A Rotational Cultivation System for Indoor-Grown Lettuce: Feasibility in Terms of Yields, Resource Efficiency, Quality, and Postharvest Storage Capacity

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript explores the feasibility of using a rotational cultivation system for indoor lettuce production by comparing yield, resource efficiency, harvest quality, and postharvest storage capacity with a conventional horizontal cultivation system.

While the study has practical applications, certain limitations exist in the experimental design, data volume, and reasoning behind the conclusions. The following aspects warrant further consideration:

Given that the study compares two-dimensional (horizontal) and three-dimensional (rotational) cultivation systems, should yield and production efficiency be assessed per unit area (m²) or per unit volume (m³)? This distinction is crucial and warrants further discussion.

The study reports a uniform light intensity of 370 ±20 µmol photons m⁻² s⁻¹. However, due to the rotational nature of the system, yield might be lower compared to the horizontal control. Light distribution plays a critical role in this difference. Is the reported intensity measured at the leaf surface or at a fixed distance from the light source? A clearer description of light distribution is needed to enhance reproducibility and verification.

The experiment may be significantly influenced by external environmental factors such as light conditions. Has the number of experimental repetitions been sufficient to ensure robust results?

Lighting energy consumption should be analyzed separately from climate control energy consumption to provide a more accurate assessment of EUE. Detailed data on energy consumption breakdown (e.g., the proportion of energy used for lighting) is necessary to determine whether energy savings in the rotational system are primarily due to a reduced number of lamps. This clarification is essential for understanding the true efficiency gains of rotational cultivation.

Separate lighting energy consumption from climate control energy consumption to more accurately assess energy use efficiency (EUE). Providing detailed data on the breakdown of energy consumption (e.g., the proportion of energy used for lighting) is necessary to verify whether energy savings in crop rotation systems are primarily attributable to the reduction in the number of lamps. This clarification is essential to understanding the true efficiency gains of the rotational cultivation system.

The study attributes the decline in photosynthesis to disturbances in gravity perception but does not reference direct studies on the effects of microgravity or centrifugal force on plant physiology (e.g., research on Arabidopsis or wheat). Expanding the discussion on potential mechanisms, supported by relevant literature from space biology, would strengthen the mechanistic understanding of how gravity perception influences plant physiology in rotational cultivation.

Principal Component Analysis (PCA) reveals significant differences in polyphenol profiles between ROT and CT lettuces. However, the discussion primarily focuses on caftaric acid derivatives (e.g., chlorogenic acid and chicoric acid). A broader analysis would provide a more comprehensive understanding of how the rotational cultivation system affects overall lettuce quality.

More data are needed to substantiate the reasons behind the observed decline in yield and photosynthetic rate. Strengthening this analysis would improve the reliability of the findings.

ROT lettuces had a significantly higher respiration rate than CT lettuces on day 3 of storage， but does not explore the implications of this finding. Further discussion on the potential physiological reasons and postharvest consequences would add value to the manuscript.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This manuscript presents a study on the feasibility of a rotational cultivation system for indoor lettuce production, comparing it to a conventional horizontal system. While the study provides valuable insights into energy use efficiency and crop quality, several areas require further refinement.

The introduction successfully contextualizes the relevance of controlled environment agriculture (CEA) and the challenges of energy consumption in indoor farming. However, the transition from general indoor farming issues to a specific focus on rotational cultivation is somewhat abrupt. The rationale for selecting a rotational system as opposed to optimizing existing horizontal methods needs further justification, particularly in terms of scalability and economic feasibility. 
Additionally, while the study references previous research on lettuce cultivation in vertical systems, a more explicit discussion of how this work builds upon or diverges from prior studies would strengthen its impact.
To what extent does the proposed rotational system offer distinct advantages over well-established vertical farming approaches? Given that energy efficiency is a primary concern, how do the reported savings translate into practical benefits for large-scale production?

