Optimizing Light Intensity and Salinity for Sustainable Kale (Brassica oleracea) Production and Potential Application in Marine Aquaponics

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This research is an observable study in terms of utilisation for phytoremediation against salinity stress and/or crop biomass and nutrient management in hydroponic. However, to improve the quality of the manuscript, there are some comments:

L30 This Introduction part should be fully rewrite by addressing current situation of salinization caused by drought or others, and then find natural flows by mentioning my kale has been chosen for this research and why light intensity should be conducted (e.g., to maximize crop production, minimize the salinity stresses or etc.).

L58 It's too broad and vague. It would be great to add some literature/references regarding empirical experimental results of the effects of light intensity on kale growth.

L75 For readers, can you please briefly explain what Kratky method is in one sentence in your manuscript?

L79 Any reasons why this experimental setup? (i.e., projection scenarios or stressed levels in other literature reviews)?

L87 Any reason have you used ppt unit rather than mM of sodium?

L91 Is there any salinity stresses study regarding Russian kale cultivation so far?

L117 How often did you change the solution during your experimental period?

L120 This can be moved to L75.

L122 I am just wondering if ppt unit is common among hydroponic experimental setup in other literature.

L499 Discussion part should be addressed by each result. Please add each title of them in the Discussion part.

L584 Can you suggest which light intensity and salinity level was beneficial to biomass yield and nutrient contents in kale?

L717 Check if this format works.

L732 Check if this format works.

Comments for author File: Comments.pdf

Author Response

Thank you for your insightful feedback, we have incorporated your suggestions. I acknowledge the time and effort of our co-authors in revising the manuscript to suit the aim and scope of the journal. Below are our point-by-point responses to the comments:

Comments 1: This research is an observable study in terms of utilisation for phytoremediation against salinity stress and/or crop biomass and nutrient management in hydroponic. However, to improve the quality of the manuscript, there are some comments:

Response 1: Thank you for your time and effort to review our paper. Your comments and suggestions are really important to improve our work.

Comments 2: L30 This Introduction part should be fully rewrite by addressing current situation of salinization caused by drought or others, and then find natural flows by mentioning my kale has been chosen for this research and why light intensity should be conducted (e.g., to maximize crop production, minimize the salinity stresses or etc.).

Response 2: Thank you for stressing this out. We have rewritten the introduction part and incorporated your suggestions.

Comments 3: L58 It's too broad and vague. It would be great to add some literature/references regarding empirical experimental results of the effects of light intensity on kale growth.

Response 3: Thank you for this suggestion. We have revised the discussion and included some literature and references on related experiments regarding light intensity on kale growth.

Comments 4: L75 For readers, can you please briefly explain what Kratky method is in one sentence in your manuscript?

Response 4: We included a brief description/explanation of Kratky method in the manuscript.

Comments 5: L79 Any reasons why this experimental setup? (i.e., projection scenarios or stressed levels in other literature reviews)?

Response 5: Some studies experimented on short-term salinity exposure with similar levels of salinity stress. We wanted to see how the kale plants perform in prolonged salinity exposure, which is the actual scenario in salinized farmlands or brackish conditions.

• Pavlović, I.; Mlinarić, S.; Tarkowská, D.; Oklestkova, J.; Novák, O.; Lepeduš, H.; Bok, V.V.; Brkanac, S.R.; Strnad, M.; Salopek-Sondi, B. Early Brassica Crops Responses to Salinity Stress: A Comparative Analysis Between Chinese Cabbage, White Cabbage, and Kale. Front. Plant Sci. 2019, 10, doi:10.3389/fpls.2019.00450.
• Kucukyumuk, Zeliha, and Donald L. Suarez. "The effect of selenium on salinity stress and selenate–sulfate comparision in kale." Journal of plant nutrition20 (2021): 2996-3004.

Comments 6: L87 Any reason have you used ppt unit rather than mM of sodium?

Response 6: We chose to use parts per thousand (ppt) due to the practical ease of preparing and managing salt concentrations in solution. Specifically, using ppt allows for straightforward mixing, where 1 g of salt dissolved in 1 liter of water equates to 1 ppt, making adjustments simple and reproducible in a hydroponics or aquaponics setting. Conversely, preparing precise millimolar (mM) solutions requires more complex calculations and measurements, which can be challenging when adjusting concentrations quickly or in large volumes. By using ppt, we align with standard practices in salinity management, ensuring both accuracy and ease of application.

Comments 7: L91 Is there any salinity stresses study regarding Russian kale cultivation so far?

