the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 14 Dec 2022
Effects of Warming and Increased Precipitation on Soil Microbial Residues on the Qinghai–Tibet Alpine Meadows
Abstract. Amino sugars, as the biomarkers of microbial residues, help explore soil microorganisms’ response to global climate change. However, research on how microorganisms in the alpine meadows regulate the soil carbon cycle under the influence of climate change is limited. We hypothesized that climate change might cause different effects on soil microbial residues due to the impact on soil physical properties, chemical properties, and enzyme activities. Therefore, we conducted four-year continuous warming and increased precipitation experiments in the semi-arid grasslands to examine the differences in soil microbial residues at different depths under simulated changes. The results showed warming stimulated the accumulation of microbial residues, while increased precipitation led to their decline. The Glucosamine/Muramic Acid ratio trend indicates that the contribution of fungal residues was more significant than that of bacteria with increased precipitation, whereas that of bacterial residues exceeded that of fungi with warming. The increased precipitation had no significant effect on soil extracellular enzyme activities and amino sugar concentrations. In addition, changes in the different enzyme activities led to soil carbon loss and different amino sugar accumulation patterns under the warming treatment. These results may aid in assessing the responses of soil microorganisms to future climate change scenarios.
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RC1: 'Comment on egusphere-2022-1290', Anonymous Referee #1, 31 Dec 2022
Weng et al. studied the warming and increased precipitation effects on soil microbial necromass, they found the different response of residue to warming and increased precipitation. The research topic is very relevant especially under the multiple global change scenarios. However, there exists some flaws to prevent the current version to publish. Specific comments are as follows:
Abstract:
L 10-15: “The results showed warming stimulated the accumulation of microbial residues, while increased precipitation led to their decline.” This contradicts the contents of Table 3. From Table3, I can see that warming slightly decrease amino sugars concentrate but increased precipitation increase their concentrate. Please check which one is correct.
L 15: the contribution of fungal residue to what. SOC or microbial residue?
L 15-20: “The increased precipitation had no significant effect on soil extracellular enzyme activities and amino sugar concentrations”. Authors wrote that 'increased precipitation led to their decline' (L 10-15). However, increased precipitation do not affect amino sugar in here. It is very confused. Is there a different “accumulation of microbial residues” between “amino sugar concentrations”?
Introduction:
L 30-35: “Indicators of bacterial and fungal biomass.” It should be necromass or residue rather living biomass.
L 30-35: “amino sugars can be effective indicators for studying the different mechanisms of soils” Which mechanisms you mean here, please clarify.
L 40: “aboveground and underground biomass” it is should be “aboveground and underground plant biomass”
L 40-45: “Existing research on how the soil responds to climate change has primarily been based
on transect data, including soil respiration, carbon, nitrogen pools, and pH” This sentence makes no sense here.
L 60: The hypothesis is too general, it should be more specific and given the correspond explanation.
Second paragraph of Introduction Section: the key point of this paragraph in unclear, author should not give many statements about enzymes. The objective of this paper is global change effects on amino sugars, these should be strengthened. The last few sentences of the second paragraph are pretty weak, it doesn't make any sense to me.
L 60-65: “soil extracellular enzyme activity, biomass, and C and N concentrations for 4 scenarios in 4 fields.” The C and N content of what? soil or microbe?
Material and methods:
The duration of the experiment is not introduced. Please clarify that why increasing rainfall only in July and August.
L75-80: Please move the relevant content about “Soil moisture and temperatures measurement” to Section 2.2.
L 85-90: I wonder what biomass is this, microbial biomass? Soil faunal biomass? Please clarify that “Biomass” is actually plant biomass.
L 120-125: I am not sure why author use glucose as the internal standard 2. As far as know, it should be N-methylglucamine.
Section 2.3 : The other analysis such as correlation analysis and variance analysis should be added.
Results:
L 140-145: 3 Material and methods. It should be results.
“3.2.2 Soil extracellular enzyme and amino sugars” I can not find anything about the enzymes in this section.
Discussion:
L 200-205: I am not sure why decline in GalN will decrease the proportion of GluN in ASs.
L 215-220: If “fungal residues are more difficult to decompose than bacterial”. Bacterial necromass will be degraded faster, and the fungal necromass will be persisted longer. The more fungal necromass and less bacterial necromass should increase GluN/MurN ratio.
L 235-250: Discussion about mechanisms of warming effects on amino sugars is pretty weak, please add more related content.
L 260-265: Why TC inhibit the synthesis of GluN, and TN inhibit GalN but increase MurA? Can authors please explain these phenomenon. “It may be since increased nitrogen input can attenuate soil respiration (Xing et al., 2022), affecting different microbiota evolution.” This is oversimplify for me.
L 275-280: It's pH, not PH.
Table 1 and 3: I can not see the significance between treatments. Also, is there any interaction effects of warming and increased precipitation on amino sugars?
Figures 4-6: Authors should combine all amino sugars (GluN, MurN, GalN) into one SEM, rather than measuring the global change effects on GluN, MurN, and GalN separately.
Citation: https://doi.org/10.5194/egusphere-2022-1290-RC1 -
AC1: 'Reply on RC1', Zhaoyu Dong, 23 Jan 2023
We thank the reviewer for his/her positive evaluation of our manuscript. We address below all the comments and criticisms raised.
Abstract:
Line 10-15: “The results showed warming stimulated the accumulation of microbial residues, while increased precipitation led to their decline.” This contradicts the contents of Table 3. From Table3, I can see that warming slightly decrease amino sugars concentrate but increased precipitation increases their concentrate. Please check which one is correct.
Response: We checked the data and structural equations in Table 3. We believe the main reason is that although air temperature has a negative effect on the amino sugars in Table 3, this effect is not statistically significant (see Table S2). In the structural equation model, the increase of air temperature was connected with amino sugar through indirect and insignificant direct effects. In all, we will emphasize important results and significant conclusions in the revised manuscript.
Line 15: the contribution of fungal residue to what. SOC or microbial residue?
Response: It means the contribution of fungal residues was more significant than that of bacteria to soil nitrogen transformation and accumulation.
Line 15-20: “The increased precipitation had no significant effect on soil extracellular enzyme activities and amino sugar concentrations”. Authors wrote that 'increased precipitation led to their decline' (L 10-15). However, increased precipitation do not affect amino sugar in here. It is very confused. Is there a different “accumulation of microbial residues” between “amino sugar concentrations”?
Response: Sorry for the vague words. Our original intention is the change of amino sugar reflected by the increase of precipitation in Table 3, but this change is not significant. We will modify this part of the expression.
Introduction:
Line 30-35: “Indicators of bacterial and fungal biomass.” It should be necromass or residue rather living biomass.
Response: We will replace “Indicators of bacterial and fungal biomass” with “Indicators of bacterial and fungal residue” in the revised manuscript.
Line 30-35: “amino sugars can be effective indicators for studying the different mechanisms of soils” Which mechanisms you mean here, please clarify.
Response: The characteristics of soil amino sugar accumulation and change reflect the microbial regulation mechanism of soil organic matter cycle.
Reference: Li, L., Wilson, C.B., He, H., Zhang, X., Zhou, F., Schaeffer, S.M., 2019. Physical, biochemical, and microbial controls on amino sugar accumulation in soils under long-term cover cropping and no-tillage farming. Soil Biology and Biochemistry 135, 369-378.
Line 40: “aboveground and underground biomass” it is should be “aboveground and underground plant biomass”
Response: We agree and will make the change in the revised manuscript.
