Change Characteristics of Soil Organic Carbon and Soil Available Nutrients and Their Relationship in the Subalpine Shrub Zone of Qilian Mountains in China

Round 1

Reviewer 1 Report

The manuscript entitled “Change characteristics of soil organic carbon and soil available nutrients and their relationship in the subalpine shrub zone of Qilian Mountains in China” is of interest regarding the availability of nutrients linked with soil organic carbon in hilly areas. Although the manuscript contains good information but there are some flaws that may be addressed and fulfilled for the validation of study and outcomes. Most of the issues are highlighted in the attachment.

Abstract

Improve the write up and always add full name before using the short terms or abbreviations. Please explain the term ‘soil available nutrients’.

Introduction

Line 41: What do you mean by soil mechanical composition?

Line 68-70: Rewrite.

Line 71: What is SAP?

Introduction section is not well managed and needs comprehensive improvement regarding scientific quality and language.

Material and methods

This section is presented appropriately but needs little improvements as highlighted in attachment.

Result

Improve this section with interpretation of significant findings. It looks too lengthy. Exclude the discussion portion from results and add it into discussion section. Add lettering in the figures if possible. Improve the reporting language and avoid jargon. Directly state the results. Authors must quantitatively report their results. Make the results section concise and specific.

Discussion

Improve this section with logical and scientific approach. Rewriting of previous studies/results deteriorate the quality of manuscript. It is quite simple and easy to read. Discussion section may be improved with recent citation. Findings are again presented in the discussion section.

Try to discuss results with recent literature with logical reasoning.

Remove subheadings from the discussion section.

Conclusion

Conclusion sections is more lengthy than abstract. Make it concise and quantify if possible. Rewrite the whole conclusion section again.

Follow the journal guidelines for the references style within the text and in the bibliographic section.

For further details, find the attachment please.

Comments for author File: Comments.pdf

Extensive editing of English language required.

Author Response

Response to Reviewer 1 Comment

The manuscript entitled “Change characteristics of soil organic carbon and soil available nutrients and their relationship in the subalpine shrub zone of Qilian Mountains in China” is of interest regarding the availability of nutrients linked with soil organic carbon in hilly areas. Although the manuscript contains good information but there are some flaws that may be addressed and fulfilled for the validation of study and outcomes. Most of the issues are highlighted in the attachment.

Response: Thank you very much. We really appreciate your efforts in reviewing our manuscript. We have revised the manuscript accordingly. Our point-by-point responses to the comments are detailed below.

Abstract

Point 1：Improve the write up and always add full name before using the short terms or abbreviations.

Response: Thank you very much. We have added the full name before using the short terms or abbreviations. The revised content is as follows:

L12-14: Studying the spatial and temporal distribution of Soil organic carbon (SOC) content in high-altitude mountainous areas and its correlation with soil nutrients provides a basis for understanding soil carbon stocks and factors affecting the local carbon cycle.

L25-29: The SOC content was more obviously correlated with soil available phosphorus (SAP) content in the soil layers of 30-40 cm (r=0.57) on the semi-sunny slop; The SOC content was more obviously correlated with SAP content in the soil layer of 60-70 cm (r=0.55) and with soil available potassium (SAK) content in the soil layer of 70-80 cm (r=0.84) on the semi-sunny slope.

Point 2：Please explain the term ‘soil available nutrients’.

Response: Thank you very much. Soil available nutrients refer to the nutrients in the soil that can be directly utilized by the plant. SAN, SAP, and SAK are the main components of soil available nutrients. The level of SAN, SAP, and SAK content mainly reflects the ability of the soil to supply the actual nitrogen, phosphorus, and potassium to plants. Moreover, their contents in soils directly affect plant growth and the evaluation of soil quality. We have added an explanation of soil available nutrients to the article. The revised content is as follows:

L70-74: Soil available nutrients refer to the nutrients in the soil that can be directly utilized by the plant [15]. As the main components of soil available nutrients, the levels of SAN, SAP, and SAK content mainly reflect the ability of the soil to supply the actual nitrogen, phosphorus, and potassium to plants [15]. Moreover, their contents in soils directly affect plant growth and the evaluation of soil quality [16-19].

