Responses of Soil and Microbial C:N:P Stoichiometry to Vegetation Succession in a Karst Region of Southwest China
Round 1
Reviewer 1 Report
The authors improved the manuscript. Still I have some concerns (see below)
Introduction
L. 46/47 the relative clause should be separated from the rest of the sentence by commas.
L. 53 replace "interacted" with "interconnected"
L. 60 what is "etc." supposed to mean? The authors either have to tell the reader additional factors or delete the "etc."
L. 74 "...where outcropping carbonate rock covers about 51 million ha..." are these really bare rocks? Or have these rocks been parent material for soil formation? Based on the following sentence, it seems that forest grows on these rocks, which means there has to be soil. The authors have to clarify.
L. 77 what is rock desertification?
L. 107 stoichiometric ratio of soil or soil microorganisms?
Materials and Methods
L. 140 still no info about why the 15 top cm were sampled
L. 146 "...was ground to pass through a 0.25 mm sieve..."
Results
L. 202 "...a significant relationshipt was found..."
Discussion
L. 218 ff From here until the end of the section, results are repeated and compared to the results of other studies. Yet, the data is not discussed. If the authors do not have any new results to add to the already existing knowledge from the literature, they should shorten this section and incorporate it into the following section.
Author Response
Point 1: L. 46/47 the relative clause should be separated from the rest of the sentence by commas.
Response 1: Changed as suggested.
Point 2: L. 53 replace "interacted" with "interconnected"
Response 2: Changed as suggested
Point 3: L. 60 what is "etc." supposed to mean? The authors either have to tell the reader additional factors or delete the "etc."
Response 3: We deleted the "etc."
Point 4: L. 74 "...where outcropping carbonate rock covers about 51 million ha..." are these really bare rocks? Or have these rocks been parent material for soil formation? Based on the following sentence, it seems that forest grows on these rocks, which means there has to be soil. The authors have to clarify.
Response 4: Yeah, these rocks are parent material for soil formation. Although some special shrubs can grow on these rocks, most plant species, including all crops, still need to grow on soil. Just because soil formation processes on these bedrocks are quite slow, once soils being lost, it is very hard to restore, so the limited soil resource is quite important for agriculture, or ecological sustainability.
Point 5: L. 77 what is rock desertification?
Response 5: Karst rocky desertification (KRD) refers to a land degradation process, due to the human interference causing continued vegetation degradation, soil and water loss and even loss of resources, land productivity decline, and bedrock exposed similar to that in a desert landscape.
Wang, S., Liu, Q. and Zhang, D. (2004) Karst Rock Desertification in Southwestern China: Geomorphology, Land Use, Impact and Rehabilitation. Land Degradation & Development, 15, 115-121.
Point 6: L. 107 stoichiometric ratio of soil or soil microorganisms?
Response 6: Yes, it is.
Point 7: L. 140 still no info about why the 15 top cm were sampled
Response 7: We added statement about why the top 15 cm were sampled.
Point 8: L. 146 "...was ground to pass through a 0.25 mm sieve..."
Response 8: Changed as suggested.
Results
Point 9: L. 202 "...a significant relationshipt was found..."
Response 9: Corrected as suggested.
Point 10: L. 218 From here until the end of the section, results are repeated and compared to the results of other studies. Yet, the data is not discussed. If the authors do not have any new results to add to the already existing knowledge from the literature, they should shorten this section and incorporate it into the following section.
Response 10: We shortened this section as suggested.
Reviewer 2 Report
GENERAL
The quality of figures 1 and 2 must be improved - it is difficult read vegetation types. I suggest to increase fonts in all axis, and to increase the size and resolution of diagrams.
SPECIFIC
Abstract
Line 20: I suggest to modify the first phrase from: "Spontaneous vegetation succession after agricultural abandonment is a general phenomenon in degraded karst regions of China" to "Spontaneous vegetation succession after agricultural abandonment is a general phenomenon in many areas of the world", because such succession occurs not only in China, but also in temperate areas of Europe and also in tropical and subtropical areas of Latin America and many other regions of the world.
Line 34: please, modify a phrase by adding "in": "...were significantly greater in grassland than in other three...."
1. Introduction
Line 86: Such succession of abandoned agricultural land is, according tomy knowledge, an universal phenomenon not limited only to karst region of southwest China. Such succession, through grassland, shrubland and secondary forest occurs in many areas of the world of different climate (tropical, subtropical, temperate), if the rainfall is sufficient to sustain tree growth. Such information should be easy to find in any book on ecology. I recommend authors to check this, and than add respective citation and reference in the paper.
