The Dynamics of Soil Macropores and Hydraulic Conductivity as Influenced by the Fibrous and Tap Root Systems
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe reviewed article presents the results of a study of temporal changes in soil macroporosity and saturated hydraulic conductivity under the influence of herbaceous plants with fibrous roots (Cynodon dactylon) and tap roots (Medicago sativa L.). Computed tomography was used to quantify soil macroporosity indices, and saturated hydraulic conductivity was measured using the constant gradient method. The parameter measurements were made three times at different stages of plant development.
The reviewed manuscript is thematically appropriate for “Agriculture” journal, however I my opinion “Soil systems” is more suitable for publication of such data. The introduction provides sufficient background and supports the research topic of the study. The description of the research methodology used is accurate (however requires some additions). In my opinion, the presentation of research results also needs some corrections. Discussion is well written. The conclusions presented in the article result from the conducted research and analysis.
Major comment:
- In section “2.4 Measure of saturated hydraulic conductivity” Authors use symbols for saturated hydraulic conductivity Kq and K10 (equations 1-2) whereas in results and discussion symbol Ks. Please unified the symbols.
Minor comments:
Line 100 – “from April 2021 to December 2022” is it true?
Line 188-189 – “and the water temperature during infiltration was measured by a thermometer (Figure 1)” – where is thermometer in Fig. 1?
Table 1 – why Sep and Nov in capital letters, pleas provide units for MD and HD and also standard deviation for CK treatment
Table 2 – “the average variation coefficient “? Why average? I think proper expression is the variation coefficient
Table 3 – please provide N description, and add units
Figure 3 pleas provide data for CK for the top layer and lower layer
Author Response
Comments 1: In section “2.4 Measure of saturated hydraulic conductivity” Authors use symbols for saturated hydraulic conductivity Kq and K10 (equations 1-2) whereas in results and discussion symbol Ks. Please unified the symbols.
Response 1 : Thank you very much for the suggestion. We have unified the symbols for saturated hydraulic conductivity throughout the manuscript. We replaced all instances of Kq and K10​​ with Ks in Section 2.4, Equations (1) and (2), and the Results and Discussion sections for consistency.
Comments 2: Line 100 – “from April 2021 to December 2022” is it true?
Response 2 : Thank you for your comment. We apologize for the inaccurate statement about the timing of our research. This study is part of a series of research projects that began in April 2021. The experiment in this study started in April 2022 and ended in December 2022. We have made a revision in L101-102 of the new manuscript.
Comments 3 : Line 188-189 – “and the water temperature during infiltration was measured by a thermometer (Figure 1)” – where is thermometer in Fig. 1?
Response 3 : Thank you very much for the comment. We apologize for the inaccurate citation of Figure 1. The citation of Figure 1 has been removed as it relates to the process of soil column sampling and CT scanning, not the infiltration experiment where the thermometer was used.
Comments 4 : Table 1 – why Sep and Nov in capital letters, pleas provide units for MD and HD and also standard deviation for CK treatment.
Response 4 : Thank you very much for the suggestion. We have made the following revisions to Table 1: changed "Sep" and "Nov" to lowercase, added units for HD and MD, and included the standard deviation for the CK treatment.
Comments 5 : Table 2 – “the average variation coefficient “? Why average? I think proper expression is the variation coefficient.
Response 5 : Thank you very much for the suggestion. You are right about the expression of the variation coefficient. We have made revisions in Table 2 and use "the variation coefficient" as you suggested.
Comments 6: Table 3 – please provide N description, and add units.
Response 6 : Thank you very much for the suggestion. We have added a description for N as the number of samples in Table 3.
Comments 7: Figure 3 pleas provide data for CK for the top layer and lower layer.
Response 7 : Thank you very much for the suggestion. In this study we divided the soil column into two different layers to investigate the effect of grass roots on Ks at different depths. As CK is a control treatment with no plant growth and is not affected by grass roots, we did not divide this type of sample into upper and lower layers as the soil columns with grass growth. To clarify this issue, we have added text “To investigate the effect of grass roots on Ks at different depths” in L 180-181, and “The CK treatment was not divided into top and lower layers.” in L313-314.