Introduction

Point 3：Line 41: What do you mean by soil mechanical composition?

Response: Thank you for the question. Soil mechanical composition is also known as soil texture which characterizes the assemblage of soil particles. We have changed it to soil texture in the manuscript. The revised content is as follows:

L43-44: Such as soil moisture content, soil nutrients, soil texture, climate, and topography, various soil factors affect regional SOC content and its dynamic variations [3].

Point 4：Line 68-70: Rewrite.

Response: Thank you very much. We have rewritten Lines 68-70. The revised content is as follows:

L70-75: Soil available nutrients refer to the nutrients in the soil that can be directly utilized by the plant [15]. As the main components of soil available nutrients, the levels of SAN, SAP, and SAK content mainly reflect the ability of the soil to supply the actual nitrogen, phosphorus, and potassium to plants [15]. Moreover, their contents in soils directly affect plant growth and the evaluation of soil quality [16-19]. SOC is closely related to soil available nutrients.

Point 5：Line 71: What is SAP?

Response: Thank you for the question. SAP refers to soil available phosphorus. We have added the full name before using the abbreviation. The revised content is as follows:

L25-27: The SOC content was more obviously correlated with soil available phosphorus (SAP) content in the soil layers of 30-40 cm (r=0.57) on the semi-sunny slope;

Point 6：Introduction section is not well managed and needs comprehensive improvement regarding scientific quality and language.

Response: Thank you very much. We have improved the writing of the introduction section. The revised content is as follows:

L34-38: SOC and soil nutrients play pivotal roles in the carbon cycle. SOC, as a crucial element of soil organic matter (SOM), plays a vital role in evaluating soil quality and structure. Meanwhile, soil nutrients, as the cornerstone of soil fertility, have a significant impact on the carbon exchange between plants and the atmosphere, making them highly influential [1].

L46-49: It's worth noting that the factors impacting SOC content vary across different soil layers [1]. For instance, the main influencing factor of SOC is the climate in shallow soil, while is clay content in deep soil, with a significant positive correlation between them.

L54-55: Scholars have extensively researched on SOC, especially in high-altitude mountainous areas where the region is more sensitive to climatic factors [8].

L58-60: Makarov et al. [11-12] pointed out that soil organic carbon decreased with increasing soil moisture and microbial biomass decreased with decreasing soil moisture.

L70-75: Soil available nutrients refer to the nutrients in the soil that can be directly utilized by the plant [15]. As the main components of soil available nutrients, the levels of SAN, SAP, and SAK content mainly reflect the ability of the soil to supply the actual nitrogen, phosphorus, and potassium to plants [15]. Moreover, their contents in soils directly affect plant growth and the evaluation of soil quality [16-19]. SOC is closely related to soil available nutrients.

L85-88: In recent years, there have been more studies on SOC in the Qilian Mountains [1, 24-28]. For example, scholars primarily studied on the impacts of soil depth, plant type, climate, soil moisture, soil physicochemical properties, and elevation on SOC content in the Qilian Mountains [1, 26-28].

Material and methods

Point 7：This section is presented appropriately but needs little improvements as highlighted in attachment.

Response: Thank you very much. The revised content is as follows:

L160-161: The following formula was used to calculate SOC content:

Result

Point 8：Improve this section with interpretation of significant findings. It looks too lengthy. Exclude the discussion portion from results and add it into discussion section. Add lettering in the figures if possible. Improve the reporting language and avoid jargon. Directly state the results. Authors must quantitatively report their results. Make the results section concise and specific.

Response: Thank you very much for your important suggestion. Based on your suggestions, we have revised the results section and added the letters in the upper left corner of Figure 3. The revised content is as follows:

L209-217: The SOC content of different slope orientations significantly differed during the growing season. During the growing season (Figure 4a), SOC content of the semi-shady slope reached the highest value (80.20 g/kg) in September and the minimum value (53.17 g/kg) in May. While SOC content of the semi-sunny slope of the maximum value (63.43 g/kg) and the minimum value (57.84 g/kg) occurred in May and July, respectively. In September on the semi-shady slope and in May on the semi-sunny slope, SOC content was significantly different from that in other months (P<0.05). Compared to the semi-sunny slope, the SOC content of the semi-shady slope was lower in May and June but was significantly higher from July to October.

