Interactive Effects of Light and Nitrogen on Pakchoi (Brassica chinensis L.) Growth and Soil Enzyme Activity in an Underground Environment

Round 1

Reviewer 1 Report

Agronomy_ 986408

Title: Interactive effects of light and nitrogen on pakchoi (Brassica chinensis L.) growth and soil enzyme activity in an underground environment

Author: Songsong Li

General Comments

The paper examines growth of pak choi to light and nitrogen. This is not a new idea, but the data are okay.

The paper needs a bit of reorganization. The Introduction, in particular, is difficult to follow. The other parts of the paper are more readable. 

Specific Comments

• The Abstract is okay. However, 'toxic effect theory' is not defined, and thus I doubt readers will understand the logic. Indeed, I am not sure that I understand the last sentence. What are you trying to say?

• The Introduction is confusing because 'underground space utilization' is not defined exactly. Do you mean soil from the mine, or within the mine per se. It would help readers if in the first sentence you describe the specific situation about the mine you are studying. What is the question, growing plants without sunlight?

• You need to add much more justification to the Introduction about growing plants underground. The literature review of light and nitrogen on crop growth is to general. Determining the light, nitrogen requirement of a plant is not novel. What is novel about your study?

• The Method section needs reorganization. The section on Toxic Effect Theory belongs in the Introduction. Also, the section needs justification related specifically to pak choi. The toxic effect varies with species.

• The same applies to the section on plant-microbe interaction. This section also belongs in the Introduction, not the Methods. It is justification for the experimental design. Actually, it is not clear to me if it is appropriate since you have not included phosphorus in the experiment.

• The Results section is fairly straightforward.

• In the Discussion section, I believe the height, light relationship is simply a function of plant competition for light. Plants grow tall at low light levels to better compete for light. However, when light levels are high, there is no need to compete.

• Otherwise the Discussion is fairly straightforward.

• The Conclusion could be much better. As written it is mostly an abstract of the results. Rather than repeated results, focus on the implications of the research and what you have learned from it.

Technical Comments

• Line 10: describe 'underground situations' to a more descriptive term. Within the mine?

• Line 12: delete 'underground environment.'

• Line 19: change 'while' to 'whereas.'

• Line 30: delete 'shallow earth'. Say 'resource use.'

• Line 33 to 38: redundant wording. Try to say this in one sentence, i.e., light and nitrogen are critical.

• Line 39: you are unaware of the literature. There must be more than a thousand studies of light, nitrogen interaction. Delete this sentence. A better sentence is the impact of light and nitrogen on the plant that you are using.

• Line 41 to 58: avoid simply reporting the findings in other's work. Your paper is not a literature review. Indeed, the two paragraphs could be reduced to one or two sentences, i.e., the level of nitrogen that simulates growth before being toxic is unknown.

• Line 99: add a reference for the CCI measure, such as: Fitzgerald, G., Rodriguez, D., & O’Leary, G. (2010). Measuring and predicting canopy nitrogen nutrition in wheat using a spectral index—The canopy chlorophyll content index (CCCI). Field Crops Research, 116(3), 318-324.

• Line 230: awkward wording. Consider saying, 'height decreased with increasing light'.

• Line 264: reference is missing.

Author Response

Dear reviewer,

We feel appreciated for your kindness in reviewing our manuscript entitled “Interactive effects of light and nitrogen on pakchoi (Brassica chinensis L.) growth and soil enzyme activity in an underground environment”. We have carefully read the comments from you, which was really useful for our revision of this manuscript. We have made a substantial revision on this manuscript and made a point-to-point reply to all the comments.

In the following, we will show a detailed point-to-point reply on the comments. The original comments with be shown with black color, and the reply will be shown in red color.

Thanks for your time in reviewing our manuscript.

Best regards

Response to Reviewer#1 Comments

General Comments

The paper examines growth of pakchoi to light and nitrogen. This is not a new idea, but the data are okay. The paper needs a bit of reorganization. The Introduction, in particular, is difficult to follow. The other parts of the paper are more readable. 

Response: Thanks for your valuable advice. The introduction has been reorganized and the whole paper has been carefully checked according to the specific comments.

 Specific Comments

Point 1: The Abstract is okay. However, 'toxic effect theory' is not defined, and thus I doubt readers will understand the logic. Indeed, I am not sure that I understand the last sentence. What are you trying to say?

Response 1: Sorry for the unreadable expression. We have changed “toxic effect theory” to “toxic effect of excessive nitrogen” in Line 21. In the last sentence, we tried to express two points: (1) toxic effect of excessive nitrogen explained our results better than the plant-microbe interaction framework. (2) the critical toxicity level of nitrogen for pakchoi was negatively affected by light intensity. We have divided the sentence into two sentences.

Line 21-24: Our results suggested that the toxic effect of excessive nitrogen was a better explanation for the interactive effects of light and nitrogen than the plant-microbe interaction framework. The critical toxicity level of nitrogen for pakchoi was determined and showed a negative correlation with light intensity.

