Soil C:N:P Stoichiometry Succession and Land Use Effect after Intensive Reclamation: A Case Study on the Yangtze River Floodplain
, He Jiao 1, Shuangwen Yi 1 and Chao Gao 1,*Round 1
Reviewer 1 Report
My overall opinion on this paper is that it presents valuable research on the effects of land reclamation and land use patterns on soil C:N:P stoichiometry. The study is well-structured, and the methodology is sound. The results provide important insights into the decoupling of soil C, N, and P cycles and the factors that drive the observed patterns in soil nutrient dynamics. The paper provides an extensive background on the importance of C, N, and P in soil, as well as the potential effects of reclamation and land use on soil nutrients. The authors effectively show the relationship between reclamation duration, land use patterns, and soil properties. The grammar and spelling in the paper are generally good, with a few minor errors and areas for improvement. I appreciate the depth of the research, but I have a few suggestions and questions to improve the clarity and readability of the paper.
Abstract
1. Lines 25–26. The sentence "Land use analysis revealed another imbalance between soil C, N and P" is ambiguous. Please clarify the nature of the imbalance and how it relates to the findings.
2. Lines 38–30. In the sentence "Based on the redundancy analysis and Random Forest model, soil OC and TN were mainly affected by the bacterial functional gene related to Cellulolysis, while metal oxides, including Fe2O3 and CaO could best predict TP," it would be helpful to briefly explain the role of the redundancy analysis and the Random Forest model in your research methodology.
3. Lines 30–31. In the sentence "Soil RCP and RNP were mainly driven by soil texture, especially the proportion of clay particles," consider specifying whether these ratios increased or decreased with changes in the proportion of clay particles.
4. Lines 31–32. In the concluding sentence, consider briefly mentioning the possible consequences of not addressing the nutrient imbalances, to emphasize the importance of your research.
Introduction
5. Lines 41–43. In the sentence "Elemental stoichiometry is a well-established theory for examining the relationship between different substances and discovering an optimal utilization strategy [1,4]." consider specifying which optimal utilization strategy you are referring to in the context of your research.
6. Lines 45–47. In the sentence "Although soil C-N-P stoichiometric ratios are generally stable [10], many have hypothesized that they will vary dramatically under a changing environment [11–13]." it would be helpful to briefly mention the factors that could cause these variations in a changing environment.
7. Lines 58–60. The sentence "Whether this opposite process will decouple soil C:N:P stoichiometry, and if this decoupling will continue to intensify with increasing reclamation time remains largely unknown" could be rephrased for better readability.
8. Lines 71–72. In the sentence "Thus, reclamation time and land use patterns may interactively affect soil nutrient structure," it would be beneficial to provide examples of how these interactions might occur.
9. Lines 74–75. The sentence "In a changing environment, alterations in edaphic properties can have a significant impact on the soil nutrient cycle [24–26]" could be improved by providing a brief explanation of the term "edaphic properties".
10. Lines 84–85. When discussing the Yangtze River in the context of wetland reclamation, it might be helpful to provide some basic geographical information about the river (e.g., its length or the region it spans) to establish its significance.
11. Lines 85–86. In the sentence "Since the 1950s, over 2.2 × 104 km2 of land has been reclaimed in this region [32]." consider using a more common notation for the area (e.g., 22,000 km2) to improve readability.
12. Lines 96–98. In the research questions section, consider using more direct and concise phrasing. For example, rephrase question (ii) as: "How do different land uses, and human management practices influence the effects of reclamation years on soil nutrients?" This will make the questions easier to read and understand.
13. Lines 99–103. In your hypotheses, consider rephrasing them as statements to improve readability. For example, rephrase hypothesis (i) as: "Prolonged reclamation time is expected to increase the content of OC and TN, but reduce the TP reserve.". In hypothesis (iii), you mention "geochemical variables and biological variables" dominating different nutrient indexes. It would be helpful to specify which nutrient indexes are dominated by each type of variable to provide greater clarity.
Materials and Methods
14. Lines 120–121. In the description of the study sites, you mention using OSL dating for the two oldest sites. Please provide the estimated reclamation duration for these two sites to help readers understand the full range of reclamation times in your study.
15. Lines 174 – 177. For the bacterial functional genes analysis, consider providing the rationale behind the selection of the three specific genes (Chemoheterotrophy, Nitrogen fixation, and Cellulolysis) to clarify their relevance to the study.
16. Lines 195–196. For the RF model, provide the rationale for choosing the specific values for the number of trees in the forest, variables tried at each split, and node size. Also, consider briefly explaining how these values were selected.
Results
17. Lines 248–250. In Section 3.2, it is mentioned that "OC and TN contents in paddies and woodland were observed significantly higher than that in dryland at each reclamation stage (p < 0.05) (excluding y3000)." Please clarify why the year 3000 was excluded from this observation.
