About half of the essential plant nutrients are macronutrients; among which…

Concept

Plant nutrition recognises about 17 essential elements. Roughly half of these are needed in large amounts and are called macronutrients (the others are micronutrients). Among the macronutrients, the elements carbon, hydrogen and oxygen are obtained mainly from air and water and together make up the bulk of a plant's dry matter, because they form the structural backbone of every organic molecule.

Application

Carbohydrates, proteins, nucleic acids and most other plant compounds are all organic molecules — their defining feature is a skeleton of carbon–carbon and carbon–hydrogen bonds. Carbon's four bonding sites let it link into the long chains and rings on which all these biomolecules are built, so it is the single element that is structurally indispensable to every one of them.

Contrast

• Nitrogen — a macronutrient present in proteins and nucleic acids, but it is not a constituent of carbohydrates, so it is not the element common to all the compounds named.

• Sulphur — a secondary macronutrient found in a few amino acids and proteins only; it does not build carbohydrates or nucleic acids.

• Sodium — not even an essential macronutrient for most plants (at most a beneficial element for some species); it plays no structural role in these organic compounds.

Result

The element foremost vital to form carbohydrates, proteins, nucleic acids and other organic compounds is carbon.