Materials and Methods Sections 2.1, 2.4, and the first half of Section 2.5 show very high plagiarism rates. This makes the research seem less novel and can be misconstrued as having low scientific soundness. I suggest that the authors paraphrase these sections to reduce the plagiarism rate.
The rotational cultivation system introduces a novel approach to light distribution, but there is limited discussion on the potential drawbacks of continuous plant rotation. While the effects of gravity perception on photosynthesis are explored, the manuscript does not thoroughly consider how rotation-induced mechanical stress may influence other physiological traits, such as root development and water uptake. 
Additionally, while energy consumption is measured, a breakdown of how lighting, ventilation, and system movement contribute to overall energy use would enhance the study’s applicability.
How does plant rotation impact root architecture and water absorption over time? Are there any potential long-term physiological trade-offs associated with continuous movement?

The results effectively compare fresh weight, dry weight, and various resource use efficiencies between the two systems. The improved energy and land use efficiencies in the rotational system are notable, but the observed reductions in net photosynthesis and sugar content raise concerns about potential trade-offs in crop quality. 
The statistical analyses are generally well-executed, but the manuscript would benefit from a more detailed discussion of variance between treatments. Additionally, while polyphenol profiling is included, the study does not explore whether the differences observed have any implications for consumer acceptance or nutritional value.
To what extent do changes in sugar and polyphenol content affect the overall sensory and nutritional quality of lettuce? Given that the rotational system modifies metabolite profiles, could it inadvertently influence postharvest longevity or marketability?

The discussion integrates the findings with broader trends in controlled environment agriculture, emphasizing the potential for improved efficiency in plant factories. However, the manuscript does not fully explore the practical implications of implementing rotational cultivation at an industrial scale. While stacking multiple rotational systems is mentioned as a way to improve land use efficiency, logistical considerations such as labor requirements, automation potential, and maintenance costs are not addressed in depth. 
Furthermore, the economic feasibility of adopting this system compared to existing high-density vertical farms remains an open question.
What are the labor and infrastructure requirements for integrating rotational systems into commercial-scale plant factories? How do the initial setup costs compare to conventional vertical farming configurations?

The conclusions summarize the main findings but do not provide concrete recommendations for future optimization. While the study demonstrates the feasibility of rotational cultivation, additional research is needed to refine the approach and ensure that yield and quality remain competitive with existing systems. A clearer articulation of future research directions particularly regarding improvements in energy efficiency, plant response to rotation, and economic viability would enhance the manuscript’s impact.

Please consider the above points and strengthen the content of the manuscript to ensure clarity.

Thank you.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

I have carefully reviewed the manuscript entitled “A rotational cultivation system for indoor-grown lettuces: feasibility in terms of yields, resource efficiencies, quality, and postharvest storage capacity” submitted by Dresch et al. to a MDPI journal Agronomy. Indoor farming in Plant Factories with Artificial Lighting (PFAL) offers optimized growing conditions and higher water, light, and land surface use efficiencies compared to greenhouses or open field agriculture but faces challenges related to energy consumption. The objective of this study was to evaluate the feasibility of using a rotational cultivation system for indoor-grown lettuce production. Authors compared a rotational cultivation system to a horizontal control cultivation system in terms of yields, resource efficiencies, quality at harvest, and postharvest storage capacity. The results shown that there was no significant difference in yields, WUE, LUE and postharvest storage capacity between treatments. However, energy and land surface use efficiencies were higher in the rotational cultivation system compared to the control. Besides, the rotational cultivation system modified lettuces quality. Based on yields and efficiencies, this study highlights the feasibility of using a rotational cultivation system for indoor lettuce production.

The experimental design, statistical methods, and testing and calculation procedures were all correct. The manuscript was also well-written and well-structured. Moreover, this study had good practical production significance. The results obtained from this study could help to guide the optimal cultivation of leafy vegetable crops in controlled environments/conditions. I only found some small shortcomings in the manuscript and therefore, I advise accepting this manuscript for publication after a minor revision. Some comments are as the following:

1. Line 24. What were WUE and LUE? Adding full names.
2. Replacing Table 1 with a dynamic line plot.
3. For leaf quality, glucose, fructose, sucrose, and total soluble sugars contents were tested here. Citamin C (Vc) also is an important quality indicator. Why was Vc not determined? In addition, I am curious whether lettuce in ROT system have a stronger ability to absorb nitrogen and other elements as compared to that in CT system, considering ROT plants with better light interception?
4. For Figure 3, supplementing the data involved in transpiration rate and intercellular CO₂ concentration. In addition, leaf chlorophyll content is a very important indicator. Is there the data associated with chlorophyll content? Why was net photosynthesis rate for the lettuces in ROT system lower than those in CT system during the first two hours and at the end of the lighting period? In my opinion, the perturbation of gravity perception was not a very important reason and the key factor should be nitrogen content in leaves.
5. The economic benefit analysis between systems is necessary.