Reviewer 2 Report
Comments and Suggestions for AuthorsThis article focuses on the role of roots in the development of soil porosity and the variation in soil hydraulic conductivity at saturation. It is an experimental study with a clear presentation of the objectives and experimental design. The results are clearly presented and the discussion provides interesting elements for interpreting the results. These results amply deserve to be published and it would be desirable if the data (raw and interpreted) could be exploited by being opened up and presented in a data paper.
The presentation of the article would benefit from clarifying a certain amount of information.
- Clarify from the beginning that the roots appear as macropores from the scanner image interprétation
- Specify the physical meaning of each variable:
o On which variables is the fractal dimension calculated and how one can interpret the values?
o How is MPLL (the cross section offering the minimum porosity) determined?
o What does HD correspond to?
o What does global connectivity correspond to?
Without necessarily giving details of the calculations of these quantity, it would be useful to specify the definition of these quantities, their meaning regarding the porosity and the conductivity and justify their choice in the study
- The definition of the upper and lower layers is not clear. What are the sampling dimensions? We understand that the cylinders are taken separately and that they are brought together to be scanned. Is the upper and lower sampling made contiguously at the same place? Concerning connectivity, isn't there a bias induced by the superposition of the two layers taken separately and the presence of an interface that may break the continuity between poral space?
Detailed comment
L 197 give a reference equation 1 (likely the introduction of water viscosity, which is impacted by the tempertaure)
Table 1 : Why not reporting PN as well (an average per ROI)
Table 2 : are the reported values merge all dates (information to be given in the caption and the text
L267-269 I see the contrary NP greater in upper layer
Figure : the reduction of Ks in MS-DO in november could be discussed in the discussion part. (large root may shrink the porosity in adjacent soil material
L310 : 0.59 in the figure rather than 0.58
L317 which other relationship (not clear)
L 318 are the rate of explained variability correspond to r²? say it clearly. If so 44% is not consistant R of CD treatment (0.68). Should be 46%
L380 superior is speculative. Not an appropriate term
L342 344 not a good sentence, a statement is expected. Since …. Then ...
Author Response
Comments 1： Clarify from the beginning that the roots appear as macropores from the scanner image interprétation.
Response 1: Thank you very much for the suggestion. We have clarified this issue and added a sentence “The grass roots appear as macropores from the scanned image interpretation.” in L160 of the manuscript.
Comments 2： Specify the physical meaning of each variable:
o On which variables is the fractal dimension calculated and how one can interpret the values?
o How is MPLL (the cross section offering the minimum porosity) determined?
o What does HD correspond to?
o What does global connectivity correspond to?
Without necessarily giving details of the calculations of these quantity, it would be useful to specify the definition of these quantities, their meaning regarding the porosity and the conductivity and justify their choice in the study
Response 2: Thank you very much for the suggestion. We have clarified the definition of these quantities and added contents in L168-175: MP represents the overall macropore volume within the sample. MPLL was defined as the minimum macroporosity value along the ROI depth. MD refers to the average diameter of macropores. HD was calculated as the ratio of macroporous volume to macroporous surface area. Γ represents the probability that two pores are part of the same network, with Γ = 1 indicating complete connectivity and Γ ≈ 0 indicating scattered, unconnected pores. FD calculated with the BoneJ plugin in ImageJ, reflects soil pore size and the irregularity of interfaces between pores and particles.
Comments 3： The definition of the upper and lower layers is not clear. What are the sampling dimensions? We understand that the cylinders are taken separately and that they are brought together to be scanned. Is the upper and lower sampling made contiguously at the same place? Concerning connectivity, isn't there a bias induced by the superposition of the two layers taken separately and the presence of an interface that may break the continuity between poral space?
