Definition of nutrients / minerals
Nutrient elements are elements of the chemical periodic table that are essential for the nutrient and energy metabolism of plants.
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Nutrient elements are elements of the chemical periodic table that are essential for the nutrient and energy metabolism of plants.
Nutrient elements are neither present in water nor in the plant in elemental form1). They form compounds with other elements and then form salts, which dissolve in water as charged ions (e.g. K++ Cl-) or uncharged molecules (e.g. CO2, H3BO3). Ions and molecules are collectively referred to as minerals (Finck, 1991).
Minerals are present in the water or in the water bed and can be taken up by aquatic plants via the leaf surface or the roots (Watson, 2007). The uptake of K, Ca, Mg, Cl and S minerals occurs mainly via the leaf surface, while minerals of P, Fe and other trace elements are mainly taken up by the roots(Walstad, 1999). Table 1 provides an overview of the elements essential for plant nutrition and their corresponding minerals.
Tab. 1 Main and trace elements and their corresponding minerals taken up by aquatic plants (from Finck, 1991)
|
Element |
Symbol |
Uptake as |
|
Main nutrients |
||
|
Carbon |
C |
Gas, carbonate ion2) |
|
Oxygen |
O |
water |
|
Hydrogen |
H |
water |
|
Nitrogen |
N |
ion |
|
Phosphorus |
P |
ion |
|
Potassium |
K |
ion |
|
Sulphur |
S |
ion |
|
Magnesium |
Mg |
ion |
|
Chlorine |
Cl |
ion |
|
Trace elements |
||
|
Iron |
Fe |
ion |
|
Manganese |
Mn |
ion |
|
Zinc |
Zn |
ion |
|
copper |
Cu |
ion |
|
Boron |
B |
Ion/molecule |
|
Molybdenum |
Mo |
ion |
If we look at the chemical structure of plants, we can distinguish between two basic building blocks. Plant biomass consists of 90 % complex compounds of the elements carbon (C), oxygen (O) and hydrogen (H). Compounds of these elements are also known as organic compounds.
Organic compounds include the structural plant framework (e.g. cell walls), storage substances (e.g. starch) and energy sources (e.g. sugar). What organic compounds have in common is that they can be completely burnt to carbon dioxide (CO2) and water (H2O). They are formed by photosynthesis and subsequent physiological processes in the plant from their basic elements with the co-operation and incorporation of other nutrients.
Explanations
1) Humans generally consume iron as a food supplement in the form of salts and not as a metal
2) from Walstad (1999)
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