extreme conditions in winter. Drought deciduous species, depending on the region it is situated, would undergo abscission not necessarily due to cold weather, they may undergo this process due to shortage of water which may be limited due to relatively low rainfall and summers with a relatively higher temperature or unexpected prolonged season. Conversely, evergreen plant species carry out abscission in a smaller scale continuously in any seasons throughout the year.

Mechanisms that trigger leaf drop is a process which includes physiological and chemical pathways happening within the plants. These include hormonal changes to gradually reduce the use of chlorophyll and generation of certain pigments which is used normally to generate energy via photosynthesis in summer, which gives the autumn colour of the leaves. Carotenoids are the pigmentation that is responsible for the yellow or brown colour of the leaves as they started to lose the presence of chlorophyll. Anthocyanin is another type of pigmentation that is responsible for giving out red or purple colour of leaves. [3] These pigmentations or the colour of leaves are generated by different concentrations of carbohydrate, nitrogen and chlorophyll. [4] In relationship with the discolouring of leaves, deciduous plant species are able to reabsorb nutrients from the leaves as they progress into abscission.

The formation of abscission layer between the stem and the leaf petiole signifies the initiation of abscission. Abscission layer is

Encelia farinosa is a type of Drought Deciduous plant among the Broadleaf species. As indicated in the image, the plant is flowering after abscission as there are no leaves. Grand Canyon Nat. Park - brittlebush (Encelia farinosa) - 32582817617.jpg
Encelia farinosa is a type of Drought Deciduous plant among the Broadleaf species. As indicated in the image, the plant is flowering after abscission as there are no leaves.

the region of separation between the leaves and the plant or the lamina and leaf base depending on plant species, which is referred collaboratively as the abscission zone. Within the abscission zones the types of cells are the same as the other parts of the plant, but with slight difference in abundance or quality.  Sclerenchyma cells appears to be less abundant or weakly developed, Parenchyma cells are thin walled and compactly set with no intracellular spaces and there will be no presence of Collenchyma cells. This combination of cells makes the abscission zone particularly sensitive to the plant hormone known as auxin. [5] Under normal condition, the flow of auxin remain consistent throughout the structures of the plant. When the plant is under stress, either due to climate or environmental factors, the auxin flow will be disrupted or stopped affecting the auxin levels reaching the abscission layer of leaves triggering the elongation of the plant cells within the zone. Subsequently, the abscission zone will break allowing the leave to set apart from the plant.

Function

Deciduous plant will undergo the process of abscission either seasonally or due to external stress caused by the environment. By doing so, there are both advantages and disadvantages for the plant to lose its leaves rather than solely conserving nutrients and water. Many deciduous plant species make use of their leafless period efficiently by triggering reproductive processes such as flowering. Abscission allows the plant to perform dissemination of reproductive bodies, which includes seeds, fruits and pollens, [6] some deciduous plant species prefer to flower after undergoing abscission. This allows the plant to take greater advantage in reproductive perspective as the plant takes much less energy to maintain itself and survive without the presence of leaves, the plant can utilise wind transmission of pollens effectively. [7] Without the presence of leaves also allows the plant to utilise wind transmission of pollen more effectively or increasing the visibility of flowers allowing insects to spot and access to flowers easier thus pollinating plants. [8]

Due to the natural structure of deciduous plant species, it has a higher tolerance to environmental stress factors which may cause damages such as branch and trunk breakage when compared to evergreen species.  Abscission can also be noted as self-pruning of the plant, [6] as the plant will shed leaves along with branches, flowered parts, fruits and injured parts. It is an excretory function of the plants as it removes waste materials that it accumulated throughout the year. Self-pruning also serves the original purpose of deciduous plant which is to remove excessive parts deemed unnecessary by the plant that might be competitive for water and nutrients. Without the presence of leaves can reduce the excessive energy required to repair damages of leaves to keep them functional which can be caused by predation from insects or other physical factors. As deciduous plant species would commit to full abscission to survive environmental stress, they must expend the extra energy that evergreen species will never need to in order to regrow a full new foliage when the harsh environmental condition resile or approaching to the next growing season.

