Salt plant
Salt plants or halophytes (from ancient Greek ἅλς hals , "salt" and φυτόν phytón , "plant") form an ecologically delimited group among the Higher Plants , which are adapted to increased levels of easily soluble salts at their location and can reproduce under these conditions .
Salt plants colonize salt-rich locations largely regardless of width in dry to flooded habitats, often near the sea and on salt lakes . The as yet little researched mechanisms with which plants can adapt to extreme environmental conditions and remain photosynthetically active are very diverse. Some salt plants (the obligate halophytes ) are promoted in their growth by moderate salt contents, other salt plants do not need salt for their vital activity. They thrive much better on salt-free soils, but there they are inferior to the competition of other plants.
Definitions
There are several definitions of the term salt plant or halophyte. One criterion, for example, is that the plants can grow on salt soil with more than 0.5 percent salt in the dry soil weight. This value is easy to determine, but more important for the plant is the salt or ion concentration in the soil water. The definition by Jennings (1976), which is also often used, describes halophytes as the natural flora on salt sites . Already Warming (1909), which defined the term Halophyt first time, wrote: must be present before a halophytic vegetation leads to a certain amount of soluble salts; the type of salt does not seem to matter. Mann et al. (1983) described the sites as follows: "[...] contain salt water with an osmotic pressure of over 3.3 bar" , which corresponds to a concentration of 70 m M monovalent salts.
Plants that do not survive in salt locations even if competition is excluded are often called glycophytes in German-speaking countries . This expression is derived from the word "fresh water" and can only be found in the German language. More appropriate but less frequently used names for the same term are halophobic plants or simply non-halophytes .
Salt-tolerant organisms are generally referred to as halophilic , namely when they are no longer able to exist in the absence of salt due to the evolutionary salt resistance. This salt resistance has developed independently several times. Therefore, no salt plants monophyletic lineage, although they in some plant genera and - families frequently occur.
Among the higher plants, halophytes are found only among the angiosperms. There are around 1,500 known species of halophytes . Families with numerous representatives are the Chenopodiaceae , Aizoaceae , Frankeniaceae , Plumbaginaceae and among the mangroves the Rhizophoraceae , Lythraceae , Avicennioideae within the acanthus family , Combretaceae and Myrsinaceae . There are also halophytes among the sweet and sour grasses and the Juncaceae .
There are 54 halophytes in Germany. In addition, there are some transitional forms and intermediate species that rarely develop halo tolerance or are considered hybrids of littoral ( Ammophila arenaria ) and inland ( Calamagrostis epigeios ) species. The existence of such special littoral forms of otherwise widespread halophytic or sand-dwelling grasses is the best proof that these must have taken possession of their current location for a very long time and created the forms corresponding to it.
Classification according to salt dependency
Obligate halophytes
The obligatory halophytes ( obligatory = obligatory ), also called Eu halophytes, are bound to their salty environment. Without a certain concentration of salt as the basis of life, these plants would not be able to thrive and germinate, as they have largely adapted to the extreme conditions of this environmental factor. The tolerance range of the obligatory halophytes to salt is accordingly very large, so that they can exist even with constant flooding with seawater. The best-known domestic genera are samphire ( Salicornia ), rushes ( Juncus ), salt marsh ( Suaeda ) and silt grasses ( Spartina ).
Facultative halophytes
The optional halophytes ( optional = optional) have the ability to grow in salt locations, but are not bound to them. Representatives such as the goose weed ( Potentilla anserina ), the beach aster ( Aster tripolium ), the beach plantain ( Plantago maritima ) and the beach mugwort ( Artemisia maritima ) can also occur in maritime areas. However, they only achieve their optimal vital functions on soils that are predominantly salt-free or have only a slight salt content. Since they are increasingly facing competition from other plants in these areas, these salt plants are often at a disadvantage compared to the freshwater plants found there. These are better adapted to their environment and multiply faster. Facultative halophytes have a more restricted tolerance range to the salinity of the soil than obligatory halophytes.
Indifferent halophytes
So-called location-indifferent halophytes form a transition form to the freshwater plants and are usually only found in salt-free areas. Their tolerance range is relatively small, but they can still cope with salty soils, which have a lower concentration. In these cases, the habitus of the corresponding plant changes in a wide variety of ways and deviates from the basic appearance. Representatives of this group are: red fescue ( Festuca rubra litoralis ), white ostrich grass ( Agrostis stolonifera ), toad bulrush ( Juncus bufonius ), creeping buttercup ( Ranunculus repens ) and stonecrop ( Sedum ).
