how plants cope in the mangroves: breathing roots

CONTENTS

Fauna index

How plants cope in the mangroves

Peter K L Ng and N Sivasothi (editors)

Breathing Roots
An aerial root may be defined as a root which, for part of the day at least, is exposed to the air. The mangrove mud is rather anaerobic (oxygen poor) and unstable and different plants have root adaptations to cope with these conditions.

Pneumatophores
Pneumatophores are erect roots that are some form of upward appendage or extension of the underground root system. Because these roots are exposed at least part of the day and not submerged underwater, the root system can obtain oxygen in an otherwise anaerobic substrate.

In Avicennia and Sonneratia species, the pneumatophores are erect side branches of the horizontal roots which grow just below the soil. In Avicennia, they are pencil-like and grow up to only 30 cm tall, whereas in Sonneratia, they grow more slowly to become woody and may even reach 3 m in height, though most will be less than 50 cm tall. The widely spreading horizontal roots, from which the pneumatophores grow, improve anchorage in the unstable mud.

Pneumatophores of
Avicennia

Prop and Stilt Roots
In Bakau (Rhizophora species), branched, looping roots arise from the trunk and lower branches. At this stage, they are known as prop roots.

They become stilt roots only when they take the function of flying buttresses when the tree is older and the bottom of the trunk becomes upside down conical and may even lose contact with the ground. A flying buttress is a structure found in Gothic architecture and consists of an inclined bar carried on an arch (equivalent to the root here), which rests against a support (ground) to receive the weight of a wall (trunk). The stilt roots also improve the stability of the tree by providing a broader base and support in the soft and unstable mud. They also help in aeration as they are exposed for at least most of the day between tides.

Prop roots of
Rhizophora

Kneed Roots
In Bruguiera and Ceriops the horizontal roots growing just below the soil surface periodically grow vertically upwards then immediately loop downwards to resemble a bent knee. By repetition, a single horizontal root develops a series of knees at regular intervals.

The aerial portions (knees) of these roots help in aeration of the whole root which because it spreads so widely, improves anchorage in the unstable mud.

Lumnitzera species also produce inconspicuous, small kneed roots which appear to be intermediate in structure between those of the above species and pneumatophores.

Kneed roots of
Bruguiera cylindrica

Plank Roots
In Nyireh bunga (Xylocarpus granatum), the horizontal roots grow vertically upwards on the upper side for the entire length. They also curve in a snake like fashion so wavy, plank-like structures radiate outwards from the trunk base. The exposed vertical portions help in aeration and the widely spreading roots help improve anchorage in the unstable mud.

Other adaptations to cope in the mangroves
Salt secretors and ultrafiltrators
Vivipary

Plank roots of
Xylocarpus granatum

What is mangrove?
Introduction

The Ecosystem
Abiotic
Biotic

Value
Intro
Products
Indirect uses
Potential uses

About Mangroves
in Singapore
History
Mangroves to visit
Conservation

From "A Guide to Mangroves of Singapore", Peter K. L. Ng and N. Sivasothi (editors)
Volume 1: The Ecosystem and Plant Diversity and Volume 2: Animal Diversity
Authors: Kelvin K. P. Lim, Dennis H. Murphy, T. Morgany, N. Sivasothi, Peter K. L. Ng,
B. C. Soong, Hugh T. W. Tan, K. S. Tan & T. K. Tan
BP Guide to Nature Series published by the Singapore Science Centre, sponsored by British Petroleum
© 2001 Raffles Museum of Biodiversity Research, The National University of Singapore & The Singapore Science Centre