Arrange the mean residence time (in years) of phosphorus for the following ecosystem types in descending order:
A. Tropical rain forest B. Temperate coniferous forest C. Boreal forest D. Temperate deciduous forest
Choose the correct answer:

Correct option is D

The mean residence time of phosphorus in different ecosystems varies based on temperature, soil type, and the rate of nutrient cycling. Here is the descending order based on phosphorus retention:
1. C. Boreal forest – Boreal forests, characterized by cold temperatures and slow decomposition rates, have a long residence time for phosphorus because nutrient cycling is slow.
2. B. Temperate coniferous forest – These forests also have a relatively long residence time due to moderate temperatures and acidic soils that slow down nutrient cycling.
3. D. Temperate deciduous forest – Nutrient cycling is faster here compared to boreal and coniferous forests due to higher temperatures and microbial activity.
4. A. Tropical rain forest – Tropical forests have the shortest phosphorus residence time because of rapid decomposition and nutrient cycling due to warm temperatures and high rainfall.
Information Booster:
1. Phosphorus Cycling:
· Phosphorus cycles through the lithosphere, hydrosphere, and biosphere. It is a critical nutrient for plants but is typically not very mobile in soil.
2. Factors Affecting Residence Time:
· Temperature: Colder environments slow down decomposition, increasing residence time.
· Soil Type: Acidic or nutrient-poor soils can retain phosphorus for longer periods.
· Decomposition Rates: Faster in warm, humid environments and slower in cold or dry environments.
3. Examples:
· Boreal Forest: Found in regions like Canada and Siberia, characterized by slow nutrient cycling.
· Temperate Coniferous Forest: Examples include forests in the Pacific Northwest, USA.
· Temperate Deciduous Forest: Found in eastern North America, Europe, and Asia.
· Tropical Rain Forest: Found near the equator, such as the Amazon and Congo forests.
Additional Knowledge:
· Option (a) A, B, D, C: Incorrect because tropical rain forests have the fastest nutrient cycling, not the slowest.
· Option (b) A, D, B, C: Incorrect as it incorrectly places tropical forests before boreal forests in terms of phosphorus retention.
· Option (c) B, C, D, A: Incorrect because boreal forests have the longest residence time compared to temperate coniferous forests.