Nitrogen Cycle

Ammonification is the process by which the organically bound nitrogen of microbial, plant, and animal biomass is recycled after their death. Ammonification is carried out by a diverse array of microorganisms that perform ecological decay services, and its product is ammonia or ammonium ion. Ammonium is a suitable source of nutrition for many species of plants, especially those living in acidic soils. However, most plants cannot utilize ammonium effectively, and they require nitrate as their essential source of nitrogen nutrition.

Nitrate is synthesized from ammonium by an important bacterial process known as nitrification. The first step in nitrification is the oxidation of ammonium to nitrite (NO^- ₂ ), a function carried out by bacteria in the genus Nitrosomonas. Once formed, the nitrite is rapidly oxidized further to nitrate, by bacteria in the genus Nitrobacter. The bacteria responsible for nitrification are very sensitive to acidity, so this process does not occur at significant rates in acidic soil or water. This is the reason why plants of acidic habitats must be capable of utilizing ammonium as their source of nitrogen nutrition.