Effects of Litter Input on Soil Enzyme Activities and Their Stoichiometric Ratios in Sandy Soil

Response to Reviewers’ Comments

1. Summary

Thank you very much for your insightful comments. We have carefully considered your suggestions and made the necessary revisions accordingly.

2. Questions for General Evaluation2.

Reviewer’s Evaluation

Response and Revisions

Does the introduction provide sufficient background and include all relevant references?

Yes

Are all the cited references relevant to the research?

Yes

Is the research design appropriate?

Yes

Are the methods adequately described?

Yes

Are the results clearly presented?

Yes

Are the conclusions supported by the results?

Yes

3. Point-by-point response to Comments and Suggestions for Authors

Comments 1: The submitted article is interesting and raises an important topic of trying to improve the quality of poor soils in dry areas. The manuscript is written in a logical and orderly manner. All individual chapters of the work contain all the relevant information. However, before publishing it, I suggest that you read the manuscript carefully again in order to eliminate minor language errors.

Response 1: Thank you for highlighting the language errors. We appreciate your feedback and fully concur with this observation. We have enlisted the services of a professional editing team to enhance the quality of our manuscript. They assisted us in rectifying grammatical inaccuracies, refining sentence structure, and elevating the overall language to improve readability.

Comments 2: In addition, it would also be worth answering the question whether, if the solution proposed by the authors were to be implemented on a larger scale, the amount of available litter from trees used in the experiment is large enough in the given regions for such use to be realistic. If the amount of available material is limited, it would be worth considering a different selection.

Response 2: Your suggestion is truly appreciated. However, I would like to note that the four types of vegetation selected for this experiment—Corethrodendron fruticosum, Caragana korshinskii, Amorpha fruticosa, and Salix cheilophila—are well-known sand-fixing shrub species commonly utilized in the Mu Us sandy land. They have been extensively planted across large areas. The amount added in this experiment was 10 grams, which was carefully chosen based on the surface litter observed in the four plots of Corethrodendron fruticosum, Caragana korshinskii, Amorpha fruticosa, and Salix cheilophila that have undergone restoration over ten years. Therefore, we believe this approach is both realistic and feasible.

4. Response to Comments on the Quality of English Language

Response 1: We have enlisted the assistance of a professional editing service to enhance the language quality of our manuscript. Their expertise has enabled us to rectify grammatical errors, refine sentence structures, and elevate the overall readability of the text.

5. Additional clarifications

Any additional changes in the text have been highlighted in red for your convenience.

Response to Reviewer’Comments

1. Summary

Thank you very much for your insightful comments. We have carefully considered your suggestions and made the necessary revisions accordingly.

2. Questions for General Evaluation2.

Reviewer’s Evaluation

Response and Revisions

Does the introduction provide sufficient background and include all relevant references?

Must be improved

The author give corresponding response in the point-by-point response letter. The same as below

Are all the cited references relevant to the research?

Can be improved

Is the research design appropriate?

Can be improved

Are the methods adequately described?

Can be improved

Are the results clearly presented?

Must be improved

Are the conclusions supported by the results?

Must be improved

3. Point-by-point response to Comments and Suggestions for Authors

Comments 1: The introduction reads well but would be significantly enhanced by adding a few hypotheses. The literature on the effects of litter addition on soil stoichiometric ratios and soil nutrients is quite important, and I recommend incorporating hypotheses based on available literature and specific context related to this arid environment.

Response 1: Thank you so much for bringing this to our attention. We truly appreciate your feedback and have taken the opportunity to optimize the references while incorporating the hypothesis into the text. For further details, please refer to lines 102-106 of the document.

“Specifically, based on previous studies, we hypothesized that (1) litter input in sandy ecosystems may promote the increase of soil enzyme activity in sandy soils, and (2) different types of litter input can enhance soil enzyme activity and improve soil chemical properties, thereby causing the stoichiometric ratio of soil enzyme activity to shift in a direction that is favorable for litter decomposition.”

Comments 2: The materials and methods: I have some concerns about the materials and methods section. Litter from the four plants was collected, dried, and cut into 2 mm pieces. Additionally, soil from depths of 0-10 cm was sampled, sieved to 2 mm, and adjusted to 60% WHC. I find this approach very manipulative and potentially yielding results quite different from field conditions. Soil sieving disrupts aggregates, and cutting litter into small pieces makes them very susceptible to microbial utilization within a very short time. Furthermore, adjusting soil water to 60% WHC raises serious concerns, as these soils likely do not experience such conditions. It would have also been interesting to test different litter addition rates.

Response 2: Thank you for your comments, I will answer your questions:

1. The litter was dried and cut into 2 mm pieces to avoid the influence of the physical size of the leaves on the research results and to better compare the differences between different litters.

2. The sandy soil was sieved through a 2mm sieve to remove large plants, animals, and litter remains, ensuring the consistency of the soil to be used without destroying the soil particle size ratio.

3. Adjusting the soil moisture content to 60% of the field water holding capacity can balance soil moisture and aeration, effectively avoiding the interference of hypoxia or drought on experimental data. Uniform moisture conditions are helpful for comparing the results of different experiments. The value of 60% was chosen by scientifically comparing biological needs and the experimental control. The difference between this value and that in the field is a necessary trade-off for our experimental design, which aims to improve data stability and mechanism analyses.

