Drought Hardening of European Beech (Fagus sylvatica L.) and Silver Fir (Abies alba Mill.) Seedlings in Mixed Cultivation
Round 1
Reviewer 1 Report
General comments
I have read the manuscript (forests-1864177). Entitle Drought hardening of European beech (Fagus sylvatica L.) and silver fir (Abies alba Mill.) seedlings in mixed cultivation written by Fengli Yang et. al., for publication of forests MDPI. In this study, the author investigated the significance of water deprivation in mixtures of beech and fir seedlings on the foliar relative water content (RWC), δ 13C signature, total C and N contents, and C: N ratios of both species in a drought-rewetting cycle. In this study author mainly found that moderate drought triggered increased RWC in beech leaves and current year fir needles. Total C contents of beech leaves were significantly increased upon drought and rewatering but remained constant in fir needles.
The overall research is well conducted, and research is obvious application potential for the readers because this study provides results indicating that drought hardening in mixtures of beech and fir. In this sense, the manuscript is much valuable. However, I found some points, especially the flow of the text and lack of potential references, and lack of connection of story in different paragraphs, especially in the introduction and discussion sections. The author should provide enough examples and their interpretation of different traits of physiological and biochemical responses by the latest and appropriate references, some of which I mentioned below. Overall after I evaluate and request the author for this manuscript as a “MAJOR REVISION”.
Major suggestions
1) Introduction: The introduction is well starting with the important issue of climate change and its impact on forest plantations which is much appreciated. However, the overall direct effect of drought needs to mention primarily in the introduction section somewhere in the second paragraph. The article https://DOI:10.1016/j.scienta.2018.11.021” better presented the drought effect. Please follow this article as a reference and mentioned that “drought reduced the morphological and physiological traits, reduce the photosynthesis, leaf water potential and sap movement and reduction of stomatal closure due to mainly closure of the stomatal in the plants”.
2) Hypothesis and objectives in the introduction: The author should make more clearly present the research hypothesis first and then only its objectives parts secondly. The author should be well connected to these two parts while mentioning the research objective. Please rephrase it slightly from Ln. 71 to 74 for further connection to the hypothesis and its objectives. The hypothesis should be very clear in the introduction sections because, without appropriate literature, questions, or hypotheses in the introduction section the entire text will be unclear.
3) Discussion: Author should improve the discussion section 4.1 section while dealing with the WUE and transpiration rate, those are very important traits for discussion section which is generally controlled by the stomatal conductance (gs). Therefore, the author should deal with gs as well because gs plays a very important role in controlling the mechanism for the plant water status. Because stromal full or partial opening causes the turgid the plant part that also determines the plant water use efficiency foliar water relations”.
Some other comments
4) Line no. 179: Please improve the figure’s x-axis and Y-axis as well as the letters inside the figures because these are not clear and very small. Please increase its font size and correct its alignments. Please apply this in other figures too.
5) Line 279- 286: Author should improve the related text about δ13C in the 4.1 section while dealing with the foliar plant water relations. Increased δ13C and/or decreased leaf hydration are commonly observed in plantation seedlings. Refer to and cite this literature https://doi.org/10.1016/j.foreco.2020.118099 of carbon isotopic discrimination (stable isotope/ δ13C) is the proxy of WUE and plant water relation and the useful method to determine the drought resistance to provide insights of the chemical, physical and metabolic process involved in carbon transformation in the stressed plant that determines the water utility and water conservation status for the forest species”
6) Line no. 363 (Conclusion): The conclusion should not be repetitive in the abstract or a summary of the results section. Generally, to cite some papers is not good to mention in the conclusion section as well, please consider the Ln 365 367. I would love to read striking points and take-home messages that will linger in the readers’ minds. What is the novelty, how does the study elucidate some questions in this field, and the contributions the paper may offer to the scientific community?
7) Line no. 395 (Reference): please double-check the citations, their style, spell check, and other grammatical errors. moreover, I request
Author Response
Major suggestions
1) Introduction: The introduction is well starting with the important issue of climate change and its impact on forest plantations which is much appreciated. However, the overall direct effect of drought needs to mention primarily in the introduction section somewhere in the second paragraph. The article https://DOI:10.1016/j.scienta.2018.11.021” better presented the drought effect. Please follow this article as a reference and mentioned that “drought reduced the morphological and physiological traits, reduce the photosynthesis, leaf water potential and sap movement and reduction of stomatal closure due to mainly closure of the stomatal in the plants”.
Responses: One sentence about the overall direct effect of drought has been added in line 52-55, i.e., “Drought is one of the most detrimental abiotic stresses strongly impacting morphological, physiological and biochemical processes of plants, including the reduction of leaf water potential and sap movement as well as impaired photosynthesis due to stomatal closure [4,10,11].” The article from Bhusal et al., 2019 has been cited in No. 11.
