The Fluid–Solid Interaction in the Nonlinear Pressure–Flux Relationship of Bordered Pits in Oriental Arborvitae (Platycladus orientalis)

Round 1

Reviewer 1 Report

Dear Authors,

please find the detailed review in the form of the comments and suggestions for the paper „Fluid-solid interaction for the nonlinear pressure-flux relationship of bordered pits in conifers“ below. The topic is generally very interesting from the point of structure-function relationship and the results could certainly contribute to better understanding of this topic. The paper is very lengthy, with a substantial number of graphical figures and explanations. Please correct the name of the species Platycladus orientalis into italic throught the whole text.

The title

·       Are the results of this study applicable to all, or at least, most conifer species? „...in conifers“ is too general, while it is assumed the study includes at least several species. The suggestion is to modify the title: the paper is dealing with one specific confier species (Platycladus orientalis) and this should somehow be highlighted in the title. The statement from the Discussion (L 534-536) supports this suggestion.

1.       Introduction

·       The introduction is generally too long. The first paragraph (L 27-39) clearly introduces the topic of the study. The second paragraph (L 42-76) and the third paragraph (L 79-104) are presenting valuable conclusions from the associated topics in the literature, however, the descriptions are too long and should be summarized.

·       Why was Platycladus orientalis chosen as a species in this study? Is it a specific example of the conifer wood anatomical structure regarding bordered pits? Are bordered pits somehow a specific anatomical characteristic of different conifer species? This should be explained in the introduction, while the previous study from the same authors that was cited in this paper as well did not introduced the importance of this species.

·       The aim of the study is not cleary defined. The sentences (L 40-41, L 76-77, L 104-105 and L 132-133) should be formed to the describe the exact aim of the study.

·       The last paragraph should define the aim of the study, whereas L 134-143 are providing a summary more appropriate for the abstract.

2.       Materials and Methods

·       The title of the section 2.1. addresses a theoretical description and should be reformulated to be more suitable for the M&M section (e.g. The development of FEM model or The theoretical approach to fluid mechanics).

3.       Results

·       „As depicted in Figure 4, a negative correlation was observed between the pit diameter and the pit resistance (p=0.3195) which .....,“ – the text is missing after which, please complement that.

·       The sentence (L 374 – 381) is too long and should be shortened to be more understandable.

4.       Discussion

· 

·       If this study is preliminary (L 478), it should be also mentioned in the introduction.

·       Please check and correct the English language (L 499 – 519).

5.       Conclusion

A theoretical model was developed and explainded in this paper. Is there and what would it be a practical application of this research?

The English language is mostly satisfactory throughout the whole text. Please see the specific comments for correction in the review document.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

I have enjoyed a lot reading your paper. It is absolutely fascinating the way you deepen in the micro functioning of this mechanism. I am not sure if many readers will enjoy reading your work, as it implies a certain effort to keep in mind both the anatomy and function.

I cannot give you many good advices but, as a reader I encourage you to provide schematic representation of 1) the theoretical basis, 2) your hypothetical view.

Once in discussion, you can also give such schematic representación besides the outputs of Fluent. You must consider that most of the readers of this journal might not have your knowledge in biophysics and fluid dynamic, so a simplified output should be wellcome. 

I am not a native english speaker but some evident mistakes are found in the first part of the paper.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

The abstract presents valuable insights into the mechanics of fluid flow within bordered pits, leveraging advanced microscopy techniques and modeling. Strengthening the presentation with quantitative data and clearer explanations of the implications could further enhance the impact and accessibility of the study to a wider audience.

 The introduction provides an extensive overview of the significance of bordered pits in conifer xylem and their role in water transport, embolism prevention, and flow regulation, collates a wide range of studies, offering a comprehensive background on the subject.

+Positively, the introduction comprehensively synthesizes existing literature on the function and mechanics of bordered pits, highlighting their crucial role in controlling sap flow and preventing embolism. The references to various studies offer a rich background supporting the importance of investigating the intricacies of fluid-solid interaction for a thorough understanding of pit functionality.

+The objective of the research is well-articulated: to develop a fluid-solid interaction model focusing on the torus-margo structure within bordered pits and investigate its impact on the nonlinear pressure-flux relationship. This objective aligns well with the established gaps in understanding the detailed mechanics of how these structures regulate water flow and resist cavitation.