Classification according to the type of influence of the salt
Salt can act on the plant in a variety of ways, according to which halophytes can basically be described as air thalena ( aerohalin ), water haline ( hydrohalin ) or terrestrial haline . The two last-mentioned categories interlock, which is why the collective term hydroterrestrial haline is often used.
Air thalenes
Breaking waves and spray on the oceans lead through a dispersion process ( bulk to particle conversion ) to the release of small droplets ( sea spray ) in the air. Significant parts of it are transported upwards by the turbulence of the marine boundary layer and can partially dry out. The aerosol created by such surf atomization , which is collectively referred to as sea salt aerosol , has an effect on plants in areas near and far from the sea due to the high salt air concentration. Many air thaline species are also water haline, so that there is a closer connection between the two categories. The strictly aerohaline species live as a transition from the maritime to the terrestrial area in a remote environment to the sea and take up salt almost exclusively through the leaf surface. The salt content of the leaves on the windward side can be up to ten times higher than that of leaves of the same plant in the slipstream. The yellow horn poppy ( Glaucium flavum ) is insensitive to salt dust and splash water, but does not tolerate salt in the soil.
In the vicinity of evaporation basins, i.e. certain inland salt lakes that regularly dry out in periods of drought and leave behind a salt desert ( desertification ), there are also numerous species of salt plants. The salt present in the air can be traced back to such evaporation processes of the salt water and is absorbed by the flora living there from the aerobic environment.
Water haline
The marine species live in the vicinity of both salt and brackish water and can be found from the intertidal zone via estuaries into the interior of inland salt waters . Hydrohaline plants are all those species that are either completely or semi- aquatic, i.e. have their center of life in or near the water. If the soil is dry and sandy, in the narrower sense on beaches and dunes, the arenicolous halophytes there have usually adapted to their environment with a further, deeper root system. On the muddy, often flooded subsoil, which ensures direct water absorption, plants with smaller, but also stronger, roots that cannot be washed away tend to appear. Some closed plant formations have evidently specialized in the thinned sea water of the river deltas and river mouths as habitats, whereas others live in a pronounced sand gap flora on salt-concentrated lakes and inland seas such as the Dead Sea . The salt content of thalassohalin sites varies over a wide range and can correspond to that of seawater (3.5%) up to the salt content of a saturated sodium chloride solution (30%). The transitional forms to the terrestrial and aerohaline salt plants also form areas of diversity remote from salt water, which have settled above the water level usually reached at high tide on normal earth or rock rubble (preferably Sedum species) and are normally only reached by the salty spray .
Terrestrial haline
Terrestrial halines are all terrestrial species that specialize in inland salt pits . They only absorb salt through the soil. The salt plants that do not appear on the beach include, for example, rock mugwort ( Artemisia rupestris ), slit-leaved mugwort ( Artemisia laciniata ) or land riding grass ( Calamagrostis epigeios ). Also plants that occur in desert and steppe regions, such as species of the genus Atriplex, are to be understood as forms remote from the water, which can preferably be found under location-indifferent halophytes .
Classification according to the salinity of the soil
The classification according to the salt content in the soil is graded using data in per mille (1 ‰ corresponds to 1 g / L). Since many terrestrial halophytes are at the same time water haline, the scheme of the classification applies to both categories and also to geology and soil science .
- Oligohaline (Greek oligos - little ) plants tolerate a salt concentration of 0.5 to 5 ‰ and have a very low tolerance range with regard to salt. Most marine and terrestrial species count in this order.
- Mesohaline (Greek meso - middle , middle ) are the names of plants that are located in areas with 5 to 18 ‰ salt content. Communities of this ecological group can be found near salt marshes or lakes of medium salinity.
- Polyhalins (Greek poly - several , much ) have a salt content of up to 30 ‰ in their environment. These are plants that live on exceptionally salty lakes.
Effects of salt on the plant
The effects of the salt are visible on three levels. In the case of non-halophytes, this leads to damage, while the halophytes are adapted by different mechanisms.
- Osmotic effects make it difficult to absorb water from the salty medium ( physiological dryness ).
- The excess of sodium leads to an ion imbalance, as the vital ions potassium, calcium and nitrogen can no longer be sufficiently absorbed by plants that have not adapted. There is a sodium-induced potassium deficiency.
- Salt ions also have specific effects on different metabolic areas. Examples are the inhibition of protein metabolism, an increase in the activity of the pentose phosphate cycle and a decrease in glycolysis .
