From the journal Environmental Science: Atmospheres Peer review history

27-May-2022

Dear Dr Tyagi:

Manuscript ID: EA-CRV-12-2021-000102
TITLE: Terrestrial carbon cycle: a tipping edge of climate change between atmosphere and biosphere ecosystems

Thank you for your submission to Environmental Science: Atmospheres, published by the Royal Society of Chemistry. I sent your manuscript to reviewers and I have now received their reports which are copied below.

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************

Reviewer 1

The authors did a good job by summarising the terrestrial Carbon feedbacks in the atmosphere. I suggest a minor revision of the work with the following comments to improve:
1. Kindly remove the word ‘explicitly’ from the sentence: “This review explicitly brings out….” In the abstract.
2. I suggest rephrasing the sentence on page 1 of the introduction: “The feedback from such processes are subjective to multiple spatial and temporal scale, are a problematic hardship to quantify continuously.”
3. Page 4 of 27, Section 3: “The vital fluxes and the stocks of the terrestrial ecosystem are…”. Here the authors are listing GPP, NEP, NPP and other things. I suggest removing vital fluxes from the sentence here to avoid confusion.
4. Same as above section, Line “They are defined and systematically presented”. Kindly remove systematically.
5. Page 6 of 27, Section 4.2.1 Eddy Covariance. I disagree with 30-50 m. The height of the tower may be 30-50 m in some cases. But on various occasions, even a 10 m tower has an eddy covariance setup too. Kindly change that number with proper reference.
6. Page 6 of 27, Section 4.2.1 “Various such eddy covariance sites and their networks across the globe are listed in Table 2”. Maybe you mean to say, ‘Some of the eddy covariance sites and their network….’?
7. Section 7, C Trend: The authors are primarily focusing their review over India. Why so?
I believe if they can say something about the C trends over other regions of the world, and then compare India as a Special case study, it will be more appealing.
8. Can you comment on the Carbon trends of neighbouring countries to India, e.g., Pakistan, Afghanistan, Nepal, Bangladesh, Sri Lanka?
9. Authors discussed the Keeling curve at Mauna Loa observatory in just one sentence without going into the discussions (reference of Wang et al., 2020, no. 136) in section 4.2.4, Page 7 of 27. I believe the Keeling curve may be discussed a bit more.
10. Recently, some global regions are coming up as C sinks. Though they are small countries and have certain advantages with this C sink budgeting. I suggest authors take this point in their discussion and comment on these findings exploring the possibilities for the rest of the world.

Reviewer 2

Regarding the manuscript, this review paper submitted for publication in 'Environmental Science: Atmospheres" is appropriate to publish in this journal as a proposed critical review article. The paper has covered most of the areas that are selected for the topical objectives. I have some comments to improve the manuscript and easy readable, that are as follows:
1. The manuscript is too long and too descriptive. There are many contents of the topic that are repeated, so some of the repeated parts can be sorted out.
2. The manuscript has some words that are very rare to use in the scientific research paper. So, these words can be replaced with the appropriate understandable words.
3. As you have mentioned that India is a tropical nation and agroecosystems are also popular but this review doesn't focus on the tropical ecosystems and agroecosystems. Because most of the forest area contributed to the carbon sink and source of the carbon are from tropical regions as the country is dominated by the tropical climate. Why not include them?

The minor comments are addressed in the manuscript which is attached herewith.
The manuscript could be published in the journal after some suggested revisions.

This text has been copied from the PDF response to reviewers and does not include any figures, images or special characters.

Response to the reviewers on
Terrestrial carbon cycle: A tipping edge of climate change between atmosphere and biosphere ecosystems

Manoj Hari and Bhishma Tyagi *
Correspondence to: Bhishma Tyagi (tyagib@nitrkl.ac.in)

We appreciate the constructive comments and suggestions provided by the two reviewers and in accordance, we have substantially revised our manuscript, which has significantly improved the readability and robustness of our study. We hope that you will find our revisions are sufficient and satisfactory and may recommend publication after these changes have been made. Below we respond to the reviewer's comments in blue font. All page numbers refer to the clean version of the revised manuscript without tracked changes.
 
Response to the comments of Reviewer 1
The authors did a good job by summarising the terrestrial Carbon feedbacks in the atmosphere. I suggest a minor revision of the work with the following comments to improve.

The authors are very thankful to the reviewer for providing such positive and details suggestions regarding the manuscript. We have improved our work as per the concern of the reviewer.

