Effects of Understory Vegetation Heterogeneity on Soil Organic Carbon Components in Cunninghamia lanceolata Plantation
Round 1
Reviewer 1 Report (Previous Reviewer 2)
Land-2091777
Effects of understory vegetation heterogeneity on soil organic carbon components in Cunninghamia lanceolata plantation
Review: revised manuscript.
Overall
The authors have considerably improved the quality of this submission in this revised version. Some issues remain, particularly the description of the soil at the study site, and a few problems related to proof-reading remain but are much reduced compared to the previous version. I believe only minor adjustments need to be made to ready this manuscript for acceptance.
Introduction
LN53-54: “the various soil carbon pool components are able to transform each other” – this statement seems to be missing a word, “into”, as in “are able to transform into each other”. As it is currently written, this statement suggests that the three carbon pools are active agents in their own and each other’s transformations, implying enzymatic or cellular-metabolic capacity among operational categories of organic molecules. Instead, I believe the intention here is to emphasize that some part of each category may be transformed into other categories by the actions of living organisms or abiotic processes, rather than by themselves.
Materials and Methods
LN99: the mention of the vague “red soil” remains, but with the addition of a citation. Reference [24] describes the soil at a site in a different province of China as “orthic Acrisol” and they cite:
Liu, R.J.; Wu, Y.C.; Zhang, Y.; Li, Z.C.; Ma, S.J.; Wang, B.; Geri, L.T. Comparison of soil labile organic carbon in Chinese fir plantations and natural secondary forests in north subtropical areas of China. Chin. J. Plant Ecol. 2012, 36, 431–437, (In Chinese with English abstract).
If Liu et al (2012) provides a suitable descripition of the soil at the Xiqin Teaching Forest Farm in Fujian Province, why not cite it directly, rather than citing another study conducted in another province?
Repeating my question from the previous version of this paper: what is “red soil”? This is a study of soil organic matter, the taxonomy and features of the soil is of crucial importance, and must be described sufficiently.
LN101: repeating another comment from the previous version: what does “pure” mean here? It is a very odd word choice. Perhaps “monoculture” would be more suitable?
LN142: inconsistent use of superscripts remains a problem.
Discussion
LN299: is “relatively single” the same as “pure”?
Author Response
Response to Reviewer Comments
Manuscript ID: land- 2091777
Title: Effects of understory vegetation heterogeneity on soil organic carbon components in Cunninghamia lanceolata plantation
First of all, thank you again for your valuable suggestions and opinions on this research paper. Thank you for your hard work on this paper. On behalf of all the authors of this paper, I would like to express my sincere gratitude and respect to you. In view of the problems existing in this paper, combined with your suggestions for modification, I have carefully modified the paper, and now I will explain the relevant modifications one by one:
Point 1: LN53-54: “the various soil carbon pool components are able to transform each other” – this statement seems to be missing a word, “into”, as in “are able to transform into each other”. As it is currently written, this statement suggests that the three carbon pools are active agents in their own and each other’s transformations, implying enzymatic or cellular-metabolic capacity among operational categories of organic molecules. Instead, I believe the intention here is to emphasize that some part of each category may be transformed into other categories by the actions of living organisms or abiotic processes, rather than by themselves.
Response 1: This content of the thesis has been revised and added. See the revised draft (line 53-54) for details.
Point 2: LN99: the mention of the vague “red soil” remains, but with the addition of a citation.
Response 2: This content of the thesis has been revised and added. See the revised draft (line 98-99) for details.
Point 3: LN101: repeating another comment from the previous version: what does “pure” mean here? It is a very odd word choice. Perhaps “monoculture” would be more suitable?
Response 3: This content of the thesis has been revised and added. See the revised draft (line 102, 105) for details.
Point 4: LN142: inconsistent use of superscripts remains a problem.
Response 4: This content of the thesis has been revised and added. See the revised draft (line 143) for details.
Point 5: LN299: is “relatively single” the same as “pure”?
Response 5: This content of the thesis has been revised. See the revised draft (line 300-301) for details.
