Section 2
Soil and Plant Microbiology
By Boundless
![Thumbnail](../../../../../../figures.boundless-cdn.com/19425/square/figure-31-02-01.jpg)
Soil is a mix of varying amounts of inorganic matter, organic matter, water, and air.
![Thumbnail](../../../../../../figures.boundless-cdn.com/19427/square/figure-31-02-03.jpeg)
Soils are made up of combinations of four distinct layer types or horizons: O horizon, A horizon, B horizon, and C horizon.
![Thumbnail](../../../../../../figures.boundless-cdn.com/16113/square/zal-root-tips-28amanita-29.jpeg)
A mycorrhiza is a symbiotic association between a fungus and the roots of a vascular plant.
![Thumbnail](../../../../../../figures.boundless-cdn.com/5133/square/518px-foodweb.jpeg)
Wetlands are considered one of the most biologically diverse of all ecosystems.
![Thumbnail](../../../../../../figures.boundless-cdn.com/5135/square/soybean-root-nodules.jpeg)
An endophyte is an endosymbiont, often a bacterium or fungus, that lives within a plant for at least part of its life without causing apparent disease.
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Many plants form associations called mycorrhizae with fungi that give them access to nutrients in the soil, protecting against disease and toxicities.
![Thumbnail](../../../../../../figures.boundless-cdn.com/268/square/aic-virus-symptoms-tobacco.jpeg)
There are four main bacterial pathogenicity factors: cell wall degrading enzymes, toxins, phytohormones, and effector proteins.
![Thumbnail](../../../../../../figures.boundless-cdn.com/19430/square/figure-31-03-02ab.jpeg)
Plants cannot extract the necessary nitrogen from soil, so they form symbiotic relationships with rhizobia that can fix it as ammonia.