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Nitrogen is the most critical element obtained by plants from the soil, to the exception of moist tropical forests where phosphorus is the limiting soil nutrient, [36] and nitrogen deficiency often limits plant growth. [37] Plants can use nitrogen as either the ammonium cation (NH 4 +) or the anion nitrate (NO 3 −).
Plant remains, including those that animals digested and excreted, contain organic compounds: sugars, starches, proteins, carbohydrates, lignins, waxes, resins, and organic acids. Decay in the soil begins with the decomposition of sugars and starches from carbohydrates, which decompose easily as detritivores initially invade the dead plant ...
The macronutrients are taken-up in larger quantities; hydrogen, oxygen, nitrogen and carbon contribute to over 95% of a plant's entire biomass on a dry matter weight basis. Micronutrients are present in plant tissue in quantities measured in parts per million, ranging from 0.1 [3] to 200 ppm, or less than 0.02% dry weight. [4]
They are resistant to decomposition. Lignins are composed primarily of carbon, oxygen, and hydrogen. Proteins composed of nitrogen, carbon, hydrogen, and oxygen; and small amounts of sulfur, iron, and phosphorus. [1] Charcoal is elemental carbon derived from incomplete combustion of organic matter. It is resistant to decomposition.
A large fraction of the chemical elements that occur naturally on the Earth's surface are essential to the structure and metabolism of living things. Four of these elements (hydrogen, carbon, nitrogen, and oxygen) are essential to every living thing and collectively make up 99% of the mass of protoplasm. [1]
Mass in plants Mass in animals Biological uses Carbon 12% 19% Found in carbohydrates, lipids, nucleic acids, and proteins. Hydrogen 10% 10% Found in water, carbohydrates, lipids, nucleic acids, and proteins. Nitrogen 1% 4% Found in nucleic acids, proteins, some lipids (e.g. sphingolipids) and some polysaccharides (e.g. chitin) Oxygen 77% 63%
The six aforementioned elements are used by organisms in a variety of ways. Hydrogen and oxygen are found in water and organic molecules, both of which are essential to life. Carbon is found in all organic molecules, whereas nitrogen is an important component of nucleic acids and proteins.
These plants are then digested by animals who use the nitrogen compounds to synthesise their proteins and excrete nitrogen-bearing waste. Finally, these organisms die and decompose, undergoing bacterial and environmental oxidation and denitrification , returning free dinitrogen to the atmosphere.