Effect of the Intensity and Spectral Quality of LED Light on Growth and Quality of Spinach Indoors

Round 1

Reviewer 1 Report

This paper investigates the responses of spinach in a plant factory to various light quality. The study meticulously examines both the phenotypic and internal qualities of the plants. Such efforts are deemed valuable for advancing foundational research in this field. However, there are numerous areas requiring improvement, including the presentation of results, narrative style, and statistical methodologies. It is recommended to thoroughly revise and re-summit. Thank you.

I recommend utilizing MDPI's English editing service for receiving professional proofreading of your manuscript or academic work. This service can enhance the quality of the English expression in your paper and incorporate professional editing. By utilizing this service, you can improve the overall quality of your manuscript.

Author Response

Reviewer 1

Comments and Suggestions for Authors

This paper investigates the responses of spinach in a plant factory to various light quality. The study meticulously examines both the phenotypic and internal qualities of the plants. Such efforts are deemed valuable for advancing foundational research in this field. However, there are numerous areas requiring improvement, including the presentation of results, narrative style, and statistical methodologies. It is recommended to thoroughly revise and re-summit. Thank you.

The manuscript has been revised and all sections of it have been improved

Comments on the Quality of English Language

I recommend utilizing MDPI's English editing service for receiving professional proofreading of your manuscript or academic work. This service can enhance the quality of the English expression in your paper and incorporate professional editing. By utilizing this service, you can improve the overall quality of your manuscript.

The manuscript has been sent to a native reviewer to improve the quality of the English

Author Response File: Author Response.pdf

Reviewer 2 Report

The purpose of these revisions is to enrich the content, increase its clarity and coherence, as well as to ensure its relevance and contribution to the corresponding field of study.

1.       Abstract

§  The sentence: "As the intensity increased so did the fresh and dry weight, leaf area, and PSII" is somewhat confusing. Revise the wording and the central idea of the sentence, e.g., Fv'/Fv', was higher with the mean intensity according to Table 2.

§  In the abstract, it is recommended to include information on the methodology followed and the parameters or variables measured (at least the most important ones).

§  The scientific name of the spinach should be in italics.

§  There is an inconsistency in line 15 with respect to phosphorus concentration and in line 220 the opposite information is presented.

§  In lines 19 and 2, this may generate confusion considering that the manuscript is focused on studying the effects of spectral intensity and quality in spinach cultivation. It is expected that light treatments are well controlled (without wavelengths such as green, FR and UV), because they can generate unwanted and/or unexplained disturbances.

2.      Keywords

§  It is suggested that it could include chlorophyll fluorescence parameters.

3.      Introduction

§  It is suggested to the authors to restructure the introduction because it starts talking about the specific and then goes to the general. It should start with the general to the specific.

§  The authors should be improving the inclusion of acronyms and abbreviations.

§  The scientific name of the species is not in italics, it would be convenient to indicate it that way.

§  It is recommended to reduce the introduction, the concepts between lines 39-52 so that it is specific.

§  A recommendation for the authors, the concepts of LED light quality and intensity. This is already widely reported in the literature. Maybe, they could simplify it.

§  The objective of the research remains ambiguous, i.e., what is to be evaluated should be stated.

§  The authors are recommended to standardize the units such as superscripts and subscripts.

§  How did you select the different intensities for your experiment 1, include it in the introduction (if it was obtained from an already reported work) or methods (if it is your own proposal).

§  The state of the art only indicates that several authors have worked with spinach, however, they do not show the results obtained. This leads to the fact that this article is a proposal.

4.      Material and Methods

§  The materials and methods are adequately explained, and the development is understood. However, too much information is included and from different parameters (section 2.2 -2.9), which generates greater complexity when presenting the results and discussion. It is recommended that the authors reduce the information presented with the parameters of greatest impact and their justification.

§  The units commonly used to present the nutrient solution are in micro grams (µg).

§  The main weakness of the manuscript is presented in the second experiment, due to the fact that significant amounts of green, infrared and ultraviolet light are not included in all the treatments. The aforementioned may affect the conclusions presented and that the results shown are not due to the different R/B ratio, it is recommended that the authors analyze this point to reduce the disturbances that could be generated by green, infrared and ultraviolet light with respect to the results obtained.

5.      Results

§  There is a lot of information (5 tables and 4 figures) in this section, which makes it difficult to follow and understand the manuscript, and the authors are advised to reduce the information.

