Review Reports - Sufficient Light Intensity Is Required for the Drought Responses in Sweet Basil (Ocimum basilicum L.)

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The article "Sufficient light intensity is required for the drought responses in sweet basil (Ocimum basilicum L.)” by Lee & Kim addresses how light intensity affects the drought responses of sweet basil (Ocimum basilicum L.). Specifically, the study examines the interaction between light intensity and drought conditions on the growth and physiological responses of sweet basil. The study is highly relevant to the field of plant physiology and environmental stress research. It addresses a critical gap concerning the interaction effects of multiple environmental factors on plant responses to abiotic stress.

Compared to other published material, this study provides valuable insights into the combined effects of light intensity and drought on sweet basil. It adds to the existing knowledge by demonstrating that drought responses, such as reductions in plant growth, stomatal conductance, and photosynthetic rate, are significantly more pronounced under high light intensity.

The conclusions of the study are consistent with the evidence and arguments presented. The experimental results clearly indicate that sweet basil exhibits more pronounced drought responses under high light intensity, supporting the authors' conclusion that light intensity is a critical factor in drought studies. All main questions posed were addressed through the specific experiments involving different combinations of light intensity and volumetric water content (VWC) thresholds. The references cited in the article are appropriate and relevant to the study's context.

This study makes a significant contribution to our understanding of the interaction between light intensity and drought on sweet basil's growth and physiological responses. While the methodology is robust, there are opportunities for further refinement and additional controls to enhance the study's comprehensiveness. The conclusions are well-supported by the experimental evidence, and the references are relevant, though inclusion of more recent studies could strengthen the contextual framework.

The article is well written, well-structured and provides important information. However, an image showing the plants undergoing different treatments would be very welcome to better illustrate their effects. I recommend including a figure showing the phenotype of these plants.

Author Response

Comments:

Thank you very much for your valuable feedback. We completely agree that including an image to illustrate the plant phenotype would greatly enhance the understanding of the treatment effects. However, unfortunately we do not have a proper image that would adequately represent this, and the figures and tables with quantitative data would show clear differences.

Reviewer 2 Report

Comments and Suggestions for Authors

[Materials and Methods]

1. (section 2.1.) 'with LED fluorescence lighting tubes' was the same lighting with T5 LED in section 2.2.?

2. (section 2.2.) There was no information on the nutrient solution, such as EC, pH, and compositions of minerals.

[Discussion]

3. Please discuss the reason for the low light condition, which was 170 umol/m2/s, used in this study.

Comments on the Quality of English Language

I think the English language is fine, and minor editing of the English language is required.

Author Response

[Materials and Methods]

Comments 1:
(section 2.1.) 'with LED fluorescence lighting tubes' was the same lighting with T5 LED in section 2.2.?

Response 1:

Yes. We used T5 LED to provide different light intensity treatments. We revised the sentence to provide a more precise explanation (Line 99).

Comments 2:

(section 2.2.) There was no information on the nutrient solution, such as EC, pH, and compositions of minerals.

Response 2:

As mentioned in our experiment, we used a soilless substrate (Sunshine Mix #4, Sun Gro Horticulture) with a pH range of 5.0 to 7.0, combined with a controlled-release fertilizer (Multicote 6; NPK 14-14-14, Haifa Chemicals, Israel) at a rate of 4 g·L⁻¹. According to the manufacturer, Multicote 6 is designed to release nutrients over a period of 6 months. Given that the experimental period of this study was only three weeks, no additional nutrients were supplied.

[Discussion]

Comments 3:

Please discuss the reason for the low light condition, which was 170 umol/m2/s, used in this study.

Response 3:

We set the low light intensity at 170 µmol·m⁻²·s⁻¹ based on common practices in controlled environments with artificial lighting. Leafy vegetables such as lettuce are often cultivated indoors under light intensity in the range between 200 and 250 µmol·m⁻²·s⁻¹ with a photoperiod of 16 to 18 h, which are optimal to improve plant growth and light use efficiency (Hesham et al. 2020). Canopy photosynthetic capacity of basil saturated at an irradiance of 500 µmol·m⁻²·s⁻¹ which enhances the productivity of edible parts of sweet basils (Beaman et al., 2009). Setting the low light treatment at 170 µmol·m⁻²·s⁻¹ aligns with standard horticultural practices and allows for meaningful comparisons with higher light intensities typically used to enhance biomass production. Additionally, the terms ‘low’ and ‘high’ used in our manuscript are intended to represent relative differences between the two light intensity treatments rather than absolute classifications of low light or high light stress conditions. The goal was not to impose stress on the plants with extremely low or high light levels, but rather to compare drought effects of these two distinct light intensities on basil. Therefore, we added the reason for selecting two levels of light intensity in the manuscript (Line 105).

