What is nutrient immobilization?

Hint: The nutrients are incorporated in a structure. They do not enter easily again into the ecosystem cycle. It means the nutrient for some time they are out of the biogeochemical cycle.

Complete answer:
In an ecosystem many organisms are interacting with each other in their environment, the nutrient does not permanently lose from the ecosystem. Rather they are recycled indefinitely in the ecosystem.
Nutrient Immobilization means when the nutrient goes at a place where they are stable and incorporated in a structure. They are less likely to easily be recycled again. Eg- phosphorus cycle, it is a biogeochemical cycle, where phosphorus travels through different parts of the ecosystem. The reservoirs are mainly found in many animals' bodies. As bones and teeth are made up of phosphorous. This phosphorus is incorporated into the bones and teeth of the animals. They do not enter easily again into the ecosystem cycle before the death of the animal. Nutrient immobilization means the nutrient for some time they are out of the biogeochemical cycle.

Additional information: Mechanisms of nitrogen immobilization: There are two mechanisms of nitrogen immobilization.
- Nitrogen accumulation in microbial biomass
- Accumulation of nitrogen in by-products of microbial activity.
Nitrogen accumulation in decomposing plant debris obeys a two-phase mechanism following the starting leaching of soluble materials from fresh detritus to carbohydrates, phenolic, small peptides, and amino acids. This is a time whereby microbial growth is rapid. With microbes converting substrate nitrogen and exogenous nitrogen into microbial biomass and excrete products of microbial activity.

Note: Immobilization is the opposite of mineralization (decomposition of the chemical compounds in organic matter). In immobilization, the inorganic nutrients are taken up by soil microbes making them unavailable for further uptake. It is a biological process controlled by bacteria.