Ammonium Phytotoxicity and Tolerance: An Insight into Ammonium Nutrition to Improve Crop Productivity
Round 1
Reviewer 1 Report
The manuscript addresses an interesting topic that would be ammonia toxicity and is well updated. The approach indicates an updated review of the subject with many works of high scientific quality. Nitrogen is a nutrient that most promotes response in plant growth and at the same time has a high cost and therefore, the optimized management of the N source can promote an increase in crop productivity without the need to increase N doses and without risk of toxicity ammoniacal. This practical implication of the topic studied is very important.
However, the manuscript needs to be revised to improve the critical analysis of the studies carried out to guide new, better-designed and scientifically more robust studies. Thus, we leave some notes for the authors to improve the quality of the manuscript.
Table 1 shows the optimum ammonium/nitrate ratio.
However, this optimal relationship depends on the studied N concentration and this needs to be included in the review. And it needs to be further discussed in the manuscript.
Another critical point in the review would be the source of ammoniacal N that the authors studied to assess the optimal ammonium/nitrate ratio. This needs to be stated in the text. For example, the increase of ammonium in the nutrient solution using the ammonium chloride source may be increased, in addition to ammonia toxicity, the salinity effect promoted by chlorine. So you have two stressors on the plants and it could be confusing and therefore the results can only be attributed to ammonium and it doesn't reflect reality. In plants sensitive to salinity, the study of ammoniacal toxicity using ammonium chloride should not be indicated because the damage to the plants is due to two stresses and not just ammonium.
It is important for the authors to address this issue in the discussion of the manuscript and many studies must be redone. In addition, we have other sources such as ammonium sulfate and therefore, the increase in N concentration from this source increases ammonium and sulfur together and can have a dual effect of ammonium and S on plant responses.
The balance of nutrients in ammonium sources need to be discussed in the manuscript. Companion ammonium ions can change plant responses and it is important to include this critical approach in the review.
We invite the authors to include research with the use of ammonium in studies in cultivated fields in irrigated systems. It is known that the nutritive process is high in cultivated field cropping systems without the use of irrigation and therefore, the use of ammonia sources induces a low risk of ammonia toxicity with the use of ammonia sources. However, in irrigated systems, the nitrification rate decreases and the use of amoacal sources has a greater risk of toxicity and these sources should be avoided. This discussion deserves to be revised and included in the manuscript.
It is important to review the grammar of the text.
Author Response
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
In this review, the authors have summarized ammonium toxicity and tolerance. Some methods were proposed to improve crop production by ammonium nutrient.
Some clarifications need to be addressed as follows.
1. Line 37: nitrates, the “s” should be removed.
2. Line 38-39: “Only when…by plants” Is this sentence correct?
3. Line 40: are the roots source organs?
4. Line 93: nitrite reduction can also occur in roots with plastids, not chloroplasts. So it may be better to change “chloroplasts” into “plastids”.
5. Line 94: Gln and Glu are not N transporters.
6. Line 109-111: Is GDH a general way to lower ammonium concentration? What factors will regulate or influence the activity of GDH?
7. Line 113: “The ability of GDH to release amino N…” what is “amino N”?
8. Figure 1 has several mistakes. First, in photorespiration, 2-OG is transported from the peroxisome to the chloroplast, not to mitochondria. Secondly, the reaction in mitochondria is also incorrect. Please check carefully.
9. Figure 1. It would be better to draw an H+-ATPase on the plasma membrane.
10. Line 179-181: Please provide more explanations about the last sentence. So under ammonium, ARG1, AUX, and PIN3 can be used for reducing the primary root inhibition?
11. Line 166 vs. Line 194: Which part is affected most by ammonium, roots or shoots?
12. Line 241-242: NRT1.1/NPF6.3 is NOT a ammonium transporter.
13. In the section “5.2 CAP1-mediated intracellular ammonium sensing responses”. In the beginning, the author mentioned CAP1 may phosphorylate AQP on the tonoplast. Then the author also mentioned that CAP1 may have transcriptional regulation on TIP2;3. Please give a suitable explanation about how a tonoplast RLK will influence the transcription. Moreover, please provide cap1 phenotypes to demonstrate CAP1 is involved in ammonium tolerance.
14. Line 296, 297, and 304: Please change NRT1.1 to NRT1.1/NPF6.3.
15. Line 321-327: It was confusing to mention polyamines here. What is the relationship between polyamines and ammonium? What is the relationship between polyamines and urea cycle?
16. Figure 3: After AMT1;3 was endocytosed, does it go degradation or storage?
17. Line 345: Please change "inactive" to "inactively".
18. Line 354-355: is the absorption of nitrate associated with the release OH-?
19. Line 373: remove “has” in front of “negatively”.
20. Line 396: what does this mean” while decreased the nitrate content in leaves.” This seemed not to fit the former sentence.
21. Line 405: “The same NH4+:NO3- ratio (25:75)…” The written ratio is not the same.
22. In Table 1, the last item on the second page, please change NRT1.5 to NRT1.5/NPF7.3. And there is no space between NRT and 1.5, NRT and 2.
The English quality is OK. There are just some minor problems.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
Most of the questions are answered. However, the reaction of photorespiration is still wrong. Please see the following citations. The reaction in mitochondria is 2 Gly --> 1 Ser + NH4++CO2. Please DO Make sure everything is correct.
https://www.sciencedirect.com/topics/medicine-and-dentistry/photorespiration
https://doi.org/10.1016/j.tplants.2010.03.006
https://doi.org/10.1146/annurev-arplant-043015-111709
Author Response
Reviewer 2
Most of the questions are answered. However, the reaction of photorespiration is still wrong. Please see the following citations. The reaction in mitochondria is 2 Gly --> 1 Ser + NH4+ + CO2. Please DO Make sure everything is correct.
https://www.sciencedirect.com/topics/medicine-and-dentistry/photorespiration
https://doi.org/10.1016/j.tplants.2010.03.006
https://doi.org/10.1146/annurev-arplant-043015-111709
Authors response
The authors greatly appreciate the sincere effort made by the reviewer to improve the quality of the manuscript by providing valuable suggestions. Thank you very much for pointing out the mistakes in the reaction of photorespiration in Figure 1. As per your suggestion, we have carefully rectified the errors in the reaction of photorespiration in both mitochondria and peroxisome. Please see Figure 1 and lines 153-158 in the revised manuscript.
Author Response File: Author Response.pdf