Line 40-45: “Existing research on how the soil responds to climate change has primarily been based on transect data, including soil respiration, carbon, nitrogen pools, and pH” This sentence makes no sense here.
Response: We agree and will remove the sentence in the revised manuscript.
Line 60: The hypothesis is too general, it should be more specific and given the correspond explanation.
Response: We organize the hypotheses and add hypotheses about the impact of depth on amino sugars, as follows:
Our hypotheses were (1) that warming and increased precipitation might cause opposite effects on soil microbial residues due to the impact on soil physical properties, chemical properties, and enzyme activities; (2) that increased depth would facilitate amino sugar accumulation in soil. To test the hypothesis, we examined GluN, MurA, GalN, soil extracellular enzyme activity, biomass, and C and N concentrations for 4 scenarios in 4 fields. We applied these data to structural equation modeling to identify key drivers of climate change impacts on soil microbial residues.
Second paragraph of Introduction Section: the key point of this paragraph in unclear, author should not give many statements about enzymes. The objective of this paper is global change effects on amino sugars, these should be strengthened. The last few sentences of the second paragraph are pretty weak, it doesn't make any sense to me.
Response: Thank you for your comments. We will shorten the statements about enzymes and strengthen the global change effects on amino sugars in the revised manuscript.
Line 60-65: “soil extracellular enzyme activity, biomass, and C and N concentrations for 4 scenarios in 4 fields.” The C and N content of what? soil or microbe?
Response: What we want to express is the soil C and N concentrations in the four sites.
Material and methods:
The duration of the experiment is not introduced. Please clarify that why increasing rainfall only in July and August.
Response: We will introduce the duration of the experiment in the revised manuscript, which is a four-year continuous warming and increased precipitation experiment. In addition, we will introduce the reason why the experiment is set in July and August, which is that the precipitation in July and August is concentrated, and according to the results of the future Shared Socioeconomic Pathways, the future precipitation in our study area will increase the fastest in July and August.
Line75-80: Please move the relevant content about “Soil moisture and temperatures measurement” to Section 2.2.
Response: We agree and will move the relevant content about “Soil moisture and temperatures measurement” to Section 2.2 in the revised manuscript.
Line 85-90: I wonder what biomass is this, microbial biomass? Soil faunal biomass? Please clarify that “Biomass” is actually plant biomass.
Response: Yes, we are referring to plant biomass, and we will clarify in the revised manuscript.
Line 120-125: I am not sure why author use glucose as the internal standard 2. As far as know, it should be N-methylglucamine.
Response: We agree and will change this sentence to the following:
- methylglucamine (internal standard 2) was thoroughly mixed and freeze-dried for 8 h and then derivatized with nitrile acetyl ester.
Section 2.3: The other analysis such as correlation analysis and variance analysis should be added.
Response: We agree and will add correlation analysis and variance analysis to Section 2.2 in the revised manuscript.
Results:
Line 140-145: 3 Material and methods. It should be results.
Response: We are very sorry for such an error, which we have corrected in the revised manuscript.
“3.2.2 Soil extracellular enzyme and amino sugars” I can not find anything about the enzymes in this section.
Response: We're sorry for the subtitle; it should be "Warming Treatment".
Discussion:
Line 200-205: I am not sure why decline in GalN will decrease the proportion of GluN in TASs.
Response: We are sorry vague sentence caused your misunderstanding. Both the effect of increasing temperature on the reduction of GluN in the experiment and the indirect positive effect shown in the structural equation model are insignificant. Although the concentration of GluN decreases during the warming treatment, the proportion of GluN in TAS increases because the concentration of GalN decreases more significantly. In the revised manuscript, we will pay more attention to the prominent transcriptional regularities and clarify the reasons for the contradictory regularities more clearly.
Line 215-220: If “fungal residues are more difficult to decompose than bacterial”. Bacterial necromass will be degraded faster, and the fungal necromass will be persisted longer. The more fungal necromass and less bacterial necromass should increase GluN/MurN ratio.
Response: Thank you for your suggestion. We will refine this section in the revised manuscript.
Line 235-250: Discussion about mechanisms of warming effects on amino sugars is pretty weak, please add more related content.
Response: Under the condition of warming, the aeration in the soil is improved when the soil moisture is reduced, and the reduction of soil moisture will not only reduce the soil microbial carbon accumulation effect by more than 20 times but also effectively reduce the soil inorganic nitrogen content. The previous research results are relatively similar to the impact path shown by the structural equation model in this study. We will supplement this part in the revised manuscript.
Line 260-265: Why TC inhibit the synthesis of GluN, and TN inhibit GalN but increase MurA? Can authors please explain these phenomenon. “It may be since increased nitrogen input can attenuate soil respiration (Xing et al., 2022), affecting different microbiota evolution.” This is oversimplify for me.
Response: After comparison, TC and TN negatively impact GluN and GalN, while muramic acid will increase with the increase of TC and TN. But it is worth noting that these paths are all indirect paths or insignificant paths. In general, soils with higher nitrogen concentration will have higher amino sugar content due to the high nutrient environment that favors microbial anabolism. However, the reason for the different turnover rules of GluN and GalN may be that the microbial community in central Tibet mentioned in this study is dominated by actinomycetes and bacteria, and the transcription process of MurA in bacterial residues is more clear.
Line 275-280: It's pH, not PH.
Response: We agree and will make the change in the revised manuscript.
Table 1 and 3: I can not see the significance between treatments. Also, is there any interaction effects of warming and increased precipitation on amino sugars?
Response: We put the significance in the supplementary Figure S1-2.
According to the conclusion of the structural equation model, there is no significant effect. As far as the interaction is concerned, the path coefficients between amino sugars are not significant, which has no practical significance.
Figures 4-6: Authors should combine all amino sugars (GluN, MurN, GalN) into one SEM, rather than measuring the global change effects on GluN, MurN, and GalN separately.
Response: We agree and will combine all amino sugars into one SEM in the revised manuscript.
Citation: https://doi.org/10.5194/egusphere-2022-1290-AC1
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AC1: 'Reply on RC1', Zhaoyu Dong, 23 Jan 2023
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RC2: 'Comment on egusphere-2022-1290', François Maillard, 12 Jan 2023
This study investigates how experimental warming and precipitation modifications affect the accumulation and composition of microbial residues in soils. The authors also quantified how soil parameters and enzyme activities respond to increased warming and precipitation. They found that increased warming and precipitation induced modifications in most measured parameters. I believe this type of work is timely and important to understand how future climates will influence the stabilization and persistence of microbial residues in soils. Yet, this manuscript presents major caveats that, I think, make it not suitable for publication in its actual state. Most notably, there is no explanation of the logical links between the different measured parameters (soil parameters, enzyme activities, and microbial residue concentrations and compositions). This makes the introduction and the discussion sections rather challenging to understand. Additionally, the authors often mixed living microbial communities and microbial residues. Finally, I have some concerns about the statistics used by the authors, notably the structural equation models.
Please see below for my feedback, which I hope might help to improve the overall quality of the manuscript.
Best regards,
Dr. François Maillard
Introduction
The introduction is hard to follow because of its lack of structure. Specifically, there is no apparent logic or causal links between the different parameters the authors assessed. It is also reflected in the fact that there are no clear hypotheses regarding the potential direct and indirect effects of warming and precipitation modifications on the composition and concentration of soil microbial residues.
Could the authors also include hypotheses related to the soil depth in this section?
Materials and methods
This section is pretty clear and well-written.
Could the authors explain why they considered their p-values significant at a threshold of 10%, not 5%, as it is typically done?
