Ready salted: adaptation to life as a halophyte
A halophyte is any plant which is able to exist and thrive in high salinity conditions, through frequent contact with high concentrations of salt found in soil and water. Due to these specific conditions they are often found on the boundary between marine and terrestrial environment. The two most common environments for halophytic plants to be found is in salt marshes and mangrove swamps. Both of these habitats actively provide protection from the open ocean and are natural sea defenses. Additionally to this, mangroves and salt marshes also act as nursery grounds for many marine fish species. Halophytes also play a commercial role in aiding agricultural companies with the development of salt tolerant crop species.
As most plant species normally absorb freshwater through their roots, special adaptations are displayed by halophytic organisms to deal with the saline conditions. Nearly all halophytes are sensitive to salt at a young age and as seedlings, which is the opposite to how they exist in their adult lives. In plants, water will move from an area of low solute concentration to an area of high solute concentration via osmosis. In freshwater the concentration of solutes is always higher inside the plant than in the surrounding water and soil, meaning that water moves into the plant. In the conditions halophytes are found in however this is the opposite. Due to increased solute concentration outside the cell, water is more likely to move out of the plant body into the surrounding area. The cells within the root system therefore, must act to prevent becoming plasmolyzed. It is key to the survival of the plant that the cells in the root system remain turgid. This is where the adaptations of halophytes are adapted uniquely to deal with their environment. Adaptations vary between different halophyte species in accordance to physical stressors related to slainity and other physical factors within the environment.
Salt marsh halophytes
The one of the most abundant plant groups found on salt marshes across the globe are Spartina spp., of which there are just under 20 species. Dominant species on the East coast of the United States are Spartina patens and Spartina alterniflora. In S. patens, it had been found that in response to salt stress the chemical make up of the cell membrane may change. With times of increased salinity level the amount of campestersol is greater in the cell wall whereas sitosterol is decreased when there is reduced salinity stress. The level of overall membrane fluidity level remained the same as when there is reduced salinity, showing a clear adaptation to changing environment conditions.
Salicornia spp. are another group of halophytes which are highly dominant across salt marshes globally, with more than 20 species existing globally. They are some of the most tolerant species to salinity of all plants. Still though, Salicornia europaea seedlings germinate at the time of year when salinity levels are at their lowest to ensure a greater chance of survival. As adults the cells of S. europaea are able to function due to the fact the compartmentalize sodium into the vacuole, this allows them to remain turgid and carry out their function properly.
Mangroves are the dominant woody plant found along tropical coastlines. They form dense forests along the coastline and are inhabited by many species of juvenile fish and invertebrates. Rhizophora mangle is the dominant species in mid florida. Adults only germinate when they are fully grown and well developed. It grows of wood-prop results which raise it out of the water, this allows it to gain air through pores situated on the non-submerged part of the root structure. The roots of the plant are highly impermeable to salt by using ultra filtration methods to remove salt from the water the root uptakes. Due to this we say that R. mangle uses salt exclusion methods to deal with salinity levels rather than salt excretion methods displayed in other mangrove species e.g. Avicennia marina.
Halophytes are pivotal as a form of natural sea defense mechanism on coast lines globally. They host a wide diversity of life and act as a nursery ground for future generations of marine life. Due to this it makes them a good place to study scientifically. They are also of environmental importance because of this, making conservation attempts to protect halophyte ecosystems well worth time. Halophytic plants are essential in the process of making salt resistant crops. They they can also be used for other purposes such as food, showing halophytes also have a solid commercial importance.