Soil Carbon and Nitrogen Pools and Their Storage Characteristics under Different Vegetation Restoration Types on the Loess Plateau of Longzhong, China
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsReview of the manuscript titled “Soil carbon and nitrogen pools and their storage characteristics under different vegetation restoration types on the Loess Plateau of Longzhong, China”
The manuscript titled “Soil carbon and nitrogen pools and their storage characteristics under different vegetation restoration types on the Loess Plateau of Longzhong, China” explores the characteristics of soil carbon and nitrogen pools and their storage under four types of vegetation restoration in the Longzhong Loess Plateau area. The manuscript is well written, contains all necessary information about experimental design and methods used, and the Results, Discussion, and Conclusion sections adequately describe and discuss the results of the study. Therefore, that manuscript addressing some minor, specific comments.
Specific comments:
In the Abstract, you do not need to introduce abbreviations if you do not use them in the Abstract (L14-15).
L22. Please use standard units, e.g., ha instead of hm-2.
L54-55. After the introduction of the abbreviation of carbon and nitrogen at L36, you can use them further in the text; check everywhere.
L92. Insert “C” before “emission reduction”. Provide a reference that proves the regional climate change in the study area.
L99. “shrublands” instead of “shrub forests”.
L163. Provide the reference for the “S” sampling method.
L206. Provide the title for the 3.1.1. subsection or remove it.
L240. Improve the resolution of Fig. 1.
L264. Improve the resolution of Fig. 2.
L300. Improve the resolution of Fig. 3.
L329. Improve the resolution of Fig. 4.
Author Response
（1）In the Abstract, you do not need to introduce abbreviations if you do not use them in the Abstract (L14-15).
Response: Done. Thank you for your valuable suggestions. We have checked and revised the abstract. We would like the current version to be more rigorous.
（2）L22. Please use standard units, e.g., ha instead of hm-2.
Response: Done. Thank you for your valuable suggestions. We have revised the units of L22 and have checked and revised the full text.
（3）L54-55. After the introduction of the abbreviation of carbon and nitrogen at L36, you can use them further in the text; check everywhere.
Response: Done. Thank you for your valuable suggestion. We have revised it and checked and revised the abbreviations throughout the text. We would like the current version to be more rigorous.
（4）L92. Insert “C” before “emission reduction”. Provide a reference that proves the regional climate change in the study area.
Response: Done. Thanks for this valuable suggestion. We have added “C” before “emission reduction” (Page 2, Line 93). We also add references where vegetation restoration contributes to mitigating regional climate change (e.g., [20] Zhang et al. 2023).
（5）L99. “shrublands” instead of “shrub forests”.
Response: Done. Thank you for your valuable suggestions. We have made changes (Page 3, Line 100). We would like the current version to be stricter.
（6）L163. Provide the reference for the “S” sampling method.
Response: Done. Thank you for kindly reminding us. We have added references to "S" sampling methods (e.g. [1, 18] Yuan et al. 2023; Liu et al. 2022) (Page 5, Line 173).
（7）L206. Provide the title for the 3.1.1. subsection or remove it.
Response: Done. Thank you for kindly reminding us. We apologize for the unnecessary misunderstandings caused. We have deleted the heading of subsection 3.1.1.
（8）L240. Improve the resolution of Fig. 1.
Response: Done. We apologize for the unnecessary misunderstandings caused. We have improved the quality of Figure 1 and we hope that the current version is more stringent.
（9）L264. Improve the resolution of Fig. 2.
Response: Done. We apologize for the unnecessary misunderstandings caused. We have improved the quality of Figure 2 and we hope that the current version is more stringent.
（10）L300. Improve the resolution of Fig. 3.
Response: Done. We apologize for the unnecessary misunderstandings caused. We have improved the quality of Figure 3 and we hope that the current version is more stringent.
（11）L329. Improve the resolution of Fig. 4.
Response: Done. We apologize for the unnecessary misunderstandings caused. We have improved the quality of Figure 4 and we hope that the current version is more stringent.