In light of the standard errors, slight differences in microbial residue concentrations, and relatively low number of replicates, I wonder if the effects of the different treatments are significant (Table 3).
Why are the concentrations in soil amino sugars expressed with different units in Table 3 and the Results section?
Results
This section, like the introduction, is challenging to follow. Parameters from different natures (soil parameters and enzyme activities) are mixed, and it isn't easy to see the point here.
Discussion
4.1 Paragraph is very confusing as the authors mixed the composition in microbial residues with potential interpretations regarding the source of these residues (i.e., bacterial and fungal community composition or abundance), that they did not assess.
Additional comments
Title Perhaps the authors could be a bit more precise about“Soil Microbial Residues”. Does it relate to microbial residue stocks or composition?
7 Maybe change “explore” for another verb like “determine”, “assess”, etc.
7-10 It lacks a logical link between microbial residues and soil carbon stocks.
10 Maybe change for “might affect soil microbial residue composition and concentration due to…”
12 Remove “the” in “the semi-arid grasslands”
13-19 I understand that “Soil Microbial Residues” relates to composition (bacteria/fungi necromass) and stocks. Yet, I think that part of the abstract is a bit confusing and could be improved by explaining the readership that the authors assessed both the composition and concentration of the microbial residues.
23 “Highly stable” regarding what? Their resistance to microbial decomposition?
24 Change “their contents” for “they”
25 If they are highly stable, how can they also be essential components of the soil’s active organic nitrogen?
26 It is redundant with l.23. Maybe try to merge both sentences?
26 Maybe explain why only these three amino sugars are quantified.
29 GluN is the major component of chitosan, but not of chitin.
30 Indicators of biomass? Or necromass? Or both? It is unclear here why authors would use biomass indicators to quantify microbial residue concentrations.
33 “Amino sugars, extracellular enzymes, and decomposers” I don’t understand the logical link between these three components in this sentence. I guess it is that decomposers secrete extracellular enzymes that break down polymers into amino sugars.
37 “soil community structures, ecosystem, and biosphere.” Again, I don’t understand the logical link here between these three things.
44 Remove “the”
58 “soil microorganisms” or the fate of soil microbial residues?
80 “field”
81 Unclear
83 “we aimed at testing the effects”
84 “this site was a suitable place”
88 Plant biomass, microbial biomass, animal biomass?
105 This would be better in the introduction section, as explaining the link between microbial residues and extracellular soil enzymes would be useful.
124 I don’t understand why the standards don’t correspond to the amino sugars measured by the authors. However, I am unfamiliar with this technic, so I apologize if it is a normal procedure.
134 The authors used SEM to test for the relationships between factors, meaning they have developed a pretty clear idea of the causal relationships between them. Thus I suggest the authors use this a priori model to improve the structure of the introduction section.
144 Is it standard to express amino sugar concentrations in ug/ml and not in ug/g of soil, for example? Also, change μg/g for μg g-1 throughout the manuscript.
200 GluN is a monomer directly accessible to most microorganisms, so it is not resistant to microbial breakdown. It might be stabilized in the soil through associations with minerals, though.
204 It sounds like “living fungal dominance”. Could the authors be less ambiguous about living or dead biomass?
206 “the population characteristics of soil microorganisms” It sounds like living fungi, not fungal residues.
215 “community structure” confusing
217 Confusing
236 Unclear
239 Unclear.
243 Amino sugars themselves are not subjected to decomposition as they are monomers. Maybe I don’t understand the technics, though. Are the amino sugars quantified after full hydrolysis of the polymers in the lab? I apologize if it is the case.
268 Unclear
SEM: Did the authors build an a priori model to test the relationships between the measured parameters? It seems that most SEM models they constructed don’t make much sense regarding my knowledge of soil microbiology (the causal link between xylosidase activity and GluN, for example?)
Citation: https://doi.org/10.5194/egusphere-2022-1290-RC2 -
AC2: 'Reply on RC2', Zhaoyu Dong, 23 Jan 2023
This study investigates how experimental warming and precipitation modifications affect the accumulation and composition of microbial residues in soils. The authors also quantified how soil parameters and enzyme activities respond to increased warming and precipitation. They found that increased warming and precipitation induced modifications in most measured parameters. I believe this type of work is timely and important to understand how future climates will influence the stabilization and persistence of microbial residues in soils. Yet, this manuscript presents major caveats that, I think, make it not suitable for publication in its actual state. Most notably, there is no explanation of the logical links between the different measured parameters (soil parameters, enzyme activities, and microbial residue concentrations and compositions). This makes the introduction and the discussion sections rather challenging to understand. Additionally, the authors often mixed living microbial communities and microbial residues. Finally, I have some concerns about the statistics used by the authors, notably the structural equation models.
Please see below for my feedback, which I hope might help to improve the overall quality of the manuscript.
Best regards,
Dr. François Maillard
We thank the reviewer for his positive evaluation of our manuscript. We address below all the comments and criticisms raised.
Introduction
The introduction is hard to follow because of its lack of structure. Specifically, there is no apparent logic or causal links between the different parameters the authors assessed. It is also reflected in the fact that there are no clear hypotheses regarding the potential direct and indirect effects of warming and precipitation modifications on the composition and concentration of soil microbial residues.
Response: We organize the hypotheses and add hypotheses about the impact of depth on amino sugars, as follows:
Our hypotheses were (1) that warming and increased precipitation might cause opposite effects on soil microbial residues due to the impact on soil physical properties, chemical properties, and enzyme activities; (2) that increased depth would facilitate amino sugar accumulation in soil. To test the hypothesis, we examined GluN, MurA, GalN, soil extracellular enzyme activity, biomass, and C and N concentrations for 4 scenarios in 4 fields. We applied these data to structural equation modeling to identify key drivers of climate change impacts on soil microbial residues.
Materials and methods
This section is pretty clear and well-written.
Response: Thank you for your encouragement.
Could the authors explain why they considered their p-values significant at a threshold of 10%, not 5%, as it is typically done?
Response: Since there are few indicators with p-values significant at a threshold of 0.05 in the SEM, we initially selected 0.1 as the threshold. But considering the consistency of the significance of the manuscript, we will modify the p-values significant at a threshold to 0.05 in the revised manuscript.
In light of the standard errors, slight differences in microbial residue concentrations, and relatively low number of replicates, I wonder if the effects of the different treatments are significant (Table 3).
Response: We have put the results of the significance in table S2.
Why are the concentrations in soil amino sugars expressed with different units in Table 3 and the Results section?
Response: We will unify the unit as μg/ml in the revised manuscript.
Results
This section, like the introduction, is challenging to follow. Parameters from different natures (soil parameters and enzyme activities) are mixed, and it isn’t easy to see the point here.
Response: We apologize for the vagueness in the manuscript. In the revised manuscript, we will describe soil physical and chemical parameters and enzyme activity separately. In addition, we also focused on enzyme activity and deleted some physical properties. For example: Under the increased precipitation treatment, soil extracellular enzyme activities (i.e., BG, LAP, NAG, XYL) and soil parameters (i.e., AGB, UGB, TC, TN, TP, SM) increased significantly.
Discussion
4.1 Paragraph is very confusing as the authors mixed the composition in microbial residues with potential interpretations regarding the source of these residues (i.e., bacterial and fungal community composition or abundance), that they did not assess.
Response: Your suggestion is very important. We have eliminated speculative discussions without experimental and literature support in the revised manuscript and will revise the overall structure.
Additional comments
Title Perhaps the authors could be a bit more precise about “Soil Microbial Residues”. Does it relate to microbial residue stocks or composition?
