Changes in Agronomic and Physiological Traits of Sugarcane Grown with Saline Irrigation Water
Round 1
Reviewer 1 Report
Overall I thought the paper was interesting and worth publishing. I just make the following suggestions to consider:
- From the discussion, I don’t think the authors emphasised (or maybe appreciate) the importance of drainage for managing saline irrigation water. Good drainage is one of the most important issues. If there is good drainage then salts can be leached through the profile, either via the irrigation water or with rainfall. By contrast, without drainage, salt levels build up over time from irrigation. With poor drainage, even with slightly saline water salts may be build up over time and cause serious problems. I think the authors should make sure they are familiar with this issue if they are not already (from the literature), and include this in their discussion. That is, to emphasise it is not just irrigation water quality (salinity) which is important but rather the combination of irrigation water quality and management of drainage which matters.
- I thought the introduction was a bit sparse in terms of reviewing past information about response to sugarcane to salinity. There are other relevant studies that should be mentioned in both introduction and discussion.
- In connection with point 1, details should be given in the methods section on how the watering of the pots during the experiment was done. How much water was applied, and how was this determined.
- The authors argue that because stem weight wasn’t impaired at 500 mg/L (significant difference only occurred at 1000 mg/L) that this should not present a problem in terms of sugarcane production. However, leaf area was affected which clearly indicates problems with growth and likely yield. The lack of significant difference at 500 mg/L probably only reflects the statistical power of the experiment – ie. if a large number of replicates were used, or plants were grown for longer, I would predict a difference in stem weight would be observed. I think the results suggest that 500 mg/L is a problem.
- There is no discussion about genetic variation – and it is a weakness of the study that only one cultivar was used. There is knowledge that different varieties vary widely in response to salinity in many countries. For example, some varieties are known to handle salinity well. I think this issue, and the potential weakness of this study should be acknowledged and discussed.
Author Response
Overall I thought the paper was interesting and worth publishing. I just make the following suggestions to consider:
We are grateful for your review and comments. Following your comments, we revised our manuscript. Kindly, please check again the revised version of our manuscript. Besides, we replied to your comments point by point as follows.
- From the discussion, I don’t think the authors emphasised (or maybe appreciate) the importance of drainage for managing saline irrigation water. Good drainage is one of the most important issues. If there is good drainage then salts can be leached through the profile, either via the irrigation water or with rainfall. By contrast, without drainage, salt levels build up over time from irrigation. With poor drainage, even with slightly saline water salts may be build up over time and cause serious problems. I think the authors should make sure they are familiar with this issue if they are not already (from the literature), and include this in their discussion. That is, to emphasise it is not just irrigation water quality (salinity) which is important but rather the combination of irrigation water quality and management of drainage which matters.
Thank you very much for your valuable advice. We were not quite familiar with this topic. Following your comment, we added some sentences regarding this to the conclusions (L401-407), but not to the discussion, because we think that our study neglects this issue and it is more like a future perspective. However, if it does not look ok in this position, please let us know.
- I thought the introduction was a bit sparse in terms of reviewing past information about response to sugarcane to salinity. There are other relevant studies that should be mentioned in both introduction and discussion.
We used some references in both the introduction (L50-55) and discussion (L306-321), but if it is not enough to meet your point, please inform us again.
- In connection with point 1, details should be given in the methods section on how the watering of the pots during the experiment was done. How much water was applied, and how was this determined.
We added some more detail regarding the water application method to the materials and methods (L90-91, L101-104).
- The authors argue that because stem weight wasn’t impaired at 500 mg/L (significant difference only occurred at 1000 mg/L) that this should not present a problem in terms of sugarcane production. However, leaf area was affected which clearly indicates problems with growth and likely yield. The lack of significant difference at 500 mg/L probably only reflects the statistical power of the experiment – ie. if a large number of replicates were used, or plants were grown for longer, I would predict a difference in stem weight would be observed. I think the results suggest that 500 mg/L is a problem.