L225-235: During the growing season (Figure 4b), the content of SAN had the maximum value (14.67 mg/kg) in October and the minimum value (6.91 mg/kg) in May on the semi-shady slope, and had the maximum value (13.75 mg/kg) in June and the minimum value (7.53 mg/kg) in October on the semi-sunny slope. On the semi-shady slope, SAN content in October was significantly different from June, July, August, and September (P<0.05), and more significantly different from May (P<0.05). On the semi-sunny slope, SAN content in June was significantly different from other months (P<0.05). It was found that SAN content was the semi-sunny slope > the semi-shady slope from May to June, and was the semi-shady slope > the semi-sunny slope from July to October. Soil available nitrogen (SAN) content was consistent with SOC content, which exhibits greater synchronization. 

L236-243: The content of SAP reached the maximum value (21.67 mg/kg) in September and the minimum value (14.21 mg/kg) in July on the semi-shady slope (Figure 4c), and also reached the maximum value (20.25 mg/kg) in September and the minimum value (13.63 mg/kg) in May on the semi-sunny slope. In September, the SAP content on both semi-shady and semi-sunny slopes was significantly different from all other growing season months (P<0.05). SAP content was the semi-sunny slope > the semi-shady slope in July and October, but it was the semi-shady slope > the semi-sunny slope in other months.

L244-252: The content of SAK showed the maximum value (187.71 mg/kg) in July and the minimum value (83 mg/kg) in October on the semi-shady slope (Figure 4d), and showed the maximum value (107.13 mg/kg) in June and the minimum value (71.75 mg/kg) in October on the semi-sunny slope. On the semi-shady slope, SAK content in July was significantly different from June and August (P<0.05) and more significantly different from May, September, and October (P<0.05). On the semi-sunny slope, SAK content in June was significantly different from other months (P<0.05), but the differences were not significant in other months. The SAK content of the semi-shady slope was consistently higher than that of the semi-sunny slope.

L218-223:

Figure 4. Temporal changes of SOC in different slope directions. (Different lowercase letters indicate significant differences in SOC and soil available nutrients among different months by LSD test (P<0.05). The same lowercase letter indicates no significant differences in SOC and soil available nutrients among different months by LSD test (P<0.05). The green and orange dashed lines represent line charts depicting the changes in SOC and soil available nutrients across different months).

Discussion

Point 9：Improve this section with logical and scientific approach. Rewriting of previous studies/results deteriorate the quality of manuscript. It is quite simple and easy to read. Discussion section may be improved with recent citation. Findings are again presented in the discussion section.

Try to discuss results with recent literature with logical reasoning.

Remove subheadings from the discussion section.

Response: Thank you very much for your important suggestion. Based on your suggestions, we have revised the discussion section. The revised content is as follows:

L356-478:

4.1 Impact of slope orientation and soil layer depth on the SOC and soil available nutrient

The variability of environmental factors across different slope directions directly impacts soil temperature, vegetation type, soil moisture, and so on. In the study area, under the same vegetation type, variations in temperature and soil moisture content resulting from differences in slope orientation were identified as the primary factors influencing the levels of SOC and soil available nutrients. These variations have a direct influence on the rate of SOC mineralization and indirectly affect the accumulation of SOC and soil available nutrients. Compared to the semi-sunny slope, the SOC content of the semi-shady slope was lower in May and June but was significantly higher from July to October (Figure 4a). Studies have shown that temperature and precipitation are positively correlated with SOC reserves on a global scale [4]. At high-altitude areas, the temperature is a limiting factor for vegetation growth [18]. Increased temperature leads microorganism decomposition rates to increase, which accelerates the decrease of SOC content [3]. In July, the semi-sunny slope was influenced by more precipitation and higher temperature (Figure 2). This caused the soil respiration to enhance and the decomposition and transformation of SOM to accelerate, which was not conducive to the accumulation of SOC on the semi-sunny slope. In September, the temperature dropped and precipitation increased in the study area, but the semi-shady slope has higher soil moisture content (SMC) (87.51%) (Figure 9). This leaded to soil microbial activity weakening and a large amount of organic matter preserved in the soil, which resulted in SOC content being higher relatively on the semi-shady slope. In addition, throughout the soil profile, the SAK content was consistently higher on the semi-shady slope than on the semi-sunny slope (Table 1), which may be related to the soil moisture content that affects the release and fixation of potassium. It has been shown that SAK content has a significant negative correlation with soil moisture [2]. According to Table 1, soil moisture content in the study area was consistently higher on the semi-sunny slope than on the semi-shady slope, resulting in lower SAK content in the former than in the latter.