Reviewer 2 Report
Comments and Suggestions for AuthorsDear authors, please find here my suggestions:
Line 45: Add this reference: https://doi.org/10.1016/j.apsoil.2021.104262
Line 51: Like also reported in the papers above.
Line 61: It is also for plants that you did not mention in the manuscript like Robinia pseudoacacia L. (https://doi.org/10.1016/j.catena.2022.106656).
Line 114: Are those depths related to the sampling or the real extensions of the profiles? I suggest you to delete the information in the parenthesis or specify the information related to those depths. In addition, you can not talk about “restoration types” as you are working with different plant species and not different plant types. Please correct.
Line 118: Also correct here.
Line 136: The soils do not report any classifications. Please report IUSS WRB or USDA classification with at least 2 classifiers. Also add some relevant information about lithology and geochemistry.
Lines 142-143: Please report the botanical classification correctly throughout the text: genus, species, author (example: Stipa bungeana Trin.).
Line 148: Was each area large 20 m x 20 m? Please report it also in the text, not only in the Table.
Sect. 2.4.1: Detail the methods. They must be replicable also by others. You missed much information.
Line 180: Was SOC measured by the Walkley-Black method? Specify.
Line 182: The parameter that you call QMBC is not the entropy but the equilibrium of microbial C on SOC, it is the microbial efficiency quotient as also reported
Line 197: “SPSS” in capital letters.
Table 3: SWC is % dry weight.
The Figures are not well visible, improve quality image.
Line 345: Like reported also in https://doi.org/10.1016/j.apsoil.2021.104262, https://doi.org/10.1016/j.catena.2022.106656
Sect 4.1: You have to discuss better your results. Detail better and report, referring to parameters, what your findings are like you did for Sect 4.2.
Sect 4.2: You can also compare your results with different environments like Mediterranean area (https://doi.org/10.1016/j.apsoil.2021.104262, https://doi.org/10.1016/j.catena.2022.106656)
Line 485: You can not talk about nitrogen storage because you did not calculate its stock. You can only talk about pool.
Line 488: What do you mean for shallow soils? If you have soils of general different depth you have to report in the Materials sections and detail better soils also in these terms.
Author Response
（1）Line 45: Add this reference: https://doi.org/10.1016/j.apsoil.2021.104262
Response: Done. We thank you for recommending an excellent research paper, which we have added as our additional reference after studying this article (Page 2, Line 46) (as in reference [5]).
（2）Line 51: Like also reported in the papers above.
Response: Done. We thank you for recommending an excellent research paper, which we have added as our additional reference after studying this article (Page 2, Line 52) (as in reference [5]).
（3）Line 61: It is also for plants that you did not mention in the manuscript like Robinia pseudoacacia L. (https://doi.org/10.1016/j.catena.2022.106656).
Response: Done. We sincerely appreciate your valuable comments. As suggested by the reviewer, we have added the references (Page 2, Line 62) (as in reference [2])recommended by the reviewer to support our ideas after checking the introductory part of the article.
（4）Line 114: Are those depths related to the sampling or the real extensions of the profiles? I suggest you to delete the information in the parenthesis or specify the information related to those depths. In addition, you can not talk about “restoration types” as you are working with different plant species and not different plant types. Please correct.
Response: Done. We would like to thank the reviewers for their careful comments on this manuscript. We have removed the information in parentheses as suggested by the reviewers. In addition, we agree with the reviewers that the treatment nomenclature we chose is for a different plant species. However, the vegetation of the four sample sites we selected was cut down in the 1990s and restored naturally in the early 21st century through artificial planting or natural abandonment to a vegetation community with typical vegetation as the dominant species (Table 1). It has been pointed out that vegetation restoration is an important measure to obtain ecological benefits, effectively increasing biodiversity (Deng et al., 2019; Yan et al., 2019), changing soil properties (Williams-Linera et al., 2021; Zhao et al., 2022), and significantly influencing the composition and function of regional ecosystems (Fu et al., 2020). However, differences in the selection of restored tree species have led to differences in the structure of the plant communities formed above ground during their long-term restoration (Fu et al., 2020; Wang et al., 2020). This may be because different vegetation types recover their components (biodiversity, richness) differently during the restoration process, resulting in large differences in the composition of species on the ground (Engel and Abella, 2011). In addition, the combination of external factors has produced a change in surface vegetation cover during the restoration process for different vegetation types (Feng et al., 2022). This change also represents, to some extent, the growth trend and condition of the vegetation (Feng et al., 2022). Therefore, by comparing the characteristics of soil carbon and nitrogen pools between vegetation restoration types named after dominant species, we may provide some theoretical support in terms of optimizing the selection of tree species in long-term vegetation restoration efforts in this region.
