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Difficulty: MediumNutrient and Biogeochemical Cycles

During extended periods of waterlogging in agricultural soils, anaerobic conditions develop rapidly. Which ecological process is enhanced under these oxygen-deficient conditions, leading to a direct depletion of soil nitrogen usable by plants?

  1. Conversion of nitrates into atmospheric nitrogen gasAnswer
  2. B
    Oxidation of ammonium ions into nitrites
  3. C
    Fixation of elemental nitrogen into organic nitrogen compounds
  4. D
    Decomposition of nitrogenous organic wastes into ammonia

Answer

Conversion of nitrates into atmospheric nitrogen gas
Under oxygen-depleted (anaerobic) conditions such as flooded or waterlogged soils, denitrifying bacteria reduce nitrates into gaseous nitrogen. This process, termed denitrification, releases nitrogen gas into the atmosphere and causes a loss of available soil nutrients.

Step-by-Step Solution

1
Identify environmental condition
Waterlogging leads to oxygen depletion (anaerobic soil conditions).
Water fills soil pore spaces, restricting oxygen diffusion needed for aerobic respiration.
2
Determine metabolic process favored by anaerobic conditions
Denitrifying bacteria reduce soil nitrates to nitrogen gas.
Anaerobic organisms such as PseudomonasPseudomonas species utilize nitrate (NO3−\text{NO}_3^-) as an electron acceptor when oxygen is scarce.
3
Assess ecological impact on soil nitrogen
Plant-usable nitrogen escapes from the soil into the atmosphere as gaseous dinitrogen (N2\text{N}_2).
Gaseous nitrogen cannot be directly absorbed by crops, leading to depleted soil fertility.

Key Concept

Denitrification under anaerobic conditions
Estimated Time:1m 0s
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Topics

Nutrient and Biogeochemical Cycles

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