The rate limiting step is ammonia oxidation, a process mediated by clades of soil bacteria and archaea Similarly with denitrification, PCR-based methods for characterizing the ecology of these organisms in ecosystems are available (detection of their respective amoA genes;Quantification of nitrification and denitrification genes may provide useful insights into the relative amounts and forms of N lost to the atmosphere, and a means of assessing functional changes in microbial communities involved in important ecosystem processesAlthough changes in the abundances of such functional genes may sometimes have relatively low productivity capacity for a biogeochemical process (e.g. Powell et al., 2015), they nevertheless provide additional perspective on the microbial community and be provide useful insights pertaining to ecosystem change