Response: We agree and will change the title to “Effects of Warming and Increased Precipitation on Soil Amino Sugars on the Qinghai–Tibet Alpine Meadows” in the revised manuscript.
Line 7 Maybe change “explore” for another verb like “determine”, “assess”, etc.
Response: We agree and will change “explore” to “determine” in the revised manuscript.
Line 7-10 It lacks a logical link between microbial residues and soil carbon stocks.
Response: We will change this passage to the following:
Amino sugars, as the biomarkers of microbial residues, help explore soil microorganisms’ response to global climate change. However, research on how microorganisms in the alpine meadow response to the simulated changes (warming and increased precipitation) due to the impact on soil physical properties, chemical properties, and enzyme activities is limited.
Line 10 Maybe change for “might affect soil microbial residue composition and concentration due to…”
Response: We agree and will change the sentence according to your comments in the revised manuscript.
Line 12 Remove “the” in “the semi-arid grasslands”
Response: We agree and will remove “the” in “the semi-arid grasslands” in the revised manuscript.
Line 13-19 I understand that “Soil Microbial Residues” relates to composition (bacteria/fungi necromass) and stocks. Yet, I think that part of the abstract is a bit confusing and could be improved by explaining the readership that the authors assessed both the composition and concentration of the microbial residues.
Response: We will change this passage to the following:
The total amino sugars mainly consisted of GluN, with concentration ranging from 136.65–264.72 μg/ml, followed by GalN and MurA at 27.94–145.53 μg/ml and 12.22–15.75 μg/ml. The results showed warming stimulated the accumulation of microbial residues, while increased precipitation led to their decline. The Glucosamine/Muramic Acid ratio trend indicates that the contribution of fungal residues was more significant than that of bacteria with increased precipitation, whereas that of bacterial residues exceeded that of fungi with warming. The increased precipitation had no significant effect on soil extracellular enzyme activities and amino sugar concentrations. In addition, cha
Line 23 “Highly stable” regarding what? Their resistance to microbial decomposition?
Response: Yes, we will change “Highly stable” to “high resistance to microbial decomposition” in in the revised manuscript.
Line 24 Change “their contents” for “they”
Response: We agree and will change the sentence according to your comments in the revised manuscript.
Line 25 If they are highly stable, how can they also be essential components of the soil’s active organic nitrogen?
Response: We will change this sentence to the following:
Amino sugars are difficult to decompose in soil, and mainly exist in the form of dead microorganisms, and generally have a strong positive correlation with soil organic carbon and nitrogen content.
Line 26 It is redundant with l.23. Maybe try to merge both sentences?
Response: We agree and will both sentences according to your comments in the revised manuscript.
Line 26 Maybe explain why only these three amino sugars are quantified.
Response: The main reason is that other amino sugars are very rare and not easy to detect, so we only tested these three amino sugars based on other people's references.
Reference: Li, L., Wilson, C.B., He, H., Zhang, X., Zhou, F., Schaeffer, S.M., 2019. Physical, biochemical, and microbial controls on amino sugar accumulation in soils under long-term cover cropping and no-tillage farming. Soil Biology and Biochemistry 135, 369-378.
Line 29 GluN is the major component of chitosan, but not of chitin.
Response: We agree and will make the change in the revised manuscript.
Line 30 Indicators of biomass? Or necromass? Or both? It is unclear here why authors would use biomass indicators to quantify microbial residue concentrations.
Response: Sorry for the vague words, we will change the “biomass” to “residual” in the revised manuscript.
Line 33 “Amino sugars, extracellular enzymes, and decomposers” I don’t understand the logical link between these three components in this sentence. I guess it is that decomposers secrete extracellular enzymes that break down polymers into amino sugars.
Response: We will change this sentence to the following:
Decomposers secrete extracellular enzymes that break down polymers into amino sugars, which may be affected by climate change (Henry, 2013; Liu et al., 2021).
Line 37 “soil community structures, ecosystem, and biosphere.” Again, I don’t understand the logical link here between these three things.
Line 44 Remove “the”
Line 80 “field”
Line 83 “we aimed at testing the effects”
Line 84 “this site was a suitable place”
Response: We agree and will change the sentence according to your comments in the revised manuscript.
Line 58 “soil microorganisms” or the fate of soil microbial residues?
Response: We will change this sentence to the following:
Clarifying the changes in soil microbial residues due to climate change will aid in assessing the response of soil microbial residues under future climate change scenarios
Line 81 Unclear
Response: We will delete this sentence in the revised manuscript.
Line 88 Plant biomass, microbial biomass, animal biomass?
Response: This refers to plant biomass.
Line 105 This would be better in the introduction section, as explaining the link between microbial residues and extracellular soil enzymes would be useful.
Response: We will move this part into the introduction section in the revised manuscript.
Line 124 I don’t understand why the standards don’t correspond to the amino sugars measured by the authors. However, I am unfamiliar with this technic, so I apologize if it is a normal procedure.
Response: Sorry for the wrong word.In the revised manuscript, we will change the sentence as follows:
N-methylglucamine (internal standard 2) was thoroughly mixed and freeze-dried for 8 h and then derivatized with nitrile acetyl ester.
Line 134 The authors used SEM to test for the relationships between factors, meaning they have developed a pretty clear idea of the causal relationships between them. Thus I suggest the authors use this a priori model to improve the structure of the introduction section.
Response: Our prior models are located in Figures S1 and S2 in the Appendix, and we will use them in the revised manuscript to improve the Introduction.
Line 144 Is it standard to express amino sugar concentrations in ug/ml and not in ug/g of soil, for example? Also, change μg/g for μg g-1 throughout the manuscript.
Response: We will change all the amino sugar concentrations from ug/ml to ug/g in the revised manuscript. And we will change μg/g for μg g-1 throughout the manuscript.
Line 200: GluN is a monomer directly accessible to most microorganisms, so it is not resistant to microbial breakdown. It might be stabilized in the soil through associations with minerals, though.
Response: Thank you for your corrections We have corrected the erroneous statements about monosaccharide breakdown in the manuscript one by one.
Line 204: It sounds like “living fungal dominance”. Could the authors be less ambiguous about living or dead biomass?
Response: During the writing of the manuscript, we believed that microbial residues do not have a community structure, so the "live fungal dominance" was not clearly expressed. We have thoroughly checked the manuscript and corrected the unclear expressions of these objects.
Line 206: “the population characteristics of soil microorganisms” It sounds like living fungi, not fungal residues.
Response: Same reply as previous suggestion.
Line 215: “community structure” confusing
Response: "structure" has been removed.
Line 217: Confusing
Response: This will be rewritten in the revised manuscript.
Line 236 Unclear
Response: This will be rewritten in the revised manuscript.
Line 239 Unclear.
Response: This will be rewritten in the revised manuscript.
Line 243 Amino sugars themselves are not subjected to decomposition as they are monomers. Maybe I don’t understand the technics, though. Are the amino sugars quantified after full hydrolysis of the polymers in the lab? I apologize if it is the case.
Response: Sorry for the confusion caused by our imprecise wording.GluN is already a monosaccharide and will not be hydrolyzed. What we want to express is closer to the decrease in the concentration of GluN in the soil due to degradation and uptake.
Line 268 Unclear
Response: This will be rewritten in the revised manuscript.
SEM: Did the authors build an a priori model to test the relationships between the measured parameters? It seems that most SEM models they constructed don’t make much sense regarding my knowledge of soil microbiology (the causal link between xylosidase activity and GluN, for example?)