Strategies in drought

Evergreen species are the opposite of deciduous species, evergreens possess a substantial amount of leaves throughout the year. [9] One of the most differentiating characteristics of these plants is featuring roots that penetrate much deeper into the ground [10] allowing evergreens to gain access to water source from underground and survive through a dry season. [11] Plant species that possess features that appear to be in between of evergreens and deciduous can be categorised as semi-deciduous, semi-evergreen depending on their annual abscission and flowering patterns. Deciduous species possess roots that penetrate much shallower into the ground when compared to evergreens, therefore when a deciduous plant is put under stress or whenever the access to nutrient and water is limited due to external factors such as normal seasonal climate change and drought. [12]

Deciduous plants will carry out abscission in the whole plant completely, which allows the plant to conserve its nutrient and energy to survive. [13] Deciduous plants have a higher photochemical efficiency when compared to evergreen species during times when it has leaves during spring and summer. [14] This allows it to take excessive energy and nutrients for storage and is the main strategy on surviving through days without the aid of chlorophyll and leaves in generating energy.

Apart from the prevention of water and nutrient loss, drought deciduous plant species can remove nutrients from leaves that are about to shed and store them as proteins in the other part of the plant. [13] It can shed their leaves drought-deciduous species can adjust to only discharge nutrient after drought relief for canopy reconstruction and leave growth. Deciduous plant species can resorb Nitrogen, Phosphorus and Potassium which are the fundamental elements required by plants. This can additionally prevent significant impacts due to nutrient losses caused by leaf abscission. During the period after abscission had occurred, reserves of twig nitrogen in drought-deciduous species change accordingly with season or external stress, whereas evergreen species had a constant twig nitrogen level throughout the year. [15]

Ecosystems

In botany, plant and leaf phenology from ecosystems that are situated in high latitudes can be predicted based on seasonal cycle, where four seasons are highly distinctive. Ecosystems that are considered semi-arid and savanna-type (SAST) are less consistent and the range in both climate and plant species within these ecosystems vary significantly. [16] Drought deciduous plants species are often found in SAST ecosystems as they have higher tolerance to unpredicted external stress factors. These plant species are also very common in areas that have relatively dry seasons especially ecosystems that situates at the edges of deserts.

Regions

Drought deciduous plant species can be found in the most part of Europe, the eastern part of North and South America, Southern part of Africa and Southern and Eastern part of Asia, [17] particularly temperate regions that require the plants to cope with water shortages over the course of dry seasons. [18] Common deciduous plant species, either temperate or drought, will appear in temperate deciduous forest biomes which alternates continuously. It usually has distinct seasonal differences, winter, spring, summer and autumn, and an obvious contrast of winter and summer.

Whereas cold-deciduous plant species are commonly found in regions towards lower latitudes of the planet. These plant species can cope with climatic conditions that are more extreme in respect of temperatures.

Examples of drought deciduous species

Drought deciduous plants are very commonly found near the borders of deserts or along the coastal areas in the Northern Americas. Encelia fairnosa (commonly known as brittlebush) is a very common broadleaf drought deciduous plant species found near the desert around the northern part of Mexico and along the West Coast of the United States. Ambrosia Dumosa (commonly known as Burroweed) is a common microphyllous drought deciduous species which is found near those same areas as it lives within similar ecosystems as the brittlebush. Although both these examples are able to undergo abscission in response to droughts or dry seasons, they are from different plant families.

See also

Related Research Articles

<span class="mw-page-title-main">Root</span> Basal organ of a vascular plant

In vascular plants, the roots are the organs of a plant that are modified to provide anchorage for the plant and take in water and nutrients into the plant body, which allows plants to grow taller and faster. They are most often below the surface of the soil, but roots can also be aerial or aerating, that is, growing up above the ground or especially above water.

<span class="mw-page-title-main">Evergreen</span> Plant that has leaves in all seasons

In botany, an evergreen is a plant which has foliage that remains green and functional through more than one growing season. This also pertains to plants that retain their foliage only in warm climates, and contrasts with deciduous plants, which completely lose their foliage during the winter or dry season.

<span class="mw-page-title-main">Deciduous</span> Plants that shed leaves seasonally

In the fields of horticulture and botany, the term deciduous means "falling off at maturity" and "tending to fall off", in reference to trees and shrubs that seasonally shed leaves, usually in the autumn; to the shedding of petals, after flowering; and to the shedding of ripe fruit. The antonym of deciduous in the botanical sense is evergreen.