Point 2: The Introduction is confusing because 'underground space utilization' is not defined exactly. Do you mean soil from the mine, or within the mine per se. It would help readers if in the first sentence you describe the specific situation about the mine you are studying. What is the question, growing plants without sunlight?

Response 2: Sorry for the vague expression. In our study, 'underground space utilization' means within the mine (not soil from the mine). The question is growing plants without natural sunlight and atmospheric nitrogen deposition.

Point 3: You need to add much more justification to the Introduction about growing plants underground. The literature review of light and nitrogen on crop growth is to general. Determining the light, nitrogen requirement of a plant is not novel. What is novel about your study?

Response 3: Thanks for your valuable advice. Researches related to grow plants underground have been added. There are numerous separate studies of light or nitrogen on crop growth, it is difficult and unnecessary to review all the literatures. In fact, the interaction of light-nitrogen on pakchoi is our focus and remains unclear. The novel aspect of this study is to investigate the mechanism of light-nitrogen interaction on pakchoi through the soil enzyme aspect and determine the critical toxicity level of nitrogen for pakchoi.

Point 4: The Method section needs reorganization. The section on Toxic Effect Theory belongs in the Introduction. Also, the section needs justification related specifically to pakchoi. The toxic effect varies with species.

Response 4: Thanks for the advice. In this paper, the Toxic Effect Theory and Plant-microbe Interaction Framework have been mentioned in the Introduction section (Line 55-58). The two theories should be described in details since they are important to interpret the results, and it is therefore inappropriate to be inserted in the Introduction. Thus, we prefer this section to stay in the M&M part.

As we mentioned in the paper, the toxic effect varies with species. Since the critical toxicity level of N for pakchoi is not clear, one of our contributions was to determine it (Line 268-270).

Point 5: The same applies to the section on plant-microbe interaction. This section also belongs in the Introduction, not the Methods. It is justification for the experimental design. Actually, it is not clear to me if it is appropriate since you have not included phosphorus in the experiment.

Response 5: Thanks for the advice. In this paper, the Toxic Effect Theory and Plant-microbe Interaction Framework have been mentioned in the Introduction section (Line 55-58). The two theories should be described in details since they are important to interpret the results, and it is therefore inappropriate to be inserted in the Introduction. Thus, we prefer this section to stay in the M&M part.

In our study, the soil available phosphorus was measured and data were shown in Table 4.

Point 6: The Results section is fairly straightforward.

 Response 6: Thanks for your advice. We have revised.

Point 7: In the Discussion section, I believe the height, light relationship is simply a function of plant competition for light. Plants grow tall at low light levels to better compete for light. However, when light levels are high, there is no need to compete.

Response 7: Thanks for pointing this out. We agree and have revised.

Line 234-235: “…plants can express the shade-avoidance syndrome by growing taller to compete for light when exposed to low light intensity.”

Point 8: Otherwise the Discussion is fairly straightforward.

Response 8: Thanks for your advice. We have updated.

Point 9: The Conclusion could be much better. As written it is mostly an abstract of the results. Rather than repeated results, focus on the implications of the research and what you have learned from it.

Response 9: Thanks for your valuable advice. The potential implications of the research were added in the Conclusion part.

Line 333-334: “…This result could provide a guide to the pakchoi planting in greenhouse or underground space...”

Technical Comments

Point 10: Line 10: describe 'underground situations' to a more descriptive term. Within the mine?

Response 10: Sorry for the unspecific expression. In our paper, underground situation means any underground space (e.g. mine) where there is no sunlight and nitrogen deposition. The information has been added.

Line 9-10: Light conditions and nitrogen fertilizer are crucial for plant growth, especially in the underground situation without sunlight and nitrogen deposition.

Point 11: Line 12: delete 'underground environment.'

Response 11: Thanks for the advice. The modifications had been made as required.

Point 12: Line 19: change 'while' to 'whereas.'

Response 12: Thanks for your valuable advice. The modifications had been made as required.

Line 19: “…whereas the activity of phosphatase...”

Point 13: Line 30: delete 'shallow earth'. Say 'resource use.'

Response 13: Thanks for your valuable advice. The modifications had been made as required.

Line 31: “…To meet the future challenges such as climate change, environment pollution and resource use…”

Point 14: Line 33 to 38: redundant wording. Try to say this in one sentence, i.e., light and nitrogen are critical.

Response 14: Thanks for pointing this out. We have shortened the sentences. However, it is difficult to conject the first paragraph and the second paragraph with only one sentence.

Point 15: Line 39: you are unaware of the literature. There must be more than a thousand studies of light, nitrogen interaction. Delete this sentence. A better sentence is the impact of light and nitrogen on the plant that you are using.

Response 15: Thanks for pointing this out. We have rewritten the sentence to express more accurately.

Line 38-40: Although most researches related to the influence of the light and nitrogen (N) on plant development have been conducted separately, the interaction between these two factors was also found and investigated for specific plants.

