Plant are auto-tropics as they can produce organic compounds necessary for them using light energy and chemicals elements from the environment. The process of production of organic compounds by green plants by using CO2 and H2O of environment with the help of light energy is called photosynthesis.
Here we will discuss about the nature of other mineral nutrition required for the plants , how they get them and how they are utilized and why are they essential ?
Carbon , hydrogen and oxygen are dominant elements in plants . About 95% of plant consist of carbon , hydrogen and oxygen .Plants also need other elements which are taken by them in organic forms. Plant can absorb these mineral nutritional elements only when their ions are dissolved in water .Roots of land plant mostly absorb the dissolved ions present in the soil. Aquatic plant absorb dissolved ions of such elements from water through shoot surface. The ions of such elements are released from rocks by weathering or from dead organic matter.
Plant can only grow if all the elements required for them are provided in adequate amount. Plant grown in nutrient solution with all required elements can grow well if the roots inside solution are properly aerated(availability of air). This fact was first demonstrated by Sachs in 1860 and thus a new technique of plant culture was introduced. Most plants normally growing in soil can be grown in aerated( available of air) solution with all the nutritional minerals . Such culture of plants is known as hydroponics. This culture method has been used to determine the essential elements needed for plant’s growth.
Chemical analysis of the plant has shown that the plant contains about 40 different elements. Some of them are necessary for normal growth and development of plants. The elements that are essential for plant’s growth and development are called as essential elements while rest are called non essential elements .Without these essential elements , the plant cannot complete its life cycle ( vegetative and reproductive growth and production of seeds). It is found that the following are the essential elements that are necessary for majority of plants.
Cu , H , O , N , P , K , Ca , S , Mg , Fe , Mn ,Zn ,B , Cu and Mo. Beside these Al , Si, Cl , Na , Co and Ga may be essential for some plants.
Esssential Elements can be classified in two groups :-
Major Elements/Macro nutrients : Those essential elements which are required by the plants in comparatively large amounts are called as major elements . They participate directly in metabolism. They are C, H, O, N, P, K , Ca , S , Mg.
Minor Elements/Micro nutrients : Those essential elements which are required by the plants in comparatively less amounts are called as minor elements . They are required for enzyme catalyzed reaction where micro nutrients work as activator. They are Mn, Zn , B , Cu and Mo.
Deficiency of essential nutrients leads to deficiency diseases in plants. Accumulation of some of these nutrients in large amount more than the tolerance limit of plant also cause diseases. The micro nutrients are generally toxic when deposited in large amount in plant than the critical concentration needed for plant.
General functions of essential elements in Plants
Constituent of protoplasm and cell walls C, H, O, N, S and P are very important and permanent constituent of protoplasm and the cell wall. C, H and O form most of the parts of plant body. N is important constituent element of protein and nucleic acid , S of proteins and P of nucleic acids. Beside these Mg is an important constituent of chlorophylls while Ca is present in cell wall in the form of calcium pectate.
Influence on the osmotic pressure of plant cells Osmotic pressure and other osmotic relations of plant cells are maintained due to the pressure of organic compounds and mineral salts dissolved in the cell sap.
Catalytic function Many elements like Fe, Cu, Zn , Mo , Mg, Mn, Cl etc. are required in catalytic amounts to carry on various enzymatic reactions in the cells.
Antagonistic or Balancing Function Some of the elements like Ca, Mg, K etc. counteract(control) the toxic effects of other mineral elements by maintaining ionic balance.