Chen et al. explored the contribution of soil fungal and bacterial necromass carbon to soil organic carbon fractions in different grassland types. Moreover, the influencing factors were explored using random forest modeling. The results showed the contents of MAOC and POC in the 0–100 cm soil layer were Meadow steppe > Typical steppe > Desert steppe > Steppe desert. FNC dominated both MAOC and POC, and its contribution was higher than the contribution of BNC. The results from this study help to understand the composition of SOC in an ecologically transitional zone. However, substantial revisions are needed to improve the MS quality.

1. The overall writing should be carefully checked, e.g., Line 80, "xxx conservation initiatives.(Hou et al., 2024)." should be "xxx conservation initiatives (Hou et al., 2024).". Line 87, "Wang et al.(Wang et al., 2021a)" should be "Wang et al. (2021a)". Too many clerical errors show the MS was not well prepared.
2. Lines 27–29, the authors stated that the quantitative contribution of MNC to distinct SOC fractions and its regulatory mechanisms across various grassland types remain largely unexplored. However, mechanisms are also not involved in this study.
3. Line 52, SOC.
4. The scientific significance is not clear based on the Introduction, e.g., why Ningxia is the representative research area.
5. In Materials and Methods, please ensure the calculation of SOC fractions is reliable.
6. Line 317, Please revise "Zhang et al.(Zhang et al., 2024), Shen et al.(Shen et al., 2024), Ji et al.(Ji et al., 2020).".
7. In figure 3, POC, rather than ROC.
8. In figure 10, R²=83.4%?
9. Regarding discussion, I recommend the authors present the key results first and discuss the results based on the published literature.
10. I recommend the authors carefully check English and improve writing quality.

Summary and recommendation:

This paper quantifies soil carbon pools across a diversity of grasslands in the Ningxia region in China, specifically total mineral-associated and particulate organic matter pools and the microbial necromass contributions thereof. The Ningxia region spans a temperature and moisture gradient, across varying soil physicochemical properties, allowing the authors to assess the contributions of climate to soil carbon stocks. Further, the authors assess these relationships down to 100 cm soil depth, allowing inferences about different soil processes.

The paper integrates standard soil physical/chemical characterization with amino sugar proxies of necromass, and uses linear regression as well as correlational and random forest modeling approaches to assess relationships. Overall, the results are robust and provide an extensive understanding of how climate, vegetation gradients, and soil physicochemical properties influence soil carbon pools, and the study provides substantial contribution to scientific progress in understanding microbial necromass in grassland ecosystems. However, the text needs significant work to improve flow and clarity. We recommend three major revisions: editing grammar and flow, explicitly including hypotheses, and including more detailed methods and soil characterization. After these major revisions, and further suggestions detailed below, we recommend this article to be accepted for publication.

1. Does the paper address relevant scientific questions within the scope of SOIL?

Yes, this paper contributes to understanding of microbial necromass dynamics across four different types of grasslands in the Ningxia region in China. This paper also contributes to understanding of microbial necromass carbon (total, fungal, and bacterial) in different soil carbon fractions at deeper soil depths, which are less studied portions of the soil profile. 

2.  Does the paper present novel concepts, ideas, tools, or data?

The paper’s novelty is in its integration of standard soil physical/chemical characterization with amino sugar proxies of necromass, and its use of correlational and random forest modeling approaches to assess relationships. Further, as mentioned above, the study is inclusive of deep soils (100 cm), which is unique to the soil necromass literature.

3. Does the paper address soils within a multidisciplinary context?

Yes: this paper integrates soil chemistry and microbial dynamics with a biogeochemical understanding of carbon cycling.

4. Is the paper of broad international interest?

Yes, microbial necromass carbon is a significant portion of soil organic matter/SOC and has potential to exacerbate or mitigate climate change. Understanding necromass dynamics across different grassland types that have varying abiotic and biotic factors is important for our predictive understanding of soil carbon.

Further, the study region in China provides a useful gradient in temperature, moisture, and soil physicochemical properties across grassland types to understand dynamics of soil carbon and necromass.

