Distribution of Molecular Weight of Humic Substances Isolated from Soils of Tallgrass Temperate Rainforests (Chernevaya Taiga)

Round 1

Reviewer 1 Report

Dear authors,

I was quite interested in reading the paper “Distribution of molecular weight of humic substances isolated from soils of tallgrass temperate rainforests (Chernevaya taiga)”.  Following a good introduction, the material and methods require additional information and clarity. My advice is to use longer sentences to better explain the concepts. Pay close attention to the results and discussion sections.You can't talk about results in the results section and vice versa.

I think the study's concept is interesting, but it must be improved.

Bests

 

Comments for author File: Comments.pdf

Author Response

The authors are very grateful to the referee for their careful attention to our manuscript. All comments made have been corrected accordingly. The Results and Discussion sections have also been updated. All corrections are shaded in yellow.

Reviewer 2 Report

The manuscript submitted by Polyakov et al. presented the molecular weight (MW) distribution of humic acids (HAs) in soils of tallgrass temperate rainforests. They found that in the soils of Chernevaya taiga accumulates up to 70% of low MW fraction. The low MW fraction correlated with the content of aromatic compounds and carboxyl structural fragments of HAs which indicated the resistance of the soil organic matter of Chernevaya taiga to biodegradation. The topic is interesting and within the scope of the journal. However, there are several major problems should be resolved.

1.     Table 1, why the depths of soil samples were different in the different sites?

2.     There was no replicate sample in all sites.

3.     L176, it should be “high MW region (A), medium MW (B) and low MW (C)”.

Author Response

The authors are very grateful to the referee for their careful attention to our manuscript. All comments made have been corrected accordingly:
1. The choice of depth was due to the formation of organomineral horizons. In the studied soil profiles, the depth of formation of organic-mineral horizons varied. The most representative soil horizons were selected.
2. Yes, you are right, no resampling was done. However, the analysis of humic acids was carried out for the same humic preparations. When analyzing NMR spectroscopy, humic preparations were not destroyed and were subsequently used to analyze the molecular weight distribution of humic substances. The methods used for the analysis of the humic substance are highly accurate, which ensures a high representative sample.
3. Corrected.

Author Response File: Author Response.pdf

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

 

Agronomy-1754780

Distribution of molecular weight of humic substances isolated from soils of tallgrass temperate rainforests (Chernevaya taiga)

 

Polyakov et al. present analyses of the organic matter of nine soils from six sites in southern Western Siberia where an interesting forest type, Chernevaya taiga, exists in close proximity to other forest types that have different soil properties. Identifying and characterising soil organic matter and the processes that transform this matter are important goals in managing forests and soils.

This paper draws heavily on previously published results produced by the same researchers. At some points in the paper, it is difficult to identify which data are new to this paper, and which are derived from previous work. Clarification here would help ensure the value of this work is more recognisable.

I found the line of reasoning of this paper difficult to follow. That three size fractions of humic acids were found is clear enough – low, medium, and high molecular weight components. Furthermore, the main study ecosystem of Chernevaya taiga has a higher fraction of humic acids in the low molecular weight category. However, I was not able to understand how this difference leads to differences in soil organic matter stability or accumulation.

The figures and tables are also difficult to understand. In several figures, an analysis of only a subset of the study soils are presented, rather than all nine soils. The Methods section includes several calculations and useful descriptive labels for the variables and outputs of these calculations, yet the column headings in Table 2. that appear to correspond in some way to these calculations are cryptic, and the table caption provides no guidance.

 

Structure and formatting

 

The Results section includes text more fitting in a Discussion section, which this manuscript lacks. I suggest adding a Discussion section, starting at about LN 233 with the paragraph that starts "Carbon sequestration to the soil organic matter".

Some references are cited by (Author Year) in the text, while most are [numbered]. It is not clear at times which reference is cited to support a sentence.

 

2. Materials and Methods

 

What do the colours (green, pale grey) indicate on the map in Figure 1? Areas of vegetation (forest) and areas where vegetation has been cleared?