2) Hypothesis and objectives in the introduction: The author should make more clearly present the research hypothesis first and then only its objectives parts secondly. The author should be well connected to these two parts while mentioning the research objective. Please rephrase it slightly from Ln. 71 to 74 for further connection to the hypothesis and its objectives. The hypothesis should be very clear in the introduction sections because, without appropriate literature, questions, or hypotheses in the introduction section the entire text will be unclear.
Responses: The text has been rephrased as “In the present study, foliar water relations as well as carbon and nitrogen contents in response to water deprivation and rewetting were determined in mixed cultivations of beech and fir seedlings with different numbers of interspecies neighbours. Specifically, based on the results of published research, we hypothesized that: i) mild drought induces drought hardening in beech and fir seedlings; ii) admixing with beech will not sacrifice the water relations of fir, irrespective of water availability; iii) foliar total N, but not total C contents are enhanced during drought and reduced upon rewetting; and iv) facilitation effects of fir on beech are related to the number of neighboring fir seedlings, i.e. more neighboring fir will induce more significant effects on beech. The objectives of this study were to elucidate the physiological impacts of moderate drought on mixed beech and fir, and to examine the effects of interspecific neighborhood density”. Please see line 75-85.
3) Discussion: Author should improve the discussion section 4.1 section while dealing with the WUE and transpiration rate, those are very important traits for discussion section which is generally controlled by the stomatal conductance (gs). Therefore, the author should deal with gs as well because gs plays a very important role in controlling the mechanism for the plant water status. Because stromal full or partial opening causes the turgid the plant part that also determines the plant water use efficiency foliar water relations”.
Responses: This information is now discussed in line 279-286. Moreover, a new reference (Damour et al. 2010) regarding the key role of stomatal control has been added.
Some other comments
4) Line no. 179: Please improve the figure’s x-axis and Y-axis as well as the letters inside the figures because these are not clear and very small. Please increase its font size and correct its alignments. Please apply this in other figures too.
Responses: The size of letters inside figures as well as on X-axis and Y-axis has been increased, please see the updated figures.
5) Line 279- 286: Author should improve the related text about δ13C in the 4.1 section while dealing with the foliar plant water relations. Increased δ13C and/or decreased leaf hydration are commonly observed in plantation seedlings. Refer to and cite this literature https://doi.org/10.1016/j.foreco.2020.118099 of carbon isotopic discrimination (stable isotope/ δ13C) is the proxy of WUE and plant water relation and the useful method to determine the drought resistance to provide insights of the chemical, physical and metabolic process involved in carbon transformation in the stressed plant that determines the water utility and water conservation status for the forest species”
Response: The relationship between δ13C and plant water relations has been provided. The paper from Bhusal et al. 2020 has been cited; please see line 279-286 and line 298.
6) Line no. 363 (Conclusion): The conclusion should not be repetitive in the abstract or a summary of the results section. Generally, to cite some papers is not good to mention in the conclusion section as well, please consider the Ln 365 367. I would love to read striking points and take-home messages that will linger in the readers’ minds. What is the novelty, how does the study elucidate some questions in this field, and the contributions the paper may offer to the scientific community?
Response: The cited references have been removed. Moreover, striking points and take-home messages “In this study, we found drought hardening upon moderate water deprivation indicated by increased foliar water relations and C contents as well as modified N partitioning of beech seedlings grown in mixed cultivation with fir. Moreover, admixing with beech did not sacrifice these parameters in fir seedlings. The number of interspecies neighbours had lit-tle effects on these responses. In addition, drought hardening distinctly altered the foliar RWC and δ13C signatures as well as C and N contents in a species-specific way, indicating that different mechanisms contributed to drought hardening in beech and fir seedlings.” have been added. Please see line 375-382.
7) Line no. 395 (Reference): please double-check the citations, their style, spell check, and other grammatical errors. moreover, I request
Response: The reference has been checked, one repetition of Fotelli et al. 2009 together with 5 other low relevant references have been removed. The numbering throughout the whole text has been updated.
Reviewer 2 Report
The article deals with the drought hardening of European beech (Fagus sylvatica L.) and silver fir (Abies alba Mill.) seedlings in mixed cultivation. In general, it is an interesting approach with useful information’s for the journal readers. Moreover, the paper is well-written and easy to follow.
Line 51. Moreover, the complex terrain in mountainous forest ecosystems requires reliable future climate projections from high resolution Regional Climate Models (RCMs). Recent studies highlighted those RCMs resolutions highly affect climate projections accuracy in comparison with previous coarse resolution models in such environments (Stefanidis 2021, Tolika et al. 2016).
Stefanidis, S. (2021). Ability of Different Spatial Resolution Regional Climate Model to Simulate Air Temperature in a Forest Ecosystem of Central Greece. J. Environ. Prot. Ecol, 22, 1488-1495.
Tolika, K., Anagnostopoulou, C., Velikou, K., & Vagenas, C. (2016). A comparison of the updated very high-resolution model RegCM3_10km with the previous version RegCM3_25km over the complex terrain of Greece: present and future projections. Theoretical and applied climatology, 126(3), 715-726.
