Plants Used for Manganese
The plants used specifically for manganese detoxification are usually those that evolved in an area with naturally occurring high levels of the metal. Some of these plants are highly adaptable, while others need a very controlled environment. Thus the choice of plant will be determined by the local environment in which the manganese levels are toxic.
Sunflowers: Although great at removing toxins from the soil and very fast growing, they do not fare well in many soil conditions. They require fertile, moist, well-drained soil with a lot of mulch. Despite this limitation, they were used to remove cesium-137 and strontium-90 from a nearby pond after the Chernobyl disaster and are considered an excellent plant for removing almost all heavy metals. (This puts sunflowers in a category all its own as most other plants are only good for one type of metal extraction.) With enough fertilization and water supply, sunflowers, with their deeper root systems, are able to reach deeper into the soil than other plant choices.
Macadamia neurophylla (Proteaceae) is the absolute best choice for phytoremediation of manganese, if it can be acquired. It can accumulate up to 1000 (?), twice the amount of the nearest other choice. The problem with this plant is that it is found rarely and confined to the southern massifs of Grand Terre in Caledonia. Obtaining a supply and seeding it over a large enough range to produce the intended effect is almost never possible.
Pacific Mosquito Fern (also known as Fairy Moss): This plant has been used as a companion plant for detoxification and nitrogen stabilizing in China for over 1000 years. It is well suited for water born phytoremediation. The downfall of this plant is that is not salt tolerant, dying off at levels above 1%.
Gossia bidwillii (Myrtaceae): This 15 -25 meter tree is a slow growing hyperaccumulator of manganese. Known as the Python Tree and native from New South Wales to Coen in Australia, it hasn’t been picked up as commercial phytoremediation plant because of its need for wet, semi-moist substrate and slow growth rate.
Phytolacca acinosa Roxb. (Phytolaccaceae) is a manganese hyperaccumulator species that grows rapidly and is easily incorporated into several different growing environments. It is a compact (1-3 meter) plant that is a good choice for use with phytomining.
Stanleya Pinnata is a potentially useful species due to its broad adaptation to semi-arid environments and ability to withstand toxic levels of both manganese and selenium.
Other plants that have been identified as potential manganese accumulators are Alyxia rubricaulis (Apocynaceae), Maytemus bureauvianus (Celastraceae), Indian Mustard, and Vetiver grass (Vetiveria zizanioides L.).
When using any of these plants to detoxify a large area of land the natural chelates released by the roots of certain plants can form complexes with metals in the rhizosphere. This can compromise the possible chemical extraction from the harvested plants. These complexes can include siderophores, organic acids and phenolics each of which would require a secondary chemical process to extract the pure metal from the plant.
Another thing that these plants may do (as well as their associated soil microbes) is release chemicals that act as biosurfactants in the soil so as to increase the absorption of metals, including manganese. These metal contaminants can be stabilized in natural and constructed wetlands through a process called phytofiltration. The use of hyperaccumulating plants, especially fast growing ones, in tandem with an induced process that includes using chemicals like synthetic chelates ethylenediaminetetracetic acid (EDTA) or acidifying chemicals (e.g., NH4SO4) increases the bioavailability of metals in the soil can significantly reduce the toxins in a relatively low period of time. A successful phytoremediation plan should take no more than ten years to completely rehabilitate a parcel of land.
It can be extremely hard to foster a long-term sustainable vegetation patch on land contaminated by manganese mine tailings. Using a bean like G.max to solve the problem of nitrogen deficiency in the soil can help replace the missing nutrient and keep the environment healthy enough for phytoremediation plants to grow.