Among the soil salts, sodium chloride has the greatest toxicity and in most locations also the largest share; Then, depending on the strength of the poisonous effect, calcium chloride , magnesium chloride , sodium and magnesium sulfate follow .
Locations
Apart from the polar regions of the Arctic and Antarctic , halophytes are common on all continents. They can be found in European marine regions as well as in humid , tropical rainforests or arid salt steppes, on the beaches of remote islands in Oceania , in the alpine area of up to 3,100 meters high salt lakes and salt springs or in the middle of the desert ( Sahara ) on sodium-rich sands. Although they are represented in all non-polar climates, the tropical and temperate latitudes are the main areas of distribution.
At the biogeographical level, the majority of the known species have a spatially restricted distribution area. Plants spread all over the world, so-called cosmopolitans , exist only sporadically and exclusively under obligatory halophytes, such as the salt bush .
Primary locations
All natural and near-natural habitats in Europe are protected by the rarity of individual salt plant species. These natural, not man-made or caused habitats are called Primary Locations. They usually have a large population density . The biodiversity is often relatively low due to the extreme location.
The two most important coastal habitats of the halophytes are the salt marshes, which occur in temperate climates and the mangrove forests, which occur in tropical and subtropical climates. Almost all salt plants, even if they are partially resistant to xerophytic dehydration, are dependent on a local water point for constant salt dilution.
Salt marsh habitat
In the shoreline areas of the temperate climate zone, there are muddy marshland areas on flat coasts in the area of the middle flood line , which are flooded at higher water levels. Such salty areas, called salt marshes , are the habitat of many flowering plants that are adapted to these extreme conditions. Settlement of the salt marshes is dependent on the height above the mean flood and thus on the salt content and is divided into different zones according to the vegetation .
In Germany, the salt marshes are largely protected, for example in the Lower Saxony Wadden Sea National Park .
Mangrove forest habitat
The ecosystem of the evergreen mangroves is found in the tidal area of flat, tropical coastal regions . Especially in the warm areas around the equator , z. Species-poor tidal forests, some more than 30 m high. Mangrove trees are one of the few trees with a pronounced salt resistance. The above-ground parts of the root system of many mangrove species are striking (e.g. stilt roots in Rhizophoreae , pneumatophores in Avicennia, etc.), which supply the underground root system in the anoxic sediment with oxygen and increase the stability of the trees. To what extent the deposition of sediments in the area of the mangrove roots stabilizes the coastline is debatable.
More locations
In Central Europe, inland salt locations are quite rare. Well-known examples are the salt marshes around the Kyffhäuser Mountains in Thuringia , the Pannlake in the Hollerland nature reserve in Bremen, the Luchwiesen in Brandenburg or the Salzlacken in Seewinkel east of Lake Neusiedl . Two factors are important for the occurrence of salt locations off the coast of the sea: There are salt deposits underground and at least in some seasons the evaporation is higher than the precipitation, so that the salts reach the soil surface and are not washed out. It is precisely at such locations that not only sodium chloride occurs, but also magnesium , carbonates and sulfates .
In addition, halophytes are found less often in the mountains, whereby salts trapped in the rock or high-altitude salt springs and lakes are the basis for this somewhat unusual habitat. During the day, the often stony subsoil offers heat absorption so that the plants do not die from cold at night. Also typical of cliffs salt-tolerant Felsbesiedler how can samphire , sea rocket , sea beet and beach Lilac occur. They are able to anchor their roots deep in the rock so as not to be washed away by storm surge.
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Salt plants occupy large areas in the dry (arid) areas of the earth, which receive at least enough precipitation that the salts can concentrate on the surface with the rising ground water due to evaporation. The salt plants of dry locations are called xerohalophytes. In the following some areas with xerophytic vegetation are presented as examples.
