Mosquito fern
Azolla caroliniana
Scientific classification
Kingdom:	Plantae
Division:	Pteridophyta
Class:	Pteridopsida
Order:	Salviniales
Family:	Salviniaceae
Genus:	Azolla Lam.[1]
Type species
A. filiculoides[1]
Species
See list below

Azolla (mosquito fern, duckweed fern, fairy moss, water fern) is a genus of seven species of aquatic ferns in the family Salviniaceae. They are extremely reduced in form and specialized, looking nothing like conventional ferns but more resembling duckweed or some mosses.

Selected species[link]

Azolla caroliniana Willd.
   [ Poss. synon. of A. filiculoides ]
Azolla circinata Oltz & Hall
Azolla filiculoides Lam.
Azolla japonica Franch. & Sav.
   [ Poss. synon. of A. filiculoides ]
Azolla mexicana C.Presl
Azolla microphylla Kaulf.
Azolla nilotica Decne. ex Mett.
Azolla pinnata R.Br.
Azolla rubra R.Br.
   [ Poss. synon. of A. filiculoides ]

List sources :^[2][3][4]

At least six extinct species are known from the fossil record:

• Azolla intertrappea Sahni & H.S. Rao, 1934 (Eocene, India)^[5]
• Azolla berryi Brown, 1934 (Eocene, Green River Formation, Wyoming)^[5]
• Azolla prisca Chandler & Reid, 1926 (Oligocene, London Clay, Isle of Wight)^[5]
• Azolla tertiaria Berry, 1927 (Pliocene, Esmeralda Formation, Nevada)^[5]
• Azolla primaeva (Penhallow) Arnold, 1955 (Eocene, Allenby Formation, British Columbia)^[5]
• Azolla boliviensis Vajda & McLoughlin, 2005 (Maastrichtian - Paleocene, Eslaboacuten Formation& Flora Formation Bolvia)^[6]

Ecology[link]

Azolla covering the Canning River

Azolla on the Canning River, Western Australia

Azolla filiculoides (Red Azolla) is the only member of this genus and of the family Azollaceae in Tasmania. It is a very common native aquatic plant in Tasmania. It is particularly common on farm dams and other still water bodies. The plants are small (usually only a few cm across) and float, but can be very abundant and form large mats. The plants are typically red, and have very small water repellent leaves.'Azolla floats on the surface of water by means of numerous, small, closely overlapping scale-like leaves, with their roots hanging in the water. They form a symbiotic relationship with the cyanobacterium Anabaena azollae, which fixes atmospheric nitrogen, giving the plant access to the essential nutrient. This has led to the plant being dubbed a "super-plant", as it can readily colonise areas of freshwater, and grow at great speed - doubling its biomass every two to three days. The only known limiting factor on its growth is phosphorus, another essential mineral. An abundance of phosphorus, due for example to eutrophication or chemical runoff, often leads to Azolla blooms.

SEM image of Azolla surface

The nitrogen-fixing capability of Azolla has led to Azolla being widely used as a biofertiliser, especially in parts of southeast Asia. Indeed, the plant has been used to bolster agricultural productivity in China for over a thousand years. When rice paddies are flooded in the spring, they can be inoculated with Azolla, which then quickly multiplies to cover the water, suppressing weeds. The rotting plant material releases nitrogen to the rice plants, providing up to nine tonnes of protein per hectare per year.^[7]

Azolla are also serious weeds in many parts of the world, entirely covering some bodies of water. 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".^[8]

Most of the species can produce large amounts of deoxyanthocyanins in response to various stresses,^[9] including bright sunlight and extremes of temperature,^[10][11] 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.^[12]

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 not tolerant to salinity; normal plants can't survive in greater than 1-1.6‰, and even conditioned organisms die in over 5.5‰ salinity.^[13]

Reproduction[link]

Scanning Electron Micrograph (SEM) of a megaspore of the genus Azolla with adhering massulae from Postglacial sediments of Laguna El Junco, Galápagos Island of San Cristóbal.