Response: We put the prior models in the supplementary Figure S1-2. β-Xylosidase mainly hydrolyzes Xylan, but there may be β-Xylosidase with transglycosylation activity in the soil of the experimental fields. In the transglycosylation process of β-Xylosidase, common sugar acceptors include glucose, Galactose, Mannose, Xylose, and Xylobiose. Under the catalysis of β-xylosidase, these sugar acceptors bind to Xylosyl groups to form new oligosaccharides. This has been verified in the structural equation models of GluN and GalN that both XYL have negative effects.
Citation: https://doi.org/10.5194/egusphere-2022-1290-AC2
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AC2: 'Reply on RC2', Zhaoyu Dong, 23 Jan 2023
Status: closed
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RC1: 'Comment on egusphere-2022-1290', Anonymous Referee #1, 31 Dec 2022
Weng et al. studied the warming and increased precipitation effects on soil microbial necromass, they found the different response of residue to warming and increased precipitation. The research topic is very relevant especially under the multiple global change scenarios. However, there exists some flaws to prevent the current version to publish. Specific comments are as follows:
Abstract:
L 10-15: “The results showed warming stimulated the accumulation of microbial residues, while increased precipitation led to their decline.” This contradicts the contents of Table 3. From Table3, I can see that warming slightly decrease amino sugars concentrate but increased precipitation increase their concentrate. Please check which one is correct.
L 15: the contribution of fungal residue to what. SOC or microbial residue?
L 15-20: “The increased precipitation had no significant effect on soil extracellular enzyme activities and amino sugar concentrations”. Authors wrote that 'increased precipitation led to their decline' (L 10-15). However, increased precipitation do not affect amino sugar in here. It is very confused. Is there a different “accumulation of microbial residues” between “amino sugar concentrations”?
Introduction:
L 30-35: “Indicators of bacterial and fungal biomass.” It should be necromass or residue rather living biomass.
L 30-35: “amino sugars can be effective indicators for studying the different mechanisms of soils” Which mechanisms you mean here, please clarify.
L 40: “aboveground and underground biomass” it is should be “aboveground and underground plant biomass”
L 40-45: “Existing research on how the soil responds to climate change has primarily been based
on transect data, including soil respiration, carbon, nitrogen pools, and pH” This sentence makes no sense here.
L 60: The hypothesis is too general, it should be more specific and given the correspond explanation.
Second paragraph of Introduction Section: the key point of this paragraph in unclear, author should not give many statements about enzymes. The objective of this paper is global change effects on amino sugars, these should be strengthened. The last few sentences of the second paragraph are pretty weak, it doesn't make any sense to me.
L 60-65: “soil extracellular enzyme activity, biomass, and C and N concentrations for 4 scenarios in 4 fields.” The C and N content of what? soil or microbe?
Material and methods:
The duration of the experiment is not introduced. Please clarify that why increasing rainfall only in July and August.
L75-80: Please move the relevant content about “Soil moisture and temperatures measurement” to Section 2.2.
L 85-90: I wonder what biomass is this, microbial biomass? Soil faunal biomass? Please clarify that “Biomass” is actually plant biomass.
L 120-125: I am not sure why author use glucose as the internal standard 2. As far as know, it should be N-methylglucamine.
Section 2.3 : The other analysis such as correlation analysis and variance analysis should be added.
Results:
L 140-145: 3 Material and methods. It should be results.
“3.2.2 Soil extracellular enzyme and amino sugars” I can not find anything about the enzymes in this section.
Discussion:
L 200-205: I am not sure why decline in GalN will decrease the proportion of GluN in ASs.
L 215-220: If “fungal residues are more difficult to decompose than bacterial”. Bacterial necromass will be degraded faster, and the fungal necromass will be persisted longer. The more fungal necromass and less bacterial necromass should increase GluN/MurN ratio.
L 235-250: Discussion about mechanisms of warming effects on amino sugars is pretty weak, please add more related content.
L 260-265: Why TC inhibit the synthesis of GluN, and TN inhibit GalN but increase MurA? Can authors please explain these phenomenon. “It may be since increased nitrogen input can attenuate soil respiration (Xing et al., 2022), affecting different microbiota evolution.” This is oversimplify for me.
L 275-280: It's pH, not PH.
Table 1 and 3: I can not see the significance between treatments. Also, is there any interaction effects of warming and increased precipitation on amino sugars?
Figures 4-6: Authors should combine all amino sugars (GluN, MurN, GalN) into one SEM, rather than measuring the global change effects on GluN, MurN, and GalN separately.
Citation: https://doi.org/10.5194/egusphere-2022-1290-RC1 -
AC1: 'Reply on RC1', Zhaoyu Dong, 23 Jan 2023
We thank the reviewer for his/her positive evaluation of our manuscript. We address below all the comments and criticisms raised.
Abstract:
Line 10-15: “The results showed warming stimulated the accumulation of microbial residues, while increased precipitation led to their decline.” This contradicts the contents of Table 3. From Table3, I can see that warming slightly decrease amino sugars concentrate but increased precipitation increases their concentrate. Please check which one is correct.
Response: We checked the data and structural equations in Table 3. We believe the main reason is that although air temperature has a negative effect on the amino sugars in Table 3, this effect is not statistically significant (see Table S2). In the structural equation model, the increase of air temperature was connected with amino sugar through indirect and insignificant direct effects. In all, we will emphasize important results and significant conclusions in the revised manuscript.
Line 15: the contribution of fungal residue to what. SOC or microbial residue?
Response: It means the contribution of fungal residues was more significant than that of bacteria to soil nitrogen transformation and accumulation.
Line 15-20: “The increased precipitation had no significant effect on soil extracellular enzyme activities and amino sugar concentrations”. Authors wrote that 'increased precipitation led to their decline' (L 10-15). However, increased precipitation do not affect amino sugar in here. It is very confused. Is there a different “accumulation of microbial residues” between “amino sugar concentrations”?
Response: Sorry for the vague words. Our original intention is the change of amino sugar reflected by the increase of precipitation in Table 3, but this change is not significant. We will modify this part of the expression.
Introduction:
Line 30-35: “Indicators of bacterial and fungal biomass.” It should be necromass or residue rather living biomass.
Response: We will replace “Indicators of bacterial and fungal biomass” with “Indicators of bacterial and fungal residue” in the revised manuscript.
Line 30-35: “amino sugars can be effective indicators for studying the different mechanisms of soils” Which mechanisms you mean here, please clarify.
Response: The characteristics of soil amino sugar accumulation and change reflect the microbial regulation mechanism of soil organic matter cycle.
Reference: Li, L., Wilson, C.B., He, H., Zhang, X., Zhou, F., Schaeffer, S.M., 2019. Physical, biochemical, and microbial controls on amino sugar accumulation in soils under long-term cover cropping and no-tillage farming. Soil Biology and Biochemistry 135, 369-378.
Line 40: “aboveground and underground biomass” it is should be “aboveground and underground plant biomass”
Response: We agree and will make the change in the revised manuscript.
Line 40-45: “Existing research on how the soil responds to climate change has primarily been based on transect data, including soil respiration, carbon, nitrogen pools, and pH” This sentence makes no sense here.
Response: We agree and will remove the sentence in the revised manuscript.
Line 60: The hypothesis is too general, it should be more specific and given the correspond explanation.
Response: We organize the hypotheses and add hypotheses about the impact of depth on amino sugars, as follows:
Our hypotheses were (1) that warming and increased precipitation might cause opposite effects on soil microbial residues due to the impact on soil physical properties, chemical properties, and enzyme activities; (2) that increased depth would facilitate amino sugar accumulation in soil. To test the hypothesis, we examined GluN, MurA, GalN, soil extracellular enzyme activity, biomass, and C and N concentrations for 4 scenarios in 4 fields. We applied these data to structural equation modeling to identify key drivers of climate change impacts on soil microbial residues.
