Symbiotic Mode of Nutrition

Several genuinely mutualistic partnerships bear directly on plant mineral nutrition. Lichens are a close mutual association between an alga and a fungus, in which the alga photosynthesises and supplies food while the fungus absorbs water and minerals and provides the physical thallus structure that houses both partners; lichens are also useful bioindicators of sulphur dioxide pollution and are typically the pioneer species that colonise bare rock in xeric succession. Mycorrhizae are associations between fungi and the roots of higher plants, including gymnosperms such as Pinus, in which the fungus improves the plant's water and mineral uptake in exchange for carbohydrates. Rhizobium's symbiosis with legumes fixes atmospheric nitrogen, as described in the nitrogen-fixation sections above. Cyanobacteria also form a sym …