18. Lines 294–295. In Section 3.3, the authors mention that "None of the investigated variables showed significant regulation on RCN, although EC was identified as the most important factor.". Please clarify if the variable EC has a significant or non-significant effect on RCN.
Discussion
19. Lines 311–314. The authors mention that OC and TN content in y3000 were unexpectedly lower than those in the y2000 site. It would be helpful to provide more context on how this result compares to other studies to better understand the implications of this finding. Additionally, it may be useful to discuss potential management practices that could mitigate the negative impacts of long-term soil degradation.
20. Lines 316–318. The authors should provide more information on the relationship between soil acidity and soil fertility. They mention that strong soil acidity could diminish soil fertility through hindering microbial activity and reducing CaCO3, but more details on the underlying mechanisms and their relative importance would be helpful.
21. Lines 390–420. The discussion on the effects of land use patterns on soil C, N, and P contents and stoichiometric ratios could be strengthened by including a comparison with similar studies in other regions or ecosystems.
22. Lines 423–425. In section 4.3, the authors mention that soil pH decreases over time due to leaching of base cations. It would be helpful to briefly explain the potential implications of the observed decrease in pH on soil fertility and plant growth.
23. Lines 442–444. In section 4.3, the authors discuss the effect of straw incorporation on soil organic matter. It would be valuable to provide some context on the frequency and extent of straw incorporation in the study area and how it compares to other agricultural practices that might also influence soil nutrient dynamics.
24. Lines 488–499. The section 4.4 discusses the differences in soil nutrient contents and stoichiometric ratios between paddies and drylands. It would be beneficial to provide some more information on how these differences might affect crop productivity and soil health in the long term.
Conclusions
25. The conclusion should emphasize the key findings of the study more explicitly. For example, the authors could state the specific values or ranges observed for OC, TN, RCP, RNP, and TP over time, as well as the differences between land uses. The authors could provide a more explicit synthesis of the key factors influencing soil C:N:P stoichiometry, including biological processes, Fe/Ca oxides, and clay particle proportions.
26. The authors could consider discussing the practical implications of the study's findings for land management and agricultural sustainability. Specifically, explaining how understanding the impact of reclamation duration and land use patterns on soil C:N:P stoichiometry can inform the development of more effective fertilization strategies or other management interventions.
27. Lines 522–525. When mentioning the need for external nutrient inputs in older soils, the authors should consider providing specific recommendations on the types and amounts of inputs required to maintain ecological balance, as well as any potential trade-offs or risks associated with their application.
28. The authors could consider briefly reiterating any limitations of the study and identify areas where future research is needed to advance understanding of soil C:N:P stoichiometry succession and its relationship with land reclamation and land use patterns.
29. The authors could briefly discuss any broader implications of the findings for understanding the long-term effects of land reclamation on soil health, ecosystem functioning, and agricultural productivity in the Yangtze River flood plain and other similar regions.
Author Response
Please see the attachment.
Author Response File: 
Author Response.docx
Reviewer 2 Report
Authors have investigated changes in soil biogeochemical processes, with particular focus on C:N:P stochiometry, related to agricultural history and practices. The study was conducted in the Yangtze River flood plain with documented history of land reclamation and agricultural usage lasting over 3000 years. Analysis of such a long documented history of land reclamation and agricultural usage is truly impressive, making this study particularly exceptional and valuable. Moreover, investigated hypothesis are clearly defined, research well planned and executed, and finally manuscript is generally well written. I have to admit, that it is a real pleasure to evaluate such well executed and presented investigations, and I have only very few comments and suggestions, mostly of editorial and linguistic or terminological nature.
Abstract
Lines 28-29:
"soil OC and TN were mainly affected by the bacterial functional gene related to Cellulolysis"
Not really appropriate statement or wording. The soil OC and TN are not really affected by bacterial genes but by bacteria, in that particular case bacteria metabolizing cellulose. Authors estimated amount of "bacterial functional gene related to Cellulolysis", but it has to be remembered that this has to be considered as an estimate of the amount of bacteria. So, this statement has to be rephrased.
Material and Methods
Line 171:
"Bacteria was the most abundant species of soil microorganisms"
Bacteria is not a species, but a group of biota. "Bacteria were the most abundant soil microbiota" would probably sound better.
Line 192:
"using CANOCO 5.0 software (Microcomputer Power, Ithaca, NY, USA)"
Citation of relevant literature would probably be more appropriate in that case, that is: "using CANOCO 5.0 software (ter Braak & Šmilauer 2002)"
ter Braak, C.J.F., Šmilauer, P., 2002. Canoco Reference Manual and User’s Guide. Software for Ordination (version 5.0). Biometris, Wageningen and ÄŒeské BudÄ•jovice.
Results
Figure 2.
Description on the figures are too small, including: (1) letters that mark particular fugutes (i.e.: a-l); (2) variables presented on particular figures, (3) numbers along both axis, (4) letters above bars indicating significance, and (5) the figures itself are also too small. I would suggest enlarging all description and enlarging the figures so the Figure would take the whole page (e.g., only two figures in a row and two in a column). With the current size these figures are virtually impossible to read.