2. Materials and methods
I recommend to add a figure containing (1) map of China nad approximated location of the study area, and (2) a map of study area showing the topography and location of soil sampling sites. A good example of such map can be found in the paper of Liu et al. (2018, Figure 1), which is available at: https://www.mdpi.com/2071-1050/11/7/2144
Line 123: The authors should revise information regarding soil classification according to WRB 2006, because: (1) in WRB 2006, the group of Lithosols was renamed into Leptosols, and (2) such soils were described as having "..continuous rock within 25cm of the soil surface" or contain "less than 20% (by volume) of fine earth averaged over a depth of 75cm from the soil surface ...". I think, that such soil would not be converted into agricultural land! Moreover, to obtain perfect study, the authors should have taken samples from sim
Lines 133-134 - Table 1: I strongly recommend to complete the table with the information regarding soil (WRB 2006 or 2015 reference group and soil texture class) and topographic data (slope and TWI - topographic wetness index) for each vegetation type within each sampling site. Such data will provide important information on additional factors which could affect the topic. The study would be perfect, if these soil and topographic parameters were identical within each sampling site for different vegetation types. However, if it was not possible, the paper, although less perfect, will be still an valuable publication! In the case of serious differences between vegetation types (succession stages) regarding soil and topography, these factors should be examined as additional causes of differences in C, N and P in soil and microbial biomass.
Line 141: In future studies, I recommend to use more soil cores (20-40) to form a composite sample.
3. Results
Line 198: I would modify the phrase by adding "significantly": "... but did not correlate significantly with TP (Table 2)."
Line 200-201: I would use consequentlythe acronims SMBC, SMBP, EMBN, when referring to content of these elements in microbial biomass. I found this phrase confusing: "....C:N ratio and C:P ratio, as well as C:P ratio and N:P ratio, in the microbial biomass were significantly corretated..." and thus I would rewrite it to: "... SMBC:SMBN ratio and SMBC:SMBP ratio, as well as SMBC:SMBP and SMBN:SMBP ratio were significantly correlated...", if this correspodns in r' intentions. Please, check this part again!
Line 205 - Table 2: Please, use the same acronims for elements in microbial biomass in the first column and in the first line! In the first column, the authors use MBC:MBN, MBC:MBP and MBN:MBP instead of SMBC:SMBN, SMBC:SMBP and SMBN:SMBP.
Line 214: I suggest to replace "profound" by "deep"
Lines 215-216: I would extend this phrase: Soil organic C and total N concetration increased synchronously durin vegetation succession in the soil layer 0-15 cm."
Line Line 216: I suggest to replace "recuperation" with "increase"
Lines 217-218: Please, mention the rocks, which can be a source of nitrogen according to Wen et al. 2016 and Xiao et al. 2018) or remove this information ("... rock N release"). If we exclude peat, guano and similar rocks of organic origin, majority of other rocks do not contain N! Please check it!
Line 22: The C:N ratio in soil of about 10:1 is common not only i subtropical China, but rather throughout a world in mineral soils of different climatic zones.
Line 249, 272, 274: The same suggestion as in the comment referring to lines 200-201.
Line 275: I suggest to replace "diverse" with "different".
Author Response
Point 1: The quality of figures 1 and 2 must be improved - it is difficult read vegetation types. I suggest to increase fonts in all axis, and to increase the size and resolution of diagrams.
Response 1: We improved the figures 1 and 2 as suggested.
Point 2: Line 20: I suggest to modify the first phrase from: "Spontaneous vegetation succession after agricultural abandonment is a general phenomenon in degraded karst regions of China" to "Spontaneous vegetation succession after agricultural abandonment is a general phenomenon in many areas of the world", because such succession occurs not only in China, but also in temperate areas of Europe and also in tropical and subtropical areas of Latin America and many other regions of the world.
Response 2: Modified as suggested.
Point 3: Line 34: please, modify a phrase by adding "in": "...were significantly greater in grassland than in other three...."
Response 3: Modified as suggested.
Point 4: Line 86: Such succession of abandoned agricultural land is, according tomy knowledge, an universal phenomenon not limited only to karst region of southwest China. Such succession, through grassland, shrubland and secondary forest occurs in many areas of the world of different climate (tropical, subtropical, temperate), if the rainfall is sufficient to sustain tree growth. Such information should be easy to find in any book on ecology. I recommend authors to check this, and than add respective citation and reference in the paper.
Response 4: Changed as suggested.