In the Ebro basin (Spain) the continental climate meets with drainless salt lakes. A number of endemic gypsophytes, for example Lygeum spartum, grow on the gypsum-rich soils . In Australia , the Chenopodiacean semi-desert ( Saltbush ) occupies large areas in the south of the continent. Species of the genera Atriplex and Maireana grow on the salty soils (only around 0.1% chloride) , while non-halophytes (acacias, etc.) grow on the sandy areas. The Maireana shrubs can live up to 300 years. In Iran , Afghanistan and large areas of Central Asia , the soils are salty. In central Afghanistan, halobiomas still occur at 3,100 meters above sea level (Dasht-e-Nawor). The inner Iranian basins, the Kawire, are often extremely salty and absolutely free of vegetation. Typical halo series rich in Chenopodiacea appear in the edge areas. In the Central Asian deserts, halophyte vegetation occurs in moist depressions ( salt pans , shory) and around salt lakes . The most salt-resistant salt plant in these areas is the cushion-forming Halocnemum strobilaceum (Chenopodiaceae). For the Karakum desert, the halophytic shrub Haloxylon persicum ( White Saxaul , Chenopodiaceae) is the character plant. The salt locations of Central Asia extend over the Caspian Sea to Europe. In the north of the Crimean peninsula there is the Lazy Sea (Sivash), which dries up in summer, and from where salt is blown north, where it causes the soil to become soda- bracing ( solonation ). The salt soils of southern Russia are called Solontschake . In the Great Basin in North America by the Great Salt Lake there are huge salt areas. The most important species is Atriplex confertifolia (English shadscale ), which covers around 150,000 km² in the USA. In Death Valley and the San Joaquin Valley in California occur borax rich salt sites, which especially Atriplex hymenelytra , Suaeda torreyana and Bassia colonized species. Salt pans can be found in the South American pampas , such as Laguna La Picaza in the province of Santa Fe , where soda - bracing can reach pH values of 10 and where distichlis turf grows in particular . In more arid areas, chloride sulphate build-up occurs more frequently, especially in the western part of the pampas.
Secondary locations
In addition to the primary locations, there are secondary, anthropogenic salt areas on mining and industrial sites as well as along traffic routes, i.e. those that were only created through human action. The flora of such habitats belongs to the ruderal vegetation , since it is herbaceous species that are not used for agriculture or forestry. The most important location factor is the increased salt content, which is caused by various actions, such as salting the roads in winter; mechanical disturbances only play a secondary role. Secondary habitats represent island habitats for halophytes and halobionte animals, so that they are also of importance for biogeographical research. The study of the settlement of overburden and residue heaps of the potash industry, which were classified as the “island mountains” of the cultural landscape, has proven to be particularly interesting . So far, rare or unobserved species have been found inland that were previously only known from primary locations. In relation to the population sizes of many threatened halophytes, the secondary sites now function as important refuges.
Adaptation strategies
Salt plants have developed diverse strategies in order to be able to grow when exposed to salt. The " ability of a plant to keep an oversupply of salts in its substrate away from the protoplasm by regulating salt or to endure an increased osmotic and ion-toxic salt load " is referred to as salt resistance. Resistance is therefore the generic term, the two sub-terms are regulation and tolerance.
Salt resistance manifests itself in morphological and physiological adaptations, which are mostly mutually dependent.
Salt regulation
shielding
The shielding (English exclusion ) is the strategy of not absorbing salt ions into the plant or not allowing them to get into sensitive (young, growing) tissue.
Shielding in the root
The exclusion principle, also known as salt filtration, limits the uptake of salt ions through the roots. As with all plants, the uncontrolled apoplastic water uptake of the mangrove family is prevented by the Casparian strip . However, the ion channels of the cell membrane are much more selective than those of non-halophytes, so that almost no sodium and chloride are absorbed, but important ions such as potassium are absorbed. The xylem sap within the root is low in salt, as opposed to the ground. When in the edge region of mangrove forests growing shrub Conocarpus erectus ( combretaceae ) in the xylem sap of the branches were only 17.6 mol m -3 chloride and 7.5 mol m -3 (measured sodium in comparison to 465 mol m -3 chloride and 362 mol m −3 sodium in sea water).
Shielding in the scion
In some species, for example Prosopis fracta , a shrub in arid salt areas, the sodium ions in particular are retained in the basal parts of the plant such as the roots and trunk ( sodium retention ). The same applies to the Andel grass ( Puccinellia peisonis ). In the grass Diplechna fusca , sodium and chloride ions are retained in the leaf sheath . In the case of the mangroves, for which this strategy would be appropriate due to the trunk volume, no such mechanism could be observed.
By retaining salt ions in the basal and older parts of the plant, the ion content in the young shoot sections and also in the physiologically active leaves is kept low.
B = bladder cell , C = cuticle,
Ch = chloroplast, E = epidermal cells,
M = mesophyll cells, P = plasmodesmata,
S = stem cell, V = vacuoles
elimination
The strategy of eliminating salt ions that have already been absorbed by the plant is called elimination. There are many different strategies here. The excretion mechanisms are a particularly effective, but also energy-consuming, method of directly excreting ingested salt and thus keeping the salt value of the cell almost constant.
