Optimizing Indoor Hemp Cultivation Efficiency through Differential Day–Night Temperature Treatment

Round 1

Reviewer 1 Report

The results presented in Figure 5 are completely illegible. Please present the results in a different form, a bar chart or table would be better. Since there are so many results, perhaps the authors would decide to present only the most significant differences. If the authors do not want to give up this form of presenting the results, please remove the numerical scale from the chart.

Line 293 – 301 - I do not see any connection between this part of the discussion and the research conducted in the experiment described in the paper. The discussion on the influence of temperature on the photosynthesis process is very well described in the scientific literature. Please complete this part of the chapter.

The results regarding the antioxidant activity of hemp were omitted from the discussion.

To sum up, this chapter should be improved and refined more thoroughly by the authors.

Conclusions

In the conclusions chapter, the authors do not provide any conclusions. There is no information whether the research conducted gave any clear recommendations regarding growing conditions. If so, what do these tests show?

 

 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Note that I am not a plant scientist. I wrote my comments from the point of view of a system modeler.

 

Synopsis:

A growth-chamber experiment was conducted to evaluate the effect of several day and night temperature differences (DIF) on the yield of hemp. Results are of two types: (1) Final state, such as total dry matter and chemical composition at harvest, and (2) Daytime rates of mature plants (?), such as photosynthesis and respiration. The results were compared to findings in similar reported experiments.

 

Evaluation:

This seems to me a straight-forward study, producing valuable new information. Unfortunately, this information seems not to be of much generalization value. Perhaps it is too early to expect a sufficient basis for a useful mechanistic model.

 

General comments:

 

(1)     I wonder if there are experimental results of interacting (total) light, (mean) temperature and CO₂ concentration in producing yield (chemical and otherwise) of hemp. DIF studies would be a second, refining, stage, in my opinion.                          

 

(2)     If the experiment was designed to produce the final state of particular treatments, to test against various (mechanistic) models, then the state at the beginning of the reproductive stage should also be provided.

 

(3)     It is not clear (to me) which is the best DIF overall. I suppose that the best treatment would be that which fetches the highest price the (pharmaceutical) industry is willing to pay (minus differences in cost of control). This would depend on chemical content and on the dry matter yield per unit area of the plant factory. Hence, in addition to the detailed information of Fig. 5, the economic value of each (chemical) combination should be given. This value, which also should weigh the relative contribution of leaves and flowers, could be used to identify the best treatment.

 

(4)     The results of Fig. 3, assuming them to have been taken near harvest, are a function of the state of the crop at harvest (parameters of the model) and the environmental conditions at the time of measurement. If the states of all plants were the same, which they are not, then the variations in Fig. 3 could be attributed to the different day temperatures (light and CO₂ concentration being the same). Therefore, it is difficult to generalize.

 

Specific comments. I wrote these as I was reading.

 

Abstract:

 

1. Introduction

No mention of interaction of temperature with light and CO₂.

 

2. Materials and Methods

2.1. Plant Materials and Experiment Design

L88: “light intensity increased from an initial 400 μmol·m-2·s-1, based on the height of the apical meristem, 700 to μmol·m-2·s-1 immediately before harvest.” (1) to 700. (2) If light was changed based on height, did different treatments receive different total light? If so, can it be justified?

Table 1: Why not apply a longer photoperiod and/or a higher PPFD in the reproductive stage? The capital cost of a plant factory seems to be a major expense, to be covered by higher production per unit factory area.

 

2.2. Measurement of Plant Growth Parameters

Not clear if just one terminal harvest or several. I suppose just one, but requires specifying.

 

2.3. Measurement of Leaf Gas Exchange

(1) Again, not clear if measured only once (just before harvest?). (2) CO₂ concentration not in Table 1. It is usually more important than humidity. (2) Were CO₂ concentration and light, when different from the treatment, maintained for 3 hours before measurement? (3) Why were light and CO₂ adjusted to the same level in all treatments, while temperature was not?

 

2.4. Analysis of Total Phenolic Compound Contents and DPPH Scavenging Activity

I have no understanding nor knowledge of these techniques.

 

2.5. Analysis of Cannabinoid Contents

Same as 2.4.

 

2.6. Calculation of Total Biomass Yield and Total Cannabinoid Yield

 

2.7. Statistical Analysis

 

3. Results

3.1. Morphogenesis and Growth Parameters of Hemp

These were presumably measured at final harvest.

 

3.2. Photosynthesis-related Parameters

 

3.3. TPCs and DPPH Scavenging Activity

 

3.4. Quantitative Analysis of Cannabinoids

Fig. 5: Change (a) (b) to (A) and (B).

 

3.5. Total Biomass Yield and Total Cannabinoid Yield

L241: ”The results differed from those of individual plant biomass”. Question: how does the value (price) of the produce depend on quantity (per area) and quality (concentration)?

 

4. Discussion

4.1. DIF treatment significantly affects the growth and flowering of hemp

L254: “the internal plant mechanisms underlying this phenomenon remain unclear”. This is unfortunate. I was expecting the current results to help clarifying the mechanisms, leading, eventually, to a mechanistic model of the crop.

L276: “DIF may not universally affect shoot growth or flower development in all plant species.” Unfortunately, this is not very helpful. Nevertheless, a mechanistic model could be developed separately for an individual species (variety).

 

4.2. Physiological Changes in Hemp Based on its Photosynthetic Capacity in Relation to Temperature

L286: “our study showed similar results” Please refer to where this is shown.

 

4.3. Optimal DIF Conditions for Indoor Hemp Cultivation and the Practical Utilization Potential of Domestic Hemp

L320: “The outdoor hemp harvest… ranged from 1.2 to 3.4 tons·ha-1” I, therefore, would have expected a (much) higher yield in the current experiment. Is the discrepancy due to a low light level?

I could not find which DIF treatment is the best.

 

5. Conclusions

More a Summary than Conclusions.

L328: “vertical farming” This is the first time ‘vertical farming’ is mentioned. Previously ‘plant factory’ was used. What is the economics of multi-layer ‘vertical’ structure vs  a ‘single-layer’ greenhouse?

L330: “hemp flower development”. While the importance of flowers was already mentioned in the abstract (L18), most of the text does not seem to emphasize this point.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

This study was conducted to determine the optimal temperature difference in day-night to enhance flower yield and functional component contents of hemp plants. And the results can contribute to advancements in indoor crop cultivation technology for hemp. However, there are a few contents need to be revised before this manuscript can be published.

 

1. In the Abstract, some results should be revised in detail. For example, “Total shoot biomass was highest at 21:27 and lowest at 30:18,” this sentence should add the specific data of the total shoot biomass.

2. The conclusion “The findings of this study indicate that the temperature difference of 6 °C between day and night conditions is optimal for female hemp flower production in limited space.” I think it is not accurate. From the results of this study, I think 27:21℃ (positive DIF) is optimal for female hemp flower production and cannabinoid content.

3. In the sentence 27, the Latin name of hemp should be Cannabis sativa L., the authors should add the dot behind the letter L.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

  Thank you for responding to my comments. All replies and changes made by the authors in the manuscript are sufficient.