Azolla is a unique freshwater fern that is one of the fastest growing plants on the planet due to its symbiotic relationship with a benign cyanobacterium (‘blue-green alga’) called Anabaena azollae (also known as Noctoc azollae). Anabaena draws down atmospheric nitrogen that fertilizes Azolla, and Azolla provides a home for Anabaena within its leaf cavities. This enables the plant to double its biomass in as little as two days, free-floating on water as shallow as one inch (2.4 cm).
Azolla‘s rapid growth enables it to sequester large amounts of the greenhouse gas carbon dioxide (CO2) which is converted directly into Azolla‘s biomass. This provides local, renewable livestock feed, biofertilizer and biofuel wherever Azolla is grown, so that this remarkable plant has the potential to help us weather the Perfect Storm – the related threats of man-made climate change and shortages of food and land as our population approaches eight billion.
Why is Azolla Unique?
Azolla is unique because it is one of the fastest growing plants on the planet – yet it does not need any soil to grow. Unlike almost all other plants, Azolla is able to get its nitrogen fertilizer directly from the atmosphere. That means that it is able to produce biofertilizer, livestock feed, food and biofuel exactly where they are needed and, at the same time, draw down large amounts of CO2 from the atmosphere, thus helping to reduce the threat of climate change.
How is it able to do this?
Azolla and Anabaena – the Perfect Marriage
Azolla is able to do this because it has a unique, mutually beneficial symbiotic relationship with Anabaena.
Each partner gives something to the other in this perfect marriage. Azolla provides a protective environment for Anabaena within its leaves. In return, Anabaena sequesters nitrogen directly from the atmosphere which then becomes available for Azolla’s growth, freeing it from the soil so that it can grow rapidly free-floating on water.
The oldest Azolla fossils are more than 80 million years old, representing the remains of plants that lived during the Late Cretaceous Period. They occur in sediments that were deposited in quiescent freshwater bodies, such as lakes, ponds and sluggish rivers, identical to those inhabited by modern Azolla.
- Fossil Azolla (left) has leaves (circled above in red) and tendrils (circled in blue) that are identical to those of modern Azolla (right). The fossil is from the Green River Formation of Colorado, dated between 50.5 and 55.5 million years. The photograph was kindly provided by Dr Ian Miller of the Denver Museum of Nature and Science.
Several other symbioses are known between plants and cyanobacteria – for example in legumes – but the Azolla-Anabaena relationship is the only known symbiosis in which a cyanobacterium passes directly to subsequent generations via the plant’s reproductive sporangia and spores.
So Azolla and Anabaena have never been apart for more than 80 million years. During that Immense period of time, the two partners have co-evolved numerous complementary ways that make them increasingly efficient.
The Azolla Superorganism: A unique biological system
In 2010, Professor Francisco Carrapiço proposed that Azolla should be designated as a Superorganism “because of its unique symbiosis in which the two partners have successful co-evolved into a system that makes important contributions to ecology, biofertilization and biotechnology” (Carrapiço, 2010).
That is the key to azolla’s multiple uses: this unique plant is a Superorganism that can help combat climate change and also produce local, renewable livestock feed, biofertlilizer, biofuel and food anywhere in the world.