by the nature of the term, this is a loop system. We cant add to it, this is quite correct, it is fixed, or else we would see fluctuating N2 levels in the atmosphere, but its honestly very stable in range %. What we are doing is generating excess NO which isnt in the system and so goes as pollution which we see clogging river systems, falling as acid rain, in our tap water as a carcinogen and destroying delicate microbes in the upper atmosphere essential for the water cycle and so on.
So everyone is clear of the process.
The nitrogen cycle is an important biogeochemical cycle in which nitrogen is converted into different chemical forms such as NH3 , NH4+, NO2-, NO3- etc. There are four major processes in the nitrogen cycle. They are fixation, ammonification, nitrification, and denitrification . Many of these processes are carried out by microorganisms, especially bacteria present in the soil. Nitrification and denitrification are the two main stages which transform atmospheric nitrogen into nitrate and nitrate back into atmospheric nitrogen.
Nitrification is the biological transformation of ammonium (NH4+) into nitrate (NO3ā) by oxidation while denitrification is the biological transformation of nitrate to nitrogenous gases (N2) by reduction. This is the key difference between nitrification and denitrification.
What synthetic N does, is short cut this system, what does it do to microbes? It alters the community as does any input. See here. from a study conducted by
Ning Ling Dima Chen Hui Guo Jiaxin Wei Yongfei Bai Qirong Shen Shuijin Hu in the Stepps region, well known to be limited in N and P in particular and as such it is a region where inputs have been extensively used and monitored.
I have added some bits in brackets to help you see which groups are dong what
"N Inputs significantly increased the relative abundance of the predicted copiotrophic groups (these also consume Glomalins after tillage, and they are part of denitrification) (
Proteobacteria and
Firmicutes) but reduced the predicted oligotrophic groups (
Acidobacteria,
N itrospirae,
Chloroflexi), with the order
Rhizobiales being most affected.
P additions significantly affected only two phyla (Armatimonadetes and
Chlorobi), which were positively correlated with P source.
Results from the structural equation modelling (SEM) showed that N additions affected the bacterial community primarily by changing the pH, while P additions did so mainly by improving P availability. Our results suggest that the below-ground bacterial communities are more sensitive to N inputs, but P inputs can also play an important role in bacterial niche differentiation. These findings improve our understanding of bacterial responses to N and P inputs, and their impacts on bacterial-mediated processes, especially in the context of increasing anthropogenic nutrient inputs."
Hope that helps