Autotoxicity is a form of allelopathy in which a species inhibits growth or reproduction of members of that same species through the production of chemicals that are released into the environment.
This mechanism will result in reduced competition between members of the same species. Inhibition on the growth of other plants will increase the availability of nutrients.
In cultivation, autotoxicity can make it difficult or impossible to grow the same species after harvest of a crop. For example, this is known in alfalfa and the tree Cunninghamia lanceolata Other species displaying autotoxicity include the rush Juncus effusus and the grass Lolium rigidum.
In alfalfa
Autotoxicity in alfalfa is produced from the first seeding of the plant. The plant emits a chemical or chemicals into the soil that reduce the effectiveness of further alfalfa seedings. Studies show that the chemical is extractable from fresh alfalfa, is water-soluble, reduces germination, and prevents root growth. Some believe that a chemical called medicarpin is responsible for autotoxicity. Roots of affected plants can be swollen, curled, discolored, and lack root hairs. Lack of root hairs reduces the plants ability to gather nutrients and absorb water. Crop rotation is used to counteract autotoxicity in alfalfa.