Desalinated hair
Blow-down hairs or bladder hairs are particularly common in goosefoot plants (Chenopodiaceae). These are specialized hairs ( trichomes ) on the leaf surface, into which ions are actively transported. The hair dies, bursts, the ions are washed off and thus removed from the plant. Bladder hairs are mostly two-celled, they consist of a bladder cell almost completely filled with the cell sap space of the vacuole, which sits on a vesicle-, plasma-, mitochondrial and chloroplast- rich stem cell. The latter connects the bladder cell with the underlying leaf tissue through numerous plasmodesmata and also occupies a very metabolically and physiologically active position in order to enable the sodium chloride transport with the subsequent accumulation. With energy consumption ( ATP ), dissolved salts are transported via the stem cell into the vacuole of the bladder cell and accumulated there. At a predetermined breaking point on the shaft, the hair kinks off when it has absorbed enough salt and falls to the ground. If this mechanism fails, the hair bursts or is removed by the precipitation with washing off and washing off.
Some species, such as Atriplex halimus or the purslane wedge ( Halimione portulacoides ) can excrete more than 80% of the ions they absorb through the hairs of their blisters.
Desalination glands
Many halophytes secrete salts through special glands on the leaf surface. In contrast to excretion and secretion , salt excretion is referred to as recretion , i. H. the substances are excreted by the plant in the form in which they were ingested and they no longer serve any special purpose after excretion.
The salt glands of individual halophytes show very different structural and functional features. One of the simplest forms can be found in the genus of silt grass ( Spartina ). In their leaves and stalks, they usually only consist of a cuticle with pores and a subcuticular space with underlying base and valve cells.
In the common sea lavender ( Limonium vulgare ), which has a very complex structure of the salt glands, exocytosis is suspected as an additional possibility of material transport. The accumulated salt vesicles ( exosomes ) fuse with the membrane of the secretion cells and emerge through pores to the surface. This can cause visible salt crystals to form on the outside of the leaf. The number and distribution of the salt glands in the leaf is also different. While the sea lavender has up to 3000 glands per cm², the sea carnation ( Armeria maritima ) shows only 590 glands and the milkweed ( Glaux maritima ) around 800 glands per cm².
Sodium and chloride ions are specifically excreted, while potassium is retained in the plant, so that the potassium / sodium ratio in the plant remains high. The amount of salt excreted by the glands can reach very high values, so Diplachne fusca can excrete five times the amount of salt absorbed in the same time, the grass Spartina alternifolia at least around half. The mangrove aegialitis annulata excretes around 38% of the amount of salt present in young leaves in 12 hours. The energy requirement for salt excretion is considerable. At Tamarix , around 20 to 24 moles of ATP are required per mole of sodium chloride excreted.
Shedding of plant parts
Rosette plants accumulate salt ions in the tissues of the oldest leaves until the toxicity limit is reached. Before these die off, the plant removes the reusable nutrients ( nitrogen ) from them and then discards them with the stored salt. The subsequent younger leaves take over the function. Well-known Central European representatives are beach plantain ( Plantago maritima ), beach trident ( Triglochin maritima ) and the beach aster ( Aster tripolium ).
Retranslocation
Retranslocation is understood as the return transport of ions from the leaves via the phloem back to the roots, where the ions are released back into the surrounding medium. This mechanism has been proven for the sweet grass Pappophorum pappiferum , which can excrete around 35% of the sodium present in the shoot via the roots within 48 hours. This mechanism is also being discussed for mangroves, since the leaves of many species can live up to 18 months with the same salinity.
Succulence
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Succulence is a strategy for diluting the ingested salt; it occurs primarily with chloride halophytes. Water is also absorbed with the ions and stored in the large vacuoles . This prevents too high an intracellular salt concentration. Depending on the succulent organ, a distinction is made between leaf succulents such as sod ( Suaeda ), Schuppenmieren ( Spergularia ) and some mangrove species, and stem succulents such as the samphire . Succulence occurs particularly frequently in the goosefoot family. In the leaf succulent mangroves Rhizophora mangle ( Rhizophora family ), Laguncularia racemosa and Conocarpus erectus (both winged family ) there is a high correlation between the chloride content on the leaf surface and the water content on the leaf surface; this correlation does not occur in salt-excreting mangroves.