Transmission Electron Micrograph (TEM) of a megaspore of the genus Azolla from Postglacial sediments of Laguna El Junco, Galápagos Island of San Cristobal.

Azolla reproduces sexually, and asexually by splitting.

Like all ferns, sexual reproduction leads to spore formation, but Azolla sets itself apart from other members of its group by producing 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 inside are numerous male sporangia. Male spores (microspores) are extremely small and are produced inside each microsporangium. Curiously, microspores tend to adhere in clumps called massulae.^[5]

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.^[14] The barbed glochidia on the male spore clusters are assumed to cause them to cling to the female megaspores, thus facilitating fertilization.

Human Use[link]

Food[link]

In addition to its traditional cultivation as a bio-fertilizer for wetland paddy (due to its ability to fix nitrogen), azolla is finding increasing use for sustainable production of livestock feed.^[15] Azolla is rich in proteins, essential amino acids, vitamins and minerals. Studies describe feeding azolla to dairy cattle, pigs, ducks, and chickens, with reported increases in milk production, 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 inputs.^[16]

Companion plant[link]

Azolla has been used, for at least one thousand years [1], in rice paddies as a companion plant, because of its ability to both fix nitrogen, and block out light to prevent any competition from other plants, aside from the rice, which is planted when tall enough to poke out of the water through the azolla layer.

Larvicide[link]

As an additional benefit to its role as a paddy biofertilizer, Azolla spp. 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.^[17]

Climatic paleontology[link]

A study of Arctic climatology reported that azolla may have had a significant role in reversing an increase in greenhouse effect that occurred 55 million years ago that caused the region around the north pole to turn into a hot tropical environment. This research conducted by the Institute of Environmental Biology at Utrecht University claims that large dense patches of Azolla growing around freshwater lakes formed by the climate change eventually consumed enough carbon dioxide for the greenhouse effect to reverse.

See also[link]

• Aquatic plant
• List of companion plants

References[link]

• Scagel, R. F., Bandoni, R. J., Rouse, G. E., Schofield, W. B., Stein, J. R., & Taylor, T. M. C. (1966). An Evolutionary Survey of the Plant Kingdom. Wadsworth.

External links[link]

Wikispecies has information related to: Azolla

• aquaplant.tamu.edu
• Germplasm Resources Information Network: Azolla
• Flora of China: Azolla species list
• Flora of North America: Azolla
• Marriage Between A Fern & Cyanobacterium
• plants.usda.gov
• royalbcmuseum.bc.ca
• NSW Flora online: Azolla
• Azolla Fact Sheet

Masanobu Fukuoka, originator of the natural farming method

Natural farming is an ecological farming approach established by Masanobu Fukuoka (1913–2008), a Japanese farmer and philosopher who described his agricultural philosophy as shizen nōhō (自然農法^?) in Japanese.^[1] It is also referred to as "the Fukuoka Method", "the natural way of farming" or "do-nothing farming". The title refers not to lack of labor, but to the avoidance of manufactured inputs and equipment. Natural farming can also be described as ecological farming and is related to organic farming, sustainable agriculture, agroforestry, ecoagriculture and permaculture but should be distinguished from biodynamic agriculture.

The system exploits the complexity of living organisms that shape each particular ecosystem. Fukuoka saw farming not just as a means of producing food but as an aesthetic or spiritual approach to life,^[2] the ultimate goal of which was, "the cultivation and perfection of human beings".^[3] He suggested that farmers could benefit from closely observing local conditions.^[4] Natural farming is a closed system, one that demands no inputs and mimics nature.^[5]

Fukuoka's ideas challenged conventions that are core to modern agro-industries, instead promoting an environmental approach.^[6] Natural farming also differs from conventional organic farming^[7], which Fukuoka considered to be another modern technique that disturbs nature.^[8]

Fukuoka claimed that his approach prevents water pollution, biodiversity loss and soil erosion while still providing ample amounts of food.^[9]

Principles[link]