 

LN 128-130: I assume the two Umbric Retisols in Table 1 are the two sites from the ancient dune massifs. Is this correct? Please provide some indication either in the text or in the table that allows the reader to match the soils to the sites and the forests.

 

3. Results

 

LN 192: coniferous forest is described as site N3. What site or sites are the Chernevaya taiga? It would be helpful to clearly link ecosystems to sampling sites.

 

Figure 2 and Figure 3 each present data from only 3 out of 6 study sites. Table 2 presents data from all 9 soils described in the Materials and Methods section. Why were some soils and some study sites not included in some analyses?

 

The figure captions need to provide more information. Why are there two panels in Figure 3? The left panel seems to correspond to a single site, N1, at three different depths. The right panel seems to correspond to three different sites, in the A horizon though why A2 was chosen for N1, a deeper soil layer (20-30cm) than the A horizons for N2 or N3 (10-20cm and 3-10, respectively).

 

The relationships between HA fractions (high-, medium-, and low MW compounds), bioavailability, organic carbon turnover rates, and microbial activity are not clearly described in this section from LN233 to LN253. Is higher turnover associated with more microbial activity? Is microbial activity associated with low MW compounds? How do the plant residues relate to "plant gigantism"? Do larger trees contribute qualitatively different organic molecules to soils? Do they contribute organic matter to different soil layers than smaller plants?

LN250: you state that the organic matter of Chernevaya taiga is relatively stable compared to the other soils studied here. How does this statement relate to the values presented in Table 2? Which of the columns in Table 2 are most representative of soil organic matter stability?

 

LN252: what is a carbon polygon?

LN253: what is a carbon farm?

 

The paragraph from LN281 to LN296 seems to be about the results of a separate study, [47] from 2015 and a different region. How do the relationships between carbon sequestration, MW of HAs, and biotic and abiotic transformations of organic matter in tundra and peat soils relate to these factors and processes in Chernevaya taiga soils located far to the south and east of the sites described in [47]?

 

4. Conclusions

The conclusions of this paper are not clearly described. This section is a series of statements summarising the results, with some out-of-place sentences about the composition of low and high MW HAs at the end.

 

Is the organic matter found in the soils of the Chernevaya taiga more or less likely to decompose and be released to the atmosphere as CO2 than the organic matter in the other soils studied? If there is a difference, how was that difference identified?

 

Typos and other small errors

 

LN99 – what number is Polyakov et al., 2021? Also on LN254

LN281 – Has' presumably should be HA's

LN293 – is Vasilevich et al., 2019b reference 47?

LN307 – "hypnotizes" presumably should be "hypotheses"?

Author Response

Response to a review of the manuscript “Distribution of molecular weight of humic substances isolated from soils of tallgrass temperate rainforests (Chernevaya taiga)”.

Dear reviewer!

Thank you for your comments, they were completely taken into account, which improved the quality of the article for publication in Journal.

Text that has been changed is marked by yellow color.

General comments:

1. This paper draws heavily on previously published results produced by the same researchers. At some points in the paper, it is difficult to identify which data are new to this paper, and which are derived from previous work. Clarification here would help ensure the value of this work is more recognisable.

Response: Thank you! We have revised the text of the article, we have indicated what data was obtained earlier.

2. I found the line of reasoning of this paper difficult to follow. That three size fractions of humic acids were found is clear enough – low, medium, and high molecular weight components. Furthermore, the main study ecosystem of Chernevaya taiga has a higher fraction of humic acids in the low molecular weight category. However, I was not able to understand how this difference leads to differences in soil organic matter stability or accumulation. LN250: you state that the organic matter of Chernevaya taiga is relatively stable compared to the other soils studied here. How does this statement relate to the values presented in Table 2? Which of the columns in Table 2 are most representative of soil organic matter stability? Is the organic matter found in the soils of the Chernevaya taiga more or less likely to decompose and be released to the atmosphere as CO2 than the organic matter in the other soils studied? If there is a difference, how was that difference identified?

Response: We decided to reduce the information on the stability of organic matter, since the distribution of molecular weights can only indirectly indicate the stability of organic matter.