Point 5: I recommend to add a figure containing (1) map of China nad approximated location of the study area, and (2) a map of study area showing the topography and location of soil sampling sites. A good example of such map can be found in the paper of Liu et al. (2018, Figure 1), which is available at: https://www.mdpi.com/2071-1050/11/7/2144
Response 5: We added a figure of the location of study area in the revised manuscript.
Point 6: Line 123: The authors should revise information regarding soil classification according to WRB 2006, because: (1) in WRB 2006, the group of Lithosols was renamed into Leptosols, and (2) such soils were described as having "..continuous rock within 25cm of the soil surface" or contain "less than 20% (by volume) of fine earth averaged over a depth of 75cm from the soil surface ...". I think, that such soil would not be converted into agricultural land! Moreover, to obtain perfect study, the authors should have taken samples from sim
Response 6: The reviewer's comment is right. We revised the information regarding soil classification.
Point 7: Lines 133-134 - Table 1: I strongly recommend to complete the table with the information regarding soil (WRB 2006 or 2015 reference group and soil texture class) and topographic data (slope and TWI - topographic wetness index) for each vegetation type within each sampling site. Such data will provide important information on additional factors which could affect the topic. The study would be perfect, if these soil and topographic parameters were identical within each sampling site for different vegetation types. However, if it was not possible, the paper, although less perfect, will be still an valuable publication! In the case of serious differences between vegetation types (succession stages) regarding soil and topography, these factors should be examined as additional causes of differences in C, N and P in soil and microbial biomass.
Response 7: Thanks for the reviewer's good suggestion. We added some information about topography of the sampling sites.
Point 8: Line 141: In future studies, I recommend to use more soil cores (20-40) to form a composite sample.
Response 8: Thanks for the reviewer's suggestion.
Point 9: Line 198: I would modify the phrase by adding "significantly": "... but did not correlate significantly with TP (Table 2)."
Response 9: Modified as suggested.
Point 10: Line 200-201: I would use consequentlytheacronims SMBC, SMBP, EMBN, when referring to content of these elements in microbial biomass. I found this phrase confusing: "....C:N ratio and C:P ratio, as well as C:P ratio and N:P ratio, in the microbial biomass were significantly corretated..." and thus I would rewrite it to: "... SMBC:SMBN ratio and SMBC:SMBP ratio, as well as SMBC:SMBP and SMBN:SMBP ratio were significantly correlated...", if this correspodns in r' intentions. Please, check this part again!
Response 10: Changed as suggested and checked this part.
Point 11: Line 205 - Table 2: Please, use the same acronims for elements in microbial biomass in the first column and in the first line! In the first column, the authors use MBC:MBN, MBC:MBP and MBN:MBP instead of SMBC:SMBN, SMBC:SMBP and SMBN:SMBP.
Response 11: Changed as suggested.
Point 12: Line 214: I suggest to replace "profound" by "deep"
Response 12: Changed as suggested.
Point 13: Lines 215-216: I would extend this phrase: Soil organic C and total N concetration increased synchronously durin vegetation succession in the soil layer 0-15 cm."
Response 13: Changed as suggested.
Point 14: Line Line 216: I suggest to replace "recuperation" with "increase"
Response 14: Changed as suggested.
Point 15: Lines 217-218: Please, mention the rocks, which can be a source of nitrogen according to Wen et al. 2016 and Xiao et al. 2018) or remove this information ("... rock N release"). If we exclude peat, guano and similar rocks of organic origin, majority of other rocks do not contain N! Please check it!
Response 15: We changed the related statement as suggested.
Point 16: Line 22: The C:N ratio in soil of about 10:1 is common not only i subtropical China, but rather throughout a world in mineral soils of different climatic zones.
Response 16: The reviewer's comment is right.
Point 17: Line 249, 272, 274: The same suggestion as in the comment referring to lines 200-201.
Response 17: Changed as suggested.
Point 18: Line 275: I suggest to replace "diverse" with "different".
Response 18: Changed as suggested.
Round 2
Reviewer 1 Report
Points to be changed:
Answer to point 5: It would be good to explain this to the reader.
Answer to point 6: My question has not been answered.
Answer to point 7: The statement added by the authors is wrong. The layer with highest microbial activity and organic matter can easily extent or remain below a depth of 15 cm. The authors should adapt their statement to something like: "...which we assumed to be the layer with...".
Author Response
Answer to point 5: It would be good to explain this to the reader.
Response: We added this explanation in the revised manuscript.
Answer to point 6: My question has not been answered.