Author Response File: 
Author Response.docx
Reviewer 2 Report (Previous Reviewer 1)
The authors have improved this study, solving the problems existing in the manuscript. I reckon that the authors have response point-by-point the suggestions provided in the last review. Besides, the added modifications in the different parts of this paper are suitable. Therefore, I consider that the study have enhanced its potential, being more coherence and comprensible.
Author Response
Thank you again for reviewing this research paper. On behalf of all the authors of this article, I would like to express my sincere thanks and respect to you.
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
This study is interesting and relevant to understand the effects of understory vegetation types on soil organic carbon components. Besides, it provides theoretical basis for understory vegetation management and sustainable management of artificial forests. Finally, it determines the characteristics of soil organic carbon and its components under different understory vegetation types in several plant species plantations.
The manuscript is clear and the performed analysis are suitable for the purpose of the study.
However, several changes should be adding to enhance the manuscript:
I suggest avoid the use of abbreviations in the abstract.
In the abstract the term “w” is not clear.
In keywords, the name of plant species should be in italics.
Overall, I do not understand why there are a blank space before the data in brackets. I recommend delete these blank spaces.
Line 43-44. The expression “Generally speaking” is not sounds formal. I recommend use another expression (i.e., Overall, In general, Generally, etc.)
Line 73. Please, add the plant species´ author. This line is the first time it appears in the text.
Line 81-82. Please, include the plant species´ authors.
Line 77 in advance. Please, you can refer “Cunninghamia lanceolata” as “C. lanceolata”. The complete name only is necessary the first time it appears in the text.
Line 94. Maybe the altitude should be referred as “meters above sea level” (m.a.s.l.).
Line 99. Please, add the author of Pinus massoniana.
Line 101. Please, define the abbreviation “DBH”.
Line 102. Please, add the canopy density units.
Line 116. The name of plant species should be in italics.
Figure 2 and 3 caption. Please, specify the difference or not difference of the letters means.
Table 2. Please, specify the difference or not difference of the letters means.
Figure 4 caption. Please, add the mean of all abbreviations in the Figure (e.g., ROC, ROOC, TOC,…)
Figure 5 caption. Please, add the mean of all abbreviations in the Figure.
Table 3. Please, specify the difference or not difference of the letters means.
In the discussion, add the plant species´ author the first time they appear.
Author Response
Response to Reviewer Comments
Manuscript ID: land-2054975
Title: Effects of understory vegetation heterogeneity on soil organic carbon components in Cunninghamia lanceolata plantation
First of all, thank you for your valuable suggestions and opinions on this research paper. Thank you for your hard work on this paper. In view of the problems existing in this paper, combined with your suggestions for modification, I have carefully modified the paper, and now I will explain the relevant modifications one by one:
Point 1: I suggest avoid the use of abbreviations in the abstract.
Response 1: This content of the thesis has been revised and added. See the revised draft (line 11-39) for details.
Point 2: In the abstract the term “w” is not clear
Response 2: This content of the thesis has been revised and added. See the revised draft (line 11-39) for details.
Point 3: In keywords, the name of plant species should be in italics.
Response 3: This content of the thesis has been revised and added. See the revised draft (line 40) for details.
Point 4: Overall, I do not understand why there are a blank space before the data in brackets. I recommend delete these blank spaces.
Response 4: This content of the thesis has been revised and added. See the revised draft for details.
Point 5: Line 43-44. The expression “Generally speaking” is not sounds formal. I recommend use another expression (i.e., Overall, In general, Generally, etc.)
Response 5: This content of the thesis has been revised. See the revised draft (line 47) for details.
Point 6: Line 73. Please, add the plant species´ author. This line is the first time it appears in the text.
Response 6: This content of the thesis has been revised. See the revised draft (line 77) for details.
Point 7: Line 81-82. Please, include the plant species´ authors.
Response 7: This content of the thesis has been revised. See the revised draft (line 86-87) for details.
Point 8: Line 77 in advance. Please, you can refer “Cunninghamia lanceolata” as “C. lanceolata”. The complete name only is necessary the first time it appears in the text.
Response 8: This content of the thesis has been revised. See the revised draft (line 80, 85, 93, etc.) for details.
Point 9: Line 94. Maybe the altitude should be referred as “meters above sea level” (m.a.s.l.)
Response 9: This content of the thesis has been revised. See the revised draft (line 98) for details.