Response 7: There were studies on salinity stress, generally for kale, but for Russian kale is limited. Also, most studies conducted were short-term applications of salinity stress. Below are some of the studies on kale salinity stress.

• Pavlović, I.; Mlinarić, S.; Tarkowská, D.; Oklestkova, J.; Novák, O.; Lepeduš, H.; Bok, V.V.; Brkanac, S.R.; Strnad, M.; Salopek-Sondi, B. Early Brassica Crops Responses to Salinity Stress: A Comparative Analysis Between Chinese Cabbage, White Cabbage, and Kale. Front. Plant Sci. 2019, 10, doi:10.3389/fpls.2019.00450.
• Kucukyumuk, Zeliha, and Donald L. Suarez. "The effect of selenium on salinity stress and selenate–sulfate comparision in kale." Journal of plant nutrition20 (2021): 2996-3004.

Comments 8: L117 How often did you change the solution during your experimental period?

Response 8: We change the water bi-weekly to adjust for any shifts in nutrient concentration and salinity, ensuring that both remain at the desired levels.

Comments 9: L120 This can be moved to L75.

Response 9: Thank you for pointing this out. We moved the portion as suggested.

Comments 9: L122 I am just wondering if ppt unit is common among hydroponic experimental setup in other literature.

Response 9:

• mM (millimolar) is widely used in scientific studies, particularly in plant physiology and biochemistry, as it provides a direct representation of ionic concentrations. Also, dS/m (decisiemens per meter) or mS/cm are commonly used in agricultural and soil science studies, including hydroponics, to represent electrical conductivity (EC), which correlates with the total ion concentration in the nutrient solution.
• In our study, we chose parts per thousand (ppt) as a practical and straightforward unit for salinity measurement. This decision was based on the need to align with real-world conditions, particularly in saline or marginal environments where salinity levels are frequently expressed in ppt, such as in marine and brackish water systems. Using ppt allows for broader applicability of our findings to contexts beyond traditional hydroponics, such as marine aquaponics, saline agriculture, and studies on salt-tolerant crops.

 

• Additionally, ppt as a unit simplifies interpretation for stakeholders such as growers, extension workers, and policymakers who may not be familiar with scientific units like mM or dS/m. This practical approach promotes easier adaptability of our results for on-the-ground applications and enhances the relevance of our research to diverse audiences, including those involved in sustainable agriculture in saline-affected regions. By using ppt, we aim to bridge the gap between scientific research and practical implementation, ensuring that our findings are accessible and actionable across various agricultural and environmental contexts.

Comments 10: L499 Discussion part should be addressed by each result. Please add each title of them in the Discussion part.

Response 10: We have breakdown the discussion per result as suggested.

Comments 11: L584 Can you suggest which light intensity and salinity level was beneficial to biomass yield and nutrient contents in kale?

Response 11: Yes, we included in the text that A light intensity of 250 PPFD and salinity levels of <1.5–5 ppt were optimal for enhancing biomass yield and macronutrient absorption in kale, as these conditions provided sufficient energy for photosynthesis without causing photoinhibition. Conversely, a lower light intensity (150 PPFD) combined with a broader salinity range (<1.5–17 ppt) promoted a greater accumulation of micronutrients, such as copper (Cu), zinc (Zn), and iron (Fe), highlighting the trade-offs between growth and nutrient composition under varying environmental conditions.

Comments 12: L717 Check if this format works.

Response 12: Thank you, we have corrected the citation format.

Comments 13: L732 Check if this format works.

Response 13: Thank you, we have corrected the citation format.

End of comments.

Reviewer 2 Report

Comments and Suggestions for Authors

Dear authors. Your work, which was sent to me by the editors for review, is very valuable and fits into the scientific trend of understanding the mechanisms of salinization of kale and its growth, as well as the possibility of using slightly saline water to irrigate plantations of this species. Your work contains a number of comprehensive results. Performing such a large scope of research and analyses certainly required a lot of effort. I greatly appreciate the work put into obtaining the results and their statistical analysis, as well as writing the manuscript of the work. As a reviewer of your work, I have several suggestions and questions that should help you improve the final version of the work that will be published.

In my opinion, the abstract needs a little editing. You should add some methodological information about your research. Indicate the levels of factors you used (lighting and salinity). Write that it was hydroponics and for how long, and provide the variety of kale.

In keywords it is better not to repeat words that are in the title of the work. It is better to provide words that will make it easier for other authors of your work who are looking for similar research results to find them. So I suggest removing the words kale; light intensity; salinity; and hydroponics; instead you can add growth, development, dry mass, or other words that you consider useful, and are not repeated in the title of the work.

