Problem 1:Anaerobic Condition

To cope with anaerobic

conditions during the high

tide period, mangrove plants

have developed mechanism to

enhance gaseous exchange, and

they include:

PneumatophoresThey are erected aerial roots, which arise from cable roots and they facilitate exchange of gases between the submerged roots and the atmosphere (e.g., Avicennia marina).They contain aerenchyma tissue (a specialized tissue with large intracellular air spaces), which allows rapid transportation of gases.

Knee JointsKnee JointsThey are roots that bend up like an arch and grow above the substrate surface (e.g., Aegiceras corniculatum Kandelia candel, Bruguiera gymnorrhiza).They are also rich in aerenchyma tissues, which facilitate the transfer of air.

LenticelsThey are small pores for gaseous exchange, which are present on pneumatophores, knee joints, and prop roots.

Problem 2: Unstable SubstratumTo cope with a soft unstable substratum, mangrove

plants have developed specialized root systems for

anchoring, they are:

Prop (or stilt) RootsThey are branched, looping aerial roots that arise from the trunk and lower branches.These supporting roots broaden the base and provide stability (e.g., Kandelia candel, Bruguiera gymnorrhiza, Aegiceras corniculatum).

Cable RootsThese roots spread horizontally and laterally just below the soil surface, and anchor the plants firmly in the soil (e.g., Avicennia marina).

Buttress RootsThese are a form of prop root, which thickens unevenly to produce flattened blade-like supporting structures and they function as flying buttresses (e.g., Heritiera littoralis; other Rhizophora species).

Problem 3:High Salinity (High NaCl Concentration)To cope with salinity, mangrove plants have developed various mechanisms to regulate the salt concentration in the plants, such as:

Salt Secretion Salt glands are present in leaves, and they concentrate and actively secrete the absorbed salts (e.g., Aegiceras corniculatum, Avicennia marina).

Storage of Salt and AbscissionExcess salt is stored in vacuoles or older leaves, which are then shed, thus reducing the salt content inside the plants (e.g., Bruguiera gymnorrhiza, Lumnitzera racemosa).

Balances Osmotic PotentialThe plants can accumulate low molecular weight carbohydrates to lower their osmotic potential, and so enable plants to absorb water from a salty environment.

Salt ExcludersThese physiologically prevent salt entering the root xylem by an active pump mechanism (e.g., Aegiceras corniculatum, Kandelia candel, Lumnitzera racemosa).

Water Storage TissueThe plants have xerophytic characteristics to reduce the intake of high salinity water, e.g., water storage tissues, waxy thick cuticle, sunken stomata and a hair surface.

Problem4:Establishment Problem

Due to the stressed environment

conditions, wave action and unstable

substratum, survival rates of seedlings are

low. Mangrove plants have evolved unique

reproductive strategies.

Viviparous ReproductionSeeds germinate inside the fruit without resting stage; early development of seedlings occurs when seeds are attached to the parent plant (e.g., Aegiceras corniculatum, Kandelia candel, Bruguriera gymnorrhiza).This allows rapid growth and establishment of young plants when they are finally detached from the plant and come into contact with the substrate.

Shape of PropagulesPropagules (dropper) are elongated and have flesh hypocotyls, so they float and disperse easily, but they also easily anchor in an up-right position; once they stick in mud, the already formed roots expand rapidly (e.g., Kandelia candel, Aegiceras corniculatum, Bruguiera gymnorrhiza).

Number of SeedsMany seeds are produced annually to enhance the reproductive success.

Adaptation for Non-viviparous SpeciesHeritiera littoralis produces large, woody fruits, containing one to several seeds, which have spongy outer layers that make them extra buoyancy.Excoecaria agallocha and Acanthus ilicifolius have an exploding capsule that releases numerous seeds.

Problem 5:DesiccationTo cope with the dry weather during exposure at low tide, mangrove plants have developed the following features:

Special Features of LeavesSunken stomata, epidermal hairs and scales, thick waxy cuticle in leaf surface to reduce evaporation and water loss (e.g., Kandelia candel, Avicennia marina, Aegiceras corniculatum, Excoecaria agallocha).

Large Water Storage TissuesMulti-layered water storage tissues to store water (e.g., Kandelal candel, Avicennia marina, Bruguiera gymnorrhiza, Aegiceras corniculatum, Lumnitzera racemosa)

White Tomentum or Scales at Lower Leaf SurfaceReflect bright light and lower plant temperature to reduce water loss (e.g., A. marina, H. littoralis).