Leaf mold is the compost produced by decomposition of shaded deciduous shrub and tree leaves, primarily by fungal breakdown in a slower cooler manner as opposed to the bacterial degradation of leaves.

<span class="mw-page-title-main">Sclerophyll</span> Type of plant

Sclerophyll is a type of vegetation that is adapted to long periods of dryness and heat. The plants feature hard leaves, short internodes and leaf orientation which is parallel or oblique to direct sunlight. The word comes from the Greek sklēros (hard) and phyllon (leaf). The term was coined by A.F.W. Schimper in 1898, originally as a synonym of xeromorph, but the two words were later differentiated.

<span class="mw-page-title-main">Tropical and subtropical dry broadleaf forests</span> Biome

The tropical and subtropical dry broadleaf forest is a habitat type defined by the World Wide Fund for Nature and is located at tropical and subtropical latitudes. Though these forests occur in climates that are warm year-round, and may receive several hundred centimeters of rain per year, they have long dry seasons that last several months and vary with geographic location. These seasonal droughts have great impact on all living things in the forest.

<span class="mw-page-title-main">Plant physiology</span> Subdiscipline of botany

Plant physiology is a subdiscipline of botany concerned with the functioning, or physiology, of plants. Closely related fields include plant morphology, plant ecology, phytochemistry, cell biology, genetics, biophysics and molecular biology.

<span class="mw-page-title-main">Perennial plant</span> Plant that lives for more than two years

A perennial plant or simply perennial is a plant that lives more than two years. The term is often used to differentiate a plant from shorter-lived annuals and biennials. The term is also widely used to distinguish plants with little or no woody growth from trees and shrubs, which are also technically perennials.

<span class="mw-page-title-main">Plant senescence</span> Process of aging in plants

Plant senescence is the process of aging in plants. Plants have both stress-induced and age-related developmental aging. Chlorophyll degradation during leaf senescence reveals the carotenoids, such as anthocyanin and xanthophylls, which are the cause of autumn leaf color in deciduous trees. Leaf senescence has the important function of recycling nutrients, mostly nitrogen, to growing and storage organs of the plant. Unlike animals, plants continually form new organs and older organs undergo a highly regulated senescence program to maximize nutrient export.

<span class="mw-page-title-main">Abscission</span> Shedding of various parts of an organism

Abscission is the shedding of various parts of an organism, such as a plant dropping a leaf, fruit, flower, or seed. In zoology, abscission is the intentional shedding of a body part, such as the shedding of a claw, husk, or the autotomy of a tail to evade a predator. In mycology, it is the liberation of a fungal spore. In cell biology, abscission refers to the separation of two daughter cells at the completion of cytokinesis.

<span class="mw-page-title-main">Marcescence</span> Retention of dead plant organs that normally are shed

Marcescence is the withering and persistence of plant organs that normally are shed, and is a term most commonly applied to plant leaves. The underlying physiological mechanism is that trees transfer water and sap from the roots to the leaves through their vascular cells, but in some trees as autumn begins, the veins carrying the sap slowly close until a layer of cells called the abscission layer completely closes off the vein allowing the tree to rid itself of the leaf. Leaf marcescence is most often seen on juvenile plants and may disappear as the tree matures. It also may not affect the entire tree; sometimes leaves persist only on scattered branches. Marcescence is most obvious in deciduous trees that retain leaves through the winter. Trees that exhibit marcescence are known as "everciduous". Several trees normally have marcescent leaves such as oak (Quercus), beech (Fagus) and hornbeam (Carpinus), or marcescent stipules as in some but not all species of willows (Salix). All oak trees may display foliage marcescence, even species that are known to fully drop leaves when the tree is mature. Marcescent leaves of pin oak complete development of their abscission layer in the spring. The base of the petiole remains alive over the winter. Many other trees may have marcescent leaves in seasons where an early freeze kills the leaves before the abscission layer develops or completes development. Diseases or pests can also kill leaves before they can develop an abscission layer.