Second paragraph of Introduction Section: the key point of this paragraph in unclear, author should not give many statements about enzymes. The objective of this paper is global change effects on amino sugars, these should be strengthened. The last few sentences of the second paragraph are pretty weak, it doesn't make any sense to me.
Response: Thank you for your comments. We will shorten the statements about enzymes and strengthen the global change effects on amino sugars in the revised manuscript.
Line 60-65: “soil extracellular enzyme activity, biomass, and C and N concentrations for 4 scenarios in 4 fields.” The C and N content of what? soil or microbe?
Response: What we want to express is the soil C and N concentrations in the four sites.
Material and methods:
The duration of the experiment is not introduced. Please clarify that why increasing rainfall only in July and August.
Response: We will introduce the duration of the experiment in the revised manuscript, which is a four-year continuous warming and increased precipitation experiment. In addition, we will introduce the reason why the experiment is set in July and August, which is that the precipitation in July and August is concentrated, and according to the results of the future Shared Socioeconomic Pathways, the future precipitation in our study area will increase the fastest in July and August.
Line75-80: Please move the relevant content about “Soil moisture and temperatures measurement” to Section 2.2.
Response: We agree and will move the relevant content about “Soil moisture and temperatures measurement” to Section 2.2 in the revised manuscript.
Line 85-90: I wonder what biomass is this, microbial biomass? Soil faunal biomass? Please clarify that “Biomass” is actually plant biomass.
Response: Yes, we are referring to plant biomass, and we will clarify in the revised manuscript.
Line 120-125: I am not sure why author use glucose as the internal standard 2. As far as know, it should be N-methylglucamine.
Response: We agree and will change this sentence to the following:
- methylglucamine (internal standard 2) was thoroughly mixed and freeze-dried for 8 h and then derivatized with nitrile acetyl ester.
Section 2.3: The other analysis such as correlation analysis and variance analysis should be added.
Response: We agree and will add correlation analysis and variance analysis to Section 2.2 in the revised manuscript.
Results:
Line 140-145: 3 Material and methods. It should be results.
Response: We are very sorry for such an error, which we have corrected in the revised manuscript.
“3.2.2 Soil extracellular enzyme and amino sugars” I can not find anything about the enzymes in this section.
Response: We're sorry for the subtitle; it should be "Warming Treatment".
Discussion:
Line 200-205: I am not sure why decline in GalN will decrease the proportion of GluN in TASs.
Response: We are sorry vague sentence caused your misunderstanding. Both the effect of increasing temperature on the reduction of GluN in the experiment and the indirect positive effect shown in the structural equation model are insignificant. Although the concentration of GluN decreases during the warming treatment, the proportion of GluN in TAS increases because the concentration of GalN decreases more significantly. In the revised manuscript, we will pay more attention to the prominent transcriptional regularities and clarify the reasons for the contradictory regularities more clearly.
Line 215-220: If “fungal residues are more difficult to decompose than bacterial”. Bacterial necromass will be degraded faster, and the fungal necromass will be persisted longer. The more fungal necromass and less bacterial necromass should increase GluN/MurN ratio.
Response: Thank you for your suggestion. We will refine this section in the revised manuscript.
Line 235-250: Discussion about mechanisms of warming effects on amino sugars is pretty weak, please add more related content.
Response: Under the condition of warming, the aeration in the soil is improved when the soil moisture is reduced, and the reduction of soil moisture will not only reduce the soil microbial carbon accumulation effect by more than 20 times but also effectively reduce the soil inorganic nitrogen content. The previous research results are relatively similar to the impact path shown by the structural equation model in this study. We will supplement this part in the revised manuscript.
Line 260-265: Why TC inhibit the synthesis of GluN, and TN inhibit GalN but increase MurA? Can authors please explain these phenomenon. “It may be since increased nitrogen input can attenuate soil respiration (Xing et al., 2022), affecting different microbiota evolution.” This is oversimplify for me.
Response: After comparison, TC and TN negatively impact GluN and GalN, while muramic acid will increase with the increase of TC and TN. But it is worth noting that these paths are all indirect paths or insignificant paths. In general, soils with higher nitrogen concentration will have higher amino sugar content due to the high nutrient environment that favors microbial anabolism. However, the reason for the different turnover rules of GluN and GalN may be that the microbial community in central Tibet mentioned in this study is dominated by actinomycetes and bacteria, and the transcription process of MurA in bacterial residues is more clear.
Line 275-280: It's pH, not PH.
Response: We agree and will make the change in the revised manuscript.
Table 1 and 3: I can not see the significance between treatments. Also, is there any interaction effects of warming and increased precipitation on amino sugars?
Response: We put the significance in the supplementary Figure S1-2.
According to the conclusion of the structural equation model, there is no significant effect. As far as the interaction is concerned, the path coefficients between amino sugars are not significant, which has no practical significance.
Figures 4-6: Authors should combine all amino sugars (GluN, MurN, GalN) into one SEM, rather than measuring the global change effects on GluN, MurN, and GalN separately.
Response: We agree and will combine all amino sugars into one SEM in the revised manuscript.
Citation: https://doi.org/10.5194/egusphere-2022-1290-AC1
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AC1: 'Reply on RC1', Zhaoyu Dong, 23 Jan 2023
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RC2: 'Comment on egusphere-2022-1290', François Maillard, 12 Jan 2023
This study investigates how experimental warming and precipitation modifications affect the accumulation and composition of microbial residues in soils. The authors also quantified how soil parameters and enzyme activities respond to increased warming and precipitation. They found that increased warming and precipitation induced modifications in most measured parameters. I believe this type of work is timely and important to understand how future climates will influence the stabilization and persistence of microbial residues in soils. Yet, this manuscript presents major caveats that, I think, make it not suitable for publication in its actual state. Most notably, there is no explanation of the logical links between the different measured parameters (soil parameters, enzyme activities, and microbial residue concentrations and compositions). This makes the introduction and the discussion sections rather challenging to understand. Additionally, the authors often mixed living microbial communities and microbial residues. Finally, I have some concerns about the statistics used by the authors, notably the structural equation models.
Please see below for my feedback, which I hope might help to improve the overall quality of the manuscript.
Best regards,
Dr. François Maillard
Introduction
The introduction is hard to follow because of its lack of structure. Specifically, there is no apparent logic or causal links between the different parameters the authors assessed. It is also reflected in the fact that there are no clear hypotheses regarding the potential direct and indirect effects of warming and precipitation modifications on the composition and concentration of soil microbial residues.
Could the authors also include hypotheses related to the soil depth in this section?
Materials and methods
This section is pretty clear and well-written.
Could the authors explain why they considered their p-values significant at a threshold of 10%, not 5%, as it is typically done?
In light of the standard errors, slight differences in microbial residue concentrations, and relatively low number of replicates, I wonder if the effects of the different treatments are significant (Table 3).
Why are the concentrations in soil amino sugars expressed with different units in Table 3 and the Results section?
Results
This section, like the introduction, is challenging to follow. Parameters from different natures (soil parameters and enzyme activities) are mixed, and it isn't easy to see the point here.
Discussion
4.1 Paragraph is very confusing as the authors mixed the composition in microbial residues with potential interpretations regarding the source of these residues (i.e., bacterial and fungal community composition or abundance), that they did not assess.
