Responses and Post-Recovery of Physiological Traits after Drought–Heatwave Combined Event in 12 Urban Woody Species

Round 1

Reviewer 1 Report

General comments

I have read the manuscript:  Forest MDPI. Entitle: Responses and post-recovery of physiological traits to drought heatwave combined event in 12 urban tree species written by Yongkang Wang et. al., for publication of forest MDPI. In this study, author investigated the effects of the drought-heatwave on 12 urban trees. Author investigated the dynamic changes on hydraulic and photosynthesis process traits, resistance, and resilience of the species during and post-drought heatwave event. Author mainly found that tree species significant decrease in Ks, Midday, gs and Anet during drought hot event, with severely drought-induced xylem embolism in hydraulic system and high PLC.

 

The overall research is well conducted but author should significantly improve this manuscript for journal acceptance. Research is obvious application potential for the readers because this research proves that the novel insight that the conifer species were less resistance toward transient drought hots than broadleaves but capable of recovery, suggesting conifers with better resilience and broadleaves companied with better resistance under short-term stress. In this sense, this manuscript is much more valuable. However, I found a lack of story connection and lack of potential references (some I suggested some below). Overall after I evaluate and request the author for this manuscript as a “MAJOR REVISION”.

 

Major Suggestions

1) Abstract: Abstract should be more informative. Author well mentions the methodology and traits of measuring indices in abstract, which should mention shortly. I encourage to author mainly focus the results and research insight in the abstract. Please consider that the abstract should short and concise.

2) Hypothesis of the study: The author well presented the objectives or main aim of the study in the Ln. 134-138. However, the research hypothesis is not still much clearly presented. Hypothesis is included the last paragraph of introduction but still it needs to specifically focus just before the objectives of the study. The research hypothesis and objectives should well-connect. The hypothesis should be very clear because, without appropriate literature, questions, or hypotheses in the introduction section the entire text will be unclear.

3). Introduction: Drought or temperature stress is one of the major stresses. Author well starting with the background of global warming which is appreciated. Higher temperature causes the drought for plant. In the first paragraph (nearly Ln. 40) author should cover the drought or temperature effect such as “reduction of plant morphology (reduced leaf size and stem length, leaf length/width, and vegetative growth) and physiological traits (reduction of photosynthesis, leaf water potential, and sap movement)”. The article help to further clarify your introduction  https://doi.org/10.1093/treephys/tpy153

 

Some other comments

4) Line no. 240-245 (Materials and methods): Author should be mentioned the methodology and internal set up to measure the photosynthesis (RH%, Internal CO2 concentration ect) as well as other instrumentation detail (for eg. Ln. 247, SPAD), May be SPAD is the Minolta, Japan. Further author should include the replication and treatment in each measurement traits.

5) Line no. 419-420 (Discussion): Author should be further discussion in this section by referring other related paper. Author discusses the urban tree species with low gs, either due to iso-hydric stomatal or an aniso-hydric behavior by referring https://doi.org/10.1016/j.scitotenv.2021.146466 this article for further clearances this section.

5) Line no. 497 (Discussion…): “Hydraulic Failure” major part and author should include the scenario of this in the 4.2 sub-section of the discussion by referring suitable articles. The article “DOI:10.1016/j.scienta.2018.11.021 and mention the text somewhere in 4.2 “drought reduced hydraulic failure of the plant under the drought stress condition and reduction the plant water status by reducing the leaf water potential and sap movement. The possible reason behind this is subsequently changing the stem anatomical structure such as xylem vessel structure such as reducing the vessel diameter and vessel area”.

6) Line no. 542 (Conclusion): I did not saw the conclusion section mention by the author. I encourage to author to include this section separately or include one additional paragraph in the last of the discussion section. The outlook and conclusion should not be repetitive in the abstract or a summary of the results section. 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 571 (References): please double-check the citations, their style, spell check, and other grammatical errors. moreover, the author should cut the old and less matching literature and include the latest literature some of them are above.

Good Luck !

Author Response

We appreciated your great suggestions and comments!  Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Dear authors,

 

I have reviewed your manuscript “Responses and post-recovery of physiological traits to drought-2 heatwave combined event in 12 urban tree species” for possible publication in Forests.

 

The topic is worthy of investigation and much needed for urban studies and you results are interesting. There are, however, some issued that require attention. First, English needs major revisions. There are too many errors that makes difficult to understand what you mean. This does not mean your results are wrong, but definitely, it distracts the reader. Second, more details about the study area are needed. In L122 you mention the trees are planted in “the same garden”, but there is not proper description in the Methods, aside from figure a star in Figure 2. Also, how many trees for each species were selected and measured? If the trees were planted in a garden, what are the broader implication of your results. This is important because you did not collected data from “typical” urban trees, all the opposite. One might argue that gardens are not typical urban landscapes, actually, they do not represent the majority of urban trees in a city. Those individuals are less frequent than street trees, for example, and their growing conditions are very different. Urban greenspaces are quite heterogeneous regarding climate, microclimates, wind, soils, water availability, interactions with people, urban heat island…. As such, gardens are quite unique and different to trees planted elsewhere within a city. Your study seems more like a common garden experiment that happens to be within a city. I don’t think this is a problem but should be brought up upfront to avoid confusion and discuss it’s applicability for urban tree species selection, for example. Especially because urban tree mortality must be much higher for street trees, as trees in gardens are managed more closely, as it is not in their intention to see their trees fail. Related to this, information about irrigation would be very useful, because probably, trees were irrigated during the high-stress periods described in the results. I have made more comments in the file attached. Finally, I think you need to add more references related to urban studies; I have provided some in the reviewed document.

