What is a halophyte?
A halophyte is a specialised type of plant that is adapted to live in saline (salty) environments. For example, plants in marshes, swamps, mangroves and seashores are all classed as halophytes. They have a number of adaptations which are useful in order to ensure they have an appropriate concentration of salt.
What are the structural adaptations for halophytes?
Aerial root systems (pneumatophores)
These aid in respiration. The muddy, oxygen-poor soils which characterise these environments do not hold the amount of oxygen needed for these trees to effectively respire. Oxygen diffuses into the spongy tissue of the pneumatophores. They grow upwards out of the water/mud in order to reach the air.
Filtration structures in roots
These present salt from entering their roots. Mangroves in particular have an ultrafiltration system that can filter approximately 90% of sodium ions from the surrounding salt water. The three layers of the filtration system surrounding the roots trap sodium ions but allow water to pass through as it is pulled into the xylem.
Salt is directed to plant surfaces, where salt glands secrete salt to reduce the salt content of the plant.
What are the physiological adaptations for halophytes?
Concentrating and storing salt in vacuoles
Some halophytes store salt in the vacuoles of the fleshy stem segments or 'beads' which can have salt concentrations of anywhere between 30 and 45 percent. The salt in the beads become highly concentrated, shrivel, die and drop off. This allows the rest of the plant to remain healthy.
Accumulating salt in leaves/bark
Salt is directed to older leaves or bark where it accumulates. The leaves or bark eventually die and drop off, removing the salt from the plant. Another name for this process is abscission.