Comment 1: Kindly remove the word ‘explicitly’ from the sentence: “This review explicitly brings out….” In the abstract.
Response: As per the reviewer’s suggestion, the word ‘explicitly’ has been revised with ‘pictures’ in the manuscript. The revised sentence in the Abstract section (Page 1) is as follows, “This review pictures a holistic understanding of the terrestrial carbon cycle and addresses its nature with different key drivers”.

Comment 2: I suggest rephrasing the sentence on page 1 of the introduction: “The feedback from such processes is subjective to multiple spatial and temporal scale, are a problematic hardship to quantify continuously.”
Response: As per the reviewer’s suggestion, we have revised the sentence as follows, “Forby, processes such are responsible for a high degree of heterogeneous feedback to the terrestrial system, intricating the carbon monitoring, constantly.” The revised statement can be noticed in the 1 Introduction section (Para 2, Page 1).

Comment 3: Page 4 of 27, Section 3: “The vital fluxes and the stocks of the terrestrial ecosystem are…”. Here the authors are listing GPP, NEP, NPP and other things. I suggest removing vital fluxes from the sentence here to avoid confusion.
Response: As solicited by the reviewer, we have excluded the sentence and revised the paragraph for readability. The revised statement can be noticed in the 3 Keys drivers of the terrestrial carbon cycle section (Para 1, Page 3).
 
Comment 4: Same as above section, Line “They are defined and systematically presented”. Kindly remove systematically.
Response: As suggested by the reviewer, we have removed the word ‘systematically’ from the statement. The revised statement can be noticed in the 3 Keys drivers of the terrestrial carbon cycle section (Para 1, Page 3).

Comment 5: Page 6 of 27, Section 4.2.1 Eddy Covariance. I disagree with 30-50 m. The height of the tower may be 30-50 m in some cases. But on various occasions, even a 10 m tower has an eddy covariance setup too. Kindly change that number with proper reference.
Response: We totally agree with the reviewer. In fact, 10m tower measurements are conventionally reasonable in the flux measurements beause of its high-quality measurements, maximized flux footprint and high consistency with subsurface fluxes and roughness properties. As per the reviewer’s suggestion, we have stated this in the 4.2.1 Eddy covariance section (Para 1, Page 5).
Additinaly, we understood the direction provided by the reviewer to us for improving the credibility of the manuscript. However, we also want to request the reviewer to reconsider our statement regarding ‘30 – 50m’ meaurements. In our defence, eddy flux meauremenrts at height ‘30 – 50m’ was preferred in the regions with high canopy strata (mostly forest based ecosystems) for the reduced footprint bias as the instruments are placed at a height above the canopy of the ecosystem. So we chose to retain it along with the ‘10m measuement’ statement in the manuscript.

Comment 6: Page 6 of 27, Section 4.2.1 “Various such eddy covariance sites and their networks across the globe are listed in Table 2”. Maybe you mean to say, ‘Some of the eddy covariance sites and their network….?’.
Response: We thank the reviewer for pointing out our muddled sentence structure. We have revised the sentence accordingly. The revised statement can be noticed in the 4.2.1 Eddy covariance section (Para 2, Page 5).

Comment 7: Section 7, C Trend: The authors are primarily focusing their review over India. Why so? I believe if they can say something about the C trends over other regions of the world, and then compare India as a Special case study, it will be more appealing.
Response: We are thankful to the reviewer for his insightful view on improving section 7 (C Trend, revised as “Terrestrial carbon cycle magnitude and trend”) of our manuscript. As per the reviewer’s suggestion, we have discussed in detail about the geographical heterogenicity of terrestrial carbon sinks and the sources. We broadly analyzed the magnitude of the sink and the sources on a continental scale. The inclusion of trend and magnitude across various nations can be noticed in the 7 Terrestrial carbon cycle magnitude and trend section (Para 2 and 3, Page 11; Yet, climate-change-induced drought stress consistently poised…).
However, to answer the reviewer’s question, our study focussed on highlighting the carbon trend in India because of its global significance. Though global carbon magnitude has been highlighted by the finest researchers, regional quantification lacks confidence due to the persistence of year-to-year variability across various biomes. Holding the most significant part of the carbon budget, countries like China and India have purveyed a considerable fraction of the global carbon cycle. On a statistical note, in the past five years, the number of studies on the terrestrial carbon cycle over India was ~3%, whereas China (~32%) and the Contiguous US (~56%) are holding the dominant share. In spite of its ecological stature, countries like India lack a continuous observational network (Fig. S1, attached below), like in the western world; the decadal and seasonal variability of India's terrestrial carbon cycle remains deciphered, and so does the global magnitude. Ergo, in this review, our focus was isolated over India to depict its significance in the global forum.


