Macronutrients:
Generally present in plant tissues in large amounts. The macronutrients include carbon, hydrogen, oxygen, nitrogen, phosphorus, sulphur, potassium calcium and magnesium. Of these carbon, hydrogen and oxygen are mainly obtained from CO2 and H2O, while the others are absorbed from the soil as mineral nutrition.
Micronutrients:
Also called Trace elements are needed in very small amounts. These include iron, manganese, copper, molybdenum, zinc, boron, chlorine and nickel.
Beneficial nutrients:
Include sodium, silicon, cobalt and selenium. They are required by higher plants.
Toxic elements:
Any mineral ion concentration in tissues that reduces the dry weight of tissues by about 10 percent is considered toxic. The toxicity symptoms are difficult to identify. Micronutrients in excess causes toxicity.
Essential elements:
Four categories on the basis of their diverse functions.
(a) As components of biomolecules and hence structural elements of cells.
e.g. carbon, hydrogen, oxygen and nitrogen.
(b) As components of energy related chemical compounds in plants.
e.g. magnesium in chlorophyll
(c) Elements that activate or inhibit enzymes, e.g. Mg2+ is an activator for both ribulose bisphosphate carboxylase oxygenase and phosphoenol pyruvate carboxylase.
(d) Elements that alter the osmotic potential of a cell.
e.g. Potassium in opening and closing of stomata.