Figure 9. Monthly variation of soil moisture in different slope directions.

Variations in soil depth directly impact soil water content, soil texture, vegetation apomixis, and variability in plant root systems. Indirectly, these variations also affect the accumulation of SOC and the content of soil available nutrients. The higher the soil clay content, the better the water retention capacity, and the better the growth of surface vegetation, and the more vegetation litter and the organic matter of surface soil [36]. Although this paper lacked sampling data on the root system of vegetation in the study area, Zhang et al. [40] have previously reported that the root system of subalpine scrub vegetation is predominantly distributed within the 0-30 cm soil layer. The surface soil has a high content of SOC, which is due to the distribution of vegetation roots and the accumulation of litter [37]. Research has shown that the thickness of the vegetation litter had a negative correlation with the soil bulk density (BD) [38]. In comparison to the semi-shady slope, the semi-sunny slope had a smaller BD in the soil layer 0-10 cm (Table 1), resulting in a thicker vegetation litter and a higher input of SOC content. However, the amount of litter and vegetation roots distribution decrease with the deepening of soil depth, so SOC content also decreases gradually. In addition, SOC content is related to many factors at the same soil depth on different slope directions, such as temperature, precipitation, illumination, soil clay content, and vegetation biomass, etc., which affect the spatial distribution pattern of SOC [2]. In the study area, the light conditions, surface soil moisture content and clay content (Table 1) were better on the semi-sunny slope than on the semi-shady slope [30], and the plant root system had a positive correlation with the soil moisture content [39], resulting in a higher distribution of plant roots and a higher biomass accumulated by vegetation on the semi-sunny slope. Therefore, the SOC content in the soil layers of 0-10cm, 10-20cm, 20-30cm, and 30-40cm was higher on the former than on the latter. With the deepening of soil depth, a large amount of SOM was accumulated and pre-served since the evaporation of soil moisture weakened. Moreover, the decomposition rate of SOM was relatively slow on semi-shady slope, which led to significant accumulation and preservation of SOC. Therefore, SOC content in the soil layer of 40-50cm and 50-60cm was higher on the semi-shady slope than on the semi-sunny slope. In addition, the level of soil available nutrient content represents the intensity of nutrients that the soil can supply to vegetation growth [9]. The content of available nutrients on different slope directions was highest in the soil layer of 0-10 cm and showed a decreasing trend with increasing soil depth, indicating that surface aggregation of soil available nutrients was significant. In the study area, most of the vegetation roots were concentrated in the soil layer of 0-30 cm [40], so the accumulation of soil available nutrients in the surface layer can provide the required nutrients for vegetation growth. This was consistent with the results obtained by Tudi et al. [14] in the Tianshan Mountains of North-western China.