Response: Sorry. It is the stoichiometric ratio of soil. We have corrected it in the revised manuscript. Answer to point 7: The statement added by the authors is wrong. The layer with highest microbial activity and organic matter can easily extent or remain below a depth of 15 cm. The authors should adapt their statement to something like: "...which we assumed to be the layer with...".
Response: Thanks very much for the reviewer's criticism and good suggestion. We adapted our statement in the revised manuscript as suggested.
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
In this study C, N and P in bulk soils and soil microbial biomass in topsoils of southwestern China were studied. Overall, this study addresses an important topic with potential significant implications on other studies dealing with C:N:P stoichiometry and feedbacks from soil to vegetation and vice versa. Unfortunately, this manuscript does not meet the standards of an international scientific journal in scientific language, citation and structure.
I don't think it is a reviewer's job to edit the manuscript and make it scientifically correct. That is why I have reviewed only the first six pages of manuscript as an example.
Line 23-24: I wouldn't just say in this region. It is rather a general problem.
Line 35-37: Please explain how soil and microbial stoichiometry responded. Please specify the statement “responded diversely”.
Line 37: "Further work" is always good, but I think it should be mentioned exactly what exactly is necessary to know in the future. Otherwise, remove this very general expression from the abstract.
Introduction in general:
I think you have overused the frequency of citations a little. General paradigms are usually presented in the introduction. You don't have to prove every half sentence.
Please rethink your positioning of your quotes as well. For example: You use Bui and Henderson 2013, Zechmeister-Boltenstern et al. 2015 in line 51 for a general statement. Later in lines 58 and 59 you again use the same publications to substantiate the statement, which are more detailed.
What is the difference an karst ecosystem special
Line 44: Carbon (C), Nitrogen (N) and Phosphorus (P)…
Line 45: “C, N and P are tightly coupled” I guess that's a question you want to answer, isn't it?!
Line 66: atomic ->molar
Line 74: I do not understand why karst landscapes should be critical to the earth’s surface system.
Line75: exposed or outcropped? Please decide.
Line 76: Please remove “Wang et al. 2004”. One is sufficiend
Line 82: Are there citations for these projects?
Line 85: Maybe a more scientific way of writing would be appropriate. Remove “Remarkably”. Plea, explain why the karst region of southwest China is also becoming a new hotspot for C sequestration in the world. Is it important for your research questions?
Line: 104-107: You mentioned that already above
Line: 107: It is not a Hypothesis that the soil C:N:P stoichiometry would change . Please explain how and why you expect that change.
Line: 108-110: Please phrase the second hypothesis better and more precisely.
Line 109: Maybe it is better to explain "homeostatic" before you use it. You have done this in lines 236-239.
115-121: A very broad description of the study area and very little information on the specific sampling spots. Please describe the soil according to the World Reference Base for Soil Resources (WRB).
144-149: Cite the methods.
144-157: There are two chapter 2.3
Author Response
Response to Reviewer 1 Comments
In this study C, N and P in bulk soils and soil microbial biomass in topsoils of southwestern China were studied. Overall, this study addresses an important topic with potential significant implications on other studies dealing with C:N:P stoichiometry and feedbacks from soil to vegetation and vice versa. Unfortunately, this manuscript does not meet the standards of an international scientific journal in scientific language, citation and structure.
I don't think it is a reviewer's job to edit the manuscript and make it scientifically correct. That is why I have reviewed only the first six pages of manuscript as an example.
Point 1: Line 23-24: I wouldn't just say in this region. It is rather a general problem.
Response 1: Deleted “in this region” as suggested.
Point 2: Line 35-37: Please explain how soil and microbial stoichiometry responded. Please specify the statement “responded diversely”.
Response 2: We have described how soil and microbial stoichiometry respond to vegetation succession.
Point 3: Line 37: "Further work" is always good, but I think it should be mentioned exactly what exactly is necessary to know in the future. Otherwise, remove this very general expression from the abstract.
Response 3: We removed this very general expression as suggested.
Introduction in general:
Point 4: I think you have overused the frequency of citations a little. General paradigms are usually presented in the introduction. You don't have to prove every half sentence.
Please rethink your positioning of your quotes as well. For example: You use Bui and Henderson 2013, Zechmeister-Boltenstern et al. 2015 in line 51 for a general statement. Later in lines 58 and 59 you again use the same publications to substantiate the statement, which are more detailed.
Response 4: Changed as suggested.
Point 5: What is the difference an karst ecosystem special
Response 5: Thanks very much for pointing out this problem. We improved our quotes throughout the revised manuscript.