Comment 8: Can you comment on the Carbon trends of neighbouring countries to India, e.g., Pakistan, Afghanistan, Nepal, Bangladesh, Sri Lanka?
Response: The authors are thankful to the reviewer for his profound view. As per the reviewer's recommendation, we have detailed the carbon trends and magnitude of the neighbouring countries to India. The discussion can be noticed in the 7 Terrestrial carbon cycle magnitude and trend section (Para 6, Pages 11 and 12; Because of the sparse ecological significance in the western front…).

Comment 9: Authors discussed the Keeling curve at Mauna Loa observatory in just one sentence without going into the discussions (reference of Wang et al., 2020, no. 136) in section 4.2.4, Page 7 of 27. I believe the Keeling curve may be discussed a bit more.
Response: We thank the reviewer for suggesting us to explore more about the trends of atmospheric CO2 and carbon fertilization which was discussed in detail by Wang et al., 2020. As pointed out by the reviewer, knowledge gaps from Wang et al., 2020 were incorporated and discussed about the trend in the 7 Terrestrial carbon cycle magnitude and trend section (Para 1, Page 11; …Inferential studies tried to break down…). We tried to fit in our discussion in section 4.2.4; however, it is more appealing in section 7.

Comment 10: Recently, some global regions are coming up as C sinks. Though they are small countries and have certain advantages with this C sink budgeting. I suggest authors take this point in their discussion and comment on these findings exploring the possibilities for the rest of the world.
Response: We thank the reviewer for this suggestion. In light of that, we have commented on multiple studies discussing the importance of nations and ecosystems in modulating the global carbon cycle in recent decades. The discussion can be noticed in the 7 Terrestrial carbon cycle magnitude and trend section (from Para 3, Page 11 – 12; Other than the atmospheric CO2…).
 
Response to the comments of Reviewer 2
Regarding the manuscript, this review paper submitted for publication in 'Environmental Science: Atmospheres" is appropriate to publish in this journal as a proposed critical review article. The paper has covered most of the areas that are selected for the topical objectives. I have some comments to improve the manuscript and easily readable, that are as follows:

We are very grateful for the valuable suggestions by the reviewer. The authors consider this as an opportunity to express sincere thanks to the reviewer for the critical evaluation and constructive suggestions to improve the manuscript. The changes addressed by the reviewer have been carefully incorporated into the manuscript in the following manner.

Comment 1: The manuscript is too long and too descriptive. There are many contents of the topic that are repeated, so some of the repeated parts can be sorted out.
Response: We have noted the concern raised by the reviewer; as per the suggestion, we have revised the draft thoroughly by excluding the repeated statements for better readability.

Comment 2: The manuscript has some words that are very rare to use in the scientific research paper. So, these words can be replaced with the appropriate understandable words.
Response: We understood the direction provided by the reviewer to us for improving the readability of this manuscript. As per the suggestion put forth by the reviewer, we have revised the jargon with simplified terms.

Comment 3: As you have mentioned that India is a tropical nation and agroecosystems are also popular but this review doesn't focus on the tropical ecosystems and agroecosystems. Because most of the forest area contributed to the carbon sink and source of the carbon are from tropical regions as the country is dominated by the tropical climate. Why not include them?
Response: The authors appreciate the reviewer for view raising this insightful question. By agreeing with the reviewer, research on the carbon cycle mostly revolves around the tropics as they are the nexus of global carbon uncertainty. Albeit, like tropical forest ecosystems, other ecosystems including: grassland, shrubland, peatland, boreal forest, agro, arid, wetland, urban etc., share significant consensus on the global carbon pools. So, to maintain the general theme, we have restricted this review by unpluming the carbon dynamics across various ecosystems.
However, as per the reviewer’s suggestion and because of its substantial contribution to the global and regional carbon cycle, we have discussed the variability of carbon in the tropical forest in section 7 Terrestrial carbon cycle magnitude and trend section (from Para 3, Page 11 – 12; …In fact, extreme environmental condition…).