3. The figures and tables are also difficult to understand. In several figures, an analysis of only a subset of the study soils are presented, rather than all nine soils. The Methods section includes several calculations and useful descriptive labels for the variables and outputs of these calculations, yet the column headings in Table 2. that appear to correspond in some way to these calculations are cryptic, and the table caption provides no guidance.

Response: Figures and tables have been revised as well as captions. In Material and Method section the additional information has been added.

4. The Results section includes text more fitting in a Discussion section, which this manuscript lacks. I suggest adding a Discussion section, starting at about LN 233 with the paragraph that starts "Carbon sequestration to the soil organic matter".

Response: Thank you! We add a discussion section and two subsections.

5. Some references are cited by (Author Year) in the text, while most are [numbered]. It is not clear at times which reference is cited to support a sentence.

Response: The references have been revised.

6. What do the colours (green, pale grey) indicate on the map in Figure 1? Areas of vegetation (forest) and areas where vegetation has been cleared?

Response: The figure 1 has been fully revised.

7. LN 128-130: I assume the two Umbric Retisols in Table 1 are the two sites from the ancient dune massifs. Is this correct? Please provide some indication either in the text or in the table that allows the reader to match the soils to the sites and the forests.

Response: the Table 1 has been revised, as well as text in Material and method section

8. LN 192: coniferous forest is described as site N3. What site or sites are the Chernevaya taiga? It would be helpful to clearly link ecosystems to sampling sites.

Response: The additional information about ecosystems has been added into the text.

9. Figure 2 and Figure 3 each present data from only 3 out of 6 study sites. Table 2 presents data from all 9 soils described in the Materials and Methods section. Why were some soils and some study sites not included in some analyses? The figure captions need to provide more information. Why are there two panels in Figure 3? The left panel seems to correspond to a single site, N1, at three different depths. The right panel seems to correspond to three different sites, in the A horizon though why A2 was chosen for N1, a deeper soil layer (20-30cm) than the A horizons for N2 or N3 (10-20cm and 3-10, respectively).

Response: Figures have been fully revised. We added all investigated HAs.

10. The relationships between HA fractions (high-, medium-, and low MW compounds), bioavailability, organic carbon turnover rates, and microbial activity are not clearly described in this section from LN233 to LN253. Is higher turnover associated with more microbial activity? Is microbial activity associated with low MW compounds? How do the plant residues relate to "plant gigantism"? Do larger trees contribute qualitatively different organic molecules to soils? Do they contribute organic matter to different soil layers than smaller plants?

Response: We decided to remove the information on microbiological activity, we cannot accurately analyze the relationship between humic substances and microbiological activity.

11. LN252: what is a carbon polygon? LN253: what is a carbon farm?

Response: The information about carbon polygon and farms has been added in discussion section.

12. The paragraph from LN281 to LN296 seems to be about the results of a separate study, [47] from 2015 and a different region. How do the relationships between carbon sequestration, MW of HAs, and biotic and abiotic transformations of organic matter in tundra and peat soils relate to these factors and processes in Chernevaya taiga soils located far to the south and east of the sites described in [47]?

Response: The information about tundra soils of European northeast of Russia has been added to discussion section.

13. The conclusions of this paper are not clearly described. This section is a series of statements summarising the results, with some out-of-place sentences about the composition of low and high MW HAs at the end.

Response: The conclusions section has been fully revised.

 

Typos and other small errors

LN99 – what number is Polyakov et al., 2021? Also on LN254

LN281 – Has' presumably should be HA's

LN293 – is Vasilevich et al., 2019b reference 47?

LN307 – "hypnotizes" presumably should be "hypotheses"?

Response: All comments have been taken into account.

 

Thank you for work of our article.

Sincerely,

Professor of Saint-Petersburg State University, Evgeny V. Abakumov.

Engineer of Saint-Petersburg State University, Vyacheslav I. Polyakov,

 

Reviewer 2 Report

The paper contains results of some interest, however I have a some concens about its content and especially references cited in the Introduction. Also the English language needs a  oderate revision.

