What is immobilization in the nitrogen cycle?

Immobilization in the nitrogen cycle refers to the process where inorganic nitrogen compounds, such as ammonium and nitrate, are converted into organic forms of nitrogen. This transformation is typically carried out by microorganisms within the soil which assimilate inorganic nitrogen to synthesize organic molecules necessary for their growth and activity. As a result, these organic nitrogen compounds become part of the biomass of the microorganisms, making them less available for plant uptake temporarily.

In the context of the nitrogen cycle, this step is crucial because it influences nitrogen availability in the ecosystem. When nitrogen is "immobilized," it is not directly accessible to plants, which primarily absorb nitrogen in its inorganic form. This can lead to a temporary decrease in soil nitrogen availability, impacting plant growth if the balance between immobilization and mineralization (the conversion of organic nitrogen back into inorganic forms) isn't maintained.

The other options describe different processes within the nitrogen cycle, such as the conversion of organic nitrogen to inorganic nitrogen or the transformation from one inorganic form to another, but they do not define immobilization as it pertains to the nitrogen cycle.