Point 10: Line 99. Please, add the author of Pinus massoniana.
Response 10: This content of the thesis has been revised. See the revised draft (line 102-103) for details.
Point 11: Line 101. Please, define the abbreviation “DBH”.
Response 11: The abbreviation for the diameter at breast height (DBH) of a forest tree has been revised in the paper. See the revised draft (line 105) for details.
Point 12: Line 102. Please, add the canopy density units.
Response 12: This content of the thesis has been revised and added. See the revised draft (line 106) for details.
Point 13: Line 116. The name of plant species should be in italics
Response 13: This content of the thesis has been revised and added.
Point 14: Figure 2 and 3 caption. Please, specify the difference or not difference of the letters means.
Response 14: The meanings between the different letters have been added to the the captions of Figures 2 and 3. Different uppercase letters indicate significant differences between understory vegetation types, and different lowercase letters indicate significant differences between soil layers. (P < 0.05). See the revised draft (line 168-170) for details.
Point 15: Table 2. Please, specify the difference or not difference of the letters means.
Response 15: The meanings between the different letters in Table 2 have been added to the paper. Different uppercase letters indicate significant differences between understory vegetation types, and different lowercase letters indicate significant differences between soil layers. (P < 0.05). See the revised draft (line 196-197) for details.
Point 16: Figure 4 caption. Please, add the mean of all abbreviations in the Figure (e.g., ROC, ROOC, TOC,…)
Response 16: The meaning of all abbreviations in Figure 4 has been added to its caption. See the revised draft (line 228-235) for details.
Point 17: Figure 5 caption. Please, add the mean of all abbreviations in the Figure.
Response 17: The meaning of all abbreviations in Figure 5 has been added to its caption. See the revised draft (line 237-242) for details.
Point 18: Table 3. Please, specify the difference or not difference of the letters means.
Response 18: The contents in Table 3 are not a major part of the paper and appear somewhat salient to some extent, so Table 3 has been removed from the treatment and the matrix data (C and N content, C/N ratio) about the litters of different understory vegetation types have been added in the discussion section of the paper.
Point 19: In the discussion, add the plant species´ author the first time they appear.
Response 19: This content of the thesis has been revised and added. See the revised draft (line 264-265) for details.
Author Response File: Author Response.docx
Reviewer 2 Report
Land-2054975
Overview
Song et al. present an analysis of soil organic carbon (SOC) categories under a monospecific forest plantation with a range of understory vegetation types. SOC can be divided in classes by the rapidity with which it is metabolised by soil microbes, which is important for considerations of soil carbon sequestration and landscape-scale greenhouse gas dynamics. Greater understanding of the role understory plants play in regulating carbon sequestration is welcome, particularly for managers of forest plantations tasked with increasing the amounts of carbon stored for long periods of time in the forests they manage.
Unfortunately, while the data collected and displayed here may be quite valuable, the presentation is unclear and difficult to interpret. Large amounts of data were collected but the analyses do not seem to highlight important patterns, and the Discussion especially suffers from a lack of distinction between existing theory from previous publications and the results of the current work, as well as puzzling shifts between statements of uncertainty (“may”) and hard certainty (“did”).
The quality of English writing is somewhat poor. Many small errors of punctuation, spacing, and word choice appear throughout every paragraph and serve to reduce the readability of the entire paper. Super- and sub-script use is inconsistent, in a manuscript that contains many instances of concentrations and other measurements in which sub- and superscripts are crucial. Similarly, names of organisations and countries, such as for the manufacturers of key equipment used in this study are inconsistently applied – “Germany” appears on line 130 but “JPN” on line 133. This manuscript needs thorough proofreading for basic writing consistency as well as correct word use. Small words, particularly “of”, “by”, and “for” are frequently used incorrectly, as on line 271 “reduced the degradation of microorganisms” presumably should be “reduced the degradation by microorganisms”.
Detailed comments below.
Introduction
LN53: what is the goal of “double carbon” in China?
LN66: redundant or double-negative: “the removal of understory removal”
LN76: what is “long-term multi-generational pure forest management” – what does the word “pure” mean in this context?
Materials and Methods
LN 91: misspelling: “areast” – do you mean “areas”?
