What is Mineral Nutrition
Mineral nutrition is not synthesized by living organisms. Plants get these mineral nutrients from soil and human beings and animals get these mineral nutrients from food sources and external food sources which are coming from plants and animals. Minerals belong to one of the part groups of essential elements. These groups are of vitamins, essential fatty acids, essential amino acid. We required some of the major minerals for our growth and proper metabolism; these are calcium, phosphorus, potassium, sodium, and magnesium. While remaining elements which are not essential in such large amounts are known as trace elements, these are sulfur, iron, iodine, cobalt, zinc, etc.
Types of nutrients depending upon their needs:
Mainly There are Two Types of Nutrient, They are:
1. Micro Nutrient: Nutrient which is required by plants and animals body in small amounts. Example: boron, copper,manganese, iron, etc.
Boron
It plays an important role in affecting membrane stability.
It helps in maintaining structural and functional integrity of plasma membranes.
Deficiency of boron affects growth of plants.
Copper
It helps in protein synthesis.
It activates several enzymes which helps in plant growth.
Iron
They play a major role in crop growth and food production.
It is mainly associated with energy transfer property, nitrogen reduction and nitrogen fixation.
Magnesium
It helps in activation of different enzymes in plants.
It activates various metabolic activities.
Molybdenum
It is useful in nitrogen fixation of both symbiotic and non-symbiotic plants.
Chlorine
It is essential for the photosynthetic process.
2. Macronutrients: Nutrients which are required by animals and plant bodies in large amounts. Example: Sulfur, nitrogen, calcium, potassium, magnesium,etc.
Phosphorous
They mainly help in boosting ripening of food along with root growth.
Their deficiency leads to premature fall of leaves.
In fruits and seeds they are in maximum amounts.
Nitrogen
They are mainly present in various coenzymes, hormones, ATP, etc.
They are important constituents of vitamins, nucleic acid, protein and many others.
It is present in the structure of porphyrin molecules which are precursors of chlorophyll.
Due to their deficiency yellowing symptoms appear last in the younger leaves.
Potassium
Potassium is present in the soil in soluble form and they are mainly exchangeable form.
More potassium is required to their proper growth.
They mainly act as a catalyst in enzymatic reactions.
They play a crucial role in carbohydrate metabolism.
Stomatal opening in higher plants requires potassium.
Potassium is essential for translocation of sugar.
Potassium deficient cereal grains develop weak stalks, and their roots become susceptible to root rotting organisms.
Potassium deficiency causes disintegration of pith cells and formation of secondary phloem in tomato plants.
Calcium
Calcium ion functions both as a structural component and as a cofactor for certain enzymes.
Calcium has been associated with the cell wall structure.
High concentration of calcium is required for nodulation and successful symbiotic nitrogen fixation.
Calcium in small amounts is necessary for normal mitosis.
Deficiency of calcium causes chlorotic patches on the leaf and root to become short and brown.
Magnesium
It acts as a structural component like calcium.
It is a component of the chlorophyll structure.
It is also required to maintain ribosome integrity.
Mg2+ ion has a direct role on potassium-sodium stimulated ATPase activity.
Magnesium ions help in protein synthesis by activating nucleic acid synthesis.
Deficiency of magnesium leads to chlorosis of the older leaves.
Magnesium deficiency causes extensive chlorenchyma development and scanty pith formation.
Sulphur
It is a main constituent of biotin, thiamine, coenzyme A and lipoic acid and all these are involved in cellular metabolism.
Deficiency of sulphur causes rapid leaf fall and curling of leaf inward direction.
Role of Nutrients
There are some salts or minerals that act against the harmful effects of the other nutrients thus they balance each other's activities.
There are several mineral cell sap which are present in either organic or inorganic form to regulate the organic pressure of the cell.
Different anions and cations of different nutrients have specific influence on the pH of the cell sap.
Carbon, Hydrogen, and Oxygen are those elements which help to construct the plant body by entering protoplasm and constitution of the wall.
Nutrients like zinc, magnesium, calcium and copper act as metallic catalysts in several biochemical reactions.
Certain minerals like arsenic and copper have a toxic effect on the protoplasm under different defined conditions.
