Land Use, Temperature, and Nitrogen Affect Nitrous Oxide Emissions in Amazonian Soils

Round 1

Reviewer 1 Report

Nitrous oxide (N2O) is a major greenhouse gas and ozone destroyer. The manuscript investigated the effects of land use change, warming, and nitrogen enrichment on soil N2O emission Brazilian Amazon. The results would help to understand the response of Amazon biome to anthropogenic disturbances, and to develop N2O mitigation strategies. Therefore, I agree to accept it for publication after minor or moderate revision.

Major concern:

The N2O emission data in the manuscript were obtained from dry-soil incubations, rather than field monitoring. Since the incubation conditions (e.g., O2 pressure, water content) are different from field conditions, N2O emissions from incubations may be quite different from those from field. Especially, denitrification under anaerobic condition has widely considered as the major source for N2O emission, while the incubations in manuscript were generally under aerobic? Though I agree that these artifacts may not influence the qualitative comparison among experimental treatments, the N2O emission may be quantitatively different from the field emission data. So, I suggest discussing these differences in the “Discussion” section.

Specific suggestions:

1.       L18, change “by” to “from”.

2.       L23, change two “or” to “and”.

3.       L50-53, the sentence is too long to follow, please consider rephrasing it.

4.       Table 1, what is about TN for three soils?

5.       Fig. 1, add the error bars

6.       L232, consider rescaling the vertical axis of Fig. 3A to show more detail data.

Table 2 and Table 3, I am not able to understand the rationale of regressions. Please note that the responses in N2O to warming and N addition are not necessarily linear.

Author Response

We thank the Reviewer and the Editor for their careful reading of our manuscript and overall supportive comments and suggestions. This constructive input has contributed to improve the manuscript significantly, where we have also had a special eye to improve clarity.

We have modified the manuscript accordingly, and detailed corrections are listed below point by point.

Nitrous oxide (N2O) is a major greenhouse gas and ozone destroyer. The manuscript investigated the effects of land use change, warming, and nitrogen enrichment on soil N₂O emission Brazilian Amazon. The results would help to understand the response of Amazon biome to anthropogenic disturbances, and to develop N₂O mitigation strategies. Therefore, I agree to accept it for publication after minor or moderate revision.

Major concern:

The N₂O emission data in the manuscript were obtained from dry-soil incubations, rather than field monitoring. Since the incubation conditions (e.g., O2 pressure, water content) are different from field conditions, N₂O emissions from incubations may be quite different from those from field. Especially, denitrification under anaerobic condition has widely considered as the major source for N₂O emission, while the incubations in manuscript were generally under aerobic? Though I agree that these artifacts may not influence the qualitative comparison among experimental treatments, the N₂O emission may be quantitatively different from the field emission data. So, I suggest discussing these differences in the “Discussion” section.

Thank you for your comment. No, this incubation was not from dry-soil. This incubation study was done at 60% of water filled pore space a relatively high soil moisture. This was done to allow the maximal N₂O production once in the literature is reported that the maximal N₂O production occurs when WFPS range 60-70%. At this soil moisture N₂O is produced both from nitrification and denitrification (Dobbie and Smith, 2003). It`s a prerequisite to fix soil moisture if you want to study the effects of soil temperature or soil N on a certain gas. If several drivers are varying at the same time, we cannot differentiate the effect of them. I don`t think that is a good idea to compare the magnitude of fluxes from an incubation with field studies.

Dobbie, K.E., Smith, K.A. Nitrous oxide emission factors for agricultural soils in Great Britain: the impact of soil water-filled pore space and other controlling variables. Glob Change Biol., 2003, 9, 204–218, doi: 10.1046/j.1365-2486.2003.00563.x

Specific suggestions:

L18, change “by” to “from”.

The authors made the requested corrections

L23, change two “or” to “and”.

The authors made the requested corrections

L50-53, the sentence is too long to follow, please consider rephrasing it.

The authors made the requested corrections

Table 1, what is about TN for three soils?