LN94: Are “red soil and yellow soil” described more fully in other publications?
LN102: the lack of superscript obscures meaning here – what unit of area (I assume area is being indicated) is described by “hm-2” ? Hectares are indicated by ha
In the first paragraph of the Materials and Methods section, the study area is described as part of the Xiqin Teaching Forest Farm, at an altitude of 200-500m, but later the experimental sample, presumably a smaller area within the Teaching Forest Farm, is described at an elevation of 100-300m, 100 m lower than the (presumably) broader area.
Please describe the study site(s) more clearly, and be consistent in the use of terminology – altitude and elevation are not synonyms.
LN110 – how did the “growth conditions” affect the placement and number of plots?
Table 1 – a notation normally used to indicate division / is used here instead of the more common parentheses. For example, height would normally be indicated as Height (cm), where in this table it seems height (in some unknown units) is being divided by cm.
The additional vegetation includes “Etc.” for DD and OF, but not for IT. Were there only 5 species of plants at IT?
LN124: the statement “the profile samples were divided into two parts by a 2 mm soil sieve.” implies that the two parts are 1) what passed through the sieve and 2) what was retained in the sieve. However, the next sentence suggests that the two parts were both what passed through the sieve.
Results
Figure 4. How were spurious correlations controlled for when so many pairwise comparisons were conducted? Was Bonferroni or a similar correction method applied?
What do the colours mean? The red-to-blue gradient on the right side is not described in the figure caption.
Discussion
Few citations appear in the Discussion. Much of the text here consists of a series of statements about pattern and process in the studied soils, yet these firm statements are not clearly based on either the results of the current study or results previously reported by others. The high level of certainty is not supported by solid chains of logic constructed from these two sources, it appears to be simply general statements chosen to support an argument about patterns of variation that are not so well described in the Results section. Statements about observations are presented as resulting from theory, such as:
LN268-273: “The C/N values of IT vegetation above and below ground in litter were significantly higher than those of DD and OF, and its litter may have more lignin, cellulose and other hard-to-decompose compounds, which reduced the degradation of microorganisms and promoted the accumulation of ROC. Therefore, it was observed that the middle and deep soil of IT had higher wROC.”
- “may have more lignin, cellulose” etc. (uncertainty)
- “which reduced” (certainty)
- This is conjecture, yet the next sentence states that the observations high wROC in deeper soil layers were caused by this uncertainty-certainty pair.
The use of the word “stable” is difficult to understand in the Discussion. In some sentences, it seems to indicate a process through time, such as the stability of soil inputs in the various SOC classes – perhaps most years the proportion of AOC relative to ROC is consistent. In other sentences, the word seems to indicate the less-active classes of soil organic carbon, and that a more-stable soil layer contains a higher fraction of ROC. It is confusing.
Conclusions
Some Discussion paragraphs end with statements about the importance of the observed patterns and inferred processes (e.g. LN315-317: “… which is important for effective management of understory vegetation… “) yet the Conclusion concludes with “to some extent.”
That different plants may affect soil organic carbon contents is not surprising. What aspects of the common understory plants at this site may have caused the observed patterns of SOC? Would C. lanceolata plantations benefit in some way from increased management of understory vegetation communities?
References
How does reference [1] support the first sentence of the Introduction, which is a statement about the distribution of soil organic carbon among global ecosystems. The abstract of He et al. 2019 (reference [1]) describes a study based on a single hectare of forest, and the abstract nowhere describes a comparison across global ecosystems. There are many other published studies that provide detailed comparisons of SOC in various global ecosystems.
Author Response
Response to Reviewer Comments
Manuscript ID: land-2054975
Title: Effects of understory vegetation heterogeneity on soil organic carbon components in Cunninghamia lanceolata plantation
First of all, thank you for your valuable suggestions and opinions on this research paper. Thank you for your hard work on this paper. In view of the problems existing in this paper, combined with your suggestions for modification, I have carefully modified the paper, and now I will explain the relevant modifications one by one:
Point 1: LN53: what is the goal of “double carbon” in China?
Response 1: This content of the thesis has been revised and added. See the revised draft (line 57-58) for details.
