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•  The impact of waterlogging on the nitrogen cycle

Waterlogging occurs when the soil becomes inundated with water, either through flooding or irrigation with poor drainage

  • Waterlogging impacts the nitrogen cycle by reducing the levels of nitrates and nitrites in the soil

Waterlogged soil will lose nitrates and nitrites via the process of denitrification

  • Waterlogging reduces oxygen availability in the soil, creating oxygen-poor conditions favoured by denitrifying bacteria
  • This bacteria (Pseudomonas) will convert available stocks of nitrates into nitrogen gas, reducing soil nitrogen content

Waterlogged soil will also lose nitrates and nitrites via the process of leaching

  • Whenever rainfall exceeds evaporation, there will be a build up of water within the porous soil
  • As this water drains downwards through the soil, soluble minerals (like nitrates and nitrites) are removed with it
  • Continual leaching impoverishes the upper layers of soil and concentrates dissolved minerals in the lower bedrock
  • Leaching is most common in highly porous soils (e.g. sandy soils) and least common in textured soils (such as clay)

Leaching in Waterlogged Soils

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•  Insectivorous plants as an adaptation for low nitrogen availability in waterlogged soils

A primary consequence of waterlogging is the reduction in nitrogen availability within the soil

  • This means that plants are unable to access sufficient quantities of nitrogen from the soil via their roots

Insectivorous plants are able to obtain nitrogen in low-nutrient environments by feeding on invertebrates

  • Insectivorous plants include the Venus fly trap, which is native to subtropical wetlands that have waterlogged soil
  • The plant’s terminal leaves form a trapping structure that is baited by nectar to attract insects
  • When trapping has occurred, the plant releases digestive enzymes that allow it to absorb nutrients from the insect
  • Insectivorous plants only obtain nitrogen from feeding on insects – they still derive energy from photosynthesis

Venus Fly Trap

Adapted from Life – Venus Fly Traps: Jaws of Death (http://www.bbc.co.uk/life)