References:
Deng, J., Yin, Y., Luo, J., Zhu, W., and Zhou, Y. (2019). Different revegetation types alter soil physical-chemical characteristics and fungal community in the Baishilazi Nature Reserve. PeerJ 6, e6251. doi: 10.7717/peerj.6251.
Engel, E.C., and Abella, S.R. (2011). Vegetation recovery in a desert landscape after wildfires: influences of community type, time since fire and contingency effects. Journal of Applied Ecology 48(6), 1401-1410. doi: 10.1111/j.1365-2664.2011.02057.x.
Feng, Y., Wang, J., Zhou, Q., Bai, M., Peng, P., Zhao, D., et al. (2022). Quantitative analysis of vegetation restoration and potential driving factors in a typical subalpine region of the Eastern Tibet Plateau. PeerJ 10, e13358. doi: 10.7717/peerj.13358.
Fu, D., Wu, X., Duan, C., Chadwick, D.R., and Jones, D.L. (2020). Response of soil phosphorus fractions and fluxes to different vegetation restoration types in a subtropical mountain ecosystem. Catena 193. doi: 10.1016/j.catena.2020.104663.
Wang, N., He, X., Zhao, F., Wang, D., and Jiao, J. (2020). Soil seed bank in different vegetation types in the Loess Plateau region and its role in vegetation restoration. Restoration Ecology 28(S1). doi: 10.1111/rec.13169.
Williams-Linera, G., Bonilla-Moheno, M., López-Barrera, F., and Tolome, J. (2021). Litterfall, vegetation structure and tree composition as indicators of functional recovery in passive and active tropical cloud forest restoration. Forest Ecology and Management 493. doi: 10.1016/j.foreco.2021.119260.
Yan, M., Cui, F., Liu, Y., Zhang, Z., Zhang, J., Ren, H., et al. (2019). Vegetation type and plant diversity affected soil carbon accumulation in a postmining area in Shanxi Province, China. Land Degradation & Development 31(2), 181-189. doi: 10.1002/ldr.3438.
Zhao, W., Yin, Y., Li, S., Liu, J., Dong, Y., and Su, S. (2022). Soil Microbial Community Varied with Vegetation Types on a Small Regional Scale of the Qilian Mountains. Sustainability 14(13). doi: 10.3390/su14137910.
（5）Line 118: Also correct here.
Response: Done. We sincerely appreciate your valuable comments. We agree with the reviewers that the treatment nomenclature we chose is for a different plant species. However, the vegetation of the four sample sites we selected was cut down in the 1990s and restored naturally in the early 21st century through artificial planting or natural abandonment to a vegetation community with typical vegetation as the dominant species (Table 1). It has been pointed out that vegetation restoration is an important measure to obtain ecological benefits, effectively increasing biodiversity (Deng et al., 2019; Yan et al., 2019), changing soil properties (Williams-Linera et al., 2021; Zhao et al., 2022), and significantly influencing the composition and function of regional ecosystems (Fu et al., 2020). However, differences in the selection of restored tree species have led to differences in the structure of the plant communities formed above ground during their long-term restoration (Fu et al., 2020; Wang et al., 2020). This may be because different vegetation types recover their components (biodiversity, richness) differently during the restoration process, resulting in large differences in the composition of species on the ground (Engel and Abella, 2011). In addition, the combination of external factors has produced a change in surface vegetation cover during the restoration process for different vegetation types (Feng et al., 2022). This change also represents, to some extent, the growth trend and condition of the vegetation (Feng et al., 2022). Therefore, by comparing the characteristics of soil carbon and nitrogen pools between vegetation restoration types named after dominant species, we may provide some theoretical support in terms of optimizing the selection of tree species in long-term vegetation restoration efforts in this region.