Additional comments
Title Perhaps the authors could be a bit more precise about“Soil Microbial Residues”. Does it relate to microbial residue stocks or composition?
7 Maybe change “explore” for another verb like “determine”, “assess”, etc.
7-10 It lacks a logical link between microbial residues and soil carbon stocks.
10 Maybe change for “might affect soil microbial residue composition and concentration due to…”
12 Remove “the” in “the semi-arid grasslands”
13-19 I understand that “Soil Microbial Residues” relates to composition (bacteria/fungi necromass) and stocks. Yet, I think that part of the abstract is a bit confusing and could be improved by explaining the readership that the authors assessed both the composition and concentration of the microbial residues.
23 “Highly stable” regarding what? Their resistance to microbial decomposition?
24 Change “their contents” for “they”
25 If they are highly stable, how can they also be essential components of the soil’s active organic nitrogen?
26 It is redundant with l.23. Maybe try to merge both sentences?
26 Maybe explain why only these three amino sugars are quantified.
29 GluN is the major component of chitosan, but not of chitin.
30 Indicators of biomass? Or necromass? Or both? It is unclear here why authors would use biomass indicators to quantify microbial residue concentrations.
33 “Amino sugars, extracellular enzymes, and decomposers” I don’t understand the logical link between these three components in this sentence. I guess it is that decomposers secrete extracellular enzymes that break down polymers into amino sugars.
37 “soil community structures, ecosystem, and biosphere.” Again, I don’t understand the logical link here between these three things.
44 Remove “the”
58 “soil microorganisms” or the fate of soil microbial residues?
80 “field”
81 Unclear
83 “we aimed at testing the effects”
84 “this site was a suitable place”
88 Plant biomass, microbial biomass, animal biomass?
105 This would be better in the introduction section, as explaining the link between microbial residues and extracellular soil enzymes would be useful.
124 I don’t understand why the standards don’t correspond to the amino sugars measured by the authors. However, I am unfamiliar with this technic, so I apologize if it is a normal procedure.
134 The authors used SEM to test for the relationships between factors, meaning they have developed a pretty clear idea of the causal relationships between them. Thus I suggest the authors use this a priori model to improve the structure of the introduction section.
144 Is it standard to express amino sugar concentrations in ug/ml and not in ug/g of soil, for example? Also, change μg/g for μg g-1 throughout the manuscript.
200 GluN is a monomer directly accessible to most microorganisms, so it is not resistant to microbial breakdown. It might be stabilized in the soil through associations with minerals, though.
204 It sounds like “living fungal dominance”. Could the authors be less ambiguous about living or dead biomass?
206 “the population characteristics of soil microorganisms” It sounds like living fungi, not fungal residues.
215 “community structure” confusing
217 Confusing
236 Unclear
239 Unclear.
243 Amino sugars themselves are not subjected to decomposition as they are monomers. Maybe I don’t understand the technics, though. Are the amino sugars quantified after full hydrolysis of the polymers in the lab? I apologize if it is the case.
268 Unclear
SEM: Did the authors build an a priori model to test the relationships between the measured parameters? It seems that most SEM models they constructed don’t make much sense regarding my knowledge of soil microbiology (the causal link between xylosidase activity and GluN, for example?)
Citation: https://doi.org/10.5194/egusphere-2022-1290-RC2 -
AC2: 'Reply on RC2', Zhaoyu Dong, 23 Jan 2023
This study investigates how experimental warming and precipitation modifications affect the accumulation and composition of microbial residues in soils. The authors also quantified how soil parameters and enzyme activities respond to increased warming and precipitation. They found that increased warming and precipitation induced modifications in most measured parameters. I believe this type of work is timely and important to understand how future climates will influence the stabilization and persistence of microbial residues in soils. Yet, this manuscript presents major caveats that, I think, make it not suitable for publication in its actual state. Most notably, there is no explanation of the logical links between the different measured parameters (soil parameters, enzyme activities, and microbial residue concentrations and compositions). This makes the introduction and the discussion sections rather challenging to understand. Additionally, the authors often mixed living microbial communities and microbial residues. Finally, I have some concerns about the statistics used by the authors, notably the structural equation models.
Please see below for my feedback, which I hope might help to improve the overall quality of the manuscript.
Best regards,
Dr. François Maillard
We thank the reviewer for his positive evaluation of our manuscript. We address below all the comments and criticisms raised.
Introduction
The introduction is hard to follow because of its lack of structure. Specifically, there is no apparent logic or causal links between the different parameters the authors assessed. It is also reflected in the fact that there are no clear hypotheses regarding the potential direct and indirect effects of warming and precipitation modifications on the composition and concentration of soil microbial residues.
Response: We organize the hypotheses and add hypotheses about the impact of depth on amino sugars, as follows:
Our hypotheses were (1) that warming and increased precipitation might cause opposite effects on soil microbial residues due to the impact on soil physical properties, chemical properties, and enzyme activities; (2) that increased depth would facilitate amino sugar accumulation in soil. To test the hypothesis, we examined GluN, MurA, GalN, soil extracellular enzyme activity, biomass, and C and N concentrations for 4 scenarios in 4 fields. We applied these data to structural equation modeling to identify key drivers of climate change impacts on soil microbial residues.
Materials and methods
This section is pretty clear and well-written.
Response: Thank you for your encouragement.
Could the authors explain why they considered their p-values significant at a threshold of 10%, not 5%, as it is typically done?
Response: Since there are few indicators with p-values significant at a threshold of 0.05 in the SEM, we initially selected 0.1 as the threshold. But considering the consistency of the significance of the manuscript, we will modify the p-values significant at a threshold to 0.05 in the revised manuscript.
In light of the standard errors, slight differences in microbial residue concentrations, and relatively low number of replicates, I wonder if the effects of the different treatments are significant (Table 3).
Response: We have put the results of the significance in table S2.
Why are the concentrations in soil amino sugars expressed with different units in Table 3 and the Results section?
Response: We will unify the unit as μg/ml in the revised manuscript.
Results
This section, like the introduction, is challenging to follow. Parameters from different natures (soil parameters and enzyme activities) are mixed, and it isn’t easy to see the point here.
Response: We apologize for the vagueness in the manuscript. In the revised manuscript, we will describe soil physical and chemical parameters and enzyme activity separately. In addition, we also focused on enzyme activity and deleted some physical properties. For example: Under the increased precipitation treatment, soil extracellular enzyme activities (i.e., BG, LAP, NAG, XYL) and soil parameters (i.e., AGB, UGB, TC, TN, TP, SM) increased significantly.
Discussion
4.1 Paragraph is very confusing as the authors mixed the composition in microbial residues with potential interpretations regarding the source of these residues (i.e., bacterial and fungal community composition or abundance), that they did not assess.
Response: Your suggestion is very important. We have eliminated speculative discussions without experimental and literature support in the revised manuscript and will revise the overall structure.
Additional comments
Title Perhaps the authors could be a bit more precise about “Soil Microbial Residues”. Does it relate to microbial residue stocks or composition?
Response: We agree and will change the title to “Effects of Warming and Increased Precipitation on Soil Amino Sugars on the Qinghai–Tibet Alpine Meadows” in the revised manuscript.
Line 7 Maybe change “explore” for another verb like “determine”, “assess”, etc.
Response: We agree and will change “explore” to “determine” in the revised manuscript.
Line 7-10 It lacks a logical link between microbial residues and soil carbon stocks.
Response: We will change this passage to the following:
Amino sugars, as the biomarkers of microbial residues, help explore soil microorganisms’ response to global climate change. However, research on how microorganisms in the alpine meadow response to the simulated changes (warming and increased precipitation) due to the impact on soil physical properties, chemical properties, and enzyme activities is limited.
