Monitoring Suaeda salsa Spectral Response to Salt Conditions in Coastal Wetlands: A Case Study in Dafeng Elk National Nature Reserve, China
Round 1
Reviewer 1 Report
This paper investigates Suaeda salsa response to a series of salt concentrations using plant growth and physiological parameters. The study further explores the capability of detecting chlorophyll content in Suaeda salsa plants at different salt concentrations using empirical relationships between salt concentration - total chlorophyll content and total chlorophyll content - remotely sensed vegetation indices. Results indicate that 50 – 200 mmol/L as the most suitable salt concentration for Suaeda salsa growth. The study further shows that spectral indices outperform the red edge parameters detecting salt concentrations. The whole experiment time is two weeks and not sure how they determined that time is long enough to make conclusions. The authors have ended the experiment as the plants at highest salt concentration withered after two weeks. However, they could have kept the other plant longer at least for few months. This is mainly because, some plants do grow better in first phase and wither later even if the same conditions persisted. If they kept longer for some time, this could have been identified and this paper would be more scientifically sound as the purpose is to find plant growths with salt concentrations and to provide some insights to the field.
Detailed comments:
28-30: Not clear. Please revise.
41: This doesn’t say anything about the causes, but the empirical relationships. The authors may need to search more to find what causes these changes (what’s going on within plants under these salt concentrations to give these chlorophyll contents etc.)
140: Wasn’t sure why the authors kept 0 mmol/L for the control. I’d rather keep the soil the plants were collected from for the control. Now seems like the control also stressed.
Table 3: As you have measured the plant growth parameters (height, branch numbers, root length etc.) before the experiment and at the end of the experiment, I suggest showing the difference. Though it seems these numbers are different between groups, the difference may be the same as your initial plant heights/ branch numbers, root lengths are not equal between plants or at least to the control at the beginning of experiment.
Figure 3: I suggest removing those letters over the bars as you have mentioned the significance in the text. These letters make the figure more crowdy and difficult to understand.
Figure 5 & 7: At some parameters, the control plants have the largest variability. How would explain the variability or the behavior of other plant groups with this control? Why that large variability is in the control group?
338-341: Please revise the sentence.
401: ANOVA and analysis of variance means the same. Put one within brackets or remove or just say “ANOVA of red edge….”
411-412 : Not clear. Please revise.
424 – 427: What’s the difference in this sentence and the information in the paragraph above this (411 -420)? I think it’s just a repetition of the same information.
Author Response
Dear Reviewer:
Thank you very much for your comments and suggestions.
We have revised and also replied all your comments as attached.
Please let us know if any more questions.
Yours sincerely,
Yuanzhi Zhang
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Dear authors,
Thanks for the new version of this manuscript.
As you can see below, there is still some correction to apply to the manuscript. It doesn't seems serious for a 3rd version of the manuscript.
L24: “ A total of 21 pot experiments” mean that 21 experiments have been done using pots, please rephrase
L28: Physiological indicators sensitivity, please delete of
L30: “physiological parameters remotely sensing sensitive” keep it simple please…
L31: the total chlorophyll content
L32-33: whereas the differences observed for the morphological parameter were the highest at 200 mmol/L
L36: too complicated sentence…loose the meaning. “were strongly correlated with the total chlorophyll content” should be sufficient. We already know that the plant considered is Suaeda salsa and the condition are salt stress
L34-38: please rephrase, it seems redundant
L63-65: it seems suggested that the change in canopy spectral properties is causing the change in biomass and chlorophyll. Please rephrase.
L203: “of salt-induced”: salt-induced by itself doesn’t mean a lot. salt-induced stress? Or salt induced response? Please homogenise across the manuscript
L238-287: Please delete Table 3: it is redundant information of the Figure 3.
L289-290: for which wavelength? Is each wavelength been tested separately? Of it is the global spectrum?
L307-308: did not showed significance difference in response to salt concentration
L330: Figure 6b and 6d
L373-374: result suggest that salt concentration round 200 is the optimal condition for growth of Suaeda salsa
L383-384: the logical of this sentence is not clear and rather confusing. Usually the spectral measurement are done to monitor some physiological parameter such as chlorophyll content. The way the sentence is written since indicate the opposite…which is a bit weird. Please homogenise it across the full text
L384-385: what “its” refers to? To the chlorophyll content? There is no senescence of the chlorophyll content, it doesn’t make sense.
