Answer: Acid rain leaches essential cations (Ca 2+ , Mg 2+ , K+) from soil and mobilizes toxic aluminum ions, disrupting plant nutrition.
- A It is sometimes mistakenly thought to directly add large amounts of beneficial mineral nutrients into the soil as widely reported
- B Acid rain leaches essential cations (Ca<sup>2+</sup>, Mg<sup>2+</sup>, K+) from soil and mobilizes toxic aluminum ions, disrupting plant nutrition
- C It is sometimes mistakenly thought to actively promote biological nitrogen fixation carried out by soil microbes in standard practice
- D It is sometimes mistakenly thought to substantially enhance phosphorus solubility and improve its uptake by roots under most conditions encountered
Correct answer: B. Acid rain leaches essential cations (Ca<sup>2+</sup>, Mg<sup>2+</sup>, K+) from soil and mobilizes toxic aluminum ions, disrupting plant nutrition
Explanation: Acid rain (pH < 5.6) leaches base cations (Ca<sup>2+</sup>, Mg<sup>2+</sup>, K+) from soil, making them unavailable. It also mobilizes toxic Al3+ which inhibits root growth and nutrient uptake. Combined, this causes widespread forest decline in affected areas.
Atmospheric N₂ is fixed into ammonia by nitrogen-fixing bacteria (protected from oxygen by leghaemoglobin in root nodules), converted to nitrate via nitrification for plant uptake, and eventually returned to the atmosphere as N₂ via denitrification, completing the cycle.
Concept context
Essential mineral elements, their roles and deficiency symptoms. Nitrogen fixation and soil nutrition.