Question

What is a limiting nutrient in an ecosystem?

Answer 1

Hint: The storage and movement of nutrient elements through the various components of the ecosystem is called nutrient cycling. The main nutrients of an ecosystem are carbon and phosphorus. Depletion of such nutrients can cause limitation of them in the atmosphere or in the ecosystem.

Complete answer-
An ecosystem can be visualized as a functional unit of nature, where living organisms interact among themselves and also with the surrounding physical environment. Ecosystem varies greatly in size from a small pond to a large forest or a sea. Many ecologists regard the entire biosphere as a global ecosystem, as a composite of all local ecosystems on Earth.
Limiting nutrient is the nutrient that is present in the least amount in the ecosystem. These hampers the growth of the plants when not present in an apt quantity. When returned to the lacking environment, limiting nutrients jump- start productivity and it will continue till the time limiting nutrients again is depleted. Carbon and phosphorus are the major nutrients that are present in the ecosystem. Lowering the content of either of them in the ecosystem, we can term it as a limiting nutrient.
CARBON- According to one estimate 4 X $10^{13}$ kg of carbon is fixed in the biosphere through the process of photosynthesis. Decomposers contribute to the carbon dioxide poll by their processing of waste material and dead organic matter of land or oceans. Some of it is fixed, lost to sediments and removed from circulation. Many activities contribute to maintaining its level in the air. Lowering down of these activities can cause carbon as a limiting nutrient.
PHOSPHOROUS- It is a major constituent of biological membrane, nucleic acids and cellular energy transfer system. Many animals need large quantity of this element to make shell, bones and teeth. The natural reservoir of phosphorus is rock, which contains phosphorus in the form of phosphate. Even the waste products and the dead organisms are decomposed by phosphate- solubilizing bacteria releasing phosphorus. Depletion in any activity of human can limit this nutrient in the atmosphere.

Note:
Major and important differences between carbon and phosphorus cycle are firstly, atmospheric inputs of phosphorus through rainfall are much smaller than carbon inputs, and secondly, gaseous exchanges of phosphorus between organisms and environment are negligible.