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Alpine plant

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Alpine plantsareplantsthat grow in analpine climate,which occurs at highelevationand above thetree line.There are many different plant species andtaxathat grow as aplant communityin thesealpine tundra.[1]These includeperennial grasses,sedges,forbs,cushion plants,mosses,andlichens.[2]Alpine plants are adapted to the harsh conditions of the alpine environment, which include low temperatures, dryness, ultraviolet radiation, wind, drought, poor nutritional soil, and a short growing season.

Some alpine plants serve asmedicinal plants.

Alpine meadows in theKazbegi National Park,Georgia

Ecology

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Further information:Alpine tundra

Alpine plants occur in atundra:a type ofnatural regionor biome that does not contain trees. Alpine tundra occurs in mountains worldwide. Ittransitionsto subalpine forests below the tree line; stunted forests occurring at the forest-tundraecotoneare known asKrummholz.With increasing elevation, it ends at thesnow linewhere snow and ice persist through summer, also known as the Nival Zone.

Alpine plants are not limited to higherelevations.However, high-elevation areas have different ecology than those growing at higher latitudes.[3]One of the biggest distinctions is that the lower bound of a tropical alpine area is difficult to define due to a mixture of human disturbances,dry climates,and a naturally lacking tree line.[4]The other major difference between tropical and arctic-alpine ecology is the temperature differences. The tropics have a summer/winter cycle every day, whereas the higher latitudes stay cold both day and night. In the northern latitudes, the main factor to overcome is the cold.Frost actionprocesses have a strong effect on the soil and vegetation of arctic-alpine regions.[5]Tropical alpine regions are subject to these conditions as well, but they seldom happen. Because northern alpine areas cover a massive area it can be difficult to generalize the characteristics that define the ecology.[6]One factor in alpine ecology is wind in an area. Windpruningis a common sight within northern alpine regions. Along with wind pruning, wind erosion ofvegetation matsis a common sight throughoutAlaska.[7]

Growth

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Saxifraga

Long-livedperennial herbsare the most common type of plant in alpine environments, with most having a large, well-developedrootand/orrhizomesystem.[8]These underground systems storecarbohydratesthrough the winter which are then used in the spring for new shoot development.[8]Some species ofsaxifrageshave small root systems, but areevergreen.[8]The leaves of these plants store energy in the form of carbohydrates andlipids.[8]Alpine plants go intovegetative dormancyat the end of the growing period, formingperennating budswith the shorteningphotoperiod.[8]

Seedlingestablishment is very slow and occurs less often thanvegetative reproduction.[8]In the first year of growth of perennial alpine plants, most of thephotosynthateis used in establishing a stable root system which is used to help prevent desiccation and for carbohydrate storage over winter.[8]In this year, the plant may produce a few true leaves, but usually, only thecotyledonsare produced.[8]It usually takes a few years for plants to become well established.[8]

Adaptations

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Alpine plants can exist at very high elevations, from 300 to 6,000 metres (1,000 to 20,000 ft), depending on location.[8][9]For example, there is amossthat grows at 6,480 m (21,260 ft) onMount Everest.[9]Arenaria bryophyllais the highest flowering plant in the world, occurring as high as 6,180 m (20,280 ft).[10]

To survive, alpine plants are adapted to the conditions at high elevations, including cold, dryness, high levels ofultraviolet radiation,and difficulty of reproduction. These conditions are linked to topographical slope, ultimately affecting plant diversity and distribution.[11]This is due to steeper slopes causing faster soil erosion which in turn impedes plant growth, seed distribution, and seed settlement. Furthermore, the slope of the topography directly affects many other abiotic factors including temperature, solar radiation, moisture content, and nutritional content in the soil.