References:
Deng, J., Yin, Y., Luo, J., Zhu, W., and Zhou, Y. (2019). Different revegetation types alter soil physical-chemical characteristics and fungal community in the Baishilazi Nature Reserve. PeerJ 6, e6251. doi: 10.7717/peerj.6251.
Engel, E.C., and Abella, S.R. (2011). Vegetation recovery in a desert landscape after wildfires: influences of community type, time since fire and contingency effects. Journal of Applied Ecology 48(6), 1401-1410. doi: 10.1111/j.1365-2664.2011.02057.x.
Feng, Y., Wang, J., Zhou, Q., Bai, M., Peng, P., Zhao, D., et al. (2022). Quantitative analysis of vegetation restoration and potential driving factors in a typical subalpine region of the Eastern Tibet Plateau. PeerJ 10, e13358. doi: 10.7717/peerj.13358.
Fu, D., Wu, X., Duan, C., Chadwick, D.R., and Jones, D.L. (2020). Response of soil phosphorus fractions and fluxes to different vegetation restoration types in a subtropical mountain ecosystem. Catena 193. doi: 10.1016/j.catena.2020.104663.
Wang, N., He, X., Zhao, F., Wang, D., and Jiao, J. (2020). Soil seed bank in different vegetation types in the Loess Plateau region and its role in vegetation restoration. Restoration Ecology 28(S1). doi: 10.1111/rec.13169.
Williams-Linera, G., Bonilla-Moheno, M., López-Barrera, F., and Tolome, J. (2021). Litterfall, vegetation structure and tree composition as indicators of functional recovery in passive and active tropical cloud forest restoration. Forest Ecology and Management 493. doi: 10.1016/j.foreco.2021.119260.
Yan, M., Cui, F., Liu, Y., Zhang, Z., Zhang, J., Ren, H., et al. (2019). Vegetation type and plant diversity affected soil carbon accumulation in a postmining area in Shanxi Province, China. Land Degradation & Development 31(2), 181-189. doi: 10.1002/ldr.3438.
Zhao, W., Yin, Y., Li, S., Liu, J., Dong, Y., and Su, S. (2022). Soil Microbial Community Varied with Vegetation Types on a Small Regional Scale of the Qilian Mountains. Sustainability 14(13). doi: 10.3390/su14137910.
（6）Line 136: The soils do not report any classifications. Please report IUSS WRB or USDA classification with at least 2 classifiers. Also add some relevant information about lithology and geochemistry.
Response: Done. We sincerely thank the reviewers for their valuable comments. We have added information such as soil classification (Page 3, Lines 139-144) based on the reviewers' comments as follows. We hope that the present version is more rigorous.
“The soils in the study area are secondary loess soils (Entisols in soil taxonomy of the USDA) characterized as yellowish, loose, and macroporous with a clayey or loamy texture [33]. The soil developed from a loose loess parent material formed under cold and dry climatic conditions during the Quaternary period, and is rich in secondary calcium carbonate and small amounts of gypsum, iron, and manganese oxides, with quartz and feldspar dominating its mineral composition [34].”
（7）Lines 142-143: Please report the botanical classification correctly throughout the text: genus, species, author (example: Stipa bungeana Trin.).
Response: Done. We sincerely thank the reviewers for their valuable comments. We have added the plant classification (genus, species, author) based on the reviewers' comments (page 4, lines 150-151). We hope that the present version is more rigorous.
（8）Line 148: Was each area large 20 m x 20 m? Please report it also in the text, not only in the Table.
Response: Done. We sincerely thank the reviewers for their valuable comments. In our study, we selected four typical vegetation restoration test areas in the region with similar soil types and soil disturbance history, each measuring approximately 20 × 20 m . We used a completely randomized design in which three replicate small sample plots (8 × 8 m) were randomly selected and sampled within each test area. We have reported this part of the information in the main text.