Point 16: Line 41 to 58: avoid simply reporting the findings in other's work. Your paper is not a literature review. Indeed, the two paragraphs could be reduced to one or two sentences, i.e., the level of nitrogen that simulates growth before being toxic is unknown.

Response 16: The mechanism of light-nitrogen interaction is complex and still unclear. There are two questions need to be solved: (1) is the reduction in plant yield caused by toxic effect of nitrogen or the imbalance of N/P? (2) what is the level of nitrogen that simulates plant growth before being toxic? Hence, we believe that review of previous studies could show the current research status better rather than simple conclusion.

Point 17: Line 99: add a reference for the CCI measure, such as: Fitzgerald, G., Rodriguez, D., & O’Leary, G. (2010). Measuring and predicting canopy nitrogen nutrition in wheat using a spectral index—The canopy chlorophyll content index (CCCI). Field Crops Research, 116(3), 318-324.

Response 17: Thanks for the valuable advice. This reference had been cited in Line 102.

Point 18: Line 230: awkward wording. Consider saying, 'height decreased with increasing light'.

Response 18: Thanks for the advice. We have rewritten the sentence.

Line 233: Pakchoi height decreased with increasing light.

Point 19: Line 264: reference is missing.

Response 19: Sorry for the mistake. We have fixed the error.

line 267: “As shown in Figure 1C…”

Reviewer 2 Report

Dear Editor and Authors,

 This is interesting research with positive results to support the study question. However, the novelty of the research is average, based on the simple experiments performed and the lack of in-depth explanations in the results and discussion section.                                                                                   Given the current situation (health confinement and online pedagogic teaching), I interpreted the manuscript but I was not able to make any corrections. There are some grammatical errors, please identify them with an English editor. The title could be improved to describe better the contained of the manuscript. 
 In general, I find that the manuscript is well written with sufficient results and well designed. I encourage this type of research that can meet future challenges. 

Best regards,

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 3 Report

This is an interesting manuscript illustrating the interactive effect of light and nitrogen (N) on plant growth conducted in the underground environment. Soil enzymatic activities for both P and N (phosphatase and urease) were also considered. According to author, originality lies in the “interactive effect of light and nitrogen on crop growth” and, the inclusion of soil enzymatic activities. Research design and data analysis is appropriate to support the results and conclusion. In general, the manuscript is well written. Some general and specific comments are listed below for the further improvements.  

General comments

For introduction section, I would suggest adding literatures about light and N effects, focusing specifically on (Brassica chinensis L.) or other cruciferous crops. In line 48-49, author has mentioned that the light and N effects might be crop specific. Furthermore, the effect could vary based on soil types, thus, I would suggest including study that was performed in silty loam soil.

For materials and method (M&M) section, you may add details on soil sampling techniques and method analysis used in the study. Further, you need to add details on statistical methods and model that you have used to generate table and graphs. For example, you have shown regression analysis graph in result section (figure 2) but not included the approach in statistical analysis part under M&M section.

For result and discussion section, see the specific comments below.

Specific comments

Line 12: N kg^-1 soil?

Line 33: Is nutrient the environmental factor? Environmental factors such as light, rainfall may affect the mineralization rate, nutrient release and availability.

Line 34: I would write, crop yield and production costs.

Line 45: Mention the N dose and light intensities used in this study. Same comments in the line 52.

Line 47: you mentioned 185 kg N ha^-1, a moderate level. How did you define this rate a moderate level, based on N recommendation in the country for specific crop or something else? please specify.

Line 77: Mention the amount used and the %N content in the urea.

Line 84:  Mention the number of days as well for the experiment duration.

Line 85: Add details about soil sampling techniques (for example, equipment’s used, soil depth, replications etc.).

Line 88: Mention the methods used to analyze the soil physicochemical properties that was presented in the table 2.

Line 90: 2.1 kg dry soil?

Line 99: Did you measure foliar CCI for all plants or you sampled some? How many measurements did you take for each plant? Please specify.

Line 147: You may need to add statistical details for each analysis that you have performed. Add the type of regression model (for example, linear, quadratic, polynomial etc..) that you have used (Figure 2).

Line 160; In figure 1, I would suggest presenting only plant height and dry weight (remove fresh weight graph) as both shows consistent trend on biomass production, which is obvious (you have mentioned in this in the “line 190” as well).

Line 170: Difficulty in reading the value presented in table 3 (Phosphatase column). Please check and fix.

Line 204. But in table 3, light conditions have also shown significant effect on CCI, which is obvious based on the figure 3. Same comments in line 208. Your result illustrates that there was significant effect of T, L and N but not their interaction effect on CCI?  

line 258. I would write, “nutrition addition beyond the optimum rate”? Also provide dose of nutrient added in the mentioned study, beyond which yield start decreasing!  

Line 264. Please check the reference and fix.

Line 297: Did you analyze soil organic carbon? If yes, present the result in Table 2. This would be helpful to illustrate the proportion of C/N and its effect on urease activity.  

Line 305: Did you measure available P as well, which, could be helpful to see if P was limiting factor or not!

Author Response

Please see the attachment

Author Response File: Author Response.pdf