Line 60. However, trend analysis reports claim that fir stands are serious threaten from climate variability in high altitudes areas where limited meteorological stations operate, due to the difficulties of installation and maintenance of meteorological instruments, especially at the high elevations of the mountainous regions (Stefanidis and Alexandridis 2021, Jarzyna 2021)
Stefanidis, S., & Alexandridis, V. (2021). Precipitation and potential evapotranspiration temporal variability and their relationship in two forest ecosystems in Greece. Hydrology, 8(4), 160.
Jarzyna, K. (2021). Climatic hazards for native tree species in Poland with special regards to silver fir (Abies alba Mill.) and European beech (Fagus sylvatica L.). Theoretical and Applied Climatology, 144(1), 581-591.
Line 70. At the end of the introduction clearly state the novelty points of the current approach. What’s new compared to similar studies? Which was the research gap?
Line 82-83. A location map of the study area is missing from this article. Please provide a map of the study area giving the borders and the wider location of the study area. It would be useful to have a background from satellite images.
Add some targets for future research that derived from the outputs of this study.
In general, this is a very interesting article and highly important for the readers of the journal. My suggestion in the aforementioned parts I believe that will strengthens the sound of the research.
Author Response
Line 51. Moreover, the complex terrain in mountainous forest ecosystems requires reliable future climate projections from high resolution Regional Climate Models (RCMs). Recent studies highlighted those RCMs resolutions highly affect climate projections accuracy in comparison with previous coarse resolution models in such environments (Stefanidis 2021, Tolika et al. 2016).
Response: This is a good point, but the statement is not correlated with the present paper focusing on physiological response of beech and fir seedlings in response to drought hardening in microcosms.
Stefanidis, S. (2021). Ability of Different Spatial Resolution Regional Climate Model to Simulate Air Temperature in a Forest Ecosystem of Central Greece. J. Environ. Prot. Ecol, 22, 1488-1495.
Response: This publication is cited, please see line 45.
Tolika, K., Anagnostopoulou, C., Velikou, K., & Vagenas, C. (2016). A comparison of the updated very high-resolution model RegCM3_10km with the previous version RegCM3_25km over the complex terrain of Greece: present and future projections. Theoretical and applied climatology, 126(3), 715-726.
Response: This paper is interesting. Unfortunate, this literature is not relevant to the present paper.
Line 60. However, trend analysis reports claim that fir stands are serious threaten from climate variability in high altitudes areas where limited meteorological stations operate, due to the difficulties of installation and maintenance of meteorological instruments, especially at the high elevations of the mountainous regions (Stefanidis and Alexandridis 2021, Jarzyna 2021)
Response: This is an important point, but not relevant to the present paper.
Stefanidis, S., & Alexandridis, V. (2021). Precipitation and potential evapotranspiration temporal variability and their relationship in two forest ecosystems in Greece. Hydrology, 8(4), 160.
Response: This is a very interesting paper for southern Europe forest systems. And the fir species (Abies borisii regis) in this paper is not the same species as silver fir (Abies alba Mill.). The climatic conditions are distinct with central Europe where summer drought is more prevalent, whereas autumn drought is more problematic in Greece according to this study.
Jarzyna, K. (2021). Climatic hazards for native tree species in Poland with special regards to silver fir (Abies alba Mill.) and European beech (Fagus sylvatica L.). Theoretical and Applied Climatology, 144(1), 581-591.
Response: Has been cited, please see line 60.
Line 70. At the end of the introduction clearly state the novelty points of the current approach. What’s new compared to similar studies? Which was the research gap?
Response: This is a good point. And we elaborated the novelty and the gap in the Conclusion part instead of the end of the Introduction. Please see line 375-382.
Line 82-83. A location map of the study area is missing from this article. Please provide a map of the study area giving the borders and the wider location of the study area. It would be useful to have a background from satellite images.
Response: Since this is an indoor experiment under controlled conditions (except winter when the plants were outside), we think a location map is not required. Instead the geographic coordinates of the institute have been provided in the text. Please see line 89.
Add some targets for future research that derived from the outputs of this study.
Response: One more future research suggestion has been added, in total there are already two points suggested. Please see line 384-389, as well as line 304-307.
Round 2
Reviewer 1 Report
Dear Author
I have read the revised manuscript (Forests-1864177). Titled: Drought hardening of European beech (Fagus sylvatica L.) and silver fir (Abies alba Mill.) seedlings in mixed cultivation for publication of Forests MDPI. This is the second submission made by the author. The author addressed all the questions and suggestions that I raised the issue in the review of the original manuscript. I satisfy the author’s revisions throughout the paper. Author well addresses the abstract issues. Especially author improved the introduction and discussion section very well inflow. Now, this manuscript improved the flow of writing, which was comparatively shallow in the original version but in this revised copy author addressed all the quarries and suggestions very well. Before accepting this manuscript if there is anything needed to be revised by the author, especially English grammar, or spell check, I request this manuscript is currently in “Minor Revision” and any grammatical error author may improve in this stage. Thank you.
Reviewer 2 Report
The article improved and noe can be accepted