Surviving low temperature extremes

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Alpine habitat onMont Blanc Massif

Most alpine plants are faced with low-temperature extremes at some point in their lives. There are several ways that a plant can survive these extremes. Plants can avoid exposure to low temperature by using different forms of seasonalphenology,morphology,or by variable growth form preference. One way is to hide most of the plant in the soil and only letting the flowers and leaves be exposed to air.[12]They can also avoid the freezing of their exposedtissuesby increasing the number of solutes in their tissues, known asfreezing-point depression.Another, somewhat similar, method plants may use to avoid freezing issupercooling,which preventsicecrystallization within plant tissues. These methods are only sufficient when the temperature is only moderately cold. In the alpine zone, temperatures are often low enough that these methods are not sufficient.[13]When plants need a more permanent solution, they can developfreeze tolerance.Plants can alsodehydratetheir cells by movingwaterintointercellular spaces.This causes ice formation outside of thecellwhereice crystalswill not cause damage. When all of these strategies fail to preventfrostdamage, alpine plants often have the capacity to repair or replace theorgansdamaged. As it is often difficult to prevent damage, many alpine plants depend on the replacement of their organs.[14]They help make this possible by placing theirmeristemsbelow ground, where temperatures are generally warmer.[13]

Photosynthesis and respiration rates

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Photosynthesisandrespirationrates are not uniform throughout the growing season.[15]At the start of the growing season, new shoots have low net photosynthesis rates and high respiration rates due to rapid growth of new shoots.[15]As the temperature rises in a plantsmicroclimate,the net photosynthesis rates will increase as long as ample water is available and will peak during flowering.[15]Alpine plants are able to start photosynthesizing and reach maximum photosynthesis rates at lower temperatures compared to plants adapted to lower elevations and warmer climates.[15]This is due to the combined effects ofgenotypeand environmental factors.[15]

Avoidance of desiccation

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A common alpine lichen,Xanthoria elegans

In alpine areas, water availability is often variable.Bryophytesandlichensexhibit highdesiccationtolerance, which contributes to their abundance throughout all alpine areas habitats.[16]Amonghigher plants,tissue desiccation is rare at high elevation. If it does occur, it normally happens to plants growing on exposed sites, wherewindstress is increased. Alpine plants avoid water loss by deeprootingand increasedstomatalcontrol. Plants at low elevation normally reach a maximum stomatal opening in the morning while alpine plants reach maximum opening mid-day when the temperature is greatest. Alpinesucculent plantsoften utilizeCAM photosynthesisto avoid water loss.

Avoidance of ultraviolet radiation

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Becauseultravioletradiation tends to increase with elevation, it is often assumed to be a stress factor among alpine plants. In the past, there have been many attempts to research how ultraviolet radiation may influence alpine plant forms. However, it is uncertain if the growth and development of plants are affected by ultraviolet radiation. It is also not clear if the radiation is responsible for promoting genetic differentiation, leading to stunted growth forms.[13]

Reproduction

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Alpine plants use bothsexual reproductionandasexual reproduction.Sexual reproduction has limits in high alpine areas, especially in areas with a shortgrowing seasonin alpine zones at high latitudes. In tropical alpine zones with a year-round growing season, such as the northernAndes,plants can flower year-round. Regardless of when alpine plants flower, pollinators are often scarce. The activity of pollinators decreases with increasing elevation.[17]The most commonpollinatorsin the alpine zone arebumblebeesandflies.[17]Plants utilize different strategies to deal with these limits, including alternate flowering time and clonal propagation.

Early flowering plants

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Glory-of-the-Snowis an alpine plant that preforms its flowers in the previous season so that it can flower as soon as the snow starts to melt in spring

Some plants flower immediately after snow melting or soil thawing. These early flowering plants always form their flowers in the previous season, called preformation. This flowerprimordiumis produced one to three years before flowering which ensures that flowering is not delayed after snowmelt and that with the right environmental conditions, there will be enough time for seed set.[8]Consequently, they risk frost damage to the preformedinflorescence.[17]In order to minimize frost damage, preformed flowers are often surrounded by tightly packedbractsthat are densely covered intrichomes.This helps to keep the interior of a flowerbudwarm.[18]Because of early-season pollinator limitation, plants that bloom early generally have a low rate of reproductive success.[17]One advantage of flowering early is that seeds that are produced have a greater chance of developing to maturity before the next freeze. They also have a highoutcrossingrate, which helps to increasegenetic diversity.[17]Speed and time of flowering is dependent on the time of snowmelt, temperature, and photoperiod, but usually occurs 10 to 20 days after snowmelt.[8]Thealpine snowbellis a plant with a high enough metabolism that the heat is able to melt the surrounding snow.[19]

