Lodging Variability in Sorghum Stalks Is Dependent on the Biomechanical and Chemical Composition of the Stalk Rinds
Round 1
Reviewer 1 Report
Comments and Suggestions for Authors
This study examined the relationship between mechanical properties and chemical composition of sweet sorghum stalk rinds. Two sweet sorghum varieties with large differences in mechanical properties were selected for the study. They measured the mechanical properties (flexural strength, flexural modulus, viscoelasticity, stress relaxation, creep compliance, etc.) of these two sorghum varieties, as well as the characteristics of the stalk rind cell walls. The authors concluded that the differences in mechanical properties of sorghum stalk rinds were due to variations in cell wall composition. These differences were positively correlated with the lignin and cellulose features, but not with the hemicellulose.
Some comments:
1. Plant cell walls play a crucial role in providing mechanical support. Most of the research evidence is in agreement with the findings of the authors. If possible, a determination should be made of the structure and composition of the hemicellulose monosaccharide, particularly the ratio of xylose to arabinose.
2. I suggest separating results from discussion.
3. It is necessary to improve the consistency of the notes in the figures. For example, if color is used to distinguish between categories, consistency should be maintained across all figures.
4. Line 10: The abstract does not provide a clear explanation of the rationale for the study. For example, what will this study contribute to current or future research?
5. It would be better if Fig 2 was divided into three.
6. Please check the statistical results in Figures 1d&f and address the method used (LSD or other?). The letters on the bar graphs are clearly incorrectly labeled.
7. Initially, the authors examined the mechanical properties of various internodes of sorghum and observed differences between them. For further analysis of the mechanical properties and composition of an internode, it is unclear which internode was selected.
8. Line 146-151: The experimental results presented here are very important; however, I have only seen the authors' statements and not the graphs accompanying those descriptions.
9. According to Table 2-4, the results did not include any statistical analysis.
10. Line 614: How is the bending property (e.g. FM) calculated? Please provide the calculation formula.
Author Response
REVIEWER 1.
This study examined the relationship between mechanical properties and chemical composition of sweet sorghum stalk rinds. Two sweet sorghum varieties with large differences in mechanical properties were selected for the study. They measured the mechanical properties (flexural strength, flexural modulus, viscoelasticity, stress relaxation, creep compliance, etc.) of these two sorghum varieties, as well as the characteristics of the stalk rind cell walls. The authors concluded that the differences in mechanical properties of sorghum stalk rinds were due to variations in cell wall composition. These differences were positively correlated with the lignin and cellulose features, but not with the hemicellulose.
Some comments:
- Plant cell walls play a crucial role in providing mechanical support. Most of the research evidence is in agreement with the findings of the authors. If possible, a determination should be made of the structure and composition of the hemicellulose monosaccharide, particularly the ratio of xylose to arabinose.
Response: We have measured the neutral sugar composition of the stalks. We focused mainly on Xylose since it was in high abundance and representative of the hemicellulose fraction. Arabinose and mannose contents were each <1% and therefore we did not discuss.
- I suggest separating results from discussion.
Response: This would be a total rewrite of the manuscript. I don’t not believe I can achieve this in the tight timeframe set by the editor for resubmission. My preference is to discuss the results in a combined R&D section and that way we are not going back and forth between sections.
- It is necessary to improve the consistency of the notes in the figures. For example, if color is used to distinguish between categories, consistency should be maintained across all figures.
Response: The figures are revised, and color coding is used in a more consistent way in most of the figures. But still, there are cases where this cannot be applied, as there are other parameters besides varieties. Figure 4, Fig 6 and Fig 7 are such a typical case we cannot apply the same color coding we used for other figures, so decided to leave them as was.
- Line 10: The abstract does not provide a clear explanation of the rationale for the study. For example, what will this study contribute to current or future research?
Response: We have revised the opening sentence as follows:
“Stalk lodging contributes to significant crop yield losses. Therefore, understanding the biomechanical strength and structural rigidity of grain stalks can contribute to improving stalk lodging resistance in crops.”
- It would be better if Fig 2 was divided into three.