Author Response

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Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

Dear authors,

 

Line 330- make the 2 subscript

In introduction add some information about indoor farming in your country (or the area where you the study is conducted). How much land is used for indoor farming in the country? How many (number) indoor farms are there? How many lettuce indoor farms are in the area? is it the first one? Add explanation in the article please.

Line 262- 266- please move this as an explanation in the text and not in the figure description

Line 269-271- please move this as an explanation in the text and not in the table description

The explanations for table 1 must be before the table. Please move them after Figure 2.

Lines 279-282- please move this as an explanation in the text and not in the table description

Why is lettuce important in the area where is cultivated? Is it consumed daily there? Otherwise why did you choose it? Please add in the paper the explanation

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

This manuscript explores the feasibility of crop rotation cultivation system in indoor lettuce production by comparing the yield, resource efficiency, harvest quality, and post-harvest storage capacity of the traditional horizontal cultivation system. This study has certain application value. The author also supplemented and explained the questions raised one by one. 

Author Response

There are no other questions for publication.

Reviewer 2 Report

Comments and Suggestions for Authors

The paper seems to be slightly improved compared to the previous one.

Below are some additional questions.

How might continuous gravity perturbation influence photosynthetic efficiency, stomatal conductance, or nutrient uptake compared to static horizontal systems? It remains unclear why the rotational system is expected to maintain or enhance lettuce quality, particularly regarding secondary metabolite accumulation.

The rationale for selecting lettuce as the model crop is based on its commercial relevance and standard use in indoor farming. However, the study does not discuss whether the observed effects are specific to lettuce or if they could be generalized to other leafy greens or crops with different growth habits. How would the rotational system affect plants with more complex architectures or those requiring different light spectra for optimal growth?

The environmental variables are meticulously controlled, the choice of light spectrum and photoperiod is not adequately justified. It is not clear whether the chosen Red:Green:Blue ratio and 16-hour photoperiod were optimized for lettuce growth under rotational conditions or simply replicated from the control system. Would a different light spectrum or photoperiod enhance photosynthetic efficiency and resource use under continuous rotational motion? What do you think?

The choice of cultivar and growing medium is consistent, the study does not consider potential interactions between rotational motion and root architecture or nutrient uptake dynamics. Would a hydroponic system or another growing medium yield different results, particularly regarding root growth and water use efficiency?

Additionally, the study calculates resource use efficiencies, including Water Use Efficiency (WUE), Light Use Efficiency (LUE), Energy Use Efficiency (EUE), and Land Surface Use Efficiency (LSUE). While these metrics provide valuable insights, the study does not discuss potential trade-offs between these efficiencies. For example, could the increased EUE in the rotational system be offset by reduced LUE or compromised photosynthetic efficiency during certain lighting periods?

The discussion attributes the decrease in photosynthetic activity to the continuous perturbation of gravity perception, reducing stomatal conductance and PSII efficiency. However, this interpretation remains speculative, as the study does not provide direct evidence of altered gravity signaling pathways or associated phytohormone responses. How might altered auxin gradients or changes in abscisic acid content contribute to the observed stomatal behavior?

The study highlights increased respiration rates in rotationally grown lettuce after three days of storage but finds no significant differences in postharvest storage capacity or overall visual quality. While the discussion suggests that higher respiration rates may result from structural changes or increased mitochondrial activity, this hypothesis is not experimentally validated..

The manuscript demonstrates the feasibility of rotational cultivation for indoor lettuce production but would benefit from a deeper exploration of the underlying physiological mechanisms, broader crop applicability, and economic trade-offs.

Thank you.

Author Response

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Author Response File: Author Response.docx