Fairy Moss and the Fixation of Atmospheric Nitrogen
| The Fairy Mosses or Azolla species are quite remarkable in that in a symbiotic relationship with a bacterium, Anabena azollae, they are capable of fixing atmospheric nitrogen. The fixation of nitrogen is the reduction to ammonium ions (NH4+), a process that can only succeed with a bacteria or a related filamentous organism called Frankia. There has never been a case of a green plant having the capability of fixing atmospheric nitrogen without such an association.
|
 Azolla has a symbiotic relationship with a bacterium, Anabena azollae.
|
| Anabena are known as a photosynthetic cyanobacteria, A.azollae associating solely with the various species of Azolla. Filaments of Anabena can be found in the proximity of the apical growing point of the Azolla stem. Pieces of the filaments then become enclosed in the lobes of the leaves as they form, thereby being given protection. A small depression forms in the lower surface of the upper leaf lobe and within this depression there is a prominent branched hair. The cells of Anabena become associated with this hair and the depression becomes a cavity into which the cells are confined. As the cavity finally closes, the Anabena cells form heterocysts, nitrogen-fixing organs, and hence, the fixation of atmospheric nitrogen commences. The ammonium ions are released into the cavity and taken up by the fern. Azolla species are widely grown across both the temperate and tropical world, although they are very much regarded as sub-tropical or tropical aquatics.
|
 Azolla is widely grown across the temperate and tropical world.
|
They occur widely outside water gardens and are encouraged in many of the rice paddies of the world, where they are used as a source of nitrogen for the growing rice crop. It has been estimated that Azolla with its associated Anabena, can contribute as much as 50 kilogrammes of nitrogen per hectare per crop of rice. As the rice grows taller the surface covering Azolla is shaded and dies.
|
| This releases the nitrogen to the crop. It is recorded that improved rice yields of up to 20% have been achieved with the careful use of Azolla. Under ideal conditions it is estimated that Azolla can fix around 5-8 kilogrammes of nitrogen per hectare per day. The benefits of this to decorative aquatic plant cultivation are limited. Presumably similar benefits can accrue to commercial crops of Nelumbo for the garden trade grown with Azolla, their parsol-like leaves shading out the Fairy Moss in the same way as the rice. Conversely, it is important to know that the destroying of excess Azolla in a water feature by the use of herbicides or oils brings two serious potential hazards if the dying plants are not removed.
|
As with all vegetation decomposition in water oxygen depletion results with the potential for causing problems with the fish. The release of a considerable amount of nitrogen-rich nutrients also brings the potential for a period of thick green algae-laden water, a direct result of the ability of Azolla to capture nitrogen from the air.
Click to join pondmessenger
|
 Improved rice yields of up to 20% have been achieved with Azolla.
|
|
America 
Australia 
Canada 
Europe 
International 
New Zealand 
South Africa 
United Kingdom 
