For example, nirK is pivotal for N cycle processes, as it plays a role in ammonia oxidization to nitrite in nitrification (Nitrosomonas europaea), and regulates dissimilatory nitrate reduction in denitrification. Hence, nirK abundance by itself cannot be used to apportion in situ N2O emissions from denitrification vs. nitrification sources, but it is a valuable indicator of the potential for one or both of these processes to occur.