Processes
Plants uptake essential elements from the soil through their roots and from the air (mainly consisting of nitrogen and oxygen) through their leaves. Green plants obtain their carbohydrate supply from the carbon dioxide in the air by the process of photosynthesis.Carbon and oxygen are absorbed from the air, while other nutrients are absorbed from the soil. .Nutrient uptake in the soil is achieved by cation exchange, wherein root hairs pump hydrogen ions (H+) into the soil through proton pumps. These hydrogen ions displace cations attached to negatively charged soil particles so that the cations are available for uptake by the root. In the leaves, stomata open to take in carbon dioxide and expel oxygen. The carbon dioxide molecules are used as the carbon source in photosynthesis.
Although nitrogen is plentiful in the Earth's atmosphere, very few plants can use this directly. Most plants therefore require nitrogen compounds to be present in the soil in which they grow. This is made possible by largely inert atmospheric nitrogen being changed in a nitrogen fixation process to biologically usable forms in the soil by bacteria.
Plant nutrition is a difficult subject to understand completely, partially because of the variation between different plants and even between different species or individuals of a given clone. Elements present at low levels may cause deficiency symptoms, and toxicity is possible at levels that are too high. Furthermore, deficiency of one element may present as symptoms of toxicity from another element, and vice-versa.
Read more about this topic: Nutrition, Plant Nutrition
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—Willa Cather (1873–1947)
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—Thomas Henry Huxley (1825–95)