Morphological and Physiological Screening to Predict Lettuce Biomass Production in Controlled Environment Agriculture
Round 1
Reviewer 1 Report
The article presents a study on the use of chlorophyll fluorescence imaging complemented with electron transport rate measurements to predict the canopy size of eleven lettuce cultivars. The authors have chosen cultivars of different morphology and pigmentation, which improves the quality and strength of the paper. The experimental design, including growing conditions, data collection, and analysis have been carried out appropriately. Data has been adequately presented and interpreted. The conclusions drawn are consistent with the results and previous investigations. The research could be of great interest to lettuce breeders. In general, the reviewer didn't detect any major flaws in the manuscript.
However, some figures are messy and almost all of them are sort of blurry, not sure if it is the low resolution, but the lines look like they are not continuous and this can ruin the overall impression on an otherwise great article. Specifically, Figures 3, 5 & 6 should be more clear, maybe instead of letters, only markers would look better in the figures. What is the use of using letters (or cultivar names) if they cannot be distinguished from each other in the graphs?
Author Response
Thank you for your time and effort to review our manuscript.
We understand your point about the use of symbols in these plots and have struggled with how to best format those figures. However, we would like to keep the current formatting. We tried various ways to best design these plots. When we used filled circles to indicate data points, it clearly shows the trend that a larger early PCS results in higher biomass in green cultivars. However, using the same symbols for all cultivars obscures clear differences that exist among some of the cultivars. We believe that it is important for readers to be able to tell which cultivar(s) are very different from other cultivars. We also tried using different symbols for each cultivar, but the figure legend became very long and distracted from the most important information in the figure. We have not been able to find a way to better visualize these data, in a way that shows both the trend and identifies cultivars that greatly differ from others. In addition, having cultivar names in these plots is consistent with the other plots in our manuscript, which helps readers to understand what we found. Unfortunately, that does indeed mean that for some cultivars, the abbreviations of the names overlap, making it very hard to see individual datapoints or easily identify which data point corresponds to which cultivar. However, when that happens, the main point is that those cultivars responded very similarly anyway, making it much less important to identify exactly which data point is from which cultivar. However, if you insist, we can remake the figures and replace the lettering with symbols.
We suspect compression of images by Word may result in a low resolution of these images. To solve that, we also attach the original plots in a high resolution. In addition, we changed the direction of Figure 3 to vertical from horizontal, to make the figure larger and easier to see. We will work with the editor to assure that the published version will have high-resolution figures.
Reviewer 2 Report
The authors clarify that quantifying the projected canopy size is a useful tool for selection of fast-growing green lettuce phenotypes using chlorophyll fluorescence imaging and electron transport rate (ETR) measurements.
Although the topic of the manuscript is of wide interest in agricultural remote sensing community, there are some issues the author may need to address.
LL. 156-158
This equation holds for the situation on the assumption that there are no changes in the accumulating ratio of PSI to PSII or their antenna size. However, the chl a: chl b ratio increases sharply in a linear manner at low light intensity but increases gradually and linearly at higher light intensities. Could you offer the details on the chlorophyll a and b contents?
3.2. Biomass and Projected Canopy Size were Correlated
You said that the PCS of the red cultivars was not correlated with the dry weight. However, it looks like there are some correlation except for 'Teodore'. Could you offer more details?
When writing the discussion section, you should carefully consider some statistics of chlorophyll a and b contents.
3.5. Light Use Efficiency
Did you measure the light response curves of photosynthesis in leaves?
Author Response
Dear reviewer 2,
Thank you for your time and effort in the review process.
"Could you offer the details on the chlorophyll a and b contents?"
We agree with your comment. The equation makes multiple assumptions, which are rarely checked, included equal excitation of photosystem I and II, a leaf absorptance of 0.84, and that all absorbed photons are absorbed by photosynthetic pigments. None of these assumptions are likely to be 100% valid, but they have proven to be ‘adequate’ for much plant physiological research.
We unfortunately did not measure pigment concentrations of these cultivars. Only when we started to analyze our data did we realize that this information could have been very useful. Therefore, we cannot elaborate chlorophyll a/b ratio in these cultivars and how it influences the estimation of electron transport rate. The goal of our study was to identify a simple screening method to predict plant growth. We thus decided to make the standard assumptions typically used for these measurements. Having to test the underlying assumption for each genotype would make the method unsuitable for rapid screening.
"3.2. Biomass and Projected Canopy Size were Correlated"
You are correct regarding the significant correlation among red cultivars (R2 = 0.36) if ‘Teodore’ is excluded. However, we cannot simply eliminate a specific cultivar, because doing so results in a significant correlation. For example, removing ‘Xandra’ would eliminate any significance, regardless of which other cultivars are included. In all our analyses we separated the cultivars based on green versus red leaf pigmentation, and compared those two groups to each other. This resulted in a significant statistical difference in many growth parameters (table 1), suggesting that this grouping is meaningful.
As mentioned above, we do not have data on pigment concentrations, but we are following up on this topic and we plan to publish on this topic in the future.
"3.5. Light Use Efficiency
Did you measure the light response curves of photosynthesis in leaves?"
The light use efficiency (g mol-1) we refer to in our manuscript is a calculated value (see the third paragraph in section 2.6 for our definition) and is not based on light response curves of photosynthesis. We did not measure the carbon assimilation rates in this study. To calculate light use efficiency, we (1) estimated projected canopy size (cm2) based on the function of cumulative light integral vs PCS at 20 min intervals, (2) calculated incidental light (µmol of photons s-1) by multiplying the PCS by PPFD, (3) integrating incident light over the growing cycle as total incidental light (mol of photons), and (4) dry weight was divided by the total incident light, which is light use efficiency (g of biomass per mol of photons).
Round 2
Reviewer 2 Report
This paper is an important contribution and I recommend that it be accepted for publication.