L401: Please delete either “ANOVA” or “analysis of variance”: the 2nd is the long version of the 1st
L404: trendlines
L405-406: the p-values in regression is only indicating how the regression line differs from the 1:1 slope. If p<0.05 that means the regression line is significantly different from the 1:1 slope. That’s it and not how good or bad is the fitting….RMSE will be a better indicator
L411: “the x, y ….d_NDVI”it doesn’t mean anything. I supposed you wanted to says that the optimal wavelengths used to compute D_RVI and D_NDVI
L447: same as for the introduction: “21 pot experiments” mean that there is 21 experiment using pots.
Author Response
Dear Reviewer:
Thank you very much for your comments and suggestions.
We have revised and also replied all your comments as attached.
Please let us know if any more questions.
Yours sincerely,
Yuanzhi Zhang
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Thank you very much for the revisions. Below minor revisions are suggested to improve the clarity and the manuscript.
L 24-25: We treated 21 Suaeda salsa seedlings planted in pots with 7 different salt concentrations (n=3 for each concentration) to assess Suaeda salsa response to salt condition.
447: Applying 7 different salt concentrations...... (Not the number of plants but the different salt concentration matters here the most)
Author Response
Dear Reviewer:
Thank you very much. We have revised and updated as suggested.
Yours sincerely,
Yuanzhi Zhang
Author Response File: Author Response.pdf
This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.
Round 1
Reviewer 1 Report
The manuscript remotesensing-789499, “Monitoring Suada Salsa response to slat stress in coastal wetlands: A case study in the Dafeng Elk National Nature Reserve, China” written by Liu and Co proposed to look at Suaeda salsa response to salt stress for biomass, morphological and physiological parameter as well as hyperspectral data.
The paper is interesting, but its potential is been down by the choice of the authors to only look at link between red-egde parameter and chlorophyll content. It would be interested to see the relationship of other plant parameter vs spectral indices.
There is few things that need to be fixed too:
- Some inaccuracy in the introduction: thanks to check the references and how it is summarised in the introduction: not always accurate
- Homogenise Suaeda Salsa in the whole manuscript: different typography more that often
- Table and figure do not fit the pdf format
- Bad qualities figures: can be read correctly
- References are not homogenised
- Results quite difficult to read: try to make it simple please
Results
The plant control-2 (Fig2-B) seems to have a problem of growth. Di something happens during the experiment or was this plant that bad since the beginning? Same for the 600-2: effect of high salinity stress or poor development since the beginning. It seems to me that both are creating a big variability, especially for the control which is resulting in a not clear effect when looking at spectral data. That might be something to discuss in the discussion.
Detailed comments:
L17: Suaeda Salsa: in italic. Please, check it in the whole manuscript
L17-18: please rephrase.
L43-44: where? in china?
Figure 2: at what time of the experiment those pictures have been taken?
L110-112: what L-L, L-M, L-H, M-L, M-H and H means?
L121-134: what is the duration of the experiment? If height has been taken weekly, does it have any used in this paper?
L147-153: why only using the region 500-900 and not up the 2500 nm? At which point of the experiment this measurement has been done? Same day as harvest?
L155: please provide a figure describing the different red-edge parameter and their biological meaning
Table 1: what is R’?
L164-165: It does not make sense to say that NDVI and RVI has been chosen then saying that you are looking at all the band combinations to build the ratio index and the normalizer difference index. Please rephrase in a more comprehensive way.
L194: p = 0.056 do not make a significant difference. Just on the edge
L191-246: Thanks to do short sentence as much as possible. It is confusing and hardly readable for now
Figure 4: it seems there is a problem with the reflectance of the control group: the visible reflectance is much higher than the other group. Is all spectra measurement from the control plants are that far different from other in the visible?
L285-286: why only looking at chlorophyll content and not at biomass, height, succulence and other plant parameters? It will be a more interesting paper.