Thanks for the comment, we did not analyze the total N, once we run mineral N content that drives N2O emissions.

Fig. 1, add the error bars

The authors made the requested corrections

L232, consider rescaling the vertical axis of Fig. 3A to show more detail data.

The initial idea is to keep the scale of the flow Y axes the same, to maintain a standard throughout the paper.

Table 2 and Table 3, I am not able to understand the rationale of regressions. Please note that the responses in N2O to warming and N addition are not necessarily linear.

Thanks for your comment, we performed linear, quadratic and cubic models for each treatment. Only the significant model is presented in the table. For more details, please see the section statistical analyses.

Author Response File: Author Response.docx

Reviewer 2 Report

The topic of the manuscript, "Land use, temperature and nitrogen affect nitrous oxide emissions in Amazonian soils" is in line with the scope of the journal. It raises the important issue of one of the main greenhouse gases, which is N2O, and the way of land use, which has a significant impact on the aggravation of the greenhouse effect. The paper was prepared in a manner typical of scientific papers. Correct division into chapters was used. The collected results are presented in a correct way in the form of figures and tables, but minor corrections should be made to improve their readability. The authors have used correct analytical methods, obtaining interesting results The cited literature is sufficient. The paper is well written, correctly interpreted, and the results should be disseminated. I recommend the manuscript for publication in this journal, but with minor revisions. I provide detailed comments below.

Abstract

Line 24-27 - please read this section again. Once the authors write that the highest N₂O emission was in agricultural soil, and a sentence further on that in agricultural soil and pastures. So where were the highest N2O emissions?

Resultas

Fig. 2 - The graph is not very readable. Reduce the scale and enter colors.

Line 196 - 208 and Table 2 - the authors in this passage talk about different levels of significance and refer to Table 2. but where and how in Table 2 is significance related to the 0.01 level, for example, marked? Please correct this

Tab 2 - why there are no letters referring to the Tukey test at 35 and 40 °C? Explain.

Fig. 3 - The graph is not very clear. Enter colors

Line 239– 248 and table 3 - the authors in this passage talk about different levels of significance and refer to Table 3. but where and how in Table 3 is significance related to the 0.01 level, for example, marked? Please correct this

Tab 3 - why are there no letters referring to the Tukey test at doses 0 and 90? Explain.

Fig. 4 - The graph is not very clear. Enter colors

Line 280-281 - expand on this passage. Describe the results found in Table 4, which you refer to in this paragraph.

Table and Fig. - think about standardizing units throughout the text (ng or µg)

Discussion

Line 301- 304 - Explain what influences tropical forest resilience? The authors write about tropical forest resilience traits influencing GHG mitigation, but what are these traits specifically and how are they related or influence the results presented in the paper. Expand on this passage.

Line 320-325 - repeated sentences. There is the same content in these two sentences just framed differently - correct it.

Line 357 - 359 - what disturbances in agricultural ecosystems did the authors have in mind that influenced the highest N2O emissions? where are the changes in microbial abundance and structure described? This is too general, please elaborate.

Conclusions

Develop your conclusions more fully, write what practical application does your research have? E.g. Can these results/research contribute to solving or reducing the greenhouse effect? If so, in what way?

Reference

Line 443, 474, 481 – bold year

Line 469-471 – no DOI

Author Response

We thank the reviewer and the Editor for their careful reading of our manuscript and overall supportive comments and suggestions. This constructive input has contributed to improve the manuscript significantly, where we have also had a special eye to improve clarity.

We have modified the manuscript accordingly, and detailed corrections are listed below point by point.

Review 2

The topic of the manuscript, "Land use, temperature and nitrogen affect nitrous oxide emissions in Amazonian soils" is in line with the scope of the journal. It raises the important issue of one of the main greenhouse gases, which is N₂O, and the way of land use, which has a significant impact on the aggravation of the greenhouse effect. The paper was prepared in a manner typical of scientific papers. Correct division into chapters was used. The collected results are presented in a correct way in the form of figures and tables, but minor corrections should be made to improve their readability. The authors have used correct analytical methods, obtaining interesting results The cited literature is sufficient. The paper is well written, correctly interpreted, and the results should be disseminated. I recommend the manuscript for publication in this journal, but with minor revisions. I provide detailed comments below.

