Azolla (Azolla sp.) is an aquatic fern consisting of a short, branched, floating stem, bearing roots which hang down in the water. The leaves are alternately arranged, each consisting of a thick aerial dorsal lobe containing green chlorophyll and a slightly larger thin, colourless, floating ventral lobe. Under some conditions, an anthocyanin pigment gives the fern a reddish-brown colour. Plant diameter ranges from 1-2.5 cm for small species such as Azolla pinnata, to 15 cm or more for Azolla nilotica. Azolla plants are triangular or polygonal in shape, and float on the surface of the water, individually or in mats. They give the appearance of a dark green to reddish carpet, except Azolla nilotica that does not produce the red anthocyanin pigment. The most remarkable characteristic of azolla is its symbiotic relationship with the nitrogen-fixing blue-green alga (cyanobacterium) Anabaena azollae. The fern provides nutrients and a protective cavity in each leaf to Anabaena colonies in exchange for fixed atmospheric nitrogen and possibly other growth-promoting substances Azolla has a historical role in agriculture. For centuries, it has been recognized as a useful plant in Southern China and Northern Vietnam, where it has been used as a biofertilizer and green manure for the rice crop due to its N-fixing abilities Azolla was also mentioned as a poultry feed in Peru in the 18th century. Azolla production was heavily promoted in the early 1960s in China and Vietnam, resulting in a rapid expansion in these countries. It attracted international attention in the 1970s as a result of the oil crisis and the rising prices of fossil fuel-dependent N fertilizers. Azolla became a potential replacement for these as it was believed that it could bolster rice production in many tropical countries. However, enthusiasm for azolla faded in the 1980s and was followed by a period of scepticism. Azolla production in China and Vietnam declined (perhaps due to the increasing use of land for
Trustpilot
1 week ago
1 day ago