Line 104-106 "The product consists of three components: FloraGro, FloraBloom, and FloraMicro with guaranteed nitrogen phosphorus-potassium (N-P-K) analysis ratios of 2-1-6, 0-4-5, and 5-0-1, respectively." Since elements such as Mg, Fe and t were also assessed, it is worth providing the basic composition of how many of the tested elements were contained in these fertilizers. This is a very important point of the methodology.

Line 111 -The water temperature was measured at 19.5 to 23.5 °C, and the pH levels ranged from 5.4 to 7.2 throughout the growth period." You have further stated that the decrease in pH resulted from the decomposition of dead root debris, but it is worth mentioning how often the water was changed. Temperature is also an important factor in plant metabolism. Here the fluctuation was quite large. So I have a question: could these extreme temperature values ​​have had an impact on the results of your research, or was the temperature rather constant, and these extreme values ​​from the given range were rare enough not to disturb the results of the research?

Line 141 Fresh weight was recorded immediately upon harvest, and the dry biomass was determined by oven-drying it at 60 °C for 24 hours until a constant weight was achieved [24]. - Was air circulation used?

Line 165 - We hypothesized that there is a significant effect of light intensity, salinity, and their interactions on kale growth, yield, and nutrient composition. - it is better to move the research hypothesis to the end of the introduction

Line 183 reaching approximately 42.50 cm at 112 DAT. In contrast, the smallest plant, measuring 22.93 cm - there is no point in repeating the values ​​from the table that are included in it. I suggest giving, for example, the % difference between the highest plant and the lowest

Table 1 is first cited in the text and then Figure 1, and below the text is placed figure 1. Change the order of the table so that it is first after the text. Similarly in the whole work. Giving the table first in the text and placing it much lower causes confusion for the reader.

Line 352- The highest water productivity, 352 with 34.14 g/L, does the gram value refer to dry mass. Plese specify

Line 558 Sodium and K ions are transported to the plant with similar pathways, and 558 the higher concentration of salt can block or reduce potassium absorption [48]. Magnesium deficiency can cause a decrease in chlorophyll content as a result of salt stress, leading to reduced growth and plant development [49]. You have some very interesting observations here. This is correct, but I would add one more piece of information from the literature here. In the greenhouse experiment, the effect of the K2SO4dose (0.4, 0.8, 1.2, 1.6g K·dm–3) was analyzed against the background of two doses of calcium carbonate (5 and 15 g CaCO3·dm–3) on yielding, chemical composition and biological value of feces. The largest fecal yieldwas obtained after applying1.2 g K·dm–3in the medium;both higher and lower potassium dosesreduced the yield. A significant increase in the content of nitrogen and potassium in plants was found, along with anincrease in potassium sulfate dose. to Fragment of research results from the work PITURA, K., JAROSZ, Z. Chemical composition and biological value of feces depending on the varied mineralfertilization. Agronomy Science 2020, 75(4), 97-107.https://doi.org/10.24326/as.2020.4.8.

In the attachment is your manuscript of the work, where I have made some minor remarks regarding commas. In particular, the sentence starting on line 569 is unclear due to the lack of a comma.

Comments for author File: Comments.pdf

Author Response

Thank you for your insightful feedback, we have incorporated your suggestions. I acknowledge the time and effort of our co-authors in revising the manuscript to suit the aim and scope of the journal. Below are our point-by-point responses to the comments:

Comments 1: Dear authors. Your work, which was sent to me by the editors for review, is very valuable and fits into the scientific trend of understanding the mechanisms of salinization of kale and its growth, as well as the possibility of using slightly saline water to irrigate plantations of this species. Your work contains a number of comprehensive results. Performing such a large scope of research and analyses certainly required a lot of effort. I greatly appreciate the work put into obtaining the results and their statistical analysis, as well as writing the manuscript of the work. As a reviewer of your work, I have several suggestions and questions that should help you improve the final version of the work that will be published.

Response 1: Thank you for the positive feedback and for taking the time to review our manuscript. We have revised the manuscript to address your comments and suggestions.

Comments 2: In my opinion, the abstract needs a little editing. You should add some methodological information about your research. Indicate the levels of factors you used (lighting and salinity). Write that it was hydroponics and for how long, and provide the variety of kale.

Response 2: The abstract was improved and indicated the levels of factors, the duration of the experiment, the kale variety used, and it was also written that the experiment was in hydroponics.