Abstract

Line 24-27 - please read this section again. Once the authors write that the highest N₂O emission was in agricultural soil, and a sentence further on that in agricultural soil and pastures. So where were the highest N₂O emissions?

The first statement concerns experiment 1, where only land uses were tested. The second statement concerns the effects of temperature on emissions, where the increase in temperature to 30 °C provided similar levels of emission between soils.

Results

Fig. 2 - The graph is not very readable. Reduce the scale and enter colors.

The authors made the requested corrections, improved all graphs.

Line 196 - 208 and Table 2 - the authors in this passage talk about different levels of significance and refer to Table 2. but where and how in Table 2 is significance related to the 0.01 level, for example, marked? Please correct this

Thank you for catching it. We prefer to keep p-value in the text, we removed the table call in this part.

Tab 2 - why there are no letters referring to the Tukey test at 35 and 40 °C? Explain.

We include ns for the non-significant. Because it was observed significance effect only for the 25 and 30 °C of temperature, with p-value present in the text.

Fig. 3 - The graph is not very clear. Enter colors and

The authors made the requested corrections

Line 239– 248 and table 3 - the authors in this passage talk about different levels of significance and refer to Table 3. but where and how in Table 3 is significance related to the 0.01 level, for example, marked? Please correct this

Thank you for catching it. We prefer to keep p-value in the text, we removed the table call in this part.

Tab 3 - why are there no letters referring to the Tukey test at doses 0 and 90? Explain.

We include ns for the non-significant. Because it was observed significance effect only for the 0 and 90 kg of temperature, with p-value present in the text.

Fig. 4 - The graph is not very clear. Enter colors

The authors made the requested corrections

Line 280-281 - expand on this passage. Describe the results found in Table 4, which you refer to in this paragraph.

The authors expanded this passage

Table and Fig. - think about standardizing units throughout the text (ng or µg)

Thank you for your suggestion but is not possible. In the figures we present fluxes and in the table, total emission. 

Discussion

Line 301- 304 - Explain what influences tropical forest resilience? The authors write about tropical forest resilience traits influencing GHG mitigation, but what are these traits specifically and how are they related or influence the results presented in the paper. Expand on this passage.

The authors added a citation explaining the main causes of the resilience of forest soils.

Line 320-325 - repeated sentences. There is the same content in these two sentences just framed differently - correct it.

The authors remove one sentences.

Line 357 - 359 - what disturbances in agricultural ecosystems did the authors have in mind that influenced the highest N2O emissions? where are the changes in microbial abundance and structure described? This is too general, please elaborate.

The authors detailed the disturbances in soil agricultural ecosystems, and their effects in the microbiological community.

Conclusions

Develop your conclusions more fully, write what practical application does your research have? E.g. Can these results/research contribute to solving or reducing the greenhouse effect? If so, in what way?

Thank you for your suggestion, we included the practical application of this research.

Reference

Line 443, 474, 481 – bold year

The authors made the requested corrections

Line 469-471 – no DOI

This reference is from a USDA book, there is not DOI

Author Response File: Author Response.docx

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

The manuscript suffers from lack of infomation and shows mistakes that do not recommend its acceptation for publication in such quality journal.

Comments for author File: Comments.pdf

Reviewer 2 Report

Anib al C. do Rego and seven co-authors have submitted a manuscript titled ”Land use, temperature and nitrogen affect nitrous oxide emissions in Amazonian soils” for review to be published in Agronomy. Nitrous oxide emissions were measured in rainforest, pasture and arable land, and incubation experiments were carried out to elucidate the effect of temperature and nitrogen additions to the emissions. The topic is interesting and suitable to be published in this journal. The results are somewhat alarming about the effects of clearing rainforest for agricultural use. This manuscript will probably be eventually accepted for publication but it requires substantial revision to reach that stage.

