Explain with examples: Toxic elements.

Hint: The elements that can induce toxicity in plants under certain conditions such as when present in excess amount are known as toxic elements. The micronutrient elements like manganese may act as toxic elements if they are in excess amount.

Complete answer:
• Plants require two types of elements for their growth and development. Some elements are required in large or major quantities. These are called macronutrients. Macronutrients include elements like carbon, hydrogen, oxygen, nitrogen, calcium, phosphorus etc.
• On the other hand, some nutrients are required in small or minor quantities. These are called micronutrients. Micronutrients are also known as trace elements, because they are required in trace amounts. Micronutrients include elements like manganese, iron, cobalt, molybdenum, zinc etc.
• Micronutrients are present in plants in small amounts. They are very essential in plants. But if their concentration in plants increases beyond a certain limit i.e. if they occur in excess, then these same micronutrients can produce toxicity in plants acting as toxic elements. Toxic elements can reduce the dry weight of plants by 10%.

For example – If manganese is present in excess, then it may affect metabolism that may lead to deficiency of other elements like iron, calcium and magnesium. Deficiency of these elements is detrimental for the health of plants. It can affect normal growth and development of a plant.

Note: The toxic elements can only become toxic under certain conditions. To induce toxicity they must enter the plant in large amounts and they can enter a plant only when they are available to the plants in the form that can penetrate the plant tissues such as in solution or aqueous form by which plants mainly absorb minerals.