Response: We have revised Figure 2 into 3 graphs (a, b & c)
- Please check the statistical results in Figures 1d&f and address the method used (LSD or other?). The letters on the bar graphs are clearly incorrectly labeled.
Response: This is changed into box plot, which gives more statistical insight than bar plot.
- Initially, the authors examined the mechanical properties of various internodes of sorghum and observed differences between them. For further analysis of the mechanical properties and composition of an internode, it is unclear which internode was selected.
Response: Thanks for pointing this out that we forgot to mention which internode was tested, internode 1 (IN1) in the methods and R&D sections. We tested the viscoelastic properties and chemical analysis on IN1 specimens. We examined the flexural modulus and strength of each internode (see fig 1c and 1e). We also compared the average flexural modulus and strength of all internodes in each sample (see Fig 1 d and 1f). We have revised the text accordingly. In addition, we included in the methods section that we sampled 4 plants per variety.
- Line 146-151: The experimental results presented here are very important; however, I have only seen the authors' statements and not the graphs accompanying those descriptions.
Response: This has been modified to show the results are our center of discussion.
- According to Table 2-4, the results did not include any statistical analysis.
Response: We don’t agree with this bald statement. The statistical results are summarized in the tables. The most important parameters (modulus of relaxation, relaxation times, in table 2) and creep compliance parameters in Table 3, and CI in table 4 are all included in the analysis and in the table with statistical summary. The reviewer could mention a specific example and make it clear. The standard error means are included for initial modulus (E0) for table 2 and grain size (L) on table 4 if it was meant specifically for those. We believe these tables summarize all the statistical results and are enough.
- Line 614: How is the bending property (e.g. FM) calculated? Please provide the calculation formula.
Response: The flexural modulus was calculated using the DMA instrument software (that is the slope of the flexural stress-strain curve) based on the thickness and width of the specimen and span length of the fixture. Flexural strength was determined from the max value in the stress-strain curve from the DMA instrument software. We believe we do not need to include formulas.
Reviewer 2 Report
Comments and Suggestions for Authors
Reviewer comments to Mengistie et al. Correlation of Biomechanical and Viscoelastic Properties with the Composition and Structure of Sorghum Stalks, submitted to Crops.
This article presents an extensive exploration of biomechanical and chemical traits in the stalks of two varieties of sorghum. Their main results are that the mechanical properties of Della variety, due to its chemical composition in the rids, outpass RG variety, which can be used as an indication to avoid lodging of the stalks, thus enhancing agronomic management.
This article is outstanding in its methodological systematicity. The authors clearly present a case of importance to the agronomic community, and they produce a step-by-step search to find the rationale of one species supporting better lodging than the other. The article is generally well-written, and the conclusions are clear and straightforward. Having such massive work, I have only minor suggestions to improve clarity, aiming to enhance the visibility and attraction of a wider community other than plant biomechanics for this document:
1) Change the document title. This is not a strong critique, but having millions of articles published each year, the title would be attractive to a small set of specialists. I would urge the authors to publicize their work, as it shows the relevance of biomechanics and chemistry to solving societal problems. I would suggest a title like: "Lodging variability in Sorghum stalks is dependent on the biomechanics and chemical composition of the stalk rinds" (please feel free to improve this title).
2) Figure order is messy.
2.1) Figure 1 should be ordered in rows, with a and b in a superior row, c and d in the intermediate row, and e and f in the lower row. I would arrange so b, c, and e are to the right, each one aligned to the lower, and a, d, f aligned to the left. For d and f, I would not use bar graphs, as they are statistically irrelevant (only showing mean and SD values at best). I would suggest changing bars for box-plots, violin graphs, as they are much more informative than simple bars.
2.2) Fig 2. should be partitioned in three panels, one for E' (A. superior row), one for E'' (B. intermediate row), and one for damping factors (c. lower row). It is currently a mess, and readers must take too much time checking the correct Y axis for each set of graphs.
2.3) Fig. 5 would help readers if they indicated the peaks for lignin and CoC glycosidic linkage in the graph space.
3) To enhance readability, I would suggest double-checking the results and discussion section to remove any paragraphs and phrases that should be on methods. For example, the first paragraph of this section is mainly methodological information, which is subsequently presented in the methods section.