We certainly observed reductions in leaf area and CO2 assimilation rate in the 500 mg L-1 group but stem length and weight were not greatly affected. Sugarcane has a leaf area index that can be minimized without affecting its growth and quality and the observed reduction of leaf area in the 500 mg L-1 group did not reach below the critical level. This part is mentioned in the discussion (L296-299).
- There is no discussion about genetic variation – and it is a weakness of the study that only one cultivar was used. There is knowledge that different varieties vary widely in response to salinity in many countries. For example, some varieties are known to handle salinity well. I think this issue, and the potential weakness of this study should be acknowledged and discussed.
As you pointed out, only one cultivar was used for the study and it is a weakness of our paper. Salt stress had not been considered to be a serious problem in our country and probably sugarcane screening will not be performed in terms of salinity resistance even in the future. In this paper, we however wanted to direct questions at the sugarcane industry why this issue has been neglected in our country though it has been extensively studied in other countries. For the next step, salt resistances of the major cultivars will be examined for sure and it is mentioned in the conclusions (L396-398).
We are looking forward to hearing from you again. Thank you.
Author Response File: 
Author Response.docx
Reviewer 2 Report
The manuscript describes research work aimed at characterizing the growth and physiological response of sugarcane under saline conditions. The work is based on glasshouse experimentation. This topic has been studied extensively by several research groups. The authors should familiarize themselves with all the literature on this topic and attempt to convince the reader that any ‘novel’ findings flowed from this work.
The manuscript should acknowledge that results from glasshouse experimentation cannot be extrapolated to field commercial productions systems. It should also acknowledge that the use of a single genotype is a major shortcoming and as such the usefulness of the data cannot be extrapolated to the commercial sugarcane system.
Many of the parameters measured in this study will vary greatly between different genotypes. As such much of the discussion should be rewritten as it is only applicable to the specific variety used in this study.
Specific comments:
Line 44-48; This needs better explanation. Why would there be a difference between the effect of saline conditions in Japan versus other countries?
Line 52; This is a very lose statement. What concentrations of salt will cause fatal damage? This statement needs references.
Line 72-85; Needs more details. Temperature, light conditions etc. What is implied by water was applied when needed. Was soil moisture determined or how was the timing irrigation controlled?
Line 158-169; This is a strange result. If photosynthesis is decreased then there will be an effect on the electron transport chain and uncoupling will occur. Is this a reflection of the light quality and irradiance in the glasshouse?
Line 187 and throughout the manuscript; Sugarcane is a member of the grass family and hence botanically it is not correct to refer to stems. Instead use stalk and even botanically more correct culm.
Line 191-193; The double effect of reduced photosynthesis per leaf area and smaller total leaf area will have an additive negative effect on carbon available for export to the sink (stalks). This needs to be properly discussed.
Line 274; It looks to be a significant effect and not merely a tendency.
Line 279-280; The results do not show any damage. It merely shows reduced photosynthesis and therefore reduced growth of the sink (stalk).
Line 346-351; This would be the case for the variety used in this study and cannot be a generalized statement. It also is relevant to plant grown in pots in glasshouse conditions. It is highly likely that many of the differences between these results and other published work relates to the fact that only glasshouse experiments were conducted.
Author Response
The manuscript describes research work aimed at characterizing the growth and physiological response of sugarcane under saline conditions. The work is based on glasshouse experimentation. This topic has been studied extensively by several research groups. The authors should familiarize themselves with all the literature on this topic and attempt to convince the reader that any ‘novel’ findings flowed from this work.
The manuscript should acknowledge that results from glasshouse experimentation cannot be extrapolated to field commercial productions systems. It should also acknowledge that the use of a single genotype is a major shortcoming and as such the usefulness of the data cannot be extrapolated to the commercial sugarcane system.
Many of the parameters measured in this study will vary greatly between different genotypes. As such much of the discussion should be rewritten as it is only applicable to the specific variety used in this study.
