What process reverses mineralization by converting inorganic nitrogen back into organic forms?

Immobilization is the process that effectively reverses mineralization, as it converts inorganic nitrogen into organic forms. During this process, microorganisms take up inorganic nitrogen compounds, such as ammonium or nitrate, and incorporate them into their biomass, thus transforming these minerals into organic matter. This is significant in nutrient cycling, as it temporarily retains nitrogen in a form that is not immediately available for plant uptake.

In contrast, nitrogen fixation involves the conversion of atmospheric nitrogen into forms that can be used by plants, primarily converting diatomic nitrogen gas into ammonia. Nitrification is the biological oxidation of ammonium to nitrate, making nitrogen available in a form that plants can utilize, but it does not convert inorganic nitrogen back into organic forms. Ammonia volatilization refers to the loss of ammonia from the soil to the atmosphere, which also does not represent a conversion to organic forms. Thus, immobilization stands out as the correct choice since it directly represents the transformation of inorganic nitrogen back into organic matter.