Adaptations of mangrove trees to the environment

Adaptations of mangrove trees to the environment

Mangroves 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.

1. Describe any special features that enable Kandelia to gain firm anchorage in the muddy substratum?

The roots of the mangroves expand horizontally as buttress roots to enable them to have firm anchorage on the ground.

2. Look at other mangrove tree species (e.g. Avicennia marina). What other adaptations for anchorage can you see?

Avicennia marina has under ground roots called 'cable roots' which expand in a horizontal direction to gain anchorage.

b) 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.

1. What is the significance of Avicennia having such a pneumatophore root system?

As 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.

c) Salinity stress:
Below are some recommended questions to help students to think about the adaptations of mangrove plants to tolerate salinity stress.

1. Locate the mangrove tree Aegiceras corniculatum. Look carefully at the leaf surface. Can you find any white crystals on the surface? What are they?

The white crystal is salt.

2. What is the significance of this phenomenon?

To 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?

Kandelia 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?

To 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.

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