4.2 Impact of slope orientation and soil layer depth on the relationship between SOC and soil available nutrient

Variation in slope orientation affects the relationship between SOC and soil available nutrients. For instance, on the semi-shady slope, there was a significant positive correlation between SAN content and SOC content in the soil layer of 30-40 cm. However, this correlation was negligible in the same soil layer on the semi-sunny slope. These findings suggest that SAN has a limited impact on the variation of SOC content in the soil layer of 30-40 cm on the semi-sunny slope. Interestingly, the correlation between SOC content and SAN content was higher in the same soil layer on the semi-shady slope than on the semi-sunny slope (Figure 6). This could be attributed to the weaker evaporation and higher soil moisture content (as indicated in Table 1) on the semi-shady slope, which facilitated the accumulation of SAN content. Compared to the semi-shady slope, the relationship between SOC content and SAP content was more significant on the semi-sunny slope (Figure 7). Phosphorus of vegetation growth mainly comes from the soil, with vegetation root activity directly or indirectly influencing the changes in SAP content, and vegetation roots of different soil depths speeding up the soil phosphorus cycle [41]. Therefore, more phosphorus enriched in the soil promotes vegetation growth and contributes to vegetation photosynthesis, which in turn affects SOC content. The growth of vegetation on the semi-sunny slope was better than on the semi-shady slope, with a large amount of vegetation litter accumulating on the surface. The root system of subalpine scrub in the study area was shallowly distributed [40], which led to the vigorous root growth of its vegetation [39]. This increased SOC input and resulted in a higher correlation between SOC content and SAP content on the semi-sunny slope. The correlation between SAK content and SOC content was more significant on the semi-sunny slope than on the semi-shady slope, which was consistent with the correlation between SOC content and SAP content.

The correlation between SOC and soil available nutrients exhibited variations across different depths within the soil profile. For example, in the case of the semi-sunny slope, SOC content was moderately and positively correlated with SAN in the soil layer of 0-10 cm (r= 0.47). This is because SAN is the main form in which plants obtain nitrogen directly from the soil [42]. Soil nitrogen content mostly comes from the return of vegetation litter and roots, organic matter formed by microbial decomposition and synthesis, artificial fertilization, etc. [20]. However, the study area belongs to the subalpine scrub area, where vegetation growth is weakly disturbed by anthropogenic factors (there is slight grazing activity), so the content of SAN is only related to the content and quality of SOM [43]. It has been shown that SAN content adds with the increase of SOC content [35], while soil nitrogen mainly contributed to the decomposition of organic matter through microbial activity and vegetation growth [44]. Since vegetation litter and plant roots are primarily distributed in the surface layer of the soil [40], the correlation between SOC and SAN becomes more apparent. In the semi-sunny slope, there was a moderate and negative correlation observed between SOC and SAP in the soil layer of 40-50 cm. This was because SOC content decreased while SAP increases (due to the reduced consumption of SAP by the plants) in this soil layer, which caused a negative correlation between them. This is similar to previous research findings [20]. There was a significant positive correlation with SAK content in the soil layer of 70-80 cm on the semi-sunny slope (r=0.84, P<0.05) (Figure 8), which may be the result of the influence of mineral composition in the parent rock. This was consistent with the results obtained by Liu et al. [16] in the forestlands. SAK is mainly influenced by land type, soil-forming parent material, soil texture, topography, and hydrology [20, 45], and its main sources are mineralization of vegetation litter and weathering of parent layer minerals [20, 46]. Therefore, the deeper soils are most affected by SAK, which is because SAK is associated with weathering of parent layer material. The high potassium soils are supplied by the high potassium-bearing minerals such as mica or feldspar in the soil parent material [2]. This was also proved by Li et al. [47], which the SAK content was the highest in the sandstone residual slope deposits, moderate in the Quaternary alluvium, and the lowest in the granite residual slope deposits. The soils in the study area are sandstone weathering deposits, which also have a higher SAK content.

Conclusion

Point 10：Conclusion sections is more lengthy than abstract. Make it concise and quantify if possible. Rewrite the whole conclusion section again.

Response: Thank you very much for your important suggestion. Based on your suggestions, we have revised the conclusion section. The revised content is as follows:

L484-489: SOC content and soil available nutrients are mainly on the semi-shady slope > semi-sunny slope during the growing season, and they decreased with the deepening of soil depth in different slope directions, which showed obvious surface aggregation. At the same soil depth, SOC content showed the semi-sunny slope > the semi-shady slope in soil layers of 0-40cm and showed the semi-shady slope > the semi-sunny slope in soil layers of 40-60cm.

L490-497: SOC content was significantly positively correlated with soil available nutrients content in the study area. However, the correlation between SOC and soil available nutrients varied among different soil layers and slope orientations. For example, the SOC content was more obviously correlated with SAN content in the soil layer of 30-40 cm (r=0.67, P<0.05) on the semi-shady slope. The SOC content was more obviously correlated with SAP content in the soil layers of 30-40 cm (r=0.57) and 60-70 cm (r=0.55) on the semi-sunny slope. The SOC content was more obviously correlated with SAK content in the soil layer of 70-80 cm (r=0.84) on the semi-sunny slope.