The manuscript needes necessarily a comprehensive linguistic revision. The text is mostly understandable, though, but it is not correct English. I am not pointing the mistakes out in detail and make the revisions because it is not a reviewer’s duty but it is the authors’ duty.

L23: ”the the amazon”-> the Amazon

L27: ”altered”. Tell the reader whether it increased or decreased.

L30: ”providing emit N2O”. What does this mean?

Abstract in general: Please add an sentence indicating that emissions from the three land uses were measured in the field and the effects of temperature and nitrogen additions were investigated in the laboratory.

L38: ”2,200 mm year-1 of rainfall throughout the basin” -> 2,200 mm of rainfall annually throughout the basin

L44: ”better understood.” -> better understood and and more comprehensively quantified.

L59: ”The presence of nitrogen”-> The presence of mineral nitrogen

L61: excreter -> excreta

L65: Delete ”studies reporting”

L75: Delete ”that of”

L82: ”with different land use systems, wet…”-> with three different land use systems, i.e., wet

L88: ”oxisols” -> Oxisols

Table 1: ”Silent”-> Silt. The percentages of the textural fractions should sumu p at 100%. Now it is not always the case. Please correct.

Methods of soil analyses need to be described. It is particularly important for P because so many methods are available. Without knowing the method, the numbers don’t mean anything because the reader cannot interprete them.

L104-105: P or P2O5? K or K2O?

L111, 114, 118: ”evaluate” for what? Obviously N2O emissions, but it has to be explicitly mentioned.

L120: How was the amount of nitrogen determined to correspond to certain amounts applied at kg/ha in the field? Did you use the surface area of the bottle, or did you calculate the needed amount from the weight or volume of soil?

L124: There is something strange in the sentence ”Next…”. Please clarify, correct.

L131: ”as an exception to”-> with the exception of

L134: Delete ”N”

L135: ”oven”? Rather a constant temperature chamber, I suppose.

L142: ”at 1”-> at incubation 1

L160: ”N-inorganic”-> mineral N

L161: ”KCl 2 M” -> 2 M KCl

L165: ”variance analysis”-> analysis of variance

Results (throughout the chapter): The authors now use the present tense when they tell about their results. It is customary in scientific writing that past tense is used. Please revise.

L174: As usual, the auhtors present their results with unrealistic accuracy. Here, they should present the emissions as ug g-1 without any decimals, i.e. 199.68 -> 200. Please go through all the numbers in this manuscript and evaluate what the realistic accuracy is. I don’t repeat this criticism later on.  

L185-187: ””This section…” Strange text here.

L195-196: ”Interactions…”-> Interactions were observed between land use and incubation temperature (p=0.0197) on N2O emissions…

L196: ”all three soil types”-> all three land uses???

L201: ”differed according to land use”-> differed among the land uses

Table 2 and 3: The R2 values have been presented with unrealistic accuracy. Full percentages are enough.

L 209, 249: ”in the same”-> within a

L211: ”little variation”. What variation do you refer to? Temporal or between the replicates or what?

L213. Here you use ng as a unit. It is confusing. Why not present all the emission results as ug? I strongly recommend changing the unit in the text and in the respective figures.

L221: ”nineteenth”-> 19th

L242: ”proportional”. What does it mean? Is that word needed? This word appears later on as well. Please consider deleting it from everywhere.

L280, 331: ”N-mineral”-> mineral N

L283: ”N-NH4”-> NH4+-N

Section 4.3. Results of mineral N have been presented with unrealistic accuracy. If you give the results as mg/kg, full milligrams is a sufficient accuracy, with no decimals. In this section, there are too many numbers. Please present them in a Table format.

Discussion: Were the soils similar enough to justify the conclusion that the differences in emissions were caused by the land use? Were the soils representative of the area?

L359: ”according to the ecosystem”-> in different ecosystems

L363: Delete ”this”.

L418: ”by nitrogen temperature and availability”????

Please check that all the subscripts are correcly written.