• light intensity (150 and 250 photosynthetic photon flux density)
• salinity levels (<1.5, 5, 10, and 17 parts per thousand)
• Russian kale variety
• The experiment run for five months, from September 2023 to January 2024
• Indoor hydroponics

Comments 3: In keywords it is better not to repeat words that are in the title of the work. It is better to provide words that will make it easier for other authors of your work who are looking for similar research results to find them. So I suggest removing the words kale; light intensity; salinity; and hydroponics; instead you can add growth, development, dry mass, or other words that you consider useful, and are not repeated in the title of the work.

Response 3: Thank you for the suggestions.

• The keywords were improved as suggested (growth; development; dry biomass; salt intrusion; nutrient content; food security; sustainability)

Comments 4: Line 104-106 "The product consists of three components: FloraGro, FloraBloom, and FloraMicro with guaranteed nitrogen phosphorus-potassium (N-P-K) analysis ratios of 2-1-6, 0-4-5, and 5-0-1, respectively." Since elements such as Mg, Fe and t were also assessed, it is worth providing the basic composition of how many of the tested elements were contained in these fertilizers. This is a very important point of the methodology.

Response 4: We appreciate this important observation.

• We added a detailed analysis of the nutrients used in the paragraph:
• FloraGro provided 2.0% total nitrogen (N), 1.0% phosphate (P₂O₅), 6.0% potash (K₂O), and 0.5% magnesium (Mg). FloraBloom contained 5.0% phosphate (P₂O₅), 4.0% potash (K₂O), 1.5% magnesium (Mg), and 1.0% sulfur (S). FloraMicro contained 5.0% total nitrogen (N), 1.0% potash (K₂O), and 1.0% calcium (Ca), along with an array of essential micronutrients, including 0.0005% cobalt (Co), 0.01% chelated copper (Cu), 0.1% chelated iron (Fe), 0.05% chelated manganese (Mn), 0.0008% molybdenum (Mo), and 0.015% chelated zinc (Zn)

Comments 5: Line 111 -The water temperature was measured at 19.5 to 23.5 °C, and the pH levels ranged from 5.4 to 7.2 throughout the growth period." You have further stated that the decrease in pH resulted from the decomposition of dead root debris, but it is worth mentioning how often the water was changed. Temperature is also an important factor in plant metabolism. Here the fluctuation was quite large. So I have a question: could these extreme temperature values ​​have had an impact on the results of your research, or was the temperature rather constant, and these extreme values ​​from the given range were rare enough not to disturb the results of the research?

Response 5: Thank you for pointing this out. We do think that the temperature ranges have not affected the results of our study. We have included references to support and justify that the temperature range in our study was within ideal growing conditions for kale.

• Bi-weekly change of water is added to the statement in relation to the pH fluctuation due to decomposition of roots.
• A similar study of Chowdhury et al. (2021) titled: “Effects of Temperature, Relative Humidity, and Carbon Dioxide Concentration on Growth and Glucosinolate Content of Kale Grown in a Plant Factory” observed an optimal temperature between 20-23 °C for growth of kale.
• The study of Catigday et al. (2023) on "Relationships of Water Quality Parameters for Hydroponic Production of Kale (Brassica oleracea) with In-Ground Passive Cooling System.” signified an optimum temperature of 18-28 °C.

Comments 6: Line 141 Fresh weight was recorded immediately upon harvest, and the dry biomass was determined by oven-drying it at 60 °C for 24 hours until a constant weight was achieved [24]. - Was air circulation used?

Response 6: Yes.

Comments 7: Line 165 - We hypothesized that there is a significant effect of light intensity, salinity, and their interactions on kale growth, yield, and nutrient composition. - it is better to move the research hypothesis to the end of the introduction

Response 7: Thank you for the suggestion. The hypothesis was now moved to the last part of the introduction.

Comments 8: Line 183 reaching approximately 42.50 cm at 112 DAT. In contrast, the smallest plant, measuring 22.93 cm - there is no point in repeating the values ​​from the table that are included in it. I suggest giving, for example, the % difference between the highest plant and the lowest

Table 1 is first cited in the text and then Figure 1, and below the text is placed figure 1. Change the order of the table so that it is first after the text. Similarly in the whole work. Giving the table first in the text and placing it much lower causes confusion for the reader.

Response 8: Thank you for pointing it out.

• We have reorganized the manuscript to ensure clarity and logical flow by presenting the text first, followed by the corresponding Figure or Table it discusses. This structure is applied consistently throughout the manuscript to enhance readability and coherence.
• The discussion section has been enhanced by including a comparison of the tallest and smallest plants, expressed as a percentage difference, to provide a clearer perspective on the variations observed. The same is through for the rest of discussions.

Comments 9: Line 352- The highest water productivity, 352 with 34.14 g/L, does the gram value refer to dry mass. Plese specify

Response 9: The water productivity was indicated as fresh biomass.