As compared to other ecosystem, karst ecosystems can be characterized for fragile habitat, shallow soil layer, high calcium, high pH, etc. Therefore, the biogeochemical cycling of elements may differ from other ecosystems.
Point 6: Line 44: Carbon (C), Nitrogen (N) and Phosphorus (P)…
Response 6: Changed as suggested.
Point 7: Line 45: “C, N and P are tightly coupled” I guess that's a question you want to answer, isn't it?!
Response 7: Yes, it is.
Point 8: Line 66: atomic ->molar
Response 8: Changed as suggested.
Point 9: Line 74: I do not understand why karst landscapes should be critical to the earth’s surface system.
Response 9: Karst areas represent an important environment for various reasons. First, karst landscapes occupy up to 10% of the Earth’s land surface. Karst aquifers contain the most important water resources of mountainous countries, and as much as a quarter of the world’s population is supplied by karst water. Second, karst landscapes are sometimes referred to as very conservative because the action of surficial runoff is low. Moreover in karst areas we find underground systems of caves: these probably are the most conservative environments of the earth surface. In them we can find records of the main environmental changes that occurred during the evolution of deep karst. Third, in karst environments we often find important biotopes with endemic and relict species. So, karst landscapes play an important role in biodiversity conservation.
On the other hand, karst responds with great sensitivity to environmental changes, and karst features (especially speleothems) contain many clues to past climatic and hydrological events and changes at a variety of time scales. It is uncertain whether future conditions can be interpreted from karst features, because many changes tend to be abrupt and discontinuous (Taminskas et al., 2006).
Taminskas, J. , Paskauskas, R. , Zvikas, A. , & Satkunas, J. . (2006). Karst and Ecosystems. Geology and Ecosystems. Springer US.
Point 10: Line75: exposed or outcropped? Please decide.
Response 10: We deleted exposed in the revised manuscript.
Point 11: Line 76: Please remove “Wang et al. 2004”. One is sufficient
Response 11: Changed as suggested.
Point 12: Line 82: Are there citations for these projects?
Response 12: We have added some citations for these projects.
Point 13: Line 85: Maybe a more scientific way of writing would be appropriate. Remove “Remarkably”. Plea, explain why the karst region of southwest China is also becoming a new hotspot for C sequestration in the world. Is it important for your research questions?
Response 13: Removed “Remarkably” as suggested. Since the Chinese government has implemented a series of ecological restoration projects, especially in the degraded karst region of southwest China, large scale vegetation restoration results in enormous C sequestration in the terrestrial ecosystem. On the other hand, it is generally recognized that potential for C sequestration in the terrestrial ecosystem can be largely limited by nutrient availability, including N and P. Changes in soil nutrient stoichiometry may have great consequences for C sequestration. Therefore, a better understanding of the changes in soil nutrient stoichiometry would help predict regional C sequestration potential more accurately.
Point 14: Line: 104-107: You mentioned that already above
Response 14: Removed the relate sentence as suggested.
Point 15: Line: 107: It is not a Hypothesis that the soil C:N:P stoichiometry would change . Please explain how and why you expect that change.
Response 15: We revised the hypothesis as suggested.
Point 16: Line: 108-110: Please phrase the second hypothesis better and more precisely.
Response 16: We rephrased the second hypothesis as suggested.
Point 17: Line 109: Maybe it is better to explain "homeostatic" before you use it. You have done this in lines 236-239.
Response 17: Changed as suggested.
Point 18: 115-121: A very broad description of the study area and very little information on the specific sampling spots. Please describe the soil according to the World Reference Base for Soil Resources (WRB).
Response 18: We have added the related description of the soil as suggested.
Point 19: 144-149: Cite the methods.
Response 19: We have added citations for the methods.
Point 20: 144-157: There are two chapter 2.3
Response 20: Sorry for this negligence. We have corrected it.
Reviewer 2 Report
The manuscript investigates soil and microbial C:N:P ratios in different stages of vegetation succession. The manuscript is generally well-written with respect to language and may be suitable for publishing in Forests. Based on the content of the discussion, however, I do not see any novelty. The authors should revise their discussion accordingly and highlight what makes their study different from others/what kind of novel conclusions could be drawn from the data.
Conclusions and abstract should then be revised accordingly. More detailed comments below.