Line 10 Maybe change for “might affect soil microbial residue composition and concentration due to…”
Response: We agree and will change the sentence according to your comments in the revised manuscript.
Line 12 Remove “the” in “the semi-arid grasslands”
Response: We agree and will remove “the” in “the semi-arid grasslands” in the revised manuscript.
Line 13-19 I understand that “Soil Microbial Residues” relates to composition (bacteria/fungi necromass) and stocks. Yet, I think that part of the abstract is a bit confusing and could be improved by explaining the readership that the authors assessed both the composition and concentration of the microbial residues.
Response: We will change this passage to the following:
The total amino sugars mainly consisted of GluN, with concentration ranging from 136.65–264.72 μg/ml, followed by GalN and MurA at 27.94–145.53 μg/ml and 12.22–15.75 μg/ml. The results showed warming stimulated the accumulation of microbial residues, while increased precipitation led to their decline. The Glucosamine/Muramic Acid ratio trend indicates that the contribution of fungal residues was more significant than that of bacteria with increased precipitation, whereas that of bacterial residues exceeded that of fungi with warming. The increased precipitation had no significant effect on soil extracellular enzyme activities and amino sugar concentrations. In addition, cha
Line 23 “Highly stable” regarding what? Their resistance to microbial decomposition?
Response: Yes, we will change “Highly stable” to “high resistance to microbial decomposition” in in the revised manuscript.
Line 24 Change “their contents” for “they”
Response: We agree and will change the sentence according to your comments in the revised manuscript.
Line 25 If they are highly stable, how can they also be essential components of the soil’s active organic nitrogen?
Response: We will change this sentence to the following:
Amino sugars are difficult to decompose in soil, and mainly exist in the form of dead microorganisms, and generally have a strong positive correlation with soil organic carbon and nitrogen content.
Line 26 It is redundant with l.23. Maybe try to merge both sentences?
Response: We agree and will both sentences according to your comments in the revised manuscript.
Line 26 Maybe explain why only these three amino sugars are quantified.
Response: The main reason is that other amino sugars are very rare and not easy to detect, so we only tested these three amino sugars based on other people's references.
Reference: Li, L., Wilson, C.B., He, H., Zhang, X., Zhou, F., Schaeffer, S.M., 2019. Physical, biochemical, and microbial controls on amino sugar accumulation in soils under long-term cover cropping and no-tillage farming. Soil Biology and Biochemistry 135, 369-378.
Line 29 GluN is the major component of chitosan, but not of chitin.
Response: We agree and will make the change in the revised manuscript.
Line 30 Indicators of biomass? Or necromass? Or both? It is unclear here why authors would use biomass indicators to quantify microbial residue concentrations.
Response: Sorry for the vague words, we will change the “biomass” to “residual” in the revised manuscript.
Line 33 “Amino sugars, extracellular enzymes, and decomposers” I don’t understand the logical link between these three components in this sentence. I guess it is that decomposers secrete extracellular enzymes that break down polymers into amino sugars.
Response: We will change this sentence to the following:
Decomposers secrete extracellular enzymes that break down polymers into amino sugars, which may be affected by climate change (Henry, 2013; Liu et al., 2021).
Line 37 “soil community structures, ecosystem, and biosphere.” Again, I don’t understand the logical link here between these three things.
Line 44 Remove “the”
Line 80 “field”
Line 83 “we aimed at testing the effects”
Line 84 “this site was a suitable place”
Response: We agree and will change the sentence according to your comments in the revised manuscript.
Line 58 “soil microorganisms” or the fate of soil microbial residues?
Response: We will change this sentence to the following:
Clarifying the changes in soil microbial residues due to climate change will aid in assessing the response of soil microbial residues under future climate change scenarios
Line 81 Unclear
Response: We will delete this sentence in the revised manuscript.
Line 88 Plant biomass, microbial biomass, animal biomass?
Response: This refers to plant biomass.
Line 105 This would be better in the introduction section, as explaining the link between microbial residues and extracellular soil enzymes would be useful.
Response: We will move this part into the introduction section in the revised manuscript.
Line 124 I don’t understand why the standards don’t correspond to the amino sugars measured by the authors. However, I am unfamiliar with this technic, so I apologize if it is a normal procedure.
Response: Sorry for the wrong word.In the revised manuscript, we will change the sentence as follows:
N-methylglucamine (internal standard 2) was thoroughly mixed and freeze-dried for 8 h and then derivatized with nitrile acetyl ester.
Line 134 The authors used SEM to test for the relationships between factors, meaning they have developed a pretty clear idea of the causal relationships between them. Thus I suggest the authors use this a priori model to improve the structure of the introduction section.
Response: Our prior models are located in Figures S1 and S2 in the Appendix, and we will use them in the revised manuscript to improve the Introduction.
Line 144 Is it standard to express amino sugar concentrations in ug/ml and not in ug/g of soil, for example? Also, change μg/g for μg g-1 throughout the manuscript.
Response: We will change all the amino sugar concentrations from ug/ml to ug/g in the revised manuscript. And we will change μg/g for μg g-1 throughout the manuscript.
Line 200: GluN is a monomer directly accessible to most microorganisms, so it is not resistant to microbial breakdown. It might be stabilized in the soil through associations with minerals, though.
Response: Thank you for your corrections We have corrected the erroneous statements about monosaccharide breakdown in the manuscript one by one.
Line 204: It sounds like “living fungal dominance”. Could the authors be less ambiguous about living or dead biomass?
Response: During the writing of the manuscript, we believed that microbial residues do not have a community structure, so the "live fungal dominance" was not clearly expressed. We have thoroughly checked the manuscript and corrected the unclear expressions of these objects.
Line 206: “the population characteristics of soil microorganisms” It sounds like living fungi, not fungal residues.
Response: Same reply as previous suggestion.
Line 215: “community structure” confusing
Response: "structure" has been removed.
Line 217: Confusing
Response: This will be rewritten in the revised manuscript.
Line 236 Unclear
Response: This will be rewritten in the revised manuscript.
Line 239 Unclear.
Response: This will be rewritten in the revised manuscript.
Line 243 Amino sugars themselves are not subjected to decomposition as they are monomers. Maybe I don’t understand the technics, though. Are the amino sugars quantified after full hydrolysis of the polymers in the lab? I apologize if it is the case.
Response: Sorry for the confusion caused by our imprecise wording.GluN is already a monosaccharide and will not be hydrolyzed. What we want to express is closer to the decrease in the concentration of GluN in the soil due to degradation and uptake.
Line 268 Unclear
Response: This will be rewritten in the revised manuscript.
SEM: Did the authors build an a priori model to test the relationships between the measured parameters? It seems that most SEM models they constructed don’t make much sense regarding my knowledge of soil microbiology (the causal link between xylosidase activity and GluN, for example?)
Response: We put the prior models in the supplementary Figure S1-2. β-Xylosidase mainly hydrolyzes Xylan, but there may be β-Xylosidase with transglycosylation activity in the soil of the experimental fields. In the transglycosylation process of β-Xylosidase, common sugar acceptors include glucose, Galactose, Mannose, Xylose, and Xylobiose. Under the catalysis of β-xylosidase, these sugar acceptors bind to Xylosyl groups to form new oligosaccharides. This has been verified in the structural equation models of GluN and GalN that both XYL have negative effects.
Citation: https://doi.org/10.5194/egusphere-2022-1290-AC2
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AC2: 'Reply on RC2', Zhaoyu Dong, 23 Jan 2023
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