| 23 Apr 2026
Ideas and perspectives: Nitrite turnover controls nitrogen fate across redox gradients
Abstract. Reactive nitrogen fate in natural systems remains difficult to predict because pathway partitioning occurs at the stage of nitrite turnover, where rapid and tightly coupled production and consumption processes obscure the underlying fluxes. Concentration-based assessments emphasize the dominant pools — nitrate and ammonium — and pathway divergence is determined at the stage of nitrite turnover, independently of pool size. Nitrite is the only inorganic nitrogen species produced under both oxidative and reductive regimes and the obligatory precursor to all downstream dissolved and gaseous products. Because nitrite rarely accumulates, it has often been treated as a transient intermediate of limited interpretive value. This apparent invisibility reflects rapid, tightly coupled turnover and does not indicate functional insignificance. Nitrogen retention, recycling and atmospheric loss are resolved at the stage of nitrite turnover, where competing pathways partition fluxes under kinetic and environmental constraints.
Observed concentrations integrate formation and consumption into a net signal that masks opposing fluxes when internal cycling is rapid. Coupled δ¹⁵N–δ¹⁸O measurements of nitrite constrain simultaneous production and consumption and differentiate biological from abiotic pathways. Partial oxygen isotope exchange with water increases the diagnostic primacy of δ¹⁵N in resolving hidden turnover. Centering nitrogen-cycle interpretation on nitrite dynamics and isotopic expression across redox gradients from oxic soils to oxygen minimum zones, provides a mechanistic basis for predicting nitrogen budgets, N₂O emissions, and ecosystem sensitivity to increasing redox variability under climate change and land-use intensification.
Review
Ideas and perspectives: Nitrite turnover controls nitrogen fate across redox gradients
Dear authors,
This is a very valuable summary manuscript highlighting the unique, important and still very underused N-compound. I definitely agree with the manuscript thesis of the critical role of nitrite turnover in controlling the N cycling dynamics. The manuscript provides an interesting overview of N-transformations from the nitrite perspective as a central compound of the N-cycle. I appreciate your in-depth insight into the N-cycle and the role of nitrite, that provides a “snapshot” of the currently undergoing processes. I like very much your statement: “A nitrite-centred framework shifts emphasis from storage to flux, from accumulation to coupling, and from static pools to dynamic turnover”, these are very important observations, however not totally novel, but definitely still undervalued.
However, while the general idea is precious and worth publishing, the manuscript is not complete and up-to-date, hence needs to be complemented and updated. Quite a few very important and most recent research on nitrite role and isotope characteristics were omitted. It seems like the manuscript was prepared a few years ago, since the most recent citation is from 2021, except authors own paper from 2026. At least these important literature positions are missing, not only as citations, but also in referring to the progress presented by these authors:
Müller, C., Laughlin, R. J., Spott, O., and Rütting, T.: Quantification of N2O emission pathways via a 15N tracing model, Soil Biol. Biochem., 72, 44–54, https://doi.org/10.1016/j.soilbio.2014.01.013, 2014. – first idea that nitrite play a central role in N cycle – applied for N-trace model
Lewicka-Szczebak, D., Jansen-Willems, A., Müller, C., Dyckmans, J., and Well, R.: Nitrite isotope characteristics and associated soil N transformations, Sci. Rep., 11, 5008, https://doi.org/10.1038/s41598-021-83786-w, 2021. – first isotope analyses of soil nitrite, with modelling approach for natural abundance and 15N-traced systems
Deb, S., Espenberg, M., Well, R., Bucha, M., Jakubiak, M., Mander, Ü., Jędrysek, M.O., Lewicka-Szczebak, D.: N transformations in nitrate-rich groundwaters: combined isotope and microbial approach, Biogeosciences, 22 (19), 5535-5556, doi.org/10.5194/bg-22-5535-2025. – first application of nitrite isotopes for groundwater studies, together with nitrates and N2O, indication of simultaneous reduction and oxidation processes
Deb, S., Lewicka-Szczebak, D., and Rohe, L.: Microbial nitrogen transformations tracked by natural abundance isotope studies and microbiological methods: a review, Sci. Total Environ., 926, 172073, https://doi.org/10.1016/j.scitotenv.2024.172073, 2024 – most recent review paper on application of stable isotopes of different N-compounds including nitrite, also describing it as the central N-compound
Zheng, J., Fujii, K., Koba, K., Wanek, W., Müller, C., et al., Revisiting process-based simulations of soil nitrite dynamics: Tighter cycling between nitrite and nitrate than considered previously, Soil Biology and Biochemistry, 178, 108958, doi.org/10.1016/j.soilbio.2023.108958 – new N-trace modelling approach with even more emphasis on nitrite central role
Only after taking into account all the recent research on this topic the proposed perspective manuscript can be considered for publication.
Detailed comments:
P3, L55-56 “Nitrite is the only inorganic nitrogen species produced by both oxidative and reductive processes” – not really, what about N2O?! it can be produced due to nitrate reduction and as well from ammonia and hydroxylamine oxidation – this nitrification pathway is missing in the Figure 1!
P3 L62 you should also add newer N-cycle reviews here, eg. Denk et al., 2017, Deb et al, 2024
P4 L73 also some more recent technical developments of nitrite isotope measurements should be mentioned: Deb and Lewicka-Szczebak, 2025 (doi.org/10.3389/fenvs.2025.1536882), Hu et al., 2026 (doi.org/10.1039/D5JA00363F)
P5 L122 – this was also observed in the recent case study (Deb et al., 2025)
P5 L 136 – the nitrifier denitrification pathway that you describe here is also omitted in your Fig.1
P6 Fig 2 – I don’t understand the bottom left panel illustrating delta 15N for dominating production, what do the 2 arrows mean? Two following graphs are clear, present the expected possible trends in isotope changes, but the first graph do not show change in time, just as one-point?
P7 L198 – the sentence beginning with “Direct determination…” is a totally different topic, you said about analytical techniques before and here the paragraph was about N2O. Also, a citation for N2O reduction overprinting its isotopic signal should be added here.
P9 Fig.3 – really great figure with perfect presentation of nitrite central role
P10 L262 The oxygen exchange with water is also an important tracer because allows us to estimate the nitrite residence time and rates of biological NO2 turnover relative to abiotic exchange (Lewicka-Szczebak et al., 2021, Buchwald and Casciotti, 2013)
P10 L279 I am missing the chapter on limitation of this approach. Most difficult one is the chemical instability of nitrite and its very low concentrations. If improperly stored and not analysed immediately it is quickly partially oxidised to nitrate and the isotope signal can be totally changed. Therefore, the analysis should be performed immediately, and the samples must be carefully conserved, best with high pH conditions. Because of typically low nitrite concentrations, especially in terrestrial environments, the development of new analytical methods for lowering the detection limit for its isotope analysis is critical (Deb and Lewicka-Szczebak, 2025). I think these are important points because these analytical challenges are most probably the main reasons why nitrite isotope analyses in terrestrial systems are still very rare.