Abstract
L. 21 I recommend to remove the ":" since it is a list of elements.
L. 31 What do these abbreviations stand for?
Introduction
L. 65 what kind of biomass? Plant, microbial?
Materials and Methods
L. 116 "..., which belongs..."
L. 121 according to which classification system? Reference?
L. 134 a blank is missing in this sentence.
L. 135 How far were the sampling sites from each other?
L. 136 Why were the top 15 cm sampled? Do they correspond to genetic soil horizons?
L. 140 "stones"
L. 142 Why was only the fraction of soil <0.25 mm analyzed for C, N, and P?
L. 145 Reference for the method?
L. 146/147 Reference for the method?
L. 176 What is MBC, MBN, MBP? Shouldn't this be SMBC, SMBN, SMBP? This has to be revised throughout the manuscript.
Results
L. 189 The correlation analyses were not mentioned in the Materials and Methods and should be added to that section.
Discussion
L. 215 - 222 If other studies found the same, what is new with the current data? The authors should elaborate more the novelty of their data (if any) with respect to other studies, perhaps also with respect to management strategies or implications for the karst region of China.
L. 233 "This could result..." or "This could have resulted..."
L. 245/246 Similar to one of my previous comments: If many other studies have shown that microbial C:N:P stoichiometry is variable, what are the novel findings of the current study?
Figure 1 and 2 An indication is missing of what the letters in the panels stand for.
Table 2 Which data was correlated here? Data across all vegetation sites? What is the rationale behind this? What do the asterisks indicate?
Author Response
Response to Reviewer 2 Comments
The manuscript investigates soil and microbial C:N:P ratios in different stages of vegetation succession. The manuscript is generally well-written with respect to language and may be suitable for publishing in Forests. Based on the content of the discussion, however, I do not see any novelty. The authors should revise their discussion accordingly and highlight what makes their study different from others/what kind of novel conclusions could be drawn from the data.
Conclusions and abstract should then be revised accordingly. More detailed comments below.
Abstract
Point 1: L. 21 I recommend to remove the ":" since it is a list of elements.
Response 1: changed as suggested. Point 2: L. 31 What do these abbreviations stand for?
Response 2: SMBC and SMBN stand for soil microbial biomass C and microbial biomass N. We have added the full name in the revised manuscript. Introduction
Point 3: L. 65 what kind of biomass? Plant, microbial?
Response 3: It is microbial biomass. We specified it in the revised manuscript.
Materials and Methods
Point 4: L. 116 "..., which belongs..."
Response 4: Corrected in the revised manuscript. Point 5: L. 121 according to which classification system? Reference?
Response 5: The soil is categorized according to the FAO classification system. We have added the reference in the revised manuscript. Point 6: L. 134 a blank is missing in this sentence.
Response 6: Corrected in the revised manuscript.
Point 7: L. 135 How far were the sampling sites from each other?
Response 7: The distance for the adjacent sampling sites ranged from about 500 m to 2 km. We have supplemented related interpretation in the revised manuscript.
Point 8: L. 136 Why were the top 15 cm sampled? Do they correspond to genetic soil horizons?
Response 8: It does not correspond to genetic soil horizons, and just roughly represent the surface soil, like other studies (Xiao et al., 2018; Wang et al., 2018).
Xiao, K., Li, D., Wen, L., Yang, L., Luo, P., & Chen, H., et al. (2018). Dynamics of soil nitrogen availability during post-agricultural succession in a karst region, southwest china. Geoderma, 314, 184-189.
Wang, M., Chen, H., Wei, Z., & Wang, K. (2018). Soil nutrients and stoichiometric ratios as affected by land use and lithology at county scale in a karst area, southwest china. Science of the Total Environment, 619, 1299-1307.
Point 9: L. 140 "stones"
Response 9: Corrected in the revised manuscript.
Point 10: L. 142 Why was only the fraction of soil <0.25 mm analyzed for C, N, and P?
Response 10: Sorry for making confusion here. In fact, soils were air-dried, ground and passed through 0.25 mm sieve to measure total soil C, N, and P. We supplemented “ground” in the revised manuscript to avoid confusion.
Point 11: L. 145 Reference for the method?
Response 11: Reference for the method has been added in the revised manuscript.
Point 12: L. 146/147 Reference for the method?
Response 12: Reference for the method has been added in the revised manuscript.
Point 13: L. 176 What is MBC, MBN, MBP? Shouldn't this be SMBC, SMBN, SMBP? This has to be revised throughout the manuscript.
Response 13: Sorry for this confusion. We uniformed the presentation throughout the manuscript, i.e. SMBC, SMBN, and SMBP.
Results
Point 14: L. 189 The correlation analyses were not mentioned in the Materials and Methods and should be added to that section.
Response 14: We added the statement of correlation analyses in the section of Materials and Methods.
