Question

Which of the following do not increase nitrate concentration in plants?

• A. 2, 4 D
• B. High soil pH
• C. Excessive rain
• D. Deficiency of Molybdenum in soil

Hint:

To remember: Drought increases plant nitrate concentration (because the plant absorbs water but can't metabolize nitrates without sunlight), while excessive rain decreases it by leaching highly soluble nitrates deep into the soil.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Nitrate poisoning in livestock occurs when animals ingest plants containing high concentrations of nitrate ($NO_3^-$).
Various environmental, chemical, and soil factors can influence the uptake and accumulation of nitrates in plant tissues.

Step 2: Detailed Explanation:
Let us analyze how each option affects nitrate accumulation in plants:
- 2,4-D (A): Application of the herbicide 2,4-Dichlorophenoxyacetic acid (2,4-D) disrupts the plant's metabolism, increasing the rate of nitrate uptake from the soil while inhibiting the plant's ability to convert it into protein, leading to heavy nitrate accumulation.
- High soil pH (B): Alkaline soil conditions generally enhance the solubility and availability of nitrates in the soil, promoting their uptake by plant roots.
- Deficiency of Molybdenum in soil (D): Molybdenum is an essential cofactor for the plant enzyme nitrate reductase, which is responsible for converting nitrates ($NO_3^-$) to nitrites ($NO_2^-$) for eventual protein synthesis. A deficiency of molybdenum inhibits this enzyme, preventing the conversion of nitrates and causing them to accumulate to toxic levels within the plant.
- Excessive rain (C): Nitrates are highly water-soluble anions. Heavy or excessive rainfall causes rapid leaching of nitrates deep into the soil profile, away from the root zone of plants. This reduces the amount of nitrate available for plant uptake, thereby decreasing (or not increasing) the nitrate concentration in plants.

Step 3: Final Answer:
The factor that does not increase nitrate concentration in plants is Excessive rain, corresponding to option (C).