I hope these comments are useful to the authors,
sincerely
Author Response
Reviewer 2.
Reviewer comments to Mengistie et al. Correlation of Biomechanical and Viscoelastic Properties with the Composition and Structure of Sorghum Stalks, submitted to Crops.
This article presents an extensive exploration of biomechanical and chemical traits in the stalks of two varieties of sorghum. Their main results are that the mechanical properties of Della variety, due to its chemical composition in the rids, outpass RG variety, which can be used as an indication to avoid lodging of the stalks, thus enhancing agronomic management.
This article is outstanding in its methodological systematicity. The authors clearly present a case of importance to the agronomic community, and they produce a step-by-step search to find the rationale of one species supporting better lodging than the other. The article is generally well-written, and the conclusions are clear and straightforward. Having such massive work, I have only minor suggestions to improve clarity, aiming to enhance the visibility and attraction of a wider community other than plant biomechanics for this document:
- Change the document title. This is not a strong critique, but having millions of articles published each year, the title would be attractive to a small set of specialists. I would urge the authors to publicize their work, as it shows the relevance of biomechanics and chemistry to solving societal problems. I would suggest a title like: "Lodging variability in Sorghum stalks is dependent on the biomechanics and chemical composition of the stalk rinds" (please feel free to improve this title).
Response: Revised title as suggested.
2) Figure order is messy.
2.1) Figure 1 should be ordered in rows, with a and b in a superior row, c and d in the intermediate row, and e and f in the lower row. I would arrange so b, c, and e are to the right, each one aligned to the lower, and a, d, f aligned to the left. For d and f, I would not use bar graphs, as they are statistically irrelevant (only showing mean and SD values at best). I would suggest changing bars for box-plots, violin graphs, as they are much more informative than simple bars.
Response: Figure 1 is revised and corrected accordingly, box plots are included and the arrangements are made based on the suggestion.
2.2) Fig 2. should be partitioned in three panels, one for E' (A. superior row), one for E'' (B. intermediate row), and one for damping factors (c. lower row). It is currently a mess, and readers must take too much time checking the correct Y axis for each set of graphs.
Response: Figure 2 is corrected.
2.3) Fig. 5 would help readers if they indicated the peaks for lignin and CoC glycosidic linkage in the graph space.
Response: Figure 5 is revised.
3) To enhance readability, I would suggest double-checking the results and discussion section to remove any paragraphs and phrases that should be on methods. For example, the first paragraph of this section is mainly methodological information, which is subsequently presented in the methods section.
Response: We have gone through the manuscript and removed any method phrases from the R&D section.
Reviewer 3 Report
Comments and Suggestions for Authors
General Comments:
This paper is scientifically interesting, however the mechanical engineering jargon does not make it accessible to plant scientists who would read Crops. Special attention should be given to translating what each test infers to the understanding of sorghum/ grass structures.
Methodology – How many stalks were sampled of each line? Sample sizes for each test are variable however not all tests indicate what the sample size. The lignin and carbohydrate analysis does not identify if material was homogenized from multiple samples or one plant. The type of sample (biological rep vs technical rep) indicates what type of comparisons can be made. In the papers current form, it is difficult to determine if the stats were conducted appropriately. Additionally, is the biological representation large enough to run a mixed model to determine if year or genotype had more of an impact on tests?
Discussion - Because part of the rind is being excised, it needs to be made clear in the discussion that the structure of the stem is not being assessed but only a portion of the rind. Also, the discussion then needs to relate that to the whole plant response as a function of being a grass.
Example of minor suggestions:
Line 63: silicon does not need to be capitalized.
Line 58-65: Describe in more detail how each of the major cell wall contributes to strength and rigidity. Also address where silicon plays a role in structures.
Line 69: remove “the study shows”
Line 108, 114, 135, 289: “It” at the beginning of a sentence is grammatically incorrect in formal writing.
Line 114 – 118: Sentences should be rearranged for clarity.
Line 122, 195, 287: “This” at the beginning of sentence requires a noun following it or the phase is grammatically incorrect for formal writing.
