In what form and how nitrogen is taken by plants?
Answers
Plants take nitrogen from the soil by absorption through their roots as amino acids, nitrate ions, nitrite ions, or ammonium ions.
Plants do not get their nitrogen directly from the air. Although nitrogen is the most abundant element in the air, every nitrogen atom in the air is triple-bonded to another nitrogen atom to form molecular nitrogen. This triple bond is very strong and very hard to break (it takes energy to break chemical bonds whereas energy is only released when bonds are formed. As a result, even though nitrogen in the air is very common, it is energetically unfavorable for a plant to split the nitrogen molecule in order to get the raw atoms that it can use.
The act of breaking apart the two atoms in a nitrogen molecule is called "nitrogen fixation". Plants get the nitrogen that they need from the soil, where it has already been fixed by bacteria and archaea. Bacteria and archaea in the soil and in the roots of some plants have the ability to convert molecular nitrogen from the air to ammonia, thereby breaking the tough triple bond of molecular nitrogen. Such organisms are called "diazotrophs". From here, various microorganisms convert ammonia to other nitrogen compounds that are easier for plants to use. In this way, plants get their nitrogen indirectly from the air via microorganisms in the soil and in certain plant roots. Lightning and high-energy solar radiation can also split the nitrogen molecule, and therefore also fixes the nitrogen in the air