Response 3: Thank you very much for the suggestion and comment. We apologize for the unclear description of the experimental design in the manuscript. In the experiment of this study, we have joined two 5-cm-high PVC cylinders together with tape as one 10-cm-high cylinder. Then the 10-cm-high PVC cylinder was inserted into soil to form a soil column. Thus, the soil column contains 10-cm-high intact soil body within which the grass roots can develop during the experimental period. At different stages, the 10-cm-high soil columns were taken for CT scanning. After the CT scanning, these10-cm-high soil columns were divided in the middle as two 5-cm-high soil columns with a knife. By conducting infiltration experiments with these 5-cm-high soil columns, we can measure the Ks for the upper and lower 5-cm-high soil layers. As the soils and grass roots of the two layers were collected as one intact sample for CT scanning, the continuity of soil poral space could be ensured. To avoid misunderstanding, we have revised the content in the method section in L111-114 and L184-189.
Comments 4： L197 give a reference equation 1 (likely the introduction of water viscosity, which is impacted by the temperature).
Response 4: Thank you very much for your comment and suggestion. We have added a new reference citation [48] to support Equation 1.
Comments 5: Table 1: Why not reporting PN as well (an average per ROI).
Response 5: Thank you very much for the comments. The macropore number is an important index and has been reported in many studies where this index has been analyzed by exploring the detailed vertical variation with soil depth. In order to provide accurate detailed soil macropore information and to ensure comparability of our results with other studies, we have analyzed the detailed PN variation in Section 3.1.3 and Figure 2. Comparisons have been made between different soil layers, grass types and growth periods. To avoid repetition of information and analysis within the manuscript, we have not included the average PN in Table 1. However, if you feel that the average PN value is necessary, we can add this information to the table.
Comments 6: Table 2: are the reported values merge all dates (information to be given in the caption and the text
Response 6: Thank you very much for the suggestion. The values reported in Table 2 merged all dates and averaged according to different layers. We have clarified in the caption and text L245-246 that the values reported in Table 2 represent data merged from all dates.
Comments 7 ：L267-269 I see the contrary NP greater in upper layer.
Response 7: Thank you very much for your comments. The authors apologize for the writing mistake. We have made revisions in L279-281 and show that the macropore number in the upper layer was greater than that in the lower layer.
Comments 8： Figure: the reduction of Ks in MS-DO in November could be discussed in the discussion part. (large root may shrink the porosity in adjacent soil material
Response 8: Thank you for your suggestion regarding the reduction of Ks in MS-DO in November. The following contents “The reduction in Ks in the lower layer of MS in November may be related to large roots compressing and shrinking the porosity of the adjacent soil material. This compression could reduce the soil's water conductivity in that layer.” has been added in L422-424 of the revised manuscript.
Comments 9：L310: 0.59 in the figure rather than 0.58.
Response 9: Thank you very much for the suggestion. We have revised the data accordingly.
Comments 10：L317 which other relationship (not clear).
Response 10: Thank you for your comments. The authors apologize for the unclear statement. We have revised the sentence “Compared with other fitted relationships, the above pore indexes all showed better linear fits with Ks (Figure 5)” more accurately as “Based on the above pore indexes which had the strongest correlations with Ks, further regression analysis was carried out and linear fit equations were established (Figure 5).” in L331-334.
Comments 11：L318 are the rate of explained variability correspond to r²? say it clearly. If so 44% is not consistent R of CD treatment (0.68). Should be 46%
Response 11: Thank you for your valuable comments. The rate of explained variability is corresponding to r². We have made revision in L335 to clarify this point. The 44% variation for CD treatment explained by macropore number was determined by the Adjusted r², which is slightly lower than the r² of the regression equation. To ensure consistency, we have changed the Adjusted r² of 0.44 to the r² value of 0.46 in Figure 5 and L334.
Comments 12： L380 superior is speculative. Not an appropriate term
Response 12: Thank you very much for the suggestion. We have revised the sentence “the macropore indicators of the upper soil layer were superior to those of the lower soil layer for the same herbs.” as “the macropore indicators of the upper soil layer were generally more effective compared to the lower soil layer for the same herbs.” in L386-388.
Comments 13： L342 344 not a good sentence, a statement is expected. Since …. Then ...
