6.4 KiB
| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Mangrove | 2/7 | https://en.wikipedia.org/wiki/Mangrove | reference | science, encyclopedia | 2026-05-05T07:35:22.795957+00:00 | kb-cron |
=== Limiting salt intake === Red mangroves exclude salt by having significantly impermeable roots that are highly suberised (impregnated with suberin), acting as an ultrafiltration mechanism to exclude sodium salts from the rest of the plant. One study found that roots of the Indian mangrove Avicennia officinalis exclude 90% to 95% of the salt in water taken up by the plant, depositing the excluded salt in the cortex of the root. An increase in the production of suberin and in the activity of a gene regulating cytochrome P450 were observed in correlation with an increase in the salinity of the water to which the plant was exposed. In a frequently cited concept that has become known as the "sacrificial leaf", salt which does accumulate in the shoot (sprout) then concentrates in old leaves, which the plant then sheds. However, recent research on the Red mangrove Rhizophora mangle suggests that the older, yellowing leaves have no more measurable salt content than the other, greener leaves.
=== Limiting water loss ===
Because of the limited fresh water available in salty intertidal soils, mangroves limit the amount of water they lose through their leaves. They can restrict the opening of their stomata (pores on the leaf surfaces, which exchange carbon dioxide gas and water vapor during photosynthesis). They also vary the orientation of their leaves to avoid the harsh midday sun and so reduce evaporation from the leaves. A captive red mangrove grows only if its leaves are misted with fresh water several times a week, simulating frequent tropical rainstorms.
=== Filtration of seawater === A 2016 study by Kim et al. investigated the biophysical characteristics of sea water filtration in the roots of the mangrove Rhizophora stylosa from a plant hydrodynamic point of view. R. stylosa can grow even in saline water and the salt level in its roots is regulated within a certain threshold value through filtration. The root possesses a hierarchical, triple layered pore structure in the epidermis and most Na+ ions are filtered at the first sublayer of the outermost layer. The high blockage of Na+ ions is attributed to the high surface zeta potential of the first layer. The second layer, which is composed of macroporous structures, also facilitates Na+ ion filtration. The study provides insights into the mechanism underlying water filtration through halophyte roots and could serve as a basis for the development of a bio-inspired method of desalination. Uptake of Na+ ions is desirable for halophytes to build up osmotic potential, absorb water and sustain turgor pressure. However, excess Na+ ions may work on toxic element. Therefore, halophytes try to adjust salinity delicately between growth and survival strategies. In this point of view, a novel sustainable desalination method can be derived from halophytes, which are in contact with saline water through their roots. Halophytes exclude salt through their roots, secrete the accumulated salt through their aerial parts and sequester salt in senescent leaves and/or the bark. Mangroves are facultative halophytes and Bruguiera is known for its special ultrafiltration system that can filter approximately 90% of Na+ions from the surrounding seawater through the roots. The species also exhibits a high rate of salt rejection. The water-filtering process in mangrove roots has received considerable attention for several decades. Morphological structures of plants and their functions have been evolved through a long history to survive against harsh environmental conditions.
=== Increasing survival of offspring ===
In this harsh environment, mangroves have evolved a special mechanism to help their offspring survive. Mangrove seeds are buoyant and are therefore suited to water dispersal. Unlike most plants, whose seeds germinate in soil, many mangroves (e.g. red mangrove) are viviparous, meaning their seeds germinate while still attached to the parent tree. Once germinated, the seedling grows either within the fruit (e.g. Aegialitis, Avicennia and Aegiceras), or out through the fruit (e.g. Rhizophora, Ceriops, Bruguiera and Nypa) to form a propagule (a ready-to-go seedling) which can produce its own food via photosynthesis. The mature propagule then drops into the water, which can transport it great distances. The propagules of some species, such as red mangrove, can survive desiccation and remain buoyant and viable for up to a year before arriving in a suitable environment. Once in a suitable, low salinity environment, air-filled intercellular spaces flood with water so that the elongated shape now floats vertically rather than horizontally. In this position, it is more likely to lodge in the mud and root. If it does not root, it can regain buoyancy and drift again in search of more favorable conditions.
== Taxonomy and evolution == The following listings, based on Tomlinson, 2016, give the mangrove species in each listed plant genus and family. Mangrove environments in the Eastern Hemisphere harbor six times as many species of trees and shrubs as do mangroves in the New World. Genetic divergence of mangrove lineages from terrestrial relatives, in combination with fossil evidence, suggests mangrove diversity is limited by evolutionary transition into the stressful marine environment, and the number of mangrove lineages has increased steadily over the Tertiary with little global extinction. However, the first mangroves were composed of marine taxa that had become adapted to coastal, brackish environments, and these are documented as early as the Pennsylvanian, and other examples are known from the early Cisuralian. It is likely that mangroves are even older than that, given that life originated in the seas, and that many environments previously thought to be freshwater (and many of which had an abundant flora) display evidence of marine influence.
=== True mangroves ===
=== Other mangroves ===
== Species distribution ==
Mangroves are a type of tropical vegetation with some outliers established in subtropical latitudes, notably in South Florida and southern Japan, as well as South Africa, New Zealand and Victoria (Australia). These outliers result either from unbroken coastlines and island chains or from reliable supplies of propagules floating on warm ocean currents from rich mangrove regions.