§  Figure 3 shows important information, however, it is not very clear. It is recommended to use colors or another type of graphic to present this information.

§  Regarding Table 2 and Table 3 consider their importance in the form of a table that can be explained in written form.

§  Concerning Table 4, Table 5 and Table 6 where it reports the concentration of amino acids, organic acids and non-structural carbohydrates, it is recommended that the authors reconsider the importance of the parameters in each table, unify the information in a single table, exclude parameters or explain the impact it could have for the consumer, producer, biologists, to mention a few.

§  Figure 4 is intended to show a summary; however, it generates confusion at the time of understanding the results obtained. Include the reference (control) treatments, which are 150 µmol m-2 s-1 and 2R/B.

6.      Discussion

§  The discussion section is very extensive and complicated to understand, including Figures 5 and 6 (from the materials and methods section), it is recommended that the authors address the comments and suggestions indicated in the Materials and Methods section, which could lead to a restructuring of the section in order to facilitate its understanding.

§  Derived from the treatments presented in Table 1, there are treatments that include green, ultraviolet and infrared wavelengths. Since they are not present in the treatments, the scientific method may not be well applied.

§  In this section, it is required to strengthen whether the results obtained are due to the presence of green, ultraviolet and infrared or to the R/B ratios. It is important that the authors consider this point, because it would cause the results presented in the manuscript to be questionable

7.      Conclusions

§  The conclusions should be rewritten including the most relevant points of the research. As well as the recommendations mentioned above.

Please check the comments and suggestions in attached file

Comments for author File: Comments.pdf

Author Response

Reviewer 2

1. Abstract

• The sentence: "As the intensity increased so did the fresh and dry weight, leaf area, and PSII" is somewhat confusing. Revise the wording and the central idea of the sentence, e.g., Fv'/Fv', was higher with the mean intensity according to Table 2.

The sentence has been revised and modified to clarify it

• In the abstract, it is recommended to include information on the methodology followed and the parameters or variables measured (at least the most important ones).

The methodology used (light intensity and spectrum) and parameters measured have been included in the abstract

• The scientific name of the spinach should be in italics.

The scientific name of the spinach has been changed to italic

• There is an inconsistency in line 15 with respect to phosphorus concentration and in line 220 the opposite information is presented.

The sentence in abstract has been corrected

• In lines 19 and 2, this may generate confusion considering that the manuscript is focused on studying the effects of spectral intensity and quality in spinach cultivation. It is expected that light treatments are well controlled (without wavelengths such as green, FR and UV), because they can generate unwanted and/or unexplained disturbances.

We agree with the reviewer, and we think that the treatments are well-controlled. But the objective of this work as indicated is to compare commercial spectrum lights that are very common in the indoor industry. Therefore, without the possibility of suppressing green wavelength Fr or UV

2. Keywords

• It is suggested that it could include chlorophyll fluorescence parameters.

This keyword Has been included

3. Introduction

• It is suggested to the authors to restructure the introduction because it starts talking about the specific and then goes to the general. It should start with the general to the specific.

The introduction has been restructured and improved

• The authors should be improving the inclusion of acronyms and abbreviations.The scientific name of the species is not in italics, it would be convenient to indicate it that way.

The acronyms and abbreviations have been included and the name of species changed to italics

• It is recommended to reduce the introduction, the concepts between lines 39-52 so that it is specific.

The introduction has been reduced

• A recommendation for the authors, the concepts of LED light quality and intensity. This is already widely reported in the literature. Maybe, they could simplify it.

Both concepts have been simplified in the introduction section

• The objective of the research remains ambiguous, i.e., what is to be evaluated should be stated.

The objective has been modified in order to improve its understanding

• The authors are recommended to standardize the units such as superscripts and subscripts.

The superscripts and subscripts have been standardized

• How did you select the different intensities for your experiment 1, include it in the introduction (if it was obtained from an already reported work) or methods (if it is your own proposal).

The intensities for experiment 1 were established based on the bibliography and our experience in previous experiments (unpublished). we observed that above 450 μmol m−2 s−1, the plants had a strong decline in production. On the other hand, knowing that in the literature 100-150 μmol was used in most experiments and that a study determined that the highest net photosynthesis rate (Pn) was observed under 300 μmol m−2 s−1, which is consistent with our previous tests. The final decision used two extreme intensities above and below (150 and 430) and one intermediate (290)

• The state of the art only indicates that several authors have worked with spinach, however, they do not show the results obtained. This leads to the fact that this article is a proposal.

