This article is an exhaustive and detailed summary of the role of iron in nitrogen cycling in soils and addresses both the fundamental and emerging concepts. Minerals are important controls on soil organic matter cycling, but research and published reviews focus largely on carbon. This review is unique with its emphasis on specifically iron-bearing minerals and nitrogen. While the article will be very informative to the readership of Biogeosciences, revisions to the overall structure and writing are needed. The text is repetitive and could be pared down significantly. Details are at times presented in a laundry list approach rather than in a cohesive narrative. Overall, the content is appropriate but revisions to the organization and overall story will greatly improve the quality of this article.

Specific comments:

Lines 33-52: This list of evidence reflects the structure of the paper overall – many sections in the paper are stand alone “chunks” of ideas that do not cohesively tie together. As written, the sections appear as a list of ideas instead of a defined structure with a beginning, middle, and end.

Section 4: It is not clear how the structural role is distinct from the sorbent role. The mechanisms presented in Figure 2 and many described in this section are referring to adsorption/desorption processes.

Sections 7 and 8, in particular, lack an overall structure. A potential solution to the organizational issues with the writing would be to separate the properties and processes into distinct spatial scales:  1) The molecular scale at which sorption/desorption, catalysis, electron transfer occur, 2) the micro-scale, at which iron mediates soil aggregation, and 3) the meso/ecosystem-scale, at which iron may influence the priming of soil nitrogen in the rhizosphere or the response of SON cycling to global change.

This manuscript provides a detailed review of the role of iron in soil nitrogen cycling. There have been a number of excellent reviews recently on soil organic matter dynamics and N bioavailability (e.g., Blakinship et al., 2018; Cotrufo et al., 2013; Daly et al., 2021; Jilling et al., 2018; Lehman and Kleber, 2015; Whalen et al., 2022), and this manuscript has the potential to stand alongside these by addressing an important topic for which there isn’t currently a comprehensive review available. So, this manuscript fills an important niche; however, substantial revisions are needed to make the paper a strong contribution to this literature. The authors would do well to review these and other available syntheses and to put their work within that context as a way to better build a case for the novelty and importance of their work. These published reviews can also be used as guides for how to structure an impactful review paper. In general, the text needs to be shortened and streamlined to avoid redundancy and maximize impact. All of the figures could use some work to make them more nuanced and visually appealing (e.g., use of color).

Specific line/figure comments:

L33-51. This section might read better as prose rather than a list that doesn’t seem to be ordered in a particular way.

L53-70. This section provides a nice structure for the paper.

Fig. 1. Is this an original figure or taken from another source? If the latter, the source needs to be provided. If the former, I would suggest using color to make it more interesting/readable and also link it to the overarching structure of the paper. That is, if you’re going to follow the structure outlined in L53-70, then indicate how these four “roles” tie into the figure. Or develop a different overarching figure that gives a conceptual overview of the paper.

Sec. 2. This section interrupts the flow from the overarching structure of the paper laid out in L53-70 and Sec. 3 (i.e., “sorbent role”). Perhaps this material could be shortened and included in the intro section before laying out the paper objectives/structure

L127. This question doesn’t lead well into the overarching theme of this section and detracts from the main thread. Start with an introductory paragraph that introduces the topic and provides a roadmap for the rest of the section. I assume that the “sorbent role” isn’t just about enzymes, right?

Sec. 4. As noted above, starting the section with a question is not the best way to introduce the topic and provide an overview for the section. In the first paragraph, lay out what the questions or topics are and then follow up with a succinct discussion of each. Ditto this comment for all sections.

Fig. 2. I would encourage you to think about how this figure could be a bit more nuanced rather than just having “clouds” for enzymes, N substrates, etc.

Sec. 5. You skip the “electron transfer role” and go straight to “catalytic role”. If there isn’t a separate section for “electron transfer role” then remove from overview paragraph as a separate, defined “role”.

Sec. 7 and 8. As noted by the other reviewer, these sections lack structure and were not adequately introduced earlier in the manuscript.