（9）Sect. 2.4.1: Detail the methods. They must be replicable also by others. You missed much information.
Response: Done. We apologize for the unnecessary misunderstandings caused. We agree with this clearer description of the process and have updated the text as suggested. We have added detailed information to subsections 2.4.1 and 2.4.2 (Page 5, Lines 184-217; Page 6, Lines 222-237). We hope that the current version will be more stringent.
（10）Line 180: Was SOC measured by the Walkley-Black method? Specify.
Response: Done. We apologize for the unnecessary misunderstandings caused. SOC was determined by the Walkley-Black dichromate oxidation method [39]. Briefly, soil samples (0.1 g) were extracted with 7.5 ml of K2Cr2O7 (0.4 M) and 7.5 ml of concentrated H2SO4 at 180°C for 30 min, and then the SOC content was calculated based on the consumption of potassium dichromate. This part of the information we have added on page 6, lines 222-224 of the main text.
（11）Line 182: The parameter that you call QMBC is not the entropy but the equilibrium of microbial C on SOC, it is the microbial efficiency quotient as also reported
Response: Done. We thank the reviewer for bringing this issue to our attention. We sincerely appreciate your valuable comments and apologize for any unnecessary misunderstandings we may have caused. We have revised it (Page 6, Line 229) and checked the full text. We hope that the current version will be more stringent.
（12）Line 197: “SPSS” in capital letters.
Response: Done. We thank the reviewer for bringing this issue to our attention. We sincerely appreciate your valuable comments and apologize for any unnecessary misunderstandings we may have caused. We've modified it.
（13）Table 3: SWC is % dry weight.
Response: Done. We sincerely appreciate your valuable comments. In our study, SWC was determined by oven drying to constant weight at 105°C according to the method described by Zhang et al. (2019) (e.g., Ref. [36]).
（14）The Figures are not well visible, improve quality image.
Response: Done. We sincerely appreciate your valuable comments and apologize for any unnecessary misunderstandings we may have caused. We have improved the quality of Figures 1-4.
（15）Line 345: Like reported also in https://doi.org/10.1016/j.apsoil.2021.104262, https://doi.org/10.1016/j.catena.2022.106656
Response: Done. We sincerely appreciate your valuable comments. As suggested by the reviewers, we have added the references (Page 15, Line 417) recommended by the reviewers (as in references [2,5]) after checking the Discussion section of the article in support of our point of view.
（16）Sect 4.1: You have to discuss better your results. Detail better and report, referring to parameters, what your findings are like you did for Sect 4.2.
Response: Done. We sincerely appreciate your valuable comments. Based on the reviewer's suggestion, we have revised and added subsection 4.1 with reference to parameters (Page 16, Lines 450-491) as follows. We hope that the quality of the paper has now been further improved.
“We also found that soil C and N storages under the four vegetation restoration types were mainly concentrated in shallow soils at a depth of 0-20 cm, which is similar to the results of previous studies [10, 45]. Numerous studies have shown that the abundant plant and animal residues and plant roots in the surface soil [10], can provide a sufficient nutrient environment for the decomposition and release of organic matter in shallow soil [15, 46]. At the same time, the surface soil has suitable moisture and aeration structure, which is conducive to the reproduction of surface microorganisms (Table 2, Table 3, Figure 1, and Figure 4) and the decomposition and transformation of exogenous inputs [44, 47], which in turn leads to the accumulation of C and N reserves in the shallow soil. On the other hand, with the increase of soil depth, soil moisture, and aeration gradually decreased (Table 2, Table 3), which made the number of soil fauna and microorganisms participating in the biochemical reaction process of exogenous inputs in the lower layer of the soil decreased dramatically (Table 3, Figure 1), which in turn reduced the effect of soil C and N accumulation [47]. In this study, soil enzyme activity, MBC, and SWC under the four vegetation restoration types gradually decreased with increasing soil depth (Table 3, Figure 1), and soil enzyme activity, MBC, and SWC well explained the differences in the variation of soil C and N storages (Table 5, Figure 4), which further supported the finding that soil C and N storages were mainly concentrated in 0-20 cm soil.”