4. After the indoor test was completed, we conducted a large number of field litter decomposition tests in net bags based on the existing ones, with different species, different initial amounts, etc. The test is still in progress.

Comments 3: In the results section, I suggest revising the RDA analysis (Figure 7) to also include the four plants as grouping variables (represented as ellipses) so that we can observe the variation of these factors in relation to the four different plant types. Also, what is the goal of having RDA and Pearson correlations, since they show the same information? I suggest deleting figure 6 and retaining and improving figure 7.

Response 3: Thank you for pointing this out. We agree with this opinion. We have completed the modification and deleted Figure 6 and retained Figure 7. Please note that the four plants were not used as grouping variables for RDA analysis because the sample size was small and the statistical test power was insufficient, making it difficult to detect the variable effect. We hope you understand this.

Comments 4: It would be beneficial to include the chemical analyses (C, N, P, etc.) of the litter from the four plants before the experiment begins to establish a baseline before litter additions. Do the four plants differ in litter chemistry? This inquiry is also valid for soil samples used for the laboratory experiments. What about soil moisture levels at the time of soil sampling, and how much do they differ from the soil moisture adjustment during the experiment (60% WHC)?

Response 4: We concur with this perspective. Prior to the experiment, we conducted an analysis of the carbon, nitrogen, and phosphorus content in the leaves of the four types of litter, and have incorporated these findings into the manuscript (lines 143-153), as detailed in the following table. Additionally, during soil sample collection, we opted not to measure the initial water content due to its low levels and negligible impact on the overall experiment.

The initial chemical contents of the leaves of the four litters are shown in Table 2. There was no significant difference in the total carbon content of the leaves of the four litters. The total nitrogen content of NT and ZSH was significantly higher than that of SL. The total phosphorus content of ZSH was significantly higher than that of other plants.

Table 2. Initial chemical contents of leaves of four litter types.

Comments 5: The conclusion simply repeats the main results. What should we ultimately learn from all your findings? What are the key take-home messages and implications for restoration and nutrient cycling in such ecosystems? Would you suggest any specific management options for restoration to inform policies based on your findings regarding the different litter types?

Response 5: Thank you for sharing your insights. We concur with this perspective and have made revisions to the article, which are highlighted in red. The details are as follows (lines 469-494):

5. Conclusions

Litter is a key component of soil nutrient cycles in sandy land. To investigate the effects of litter quality changes on soil nutrients, enzyme activities, and stoichiometric ratios in sandy land. This study showed that the input of leaf litter of four plant species, YC, NT, ZSH, and SL, increased the contents of carbon- and nitrogen-related chemical indicators in sandy land soil. The addition of NT and YC litter significantly increased the contents of MBC and MBN. This shows that litter has a key ecological function in enhancing soil microbial activity and nutrient fixation. The addition of litter plays an important role in the activities of enzymes related to soil carbon, nitrogen, and phosphorus cycles. The addition of ZSH, NT, and YC litter alleviated phosphorus limitation, and the addition of NT litter alleviated soil nitrogen limitation. This indicates that sandy soil is subject to nitrogen limitation and nitrogen–phosphorus coordinated limitation, providing a new strategy for the coordinated regulation of nutrients in sandy soil. The results of the redundancy analysis show that the soil nutrients had different degrees of correlation with enzyme activity and its stoichiometric ratio. MBN, TN, MBC/MBN, OC, and AN were the core factors influencing soil enzyme activity and the stoichiometric ratio. Their synergistic effects predominantly regulated the coupling process of the carbon/nitrogen/phosphorus cycles in sandy soils by regulating microbial metabolic substrates and energy allocation. In addition, the brief duration of litter addition introduces certain uncertainties. The introduction of litter may influence the microbial community and induce alterations in soil enzyme activity, necessitating comprehensive experimental research for validation. In summary, this study provides a theoretical basis for the optimization of litter management in sandy ecological restoration. The priority selection of efficient litter types, such as ZSH, NT, and YC, can simultaneously alleviate nitrogen and phosphorus limitations and enhance microbially mediated nutrient cycles, thereby improving the ecological function of sandy soils.

Comments 6: Line 18: Please spell out CK as it is used for the first time. This also applies to terms like E_C/P and E_N/P in line 23.

Response 6: Thank you very much for your valuable comments. We have made some adjustments: CK has been changed to "no litter added (CK)," and E_C/P and E_N/P have been updated to "Enzymatic C:P acquisition ratio (E_C/P)" and "Enzymatic N:P acquisition ratio (E_N/P)," respectively; see lines 28–30 of the text.

Comments 7: Line 121: Please delete "Roots and litter were removed from the soil samples." This is a repetition.
Response 7: Thank you very much for your comment. We appreciate your input and have decided to remove it as suggested.

4. Response to Comments on the Quality of English Language

Response 1: We have engaged a professional editing service to improve the language of our manuscript. They helped us correct grammatical errors, improve the sentence structure, and improve the language for better readability.

5. Additional clarifications