Product Code Database
Azolla (commonly called mosquito fern, water fern, and fairy moss) is a genus of seven species of aquatic plant in the family Salviniaceae. They are extremely reduced in form and specialized, having a significantly different appearance to other ferns and more resembling some or even Lemnoideae. Azolla filiculoides is one of two fern species for which a reference genome has been published. It is believed that this genus grew so prolifically during the Eocene (and thus absorbed such a large amount of carbon) that it triggered a global cooling event that has lasted to the present.
Azolla may establish as an invasive plant in areas where it is not native. In such a situation, it can alter aquatic ecosystems and biodiversity substantially by exhausting oxygen and covering water surface making underwater plants unable to photosynthesise.
At least six extinct species are known from the fossil record:
Azolla floats on the surface of water by means of numerous small, closely overlapping scale-like Leaf, with their roots hanging in the water. They form a symbiosis relationship with the cyanobacterium Anabaena, which lives outside the cells of its host and which fixes atmospheric nitrogen. The typical limiting factor on its growth is phosphorus; thus, an abundance of phosphorus—due for example to eutrophication or chemical runoff—often leads to Azolla blooms. Unlike all other known plants, its symbiotic microorganism transfers directly from one generation to the next. A. azollae is completely dependent on its host, as several of its genes have either been lost or transferred to the cell nucleus in Azolla's cells.
The nitrogen-fixing capability of Azolla has led to widespread use as a biofertiliser, especially in parts of southeast Asia. The plant has been used to bolster agricultural productivity in China for over a thousand years. When paddy field are flooded in the spring, they can be planted with Azolla, which then quickly multiplies to cover the water, suppressing weeds. The rotting plant material resulting from the die-off of this Azolla releases nitrogen into the water for the rice plants, providing up to nine tonnes of protein per hectare per year.
Azolla are in many parts of the world, entirely covering some bodies of water. While Azolla reduces the rate at which mosquito larvae survive, it is a myth that no mosquito can penetrate the coating of fern to lay its eggs in the water that gives the plant its common name "mosquito fern".
Most species can produce large amounts of deoxyanthocyanins in response to various stresses, including bright sunlight and extreme temperatures, causing the water surface to appear to be covered with an intensely red carpet. Herbivore feeding induces accumulation of deoxyanthocyanins and leads to a reduction in the proportion of polyunsaturated fatty acids in the fronds, thus lowering their palatability and nutritive value.
Azolla cannot survive winters with prolonged freezing, so is often grown as an ornamental plant at high latitudes where it cannot establish itself firmly enough to become a weed. It is also not tolerant of salinity; normal plants cannot survive in greater than 1–1.6‰, and even conditioned organisms die if grown in water with a salinity above 5.5‰.
Like all ferns, sexual reproduction leads to spore formation, but unlike other members of this group, Azolla is heterosporous, producing spores of two kinds. During the summer months, numerous spherical structures called sporocarps form on the undersides of the branches. The male sporocarp is greenish or reddish and looks like the egg mass of an insect or spider. It is two millimeters in diameter, and bears numerous male Sporangium. Male spores (microspores) are extremely small and are produced inside each microsporangium. Microspores tend to adhere in clumps called massulae.
Female sporocarps are much smaller, containing one sporangium and one functional spore. Since an individual female spore is considerably larger than a male spore, it is termed a megaspore.
Azolla has microscopic male and female gametophytes that develop inside the male and female spores. The female gametophyte protrudes from the megaspore and bears a small number of archegonia, each containing a single egg. The microspore forms a male gametophyte with a single antheridium which produces eight swimming sperm. 658 pp. The barbed glochidia on the male spore clusters cause them to cling to the female megaspores, thus facilitating fertilization.
Rice farmers used Azolla as a rice biofertilizer 1500 years ago. The earliest known written record of this practice is in a book written by Jia Sixie in 554 CE in Qimin Yaoshu ( Essential Techniques for the Welfare of the People). By the end of the Ming dynasty in the early 17th century, Azolla
They contribute significantly to decreasing the atmospheric CO2 levels.
Azolla filiculoides is especially invasive because it has the ability to survive temperatures as low as and can survive thin layers of ice built up on its growth. A. filiculoides spreads at rapid pace by way of fragmentation which takes place in the rhizome (root-system). It can double its surface area and/or density in approximately 7–10 days under ideal conditions.
A. filiculoides disrupts aquatic ecosystems by altering abiotic conditions in the water. It can displace native plants in places where it is invasive, such as the duckweed Lemna minor in Poland. It is difficult to control due to its ability to reestablish itself from spores.
Applications
Food and animal feed
In addition to its traditional cultivation as a bio-fertilizer for wetland paddies, Azolla is finding increasing use for sustainable production of livestock feed. Azolla is rich in protein, essential amino acids, vitamins, and minerals. Studies describe feeding Azolla to dairy cattle, pigs, ducks, and chickens, with reported increases in Dairy, weight of broiler chickens and egg production of layers, as compared to conventional feed. One FAO study describes how Azolla integrates into a tropical biomass agricultural system, reducing the need for food supplements.
Concerns related to BMAA
Concerns about biomagnification exist because the plant may contain the neurotoxin β-methylamino-L-alanine (BMAA) that remains present in the bodies of animals consuming it, and BMAA has been documented as passing along the food chain. Azolla may contain this substance that is a possible cause of neurodegenerative diseases, including causing ALS, Alzheimer's, and Parkinson's. Azolla has been suggested as a foodstuff for human consumption; however, no long-term studies of the safety of eating Azolla have been made on humans. Previous studies attributed neurotoxin production to Anabaena flos-aquae species, which is also a type of nitrogen-fixing cyanobacteria. Studies published in 2024 have found that "the Azolla–Nostoc azollae superorganism does not contain BMAA or their isomers DAB and AEG and that Azolla and N. azollae do not synthesize other common cyanotoxins." Further research may be needed to ascertain whether A. azollae is a healthy foodstuff for humans.
Companion plant
Azolla has been used for at least one thousand years in rice paddies as a companion plant, to fix nitrogen and to block out light to prevent competition from other plants. Rice is planted when tall enough to poke through the Azolla layer. Mats of mature Azolla can also be used as a weed-suppressing mulch.
Larvicide
The myth that no mosquito can penetrate the coating of fern to lay its eggs in the water gives the plant its common name "mosquito fern". Azolla have been used to control mosquito larvae in rice fields. The plant grows in a thick mat on the surface of the water, making it more difficult for the larvae to reach the surface to breathe, effectively choking the larvae.
Paleoclimatology and climate change
Azolla has been proposed as a carbon sequestration modality. The proposal draws upon the hypothesized Azolla event that asserts that 55 million years ago, Azolla covered the Arctic – at the time a hot, tropical, freshwater environment – and then sank, permanently sequestering Tonne of carbon that would otherwise have contributed to the planet's greenhouse effect. This ended a warming event that reached warmer than present-day averages, eventually causing the formation of in Antarctica and the current "icehouse period".
Invasive species
This fern has been introduced to other parts of the world, including the United Kingdom, where it has become a pest in some areas. A nominally tropical plant, it has adapted to the colder climate. It can form mats up to thick and cover 100% of a water surface, preventing local insects and amphibians from reaching the surface.
Bioremediation
Azolla can remove chromium, nickel, copper, zinc, and lead from effluent. It can also remove lead from solutions containing 1–1000 ppm.
Notes
External links
|
|