Comment 4: The minor comments are addressed in the manuscript which is attached herewith.
Response: We thank the reviewer for pointing out our muddled word structure. We have revised the draft by addressing the comments. Point-wise replies to the comments are tabulated:

No. Comments Response
1 Mention the layer in bracket Revised accordingly in the Environmental significance statement on page 1.
2 Lower case The word ‘carbon’ has been revised with lower case in the Abstract section of page 1.
3 Write full form of CO2 and short form in bracket Included full form of CO2 in Abstract section of page 1.
4 Choose another word Changed the word ‘…enviro-climate’ by revising the statement as ‘…in understanding the importance of carbon-climate feedbacks.’ in the Abstract section of page 1.
5 Lower case The word ‘carbon’ has been revised with lower case in 1 Introduction section of page 1.
6 Full form for the first time Included full form of ‘enviro-climatic’ with ‘environmental and climatic’ in 1 Introduction section of page 2.
7 Citation missing? Checked for the missing citation and revised accordingly in 2 Background: Terrestrial C source and sink section of page 2.
8 Replace the word for soft portrayal Revised the word ‘…provoked terror…’ as ‘…kindled terror’ in 2 Background: Terrestrial carbon source and sink section of page 2.
9 Replace the word with ‘eagerly’ Replaced the word ‘…sophisticatedly…’ for ‘…eagerly analyzing…’ in the 2.1 Terrestrial carbon sources section of page 2.
10 Sentence is difficult to understand. Rewrite the sentence As solicited by the reviewer, the sentence ‘Researches have universality…is still in debate’ has been revised as ‘Researchers, with the sophisticated measurement techniques, share congruence in understanding the fluctuations in the carbon sink, albeit, the importance of the factors in the assessment is still in debate’ in 2.2 Terrestrial carbon sinks section of page 2.
11 Replace the word; not suitable for this sentence Replaced the word ‘…heuristic…’ with ‘…empirical estimation…’ in the 2.2 Terrestrial carbon sinks section of page 2.
12 Citation missing? Checked for the missing citation and revised accordingly in the 2.2 Terrestrial carbon sinks section of page 3.
13 ‘Predominantly?’ Change it as adjective Replaced the word ‘…predominantly…’ with its adjective form ‘…predominant…’ in the 2.2 Terrestrial carbon sinks section of page 3.
14 Replace the word; not suitable for this sentence Replaced the word ‘…minuscule…’ by revising the statement to ‘Encountering a small disturbance…’ in the 3 Keys drivers of terrestrial carbon cycle section of page 3.
15 Write the full form as ‘carbon’ Revised the whole manuscript by replacing ‘C’ with ‘carbon’.
16 ‘Highlights?’ Change the tense Replaced the tense of the word ‘…highlights…’ to ‘…highlight…’ in the 3.1.2 Gross Primary Production (GPP)… section of page 3.
17 ‘Indicate?’ Change the tense Replaced the tense of the word ‘…indicate…’ to ‘…indicated…’ in the 3.1.3 Net Biome Production (NBP) section of page 3.
18 Not only anthropogenic, but also climate and biological factors As per the reviewer’s suggestion, the statement has been revised by including the terms ‘…climatic and biophysical factors’ in the 3.1.4 Net Ecosystem Exchange (NEE)… section of page 4.
19 Replace with ‘ecosystem’ Replaced the word ‘…ecosystems’…’ to ‘…ecosystem…’ in the 4.2 Non-destructive method section of page 5.
20 Delete repeated word The repeated word ‘nature’ has been removed from the sentence in 5.1 C and N: The rejoinder section of page 9.
21 Which one is appropriate? The statement has been revised as ‘One such regulator is the hydrology.’ by removing the repeated words in the 5.2 Hydrological linkages to carbon section of page 9.
22 Carbon source is correct here. The authors thank the reviewer for pointing out the mistake. The statement has been revised as ‘…factors are reasons for C sinks in the aforesaid states of India.’ in the 7.2 Stock trend in India section of page 13.

17-Jul-2022

Dear Dr Tyagi:

Manuscript ID: EA-CRV-12-2021-000102.R1
TITLE: Terrestrial carbon cycle: a tipping edge of climate change between atmosphere and biosphere ecosystems

Thank you for submitting your revised manuscript to Environmental Science: Atmospheres. I am pleased to accept your manuscript for publication in its current form. I have copied any final comments from the reviewer(s) below.

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Reviewer 1

The authors have answered all the comments and suggestions in the revised manuscript, which has significantly improved the final draft. I am satisfied and may recommend it for publication in the journal.