Point 2: LN66: redundant or double-negative: “the removal of understory removal”.
Response 2: This content of the thesis has been revised. See the revised draft (line 70) for details.
Point 3: LN76: what is “long-term multi-generational pure forest management” – what does the word “pure” mean in this context?
Response 3: "Long-term multi-generation pure forest management" means that only a single tree species, Cunninghamia lanceolata (Lamb.) Hook., is planted in the forest for a long time.
Point 4: LN 91: misspelling: “areast” – do you mean “areas”?
Response 4: This content of the thesis has been revised. See the revised draft (line 95) for details.
Point 5: LN94: Are “red soil and yellow soil” described more fully in other publications?
Response 5: This content of the thesis has been revised with the addition of a new revised reference. See the revised draft (line 98-99, 4442-443) for details.
Point 6: LN102: the lack of superscript obscures meaning here – what unit of area (I assume area is being indicated) is described by “hm-2” ? Hectares are indicated by ha.
Response 6: This content of the thesis has been revised. See the revised draft (line 106-107) for details.
Point 7: In the first paragraph of the Materials and Methods section, the study area is described as part of the Xiqin Teaching Forest Farm, at an altitude of 200-500m, but later the experimental sample, presumably a smaller area within the Teaching Forest Farm, is described at an elevation of 100-300m, 100 m lower than the (presumably) broader area.
Please describe the study site(s) more clearly, and be consistent in the use of terminology – altitude and elevation are not synonyms
Response 7: This content of the thesis has been revised with the addition of a new revised reference. See the revised draft (line 96-110, 442-443) for details.
Point 8: LN110 – how did the “growth conditions” affect the placement and number of plots?
Response 8: This content of the thesis has been revised. See the revised draft (line 114-118) for details.
Point 9: Table 1 – a notation normally used to indicate division / is used here instead of the more common parentheses. For example, height would normally be indicated as Height (cm), where in this table it seems height (in some unknown units) is being divided by cm.
The additional vegetation includes “Etc.” for DD and OF, but not for IT. Were there only 5 species of plants at IT?
Response 9: This content of the thesis has been revised. See the revised draft (Table 1) for details.
Point 10: LN124: the statement “the profile samples were divided into two parts by a 2 mm soil sieve.” implies that the two parts are 1) what passed through the sieve and 2) what was retained in the sieve. However, the next sentence suggests that the two parts were both what passed through the sieve.
Response 10: This content of the thesis has been revised. See the revised draft (line 127-129) for details.
Point 11: Figure 4. How were spurious correlations controlled for when so many pairwise comparisons were conducted? Was Bonferroni or a similar correction method applied?
Response 11: Figure 4 shows the correlation coefficient matrix between soil physicochemical properties, organic carbon and its components, and the correlation between organic carbon components and soil physicochemical properties was examined by Pearson's method.
Point 12: What do the colours mean? The red-to-blue gradient on the right side is not described in the figure. caption.
Response 12: This content of the thesis has been revised and added. See the revised draft (line 228-235) for details.
Point 13: Few citations appear in the Discussion. Much of the text here consists of a series of statements about pattern and process in the studied soils, yet these firm statements are not clearly based on either the results of the current study or results previously reported by others. The high level of certainty is not supported by solid chains of logic constructed from these two sources, it appears to be simply general statements chosen to support an argument about patterns of variation that are not so well described in the Results section. Statements about observations are presented as resulting from theory.
Response 13: This content of the thesis has been revised with the addition of a new revised reference. See the revised draft (line 244-362) for details.
Point 14: LN268-273: “The C/N values of IT vegetation above and below ground in litter were significantly higher than those of DD and OF, and its litter may have more lignin, cellulose and other hard-to-decompose compounds, which reduced the degradation of microorganisms and promoted the accumulation of ROC. Therefore, it was observed that the middle and deep soil of IT had higher wROC.”
- “may have more lignin, cellulose” etc. (uncertainty)
- “which reduced” (certainty)
- This is conjecture, yet the next sentence states that the observations high wROC in deeper soil layers were caused by this uncertainty-certainty pair.
Response 14: This content of the thesis has been revised with the addition of a new revised reference. See the revised draft (line 290-294) for details.