Discussion
Point 15: L. 215 - 222 If other studies found the same, what is new with the current data? The authors should elaborate more the novelty of their data (if any) with respect to other studies, perhaps also with respect to management strategies or implications for the karst region of China.
Response 15: Thanks for the reviewer’s critical comments. Although a number of studies have investigated the changes in stoichiometry of nutrients, few have comprehensively taken both soil and microbial nutrient stoichiometry into account. The results of this study supplemented the knowledge about the characteristics of nutrient stoichoimetry in soil and microorganisms in the karst ecosystems.
Point 16: L. 233 "This could result..." or "This could have resulted..."
Response 16: Corrected as suggested.
Point 17: L. 245/246 Similar to one of my previous comments: If many other studies have shown that microbial C:N:P stoichiometry is variable, what are the novel findings of the current study?
Response 17: Although a number of studies have investigated the changes in stoichiometry of nutrients, few have comprehensively taken both soil and microbial nutrient stoichiometry into account. Therefore, these results could help advance our understanding of the covariation and interaction between soil and microorganisms.
Point 18: Figure 1 and 2 An indication is missing of what the letters in the panels stand for.
Table 2 Which data was correlated here? Data across all vegetation sites? What is the rationale behind this? What do the asterisks indicate?
Response 18: Different letters denote significant difference between successional stages at P < 0.05.
Table 2 showed the Pearson’s correlation coefficients (r) between stoichiometric ratios of C:N, C:P and N:P in the soil and microbial biomass across all vegetation sites. The asterisks indicate correlation is significant at P < 0.05 and P < 0.01, respectively. We have added related interpretation in the revised manuscript.
Reviewer 3 Report
The authors present soil and microbial C, N and P data from a series of vegetation types reflecting a successional gradient in a degraded karst landscape. The study objectives are useful and for the most part the paper is well written and adequately presented. My major concern is the layout of the study as it is not clear whether the six sampling sites per vegetation type are truly replicates (see below). Clarifying a few key points will also help the manuscript as follows:
· Line 135. Are these six sampling sites independent enough to be considered true replicates, or are they all from a contiguous area of each vegetation type? Latitude and longitude should be provided for each sampling site in a Table, or/and some comment about distance between sampling sites. Most importantly, if the 6 sites are clustered within each vegetation type then the data should not be treated as replicates in the ANOVA but subsamples instead (i.e., avoid pseudoreplication)
· Total P with an acid digestion includes inorganic and organic forms. In their review, Tipping et al. (2016. Biogeochemistry 130: 117-131) emphasized that carbon ratios should be based on organic P, rather than total P, to be truly focused on soil organic matter dynamics. The authors should either do the same or alternatively describe how C:P ratios etc. would compare between measures of total P and organic P.
· Figures 1 and 2 are too small and of low resolution, it is difficult to appraise them on the printed page.
· Line 215-222. This is a critical discussion point and I question whether C:P or N:P ratios alone adequately reflect P deficiencies. Note that soil P was not significantly different among the 4 vegetation types (Fig. 1c), rather it was C and N that changed. In the literature, ecosystem P deficiencies are generally linked to a measureable loss in P supply (e.g., Vitousek et al. 2010. Ecological Applications 20: 5-15). Can the authors provide better evidence that this vegetation is exhibiting P deficiencies? If so, how might they explain the nature of P deficiencies where total P is unchanged?
· Line 173, 236. To gauge the degree of microbial homeostasis it would also be helpful to see the relationship directly between microbial N and P with soil N and P concentrations, rather than solely across these vegetation types.
· Line 247. Forest ecosystems generally have more fungal biomass than earlier successional stages, and furthermore it is apparent that symbiotic fungi can have quite distinct stoichiometry compared to saprotrophic fungi (Kranabetter et al. 2019. New Phytologist 221: 482-492). What is the mycorrhizal nature of the secondary and primary forests (many readers will be unfamiliar with the species listed in Table 1)? Is there any information on how bacterial and fungal biomass would compare across these vegetation types?
Author Response
Response to Reviewer 3 Comments
The authors present soil and microbial C, N and P data from a series of vegetation types reflecting a successional gradient in a degraded karst landscape. The study objectives are useful and for the most part the paper is well written and adequately presented. My major concern is the layout of the study as it is not clear whether the six sampling sites per vegetation type are truly replicates (see below). Clarifying a few key points will also help the manuscript as follows:
Point 1: Line 135. Are these six sampling sites independent enough to be considered true replicates, or are they all from a contiguous area of each vegetation type? Latitude and longitude should be provided for each sampling site in a Table, or/and some comment about distance between sampling sites. Most importantly, if the 6 sites are clustered within each vegetation type then the data should not be treated as replicates in the ANOVA but subsamples instead (i.e., avoid pseudoreplication)
Response 1: Yes, six sampling sites for each successional stage were independent. The distance for each sampling sites ranged from about 500 m to 2 km.