5. Are clear objectives and/or hypotheses put forward?

The study’s objective is to understand the contribution of necromass to different soil carbon pools (particulate and mineral-associated organic carbon) and to understand the vertical distribution of these pools across a diversity of grasslands.

However, there are no clear hypotheses in the manuscript. Adding hypotheses that drove the research approach would strengthen this paper, and we suggest including the hypotheses that drove your research questions and approach at the end of the introduction. For example, based on precipitation or temperature differences across grassland types, did you hypothesize differences in total MAOC or POC, or different necromass contributions to MAOC or POC? What depth patterns did you expect?

Because there aren’t clear hypotheses, the results and discussion sections read as more data exploration rather than testing hypotheses. We recommend clearer inclusion of hypotheses to help frame the results and discussion.

6. Are the scientific methods valid and clear outlined to be reproduced?

The methods need to be significantly revised to include more details of procedures used, especially those used for soil physicochemical analyses. Either methodological details or citations that include such details should be added in the text. For example, what standard protocols did you use for your phosphorus and potassium measurements (Line 159)?

In the manuscript, it is written that soil was sieved through 2mm and 0.15 mm sieves, and then also separated by density fractionation. How do these methods relate to each other for determination of MAOC and POC?

Authors could go into greater detail about the distribution of the data and why parametric test and linear regression was most appropriate for the data.

Please include the significance level used for statistical tests (e.g., alpha = 0.05).

7. Is the soil type/classification adequately described?

No, the soil type/classification or geologic information was not described. There was no mention of soil texture, or soil horizon but the authors used the phrase soil profile throughout the manuscript. This paper would greatly benefit from inclusion of soil type/classification into the methods/sampling site section. Soil variables such as texture, soil horizon, or soil taxa could be important independent variables of MNC/FNC/BNC/SOC/MAOC/POC as this can regulate soil carbon dynamics.

Line 139: Why were these soil depths chosen? Were there soil horizons or other soil characteristics unique at these depths (e.g., pH, texture, mineral composition, organic matter, etc.)?

8. Are analyses and assumptions valid?

It is unclear. At first glance, analysis and assumptions appear valid but the authors did not mention if the distribution of the data was normal or non-normal, and why parametric test/linear regression was suited for the data. If the data was normally distributed, the authors analysis is appropriate but if the data is not normally distributed then alternative non-parametric statistical analysis should be used.

9. Are the presented results sufficient to support the interpretations and associated discussion?

Yes. However, most of the figures are lacking legends and clear figure captions that explain abbreviations, symbols, or colors. Figure captions for figures 3-10 all need to be updated to meet this requirement. Additionally, figures 5, 6, 7, and 8 do not have the legend to differentiate grassland type.

We recommend that the authors expand on why the 20 - 100 cm layers were combined together in Figures 9 and Figures 10. Soil depths were analyzed separately throughout the analysis and the vertical distribution of necromass was a knowledge gap the authors identified in the introduction. Further, do Figures 9 and 10 aggregate all grassland types? Please include this information in the caption.

Panel letters should be added to the figures to allow easier reading.

Line 132-135: How do the four grassland types (MS, TS, DS, and SD) relate to the abbreviations next to the number of sampling sites (CD, HM, DX, CH)? These abbreviations are then used interchangeably in the presentation of the results and discussion and in the figures, making it very difficult to follow which grassland type you are referring to. Please streamline the use of abbreviations to improve clarity.

Finally, we recommend that if possible, authors should adopt a more accessible color palette for figures to make figures more accessible for readers with color-blindness. 

10. Is the discussion relevant and backed up?

Yes. However, because the authors identify optimizing grassland management strategies as a broader impact in the introduction (Line 114), it would strengthen the manuscript to expand on this more in the discussion. Also, the authors infer that MAOC is being leached into deeper soil layers (line 346), are there any findings or relevant citations that back this up? A deeper discussion here would be interesting. 

11. Are accurate conclusions reached based on the presented results and discussion?

Yes, however it would be useful to have a clearer discussion of how the grasslands are different from each other and how this impacts potential grassland management strategies for carbon sequestration. Are there implications for how grasslands should be managed for MAOC or POC pools, or to mitigate C losses in the subsoil?

