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Physiological effects of plant essential elements and symptoms of deficiency
According to the mobility of essential elements within plants, these nutrients can be categorized into two groups: mobile and immobile. Mobile elements include nitrogen (N), phosphorus (P), potassium (K), magnesium (Mg), zinc (Zn), boron (B), and molybdenum (Mo). These elements can be transported from older parts of the plant to younger ones when the plant is deficient. As a result, deficiency symptoms typically appear on the older leaves first. In contrast, immobile elements such as calcium (Ca), sulfur (S), iron (Fe), manganese (Mn), and copper (Cu) do not move easily once they are absorbed. Therefore, their deficiency symptoms usually show up in new growth.
**1. Nitrogen (N)**
Nitrogen constitutes 1–3% of a plant’s dry matter and is primarily taken up in the form of nitrate (NO₃â»), nitrite (NOâ‚‚â»), or ammonium (NHâ‚„âº). It plays a vital role in plant metabolism by being a component of nucleic acids, enzymes, coenzymes, chlorophyll, and other essential compounds. A nitrogen deficiency causes yellowing of older leaves, sometimes with purple discoloration on stems or petioles. Severe deficiency leads to leaf drop, stunted growth, and even plant death.
**2. Phosphorus (P)**
Phosphorus is mainly absorbed as H₂PO₄⻠in acidic soils and HPO₄²⻠in alkaline soils. It is crucial for energy transfer (ATP, ADP), nucleic acid synthesis, membrane structure, and enzyme regulation. Deficiency symptoms include dark green leaves and reddish-purple discoloration on stems and leaves. Since phosphorus is mobile, symptoms appear on older leaves.
**3. Potassium (K)**
Potassium is a monovalent cation that regulates stomatal opening, water uptake, osmotic balance, and enzyme activity. It also aids in nutrient transport through the phloem. Deficiency causes marginal leaf burn and yellowing, with symptoms appearing on older leaves due to its mobility.
**4. Sulfur (S)**
Sulfur is primarily absorbed as sulfate (SO₄²â») and is involved in amino acid synthesis, membrane structure, and electron transport. Deficiency leads to stunted growth and yellowing of leaves, especially on young foliage since sulfur is not easily translocated.
**5. Calcium (Ca)**
Calcium is essential for cell wall stability, membrane integrity, and enzyme activation. It also acts as a second messenger in signaling pathways. Deficiency results in necrosis of growing tips, curled or yellowed leaves, and weak stems. Since it is immobile, symptoms appear on new leaves.
**6. Magnesium (Mg)**
Magnesium is a central component of chlorophyll and activates many enzymes, including those involved in photosynthesis. Deficiency causes interveinal chlorosis on older leaves, often accompanied by reddish-purple coloration.
**7. Iron (Fe)**
Iron is critical for chlorophyll synthesis and acts as an electron carrier in redox reactions. Deficiency leads to interveinal chlorosis, with symptoms appearing on younger leaves because iron is not easily mobile.
**8. Copper (Cu)**
Copper functions as an electron carrier in various enzymes and participates in redox processes. Deficiency causes tip necrosis and leaf drop, with symptoms appearing on older leaves.
**9. Zinc (Zn)**
Zinc is involved in enzyme function, particularly in tryptophan and auxin synthesis. Deficiency causes stunted growth, leaf curling, and mosaic patterns, especially on older leaves.
**10. Manganese (Mn)**
Manganese is important for photosynthesis and enzyme activation. Deficiency causes interveinal chlorosis and necrotic spots, which first appear on new leaves due to its low mobility.
**11. Boron (B)**
Boron supports reproductive development, pollen germination, and sugar transport. Deficiency leads to distorted growth, poor fruit set, and internal necrosis in roots, commonly seen in crops like broccoli and radishes.
**12. Molybdenum (Mo)**
Molybdenum is a key component of nitrate reductase, essential for nitrogen assimilation. Deficiency causes stunted growth, dull leaf color, and necrotic spots.
**13. Chlorine (Cl)**
Chlorine is involved in water splitting during photosynthesis and root development. Deficiency leads to wilting and yellowing of leaves.
**14. Carbon (C)**
Carbon is the backbone of all organic molecules in plants. A lack of carbon disrupts photosynthesis, leading to slow growth and underdeveloped tissues.
Understanding the mobility of these elements helps in diagnosing and managing nutrient deficiencies effectively in agricultural and horticultural practices.