Why do plants in a flooded area die?

• A. Photosynthesis stops due to low light.
• B. Pests proliferate after flooding.
• C. Roots need oxygen for respiration; water saturation reduces oxygen to roots.
• D. Flooding has no effect.

Answer: (C)

When soil is flooded, water fills the air spaces and air around the roots is replaced by water, which greatly reduces the oxygen available for the roots. Roots need oxygen to perform cellular respiration and produce the energy necessary to take up water and nutrients and keep cells alive. If oxygen is scarce, respiration slows or stops, energy production falters, nutrient and water uptake declines, and root tissue begins to die. With the root system compromised, the plant can’t transport water to the shoots, leading to wilting and eventually death. While factors like light or pests can stress plants, the immediate and primary cause in flooded areas is the lack of oxygen to the roots due to water saturation.