Nitrogen Nutrition of European Beech Is Maintained at Sufficient Water Supply in Mixed Beech-Fir Stands

Round  1

Reviewer 1 Report

Dear Editor, dear authors

The authors compare tree nutrition of European beech with and without silver-fir. In addition their sites are exposed to different climates because they assume that water scarcity is affecting nutrition. They present their results based on sound methods. Particularly the different facets of tree nutrition were measured comprehensively and these set of methods warrant high confidence in the results. To my opinion this is a very valuable study and of interest for a broader community. My only concern is that the results are solely based on measurements from one year, which in addition was quite wet. Therefore, the research question whether or not water supply could affect nutrition could not be answered convincingly. Since this study was part of a bigger project I wonder whether additional years were measured and if so, why this data was not included? If no additional data is available, I recommend discussing the aspects of water scarcity with more detail. This would also increase the balance between the introduction, wherein the climate change topic is quite prominent, and the discussion, where this topic vanished.

I am not overly happy with the graphical presentation though I admit that visualizing mixed model results is difficult. I think the barplots would gain clarity if the statistical significances could be shown. Maybe using the letter/symbols from the supplementary tables could help? Improving these figures would make it much easier to follow the respective results sections, which are sound but very hard to read.

Please check the spelling and wording of the entire manuscript or let a native speaker correct the text. I give some examples below but they are not comprehensive.

Line 74: its “forest gap”

Line 86: use “questioned” instead of “critically discussed”

Line 93: “under extreme resource limitation” what exactly do you mean by that?

Line 99-100: “aboveground competition”, “belowground competition”

Line 333: these are boxplots, right?

Figure 1: please fix the axis label

Line 530: effects on what? Be more explicit. In general, I recommend giving a short summary of the key-results at the beginning of the discussion instead of this paragraph, which is rather a repetition of the introduction.

Line 542: “shallow” instead of “small”?

Line 555-556: This is a good example where data from a dry year would help a lot. You seem to write around this issue. I recommend being frank by admitting that you can’t really say much because the measurement year was too wet. “…still reduced water availability…” is wrong wording.

Line 600-601: please cancel the part with the “…ecosystem complexity”. Also cancel “???”

Line 609-610: Sorry, but isn’t that the other way around? The foliage N concentration should determine the litter N concentration, right?

Line 638: The discussion ends very abruptly. Why not helping the reader with a short conclusion about the main findings and their implications? What was the key finding and how did it improve our knowledge? What’s next? 

Author Response

Dear Reviewer, 

Thank you for your comments and suggestions. Please find your remarks answered one by one below. 

Dear Editor, dear authors

The authors compare tree nutrition of European beech with and without silver-fir. In addition their sites are exposed to different climates because they assume that water scarcity is affecting nutrition. They present their results based on sound methods. Particularly the different facets of tree nutrition were measured comprehensively and these set of methods warrant high confidence in the results. To my opinion this is a very valuable study and of interest for a broader community. My only concern is that the results are solely based on measurements from one year, which in addition was quite wet. Therefore, the research question whether or not water supply could affect nutrition could not be answered convincingly. Since this study was part of a bigger project I wonder whether additional years were measured and if so, why this data was not included? If no additional data is available, I recommend discussing the aspects of water scarcity with more detail.This would also increase the balance between the introduction, wherein the climate change topic is quite prominent, and the discussion, where this topic vanished.

We exclusively had data for that particularly wet year 2016. We clarified that part in the manuscript in order not to mislead the reader. We also added a section about water scarcity and effects therein to the discussion part (L 578 - 591). 

I am not overly happy with the graphical presentation though I admit that visualizing mixed model results is difficult. I think the barplots would gain clarity if the statistical significances could be shown. Maybe using the letter/symbols from the supplementary tables could help? Improving these figures would make it much easier to follow the respective results sections, which are sound but very hard to read.

We initially used the letter/symbols in the Figures, precisely because we thought it would add clarity to the Figures. We then decided to remove them again, since we found the figures seemed overly loaded and had lost their easy to grasp information. 

Though, if you think this would be essential, we would be happy to review the figures and add the letter/symbol combination from the supplemental tables. 

Please check the spelling and wording of the entire manuscript or let a native speaker correct the text. I give some examples below but they are not comprehensive.

We asked a native speaker to proof read the manuscript and added her suggestions to the revised manuscript. 

Line 74: its “forest gap” corrected

Line 86: use “questioned” instead of “critically discussed” changed as suggested

Line 93: “under extreme resource limitation” what exactly do you mean by that? We clarified that line, and it now reads “under nutrient limitation”

Line 99-100: “aboveground competition”, “belowground competition” changed as suggested

Line 333: these are boxplots, right? Changed the figure caption

Figure 1: please fix the axis label  I don’t understand what you mean by that. To me the axis label appears to be correct?  Could you please clarify what you mean?

