Functional Acclimation of Quercus robur from Nine European Provenances to Repeated Drought Events

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

General comments:

This manuscript examines the responses of leaf structural traits in Quercus robur provenances after three years of experimentally induced drought, as well as gas exchange responses to subsequent drought. The topic is timely and relevant, particularly given the increasing concern about climate resilience and adaptation to environmental change. The use of three-year measurements is a clear strength and adds applied value to the study. However, despite these strengths, the manuscript currently has several substantial shortcomings.

1. Introduction

The introduction is informative, providing relevant background to the study and its objectives; however, it would benefit from a clearer formulation of the research gap and explicit hypotheses.

L10: Please provide the full scientific name at first mention, including the authority (i.e., Quercus robur L.).

L92: Please include the initial hypothesis of the study.

2. Materials and Methods

The Materials and Methods section provides important information about the studied provenances, although it would benefit from further clarification and inclusion of additional details:

L131: The CT group was watered with 4 liters of water per pot every three days. How was this amount determined? Did the authors use a specific method or calculation to ensure that this volume corresponded to 100% field capacity? What was the basis for the watering schedule? Please provide more detailed information regarding plant irrigation.

L132: The DS group plants were deprived of water from April 1 to July 21, 2015, until approximately 50% exhibited visible drought stress symptoms (leaf curling and yellowing). Please provide more details on how drought was defined. Was it based only on visible symptoms, or were additional indicators monitored (e.g., volumetric soil water content, SWC)?

L153: Please provide more information on the rationale for maintaining SWC in CT pots at 40–50%, while SWC in DT pots dropped to 16–20% during drought periods.

2.3. Leaf Structural Traits

L167: Please provide information on the total number of samples.

2.4. Measurements of Leaf Water Potential and Gas Exchange Traits

L184: Please provide information on the total number of measurements.

L189: I would suggest incorporating WUE and WUE_i, as these traits are widely acknowledged as useful indicators of plant water-use strategies under drought conditions and can be derived from the measured parameters.

L190: gₛ - the s should be lowercase - please revise this throughout the manuscript.

2.5. Statistical Analysis

L199: The use of analysis of covariance (ANCOVA) is justified, however, reporting effect sizes would greatly improve interpretability.

3. Results

The results are clear, concise, and appropriately structured into subsections.

4. Discussion

The discussion is informative and supported by relevant literature; however, a minor restructuring is suggested:

L311: First, report the observations from the study, and then relate them to relevant literature.

L341: The same comment as above applies here.

5. Conclusion

The conclusion summarizes the main findings of the study; however, it would benefit from the consistent use of abbreviations instead of full trait names (e.g., specific leaf area (SLA)).

Author Response

All responses are attached in uploaded Word file

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This study addresses an important and timely topic: how Quercus robur responds to repeated drought stress under climate change. The experimental design, using multiple provenances across a broad geographic gradient, is a clear strength and allows meaningful insights into intraspecific variability. The integration of both structural (e.g., stomatal density, leaf dry matter content, specific leaf area) and physiological traits (gas exchange) is particularly valuable and aligns well with current approaches in plant ecophysiology.

The results are generally well interpreted and support the conclusion that morphological traits play a stronger role than gas exchange traits in provenance-level adaptation to drought. The finding that drought hardening can enhance acclimation capacity has practical implications for forest nursery practices and climate-resilient reforestation strategies.

However, several points could be strengthened. First, the abstract and conclusion would benefit from clearer quantification of effect sizes and variability among provenances. Second, while the study highlights shifts in photosynthetic down-regulation, the mechanisms underlying these shifts remain somewhat vague and could be elaborated. Third, the controlled conditions limit direct extrapolation to field performance; this limitation should be more explicitly acknowledged. Finally, the suggestion for future research is appropriate, but could be more specific regarding experimental design and trait integration.

Overall, this is a solid and relevant contribution, but minor clarifications and more precise framing of the results would improve its impact.

Specific comments:

- The current title is clear, but it would benefit from improved scientific precision by explicitly including the species name. I recommend revising the title as follows: “Functional acclimation of Quercus robur from nine European provenances to repeated drought events.”

- Sentences in lines 43–48 present statements that require support from relevant literature. Please provide appropriate references to substantiate these claims.

- What is the difference between adaptedness and adaptation?

- In Plant material and provenance origin, what is the difference between MAP and MGSP ? and why Worldclim was not used to extract climatic data?

- for figure 1, you can add SWC for CT also.

- Are data normally distributed or log-transformated before statistical analyses?

- Lines 209-2013 can be deleted or moved to 2.1.

- In 3.1 are traits only correlated to MGSP?

 

Author Response

All responses are attached in Word file.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

1. Line 108: These provenances were distributed along a latitudinal gradient in Europe, from Estonia to Italy (Table 1). Is it possible to provide a study area map that would make the location easier for readers to understand?
2. Line 116: In Table 1, there are significant differences in the number of investigated plants between the control (CT) and drought (DT) treatments across the nine sites. It is necessary to explain these differences in more detail.
3. Line 224: SLA increases with MGSP with the lowest SLA values in Estonian provenance and the highest values in Croatian provenances. This is an important finding, and the major factors contributing to it should be explained in more detail.
4. Line 230: The drought-treated plants tended to exhibit increased LDMC in wetter provenances (e.g., Italy and Croatian sites). However, the value decreased for the Estonia (EE) site in Figure 2b. Please check this again and provide an explanation for this pattern.
5. Line 231: The SD value decreased in some drier provenances (e.g., Estonia, Poland, and Hungary). However, a reduction was also observed in Italy, which represents a wetter provenance. Could you explain this pattern?
6. Line 360: Adaptedness of provenances to dry habitat conditions is achieved by decreasing of SLA associated with an increase in leaf mesophyll thickness and the amount of photosynthetically active tissues. It would be better to provide some references to support this statement.

Author Response

All responses are attached in Word file.

Author Response File: Author Response.pdf