L498-506: The variability of environmental factors across different slope directions directly impacts soil temperature, vegetation type, and soil moisture, and so on. These variations have a direct influence on the rate of SOC mineralization and indirectly affect the accumulation of SOC and soil available nutrients. SOC content is closely related to soil available nutrients. Therefore, the present results demonstrate a significant positive correlation between SOC and soil available nutrients. Furthermore, they pointed out the significant influence of different slope directions and different soil layers on their spatial distribution and interrelationship. These findings provide a theoretical foundation for studying carbon stock and carbon cycle in high-altitude regions.

Point 11：Follow the journal guidelines for the references style within the text and in the bibliographic section.

Response: Thank you very much. The revised content is as follows:

L563-565:

21. Wang, J. L.; Ou, Y. H.; Wang, Z. H.; Chang, T. J.; Li, P.; Shen, Z. X.; Zhong, Z. M. Influential factors and distribution characteristics of topsoil organic carbon in alpine grassland ecosystem in the south slope of Gunga South Mountain-La Ruigangri Mountain. Chinese J. Soil Sci. 2010, 41 (02), 346-350.

L581-582:

29. 29. Cao, B. Changes in modern glaciation at Lenglongling in the eastern part of the Qilian Mountains. Master’s Thesis, Lanzhou University, Gansu, China, 2013.

L583-584:

30. Wang, X.L. A study on mountain climate in the basin of Xiying River at the east section of Qilian Mountains. Master’s Thesis, Lanzhou University, Gansu, China, 2008.

L588-589:

32. Lei, C.Y.; Li, W.; Yin, X.K.; Yuan, H.Y.; Wu, J.L. Study on the Relationship between Process of Critical Zone and Natural Ecological Restoration in the Qilian Mountains. Bul. Min., Petrology Geochemistry 2020, 39(04), 741-753.

L592-593:

34. Xiao, Y.; Zhao, Y.; Tu, Z.D.; Qian, B.; Chang, R.M. Topology checking method for low voltage distribution network based on improved Pearson correlation coefficient. Pow. Sys. Prot. Ctrl. 2019, 47(11), 37-43.

Author Response File: Author Response.pdf

Reviewer 2 Report

This manuscript (sustainability-2520295) explores the spatial and temporal distribution of soil organic carbon (SOC) content and its correlation with soil nutrients in the high-altitude mountainous areas of the eastern Qilian Mountains. The findings demonstrate a significant positive correlation between SOC and soil nutrients, with variation across different soil layers and slope orientations.

The introduction, materials, and methods sections are good and described correctly. However, the results and discussion sections require attention for restructuring and rewriting. In addition, please note the following comments.

Keyordds in alphabetic order;

L84. Double “-“

Check standardizing references, and old references;

Add an indication of north on the map (Figure 1).

In Figure 2, is it an average?

Consider rewriting all the captions, as they do not accurately reflect all the data provided.

Standardize to 'x mL' and '0.8 mol L-1' (spaces), p-values, Country for softares, and apply this to the tables presented as well. Also standardize the number of decimal places (except for those values that require four decimal places).

What do the dashed green and orange lines signify in Figure 3?

In the results section, references should not be included. Consider revising the entire section to be more direct and to only present the results obtained in your research. Leave references and discussion points for the appropriate discussion section.

Please review the x and y axes of Figure 6, 7 and 8. What is the sample size?

The conclusions need to be rewritten to avoid repeating the results. Consider adding future perspectives.

The English needs major corrections.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

The topic of SOC formation is currently highly relevant due to the requirements for SOC accumulation in the soil. Accumulation is closely related to crop growth conditions, and from this point of view, the article is very interesting, as it evaluates development according to stable conditions depending on sunlight, which are essential attributes of plant growth and can thus have a direct impact on SOC formation.

The article is very interesting from this point of view and the results are applicable for further development of the topic.

Nevertheless, a number of things need to be improved in the article, especially in the methodological part.

