Denitrification
Denitrification is a microbially mediated process consisting of a series of redox reactions, in which nitrate (NO3-) is transformed to nitrite (NO2-), nitric oxide (NO), nitrous oxide (N2O) and dinitrogen gas (N2). Denitrification mostly takes place under low oxygen conditions (in other words, in soils where pores are saturated with water). It can be seen as a form of respiration for anaerobic microbes, in which nitrate or nitrite takes over the function of oxygen as final electron acceptor. The series of denitrification reactions are catalysed by a suit of different enzymes. Different types of bacteria, archaea and fungi can facilitate the process of denitrification.
Denitrification is one of the main processes listed in the Carbon and Climate Regulation model because it produces a significant amount of nitrous oxide (N2O), a potent greenhouse gas. In the Nutrient cycling model, denitrification is included under nitrogen transformation. Through denitrification, nitrogen can be lost from soil in gaseous form (either as N2O or N2), reducing nutrient availability to plants and other organisms.
Nitrous oxide emissions can be measured in the field using flux chambers and an infrared gas analyser[1]. Denitrification can also be estimated in soil samples collected from the field by means of incubation assays using acetylene inhibition, enzymatic analyses or the quantification of functional genes involved in the series of denitrification reactions[2],[3],[4],[5].
[1] Oram NJ, et al. 2020. Can flooding-induced greenhouse gas emissions be mitigated by trait-based plant species choice? Science of The Total Environment 727: 138476.
[2]Yoshinari T et al. 1977. Acetylene inhibition of nitrous oxide reduction and measurement of denitrification and nitrogen fixation in soil. Soil Biology and Biochemistry 9: 177–183.
[3]Tiedje JM, et al. 1989. Perspectives on measurement of denitrification in the field including recommended protocols for acetylene based methods. Plant and Soil 115: 261–284.
[4] Henry S et al. 2004. Quantification of denitrifying bacteria in soils by nirK gene targeted real-time PCR. Journal of Microbiological Methods 59: 327–335.
[5] Henry S et al. 2006. Quantitative Detection of the nosZ Gene, Encoding Nitrous Oxide Reductase, and Comparison of the Abundances of 16S rRNA, narG, nirK, and nosZ Genes in Soils. Applied and Environmental Microbiology 72: 5181–5189.