The succulents are usually characterized by fleshy, swollen shoot and root parts that have been transformed into water storage organs by multi-layered storage tissue. The leaves, in which the number and size of parenchymal cells are increased, have a reduced surface area and are often tapered into the stem to restrict perspiration. With the accumulation of water, all dilution mechanisms cause an increase in the volume of the solution space and a decrease in the salt ion concentration.
The alternative to storing it in the cell vacuole is to distribute the excess salt throughout the plant, which initially reduces the salt concentration. In the case of the annual samphire or salt rush , the vegetation cycle is already over when the salt concentration becomes lethal . The salt-overloaded plant turns brown to red - a general symptom of stress - and eventually dies.
Intracellular compartmentalization
The different distribution of the absorbed ions to different cell components ( cell compartments ) is located as an adaptation mechanism between regulation and tolerance. Even plants that store salts can not tolerate any ion concentrations in the cytoplasm , since most of their enzymes are also sensitive to salt. Therefore, most of the salt ions are trapped in the vacuole . This is particularly noticeable in the succulents with their large vacuoles, but the compartmentalization is not limited to the succulents. The cytoplasm and the chloroplasts therefore contain only a relatively low concentration of salt ions. The ion transport into the vacuoles takes place through membrane ATPases . The resulting difference in the osmotic potential between vacuole and cytoplasm is balanced out by compatible solutes (see below).
tolerance
Larcher defined the salt tolerance as follows: Salt tolerance is the protoplasmic component of resistance, namely the ability to tolerate the shift in the ion ratio that occurs during salt stress and the toxic and osmotic effects associated with the increased ion concentration, depending on the plant species, tissue type and vitality status. This salt tolerance is brought about by several biochemical mechanisms.
Membrane composition
Salt plants have a different composition of their cell membranes . A higher proportion of saturated fatty acids reduces the fluidity of the membranes and thus reduces the escape of salt ions from the vacuole. This is an important prerequisite for maintaining the above-mentioned compartmentalization.
Ion pumping mechanisms
In order to compartmentalize the salt ions, the salt plants need transport mechanisms.
The accumulation of sodium and chloride ions in the vacuole depends on a pH gradient that is built up by the tonoplast ATPase. The pH gradient between the cytoplasm and vacuole then enables an H + / Na + antiport through which the sodium enters the vacuole. These H + / Na + antiporters are only formed in beach plantain ( Plantago maritima ) , for example , when there is salt stress, but not when there is a lack of salt in the growth medium.
Compatible solutes
The accumulation of the inorganic salt ions in the vacuole creates a difference in concentration to the cytoplasm. In order to balance this osmotic potential, salt plants synthesize organic compounds which they accumulate in the cytoplasm and in the chloroplasts. These compatible, i.e. non-toxic, soluble osmotics are called compatible substances or, with their English name, compatible solutes . The concentration of the compatible substances depends on the extent of the salt stress.
Frequently compatible substances are amino acids ( proline ), quaternary ammonium compounds such as glycine betaine , sugar as well as acyclic ( sorbitol , mannitol ) and cyclic sugar alcohols (so-called cyclites, e.g. pinitol ). Sugar alcohols occur particularly in mangroves. Some marine algae like Dunaliella accumulate glycerol , others like Chlorella sucrose.
Proline often occurs in plants under stress
Mannitol , a sugar alcohol often found in mangroves as a compatible substance
Sorbitol is used for example in Plantago maritima ago
The alga Dunaliella accumulates glycerol under salt stress
Transgenic tobacco has shown that compatible substances actually increase salt tolerance . Tobacco is usually sensitive to salt. As a result of the genetic engineering of the gene for the enzyme mannitol-1-phosphate dehydrogenase, the modified plants accumulated mannitol and thus grew significantly better than the wild type when exposed to salt.
Some plants store large amounts of organic substances in the vacuole in order to build up the osmotic potential necessary for water uptake and are therefore not dependent on the uptake of salt ions. These substances include oxalate , malate , aspartate (asparate), and sucrose . These increased proportions of organic substances are particularly noticeable with beach mugwort , silt grass and beach lavender .
Photosynthetic Mechanisms
In some plants, the CAM pathway of photosynthesis is activated under salt stress . This enables the plants to photosynthesize with very little water evaporation. This reduces the water uptake by the plant from the soil and thus also the salt uptake. This reduces the plant's salt load. These optional CAM plants include Mesembryanthemum crystallinum , Mesembryanthemum nodiflorum , Aptenia cordifolia, and Carpobrotus edulis .
