Photo credits: http://www.sms.si.edu/IRLspec/Mangroves.htmIn this post,
we are going to talk about
the adaptations of mangroves
to their environment over the years.
Photo credits: http://www.aims.gov.au/pages/research/mangroves/images2/Mangroves-480.gif
1. Salt resistance
Mangrove plants have evolved to adapt to salt water as they are normally found along the coastal area where freshwater is scarce. This may involve cytoplasmic tolerance of high solute concentrations, and many of the common species have in-leaves sodium and chloride ion levels that each exceed about half that of sea water. In addition, the most salt-resistant species also tend to show avoidance to salt stress. Avoidance can be achieved by excretion of crystalline salt from glands or hairs of leaves. Examples of salt excretion are Avicennia, Aegialitis annulata (family Plumbaginaceae). Another mechanism to avoid toxic levels of ions is to produce succulence, i.e., dilution of salts via having watery tissues. Salt dilution is said to be the reason for having large hypodermal cells on the upper (adaxial) side of leaves, covering the photosynthetic tissues, e.g., in Avicennia and Rhizophora, or large, vacuolate cells in the middle tissue in Sonneratia and Laguncularia.
2. Dispersal of seeds
Germination of seeds while still attached to the mother plant is called vivipary. Vivipary is exceedingly rare among plants, but these are found in many early colonizing, pioneer species of mangroves, including Avicennia, Rhizophora and all other Rhizophoraceae, Aegiceras, Pelliciera, Aegialitis, and the aggressive estuarine species Nypa fruticans. The classic example of vivipary is Rhizophora mangle, which is able to traverse broad ocean regions by producing large seedlings that float horizontally, undamaged by salinity. These seedlings can be washed up on sand or mud flats, where they settle to establish new populations. In this case, the hypocotyl develops as a long, stiff axis, sometimes exceeding a foot in length. By germinating while on the mother plant, and thereby drawing nutrients under lower salt stress, the young plant can increase its salt resistance before falling into the seawater environment where it remains dormant until it finds the soil and is able to put out roots.
3. Roots
A distinctive feature of mangroves is their far-reaching, exposed roots. These roots might come in many different shapes and sizes, however they all serve the same purpose – structural support in the soft soils. Some species of mangroves have pneumataphores, which are above-ground roots. These are filled with spongy tissue and peppered with small holes that offer structural support and allow oxygen to be transferred to the roots trapped below ground in the anaerobic (low oxygen) soils. There are mainly 4 types of roots – buttress, knee-like, pencil-like and prop roots. The roots of many mangrove species are also adapted to stop the intake of a lot of the salt from the water before it reaches the plant.
a real life mangrove sketch:
sketch 1:
Photo credits: http://www.wettropics.gov.au/pa/pa_images/roots.gif
Credits:
http://www.botgard.ucla.edu/html/botanytextbooks/worldvegetation/marinewetlands/mangal/generalcharacteristics.html
http://www.redland.qld.gov.au/Environment/Mangroves/Pages/MangroveAdaptations.aspx
