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Ecosystems

Nutrient cycling in contrasting biomes

  • 3 things to know
  • A2 Unit 4

Overview

Three stores in the Gersmehl model of nutrient cycling, transfers in the Gersmehl model and relative store sizes in a tropical rainforest.

What you need to know

Answer each one before you reveal it.

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Key term

Name the three stores in the Gersmehl model of nutrient cycling.

Key term

Name the transfers in the Gersmehl model.

Key term

Describe the relative store sizes in a tropical rainforest.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    Name the three stores in the Gersmehl model of nutrient cycling.

    Model answer

    Biomass, litter and soil.

  2. 2

    Name the transfers in the Gersmehl model.

    Model answer

    Fallout from biomass to litter, decay from litter to soil, and uptake from soil to biomass, with inputs from weathering and precipitation and losses by leaching and run-off.

  3. 3

    Describe the relative store sizes in a tropical rainforest.

    Model answer

    Biomass is by far the largest store, litter is small because decay is rapid, and soil is small because nutrients are taken up almost immediately.

  4. 4

    Explain why rainforest soils are nutrient-poor despite the luxuriant vegetation.

    Model answer

    Warmth and moisture make decomposition very fast, plants absorb the released nutrients at once, and heavy rainfall leaches whatever is not taken up.

  5. 5

    What happens to nutrient cycling when a rainforest is cleared?

    Model answer

    The main store is removed with the trees, the exposed soil is leached and eroded by heavy rain, and fertility collapses within a few growing seasons.

  6. 6

    Describe the relative store sizes in a boreal forest.

    Model answer

    Litter is the largest store because cold slows decomposition, biomass is substantial but slow-growing, and the soil store is small and acidic.

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