As a C 4 plant, the beach plantain ( Plantago maritima ) also has a water-saving photosynthesis type.
| Adaptation mechanisms in halophytes of the German salt marshes | ||||||
| Halophytes (selection) | Adjustment mechanisms | |||||
| accumulation | Succulence | Bladder hair | Leaf shedding | Salt glands | exclusion | |
| Andel ( Puccinellia maritima ) | X | - | - | - | - | - |
| Danish spoonweed ( Cochlearia danica ) | X | X | - | X | - | - |
| Beach carnation ( Armeria maritima ) | - | X | - | X | X | X |
| Samphire ( Salicornia europaea ) | X | X | - | - | - | ? |
| Brine rush ( Juncus gerardii ) | X | - | - | X | - | - |
| Salt alarm ( Atriplex halimus ) | X | - | X | - | - | - |
| Silt grass ( Spartina ) | X | - | - | - | X | X |
| Beach aster ( Aster tripolium ) | X | X | - | X | - | - |
| Beach mugwort ( Artemisia maritima ) | X | - | - | - | - | X |
| Beach trident ( Triglochin maritima ) | X | X | - | X | - | - |
| Sea lavender ( Limonium ) | X | - | - | - | X | X |
| Beach sod ( Suaeda maritima ) | X | X | - | - | - | - |
| Beach plantain ( Plantago maritima ) | X | X | - | X | - | X |
Highlighted in green : particularly strong expression
Features and use
Halophytes like the samphire or the sod belong to the pioneer plants and can contribute to sedimentation and the formation of salt marshes in marine regions. While the roots hold the soil in place, the upper part of the plant ensures that the water movement is calm. The salt and other sediments carried along by the sea water are deposited between the roots and individual parts of the plant. These then sink into the ground. A long-term repetition of this process can lead to the fact that the bottom continues to rise and rise above the water level. Such surveys in turn offer the less salt-resistant flora a basis for life. This silting-promoting effect is occasionally used by creating "halophyte beds". The wave and wind calming effect is also suitable worldwide as a natural buffer and protective function against storm surges and tsunamis ( reforestation of the mangroves in Vietnam, Thailand and India).
Another useful benefit is the prevention of abrasion on beaches and coasts. The wide root runners of some plants (for example common beach grass (Ammophila arenaria) , also beach rye ( Elymus arenarius )) anchor themselves over long distances in the soil and strengthen it. This will preventively a removal of material prevented by the water. In this way, water can be prevented or even stopped on endangered islands or bays.
The state research center Desert Research Center (DRC) in Cairo is looking for methods with which Egyptian desert regions can be made usable. The Maryout Experimental Station covers around four hectares, the DRC's largest experimental station, and has been studying the behavior of animals and crops under extreme conditions since 1968. The main research is into how well goats, sheep, rabbits and camels can tolerate feed from plants that grow in the soil even with high salt concentrations. So far, the reactions of livestock to two types of salt plants as a source of food have been tested, with researchers comparing growth, fertility and meat quality with test animals with normal feed conditions. Atriplex halimus (salt bush ) and Acacia saligna (salt acacia) only restricted growth in the experiment, which can be compensated for by high-fat food. Today they serve as a source of food in particularly dry places. Halophytes are also used to stabilize fields without limiting the growth of crops. In the meantime, the usable area in deserts has been greatly increased through mixed cultivation with salt plants .
Many salt marsh plants are also used as food in the kitchens of the northern countries. Edible salt plants (such as beach plantain , samphire as sea asparagus or beach trident as tubed cabbage) give dishes a delicate, salty to peppery taste, serve the body as a natural source of iodine and contain important minerals and nutrients .
In addition, the ashes that resulted from burning halophytes were used in the past for a wide variety of manufacturing branches, such as glass and soap, but this is no longer allowed due to the declining species population.
References
- ↑ a b c d e f Marianne Popp: Salt Resistance in Herbaceous Halophytes and Mangroves . Progress in Botany, Volume 56, Springer Verlag Berlin 1995, pp. 416-429.
- ↑ a b H. Bothe: Salt resistance in plants , 1976.
- ↑ Lexicon of Biology. Volume 7 . Spektrum Akademischer Verlag, Heidelberg 2001, p. 33, ISBN 3-8274-0332-4 -
- ↑ H. Walter, S.-W. Breckle: Ecology of the Earth. Volume 1: Basics . G. Fischer, Stuttgart, 2nd edition 1991, pp. 102-109, ISBN 3-437-20454-8 .