Beaman, A. R.; Gladon, R. J.; Schrader, J. A. Sweet Basil Requires an Irradiance of 500 μ mol·m⁻²·s⁻¹ for Greatest Edible Biomass Production. HortSci. 2009. 44(1), 64-67. https://doi.org/10.21273/HORTSCI.44.1.64.

Hesham A. A.; Tong Y.-X., Yang Q.-C. Optimal control of environmental conditions affecting lettuce plant growth in a controlled environment with artificial lighting: A review. S. Afr. J. Bot. 2020. 130, 75-89. https://doi.org/10.1016/j.sajb.2019.12.018.

Reviewer 3 Report

Comments and Suggestions for Authors

The submitted manuscript “Sufficient light intensity is required for the drought responses in sweet basil (Ocimum basilicum L.)” by authors Lee and Kim is investigating the suffered drought stress by seedlings of sweet basil under two light regimes.

I don’t thing it is worthy to accept the manuscript for publishing in a high ranked journal due to the following reasons:

- The applied light intensities are 170 and 500 µmol photons m^-2 s^-1, however in the manuscript is not indicated at what light intensities are applied for normal growth of seedlings. It is important in respect to motivate the chosen light intensities and to consider them as low or high light intensity.

- The authors followed the water content in the substrate which is good, however, in order to state that plants are suffering drought stress determination of RWC in leaves is more appropriate.

- In materials and Methods are not indicated the formulas of calculation of Fv/Fm and ΦPSII.

- The whole manuscript does not sound very scientific.

- English language gramma and styling needs significant improvement.

- The indicated results of statistical analysis in every figure are confusing.

- The Discussion section, based on the reported data is very speculative.

My general conclusion is that the manuscript should be rejected.

Comments on the Quality of English Language

The English language needs serious improvement in respect to gramma and styling

Author Response

Comments 1:

The applied light intensities are 170 and 500 µmol photons m^-2 s^-1, however in the manuscript is not indicated at what light intensities are applied for normal growth of seedlings. It is important in respect to motivate the chosen light intensities and to consider them as low or high light intensity.

Response 1:

The decision to set the low light intensity at 170 µmol·m⁻²·s⁻¹ was based on common practices in controlled environments with artificial lighting. Leafy vegetables such as lettuce are often cultivated under light intensity in the range between 200 and 250 µmol·m⁻²·s⁻¹ with a photoperiod of 16 to 18 h, which are optimal to improve plant growth and light use efficiency (Hesham et al. 2020). Canopy photosynthetic capacity of basil saturated at an irradiance of 500 µmol·m⁻²·s⁻¹ which enhances the productivity of edible parts of sweet basils (Beaman et al., 2009). Setting the low light treatment at 170 µmol·m⁻²·s⁻¹ aligns with standard horticultural practices and allows for meaningful comparisons with higher light intensities typically used to enhance biomass production. Additionally, the terms ‘low’ and ‘high’ used in our manuscript are intended to represent relative differences between the two light intensity treatments rather than absolute classifications of low light or high light stress conditions. The goal was not to impose stress on the plants with extremely low or high light levels, but rather to compare drought effects of these two distinct light intensities on basil. Therefore, we added the reason for selecting two levels of light intensity in the manuscript (Line 105).

Comments 2:

The authors followed the water content in the substrate which is good, however, in order to state that plants are suffering drought stress determination of RWC in leaves is more appropriate.