Line 530: effects on what? Be more explicit. In general, I recommend giving a short summary of the key-results at the beginning of the discussion instead of this paragraph, which is rather a repetition of the introduction. We deleted the whole paragraph, following your suggestion but summarized key results in the conclusion instead, as also recommended by the second reviewer. 

Line 542: “shallow” instead of “small”? changed as suggested

Line 555-556: This is a good example where data from a dry year would help a lot. You seem to write around this issue. I recommend being frank by admitting that you can’t really say much because the measurement year was too wet. “…still reduced water availability…” is wrong wording. We clarified that part of the discussion (see comment above).  

Line 600-601: please cancel the part with the “…ecosystem complexity”. Also cancel “???”We did. 

Line 609-610: Sorry, but isn’t that the other way around? The foliage N concentration should determine the litter N concentration, right? Correct, and changed in the manuscript. 

Line 638: The discussion ends very abruptly. Why not helping the reader with a short conclusion about the main findings and their implications? What was the key finding and how did it improve our knowledge? What’s next?  We added a conclusion after the discussion to enhance readability and refocus the line of thought.

Author Response File: Author Response.docx

Reviewer 2 Report

Authors present data describing "Nitrogen nutrition of European beech is maintained at sufficient water supply in mixed beech-fir stands" in German and Croatia. The paper has scientific merit related to the questions between water relation and nitrogen nutrition in European forests. Few comments are suggested.

1) Should follow author’s guide of the Journal (the Journal has a new format for abstract).

2) Conclusion in manuscript is mandatory.

3) L31, 32, 575: nitrogen –> N,

4) L32: where -> were

4) L128: (Table S5), delete reference 46.

5) L173: Time Domain Reflectometry (TDR): add equipment name.

6) L292: NO3-, NH4+

7) L309: Table S4

8) L602: (???)

9) Check references: Italic letter for scientific name. The first word only is capital letter.

Author Response

Dear Reviewer, 

Thank you for your comments and suggestions. Please find your remarks answered one by one below. 

Authors present data describing "Nitrogen nutrition of European beech is maintained at sufficient water supply in mixed beech-fir stands" in German and Croatia. The paper has scientific merit related to the questions between water relation and nitrogen nutrition in European forests. Few comments are suggested.

1) Should follow author’s guide of the Journal (the Journal has a new format for abstract).  Changed abstract as suggested 

2) Conclusion in manuscript is mandatory. Added conclusion to the manuscript

3) L31, 32, 575: nitrogen –> N,  changed as suggested 

4) L32: where -> were We did not change that, as we used where instead of were indicating a location not a time here.

4) L128: (Table S5), delete reference 46. Sentence deleted

5) L173: Time Domain Reflectometry (TDR): add equipment name. added equipments name and company

6) L292: NO3-, NH4+ changed as suggested

7) L309: Table S4 I’m sorry, but I don’t understand this coment. Could you please clarify it?

8) L602: (???)  removed

9) Check references: Italic letter for scientific name. The first word only is capital letter. Done

Round  2

Reviewer 1 Report

Dear Editor,

the revision did take all my comments into account. Only my suggestion as to the figures presenting the main results was discarded. I still think that adding statistical significances to these figures would improve their clarity. Nevertheless, the decision is up to the authors. The newly written parts of the discussion improve the presentation of the results a lot, congratulations! The manuscript is very confincing in its present form.

Below are a couple of very minor issues:

Line 629 (track change version): preceeding not proceeding

Line 665: don't you mean "...at sites providing a benign environment and at these sites faciliation should dominate tree performance..."

Line 733: "...would improve the assessment of dependencies..."

Author Response

Dear Reviewer, thanks again for your remarks and suggestions. Please find the answers again further down, as we answered them separately:

Dear Editor,

the revision did take all my comments into account. Only my suggestion as to the figures presenting the main results was discarded. I still think that adding statistical significances to these figures would improve their clarity. Nevertheless, the decision is up to the authors. We were able to apply minor changes to the figures enabling us to include statistical significances, we hope without having lost the easy to grasp information. Please find the revised figures in the revised manuscript as well as in the newly uploaded zip folder. 

The newly written parts of the discussion improve the presentation of the results a lot, congratulations! The manuscript is very confincing in its present form.

Below are a couple of very minor issues:

Line 629 (track change version): preceeding not proceeding changed as suggested

Line 665: don't you mean "...at sites providing a benign environment and at these sites faciliation should dominate tree performance..." We mean as we said in the sentence, but we corrected a previous sentence, as that was misleading. Now it reads: “ […]indicating a facilitative effect of silver-fir on beech on sites where soil total N concentrations were low. It supports the “stress-gradient hypothesis” (SGH), stating that facilitation was more “common in communities developing under high physical stress (…)” [82]. According to this hypothesis, such an effect would be observable at sites providing a benign environment and at these sites competition should dominate tree performance.”

Line 733: "...would improve the assessment of dependencies..." changed as suggested