（17）Sect 4.2: You can also compare your results with different environments like Mediterranean area (https://doi.org/10.1016/j.apsoil.2021.104262, https://doi.org/10.1016/j.catena.2022.106656)
Response: Done. We sincerely thank the reviewers for the valuable advice given and we agree with the reviewers that comparing the results with other regions will help to improve the quality of our paper. We have compiled the reviewer's suggestions in the Discussion 4.2 subsection of the manuscript (Page 16, Lines 479-491), comparing the team's earlier studies in the region, and the SOC content during the restoration of vegetation in the Horqin sandy and Mediterranean regions (as described below), which we hope will lead to a further improvement in the quality of our paper.
“Vegetation restoration is an important measure to enhance ecosystem benefits in ecologically fragile areas [11] and plays a very positive role in ecosystem C sinks [8, 9]. In our study, we found that long-term vegetation restoration has resulted in higher SOC content in the Loess Plateau than in the Horqin sandy area [21] and earlier studies in the region by Wang [15] and Yang [19], and lower than in the Mediterranean region in scrub and pine forests [2, 5]. This is mainly because the input and output processes of soil organic matter are subject to the combined effects of external climate, vegetation community composition, soil characteristics, bottom nutrients, and time scale in different study areas [44], which make the changes of SOC content under vegetation restoration inconsistent. Meanwhile, under long-term vegetation restoration, forest, shrub, and grassland vegetation communities become more complex and stable, the surface cover area increases and a large above-ground litter and root secretion enters into the soil [16], which increases the continuous accumulation of SOC in the soil.”
（18）Line 485: You can not talk about nitrogen storage because you did not calculate its stock. You can only talk about pool.
Response: Done. We would like to thank the reviewers for their careful comments on this manuscript. We agree with the reviewers and have revised it (page 18, line 587).
（19）Line 488: What do you mean for shallow soils? If you have soils of general different depth you have to report in the Materials sections and detail better soils also in these terms.
Response: Done. We thank the reviewer for bringing this issue to our attention. We apologize for the unnecessary misunderstandings caused. We have modified it (Page 18, Line 590) as follows and checked the full text.
“At the same time, soil carbon and nitrogen storages under the different types of vegetation restoration were mainly concentrated in the 0-20 cm layer of the soil, and the content of soil carbon and nitrogen pools decreased with increasing soil depth.”
Reviewer 3 Report
Comments and Suggestions for AuthorsThe manuscript with ID forests-2763652 titled “Soil carbon and nitrogen pools and their storage characteristics under different vegetation restoration types on the Loess Plateau of Longzhong, China”
The topic addressed in the manuscript is relevant and concerns changes in carbon and nitrogen cycles in differently managed forest ecosystems.
Generally, the manuscript is written well. Organization of the manuscript is correct. Although, the statistical data processing is sufficient, the data analyzed is based on a single sampling term.
The main drawback of the experiment is the lack of multiple (long-term) sampling. The entire data set and its explanations are based on only one sample term.
Also, it would be more valid if the results were compared with some initial or earlier soil parameters discussed in the article.
Despite these shortcomings, the paper compares the rate of change in labile nitrogen and carbon pools between different plant communities. This, to a certain extent, gives some insight into the processes of nitrogen and carbon cycling in the ecosystems under consideration.
Some comments are given below:
Lines 64: “...soil Total nitrogen...” no capital letter –check it throughout the text
Line 190: “...I is the number of soil layers...” – correct “I” for “i”. Check it throughout the text
Lines 192-193: see the comment for the line 190
Line 206: “3.1.1. Subsubsection”? – correct the caption of the sub-section
Lines 207-208: “..Sucrase, Amylase, Urease, and Protease)..” – why the names of the enzymes should be given in capital letters? Check it throughout the text
Figure 1 – the quality of Figure 1 can be improved
Line 250: sub-section: 3.3. “...Ammonium/Nitrate...” – why in capital letters?
