ammonification

Ammonification, also called mineralization, is a microbial process that converts organic nitrogen compounds into ammonium (NH4+). It is a fundamental step in the terrestrial and aquatic nitrogen cycles, releasing inorganic nitrogen from dead organic matter, waste, and detritus so it can be used by microorganisms or assimilated by plants.

The process is carried out primarily by bacteria and fungi. Complex nitrogen-bearing compounds in litter or soil organic matter, such as proteins, amino acids, and urea, are hydrolyzed by extracellular enzymes such as proteases and peptidases, releasing smaller nitrogenous molecules. These are further degraded and deaminated, ultimately producing ammonium. In aerobic environments, ammonium tends to accumulate as the end product, though it can be taken up by microbes or further transformed by other processes.

Environmental factors influence the rate of ammonification. The quality of the organic substrate and its carbon-to-nitrogen ratio are key; readily decomposable material with a lower C:N ratio generally mineralizes faster. Temperature, moisture, soil pH, and oxygen availability affect microbial activity and enzyme function. The composition of the microbial community also matters, and substrates with high C:N ratios can slow mineralization due to nitrogen immobilization by microbes.

Relation to the nitrogen cycle: the ammonium produced by ammonification serves as a substrate for nitrification and can be directly taken up by plants or microorganisms. Under certain conditions, ammonium may be lost as ammonia gas (NH3) through volatilization, especially at high pH. Ammonification thus links decomposition to nitrogen availability in ecosystems.