Spatial–Temporal Variations in Soil Organic Carbon and Driving Factors in Guangdong, China (2009–2023)

Response to Reviewer 1 Comments

1. Summary

Thank you very much for taking the time to review this manuscript. We have carefully evaluated the critical comments and thoughtful suggestions from you, and tried our best to revise the manuscript accordingly. Please find the detailed responses below and the corresponding highlighted in the re-submitted files.

2. Point-by-point response to Comments and Suggestions for Authors

General Comments 1:

The manuscript considers soil types and parent material but does not describe the vegetation types or land use types at the sampling sites. There are significant differences in soil organic carbon among different vegetation or land use types. This factor cannot be ignored when assessing the regional distribution and stock of SOC.

Response 1: Many thanks for your comments and suggestions. Vegetation and land use types are important indicators for predicting soil organic carbon stocks, which we have discussed in section 4.4. In this research, normalized vegetation cover index (NDVI) is used to represent the influence of different vegetation.

General Comments 2:

The use of only 31 samples from 2016 to evaluate the organic carbon stock and distribution in Guangdong Province raises concerns about the limited sample size, despite using the random forest model.

Response 2: All the data in this research are from the China Geochemical Baseline Project, alluvial soil samples were collected according to a Global Reference Networks grid cell in the whole mainland China. 2~3 samples in a sample grid were collected for CGB Ⅰ while 1 sample in a sample grid was collected for CGB II, resulting in 31 samples in Guangdong Province for CGB II with limited sample size relative to CGB Ⅰ. However, The sampling media, sampling methods, analytical laboratories, analytical methods and quality control are all the same for CGB Ⅰ and CGB II, making the data comparable. Moreover, we have discussed the uncertainty and limitations in section 4.4.

Comments 1:

Line 17: 0-97.1 cm is no longer considered the surface; typically, the surface is within 30 cm.

Response 1: Thanks a lot for your comments, we have deleted the surface throughout the whole manuscript.

Comments 2:

Line 139: Corg. and SOC are used interchangeably, which is confusing. The terminology should be consistent throughout the text.

Response 2: Thank you for pointing this out. All Corg. were revised into SOC including the text and figures for consistency.

Comments 3:

Line 201: In Table 2, if the data for China is from the literature, insert the reference. If it is from the article itself, please describe it in detail.

Response 3: The data for China is from Global Geochemical Baselines (GGB) project, the references describing the project were inserted.

Comments 4:

In Figure 4, explain whether the error bars represent standard deviation or standard error in the figure caption.

Response 4: Thank you for pointing this out. We have added error bar description in figure 4 caption.

Comments 5:

In Figure 5, is the y-axis title TC or SOC?

Response 5: The y-axis title is SOC, we have revised that.

Comments 6:

The discussion section needs to further address the limitations and uncertainties of the study results.

Response 6: The limitations and uncertainties of the study results were addressed, please see line 417-428 in the revised manuscript.

Comments 7:

It is recommended to appropriately reduce the number of figures and tables in the main text.

Response 7: We have reduced the number of figures and tables in the main text according to your opinion.

Response to Reviewer 2 Comments

1. Summary

Thank you very much for taking the time to review this manuscript. We have carefully evaluated the critical comments and thoughtful suggestions from you, and tried our best to revise the manuscript accordingly. Please find the detailed responses below and the corresponding highlighted in the re-submitted files.

2. Point-by-point response to Comments and Suggestions for Authors

Comments 1:

Line 50: correct the word driving, a letter is missed.

Response 1: Thanks very much for your careful review. We have revised that, please see line 51 in the revised manuscript.

Comments 2:

Figures 2-3: I suggest to increase the size of letters of the color codes. It is difficult to see those.

Response 2: We have increased the size of letters of the color codes. Thanks for your advice.

Comments 3:

paragraph lines 344-349: Authors indicated that soil with more Fe, Ca and Mg oxides presented more SOC, indicating a relation between these two factors. However, authors do not explain the mechanisms, reactions or relations behind these two variables. A deep discussion about it is suggested.

Response 3: Thank you for pointing this out. We have added to the discussion of mechanisms. Please see line 337-344 in the revised manuscript.

Comments 4:

Figure 18: I consider it unnecessary as the gray-scale colors does not help to visualize the differences along the region and the figure does not provide relevant information for the paper. I suggest to delete it.

Response 4: Thanks for your advice, we have deleted it.

Comments 5:

Conclusions:

Lines 422-423 I suggest do not repeat the result presented before. In conclusions, write this result in a more general way.

Lines 426-427 Authors summarized that there are mechanisms that explain the relation between Fe, ca, and Mg oxides and higher SOC stocks. As I said before, authors should explain which are those mechanisms involved.

Response 5:

Thank you for pointing this out. We have rephrased the “Conclusions” part. Please see line 430-438 in the revised manuscript.