Figure 2: the quality of the Figure 2 should be improved
Figure 3: the quality of the Figure 3 should be improved
Figure 4: the quality of the Figure 4 should be improved
Legend to the Figure 4: “The larger the area of the ellipse in the graph, the smaller the correlation coefficient between the two indicators; the smaller the area of the ellipse, the larger the correlation coefficient between the two indicators. The direction of the ellipse to the right indicates a positive correlation between the two indicators; the direction of the ellipse to the left indicates a negative correlation between the two indicators” - This explanatory information should be moved from the legend to the results
Author Response
（1）Generally, the manuscript is written well. Organization of the manuscript is correct. Although, the statistical data processing is sufficient, the data analyzed is based on a single sampling term. The main drawback of the experiment is the lack of multiple (long-term) sampling. The entire data set and its explanations are based on only one sample term. Also, it would be more valid if the results were compared with some initial or earlier soil parameters discussed in the article.
Response: We would like to thank the reviewer for their professional review work and the positive and constructive comments on our manuscript. We agree with the reviewer that long-term sampling trials are very necessary. In our experiment, we focused mainly on characterizing changes in soil carbon and nitrogen pools among different vegetation types after long-term vegetation restoration. However, as suggested by the reviewers, we also realize that analyzing the dynamic changes of soil carbon and nitrogen pools under different vegetation restoration types in the long term is important for further understanding the process of soil carbon and nitrogen cycling under vegetation restoration in fragile habitats. Therefore, we will seriously consider the reviewer's valuable comments in our subsequent studies.
In addition, we would like to once again sincerely thank the reviewers for their valuable suggestions, and we agree with the reviewers that comparing some of the initial or earlier soil parameters will help to improve the quality of our paper. We have compiled the reviewer's suggestions in the Discussion 4.2 subsection of the manuscript (Page 16, Lines 479-491), comparing the team's earlier studies in the region, and the SOC content during the restoration of vegetation in the Horqin sandy and Mediterranean regions (as described below), which we hope will lead to a further improvement in the quality of our paper.
“Vegetation restoration is an important measure to enhance ecosystem benefits in ecologically fragile areas [11] and plays a very positive role in ecosystem C sinks [8, 9]. In our study, we found that long-term vegetation restoration has resulted in higher SOC content in the Loess Plateau than in the Horqin sandy area [21] and earlier studies in the region by Wang [15] and Yang [19], and lower than in the Mediterranean region in scrub and pine forests [2, 5]. This is mainly because the input and output processes of soil organic matter are subject to the combined effects of external climate, vegetation community composition, soil characteristics, bottom nutrients, and time scale in different study areas [44], which make the changes of SOC content under vegetation restoration inconsistent. Meanwhile, under long-term vegetation restoration, forest, shrub, and grassland vegetation communities become more complex and stable, the surface cover area increases and a large above-ground litter and root secretion enters into the soil [16], which increases the continuous accumulation of SOC in the soil.”
（2）Lines 64: “...soil Total nitrogen...” no capital letter –check it throughout the text
Response: Done. Thanks to the reviewer for this careful comment on this manuscript. We apologize for the unnecessary misunderstandings caused. We have modified it and checked the full text. We would like the current version to be stricter.
（3）Line 190: “...I is the number of soil layers...” – correct “I” for “i”. Check it throughout the text
Response: Done. We thank the reviewer for bringing this issue to our attention. We apologize for the unnecessary misunderstandings caused. We have changed "I" to "i" (Page 6, Lines 249-251) and checked the whole text. We would like the current version to be stricter.
（4）Lines 192-193: see the comment for the line 190
Response: Done. We thank the reviewer for bringing this issue to our attention. We apologize for the unnecessary misunderstandings caused. We have changed "I" to "i" (Page 6, Lines 249-251) and checked the whole text. We would like the current version to be stricter.
（5）Line 206: “3.1.1. Subsubsection”? – correct the caption of the sub-section
Response: Done. Thanks to the reviewer for this careful comment on this manuscript. We apologize for the unnecessary misunderstandings caused. We have deleted the heading of subsection 3.1.1.
（6）Lines 207-208: “..Sucrase, Amylase, Urease, and Protease)..” – why the names of the enzymes should be given in capital letters? Check it throughout the text
Response: Done. Thank you for kindly reminding us. We have changed the names of the enzymes to lowercase letters (Page 7, Lines 266-272) and have checked and revised the whole text.