Comments 10: Line 558 Sodium and K ions are transported to the plant with similar pathways, and 558 the higher concentration of salt can block or reduce potassium absorption [48]. Magnesium deficiency can cause a decrease in chlorophyll content as a result of salt stress, leading to reduced growth and plant development [49]. You have some very interesting observations here. This is correct, but I would add one more piece of information from the literature here. In the greenhouse experiment, the effect of the K2SO4 dose (0.4, 0.8, 1.2, 1.6g K·dm–3) was analyzed against the background of two doses of calcium carbonate (5 and 15 g CaCO3·dm–3) on yield, chemical composition and biological value of feces. The largest fecal yield was obtained after applying 1.2 g K·dm–3in the medium; both higher and lower potassium doses reduced the yield. A significant increase in the content of nitrogen and potassium in plants was found, along with an increase in potassium sulfate dose. Fragment of research results from the work PITURA, K., JAROSZ, Z. Chemical composition and biological value of feces depending on the varied mineral fertilization. Agronomy Science 2020, 75(4), 97-107.https://doi.org/10.24326/as.2020.4.8.

Response 10: Thank you for this suggestion, we have added this supporting paper and references.

Comments 11: In the attachment is your manuscript of the work, where I have made some minor remarks regarding commas. In particular, the sentence starting on line 569 is unclear due to the lack of a comma.

Response 11. We have corrected it with commas, as suggested. Thank you.

End of comments.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors answered and reflected most of my questions and comments. I also agree with the author's opinion that ppt unit is practical and easier for actual users in the field (e.g., farmers). However, I still feel that the mM unit should be written together with them due to the importance of scientific references and the scientists who will refer to and/or mimic your experiment in the future. 

I would like to suggest writing mM next to B1–B4 ppt unit.

 

In addition, there are some more specific comments for your manuscript:

L22 At 10 ppt level, notable reduction of FW, but significant increased DW? If so, why? please clarify this sentence.

L23 At which salinity levels? All of B1–B4?

L71 Reference

L360 Did you explain how water consumption was measured in methodology or other parts by any chance?

L526 Just curious, there is no mortality of plants at B4 level during your whole experimental period?

L599 Limitations or Further direction?

L613 I think this sentence should be addressed in your abstract as it is kind of key finding of your study.

Comments for author File: Comments.pdf

Author Response

Thank you for your consistent and insightful feedback, we have incorporated your suggestions. Below are our point-by-point responses to the comments:

Comments 1: The authors answered and reflected most of my questions and comments. I also agree with the author's opinion that ppt unit is practical and easier for actual users in the field (e.g., farmers). However, I still feel that the mM unit should be written together with them due to the importance of scientific references and the scientists who will refer to and/or mimic your experiment in the future. 

I would like to suggest writing mM next to B1–B4 ppt unit.

Response 1: Thank you, we agree with your opinion. We have included the mM unit in the text alongside the ppt units.

In addition, there are some more specific comments for your manuscript:

Comments 2: L22 At 10 ppt level, notable reduction of FW, but significant increased DW? If so, why? please clarify this sentence.

Response 2: Thank you for pointing this out. We should have referred to the “dry matter percentage” not “dry biomass”. We have corrected the sentence.

Comments 3: L23 At which salinity levels? All of B1–B4?

Response 3: We have corrected the sentence and specified the Macronutrients and salinity levels: “The macronutrient content, particularly, total Kjeldahl nitrogen (TKN), total phosphorus (TP), and magnesium (Mg), were consistent across both light intensities (150-250 PPFD) and salinity levels between <1.5-10 ppt (<26-171 mM) but reduced at 17 ppt (291 mM)”.  For micronutrients, particularly Cu, Fe, and Zn, higher concentration was recorded at lower light intensity (150 PPFD) across salinity levels (<1.5-17 ppt).

Comments 4: L71 Reference

Response 4: Thank you. We have inserted the reference.

Comments 5: L360 Did you explain how water consumption was measured in methodology or other parts by any chance?

Response 5: No. but, we now have included it at L181-184. Thank you for pointing it out.

Comments 6:L526 Just curious, there is no mortality of plants at B4 level during your whole experimental period?

Response 6: There were no mortalities. All plants have survived.

Comments 7: L599 Limitations or Further direction?

Response 7: Thank you. We have added the limitations and replaced the “Future Works” with “Further Directions”.

Comments 8: L613 I think this sentence should be addressed in your abstract as it is kind of key finding of your study.

Response 8: Thank you for specifying this. Yes, we agree. We have addressed this in the abstract.