Fukuoka distilled natural farming into five principles:^[10]

1. No tillage
2. No fertilizer
3. No pesticides (or herbicides)
4. No weeding
5. No pruning

Though many of his plant varieties and practices relate specifically to Japan, and even to local conditions in subtropical western Shikoku, his philosophy and the governing principles of his farming systems have been applied from Africa to the temperate northern hemisphere. In India, natural farming is often referred to as "Rishi Kheti".^[11][12]

Principally, natural farming minimises human labour and adopts, as closely as practical, nature's production of foods such as rice, barley, daikon or citrus in biodiverse agricultural ecosystems. Without plowing, seeds germinate well on the surface if site conditions meet the needs of the seeds planted there. Fukuoka used the presence of spiders in his fields as a key performance indicator of sustainability.^{[citation needed]}}

The ground always remains covered by weeds, white clover, alfalfa, herbaceous legumes, and sometimes deliberately sown herbaceous plants. Ground cover is present along with grain, vegetable crops and orchards. Chickens run free in orchards and ducks and carp populate rice fields.^[13]

Periodically ground layer plants including weeds may be cut and left on the surface, returning their nutrients to the soil, while suppressing weed growth. This also facilitates the sowing of more seeds in the same area.^[why?]

For summer rice and winter barley grain crops, ground cover enhances nitrogen fixation. Straw from the previous crop mulches the topsoil. Each grain crop is sown before the previous one is harvested by broadcasting the seed among the standing crop. The result is a denser crop of smaller but highly productive and stronger plants.

Fukuoka's practice and philosophy emphasised small scale operation and challenged the need for mechanised farming techniques for high productivity, efficiency and economies of scale. While his family's farm was larger than the Japanese average, he used one field of grain crops as a small-scale example of his system.

Climax ecosystems[link]

Ladybirds consume aphids and are considered beneficial by natural farmers that apply biological control.

In ecology, climax ecosystems are mature ecosystems that have reached a high degree of stability, productivity and diversity (see old-growth forest). Natural farmers attempt to mimic those virtues, thus creating a comparable ecosystem, and employ such advanced techniques as intercropping, companion planting and integrated pest management.^{[citation needed]}

No-till[link]

This section needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (February 2012)

Natural farming recognizes soils as a fundamental natural asset. Ancient soils possess physical and chemical attributes which render them capable of generating and supporting life abundance. It can be argued that tilling actually degrades the delicate balance of a climax soil in the following ways:

1. Tilling may destroy crucial physical characteristics of a soil such as water suction, its ability to send moisture upwards, even during dry spells. The effect is due to pressure differences between soil areas. For more on this subject see water potential. Furthermore, tilling most certainly destroys soil horizons and hence disrupts the established flow of nutrients.

2. Tilling over-pumps oxygen to local soil residents, such as bacteria and fungi. As a result, the chemistry of the soil changes. Biological decomposition accelerates and the microbiota mass increases at the expense of other organic matter, adversely affecting most plants, including trees and vegetables. It is well-known to gardeners and farmers that for plants to thrive, a certain quantity of organic matter (around 5%) must be present in the soil.

3. Tilling uproots all the plants in the area, turning their roots into food for bacteria and fungi. This damages their ability to aerate the soil. Living roots drill millions of tiny holes in the soil and thus provide oxygen. They also create room for beneficial insects and annelids (the phylum of worms). Some types of roots contribute directly to soil fertility by funding a mutualistic relationship with certain kinds of bacteria (most famously the rhizobium) that can fix nitrogen.

Nature farming[link]

Another Japanese farmer and philosopher Mokichi Okada, conceived of a "no fertilizer" farming system in the 1930s which predated Fukuoka. Okada used the same Japanese characters,^[14] which are generally translated in English as "nature farming". Agriculture researcher Hu-lian Xu claiming that "nature farming" is the correct literal translation of the Japanese term.^[14]

See also[link]

	Sustainable development portal
	Systems science portal
	Ecology portal

References[link]