Comments for author File: Comments.pdf

English needs major revisions.

Author Response

We appreciate your great comments and suggestions! Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

This study examined physiological responses of 12 urban tree species to drought and heat stress and following recovery in the field. Some traits related to carbon and water relations were monitored for the pre-stress, stress and post-stress period. The authors concluded difference in resistance and resilience among tree functional groups. This study provides an interesting dataset for monitoring tree physiological responses to climate extremes in the field and is of interest to readers in this journal. However, many concerns should be addressed prior to further consideration.

 

Major comments

1. The Introduction section can be improved with more knowledge and progress in tree physiological responses to drought and heat and post-stress recovery, particularly for field grown trees and urban tree species. The methods section should add more details in the experimental design and protocol. The fashion of data presentation in the Result section should be reconsidered and revised. The Discussion section should be largely modified.

 

2. The English language should be largely improved by an expert.

 

Specific comments

Introduction

“Hot drought stress” may be better than “Drought hot stress”. Please consider revising this throughout the MS.

L60: Please be more specific on “tree metabolism”, particularly on those traits related to your research.

L70-73: The evidence of carbon starvation is rare, mainly in specific experimental conditions. Please be cautious with this. 

L72: Stomatal conductance is more common.

L74-76: What about the combined effects of heat and drought on tree physiology?

L89-92: Please review more progress in this subject, particularly on the specific physiological results over the last few years.

L94: Are there any evidence in the physiological recovery in the field?

L134-138: These two objectives are not clear. Are they similar? It is more interesting to investigate the difference between functional groups (e.g. deciduous and evergreen; gymnosperm and angiosperm).

 

Materials and Methods

L206: Was the xylem tension relaxed prior to hydraulic measurements? Otherwise, artefacts may occur.

L226: Were both gymnosperm and angiosperm flushed? Please add more details about the experiment protocol.

L245: Is the light intensity saturated for all species?

L259: Do you ensure the full saturation of leaves in 5-6 hours?

L280: The post-hoc Tukey’s comparisons test cannot be done independently. Did you conduct ANOVA before the post-hoc analysis? Please add more details.

 

Results

L286-329: Please shorten this section for environmental conditions. This is just a background of climate and the focus should be physiological responses.

L338-370: What is this section for? It only shows significant declines and recovery in the stress and post-stress period. But what is then? What message do you try to convey? I think readers are more willing to look at the dynamics of traits across the three sampling dates, but not just the significance of responses.

Table 2: Did you estimate P50? Please add more details in the method.

L373: Figure 6 is difficult to understand. Probably a figure with more direct information on differences in drought responses and recovery is helpful. Besides, were all species dried to the similar stress levels? If not, how would this affect the recovery among species?

 

Discussion

Some information in this section can be moved to Results, because these are just results but not discussions. What is the difference between 4.1 and 4.2? Besides, the discussion section can be largely improved by reorganizing the structure, logic and points that need to be discussed. More mechanistic understandings should be added as well.

The language needs to be largely improved.

Author Response

We appreciate your great comments and suggestions! Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Dear Author

I have read the revised manuscript forests-2460113. Entitled: Responses and post-recovery of physiological traits to drought-heatwave combined event in 12 urban tree species for publication in Forests. 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. Author improves their hypothesis and well connected with the research objectives in this time. This manuscript improved the flow of writing, which was comparatively shallow in the original version but in this revised copy author very well addressed all the quarries and suggestions. Before accepting this manuscript, please check again the referencing. Further 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 the author may correct any further grammatical errors (if any) the author may improve in this stage.

Thank you.

Author Response

Dear Reviewer,

 

We appreciate your great comments and suggestions. We further corrected the grammatical errors, spelling issues, format of math formulations and references as you suggested. Please find the changes in the marked version of the MS. Thanks!

 

Best wishes,

 

Jia Song

Reviewer 2 Report

Dear authors,

 

Thank you for responding to all my concerns and comments. I appreciate your patience and efforts. I have read your updated manuscript and it has improved considerably.

There are some minor errors in grammar that can be easily addressed during the final stages of publication

Author Response

Dear Reviewer,

 

We appreciate your great comments and suggestions. We further corrected the grammatical errors, spelling issues, format of math formulations and references as you suggested. Please find the changes in the marked version of the MS. Thanks!

 

Best wishes,

 

Jia Song

Reviewer 3 Report

Thanks for the revision on the MS and it seems that the MS has been improved. However, it is very difficult to check revisions in this clean version. Could you please highlight the revisions in the MS? Also, some points, such as reviewing progress in the Introduction were not appropirately added. Probably similar with other comments. Thus, more detailed highlighted version should be provided.

The language can be improved further.

Author Response

Dear Reviewer,

 

We appreciate your great comments and suggestions.

We did upload a revised version with changes highlighted last time, and we uploaded a changes marked version of MS as suggested again. We further corrected the grammatical errors, spelling issues, format of math formulations and references as you suggested. Thanks!

Best wishes,

 

Jia Song

Author Response File: Author Response.docx