We are grateful for your review and comments. Our study might not be quite novel, but still provides valuable information that could attract readers, we believe. It also has some weaknesses as you pointed out. Following your comments, however, we revised our manuscript as it becomes better and more convincing. Kindly, please check the revised version of our manuscript. Besides, we replied to your comments point by point as follows.
Specific comments:
Line 44-48; This needs better explanation. Why would there be a difference between the effect of saline conditions in Japan versus other countries?
The fact that not many researches have been conducted on salt stress effects on sugarcane in our country is just one reason for our study. We also had other aims such as to suggest an applicable range of irrigation water salinity and to investigate the relationships between salinity and nutrient compositions and thus decided to launch this study.
Line 52; This is a very lose statement. What concentrations of salt will cause fatal damage? This statement needs references.
We added some general references regarding effects of salt stress on sugarcane yield, quality and physiological changes in the introduction (L50-55). More detailed information is mentioned in the discussion (L306-321) as also seen in the original manuscript.
Line 72-85; Needs more details. Temperature, light conditions etc. What is implied by water was applied when needed. Was soil moisture determined or how was the timing irrigation controlled?
Meteorological information such as temperature, humidity, and solar radiation can be found in section 2.2. Saline irrigation water treatment (L104-107). We also have the meteorological data during the whole experimental durations, but the periods after transplanting until starting the saline irrigation water treatments were quite long (about 6 and 3 months in Exp. 1 and 2, respectively), and the data would be less different between Exp. 1 and 2 if we combined all collected data. For this reason, we think that it is reasonable to present the meteorological data during the treatment periods to better describe the growth environments of Exp. 1 and 2.
Regarding water application, we added some more detail to the materials and methods (L90-91, L101-104).
Line 158-169; This is a strange result. If photosynthesis is decreased then there will be an effect on the electron transport chain and uncoupling will occur. Is this a reflection of the light quality and irradiance in the glasshouse?
Thank you very much for your notice. We checked the concerning parameters again and realized that there were some mistakes when organizing the concerning data. We replaced Table 1 and changed relevant parts in the result (L197-201) and discussion (L352-360). The abstract was also modified (L17-18).
Line 187 and throughout the manuscript; Sugarcane is a member of the grass family and hence botanically it is not correct to refer to stems. Instead use stalk and even botanically more correct culm.
Thank you very much for your helpful comment. Since I am not a native English speaker, I could not distinguish these differences well. I replaced “stem” with “culm”.
Line 191-193; The double effect of reduced photosynthesis per leaf area and smaller total leaf area will have an additive negative effect on carbon available for export to the sink (stalks). This needs to be properly discussed.
You can find relevant sentences in the discussion (L362-365). Please let us know if the discussion is not sufficient.
Line 274; It looks to be a significant effect and not merely a tendency.
We changed the sentence according to your comment (L294).
Line 279-280; The results do not show any damage. It merely shows reduced photosynthesis and therefore reduced growth of the sink (stalk).
We changed the sentence according to your comment but moved to the conclusions (L395-396).
Line 346-351; This would be the case for the variety used in this study and cannot be a generalized statement. It also is relevant to plant grown in pots in glasshouse conditions. It is highly likely that many of the differences between these results and other published work relates to the fact that only glasshouse experiments were conducted.
As you pointed out, only one cultivar was used for the study and it is a weakness of our paper. Knowing the weakness, we added some sentences in the discussion also with some references (L304-308). Salt stress had not been considered to be a serious problem in our country and probably sugarcane screening will not be performed in terms of salinity resistance even in the future. In this paper, we however wanted to direct questions at the sugarcane industry why this issue has been neglected in our country though it has been extensively studied in other countries. For the next step, salt resistances of the major cultivars will surely be examined. We also acknowledge that results may vary between pot and field conditions. Whether the findings from this study are useful under field conditions or not will be studied. These future perspectives are mentioned in the conclusions (L396-398, L409-411).
Again, thank you very much for your effort to review our manuscript. We are looking forward to hearing from you again.
Author Response File: Author Response.docx
Round 2
Reviewer 2 Report
The modifications to the manuscript significantly improved the content.