Response 2:

Thank you for your feedback. Although we agree that RWC is a valuable parameter for indicating drought symptoms, we controlled the substrate VWC to impose drought quantitatively, which is also regarded as an appropriate tool for drought imposition. In this study, setting VWC thresholds is based on the moisture release curve which represents the relationship between volumetric water content and the matric potential, a method that can distinguish the drought levels on plants (de Boodt and Verdonck, 1972). Additionally, some research has suggested that RWC may not show significant differences between drought treatments when plants are subjected to conditions that are not extreme drought indoors (Nam et al., 2023). Instead, we measured physiological responses, such as photosynthetic reactions, to observe the effects of drought.

de Boodt, M.; Verdonck, O. The physical properties of the substrates in horticulture. Acta 321 Hortic. 1972. 26, 37-44. http://doi.org/10.17660/ActaHortic. 1972.26.5.

Nam, S.; Hong, C.; An, S.K.; Kim, J. Low substrate water content is efficient for the performance of Ficus pumila ‘Variegata’ indoors. Hortic. Environ. Biotechnol. 2023, 64, 583–591. http://doi.org/10.1007/s13580-023-00514-1.

Comments 3:

In materials and Methods are not indicated the formulas of calculation of Fv/Fm and ΦPSII.

Response 3:

Thank you for your attention to our manuscript and for raising this point. We followed a commonly used methods for calculating fluorescence parameters in reference to the article about chlorophyll fluorescence (Maxwell and Johnson, 2000). F_o (minimal fluorescence yield) is measured using a measuring light. Then, after applying a saturating flash of light, F_m (maximum fluorescence yield) is obtained by applying a saturating flash in the dark-adapted state. F_t refers to the steady-state fluorescence value just before the application of the flash. Finally, after the flash, F'_m is measured by turning off the actinic light.

The formulas of calculation of F_v/F_m and Φ_PSII: F_v/F_m = (F_m− F_o)/F_m and Φ_PSII = (F'_m− F_t)/F'_m

While we initially considered these calculations to be common knowledge and thus did not include them in the manuscript, we have now added a description of the calculation method along with the reference to the article (Line 140). If the full formulas and calculation process need to be included in the main text, we can simply make further revisions upon request.

Maxwell, K.; Johnson, G. N. Chlorophyll fluorescence—a practical guide. J. Exp. Bot. 2000, 51, 659–668. http://doi.org/10.1093/jexbot/51.345.659.

Comments 4:

The whole manuscript does not sound very scientific.

Response 4:

As the other reviewer commented, the experimental results clearly indicate that sweet basil exhibits more pronounced drought responses under high light intensity, supporting the conclusion that light intensity is a critical factor in drought studies. We tried designing the experimental set ups based on the statistical experimental design and followed the appropriate statistical analysis. We considered that objective and accurate research methodologies were employed. If there are specific sections that you find lacking in scientific rigor, please specify them, and we will revise those areas accordingly.

Comments 5:

English language gramma and styling needs significant improvement.

Response 5:

Thank you for your feedback. We have enlisted the help of a professional English editor to improve the manuscript's grammar and style. We believe these revisions have significantly enhanced the readability and overall quality of the paper. We have also attached a certificate of English proofreading. If there are specific sections where you noticed grammatical or stylistic issues, we would appreciate further details so we can address those areas more effectively.

Comments 6:

The indicated results of statistical analysis in every figure are confusing.

Response 6:

We understand that presenting three p-values for each harvest date in the figures may make them appear complex. Since the objective of our study was to show the interaction effect between light intensity and drought, we considered providing the three p-values were the best way to present the results. While we initially considered using the number of asterisks to indicate significance levels, we ultimately decided that providing the exact p-values would more accurately convey the results of our statistical analysis. We made efforts to improve readability by using different colors based on drought treatments for the post-hoc test values. Furthermore, we have included Table 1 to offer a clearer overview of the statistical results and to help simplify the interpretation of the data. If any specific confusion arises the issue, please let us know specifically.

Comments 7:

The Discussion section, based on the reported data is very speculative.

Response 7:

In our study, we presented objective results by statistically analyzing the data collected through precise experimental procedures. We discussed the results considering the relationships between various parameters related to plant growth and physiological responses, revealing differences in drought effects due to light intensity in sweet basil. Although we conducted the discussion carefully based on the results, it is unclear which parts you found to be speculative. If you could point out the specific sections that seemed speculative, we will take your feedback into account and revise the discussion accordingly.