+The explicit mention of the study's focus on Platycladus orientalis and its implications for the pressure-flux relationship provides a clear direction for the research.

-        The text describes various models and methodologies without a clear link between them or how they contribute to the investigation.

-        Assertions like "the findings enhanced the understanding of the torus-margo structure in the process of pit closure" need more specific details or references to the actual findings.

-        The aim of the research is not clear stated.

 Material and methods

The use of elastic materials theory and Hook’s law to understand stress-strain relationships within the torus-margo structure demonstrates a sound understanding of solid mechanics principles. Employing the finite element method (FEM) to solve partial differential equations for complex structures is appropriate.

The description of fluid-solid interaction processes and the iterative nature of achieving equilibrium between external fluid pressure and solid deformation exhibit a well-structured approach to analyzing these interactions.

The detailed description of sample collection, observation, and referencing a previous study for methodology strengthens the reproducibility and reliability of the experiment.

-        While assumptions are outlined, it might be beneficial to discuss potential implications or limitations arising from these assumptions. For instance, how might variations in density or viscosity affect the outcomes, and are these assumptions universally applicable?

-        The description of the finite element method (FEM) application for solid mechanics, while pertinent, might require additional clarity for readers less familiar with this approach. Simplifying technical jargon or providing illustrative examples could enhance comprehension.

-        The general process of data transfer between fluid and solid models is described; specific technical details or algorithms utilized for this transfer are missing. Elaborating on this transfer process would strengthen the methodological clarity.

-        The assumption that the water density within bordered pits remained constant and unaffected by pressure variations might not hold true in real-world scenarios. Additionally, presuming that temperature variations within the bordered pits were insignificant might oversimplify the influence of temperature changes on fluid characteristics, potentially affecting the accuracy of the model.

-        The study assumes constant material properties for the torus-margo structure without accounting for nonlinear characteristics such as material anisotropy, plasticity, or yielding. Neglecting these characteristics might limit the model's accuracy in representing the actual behavior of the material under fluid pressure.

 Results

+The positive correlation between the pit diameter and the torus diameter, as well as the significant relationship between the pit diameter and the total area of pores in the margo, are notable findings. Additionally, the detailed analysis of pressure loss and velocity distribution within the pit aperture provides valuable insights into fluid dynamics within the bordered pit structure.

+The figures and tables illustrate the data, facilitating comprehension of complex relationships. Figures 3 and 6 vividly display pressure distribution and the impact of fluid-solid interaction, while Figures 11, 12, and 13 visually represent correlations between different variables. Table 2 succinctly presents geometry data and simulation results for the pit models under different pressure conditions, aiding in a comprehensive overview of the study's findings.

-        However, there are some shortcomings that should be addressed. While the results illustrate correlations between various parameters, the underlying mechanisms or physical explanations for these relationships are not sufficiently explored. Offering insights or hypotheses regarding the biological or physiological implications of these findings would strengthen the study's significance. Addressing the variability in the margo pores and the implications of this variability on the observed relationships could contribute to a more comprehensive discussion.

-        Several areas require attention for accuracy and clarity. The presentation of statistical significance levels without exact p-values diminishes the interpretability of the results. Providing these values would enhance the rigor and credibility of the statistical relationships claimed in the study. Additionally, the textual descriptions in certain sections lack specificity and clear articulation of the findings, requiring more detailed explanations for better comprehension.

-        There's a mention of some relationships (positive, negative) between various parameters (e.g., pit diameter, torus diameter, pit depth) with statistical significance levels indicated (p-values). However, some of these relationships are described as "significant" at a threshold of p<0.05 or p<0.1 without proper statistical significance. The significance level mentioned doesn't align with the conventional threshold of p<0.05 often used in scientific studies.

 +The "Discussion" section provides a comprehensive exploration of fluid dynamics within bordered pits in Platycladus orientalis. It connects theoretical concepts like the Hagen-Poiseuille equation to practical observations, such as the behavior of pores in the margo and the influence of torus-margo structure positioning on flow resistance.

+The section demonstrates an in-depth understanding of the complex interplay between pit geometry and flow resistance, especially the impact of varying pit dimensions on resistance, as supported by previous studies. +Additionally, the discussion bridges theoretical expectations with empirical findings, highlighting discrepancies and potential reasons behind conflicting correlations observed in the study.

