Nitrogen transformation
In the Nutrient cycling model, nitrogen transformation refers to a group of four microbial processes that convert nitrogen into different forms. Nitrification and denitrification are described on separate pages because they are also included in the Carbon and climate regulation model. The other two processes are dissimilatory nitrate reduction to ammonium (DNRA) and anaerobic ammonium oxidation (Anammox).
DNRA occurs under low oxygen conditions and is most commonly carried out by bacteria. In this process, nitrate is converted to nitrite and ultimately ammonium. This process is often not considered in agricultural soils and requires more investigation to determine its relevance to nutrient cycling in agroecosystems.
In the process of Annammox, ammonium and nitrite are converted to dinitrogen gas (N2) through oxidation by bacteria. This process was discovered in aquatic systems. Since then, scientists have found anammox bacteria in soil as well. However, the importance of anammox in soil nitrogen cycling in agricultural systems needs to be further investigated.
As these processes are commonly not measured in agroecosystems, there are not that many standardized methods available. One option would be to measure functional genes to identify the abundance of ammonia-oxidizing and nitrate-reducing micro-organisms[1],[2].
[1] Junier P, et al. 2010. Phylogenetic and functional marker genes to study ammonia-oxidizing microorganisms (AOM) in the environment. Applied Microbiology and Biotechnology 85: 425–440.
[2] Pandey CB, etal. 2020. DNRA: A short-circuit in biological N-cycling to conserve nitrogen in terrestrial ecosystems. Science of The Total Environment 738: 139710.