Mid-season flowering

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Approximately half of all alpine species flower in mid-season. Flowering at the seasonal peak combines some of the advantages and risks of early flowering and late flowering plants. Some mid-season plants pre-form their inflorescences, but not all do.[17]

Late flowering

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Late flowering occurs after the main growing season ends. They have a high seed output but their seeds have a reduced rate of maturing because of time constraints. These plants tend towardsself pollination,apomixis,andvivipary.[17]

Clonal propagation

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Because investment in flowers and seed production can be costly for alpine plants, they often useclonal propagation.This strategy becomes increasingly more frequent as elevation increases, and is most common amongcryptogamsandgrasses.[17]Some alpine plants use it as their predominant method of reproduction. In these plants, sexual reproduction is rare and does not contribute significantly to reproductive output. An example of such a plant isCarexcurvula,which is estimated to have a clonal age of approximately 2000 years.[20]

Erythronium grandiflorum

After establishment, each year new shoot growth occurs rapidly from the perennating bud which is usually located close to the soil surface.[8]This growth occurs after snowmelt when the soil temperature is above 0 °C.[8]Some species, likeErythronium grandiflorum,can begin new shoot growth before snowmelt as they have their perennating buds located inbulbsburied deep in the soil.[8]As new leaves protrude from the snow, the new shoots give off heat from thermal reradiation and/or respiratory heat which melts the surrounding snow.[8]This exposes more soil tosolar radiation,heating it up and allowing new growth to accelerate.[8]

Medicinal alpine plants

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There are a number of alpine plants that are usedeconomically.In theHimalayas,hundreds of species are traded for medicinal and aromatic uses. It is estimated that the annual trade of these plants amounts to millions of US dollars. Many households in ruralNepalandIndiarely onmedicinalalpine plant trade as a source of income.[21][22]This creates an increased need to focus on plantconservationin these areas, ensuringsustainable harvestas well asecosystemsustainability. Some of the species harvested in Nepal includeNeopicrorhiza scrophulariiflora,Nardostachys grandiflora,Aconitum spicatum,Dioscorea deltoidea,Aconitum heterophyllum,Rheum australe,andBergenia.[22]In the Indian Himalayas, the alpine medicinal plants such asDactylorhiza hatagirea,Picrorhiza kurrooa,Aconitum heterophyllum,Fritillaria roylei,Podophyllum hexandrumare under severe pressure due to over-exploitation for commercial purposes.[23]

See also

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Notes

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  1. ^Körner 2003
  2. ^Körner 2003,pp. 9–18.
  3. ^Smith & Young 1987,p. 137
  4. ^Smith & Young 1987,p. 138
  5. ^Bliss 1962,p. 119
  6. ^Bliss 1971,p. 407
  7. ^Bliss 1962,pp. 127–128
  8. ^abcdefghijklmnopqBillings 1974
  9. ^ab"High Altitude Plants".Adventurers and Scientists for Conservation. Archived fromthe originalon 2012-04-25.Retrieved2016-11-22.
  10. ^Bezruchka & Lyons 2011,p. 275
  11. ^Zhang, Wang & Wang 2021
  12. ^Stegner et al. 2020
  13. ^abcKörner 2003,pp. 101–114.
  14. ^Hacker & Neuner 2008
  15. ^abcdeBillings & Mooney 1968
  16. ^Austrheim, Hassel & Mysterud 2005
  17. ^abcdefghKörner 2003,pp. 259–290.
  18. ^Tsukaya & Tsuge 2001
  19. ^Laurentino, Telma G (2018-03-19)."Witnessing Evolution and Learning how to Think about it in the Wonderful Swiss Alps".sci five.University of Basel – via Medium.com.
  20. ^Steinger, Körner & Schmid 1996
  21. ^Kala 2005
  22. ^abSmith Olsen & Overgaard Larsen 2003
  23. ^Kala 2000

References

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