 Results from studies carried out on hydroponic spinach with different intensities and light spectrums have been included.

4. Material and Methods

• The materials and methods are adequately explained, and the development is understood. However, too much information is included and from different parameters (section 2.2 -2.9), which generates greater complexity when presenting the results and discussion. It is recommended that the authors reduce the information presented with the parameters of greatest impact and their justification.

 The material and method section have been reduce significantly from 2.10 section to 2.7

• The units commonly used to present the nutrient solution are in micro grams (µg).

 Based on our experience, we think that the most nutrient solution units used are  mM y µM

• The main weakness of the manuscript is presented in the second experiment, due to the fact that significant amounts of green, infrared and ultraviolet light are not included in all the treatments. The aforementioned may affect the conclusions presented and that the results shown are not due to the different R/B ratio, it is recommended that the authors analyze this point to reduce the disturbances that could be generated by green, infrared and ultraviolet light with respect to the results obtained.

For this experiment, commercial lights (Valoya) widely used in the indoor hydroponic growing industry have been used. in which these wavelengths (green, infrared and ultraviolet) cannot be eliminated. Regarding the second part of the comment, when there was no correlation between the R/B ratio in the data obtained, it has been interpreted as a direct effect of ultraviolet or far infrared light (see discussion section), as a possible cause of the observed, these discussion are based on bibliograph.

5. Results

• There is a lot of information (5 tables and 4 figures) in this section, which makes it difficult to follow and understand the manuscript, and the authors are advised to reduce the information.

The tables and figures have been reduced to facilitate the following manuscript. Figure 1 and 2  and table 5 and 6 have been put together. Table 3 have been deleted

• Figure 3 shows important information, however, it is not very clear. It is recommended to use colors or another type of graphic to present this information.

The colors of the figure have been changed in order to clarify it

• Concerning Table 4, Table 5 and Table 6 where it reports the concentration of amino acids, organic acids and non-structural carbohydrates, it is recommended that the authors reconsider the importance of the parameters in each table, unify the information in a single table, exclude parameters or explain the impact it could have for the consumer, producer, biologists, to mention a few.

 Thanks for the comment, we have reconsidered the option of eliminating some parameters in each table and it has been possible to unify table 5 and table 6 into a single table

• Figure 4 is intended to show a summary; however, it generates confusion at the time of understanding the results obtained. Include the reference (control) treatments, which are 150 µmol m-2 s-1 and 2R/B.

 In this case, although we understand that the table may be a little confusing, we consider that including a white column (white color by 0 number) with the references would be a little more confusing, we have modified the figure caption to make it easier to understand.

6. Discussion

• The discussion section is very extensive and complicated to understand, including Figures 5 and 6 (from the materials and methods section), it is recommended that the authors address the comments and suggestions indicated in the Materials and Methods section, which could lead to a restructuring of the section in order to facilitate its understanding.

The discussion has been restructured and rewritten to reduce its length and facilitate its understanding.

• Derived from the treatments presented in Table 1, there are treatments that include green, ultraviolet and infrared wavelengths. Since they are not present in the treatments, the scientific method may not be well applied.   

 The main objective of this paper is evaluated commercial lights with complex wavelenghts. We do not understand what the reviewer means by applying the scientific method, since the objective of this work is the comparison of commercial lights and their influence on the yield and quality of spinach.

7. Conclusions

• The conclusions should be rewritten including the most relevant points of the research. As well as the recommendations mentioned above.

The conclusion have been rewritten an it has been included the most relevant point of this research

Author Response File: Author Response.pdf

Reviewer 3 Report

Manuscript entitled 'effect of the intensity and spectral quality of LED light on growth and quality of Spinach indoors' aimed to highlight its innovative approach in the detailed examination of the influence of light intensity and quality on the nutritional content of spinach, including minerals, organic acids, sugars, and amino acids, alongside primary metabolites. Additionally, it utilizes principal component analysis to enhance the visualization of data. The experimental design was fully completed and the results were interesting, however, the manuscript presents several problems that should be considered. The details are as follows:

1.      The experiments of light intensity combined with light quality were conducted as two separate trials with differing durations. What is the rationale for this setup? The section on light quality primarily aims to discuss the impact of the red to blue (R:B) ratio on growth and quality of spinach, yet it does not account for potential interference from ultraviolet or far-red light, presenting certain issues with this design.