Point 2: Total P with an acid digestion includes inorganic and organic forms. In their review, Tipping et al. (2016. Biogeochemistry 130: 117-131) emphasized that carbon ratios should be based on organic P, rather than total P, to be truly focused on soil organic matter dynamics. The authors should either do the same or alternatively describe how C:P ratios etc. would compare between measures of total P and organic P.
Response 2: Thanks for the reviewer’s helpful suggestion. In the current study, we could not examine the difference in C:P ratios between measures of total P and organic P, since no data is available on P speciation.
Point 3: Figures 1 and 2 are too small and of low resolution, it is difficult to appraise them on the printed page.
Response 3: Figures 1 and 2 have been changed to improve definition.
Point 4: Line 215-222. This is a critical discussion point and I question whether C:P or N:P ratios alone adequately reflect P deficiencies. Note that soil P was not significantly different among the 4 vegetation types (Fig. 1c), rather it was C and N that changed. In the literature, ecosystem P deficiencies are generally linked to a measureable loss in P supply (e.g., Vitousek et al. 2010. Ecological Applications 20: 5-15). Can the authors provide better evidence that this vegetation is exhibiting P deficiencies? If so, how might they explain the nature of P deficiencies where total P is unchanged?
Response 4: As the reviewer pointed out, the stoichiometric ratios of C:P or N:P in bulk soil or microbial biomass alone cannot adequately reflect ecosystem P deficiency, but they also serve as important indicators. Our results is in line with the finding of Zhang et al (2015), based on community foliar N:P and other indicators, showing that the grassland in the karst region of southwest China is N limited, that the secondary and primary forests are P limited, and that the shrubland is constrained by N and P together or by other nutrients
Reference
Zhang Wei, Zhao Jie, Pan Fujing, Li Dejun, Chen Hongsong, Wang Kelin. (2015). Changes in nitrogen and phosphorus limitation during secondary succession in a karst region in southwest china. Plant and Soil, 391(1-2), 77-91.
Point 5: Line 173, 236. To gauge the degree of microbial homeostasis it would also be helpful to see the relationship directly between microbial N and P with soil N and P concentrations, rather than solely across these vegetation types.
Response 5: Thanks for the reviewer’s good suggestion. We have added information about the relationship between microbial N and P with soil N and P concentrations in Table 2 in the revised manuscript. As shown in Table 2, there were no significant relationships between soil N and microbial biomass N (r = 0.22, P > 0.05), and microbial biomass C and P as well, while soil P and microbial biomass P correlated significantly (r = 0.46, P < 0.05), as well as microbial biomass C and N, indicating that soil P is a critical limiting nutrient for microbial growth in the karst region.
Point 6: Line 247. Forest ecosystems generally have more fungal biomass than earlier successional stages, and furthermore it is apparent that symbiotic fungi can have quite distinct stoichiometry compared to saprotrophic fungi (Kranabetter et al. 2019. New Phytologist 221: 482-492). What is the mycorrhizal nature of the secondary and primary forests (many readers will be unfamiliar with the species listed in Table 1)? Is there any information on how bacterial and fungal biomass would compare across these vegetation types?
Response 6: Thanks for this very professional question. In the current study, we did not analyze the microbial community structure. However, as a reference, Zhao et al (2019) recently reported that the abundances of the two fungal biomarkers AMF (16:1ω5c) and 18:1ω9c were varied with vegetation succession in a karst mountain ecosystem, southwest China. The values of 18:1ω9c increased in the following order: Grassland < Shrubland < Secondary forest < Primary forest. The abundance of AMF was highest in the grassland, lowest in the primary forest, and intermediate in the secondary forest. For the Fungal: Bacterial ratio, a decrease along the vegetation succession was obtained, from 0.16 under grassland stage to 0.11 under natural forest stage at 0–10 cm depth. Therefore, the changes in soil microbial community may contribute largely to the changes in nutrient stoichiometric ratio in the microbial biomass
Reference:
Zhao Chang, Long Jian, Liao Hongkai, Zheng Chunli, Li Juan, Liu Lingfei, Zhang Mingjiang.2019. Dynamics of soil microbial communities following vegetation succession in a karst mountain ecosystem, southwest China. Scientific Reports, 9:2160