<span class="mw-page-title-main">Autumn leaf color</span> Phenomenon that affects the leaves during autumn

Autumn leaf color is a phenomenon that affects the normal green leaves of many deciduous trees and shrubs by which they take on, during a few weeks in the autumn season, various shades of yellow, orange, red, purple, and brown. The phenomenon is commonly called autumn colours or autumn foliage in British English and fall colors, fall foliage, or simply foliage in American English.

<span class="mw-page-title-main">Forest dieback</span> Stand of trees losing health and dying

Forest dieback is a condition in trees or woody plants in which peripheral parts are killed, either by pathogens, parasites or conditions like acid rain, drought, and more. These episodes can have disastrous consequences such as reduced resiliency of the ecosystem, disappearing important symbiotic relationships and thresholds. Some tipping points for major climate change forecast in the next century are directly related to forest diebacks.

<span class="mw-page-title-main">Woody plant</span> Plant that produces wood and has a hard stem

A woody plant is a plant that produces wood as its structural tissue and thus has a hard stem. In cold climates, woody plants further survive winter or dry season above ground, as opposite to herbaceous plants that die back to the ground until spring.

A xerophyte is a species of plant that has adaptations to survive in an environment with little liquid water, such as a desert such as the Sahara or places in the Alps or the Arctic. Popular examples of xerophytes are cacti, pineapple and some Gymnosperm plants.

<span class="mw-page-title-main">Leaf</span> Photosynthetic part of a vascular plant

A leaf is a principal appendage of the stem of a vascular plant, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, stem, flower, and fruit collectively form the shoot system. In most leaves, the primary photosynthetic tissue is the palisade mesophyll and is located on the upper side of the blade or lamina of the leaf but in some species, including the mature foliage of Eucalyptus, palisade mesophyll is present on both sides and the leaves are said to be isobilateral. Most leaves are flattened and have distinct upper (adaxial) and lower (abaxial) surfaces that differ in color, hairiness, the number of stomata, the amount and structure of epicuticular wax and other features. Leaves are mostly green in color due to the presence of a compound called chlorophyll that is essential for photosynthesis as it absorbs light energy from the sun. A leaf with lighter-colored or white patches or edges is called a variegated leaf.

<span class="mw-page-title-main">Plant litter</span> Dead plant material that has fallen to the ground

Plant litter is dead plant material that have fallen to the ground. This detritus or dead organic material and its constituent nutrients are added to the top layer of soil, commonly known as the litter layer or O horizon. Litter is an important factor in ecosystem dynamics, as it is indicative of ecological productivity and may be useful in predicting regional nutrient cycling and soil fertility.

The nutrient content of a plant can be assessed by testing a sample of tissue from that plant. These tests are important in agriculture since fertilizer application can be fine-tuned if the plants nutrient status is known. Nitrogen most commonly limits plant growth and is the most managed nutrient.

Biomass partitioning is the process by which plants divide their energy among their leaves, stems, roots, and reproductive parts. These four main components of the plant have important morphological roles: leaves take in CO2 and energy from the sun to create carbon compounds, stems grow above competitors to reach sunlight, roots absorb water and mineral nutrients from the soil while anchoring the plant, and reproductive parts facilitate the continuation of species. Plants partition biomass in response to limits or excesses in resources like sunlight, carbon dioxide, mineral nutrients, and water and growth is regulated by a constant balance between the partitioning of biomass between plant parts. An equilibrium between root and shoot growth occurs because roots need carbon compounds from photosynthesis in the shoot and shoots need nitrogen absorbed from the soil by roots. Allocation of biomass is put towards the limit to growth; a limit below ground will focus biomass to the roots and a limit above ground will favor more growth in the shoot.

<span class="mw-page-title-main">Leaf flushing</span>

Leaf flushing or leaf out is the production of a flush of new leaves typically produced simultaneously on all branches of a bare plant or tree. Young leaves often have less chlorophyll and the leaf flush may be white or red, the latter due to presence of pigments, particularly anthocyanins. Leaf flushing succeeds leaf fall, and is delayed by winter in the temperate zone or by extreme dryness in the tropics. Leaf fall and leaf flushing in tropical deciduous forests can overlap in some species, called leaf-exchanging species, producing new leaves during the same period when old leaves are shed or almost immediately after. Leaf-flushing may be synchronized among trees of a single species or even across species in an area. In the seasonal tropics, leaf flushing phenology may be influenced by herbivory and water stress.

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