There is some repetition of the results in the mico-biomechanical bending test section. Please remove it for clarity.
Line 182-183: What about monocots like bamboo? Grasses are very different than trees, so one would expect the viscoelastic behavior to be dramatically different.
Line 204: Same comment as above. What about monocots?
Comments on the Quality of English Language
Special attention to formal scientific grammar and style writing should be made in some sections noted in the suggested edits.
Author Response
Reviewer 3
This paper is scientifically interesting, however the mechanical engineering jargon does not make it accessible to plant scientists who would read Crops. Special attention should be given to translating what each test infers to the understanding of sorghum/ grass structures.
Methodology – How many stalks were sampled of each line? Sample sizes for each test are variable however not all tests indicate what the sample size. The lignin and carbohydrate analysis does not identify if material was homogenized from multiple samples or one plant. The type of sample (biological rep vs technical rep) indicates what type of comparisons can be made. In the papers current form, it is difficult to determine if the stats were conducted appropriately. Additionally, is the biological representation large enough to run a mixed model to determine if year or genotype had more of an impact on tests?
Response: Thank you for bringing this up and we have overlooked it in the manuscript. We have revised the manuscript to mention what internodes (#1) were sampled. Also, we have included in the methods section that we sampled 4 plants per variety.
Discussion - Because part of the rind is being excised, it needs to be made clear in the discussion that the structure of the stem is not being assessed but only a portion of the rind. Also, the discussion then needs to relate that to the whole plant response as a function of being a grass.
Response: We have added the following sentence
“Stalk strength and stiffness are greatly influenced by its geometry (e.g. diameter and rind thickness). The rind constitutes up to 80% of the material strength of stalk [21]. Thus, bending tests were performed on the rind to determine the FS and FM of the internodes (Figure 1a) from their stress-strain curves (Figure 1b), which is not influenced by stalk cross section geometry.”
Example of minor suggestions:
Line 63: silicon does not need to be capitalized.
Response: corrected
Line 58-65: Describe in more detail how each of the major cell wall contributes to strength and rigidity. Also address where silicon plays a role in structures.
Response: Added the following sentences
“Cellulose contributes to the tensile strength of cells and stems, while lignin provides stiffness.“ In addition, nutrients like silicon play a vital role for the growth and development of cell walls and are associated with improving biomechanics of plants, and resistance to lodging, drought, UV radiation and pathogens”
Line 69: remove “the study shows”
Response: removed
Line 108, 114, 135, 289: “It” at the beginning of a sentence is grammatically incorrect in formal writing.
Response: corrected these.
Line 114 – 118: Sentences should be rearranged for clarity.
Response: revised sentences for clarity. “The FM of the rinds was shown to decrease from the bottom IN1 towards the top section (IN5) of the stem, which reveals the variation in physico-mechanical properties along the internodes (Figure 1c). The same trend (decrease in FM with IN height) have been reported in maize [29] and rice stems [30].”
Line 122, 195, 287: “This” at the beginning of sentence requires a noun following it or the phase is grammatically incorrect for formal writing.
Response: corrected
“These FM results reveals that both RG1 and RG2 were significantly lower than D1 and D2 variety.”
“Hydration of the cell wall polymers leads to the expansion and swelling of the cell wall microstructures, which in turn results in variation and decrease in E′ [44].”
“This variation in stress relaxation behavior was consistent with the determined relaxation modulus from the GMM, shown by their equilibrium modulus (E∞) in Table 2”
There is some repetition of the results in the mico-biomechanical bending test section. Please remove it for clarity.
Response: We have removed a few sentences to eliminate any repetition.
Line 182-183: What about monocots like bamboo? Grasses are very different than trees, so one would expect the viscoelastic behavior to be dramatically different.
Response: This shows that sorghum stalk rinds behave like wood to RH [40]. This is due to the secondary cell walls of plants have common features (composed of cellulose, hemicellulose and lignin). We have not been successful in finding similar experimental results for bamboo (VE property changes with RH).
Line 204: Same comment as above. What about monocots?
Response: Again, the sorghum stalks behaved like wood to RH. Unfortunately, was not able to find any references for bamboo.
