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Nutrient Cycle – Definition, Types
Nutrient cycling involves the following three aspects:
1. Input of Nutrients: An ecosystem receives nutrients from an external source. It stores them for further use through biological processes.
2. Output of Nutrients: Nutrients also move out of an ecosystem and many of them become input to another ecosystem.
3. Internal Nutrient Cycling: Soil is a reservoir of nutrients. Nutrients are continuously regenerated and stored in the soil in forms available to plants. Regeneration of nutrients is done by decomposers (e.g., bacteria, fungi, and actinomycetes) by the process of decomposition of detritus. These nutrients are stored in the soil for re-utilization. Plants absorb large amounts of nutrients from the soil.
The process of nutrient regeneration and absorption occurs simultaneously due to which a dynamic state of nutrients in the soil is maintained. The process of transfer and absorption of nutrients from the soil, through the plants is called uptake. During growth, these absorbed nutrients are metabolically incorporated into plants. Litter fall of vegetation, animal remains, fecal matter of animals (forming above-ground detritus) and dead plant roots (forming below-ground detritus) are acted upon by decomposers to, bring back the nutrients to the soil (regeneration of nutrients).
- Biosphere. That part of Earth’s environment in which living organisms are found.
- Detritus. Dead or partially decomposed plant and animal matter (i.e., non-living organic matter).
- Ecosphere. All the living organisms on Earth interact with the physical environment as a whole.
- Actinomycetes. A kind of filamentous bacteria.
When the uptake of nutrients is more than the amount of nutrients recycled (e.g., in a young-growing forest), a part of the uptake is retained in the standing crop. This retention of nutrients in the standing crop results in the increase in nutrient contents of the ecosystem. Therefore, Retention = Uptake – Recycle
Rates of nutrient uptake, recycling, and retention vary greatly in different ecosystems. The number of different nutrients/weights of biomass or soil can be determined by a number of chemical methods. We can calculate the nutrient budget of the ecosystem by determining changes in the nutrient concentrations and biomass with time.