2.      Does the experimental design include a control treatment? This is important to ensure that the observed changes in spinach growth are caused by light rather than other factors.

3.      Suggest adding an error bar in Figure 1. As the light intensity increases, fresh weight, dry weight, and leaf area cannot be represented by a line graph. Different light intensity treatments designed 39 days after sowing, while different light quality treatments taken for 45 days, resulting in a fresh weight of over 3 g per plant. What is the reason for this?

4.      In assessing the impact of light quality on spinach's photosystem II, why was the chlorophyll fluorescence indicator chosen not to include the maximum quantum efficiency such as Fv/Fm?

nothing

Author Response

Reviewer 3

Manuscript entitled 'effect of the intensity and spectral quality of LED light on growth and quality of Spinach indoors' aimed to highlight its innovative approach in the detailed examination of the influence of light intensity and quality on the nutritional content of spinach, including minerals, organic acids, sugars, and amino acids, alongside primary metabolites. Additionally, it utilizes principal component analysis to enhance the visualization of data. The experimental design was fully completed and the results were interesting, however, the manuscript presents several problems that should be considered. The details are as follows:

1. The experiments of light intensity combined with light quality were conducted as two separate trials with differing durations. What is the rationale for this setup? The section on light quality primarily aims to discuss the impact of the red to blue (R:B) ratio on growth and quality of spinach, yet it does not account for potential interference from ultraviolet or far-red light, presenting certain issues with this design.

In the first experiment at different light intensities (150-290 and 430μmo). The 150 light intensity treatment produced a small growth size. Therefore, for the next experiment with different spectra at the same intensity (150 μmo), it was decided to extend the experiment by a week to achieve higher yields with a commercial caliber. When there is no linear relationship in the R:B ratio, other wavelengths such as infrared and UV were considered to explain the obtained results. As mentioned earlier, this study aims to shed light on commercial lighting with complex spectra

2. Does the experimental design include a control treatment? This is important to ensure that the observed changes in spinach growth are caused by light rather than other factors.

While the utilization of controls is not necessary, given that the aim of the study is to compare different complex light spectra and light intensities. It could be noted that for the intensity experiment, the 150 μmo treatment, which is the most commonly used in the industry, has been employed as a control. For the different commercial spectrum experiment, the AP673L spectrum was utilized as another control.

3. Suggest adding an error bar in Figure 1. As the light intensity increases, fresh weight, dry weight, and leaf area cannot be represented by a line graph. Different light intensity treatments designed 39 days after sowing, while different light quality treatments taken for 45 days, resulting in a fresh weight of over 3 g per plant. What is the reason for this?

Error bars have been added in Figure 1. Regarding second comment, in the first experiment at different light intensities (150-290 and 430μmo). The 150 light intensity treatment produced a small growth size. Therefore, for the next experiment with different spectra at the same intensity (150 μmo), it was decided to extend the experiment by a week to achieve higher yields with a commercial caliber.

4. In assessing the impact of light quality on spinach's photosystem II, why was the chlorophyll fluorescence indicator chosen not to include the maximum quantum efficiency such as Fv/Fm?

The study of light kinetics (fv´/fm`) is much more comprehensive because the quantum yield divides it into two factors: the biochemical factor and the light efficiency factor (qp), thus providing much more information than fv/fm, which is a parameter measured in darkness.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

This manuscript has been improved through revisions. As a result, I think the paper was submitted and it was sufficient.

Author Response

Thank you very much for your comments and your time

Best 

Reviewer 2 Report

All comments in the previous report have been considered by the authors, the manuscript has greater clarity and shows important information for the area. However, some minor fixes may be considered.

1. Figure 2 is not classified as A and B as referenced in the results and discussion section (lines 227, 230, 408, 417, 437). In the figure it is mentioned: left or right. It is recommended to label as A and B. On the other hand, why are the amounts in the minerals not considered? only percentages are used. The authors are recommended to analyze this point.

2. The last row of table 2 must be centered.

3. Figure 4 is complicated to understand and has a reduced explanation in the manuscript. It is recommended that the authors analyze whether it is pertinent to maintain the figure and, if so, expand their explanation.

Author Response

Thank you very much for your comments and your time

Best 

Author Response File: Author Response.docx