L291: please rephrase, not clear
L292: simple ratio indices instead of numerator and denominator
Table 4: mmol/L: thanks to put the same typo
L321: Soil instead of Soli
L347: what scholar means here: thanks to find a more suitable and general expression
L348-349: “But why does the morphological parameter of phytophthora inconsistently change with the chlorophyll content?” Where does it come from?
L361: ANOVA or analyse of variance but not “ANOVA of variance”
L368-370: not clear, rephrase please
Author Response
Dear Reviewer,
Thanks for your helpful comments to improve the quality.
We have revised and also replied all comments as attcahed.
Please let us know if any more questions.
Yours sincerely,
Authors
Author Response File: Author Response.pdf
Reviewer 2 Report
Specific comments: The research discusses the impact of salt stress on Suaeda salsa vegetation in coastal wetland of China as a potential restoring solution for coastal ecosystems. The authors conduct an experiment using potted 21 Suaeda salsa seedlings, approximately the same size (aboveground height and root size). The authors initiate the study after two weeks of planting the seedlings. Keeping one set of control plants (3 plants), Hoagland’s hydroponic nutrient solution with different salt concentrations (NaCl 50 – 600 mmol/L) are applied to the remaining pots. Each concentration is added to a set of three plants. After fifteen days (15 days), morphological and canopy spectra (hyperspectral signatures) are collected. In addition, physiological features are collected using harvested plants. A set of red edge parameters and vegetation indices are generated using the hyperspectral band combinations between 500-900 nm. The physiological features are then analyzed with ANOVA, least significant difference (LSD) and correlation coefficient to infer the effect of salt stress on canopy spectra. The results show that Suaeda salsa plants can adapt well and grow well on low salinity conditions between 50-200 mmol/L. While the red edge parameters were not significant to assess the salt stress few vegetation indices (6) shows capability of assessing salt stress of Suaeda salsa. Among the physiological features, chlorophyll content is the most significant indicator for salt stress. This study tries to provide a framework to understand the impact of salt stress of Suaeda salsa plant and a way through remote sensing to detect those impacts. However, the study needs to be improved in several ways.
All the analysis, results and conclusions are based on the observations made after 15 days of experiments. The authors compare the results to control plants but have not mentioned how they have maintained the control plant over these 15-day period. Further, they haven’t measured canopy spectra or other morphological (except height and root lengths), physiological features of seedlings at the beginning of the experiment. Thus, it’s hard to say these spectral changes due to salt stress or not or the plants physiological features ever changed. After 15 days high salt concentration (600 mmol/L) to wither but do not mention why the experiment ends in 15 days. If this experiment continued at least few months period with periodic measurements of those considered spectral and physiological features, these analyses could have more validity. Authors do not justify 15-day period would be enough for a such experiment. There is no indication of the salinity of the initial dry sand they’ve used to plant the seedlings. There is no explanation of how these findings can be applied into the real ecosystem or the study area the authors used.
More specific comments:
Some figures (e.g. Figure 4, 8 and 9) are blurred and cannot read anything. Need to regenerate.
Tables: Need font adjustment so that it will not cut off at the ends and easy to read.
Abstract: Remove methodological details (e.g. list of field measurements/concentration list/etc.) Add few lines with main research question and only the main findings. And note how this study can advance the understanding of Suaeda salsa response to salt stress and how these results can be used for ecological restoration in coastal wetlands. What future studies would be needed.
Line 24: Define LSD?
Introduction: Please add more literature on control studies for these type or related projects so that the readers have an idea of validity of the experiments the authors are maintaining.
Line 83-85: How these two concepts in (1) are different?
Line 96: Authors mention coastal saline sand is the typical soil type in the study area. However, they use dry sand for the control. How the dry sand is similar/different to the normal environmental condition? What was the salinity of the dry soil? Can use this control plants as the control to see the true effect of salt stress of this plant the authors are studying? Need clarification.
Line 107: How did authors confirmed the plant are stable and healthy after two weeks?
Figure 2: What is happening in control plant 2? Can that be considered as a control?
Line 114: So, the total experiment period used for this study is 15 days? Have you measured initial condition (other than height and root lengths)/photo of these plants? How authors justify that 15-day period is enough for such experiment. Authors mentioned the changes of height measured every week. So, that would be only two measurements? Would that be enough to infer the effects of salt concentration?
