Wednesday, 17 May 2017
No plants and trees without symbiosis
Mycorrhizas are symbiotic relationships between fungi and plant roots (the term means literally 'fungus root') Perhaps more than 80% of the species of higher plants have these relationships, and so do many pteridophytes (ferns and their allies) and some mosses (especially liverworts). They are as common on crop plants (cereals,
peas, tomatoes, onions, apples, strawberry, etc.) as in wild plant communities, and in several cases they have been shown to be important or even essential for plant performance.
Alder is particularly noted for its important symbiotic relationship with Frankia alni (Actinomyces alni), an actinomycete, filamentous, nitrogen-fixing bacterium. This bacterium is found in root nodules, which may be as large as a human fist, with many small lobes, and light brown in color. The bacterium absorbs nitrogen from the air and makes it available to the tree. Alder, in turn, provides the bacterium with sugars, which it produces through photosynthesis. As a result of this mutually beneficial relationship, alder improves the fertility of the soil where it grows, and as a pioneer species, it helps provide additional nitrogen for the successional species which follow.
Alder trees have many features other than nitrogen fixation and use as green manure via its fallen leaves. They produce timber that is used in construction and furniture making, and especially for making tea boxes; their bark is used for tannins; and their leaves, roots, and bark have medicinal qualities.