Response 13: Thank you very much for the suggestion. We have revised the sentences as “Since the fibrous root and taproot herbaceous differ in terms of root morphological characteristics and developmental processes, then the differences in root architecture among herbaceous species would influence macropore formation” in L357-360 of the new manuscript.
Author Response File: 
Author Response.docx
Reviewer 3 Report
Comments and Suggestions for AuthorsDear Authors,
Below my suggestions.
Line 15: Specify CT and then use its acronym.
Line 17: you should report also the number of months.
In general, your abstract should report some numbers and acronyms for macropore index, diameter etc.
Line 32: add reference.
Lines 62-64: I think you should make it more fluid with the text.
Line 74: you should add some specifics about the two types of roots.
Line 100: mention also the number of months.
Line 114-115: specify what you mean for “regular watering and weeding”. How many times? How much water?
Line 122: sampled after how many months since the beginning of your trial?
Line 124: why “would”?
Lines 168-199: is all the text referenced 37? You should reference more, at least each 10 lines.
Figures 4 and 5: the writings should be bigger.
Kind regards
Author Response
Comments 1: Line 15: Specify CT and then use its acronym.
Response 1: Thank you very much for the suggestion. We have updated L15 to specify "Computed Tomography (CT)" before using its acronym.
Comments 2: Line 17: you should report also the number of months. In general, your abstract should report some numbers and acronyms for macropore index, diameter etc.
Response 2: Thank you very much for the suggestion. We have added the number of months in L17, and have updated L18-20 to include numbers and acronyms for macropore indexes: “The taproots had macroporosity (MP), macropore diameter (MD), and global connectivity (Γ) values that were 1.94, 2.76, and 2.45 times higher than fibrous roots”.
Comments 3: Line 32: add reference.
Response 3:Thank you very much for the suggestion. We have added a new reference citation accordingly.
Comments 4: Lines 62-64: I think you should make it more fluid with the text.
Response 4: Thank you very much for your comments. We have revised this sentence to make it more fluid and cohesive with the surrounding content in L62-64: “Plant roots are considered the primary modifiers of soil macropore structure; they influence macropores both directly by creating biopores and indirectly by re-packing and rearranging soil particles”.
Comments 5: Line 74: you should add some specifics about the two types of roots.
Response 5: Thank you for your suggestion. We have added specific details about the two types of roots in L75-77 to clarify their differences and impacts “Fibrous root systems, with their numerous fine roots, spread widely in shallow soil layers [32], while taproot systems, characterized by a thick primary root, penetrate deeply into the soil [33].”
Comments 6: Line 100: mention also the number of months.
Response 6: Thank you very much for the suggestion. We have revised the content to include the number of months in L101-102.
Comments 7: Line 114-115: specify what you mean for “regular watering and weeding”. How many times? How much water?
Response 7: Thank you very much for the suggestion. We have specified the details for "regular watering and weeding" as follows: “Water every 3 to 5 days to maintain soil moisture at 80% of field capacity and weekly weeding to reduce weed competition” in L116-117.
Comments 8: Line 122: sampled after how many months since the beginning of your trial?
Response 8: Thank you very much for the comment. We have added this information in Lines 123-126: “Therefore, after sowing in April, soil columns were sampled for CT scanning and infiltration experiments at three different stages: July, September, and November, correspond-ing to 3, 5, and 7 months after sowing, respectively.”
Comments 9: Line 124: why “would”?.
Response 9: Thank you very much for your comments. We have removed the word "would" to make the sentence more suitable.
Comments 10: Lines 168-199: is all the text referenced 37? You should reference more, at least each 10 lines.
Response 10: Thank you for your suggestion. We have added 4 more references citations [45-48] to provide better support for the text.
Comments 11: Figures 4 and 5: the writings should be bigger.
Response 11: Thank you very much for your comments. We have increased the size of the text in the two figures.
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsAll my remarks and comments have been taken into account in the current version of the article
Reviewer 3 Report
Comments and Suggestions for AuthorsDear authors, the manuscript is now improved. Kind regards