12. Do the authors give proper credit to related and relevant work and clearly indicate their own original contribution?

For the most part, although there were sections in the introduction we do believe should have a citations:

Lines 99 - 109: Here the authors identify a major knowledge gap about microbial necromass dynamics, but do not have any corresponding citations. 

Lines 119 - 127: Sampling site description has no citations. 

Line 143: Can you cite or expand on the vegetation survey method used?

Line 151: Citation for the core method

Line 155: Citation for SOC K₂Cr₂O₇ external heating method. Also, it would help to list the chemical compound name (Potassium dichromate) before listing the formula 

Line 157: Citation for Kjeldahl method

Line 159: Citation and name for the “standard protocols”

Lines 184 - 192: Data analysis section could use more description. Clearly identify how you explored the distribution of the data, what are the dependent variables, and what are the independent variables. 

Lines 191 - 192: R packages should have citations. 

13. Does the title clearly reflect the contents of the paper and is it informative?

Yes, the title clearly reflects the contents of the paper and it is informative.

14. Does the abstract provide a concise and complete summary, including quantitative results?

Yes, the abstract is concise and complete. 

15. Is the overall presentation well structured?

Yes.

16. Is the paper written concisely and to the point?

Yes, overall. However, the discussion section is lengthy and could be divided into clearer paragraphs.

17. Is the language fluent, precise, and grammatically correct?

Satisfactory. Overall, we recommend the text be revised for grammar and clarity. Several suggestions are noted below in the minor items list below, but the paper should be thoroughly edited for similar issues throughout.

18. Are the figures and tables useful and all necessary?

Figures and tables are useful, but the figure captions for many of the figures could be more informative as to what is it we are looking at and what is significant versus not significant. The figure caption for Figure 2 is excellent and explanatory, but many of the other captions lack important details.

19. Are mathematical formulae, symbols, abbreviations, and units correctly defined and used according to the author guidelines?

1. 1. Abbreviations need some more clarification and consistency 
   2. Overall, there were many abbreviations and some of these abbreviations were not used many times in the paper and could be omitted.  

20. Should any parts of the paper (text, formulae, figures, tables) be clarified, reduced, combined, or eliminated?

We recommend moving some of the 10 figures to supplemental, in order to streamline the presentation of the results.

The discussion section reiterates much of the results; this text could be streamlined to reference rather than repeat the results.

21. Are the number and quality of references appropriate?

Yes.

22. Is the amount and quality of supplementary material appropriate and of added value?

We suggest moving some figures to the supplementary materials - see question 20.

MINOR ITEMS

Line 27: Add the word “yet” to second clause

Line 29: Replace “through” with “encompasses”

Line 44: Replace “Thid” to “Third”

Line 51: Change “offering” to “offers”

Line 52: Capitalize SOC

Line 53: Change “provide” to “provides”

Line 68: Add “and” before “represents”

Line 77: Change “Therefore” to “These results” and remove comma

Line 87: Capitalize “MNC”

Line 96 and elsewhere: Consistently use the MNC abbreviation; the text alternates between the abbreviation and full spelling out of the abbreviation.

Line 101: Divide into two sentences between “...deeper soil layers (>60cm. This knowledge gap is…”

Line 116: What is the “dual-carbon” goal? This is the only time it is mentioned in the text. Perhaps reference this in the discussion again as well.

Line 126: Provide data range for large temperature variations.

Line 137: Add reference to Table 1.

Line 181: Add units to your molecular weight numbers.

Line 182: Add citation for the conversion factor.

Line 188: Define LSD, and add citation. 

Line 225: Figure 3 POC content figure is incorrectly titled “ROC content”.

Line 283: Are these correlations performed by grassland type or do they aggregate grassland types together?

Line 295: How do you define “residue carbon accumulation?”

Line 303: Delete the extra period at the end of the sentence.

Line 346: You state that MAOC could be leaching to deeper soil depths. Can this be supported with citations or expand on the mechanistic reasoning behind this? 

Line 440: You state that as elevation increases the rate of SOM decomposition decreases. But does the input of SOM also decrease? Both are key to determining overall accumulation of organic matter.