（7）Figure 1 – the quality of Figure 1 can be improved
Response: Done. We apologize for the unnecessary misunderstandings caused. We have improved the quality of Figure 1 and we hope that the current version is more stringent.
（8）Line 250: sub-section: 3.3. “...Ammonium/Nitrate...” – why in capital letters?
Response: Done. We sincerely thank you for your valuable suggestions. We have changed the name of the “Ammonium/Nitrate” to lower case (Page 9, Lines 311, 318) and have checked and corrected the entire text.
（9）Figure 2: the quality of the Figure 2 should be improved
Response: Done. We apologize for the unnecessary misunderstandings caused. We have improved the quality of Figure 2 and we hope that the current version is more stringent.
（10）Figure 3: the quality of the Figure 3 should be improved
Response: Done. We apologize for the unnecessary misunderstandings caused. We have improved the quality of Figure 3 and we hope that the current version is more stringent.
（11）Figure 4: the quality of the Figure 4 should be improved
Response: Done. We apologize for the unnecessary misunderstandings caused. We have improved the quality of Figure 4 and we hope that the current version is more stringent.
（12）Legend to the Figure 4: “The larger the area of the ellipse in the graph, the smaller the correlation coefficient between the two indicators; the smaller the area of the ellipse, the larger the correlation coefficient between the two indicators. The direction of the ellipse to the right indicates a positive correlation between the two indicators; the direction of the ellipse to the left indicates a negative correlation between the two indicators” - This explanatory information should be moved from the legend to the results
Response: Done. We sincerely thank the reviewers for their valuable comments. We have moved the explanatory information in the legend of Figure 4 to subsection 3.5 of the Results section (Page 13, Lines 376-378, 383-385). We hope that the current version is more rigorous.
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsThe review of the manuscript titled "Soil carbon and nitrogen pools and their storage characteristics under different vegetation restoration types on the Loess Plateau of Longzhong, China”
This is a third-round review of the manuscript titled "Soil carbon and nitrogen pools and their storage characteristics under different vegetation restoration types on the Loess Plateau of Longzhong, China". All the reviewer’s comments are addressed in detail. The text was significantly improved by the authors. I recommend that the manuscript for some minor corrections.
L691. Replace “Cs and Ns” with “C and N contents/storage”; check everywhere.
Author Response
We appreciate the thorough review from the Editor and reviewers and thanks for the insightful comments and suggestions. We have made the corresponding revisions. We believe that the academic quality of the revised manuscript is improved significantly. Our responses to the reviewers’ comments are addressed individually in details as enclosed.
Response to THE Comments of the manuscript
This is a third-round review of the manuscript titled "Soil carbon and nitrogen pools and their storage characteristics under different vegetation restoration types on the Loess Plateau of Longzhong, China". All the reviewer’s comments are addressed in detail. The text was significantly improved by the authors. I recommend that the manuscript for some minor corrections.
（1）L691. Replace “Cs and Ns” with “C and N contents/storage”; check everywhere.
Response: Done. Thank you for your valuable suggestions. We have changed "Cs and Ns" to "C and N storage " and have checked and revised the rest of the paper. We would like the current version to be more rigorous.
Reviewer 2 Report
Comments and Suggestions for AuthorsDear authors, the work has improved.
Regards
Author Response
Response: On behalf of all the contributing authors, I would like to thank the reviewers very much for their positive and constructive comments on our papers. It is the reviewers' sincere feedback to us that helped to improve the quality of our paper. Once again, I would like to thank the reviewers for their appreciation of our work.
Reviewer 3 Report
Comments and Suggestions for AuthorsDear authors,
you have greatly improved the manuscript. Your explanations are sufficient for me.
Author Response
Response: On behalf of all the contributing authors, I would like to thank the reviewers very much for their positive and constructive comments on our papers. It is the reviewers' sincere feedback to us that helped to improve the quality of our paper. Once again, I would like to thank the reviewers for their appreciation of our work.
