Denitrification in anaerobic soils

Steps:

• Identify key process: Bacteria use nitrates as oxygen source in low-oxygen (waterlogged) environments.
• Note waste product: Release of nitrogen gas (N₂) indicates nitrate reduction.
• Recall nitrogen cycle roles: Match to bacteria that convert nitrates to N₂.
• Eliminate mismatches: Rule out bacteria involved in other nitrogen transformations.

Why B is correct:

• Denitrifying bacteria respire anaerobically by reducing nitrates (NO₃⁻) to N₂ gas, as defined in the nitrogen cycle.

Why the others are wrong:

• A: Decomposing bacteria break down organic matter but do not specifically reduce nitrates to N₂.
• C: Nitrifying bacteria oxidize ammonia to nitrates, not break them down.
• D: Root nodule bacteria fix atmospheric N₂ into ammonia in plant roots, not release N₂ from nitrates.

Final answer: B