+Furthermore, it elucidates the implications of fluid-solid interaction on the deformation of the torus and margo, shedding light on their roles in altering flow resistance and providing a compelling basis for further investigation into material properties.

+However, the discussion, although comprehensive, occasionally suffers from verbosity and could benefit from more concise explanations to maintain reader engagement. Simplifying complex concepts without losing their depth would enhance the accessibility of the information presented.

+Additionally, it would be advantageous to explicitly mention any limitations or uncertainties associated with the study's findings, acknowledging potential areas for future research or refinements in methodology.

-        There are discrepancies noted between the correlation analysis and theoretical flow behavior. For instance, the insignificant correlation between pit depth and pit resistance contradicts the expected behavior of deeper pits having lower resistance. This incongruity needs clarification, possibly due to complexities in the dataset or the model used for analysis.

-        The interpretation of the relationship between pit diameter, pit depth, and their influence on flow resistance might need further explanation. The correlation analysis results might require additional empirical evidence to support the conclusions drawn.

 +In the "Conclusions" section, the observations regarding the changing factors influencing pit resistance as the torus position shifts are noteworthy, providing valuable insights into the dynamics of fluid flow in response to structural alterations. The correlation between torus deflection and pressure difference, coupled with the non-linear increase in flow resistance, adds depth to understanding the behavior of bordered pits under varying pressures.

+The study's findings relating to the non-linear relationship between pressure and flux within bordered pits, along with the implications for preventing gas bubble transit during tracheid cavitation, present important theoretical support that aligns with existing knowledge in the field.

Moreover, the section effectively highlights the impact of pit dimensions on resistance and flow regulation, correlating pit diameter and depth variations with changes in resistance and regulation capabilities. The role of Young's modulus in influencing the pressure-flux correlation is well-articulated, providing insight into the material properties' significance in pit behavior.

-        Additionally, the conclusions, although comprehensive, might be more impactful if they succinctly summarized the most significant findings, focusing on the key takeaways without delving too deeply into the technical aspects. This adjustment could improve accessibility and readability for a broader audience.

 +The "References" section provides a rich array of sources relevant to the study's investigation of fluid-solid interaction within bordered pits. The references cover a wide spectrum of topics, including xylem conductivities, hydraulic safety and efficiency, embolism resistance, and pit structure and function in conifers. The inclusion of recent publications, particularly those from 2020 to 2023, enriches the contemporary relevance of the sources.

+The reference list is extensive, encompassing a diverse range of studies from various researchers, spanning hydraulic mechanisms, pit structure-function relationships, and tree response to drought and stress.

+The majority of the references directly correlate with the investigation's focus on fluid dynamics within bordered pits, ensuring alignment with the study's objectives and enhancing its credibility.

+The inclusion of recent studies from 2020 onwards reflects an effort to incorporate the latest research in the field, ensuring the study is grounded in current knowledge.

However, there are a few areas for potential improvement:

-The format of the references might benefit from standardization according to a specific citation style (e.g., APA, MLA), ensuring consistency across the list.

-The references could be organized in a more structured manner, such as categorizing them based on themes or topics, to enhance readability and ease of reference for readers and researchers.

-While the references cover a broad scope, there might be room to include a few additional studies that focus specifically on certain aspects of fluid dynamics or bordered pit behavior for a more comprehensive overview of the subject.

 The text contains grammatical errors and awkward sentence structures that make it challenging to follow the scientific explanations.

Comments for author File: Comments.pdf

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 4 Report

The Authors conducted an interesting modelling study employing the high quality fluid and solid interaction models to investigate the fluid flow effects influenced by the coniferous bordered pit torus-margo structure. The work provides some insight into water flow regulation by pits and looks interesting to be published. 

There are couple comments below that should be addressed to improve the understandability and consistency of the manuscript:

Lines 173-182: deformation and Hook’s law is related to the following section named "Fluid-solid interaction" and it looks better to move it there for consistency.

Section 2.6 model verification: It sounds like the presented in the manuscript scheme is inferior to the previous Schulte’s study, inferring the possible errors due to the presented method applied. From this, it becomes unclear what are the benefits to using the presented scheme in comparison to Schulte's approach.

In the Discussion there is a lot of repetition of the Results that could be avoided if it would be summarized in the Conclusions.

Kind regards,

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The paper can be accepted in its present form.