- ^ Karlheinz Kreeb: Plants in salt locations. Natural Sciences 61 , 1974, pp. 337-343
- ↑ Walter Larcher: Ecophysiology of plants . Eugen Ulmer, Stuttgart, 4th edition 1995, p. 316.
- ↑ a b Christiane von den Berg: Salzwiese habitat - halophilia or: plant tolerance mechanisms against salt stress , status: February 2005 (accessed: April 9, 2006).
- ↑ a b Dieter Schlee: Ecological Biochemistry . Gustav Fischer, Jena, Stuttgart 1992, pp. 170-187, ISBN 3-334-60393-8 .
- ↑ a b University of Osnabrück: Plants from saline sites (halophytes) ( Memento of the original from November 27, 2005 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (Accessed April 7, 2006).
- ↑ Walter Larcher: Ecophysiology of plants . Eugen Ulmer, Stuttgart, 4th edition 1995, p. 319.
- ↑ MC Tarczynski, RG Jensen, HJ Bohnert (1993), Science 259, pp. 508-510.
- ↑ Hilmar Liebsch; Michael Thekat: Salt - a problem for agriculture In: Quarks Sendungsarchiv. Quarks & Co, broadcast: August 23, 2005 (accessed April 21, 2006).
literature
- Central European salt vegetation
- Ernst Albert Arndt: Between the dune and the seabed. Animals and plants of the Baltic Sea region . Leipzig / Jena / Berlin 1969.
- A. Gerhardt: Plants of the coast. Science in Biology Class. Aulis, Cologne 1982,5, pp. 164-174. ISSN 0342-5487
- HJ Janssen: The endangerment of the Wadden Sea . BUND information. Vol. 20. Freiburg 1983.
- F. Jantzen: Plants by the sea. Landbuch, Hannover 1968, 1978, 1987. ISBN 3-7842-0363-9
- BP Kremer: Plants on our coasts. Stuttgart 1977, 1999. ISBN 3-440-07734-9
- Richard Pott: Color Atlas North Sea Coast and North Sea Islands . Ulmer, Stuttgart 1995. ISBN 3-8001-3350-4 (good, extensively illustrated description of the vegetation on the German North Sea)
- G. Quendens: Beach and Coast . BLV, Munich 1984, 1988.
- HE Reineck (Ed.): The Watt. Kramer, Frankfurt 1978, 1982. ISBN 3-7829-1067-2
- M. Thies: Biology of the Wadden Sea . Aulis, Cologne 1985. ISBN 3-7614-0795-5
- Salt vegetation worldwide
- Georg Grabherr: Color Atlas of Earth's Ecosystems. Natural, near-natural and artificial land ecosystems from a geobotanical point of view. Ulmer, Stuttgart 1997. ISBN 3-8001-3489-6 (short overview)
- Heinrich Walter, Siegmar-W. Breckle: Ecology of the Earth . 4 vols. Gustav Fischer / Elsevier, Stuttgart / Munich 1991–2003. ISBN 3-437-20297-9 (detailed description of the earth's vegetation and its ecophysiology, including halophytes)
- physiology
- R. Albert: Halophytes . In: H. Kinzel: Plant ecology and mineral metabolism. Ulmer, Stuttgart 1982, pp. 33-204. ISBN 3-8001-3427-6
- R. Albert, G. Pfunder, G. Hertenberger u. a .: The physiotype approach to understanding halophytes and xerophytes . In: S.-W. Breckle, B. Schweizer, U. Arndt (Ed.): Results of worldwide ecological research . Heimbach, Stuttgart 2000, pp. 69-87.
- W. Baumeister, W. Ernst: Mineral metabolism and plant growth. Fischer, Stuttgart 1978. ISBN 3-437-30271-X
- Marianne Popp: Salt Resistance in Herbaceous Halophytes and Mangroves . In: Progress in Botany. Vol. 56. Springer, Berlin 56.1995, pp. 416-429. ISSN 0340-4773
- IA Ungar: Ecophysiology of vascular halophytes . CRC Press, Boca Raton 1991. ISBN 0-8493-6217-2
- Y. Waisel: Biology of Halophytes. Physiological Ecology. Edited by TT Kozlowski. New York / London 1972. ISBN 0-12-730850-4
Web links
- Halophytes in botany (overview of related web links)
- Salt marsh habitat
- List of halophytes
- Nature park around the Kyffhäuser Mountains (PDF file; 4.94 MB)
- German national parks in the Wadden Sea of the North Sea