Point 15: The use of the word “stable” is difficult to understand in the Discussion. In some sentences, it seems to indicate a process through time, such as the stability of soil inputs in the various SOC classes – perhaps most years the proportion of AOC relative to ROC is consistent. In other sentences, the word seems to indicate the less-active classes of soil organic carbon, and that a more-stable soil layer contains a higher fraction of ROC. It is confusing.
Response 15: This content of the thesis has been revised and added. See the revised draft (line 277-343) for details.
The active organic carbon (AOC) components of the soil is easily decomposed and oxidized and can participate directly in the biochemical processes of the soil. Soil ROC is difficult to be decomposed by microorganisms and responds slowly to environmental changes, so it can be used as an important indicator of soil carbon pool accumulation and carbon stability. The higher the content and proportion of ROC in soil organic carbon, the more stable that soil organic carbon pool is and the less likely it is to be decomposed and utilized. The word"stable" is used in the paper to describe the extent to which soil organic carbon and its components are decomposed and transformed by external factors in the soil.
Point 16: Some Discussion paragraphs end with statements about the importance of the observed patterns and inferred processes (e.g. LN315-317: “… which is important for effective management of understory vegetation… “) yet the Conclusion concludes with “to some extent.”
That different plants may affect soil organic carbon contents is not surprising. What aspects of the common understory plants at this site may have caused the observed patterns of SOC? Would C. lanceolata plantations benefit in some way from increased management of understory vegetation communities?
Response 16: This content of the thesis has been revised and added. See the revised draft (line 364-381) for details.
Point 17: How does reference [1] support the first sentence of the Introduction, which is a statement about the distribution of soil organic carbon among global ecosystems. The abstract of He et al. 2019 (reference [1]) describes a study based on a single hectare of forest, and the abstract nowhere describes a comparison across global ecosystems. There are many other published studies that provide detailed comparisons of SOC in various global ecosystems.
Response 17: This content of the thesis has been revised. See the revised draft (line 395-396) for details.
Author Response File: Author Response.docx
Reviewer 3 Report
In the keywords, try not to use the same words as in the title. Use other words.
The introduction is very focused on forestry, however, there is a little gap left because the work is focused on soil with carbon and component. I think a few more ideas about soil and the importance of soil in such an environment should be included.
The paper is ok, but it is a bit difficult to read the first time, as it has several factors under study.
I would like to know why there were not many differences between the different coverages as a direct conclusion of the paper. For example. The root distributions, the percentage of stoniness, or the type of soil has the capacity to store the same independent of the cover it has on the surface" so that I can better close the work with a clear conclusion. But, this conclusion must be analyzed by the authors. I have only given ideas.
Author Response
Response to Reviewer Comments
Manuscript ID: land-2054975
Title: Effects of understory vegetation heterogeneity on soil organic carbon components in Cunninghamia lanceolata plantation
First of all, thank you for your valuable suggestions and opinions on this research paper. Thank you for your hard work on this paper. In view of the problems existing in this paper, combined with your suggestions for modification, I have carefully modified the paper, and now I will explain the relevant modifications one by one:
Point 1: The paper is ok, but it is a bit difficult to read the first time, as it has several factors under study..
Response 1: The problems in the thesis have been revised and added. See the revised draft for details。
Point 2: I would like to know why there were not many differences between the different coverages as a direct conclusion of the paper. For example. The root distributions, the percentage of stoniness, or the type of soil has the capacity to store the same independent of the cover it has on the surface" so that I can better close the work with a clear conclusion. But, this conclusion must be analyzed by the authors. I have only given ideas.
Response 2: Understory vegetation types can influence the distribution characteristics of soil organic carbon and its fractions through various aspects, including apoplastic inputs (quality and quantity), root characteristics (root distribution, root secretion, root turnover, etc.), soil physicochemical properties, microbial communities, and enzyme activities, etc. However, this thesis only discusses the study of the influence of understory vegetation types on soil organic carbon and its fractions in two aspects: apoplastic inputs and soil physicochemical properties, and the study of how understory vegetation types influence soil organic carbon fractions through root characteristics, microbial communities, and enzyme activities will be conducted in the next phase of the experiment.
Author Response File: Author Response.docx