Abstract

-l.15-16: "could be decreasing"? Unclear, reword

-l.23-24: repetiton, delete

Intoduction

-I have serious concerns on most references cited in the Intoduction. For example, refs 1-3, 4-6, 7 somewhere, 9-12, 20-22 absolutely not pertinent, and refs of Piccolo et al. absolutely not pertinent. These refs should be omitted or changed with some more appropriate.

Mats & Meths

-l.126: "in comparison" not "in compared"

-l.139: "Acids"??? reword

-l.149: "wer ourified from low MW compounds"??? Very serious concern. The Authors have discussed extensively about the low MW components in HAs....So...??? This point needs clarification

-l.156: "HA preparations"

-Eqs (2) and (3) ??? Which one was applied to caclutate  Mw/Mn? Clarify

-l.174: Res & Discussion

-l.233: raplace "to the " with "in"

-l.234: "formation of supramolecular complxes" must be deleted, the Auhtors have no data to assess this

-l.233-296: all this text needs condensation, shortening, focusing, avoiding several several repetitions of concepts up and down.

Conclusions

-Almost all this text is a summary of results/Discussion not real Conclusions, thus it needs alsmost complete rewriting

 

Author Response

Response to a review of the manuscript “Distribution of molecular weight of humic substances isolated from soils of tallgrass temperate rainforests (Chernevaya taiga)”.

Dear reviewer!

Thank you for your comments, they were completely taken into account, which improved the quality of the article for publication in Journal.

Text that has been changed is marked by yellow color.

General comments:

 

1. -l.15-16: "could be decreasing"? Unclear, reword

Response: the term has been revised

2. -l.23-24: repetiton, delete

Response: the information has been deleted

3. -I have serious concerns on most references cited in the Intoduction. For example, refs 1-3, 4-6, 7 somewhere, 9-12, 20-22 absolutely not pertinent, and refs of Piccolo et al. absolutely not pertinent. These refs should be omitted or changed with some more appropriate.

Response: The references has been checked and changed.

4. -l.126: "in comparison" not "in compared"

Response: the term has been changed

5. -l.139: "Acids"??? reword

Response: the term has been revised

6. -l.149: "wer ourified from low MW compounds"??? Very serious concern. The Authors have discussed extensively about the low MW components in HAs....So...??? This point needs clarification

Response: The additional information has been added. Indeed, analysis of the molecular weight distribution data shows a significant proportion of the low molecular weight fraction in HAs (50.2–70.1%) with a median Mr value of 1.13–1.61 kDa. The data obtained do not contradict the procedure for purifying HAs from low molecular weight compounds by passing through a Sephadex G-10 column (fractionation range for globular proteins up to 700 Da) and the fractionation range of the Superdex 200 Increase 10/300 GL 1000–600000 Da column (Instruction 29027271 AH). The construction of the calibration dependence was carried out using globular proteins with a molecular weight range of 6500 - 669000 Da and polyethylene glycols 1500 - 12000 Da. The dependence is linear.

7. -l.156: "HA preparations"

Response: The term has been revised

8. -Eqs (2) and (3) ??? Which one was applied to caclutate Mw/Mn? Clarify

Response: The additional information has been added.

9. -l.174: Res & Discussion

Response: The discussion section has been added.

10. -l.233: raplace "to the " with "in"

Response: The term has been replaced.

11. -l.234: "formation of supramolecular complxes" must be deleted, the Auhtors have no data to assess this

Response: The information has been deleted.

12. -l.233-296: all this text needs condensation, shortening, focusing, avoiding several several repetitions of concepts up and down.

Response: The section has been reworked and added discussion section with two subsections.

13. -Almost all this text is a summary of results/Discussion not real Conclusions, thus it needs alsmost complete rewriting

Response: The conclusions section has been fully revised.

 

Thank you for work of our article.

Sincerely,

Professor of Saint-Petersburg State University, Evgeny V. Abakumov.

Engineer of Saint-Petersburg State University, Vyacheslav I. Polyakov,