FAQs on Minerals Nutrition
1. What is meant by mineral nutrition in plants?
Mineral nutrition is the study of how plants acquire and utilise essential inorganic elements, known as mineral nutrients, for their growth, development, and physiological functions. Plants primarily absorb these minerals from the soil through their root system. The availability and absorption of these nutrients are critical for completing the plant's life cycle.
2. What criteria must an element meet to be considered essential for a plant?
For an element to be classified as essential for a plant, it must satisfy the following criteria as defined by Arnon and Stout:
- The element must be absolutely necessary for the plant to complete its life cycle; without it, the plant cannot grow or reproduce normally.
- The requirement for the element must be specific, meaning its function cannot be replaced by another mineral element.
- The element must be directly involved in the plant's metabolism, for instance, as a component of an essential molecule or a required enzyme cofactor.
3. How are essential minerals classified, with examples?
Based on their quantitative requirements by plants, essential mineral elements are classified into two main categories:
- Macronutrients: These are required in relatively large amounts (generally >10 mmole kg⁻¹ of dry matter). Examples include Carbon, Hydrogen, Oxygen, Nitrogen, Phosphorus, Potassium, Calcium, Magnesium, and Sulphur.
- Micronutrients: Also known as trace elements, these are required in very small amounts (generally <10 mmole kg⁻¹ of dry matter). Examples include Iron, Manganese, Copper, Molybdenum, Zinc, Boron, Chlorine, and Nickel.
4. Why are Nitrogen, Phosphorus, and Potassium (NPK) considered critical macronutrients for plants?
Nitrogen, Phosphorus, and Potassium (NPK) are considered critical or primary macronutrients because they are fundamental to major structural and metabolic functions and are often limiting factors in the soil. Nitrogen is a core component of proteins, nucleic acids (DNA, RNA), and chlorophyll. Phosphorus is essential for energy transfer through ATP, and is a structural component of cell membranes and nucleic acids. Potassium plays a vital role in activating enzymes, regulating the opening and closing of stomata, and maintaining turgor pressure in cells.
5. What are the major deficiency symptoms caused by a lack of essential elements in plants?
When the supply of an essential element becomes limited, plant growth is retarded. The main deficiency symptoms include:
- Chlorosis: The yellowing of leaves due to the loss of chlorophyll. It is often caused by a deficiency of N, K, Mg, S, Fe, Mn, Zn, and Mo.
- Necrosis: The death of plant tissues, particularly leaf tissue, which is often caused by a deficiency of Ca, Mg, Cu, and K.
- Stunted Growth: The overall growth of the plant is reduced, including shorter stems and smaller leaves.
- Inhibition of Cell Division: A deficiency of elements like N, K, S, and Mo can cause cell division to slow down or stop.
6. How can an excess of one mineral element cause a deficiency of another?
This phenomenon is known as antagonism or toxicity. An excess concentration of one micronutrient can interfere with the absorption and function of another. For example, a prominent symptom of manganese (Mn) toxicity is the appearance of brown spots surrounded by chlorotic veins. This happens because excess manganese competes with iron (Fe) and magnesium (Mg) for uptake and also inhibits calcium (Ca) translocation to the shoot apex. Therefore, what appears as manganese toxicity is often a combination of deficiencies of Fe, Mg, and Ca.
7. How do plant roots absorb mineral ions from the soil?
The mechanism of mineral absorption is a two-phase process. The first phase involves a rapid, passive uptake of ions into the outer free space of the cells, known as the apoplast. This does not require metabolic energy. The second phase is an active process where ions are taken up slowly into the inner space, the symplast of the cells. This movement requires metabolic energy in the form of ATP and occurs against a concentration gradient, involving specific carrier proteins in the cell membrane.
8. Why is biological nitrogen fixation so important if nitrogen gas is abundant in the atmosphere?
Although nitrogen gas (N₂) makes up about 78% of the atmosphere, plants cannot use it directly in its gaseous form. They can only absorb nitrogen as nitrate (NO₃⁻) or ammonium (NH₄⁺). Biological nitrogen fixation is the crucial process where atmospheric nitrogen is converted into ammonia by certain prokaryotic microorganisms, such as the bacterium Rhizobium. This conversion makes nitrogen available to plants and, subsequently, to the entire ecosystem, making it a vital component of the nitrogen cycle.