Line 118: What are those abnormal bands? water absorption bands? or any other reason them to be abnormal?
Line 193: Didn't mentioned authors collected number of branches initially. Its' better to show the initial heights, root lengths, and number of branches and the difference after the experiment ended in each group.
Table 2: Indicators given in the table are cut off and cannot read. These indicators are the variables measured after the experiments. What are the differences between initial and final stage of state of these variables? Adjust the table so the ends are not cut off.
Figure 4: Need to regenerate so that the components in the figure are readable.
Table 3: Adjust the table so "indicator" will not be misunderstanding as indicato r. Adjust the table (font size?) so that the first column words are completely within a single line (indicator, amplitude, and skewness etc.)
Figure 6: Not clear what this figure shows. Do figure 4a and 4c show band correlations? Or band values with something else?
Line 306: replace index with indices
Table 4: What were the initial conditions of these plants? Were they same? How they have changed from its initial condition to this would be helpful.
Line 321 : Replace soli with soil
Line 330: The authors say number of branches and heights have increased. What are the initial values and? how much has increased?
Line 348: What is phytophthora? Be consistent with wording.
Figure 8 and 9: Hard to read anything in these figures.
Figure 10: In the first plot, the red line is not linear (change the caption accordingly)
Line 425: If its chlorophyll (first sentence) why you mix chlorophyll and carotene both here? or do both responses equally and significantly? Why again mixing with morphological features here.
Author Response
Dear Reviewer,
Thanks for your helpful comments to improve the quality.
We have revised and also replied all comments as attcahed.
Please let us know if any more questions.
Yours sincerely,
Authors
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
In general, authors did the correction asked for, but didn’t reconsider deeply their manuscript while a major revision should be the moment to do it. Thanks for them for doing the minimum correction asked.
It appears however, that there is several points that need to reconsider:
- The overuse and mis-usage of the word “stress”. Authors are calling all treatment different from control as stress. I would remind the author that a stress should decrease the growth capacity of a plant. Which is clearly not the case here as growth is optimal at 200mmol/L of salt concentration. Thanks to them to remove the word “stress” when not necessary
- That lead me to another fundamental question: should the control be one of the low or medium salt concentration, which I guess will be closer to the natural environment condition of growth of Suaeda
- And it seems for Suaeda that the control is a stress condition at it reduce growth.
While a lot have been done, the manuscript is still not convincing enough for publication. A major revision should be take as rethink the manuscript. Which has not be the case here. The abstract does not a scientific soundness, it seems there is a confusion between derivative and differential all along the manuscript (including fig and Table as well) or it is not well explained if both are used. The English should be checked by a native English person. Results and discussion should be rewritten paying attention of the mis-usage of the word stress. Figure 8, 9 and 10 are not describe in the result section, which is odd because they are clearly results.
The way the manuscript is for the moment doesn’t seems to reach the criteria for publication, especially for a 2nd version resulting from major revision. I suggest the author to rethink their manuscript.
Detailed comments
Abstract do not have scientific quality, too much
L22: delete mechanism, it is not what it is studied here
L24: treatment instead of group
L29: make it simple please: With new spectral reflectance indices
L29: change to tap for a more comprehensive verb
L29: first order differential index?
L31-32: thanks to rewrite it in a more scientific soundness: are you talking to the significance of the treatment effect on chlorophyll content and morphological parameter?
A bit hard to understand the choice of red edge parameter as index: if its to link with chlorophyll content, I guess it is ok. But the aim in this paper it the plat response to salt stress and as the result shown, red edge parameters are not the best
L69-69: rephrase please, vague. It it’s to say that hyperspectral sensor can collect data on plant materials and that’s the plant spectrum might be affect by biotic and or abiotic stress, then ok. But rephrase it in comprehensive way
L112: treatment instead of groups
L114: dot before “There”
L122: the 7 groups of the experiment
L126: double horizontal dot
L128: rephrase, for example: “The treatment names has been simplified for the rest of the manuscript: “
L138: Physiological indicators does not seem the right name here as plant height, number of branching, weight and so on are morphological parameter. The only physiological indicator is the chlorophyll and carotenoid content. May it can rename as Plant growth indicator or in situ plant measurement…
L158: title too complicate, keep it simple otherwise reader might think on something else or will loose interest: “hyperspectral measurement and pre-processing”
L178: differential or derivative: not the same. Thanks to check and please correct it in the manuscript
Table 1: again: is it differential or derivative? R both depending of the index?