Vegetation cover should be more precisely described. Vegetation is not obvious from the available map and the results achieved strongly depend on its quality. It is not described how exactly the 2x2 m squares were selected, whether shrubs or grass grew on them, and above all, it is not described how the roots were handled during the SOC measurement. The article should be accompanied by photographs of the sampling sites at the beginning of monitoring.

For sampling, it should be clearly stated that it is a long-term grassy surface or a shrub  surface.

According to the results, it can be deduced that a total of 10 samples from each territory were processed, but this should be communicated directly in the methodology, with a more precise indication of the sampling date.

The soil moisture depends to a high extent on the current rainfall during the observed period and on the stoninness. However, current precipitation and stoninness are not described.

In Fig. 3, the marking labels a, b, c are not described

It follows from the analyzed samples that the semi-shaded slope is about 100 mm shallower. An explanation for comparing the samples should be described for this fact. If the depth of the soil is greater, it is obvious that the vegetation will also be more lush.

The slope of the terrain is also characteristic for SOC formation. Although the altitude is approximately the same, the size of the slope of the two plots is not described - this should be part of the basic statistics.

It follows from the sampling that there was no stony nature on the plots, as it is not described. However, stoninness should also be part of the analysis, as it can specify the total achievable sorption complex of the soil at the site, especially if the soil has been sieved.

Line 224 Root depth should be determined more accurately to better infer the relationship with SOC formation. This analysis should also reveal the connection between the influence of leaf fall on the formation of humus. I believe that the depth of the roots of the bushes is probably greater, but it probably also depends on the sunlight.

Line 250 when comparing a semi-sunny and semi-shady slope at different depths, it is necessary to take into account the different soil depth achieved in both cases.

Fig. 6 why is only 9 monitoring indicated in the dependence for a semi-shaded slope of 20-30 cm?

In the conclusion, the different total soil depths of the two plots should be taken into account and the connection with other monitoring conditions should be added, if they are different, i.e. especially with the stoninness or the size of the slope.

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.pdf

Reviewer 4 Report

This manuscript examines the spatiotemporal distribution of soil organic carbon (SOC) and soil available nutrients in the subalpine shrublands of the eastern Qilian Mountains, China. The rationale is clearly articulated, highlighting the importance of understanding carbon dynamics in sensitive high-altitude regions. The methods of field sampling, lab analysis, and statistical analysis are appropriate for the research questions. Key findings are that SOC and nutrients are higher on the semi-shady versus semi-sunny slope, decrease with soil depth, and are positively correlated overall but show differing relationships by slope, depth, and nutrient type. The discussion meaningfully contextualizes the results. With minor revisions to improve clarity and flow, this manuscript can provide a useful contribution on mountain soil carbon and fertility.

Major Comments

Strengthen the introduction by citing prior related work on SOC in the Qilian Mountains specifically. This will better establish the novelty of your study.

Clarify in the methods any site history (grazing, etc) and soil characteristics besides texture that could influence interpretations.

Consider restructuring some parts of the results for better flow:

Combine sections 3.1 and 3.2 on temporal variations into one section

Move spatial variability results (currently mid-section 3.1.2 and 3.2.2) to follow the temporal results

Combine correlation results (currently section 4) into one section

The discussion could be enhanced by explicitly proposing mechanisms to explain the observed trends in SOC, nutrients, and their relationships.

Minor Comments

Be consistent in spelling out soil organic carbon versus abbreviating as SOC

Add units/dimensions when first mentioning depth intervals (e.g. 0-10 cm)

Carefully check that all cited references are included in the reference list. Please consider this paper, https://doi.org/10.1016/j.scitotenv.2022.158274

Improve visual clarity of Figures 5-8 by enlarging correlation circles and using different colors for positive/negative

Overall, I found this to be a well-executed study providing useful insights on soil carbon and fertility in high mountain regions. Addressing the structure and clarity points above should further improve the quality of the manuscript. I believe this work merits publication after revision.

Minor editing of English language required

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Authors have addressed most of the concerns.

English quality is appropriate.

Reviewer 2 Report

I thank the authors for responding to my comments and improving the manuscript. I believe it can be accepted for publication.

Minor editing of English language required for grammar and spelling.