of mangrove trees to the environment
are a challenging environment for plants to live in. Plants living
in mangroves have special adaptations to enable them to survive
in the environment. The aim of this session is to demonstrate
the morphological features that allow the plants to gain strong
anchorage on the ground, obtain adequate oxygen for respiration
and cope with salt and desiccation stress.
a) Mode of attachment:
Locate the mangrove tree Kandelia candel and focus your
investigation on the roots. You can ask the students to draw an
annotated diagram to illustrate the appearance of the roots of
K. candel as shown in the following:
Below are some
recommended questions to guide students to think about the morphological
adaptations of mangrove plants.
Describe any special features that enable Kandelia to gain
firm anchorage in the muddy substratum?
roots of the mangroves expand horizontally as buttress roots to
enable them to have firm anchorage on the ground.
Look at other mangrove tree species (e.g. Avicennia marina).
What other adaptations for anchorage can you see?
marina has under ground roots called 'cable roots' which expand
in a horizontal direction to gain anchorage.
The struggle for oxygen:
Locate the mangrove tree Avicennia marina which is characterized
by having "root" outgrowths from the ground called pneumatophores.
You can ask the students to draw the structures they see around
the trunks of A. marina.
What is the significance of Avicennia having such a pneumatophore
the mud of mangroves has a very low oxygen content, A.
marina has roots that grow vertically from the ground called
Pneumatophores to obtain oxygen. Pneumatophores have loosely packed
tissues to allow effective diffusion of gases into the pith.
Below are some recommended questions to help students to think
about the adaptations of mangrove plants to tolerate salinity
Locate the mangrove tree Aegiceras corniculatum. Look carefully
at the leaf surface. Can you find any white crystals on the surface?
What are they?
white crystal is salt.
What is the significance of this phenomenon?
get rid of the salt content inside the plant, A. corniculatum
has salt glands on its leaves to secrete salt out of the body.
3. What other forms of adaptation could mangrove trees show to
overcome problems of osmotic balance?
candel actively excludes salt
from entering the body in the root region. Lumnitzera racemosa
stores salt inside the leaf as salt crystals.
d) Desiccation stress:
1. Locate Lumnitzera racemosa, touch the leaves and compare
their thickness with other trees and observe the cuticle (break
the leaf to do this). Can you suggest why the leaves should be
so succulent (thick) and have such a thick cuticle?
reduce water loss from evaporation, leaves of L. racemosa
have a thick cuticle. The leaves also have loose packed cells
to store water vapour inside the leaves.