If yes please explain the things better please! It has been asked for the previous version. But not much effort has been done for a better understanding.
L186-190: why talking to RVI and NDVI when not used in this paper. Maybe go straight to what you proposed saying that you tested band combination to find the most suitable wavelength
L205: plant indicator instead of physiological. Or another expression but physiological is not the most suitable
L218-221: thanks to rephrase. An increasing trend itself does not mean a lot. What can be seen is an increase in plant height and so on from 0 to 200 salt concentration. Be careful with the use of stress. It is not because the concentration in salt is increasing, that it is a stress. And here it’s clear that 200 is the optimum medium for Suaeda development. And I guess it is close to its natural growing condition
L224:”under the stress of different salt concentration” does not mean anything, keep it simple. Under the different salt concentration is enough
L227-229: fresh weight on the ground and underground are odd. Not a comprehensive expression for this. Better to used above ground biomass and root or below ground biomass which are common expression in international literature
L247: the right term is post-hoc instead of post-examination
L250: was the highest what?
L251: under different salt concentration: remove stress. There is a stress when negative impact.
L269: No, you can’t use significantly here. It can only be used if there is statistic difference proven by the ANOVA. Not performed here. Please rephrase!
L276: is it differential really? Shouldn’t be derivative? Thanks to check across all the manuscript
L285: to salt concentration, not stress
L308: is the band combination has been done based on the reflectance data or the derivative? It is not clear.
Figure 8, 9, 10: why are they not described in the results?
L347: what specific expression mean?
L345-351: introduction, not discussion
L352-354: here a clear example of why the word stress should be used carefully. For most of the plant an increase of salt concentration will decrease the growth. In this study, it seems the 200 concentration is the optimum for growth. So It can be considered as a stress. And saying that plant grow under an increase concentration of salt is obvious is not that obvious. Thanks to rephrase and rethink the use of “stress”
L355: moderate to high salt concentration
.
Reviewer 2 Report
Summary: The research discusses the impact of salt stress on Suaeda salsa vegetation in coastal wetland of China. The authors conduct a test by potting 21 seedlings. The plants stay 2 weeks in the pots to be healthy and stable before the experiment start. However, there is no information on how the authors maintained the plants within these two weeks (whether they added water or any other nutrients, light conditions etc.). After a week, keeping one set of control plants (3 plants), Hoagland’s hydroponic nutrient solution with different salt concentrations (NaCl 50 – 600 mmol/L) are applied. Each concentration is added to a set of three plants. After fifteen days the experiment ends. The day before the experiment ends, morphological features and at the last day of experiment, the canopy spectra (hyperspectral signatures) are collected. The harvested plants at the end of experiment are used to measure the physiological features. A set of red edge parameters and vegetation indices are generated using the hyperspectral band combinations between 500-900 nm. The physiological features are then analyzed with ANOVA, least significant difference (LSD) and correlation coefficient to infer the effect of salt stress on canopy spectra. All the analysis, results and conclusions are based on the observations made after 15 days of experiments. The authors compare the results to control plants. The results show that Suaeda salsa plants can adapt well and grow well on low salinity conditions between 50-200 mmol/L. While the red edge parameters were not significant to assess the salt stress few vegetation indices (6) shows capability of assessing salt stress of Suaeda salsa. Among the physiological features, chlorophyll content is the most significant indicator for salt stress. This study aims to provide a framework to understand the impact of salt stress of Suaeda salsa plant and a way through remote sensing to detect those impacts.
Specific comments: The authors have made significant improvement in all sections (abstract to conclusion).
Line 131 – 132 : Be consistent with group naming with a dash in between or “and “ in between for all groups (e.g. low-low or low and low)
Line 386: Suaeda state is relatively good at this time? Or Suaeda state is relatively good at this concentration range?