Line 217:
"are different at p < 0.05" –> "are significantly different (p < 0.05)"
Line 218:
"are different" –> "are significantly different (p < 0.05)"
Line 225:
"fine particles"
Provide more precise information what did you mean. This relationship is only for clay, but not for silt which surely also belongs to the soil fine particles. Even sand is often considered as the soil fine fraction.
Line 234:
"fluctuated slightly”
"were relatively stable”
The following is probably be more appropriate statement: "fluctuated slightly”
Line 237:
"then slightly decreased"
As the difference is surely insignificant and can be considered in as a result of compliantly random and insignificant differences this statement is purely speculative and unjustified by the data. There should a clear statement given on lack of any significant differences between these values.
Figure 3.
Numbers given along both axes, also descriptions along vertical axes and letters indicating particular figures (a-f) should be enlarged. Enlarging significance letter would also make the figure easier to read. Some descriptions of trends overlap with data and significance letters obscuring them (see fig. a and d), so this have to be edited.
Line 247:
"The growth of woody and herbaceous plants resulted in"
This is not a result but interpretation and result discussion. Stick to results here and move their interpretation and discussion to the Discussion section.
Lines 249-250:
"were observed significantly higher" –> "were significantly higher"
Figure 4.
The figure is barley readable and should be edited to improve its readability. For details see above my comments to Figure 2.
Lines 292-293:
"The contents of Fe2O3 and CaO were found to have the strongest impact on soil TP. "
I am not sure if this is appropriate statement. I would suggest presenting results without their interpretation here (which I am not convinced if it is correct in that case anyway), this means that the following is more appropriate statement "The contents of Fe2O3 and CaO were most significantly correlated with the soil TP. "
Figure 6.
Again, numbers and descriptions along the axes (particularly along the horizontal axes) should be enlarged. Also the letter indication particular figures (a-f) should be enlarged.
Discussion
Line 304:
"Our hypothesis (i)"
I would strongly suggest to rephrase the sentence in such was that your hypothesis will be written here, so the reader will not have to search for that other parts of the article.
Line 312:
"TN content in y3000 were unexpectedly lower than"
Why "unexpectedly "? This word is redundant here and should be removed. So, change that to "TN content in y3000 were lower than"
Lines 312-313:
"lower than those in the y2000 site and providing evidence"
Grammar correction needed. "and " is redundant and should be removed. So, change that to "lower than those in the y2000 site providing evidence"
Lines 316-317:
"following mechanisms" –> "the following mechanisms"
Line 328:
"hypothesis (i)"
I would strongly suggest to avoid quoting only numbers of your hypothesis. Rephrase that to make clear what are you talking about, so the reader will not have to search for that in other parts of the article.
Line 329:
"there was an unexpected increasing trend" –> " there was an increasing trend "
There is nothing really unexpected about that.
Lines 329-330:
"It may be related that our original hypothesis was based"
Grammar correction needed.
Lines 344:
"which might be related that"
Grammar correction needed.
Lines 345:
"SOM in sediment was largely consumed by river transportation"
I doubt that "consumed" is a proper word here, probably removed or impacted would be more appropriate.
Figure 7.
Why this figure is presented in discussion. It presents results of this research and has to be given in the section Results, of course it can be quoted here but it has to be given in Results.
Line 388:
What is this strange symbol following the word "phosphorus"?
Line 398:
"The hypothesis (ii) "
As I have already indicated above, it would be good to rephrase the sentence in such was that your hypothesis will be written here, so the reader will not have to search for that other parts of the article.
Line 506:
"the abnormal river sedimentation. "
Nature is generally very variable and there is nothing "abnormal" about that, and I truly doubt if there is anything "abnormal" in that sedimentation. I would even say that it might be typical for particular conditions, so the word "abnormal" is completely irrelevant here, so this has to be rephrased.
Supplementary Materials
Table S1.
"Species of plant/crop and sampling number at each land use over different reclamation duration."
What does "sampling number" mean? Do you mean "number of collected samples (subsamples)"? Correct that in the Figure Caption and the forth Table Column.
See Note: "samples only choose" – What does that mean? How a sample (soil samples) can choose anything?
Finally, I would also strongly suggest replacing the following symbols "RCN" with "C/N", "RCP" with "C/P" and "RNP" with "N/P". it is clear that these symbols (i.e. C/N, C/P and N/P) represent ratios and such symbols are generally used in scientific literature. Moreover as the element symbols are bigger they are easier to read; on the other hand the abbreviations used by authors are difficult to read and therefore are easily mistake. I also do not really remember seeing such symbols in other literature. But replacing the symbols check carefully the whole text and all tables and figures, as well as the supplementary materials.
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Author Response
Please see the attachment.
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
I greatly appreciate the revisions you have made to the paper. I am confident that your research is a valuable contribution to the research field. Thank you for your efforts.
